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Chapter 3 Complexes of

Manganese(II), 3d5

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3.1. INTRODUCTION Manganese is a trace mineral that is present in tiny amounts in the body. It is found mostly in bones, liver, kidneys, and pancreas. Manganese helps the body form connective tissue, bones, blood-clotting factors, and sex hormones. It also plays a role in fat and carbohydrate metabolism, calcium absorption, and blood sugar regulation. Manganese is also necessary for normal brain and nerve function. Manganese is a component of the antioxidant enzyme superoxide dismutase (SOD), which helps to fight with free radicals. Free radicals occur naturally in the body but can damage cell membranes and DNA. They may play a role in aging as well as the development of a number of health conditions including heart disease and cancer. Antioxidants, such as SOD, can help to neutralize free radicals and reduce or even help to prevent some of the damage they cause. Low levels of manganese in the body can contribute to infertility, bone malformation, weakness, and seizures. Manganese is an essential to iron and steel production by virtue of its sulphur fixing, deoxidizing and alloying properties. Steel making, including its iron making component, has accounted for most domestic manganese demand presently in the range of 85% to 90% of the total demand. Among a variety of other uses; manganese is key component of certain widely used aluminum alloys and is used as oxide form in dry cell. World production of manganese (Mn) ore was estimated to have increased about 11% (contained weight) in comparison to that for 1999. China was assumed to be the largest producer on a gross weight basis; South Africa is largest producer on a contained weight basis. Batteries containing manganese, those of the alkaline type in which electrolytic manganese dioxide (EMD) is used to continue to expand their share of the market at the expense of those of the carbon-zinc type. The complexes of Mn(II) with sulphur containing ligands play an excellent role in catalytic property [1-4]. Manganese and its compounds are widely used in analytical chemistry, metallurgical processes, paints and pigment industry. The class of enzymes that have manganese cofactors are very broad and include such as oxidoreductases, transferases, hydrolases, isomerases, ligases, lectins, and intergins. The reverse transcriptase of many retroviruses (though not lentiviruses such as HIV) contains manganese. The best known manganese-containing polypeptides may be arginase, the diphtheria toxin, and Mn-containing supuroxide dismutase (Mn-SOD) [5-11], which is

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the enzyme typically present in eukaryotic mitochondria, and also many bacteria (this fact is in keeping with the bacterial origin theory of mitochondria). The Mn-SOD enzyme is probably one of the most ancient for nearly all organisms living in the presence of oxygen. It is used to deal with the toxic effects of superoxide, which are formed by the one electron reduction of dioxygen. Exceptions include a few types of bacteria such as Lactobacillus plantarum and related lactobacilli. They use different nonenzymatic mechanisms, involving manganese (Mn2+) ions complexed with polyphosphate directly. Manganese known to form compound in all oxidation states ranging from(+II) to (+VII), however due to the (Ar)d5 electronic configuration the most common and most stable oxidation state for manganese is (+II). This spherically symmetrical configuration Mn(II) 3d5 has several bearings on the biological activity of the metal ion[12]. The Mn(II) co-ordination compounds are very abundant in soil [13-14] and are essential for plant growth. In soil, these are formed by bio-degradation of lignin [15]. Mn(II) was found to be important for enzymatic systems with DNA. DNA and RNA polymerases [16] catalyze the replication and transcription of DNA and have a specific requirements for Mn(II) [17]. Manganese may help some of the following conditions: a) Manganese is one of several trace elements (including vanadium and boron) that are

necessary for bone health. There is no specific evidence that manganese can prevent osteoporosis, but one study found that taking a combination of calcium, zinc, copper, and manganese helped lessen spinal bone loss in a group of post-menopausal women.

b) People with arthritis tend to have low levels of SOD. Some experts theorize that manganese may increase SOD levels, but there is no proof that it helps treat arthritis. A few clinical studies of people with rheumatoid and osteoarthritis suggest that manganese taken along with glucosamine and chondroitin can reduce pain. However, some studies have found it has no effect.

c) In one well-designed clinical study, women who ate 5.6 mg of manganese in their diets each day had fewer mood swings and cramps compared to those who ate only1 mg of manganese. These results suggest that a manganese-rich diet may help to

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reduce symptoms of PMS. Another clinical study found that 46 patients with PMS found had significantly lower amounts of calcium, chromium, copper, and manganese in their blood.

d) Some studies show that people with diabetes have low levels of manganese in their blood. But researchers don't know if having diabetes causes levels to drop, or whether low levels of manganese contribute to developing diabetes. More studies are needed. One clinical study found that people with diabetes who had higher blood levels of manganese were more protected from LDL or "bad" cholesterol than those with lower levels of manganese.

e) Several clinical studies suggest that people who have seizure disorders have lower levels of manganese in their blood. But researchers don't know if having seizures causes low levels of manganese, or whether low levels of manganese contribute to having seizures. At least one animal study suggests that manganese supplementation does not reduce the severity or frequency of seizures in rats. More clinical studies are needed.

f) Rich dietary sources of manganese include nuts and seeds, and whole grains (including unrefined cereals, buckwheat, bulgur wheat, and oats), legumes, and pineapples.

g) Manganese is available in a wide variety of forms, including manganese salts (sulphate and gluconate) and manganese chelates (aspartate, picolinate, fumarate, malate, succinate, citrate, and amino acid chelate). Manganese supplements can be taken as tablets or capsules, usually along with other vitamins and minerals in the form of a multivitamin.

h) Metal complexes of Mn2+ are found to be active against number of fungi like Alternaria brassicae, Aspergillus niger, Fusarium oxysporum [18] and bacteria like Xanthomonas compestris, and Pseudomonas aeruginosa (19), show antitumour activities (24), antiprotozoal (37) etc.

In view of the above applications of Mn2+, the synthesis and characterization of the Mn2+ complexes with semicarbazide and thiosemicarbazide based ligands are highly desirable.

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3.2. REVIEW OF LITERATURE Mn(II), Co(II), Ni(II), Pd(II) and Pt(II) complexes having the general composition M(L)2Cl2 [where L=p-Vanillin thiosemicarbazone, M=Mn(II), Co(II), Ni(II), Pd(II) and Pt(II) (Figure 3.1.) have been synthesized by S. Chandra et al.[18] All these compounds were characterized by elemental analysis, IR, 1H NMR and electronic spectral studies. On the basis of spectral studies, an octahedral geometry has been assigned for Mn(II) and Co(II) complexes whereas square planar geometry have been assigned for Ni(II), Pd(II) and Pt(II) complexes. The free ligand and its metal complexes have been tested in vitro against a number of microorganisms in order to assess their antimicrobial properties. The antimicrobial data revealed that the metal complexes are more active antibacterial agents than the uncomplexed ligand from which theyare derived.

[where M=Mn (II), Co (II) and M’= Ni (II), Pd (II) and Pt (II)]

Figure 3.1

Mn(II), Co(II) and Cu(II) complexes with a quinquedentate Schiff base,2,6-diacetylpyridine bis(thiocarbohydrazone), of the composition [M(L)X]X, where M=Mn(II), Co(II), and Cu(II), L=2,6-diacetylpyridinebis(thiocarbohydrazone), and X=NO3- and OAc- have been synthesized by Sharma et al. [19] and characterized with the help of elemental analyses, molar conductance, magnetic susceptibility, and IR, 1H NMR, 13C NMR, mass (for ligand), UV and Electron Paramagnetic Resonance spectroscopies. The ligand with five coordination sites forms six coordinated complexes

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with octahedral geometry for Mn(II), whereas the Co(II) and Cu(II) complexes were of tetragonal geometry. The Aiso values, nephelauxetic parameter (β), and orbital reduction factor (k) indicate the covalent nature of the metal–ligand bond. The compounds have been screened for their antipathogenic activities against Alternaria brassicae, Aspergillus niger, Fusarium oxysporum, Xanthomonas compestris and Pseudomonas aeruginosa. Refat et al. [20] have synthesized Mn(II), Co(II), Ni(II) and Cu(II) complexes having the general composition M(L)2X2 [where L=2-pyridinecarboxaldehyde semicarbazone, M=Mn(II),Co(II), Ni(II) and Cu(II), X=Cl- and NO3-]. All the synthesized compounds were identified and confirmed by elemental analysis, molar conductance, magnetic susceptibility measurements, mass, IR, EPR, electronic spectral studies and thermogravimetric analysis (TG). The Molar conductance measurements of the complexes lie in the range 209–228 cm-1 mol-1 indicating that the complexes are 1:2 electrolytic in nature. Thus the complexes may be formulated as [M(L)2]X2. The magnetic moment measurements of the complexes indicated that all the complexes were in high-spin state. On the basis of spectral studies an octahedral geometry has been assigned for Mn(II), Co(II) and Ni(II) complexes whereas tetragonal geometry for Cu(II) complexes. The thermal studies suggested that the complexes were more stable compared to free ligand. This fact was supported by calculating the thermodynamic parameters by using Horowitz–Metzger(HM) and Coats–Redfern (CR) equations. The free ligand and its metal complexes were also evaluated against the growth of phytopathogenic fungi and bacteria in vitro. Mn(II), Fe(II), Co(II), and Cu(II) derivatives of two inherently chiral, Tris(bipyridyl) cages (L and L’) of type [ML](PF6)2(solvent)n and [FeL’](ClO4)2 where L was the hexa-tertiary butyl-substituted derivative of L’, were reported by Perkins et al. [21]. These products were obtained by using the free cage and metal template procedures; the latter involved the reductive amination of the respective Tris-dialdehyde precursor complexes of iron(II), cobalt(II), or nickel(II). Electrochemical, EPR, and NMR studies have been used to probe the nature of the individual complexes. X-ray structures of the Mn(II), Fe(II), and Cu(II) complexes of L and the iron(II) complex of L’ were presented; these were compared with the previously reported structures of the

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corresponding nickel(II) complex and metal-free cage (L). In each complex the metal cation occupies the cage’s central cavity and was coordinated to six nitrogens from the three bipyridyl groups. The cations [MnL]2+ and [FeL]2+ were isostructural but both exhibit a different arrangement of the bound cage to that observed in the corresponding Ni(II) and Cu(II) complexes. The latter have an exo-exo arrangement of the bridgehead nitrogen lone pairs, with the metal inducing a triple helical twist that extends ≈22 Å along the axial length of each complex. In contrast, [MnL]2+ and [FeL]2+ have their terminal nitrogen lone pairs directed endo, causing a significant change in the configuration of the bound ligand. In [FeL’]2+, the cage has both bridgehead nitrogen lone pairs orientated exo. Semiempirical calculations indicated that the observed endo-endo and exo-exo arrangements were of comparable energy. Tang et al. [22] synthesized complexes of Mn(II), Fe(II), Cu(II), Ni(II) and Zn(II) with soluble vitamin k3 thiosemicarbazone. These complexes were characterized by elemental analysis, molar conductance measurements, magnetic susceptibility measurements, mass, 1H NMR, IR., UV.vis and thermal analysis. All of the complexes possess strong inhibitory action G(+) Staphyloccocous aureus, G(-) Eschericha coli. The antibacterial activities of the complexes were stronger than that of the ligand. Mn(II) complexes having the general composition Mn(L)2X2 [where L=isopropyl methyl ketone semicarbazone (LLA), isopropylmethyl ketone thiosemicarbazone (LLB), 4-aminoacetophenone semicarbazone (LLC) and 4-aminoacetophenone thiosemicarbazone (LLD) and X=Cl-, 1/2SO42−] have been synthesized by Chandra et al. [23]. All the complexes were characterized by elemental analyses, molar conductance, magnetic susceptibility, EI-mass, 1H NMR, IR, EPR and electronic spectral studies. All the complexes show magnetic moments correspondingto five unpaired electrons. The possible geometries of the complexes were assigned on the basis of EPR, electronic and infrared spectral studies. Arvindakshan et al. [24] synthesized complexes of metals with acetoacetanillide thiosemicarbazone (Aat). These complexes were characterized by elemental analysis, molar conductance measurements, magnetic susceptibility measurements, mass, 1H NMR, IR and electronic spectral studies. The compounds have been studied for their possible antitumor activities against Ehrlich Ascites tumour cells. The complexes were found to have following

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stoichiometries [Mn(Aat)((H2O)2]n; [Zn(Aat)((H2O)2]; [M(Aat)((H2O)2] where M= Cd(II) or Hg(II) [Cu(Aat)]n; [Ag(Aat)H; [M(AatH)2; where M= Co(II) or Ni(II) and [Fe(Aat)C1((H2O)2]n. A new series of transition metal complexes of Cu(II), Ni(II), Co(II), Mn(II), Zn(II), VO(IV),Hg(II) and Cd(II) have been synthesized from the Schiff base (L) derived from 4 aminoantipyrine,3-hydroxy-4-nitrobenzaldehyde and o-phenylenediamine by Raman et al. [25]. Structural features were obtained from their elemental analyses, magnetic susceptibility, molar conductance, mass, IR, UV–Vis, 1H NMR and ESR spectral studies. The data show that these complexes have composition of ML type. The UV–Vis, magnetic susceptibility and ESR spectral data of the complexes suggest a square–planar geometry around the central metal ion except VO(IV) complex which has square–pyramidal geometry. The redox behavior of copper and vanadyl complexes was studied by cyclic voltammetry. Antimicrobial screening tests gave good results in the presence of metal ion in the ligand system. The nuclease activity of the above metal complexes shows that Cu, Ni and Co complexes cleave DNA through redox chemistry whereas other complexes were not effective.

Naskar et al. [26] synthesized, five, seven or eight coordinate Mn(II) complexes of hydrazone ligands, three, seven-coordinate neutral Mn(II) complexes: [Mn(dapA2)]n, [Mn(dapB2)(H2O)2, [Mn(dapS2)(H2O)2 from the bis-Schiff’s bases of 2,6-diacetylpyridine: dap(AH)2, dap(BH)2 and dap(SH)2 (AH=anthranilogyl-hydrazide, BH=benzolhydrazide, SH=salicyloylhydrazide, respectively. Two eight-coordinate Mn(II) compexes: [Mn(daps)2] and [Mn(dapB)2].3H2O have been synthesized from the mono-Schiff’s bases dapBH and dapSH respectively. The complexes have been characterized from the elemental analyses and by IR, UV-vis, FAB mass, EI mass and EPR spectroscopy. The molecular structures of complexes have been determined by single-crystal X-ray diffraction. The octacoordinated mono-Schiff’s base complex [Mn(daps)2] adopts dodecahedral geometry, while the hepta-coordinated bis-Schiff’s base complex [Mn(dapA2)]n forms a one-dimensional linear polymeric chain.

Thakar et al. [27] studied the condensation reaction of 4-Acyl-1-phenyl-3-methyl-2-pyrazolin-5-ones with 2-amino-4(4’-methylphenyl)-thiazole to form Schiff’s base. These Schiff bases formed complexes of type ML2.2H2O (M=Mn, Fe, Co, Ni and Cu).

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Elemental analysis, magnetic susceptibility, electrical conductance, electronic and Infrared spectral data suggested octahedral structure for the complexes. All the compounds were tested for their antibacterial activity. The result indicated that the growth of the tested organism was inhibited by most of the compounds. These Schiff bases were characterized by elemental analysis, mass spectra, 1H NMR spectra, 13C NMR spectra and FT-IR spectra. Ramalingam et al. [28] prepared birnessite type layered MnO6 oxides with increased crystallinity which were synthesized from six carbohydrates and three dihydric phenols viz, dextrose, starch, fructrose, galactose, maltose, lactose, catechole, resorcinol, quinol and KMnO4 through the formation of a sol-gel. All of the MnO6 oxides were characterized by powder XRD. The strong signal at 2θ∼12° corresponding to 7.4 A° refers to the Mn-Mn distance adjacent layers. Interlayer volume was dispersed with K+ ions is indicated by a signal at 25°, corresponding to a distance of 3.5 A°. IR Spectra of the oxide show signature bands at ca. 500 cm-1 due to the stretching modes occurring for MnO6 entity. A broad band observed at ca. 300 cm-1 was due to interlayer water molecules. Thermal analyses indicated three stage decomposition with the formation of MnO2 at ca. 600 °C through the intermediate formation of Mn(OH)n. the MnO6 exhibited remarkable CO2 scrubbing ability, which has also been investigated.

Lal et al. [29] synthesized and characterized the first unique binuclear Mn(I) salicylate. The structure of the complexes was established with the help of an X-ray crystallographic study. The structure consists of two [MnO6] units, containing octahedral Mn(I) ions, linked together by a bridging salicylato (Hsal) ligand and each Mn(I) was chelated with a (H2sal) ligand. The complexes possess a metal oxidation state of +1 and is rare example of nanocrbonyl or cyanide complex of a binuclear Mn(I) species. The effective magnetic moment per binuclear molecule (µeff) at 27°C was 8.07 µB that also described the manganese (+ I) oxidation state.

Chandra et al. [30] synthesized Mn(II), Co(II), Ni(II) and Cu(II) complexes with thiosemicarbazone (L) derived from pyrrole-2-carboxyaldehyde. These complexes were characterized by elemental analyses, molar conductance, magnetic susceptibility measurements, mass, IR, electronic and EPR spectral studies. The molar conductance

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measurements of the complexes in DMSO indicated that the complexes were non-electrolytes except Co(L)2(NO3)2 and Ni(L)2(NO3)2 complexes which were 1:2 electrolytes. All the complexes were of high-spin type. On this basis of spectral studies an octahedral geometry may be assigned for Mn(II), Co(II) and Ni(II) complexes except Co(L)2(NO3)2 and Ni(L)2(NO3)2complexes which were of tetrahedral geometry. A tetragonal geometry may be suggested for Cu(II) complexes.

Leovac et al. [31] reported the reaction of warm alcoholic solutions of acetates of Co(II), Mn(II), Zn(II) and Ni(II) with 2,6-diacetylpyridine and S-methylisothiosemicarbazide hydrogen iodide to give the complexes:[Co(H2L)I2]H2O, [Mn(H2L)(MeOH)2]I2,Zn(H2L)(MeOH)I]I and [Ni(HL)]I, H2L=pentadentatepentaaza-ligand 2,6-diacetylpyridine bis(S-methyliso-thiosemicarbazone)]. The reaction of methanolic solutions of [Ni(HL)]I and NH4NCS or LiOAc.2H2O, gave [Ni(HL)] NCS and NiL, respectively. For the complexes of Co(II), Mn(II) and Zn(II), a pentagonal bipyramidal configuration was proposed with H2L in the equatorial plane and two unidentate ligands(Iand/or MeOH) in the axial positions. The complexes [Ni(HL)]X (X= I¯or NCS¯) and NiL probably have monomeric five- and dimeric six-coordinate structures, respectively, in which only the chelate ligand is involved in coordination. Chandra et al. [32] synthesized the Mn(II), Co(II) and Ni(II) complexes of 2- methylcyclohexanonethiosemicarbazone (MCHTSCL1) and 2-methyclyclohexanone-4N-methyl-3-thiosemicarbazone (MCHMTSCL2) general composition [M(L)2X2] (where M=Mn(II), Co(II), Ni(II), L=L1 or L2 and X=Cl¯, NO3¯ and ½ SO42¯) and characterized by elemental analyses, magnetic susceptibility measurements, UV-vis., IR, EPR and mass spectral studies. Various physicochemical techniques suggested an octahedral geometry for the complexes.

Fouda et al. [33] synthesized hydrazone ligand containing the thiophene moiety via condensation of thiaphene-2-carbohydrazide with 1,5-dimethyl-3-oxo-2-phenyl-2,3-dihydro-IH-pyrazole-4-carbaldehyde. The complexes of Cu(II), Ni(II), Co(II), Mn(II), Zn(II), Pd(II), Fe(III), Ru(III), U(VI) and Ti(IV) with ligand were prepared in good yield from the reaction of the ligand with the corresponding metal salts. The ligand and complexes were characterized by using the IR, mass spectra, 1H NMR, electronic

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absorption spectra, electron spin resonance and magnetic susceptibility measurements as well as elemental and thermal analyses. The results showed that the complexes are enolic by nature, whilst the ratio between the metal ion and the ligand depends on the acidity of the metallic ions and their oxidation numbers.

Shahzadi et al. [34] synthesized the transition metal carboxylates i.e. 3-[(2,4,6-trichloroanilino) carbonyl] prop-2-enoic acid and 3-[(4-bromoanilino) carnonyl] prop-2-enoic acid. The unimolar and bimolar substituted products have been characterized by elemental analyses, IR, UV-Vis, 1HNMR and atomic absorption spectroscopy. IR data showed the bidentate nature of the carboxylate group. The transition metal complexes were tested in vitro against a number of microorganisms to assess their biocidal properties. The coordination compounds of Cr(III), Mn(II) and Co(II) metal ions derived from quinquedentate2,6-diacetylpyridine derivative have been synthesized and characterized by using the various physicochemical studies like stoichiometric, molar conductivity and magnetic, and spectral techniques like IR,1H NMR, mass, UV and EPR by Chandra et al. [35]. The general stoichiometries of the complexes were found to be [Cr(H2L)X] and [M(HL)X], where M=Mn(II) and Co(II), H2L=dideprotonated ligand, HL=monodeprotonated ligand and X=NO3−, Cl− and OAc−. The studies revealed that the complexes possess monomeric compositions with six coordinated octahedral geometry [Cr(III) and Mn(II) complexes] and six coordinated tetragonal geometry [Co(II) complexes]. A series of Mn(II) and Cu(II) complexes with reduced Schiff’s bases have been synthesized by Belaid et al. [36].The complexes were characterized by elemental analyses, TG measurements, ESR, magnetic susceptibility measurements, FT-IR, UV-Vis spectra and molar conductivity. Their antifungal activities were also evaluated on the different human pathogenic fungi.

Ajibade et al. [37] synthesized the metal complexes of the antimalarials trimethoprim (TMP), chloroquine (CQ) and pyrimethmine (pyrm) formulated as [Mn(TMP)Cl2

(CH3OH)], [Co(TMP)2Cl2(CH3OH)], [PT(CQ)2Cl2) and [Cu(pyrm)2 (CH3COO)2] and characterized on the basis elemental analyses, magnetic susceptibility measurements, IR and UV-Vis spectroscopy. The IR and electronic spectra were consistent with the

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proposed geometry for the complexes. The Mn(II) and Pt(II) complexes were four coordinated while the Cu(II) and Co(II) have octahedral geometry. The complexes were tested for their antiprotozoal activities.

Maurya et al. [38] synthesized a binucleating tetradentate Schiff’s base ligand, bis (o-vanilline)benzidine(o-v2bzH2) and its seven new binuclear complexes have been synthesized and characterized on the basis of elemental analyses, IR, 1H NMR, electronic, magnetic susceptibility measurements, thermal studies and conductance measurements. The composition of these complexes were found to be [M(o-v2bz)]2.nH2O, where, M=Cu(II), Ni(II), Zn(II), Mn(II) or UO2(VI) and [Sm(o-v2bz)(OAc)(H2O)]2. The 1H NMR spectrum of one of the compounds, Sn(o-v2bz)]2, showed the absence of the proton signal for phenolic oxygen(-OH). Low magnetic moment values, high thermal stability and insolubility in common organic solvents support the binuclear structure of the complexes. The 3D molecular modeling and analysis for bond length an bond angles have also been carried out for one of the representative compounds, [Ni(o-v2bz)]2. Mn(II), Co(II), Ni(II), and Cu(II) complexes have been synthesized by Refat et al. [39] with benzyl bis(thiosemicarbazone) (L) and characterized by elemental analyses, molar conductance measurements, magnetic susceptibility measurements, thermogravimetric studies, infrared (IR), electronic, and electron paramagnetic resonance (EPR) spectral studies. The molar conductance measurements of the complexes in DMF correspond to the non-electrolytic nature of the complexes. Thus these complexes may be formulated as [M(L)X2] (where M = Mn(II), Co(II), Ni(II), Cu(II) and X = Cl− and NO3−). On the basis of IR, electronic, and EPR spectral studies, an octahedral geometry has been assigned for Mn(II), Co(II), and Ni(II) complexes, whereas a tetragonal geometry for the Cu(II) complexes is presumed. The free ligand and its metal complexes were tested against the phytopathogenic fungi (i.e., Rhizoctonia bataticola, Alternaria alternata) in vitro.

Amiery et al. [40] synthesized (Z)-2-(pyrrolidin-2-ylidene)hydrazinecarbothioamide (L) in a good yield by the reaction of pyrrolidone with thiosemicarbazide. Co(II), Ni(II), and Cu(II) complexes of (L) were prepared and characterized by FT-IR, UV-visible spectra, 1HNMR, and CHN analyses. Moreover, charge, bond length, bond angle, twist

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angle, heat of formation, and steric energy were calculated by using the ChemOffice program, and also the DFT calculations for the complexes were done. The free ligand and its metal complexes were tested in vitro against several microorganisms (Staphylococcus aurous, E. coli, Proteus vulgaris, Pseudomonas and Klebsiellap neumoniae) to assess their antimicrobial properties. The study showed that these complexes have octahedral geometry;in addition, it has high activity against tested bacteria. New Mn(II) complexes, [Mn(H2L)(H2O)2]Cl2·xH2O, with linear and tripodaltetradentate ligands have been synthesized by Deloume et al. [41]. The complexes were characterized with the help of elemental analysis, molar conductance, IR spectra, magnetic measurements and electronic and ESR spectra. The data showed that the ligands are neutral and coordinate to manganese in a tetradentate manner; the other axial sites are occupied by the water molecules. Magnetic and ESR data showed that Mn(II) adopts a high-spin configuration in the complexes. The electrochemical behavior of the complexes, determined by cyclic voltammeter, showed that the chelate structure, ligand geometry and electron donating effect of the ligand substituent’s are among the factors influencing the redox potentials of the complexes. In addition, they noted that linear ligands stabilize the Mn(III) state to a greater extent than tripodal ligands and their complexes vigorously catalyse the disproportionation of hydrogen peroxide in the presence of added imidazole. Neutral tetradentate chelate complexes of Cu(II), Ni(II), Co(II), Mn(II), Zn(II) and VO(II) have been prepared by Raman et al. [42] in EtOH using Schiff bases derived from acetoacetanilido-4-aminoantipyrine and 2-aminophenol/2-aminothiophenol. Microanalytical data, magnetic susceptibility, FT-IR, UV-visible spectra, 1H NMR, and ESR spectral techniques were used to confirm the structures of the chelates. Electronic absorption and IR spectra of the complexes suggested a square-planar geometry around the central metal ion, except for VO(II) and Mn(II) complexes which have square-pyramidal and octahedral geometry respectively. The cyclic voltammetric data for the Cu(II) complexes in MeCN showed two waves for Cu(II) Cu(III), and Cu(II) Cu(I), couples, whereas the VO(II) complexes in MeCN showed two waves for V(IV) V(V) and V(IV) V(III) couples. The ESR spectra of the Cu(II), VO(II) and Mn(II) complexes

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were recorded in DMSO solution and their salient features reported. The in vitro antimicrobial activity of the compounds was tested against the microorganisms such as Salmonella typhi, Staphylococcus aureus, Klebsiellap neumoniae, Bacillus subtilis, Pseudomonas aeruginosa, Aspergillus niger and Rhizoctonia bataicola. Most of the metal chelates have higher antimicrobial activity than the free ligands. Mononuclear complexes of Cu(II), Ni(II), and Mn(II) with a new Schiff base ligand derived from indoline-2,3-dione and 2-hydroxybenzohydrazide, [Cu(II)(L)2], [Ni(II)(L)2], and [Mn(II)L·(AcO)·2C2H5OH] [HL=(Z)-2-hydroxy-N′-(2-oxoindolin-3 ylidene)benzohydrazide], have been prepared by Zhong et al. [43]. The complexes have been structurally characterized by X-ray crystallography. Among the three complexes, the Cu(II) complex had the novel highest antitumor activity.

Figure 3.2. Crystal Structure of the complexes.

A thiosemicarbazone derivative of the Vitamin K3 has been synthesized by Tanget al. [44]. Five transition metal complexes of the thiosemicarbazone (Mn(II),Co(II), Ni(II), Cu(II) and Zn(II) complexes) have been prepared and characterized by IR, UV-vis, molar conductance and thermal analyses. All of the complexes possess strong inhibitory action against Staphylococcus aureus, Hay bacillus, and Eschericha coli. The antibacterial activities of the complexes are stronger than those of the ligand. A series of first complexes of Co(II), Ni(II), Cu(II), Mn(II) and Fe(III) have been synthesized with Schiff base derived from isatinmonohydrazone and fluvastatin by Kulkarni et al. [45]. The complexes have been characterized in the light of elemental analyses, spectral (IR, UV-Vis., FAB-mass and ESR) and magnetic studies. The elemental analyses of the complexes confine to the stoichiometry of the typeML2.2Cl [M=Co(II), Ni(II), Cu(II) and Mn(II)] and [FeL2.2Cl]Cl. The redox properties of the

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complexes were extensively investigated by electrochemical method using cyclic voltammetry (CV).The Co(II) and Cu(II) complexes exhibited quasi-reversible single electron transfer process where as Mn(II) and Fe(III) complexes shown two redox peaks of quasi-reversible one electron transfer process. The Schiff bases and their complexes have been screened for their in-vitro antibacterial (Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and Bacillus subtilis) and antifungal (Aspergillus niger and Pencillium chrysogenum) activities by minimum inhibitory concentration (MIC) method.

Murukan et al. [46] have synthesized the complexes of Mn(III), Fe(III) or Co(III) with a bishydrazone, formed by condensation of isatinmonohydrazone with 2-hydroxy-1-naphthaldehyde. The spectral data revealed that the ligand acts as monobasic tridentate, coordinating through the deprotonated naphtholate oxygen, azomethine nitrogen, and carbonyl oxygen. Molar conductance values adequately supported the electrolytic nature of the complexes. On the basis of the above observations the complexes have been formulated as [M(NIB)2]X where M =Mn(III), Fe(III) or Co(III); X = Cl2, NO3- or OAc-; HNIB = [(2-hydroxy-1-naphthaldehyde)-3-isatin]-bishydrazone. Based on electronic spectral data and magnetic moment values, an octahedral geometry has been proposed. The Fe(III) complex has been subjected to thermal decomposition studies. The ligand and the metal complexes have been screened for their antibacterial activity and it has been observed that the complexes are more potent bactericides than the ligand. A bishydrazone was prepared by reacting isatinmonohydrazone with 2-hydroxy-1-naphthaldehyde and a seriesof metal complexes with this new ligand were synthesised by reaction with Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and Zn(II) salts by Murukan et al. [47]. The complexes were characterized on the basis of elemental analyses, molar conductance, magnetic susceptibility data, U.V-vis, IR, ESR, and NMR spectral studies, wherever possible and applicable. Analytical data reveal that the Ni(II), Cu(II) and Zn(II) complexes possess 1:1 metal–ligand ratios and that Mn(II), Fe(II) and Co(II) complexes exhibit 1:2 ratios. Infrared spectral data suggested that the bishydrazone behaves as a monobasic tridentate ligand with ONO donor sequence towards the metal ions. X-ray diffraction study of the Cu(II) complex indicated an orthorhombic crystal

Manganese(II),3d5

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lattice. The EPR spectral data showed that the metal–ligand bond has considerable covalent character. The electrochemical behavior of the copper(II) complex was investigated by cyclic voltammetry (CV). Antibacterial tests of the ligand and the metal complexes were also carried out and it has been observed that the complexes are more potent bactericides thanthe ligand. 3.3. PRESENT WORK The present work deals with synthesis and characterization of Mn(II) complexes with six semicarbazide and thiosemicarbazide based ligands (L1, L2, L3, L4,L5 and L6). These complexes were characterized on the basis of elemental analysis, molar conductance, magnetic moment, IR, electronic and EPR spectral studies. PREPARATION OF MANGANESE(II) COMPLEXES The complexes with ligands L1to L6were prepared by using semicarbazide and thiosemicarbazide based ligands and corresponding Mn(II) salts (MnCl2.4H2O, and MnSO4.H2O). Synthesis of complexes with ligands L1 to L6 A hot ethanolic (20mL) solution of corresponding metal salts (0.001 mol) was mixed with hot ethanolic solution of the corresponding ligands (L1 - L6)(0.002 mol). The mixture was refluxed at 80°C (±5). The conditions for the different metal complexes are given in the table 3.1. On cooling the contents complexes were precipitate out. These were filtered, washed with 50% ethanol and dried in vacuum over P4O10.

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Table 3.1. Reaction conditions for different metal complexes

Complex Reflux time (hr)

pH Color Melting Point / Decomposition Temperature

(°C) [Mn(L1)2Cl2] 3 8 creamish red 215 [Mn(L1)2SO4] 10 8 creamish red 220 [Mn(L2)2Cl2] 14 8 white 240 [Mn(L2)2SO4] 20 6 white 260 [Mn(L3)2Cl2] 12 8 white above 260 [Mn(L3)2SO4] 7 6 white above 260 [Mn(L4)2Cl2] 15 8 white above 260 [Mn(L4)2SO4] 7 6 white above 260 [Mn(L5)2Cl2] 31 8 yellow above 260 [Mn(L5)2SO4] 36 6 white 250 [Mn(L6)2Cl2] 14 8 white above 260 [Mn(L6)2SO4] 15 8 white above 260

3.4. RESULTS AND DISCUSSION On the basis of elemental analysis (Table 3.2) the complexes were found to have general compositions Mn(L)2X2 (where L=L1 to L6 X=CI¯, ½ SO42-]. The molar conductance data of these complexes in dimethylsulphoxide (DMSO) indicated that these complexes are non-electrolytes in nature therefore, these complexes may be formulated as [Mn(L)2X2] [X=CI¯, ½ SO42-].

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Table 3.2. Molar conductance and elemental analyses of Mn(II) complexes

Complex M.wt. Molar conductance

Yield (%)

Elemental analyses Found (Calculated)

M C H N [Mn(L1)2Cl2] 635.9 10.7 62 8.57 33.90 3.08 13.09 MnC18H20N6O2Br2Cl2 (8.63) (33.97) (3.15) (13.21) [Mn(L1)2SO4] 660.9 12.1 61 8.27 32.59 2.94 12.67 MnC18H20N6O6Br2S (8.31) (32.68) (3.03) (12.71) [Mn(L2)2Cl2] 667.9 10.8 57 8.17 32.29 2.92 12.78 MnC18H20N6Br2S2Cl2 (8.22) (32.34) (2.99) (12.86) [Mn(L2)2SO4] 692.9 10.1 59 7.87 31.13 2.89 12.07 MnC18H20N6O4Br2S3 (7.92) (31.17) (2.81) (12.12) [Mn(L3)2Cl2] 531.9 12.5 52 10.26 49.52 4.81 15.72 MnC22H26N6O2Cl2 (10.32) (49.63) (4.89) (15.79) [Mn(L3)2SO4] 556.9 13.1 54 9.78 47.33 4.61 15.01 MnC22H26N6O6S (9.86) (47.41) (4.67) (15.08) [Mn(L4)2Cl2] 563.9 11.3 53 9.71 46.78 4.54 14.87 MnC22H26N6S2Cl2 (9.74) (46.82) (4.61) (14.90) [Mn(L4)2SO4] 588.9 15.4 56 9.25 44.79 4.37 14.23 MnC22H26N6O4S3 (9.32) (44.83) (4.42) (14.26) [Mn(L5)2Cl2] 687.9 14.8 52 7.93 55.74 4.31 12.14 MnC32H30N6O4Cl2 (7.98) (55.82) (4.36) (12.21) [Mn(L5)2SO4] 712.9 15.2 54 7.74 53.81 4.18 11.71 MnC32H30N6O8S (7.70) (53.86) (4.21) (11.78) [Mn(L6)2Cl2] 719.9 13.6 54 7.59 53.31 4.13 11.62 MnC32H30N6O2S2Cl2 (7.63) (53.34) (4.17) (11.67) [Mn(L6)2SO4] 744.9 14.9 55 7.32 51.58 4.07 11.21 MnC32H30N6O6S3 (7.37) (51.55) (4.03) (11.28)

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MAGNETIC MOMENT

The ground state term in this case is 6A1g, as there is only one configuration possible with five unpaired electrons. This is corresponding to half filled d shell electrons and is spherically symmetrical. There is no temperature independent paramagnetic effect and no reduction of the magnetic moment below the spin-only value by spin-orbit coupling with higher ligand field terms. The magnetic moments are indeed found very close to spin-only value of 5.92 B.M. The magnetic moment of all the Mn(II) complexes under study at room temperature lies in the range of 5.81-5.91 B.M. (Table 3.4), corresponding to five unpaired electrons.

FT-IR FT-IR spectra of the ligands have already been explained in chapter 2. On complexation the position of bands (Figures 3.3-3.12) due to ν(>C=N) and ν(>C=O) in semicarbazone complexes (L1, L3, L5) and due to ν(>C=N) and ν(>C=S) in case of thiosemicarbazone complexes(L2, L4, L6), is shifted by 10-90 cm-1. This indicated that the coordination takes place through the nitrogen atoms of imine group, oxygen atom of the >C=O group in case of semicarbazone complexes and nitrogen atoms of imine group and sulphur atom of the >C=S group in case of thiosemicarbazone complexes and all the ligands behaved as bidentate (Table 3.3).

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Table 3.3. Important infrared spectral bands (cm−1) and their assignments.

Compounds Assignements Remarks ν(N−H) ν(C=O) ν(C=N) ν(C=S) ν(M−N) Ligand(L1)

3197

1708

1583

[Mn(L1)2Cl2] 3193 1633 1566 461 [Mn(L1)2SO4] 3195 1683 1567 458 ν3 splitted at

1128, 1067 cm-1 and 1021 while ν1

at 954 cm-1 indicating bidentate nature of SO4

2-[48] Ligand(L2) 3142 1585 852 [Mn(L2)2Cl2] 3143 1512 783 [Mn(L2)2SO4] 3171 1542 794 ν3 splitted at 1113,

1089, and 1054 while ν1 at 903 cm-1 indicating bidentate nature of SO4

2-[48] Ligand(L3) 3180 1690 1586 [Mn(L3)2Cl2] 3178 1618 1408 511 [Mn(L3)2SO4] 3174 1639 1555 501 ν3 splitted at 1112,

1054, and 1021 while ν1 at 909 cm-1 indicating bidentate nature of SO4

2- Ligand(L4) 3142 1600 846 [Mn(L4)2Cl2] 3410 1561 617 408 [Mn(L4)2SO4]

3369 1530 815 519 ν3 splitted at 1163, 1089, and 1054

while ν1 at 973 cm-1 indicating bidentate nature of SO4

2- Ligand(L5) 3147 1693 1571 [Mn(L5)2Cl2] 3196 1605 1456 497 [Mn(L5)2SO4] 3193 1524 1458 508 ν3 splitted at 1194,

1170 and 1118 while ν1 at 990 cm-1 indicating bidentate nature of SO4

2-

Ligand(L6) 3144 1601 762 [Mn(L6)2Cl2] 3143 1547 720 [Mn(L6)2SO4] 3143 1566 700 ν3 splitted at 1118,

1085 and 1031 while ν1 at 908 cm-1 indicating bidentate nature of SO4

2-

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Figure 3.3. FT-IR spectrum of [Mn(L1)2Cl2]

Figure 3.4. FT-IR spectrum of [Mn(L1)2SO4]

Manganese(II),3d5

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Manganese(II),3d5

81



Manganese(II),3d5

82



Manganese(II),3d5

83



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84

ELECTRONIC SPECTRA High-spin six coordinated Mn(II) complexes, has a d5 electronic configuration i. e. t2g3, eg2,which gives rise to ground state 6A1g. It is derived from the free ion 6S state, which is orbitally non-degenerate. It cannot be split by crystal field (of any symmetry). The absence of any other spin sextet terms implies that all crystal field transitions will be spin forbidden, as well as Laporte forbidden. The crystal field spectra of high spin d5 complexes are therefore expected to very weak. There is number of lower spin terms with three (quartets) or one (doublets) unpaired electron. Transition to spin doublets levels is highly forbidden, there being a change in the spin quantum number 2 in such cases, thus they are not expected to observe. The spin quartets 4F, 4G, 4D arise from the configuration t2g4 eg1, t2g3 eg2 and t2g2 eg3 with strong field crystal energies -10Dq respectively. Thus the quartet term 4G splits into 4T1g, 4T2g, 4A1g, 4Eg and 4D splits into 4T2g, 4Eg, while 4F splits into 4A2g which is independent of the crystal field. Same type of splitting applies whether the environment of the metal is tetrahedral or octahedral only g subscripts were omitted. Electronic spectra of complexes under study show bands in the region of 9681-18622 (ν1), 18418-27932 (ν2), 21413-30487 (ν3), 27173-34965 (ν4), cm-1 which are characteristic of octahedral geometry [Table 3.4]. The assignments are obtained by fitting the observed spectra to Tanabe-Sugano diagram. Thus these bands may be assigned to following transitions: 6A1g 4T1g (4G) (ν1) (broad) 6A1g 4Eg, 4A1g (4G) (10B+5C) (ν2) (sharp) 6A1g 4Eg (4D) (17B+5C) (ν3) and (sharp) 6A1g 4T2g (4P) (ν4) respectively. (broad) Racah and Slater Condon-shortly parameters The values of various parameters are listed in Table 3.4. Parameters B and C are linear combinations of certain Coulomb’s and exchange integral and are generally treated as empirical parameters obtained from the spectra of the free ions. Slater Condon-shortly parameters F2 and F4 are related to the Racah parameters B and C [50] as follows:

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85

B=F2-5F4 C= 35F4 The values of the parameters F2 and F4 are also listed in Table 3.4. The electron-electron repulsion in the complexes is less than that in the free ion, resulting in an increased distance between electrons and thus an effective increase in the size of the orbitals in the complexes. On increasing delocalization the value of β decreases and is less than 1 in the complexes. An estimate of the β has been obtained from the nephelauxetic parameter for the ligand (hx) and nephelauxetic parameters of the metal ion Km as (1-β) = hx� Km. The values of the parameter of the metal (hx) for the complexes have been calculated using the covalency contribution of Mn(II) ions i. e. Km = 0.07 while the B corresponds to 786 cm-1 for the free Mn(II) ions [49] has been used to calculate the values of β. The calculated values of β and hx indicate that the complexes under study have appreciable ionic character.

Figure 3.13. UV-visible spectrum of [Mn(L1)2Cl2]

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Figure 3.14. UV-visible spectrum of [Mn(L1)2SO4]


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EPR SPECTRA The high spin Mn(II) has an orbital 6S5/2 ground state term, which should not interact with the electric field in the first order case. However, the combined action the electric field gradient and the spin-spin interaction produces splitting of the energy levels due to second order spin-orbit coupling [51] between the 6A1g ground state and the lowest level of the manifold 4A2g state. The axial field splitting parameter D in the case of an axially distorted octahedral field expects the magnitude of the zero fields splitting. The spin Hamiltonian Mn(II) can be defined as H =gβH.S + D[(S2

z�1/3S(S+1))]+AS.I

Where H is the magnetic field vector, g is the spectroscopic splitting factor, β is the Bohr magneton, A is the manganese hyperfine splitting constant, S is the electron spin vector, I is the nuclear vector, S=5/2 and Sz is the diagonal spin operator. For S=5/2 and noting selection rule ∆ms=�1 five allowed transitins could arise when field separation are dependent on �, the angle between the applied magnetic field and the symmetry axis. These transitions are [52]. ∆�s=�5/2 3/2; H=H0�2D (3cos2�_1) ∆�s=�3/2 1/2; H=H0�D (3cos2�_1) ∆�s=�1/2 1/2; H=H0

Where H=hv/gβ and � is the angle between the applied magnetic field and the direction of the axial distortion [53]. When the complex is octahedral only the central ∆ms= ½ transition will be observed since it has only a second order dependence split into a sextet due to electron spin nuclear spin hyperfine coupling (55Mn, I=5/2). However, the zero field splitting is appreciable than the other electronic transitions will appear in the powder spectrum and the values of zero field splitting can thus be evaluated. In addition to allowed transitions the frozen solution spectra give low intensity pair of forbidden between each pair allowed lines. These lines are due to simultaneous change of both the electron nuclear spin by �1.

Manganese(II),3d5

89

The EPR spectra of our complexes have been recorded as polycrystalline samples [Table 3.4]. The spectra of polycrystalline sample [Figures 3.18-3.23] at room temperature are isotropic in nature. giso value lies in the range of 2.0014 – 2.0022.

Figure 3.18. EPR spectrum of [Mn(L2)Cl2]

Figure 3.19. EPR spectrum of[Mn(L2)2SO4]

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90

Figure 3.20. EPR spectrum of [Mn(L3)2Cl2]

Figure 3.21. EPR spectrum of [Mn(L3)2SO4]

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91

Figure 3.22. EPR spectrum of [Mn(L4)2SO4]

Figure 3.23. EPR spectrum of [Mn(L6)2Cl2]

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Table 3.4. Magnetic moment, electronic spectral data, and EPR Spectral data of the Mn(II)

Complexes

Complexes µeff. (B.M.) λmax (cm-1) Dq B C β F2 F4 hx giso

[Mn(L1)2Cl2] 5.91 10121,18622, 23095, 32573 703 639 2446 0.8 988 70 2.67 2.0018

[Mn(L1)2SO4] 5.84 10000, 17825, 22272, 30864 699 635 2295 0.8 963 66 2.74 2.0014

[Mn(L2)2Cl2] 5.81 18622, 22523, 26525, 28902 629 572 3361 0.7 1052 96 3.89 2.0019

[Mn(L2)2SO4] 5.92 9785, 18418, 22626, 29674, 32258 661 601 2481 0.8 956 71 3.36 2.0017

[Mn(L3)2Cl2] 5.97 9980, 17953, 22222, 34843 671 610 2371 0.8 949 68 3.2 2.0021

[Mn(L3)2SO4] 5.93 10081, 18622, 22676, 34602 637 579 2566 0.7 946 73 3.76 2.0022

[Mn(L4)2Cl2] 5.96 9681, 16920, 21413, 34965 706 642 2100 0.8 942 60 2.62 2.0015

[Mn(L4)2SO4] 5.87 1021, 18727, 23529, 28653 755 686 2373 0.9 1025 68 1.82 2.0018

[Mn(L5)2Cl2] 5.89 9709, 19193, 23310, 27173, 28248 647 588 2662 0.8 968 76 3.6 2.002

[Mn(L5)2SO4] 5.92 18330, 23052, 25157, 28854, 331 301 4009 0.4 873 115 8.82 2.0015

[Mn(L6)2Cl2] 5.99 19201, 27932, 30487, 28916 402 365 4856 0.5 1059 139 7.65 2.0014

[Mn(L6)2SO4] 5.96 18416, 22624, 27248, 32258 727 661 3204 0.8 1118 92 2.28 2.0016

3.5. CONCLUSION Thus on the basis of elemental analyses, molar conductance measurements, magnetic moment susceptibility, FT-IR, mass, electronic and EPR spectral studies the following structures may be proposed for Mn(II) complexes [Figures 3.24-3.35].

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93

Figure 3.24. Structure of complex [Mn(L1)2Cl2]

O O

OO

S

O

CH2N

NH

N

H3C

Br

O

H2NN

Mn

H3C

Br

HN

Figure 3.25. Structure of complex [Mn(L1)2SO4]

CCH3

N

O

HN

C

H2NN

O

NH

C

NH2

CH3C

Br

Mn

Cl

Br

Cl

Manganese(II),3d5

94

CCH3

N

S

HN

C

H2NN

S

NH

C

NH2

CH3C

Br

Mn

Cl

Br

Cl


H3C

N

HN

CH2N

S

Br

H3C

N

NH

CH2N

S

Br

O

O

SMn

O

O


Manganese(II),3d5

95

NHN

H2N O N NH

NH2OM

Cl

Cl



O

NH2N C

O

NH

O

O O

S

OMn

NNH

CH2N

Manganese(II),3d5

96

NHN

H2N S N NH

NH2SMn

Cl

Cl



S

NH2N C

S

NH

O

O O

SO

Mn

NNH

CH2N

Manganese(II),3d5

97

O

NHN

H2N O N NH

NH2O

O

M

Cl

Cl


O

H2N C

O

NH

O

O O

S

OMn

O

NNH

CH2N

O

N


Manganese(II),3d5

98

O

NHN

H2N S N NH

NH2S

O

M

Cl

Cl


S

H2N C

S

NH

O

O O

S

OMn

O

NNH

CH2N

O

N


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99

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