230 Tetrahydrotriazine Co n complexes Transition Metal Chemistry, 19 (1994) 230-234

4-amino-2,6-dimethyl-5-oxo-3-thioxo-2,3,4,5-tetrahydro- 1,2,4- triazine cobalt(II) complexes Gregorio S~inchez, Maria D. Santana, Maria J. Vidal, Gabriel Garcia and Gregorio L6pez* Departamento de Qu/mica Inorgdnica, Universidad de Murcia 30071-Murcia, Spain

Eduardo P6rez Departamento de Ingenieria Quimica, Universidad de Murcia Cartagena, Murcia, Spain

Summary

Cobalt(ll) complexes of 4-amino-2,6-dimethyl-5-oxo-3- thioxo-2,3,4,5-tetrahydro-1,2,4-triazine (taz) were prepared by reacting the triazine with the corresponding cobalt salt. The isolated compounds were of the types: [CoCl2(taz)], lCoXz(taz)2(H20)2 ] (X = Br or I), [CoX2(taz)2 ] (X = Br, SCN or NO3) and [Co(taz)2(HzO)2]X2(X = ClOg, BFg or NO3). Conductance, magnetic and spectroscopic (i.r. and vis.) data were used for structural assignments. Pseudooctahedral and pseudotetrahedral structures are proposed for the complexes, with the triazine molecule acting either as a monodentate nitrogen-donor or a bidentate nitrogen sulphur-donor ligand.

Introduction

4-Amino-5-oxo-l,2,4-triazines are biologically active compounds (1'2). Recently, it has been shown that 4- amino-5-oxo-3-phenylamino-l,2,4-triazine has a powerful inhibiting effect on the cell wall lignification catalysed by peroxidase t3J, and alters the integrity of the chloroplast ~4).

Complexes of nickel(II) and cobalt(II) with 4-amino-6- methyl-5-oxo-3-phenylamino-4,5-dihydro- 1,2,4-triazine tS) and 4-amino-6-methyl-5-oxo-3-thioxo-2,3,4,5-tetrahydro- 1,2,4-triazine ~6'7), and of nickel(II) (8), palladium(II) ~9) and rhodium(III) ~lm with 4-amino-2,6-dimethyl-5-oxo-3- thioxo-2,3,4,5-tetrahydro-l,2,4-triazine (taz), have been reported previously.

Here we describe the preparation ofcobalt(II) complexes of the ligand taz. Monodentate (4-amino) nitrogen donation or bidentate (4-amino and 3-thioxo) ni t rogen-sulphur donation are the proposed coordination modes of the triazine, depending upon the identity of the cobalt salt, the experimental conditions and the presence (or absence) of H20 in the complex.

Experimental

Carbon, hydrogen and nitrogen analyses were made with a Perkin-Elmer 240C microanalyser, and cobalt was determined by titration with EDTA ~11). l.r. spectra were recorded on a Perkin-Elmer 1430 spectrophotometer, with samples as Nujol mulls between polyethylene sheets. Electronic spectra were recorded on a Hitachi U 2300 instrument. Magnetic susceptibilities were measured by the Faraday method, using a DMS-5 magnetometer calibrated with Hg[Co(SCN)4] [H = 15 kG; H(OH/•z) = 29 kG cm 1]. Thermal decomposition studies were carried out using a Mettler TA-3000 system provided with a Mettler TG-50 thermobalance and DSC-20 differential scanning calorimeter. The t.g.a, and DSC curves were

* Author to whom all correspondence should be directed.

obtained at a heating rate of 10 ~ C/min under dynamic nitrogen atmosphere (100 cm3/min). Conductance measure- ments were performed with a Crison 525 conductimeter (solvent acetone; c ~ 1 0 - 3 m o l d m -3) and the experi- mental results were compared with those reported in the literature ~12).

The starting compounds Co(C104)2- 6H20 and Co(BFg) 2. 6 H 2 0 were prepared from Co(CO3) and either HC1Og or HBFg, respectively. The remaining salts were commercial products. 4-Amino-2,6-dimethyl-5-oxo-3-thioxo-2,3,4,5- tetrahydro-l,2,4-triazine was prepared as described else- wheretl 3) and was recrystallized from EtOH.

[CoCl2( taz )] (1)

An Et20 solution of the triazine (250 mg, 1.45 mmol) was added to a solution of anhydrous CoC12 (189 mg, 1.45 mmol) in E tOH (4 cm 3) and the mixture was boiled under reflux for 8 h. The product was removed by filtration, washed with E tOH Et20 (1:1) and dried in vacuo in a P401o desiccator.

[ CoBr2(taz )2( H20 )2 ] (2)

The triazine (250 mg, 1.45 mmol) dissolved in Et20 (40 cm 3) was added to a solution of CoBr2.6H20 (230 mg, 0.72 mmol) in EtOH (4 cm3), whereupon a beige-pink solid precipitated. The suspension was stirred at room temperature for 4 h. The solid was separated by filtration, washed with E t20 and dried in vaeuo in a PgO10 desiccator.

[CoBr2(taz)2] (3)

Method A. This compound was obtained when a sample of complex (2) (100 mg, 0.167 mmol) was heated at 110 ~ C for 15rain and then cooled to room temperature in a P4010 desiccator.

Method B. A solution of the triazine (260 mg, 1.51 mmol) in E t20 (20cm 3) was added dropwise, with constant stirring, to a solution of anhydrous CoBr 2 (160mg, 0.73 mmol) in Et20, whereupon a pale blue precipitate formed. The suspension was then boiled under reflux for 30min. The product was filtered off, washed with E t20 and dried in vacuo in a P4Olo desiccator.

[CoI2( taz )2(H20)2 ] (4)

Triazine (250 mg, 1.45 mmol) was added to a solution of COI2.6H20 (240mg, 0.72mmol) in E tOH (10cm a) and the mixture was stirred at room temperature for 30min. E t20 (40cm 3) was then added with constant stirring whereupon a beige solid precipitated, which was removed

0340-4285 �9 1994 Chapman & Hall

Transition Metal Chemistry, 19 (1994) 230-234 S5.nchez et al. 231

by filtration, washed with Et20 and dried in vacuo in a P4010 desiccator.

[Co(SCN)2taz)2 J (5)

A solution of the triazine (200mg, 1.16mmol) in Et20 (40 cm 3) was added dropwise, with constant stirring, to a solution of Co(SCN)2 (100 rag, 0.57 mmol) in EtOH (5 cm 3). After a few minutes a green precipitate formed and the suspension was stirred at room temperature for 2 h. The precipitate was removed by filtration, washed with Et20 and dried under nitrogen. The complex was recrystallized from Me/CO-Et20 .

[ Co( taz )z( H20 )2J X 2 [ X = ClO 4 (6), BF 4 (7) and NO 3 (8)]

In separate experiments, the triazine (250 rag, 1.45 mmol) dissolved in Et20 (40cm 3) was added to a solution of CoXz'6H20 (X=C104, BF 4 or NO3) (0.72mmol) in EtOH (4 cm3), whereupon a pink solid precipitated. The suspension was stirred at room temperature for 4 h, and the solid was removed by filtration, washed with Et20 , dried in air and recrystallized from MezCO-Et20.

[ Co( N O 3)2( taz )2 ] (9)

Addition of a solution of the triazine (250 rag, 1.45 mmol) in Et20 (40cm 3) to a solution of Co(NO3)2"6H20 in a mixture of EtzO-EtOH (10:1) caused the formation of a pink precipitate. The resulting suspension was boiled under reflux for 12 h. The precipitate was then removed by filtration, washed with Et20 and dried in vacuo in a P401o desiccator.

Results and discussion

Complexes (2), (4) and (5)- (7) were prepared by room temperature reaction of the triazine (in diethyl ether) with the corresponding cobalt salt (in EtOH) in 2:1 molar ratio. Complex (1) was obtained from COC12 and the triazine in the 1 : 1 molar ratio at reflux temperature, whilst complex (3) was formed, either by reacting the triazine and CoBr 2 in ether or from thermal dehydration of (2). Complex (8) was obtained from Co(NO3)2"6H20 and triazine in t:2 molar ratio at reflux temperature. The results of our preparative study are presented in Scheme 1 and the partial elemental analyses, colours, yields and decomposition temperatures of the complexes are listed in Table 1.

I.r. data relevant to structural assignments are collected in Table 2. The changes in the stretching and deformation modes of the 4-NH 2 group suggest that in all the com- plexes the 4-amino nitrogen atom is involved in coordi- nation to cobalt. However, the C - - O stretching vibration, at 1665 in the free triazine, is shifted to higher wave- numbers (in the 1710-1690 cm- 1 range) in all the complexes, indicating that the carbonyl group remains uncoordinated. In the i.r. spectrum of the free triazine two partially over- lapped bands are observed at 1400-1380 cm- 1, attributed to the thioamide II band (8'14) and the symmetric methyl bending mode. In some of our complexes [(2) (4) and (8)] only one band is found at ca. 1380cm -1, but the presence of an additional band at ca. 1340 c m - t in the spectra of ( I ) and (5) - (7) is attributed to additional coordination of the triazine by the sulphur atolh of the

3-thioxo group (the triazine acts as a chelating nitrogen- sulphur-donor ligand). A similar assignment has been made for [Ni(taz)/(H20)2 ] (C104)2 (8) and [(qO-p-cymene)- RuCl(taz)]BF4~l 5) where single-crystal XRD studies have confirmed the chelating nature of taz.

The magnetic moments at 300 K are listed in Table 3. The values are as expected for paramagnetic species containing three unpaired electrons, with a large orbital contribution~l 6).

The electronic spectroscopy data are collected it] Table 3. The reflectance spectrum of [CoC12L] is consistent with a pseudooctahedral environment around the Co 2 + ion, the observed band being attributed to the transition 4T10(F ) 4Ttg(p)(17). Thus, a polymeric structure with four bridging chlorine atoms and a chelating nitrogen-sulphur-donor taz ligand may be proposed for complex (1). The compound gives a blue solution in acetone and the visible spectrum shows the typical split band corresponding to a pseudo- tetrahedral configuration (17). Since the compound [NiCl/(taz)2] was previously reported (s), attempts were made to prepare the cobalt analogue by reacting cobalt(II) chloride with the triazine in 1:2 ratio, but these were unsuccessful.

The lower ability of bromine to be involved in bridging systems compared to chlorine is manifested in complex (2). The absence of a band around 1340cm -1 in the i.r. spectrum of (2) suggests that the triazine behaves as a monodentate nitrogen-donor ligand in this complex. A

taz CoOl 2

CoBr2.6H20 2 taz or ~-

Col2'H20

CI / I I cJ cI (1) (polymeric)

Me~N/N~--y,/Me taz: /~L. . .~. . . I

S ~'~'" "?" "~O

NH2

CoBr2

~ 2 taz

f S N I / x

H 2 0 - - C o - - O H 2

S i x = Br (2) or l (4)

SANN ~ B r Co.~

S,.... N Br

(3)

Co(NCS)2 2 taz NCS

N / ] SCN (5)

[ H20 12+

CoX2-6H20 2taz~ �9 [(.S--~C~o/'N~/ 2X-

2taz '~, L N H!O J X = ClO4 (6), BF4 (7) or NO3 (8)

S ~ N I .,O--pN ~ O

/ O - C o - - O O I " N - O " N I (9)

'~S

Scheme 1. Synthesis and suggested structures of the cobalt(II) complexes (NS = taz).

232 Tetrahydrotriazine Co ~ complexes

Table 1. Analytical and physical data for the complexes.

Transition Metal Chemistry, 19 (1994) 230 234

Complex Colour Yield Found (Calcd.)(~o) Decomposition (~o) C H N Co temperature (~

(1) Blue 63 20.0 2.8 18.3 19.3 188 (19.9) (2.7) (18.6) (19.5)

(2) Beige 79 19.8 3.2 18.4 9.8 81 (20.0) (3.3) (18.7) (9.8)

(3) Blue 66 21.1 2.5 19.7 10.6 175 (21.3) (2.8) (19.9) (10.4)

(4) Beige 88 17.2 2.8 15.8 8.3 102 (17.3) (2.9) (16.2) (8.3)

(5) Green 57 27.4 3.0 26.7 11.1 152 (27.7) (3.1) (27.0) (11.3)

(6) Pink 80 18.9 3.4 17.4 9.0 100 (18.8) (3.1) (17.6) (9.2)

(7) Pink 79 19.6 3.4 17.9 9.6 125 (19.6) (3.3) (18.3) (9.6)

(8) Pink 68 21.4 3.6 24.7 10.4 90 (21.3) (3.6) (24.9) (10.4)

(9) Pink 76 22.7 3.1 26.2 11.1 150 (22.8) (3.0) (26.6) (11.2)

T a b l e 2. R e l e v a n t i.r. data (cm - 1).

Compound v(NH) v(C=O) 6(NH2) v(CzS) Others

Free taz 3320 1670 1530 1380 3220

(1) 3190 1700 1610 1340 3120

(2) 3180 1695 1600 1380 3110sh 1590 3070

(3) 3180br 1700 1590 1380 3080br

(4) 3230sh 1690 1600 1380 3170 1585 3080

(5) 3160 1700 1610 1340 3100

(6) 3220 1700 1610 1325 3140

(7) 3220 1700 1610 1325 3160

(8) 3190 1705 1580 1340 3130

(9) 3230 1705 1610 1380 3150 1595

3490 (v OH) 1630 (6 H20 )

3500 (v OH) 1620 (6 HaO)

2060 (v C=N )

3560, 3380 (v OH) 1640 (6 HaO) 1140, 1050sh (v 3 ClO4) 3450br (v OH) 1630 (6 H20) 1120, 1050sh (v 3 BF4) 3400br (v OH) t600sh (6 HzO ) 1380 (v3E' NO3)

sharp, strong band at 3490 cm- 1 indicates the presence of coordinated HaO. The visible spectrum is consistent with a pseudooctahedral structure, although the electronic spectrum of the acetone solution suggests the presence of a tetrahedral species in this solvent. The t.g.a, curve of complex (2) under dynamic nitrogen atmosphere shows a first decomposition stage between 81 and 125~ in which a weight loss occurs corresponding to two HaO molecules (Figure I). The resulting compound is stable up to 175 ~ C and decomposes slowly and irregularly between 175-580 ~ C. The DSC curve of this compound shows an

endothermic peak for the dehydration, the enthalpy change for this process being + 131.3 kJmol-1 .

Complex (3) can be prepared from (2) by heating to 110 ~ C, or alternatively by reaction of anhydrous CoBr a and triazine. Its i.r. spectrum shows the absence of H 2 0 and suggests that the triazine acts as a monodentate nitrogen-donor ligand. The vis. spectrum shows the characteristic absorption of tetrahedral complexes of cobalt(II) both in the solid state and in acetone solution ~14).

The spectroscopic data indicate that (4) should be formulated as [Co(taz)z(HaO)aI2]. The complex is soluble

Transition Metal Chemistry, 19 (1994) 230-234

Table 3. Vis. spectra, molar conductance and magnetic moments.

S5.nchez et al. 233

Compound u.v.-vis. AM" #eff (B.M.) ( x 10- 3 cm- 1) (~- 1 cm 2 tool- 1) (at 300 K)

(1) NujoI: 16.9 Me2CO: 14.8 (380); 15.6sh (290)

(2) Nujol: 20.1; 18.0 M%CO: 14.8 (470); 16.Ssh (203)

(3) Nujol: 13.7; 14.2; i5.0; 15.6; 18.3 MezCO: 14.8 (406); 16.8 (205)

(4) Nujol: 19.9; 17.5sh MezCO: 14.4 (454); 16.2sh (240)

(5) Nujol: 17.2; 16.2 MezCO: 15.9 (375); 17.8 (226)

(6) Nujol: 19.9; 17.4sh MezCO: 19.8 (29)

(7) Nujol: 20.0 Me2CO: 20.0 (52)

(8) Nujol: 19.9; 22.1 MezCO: 19.0 (86)

(9) Nujol: 19.6 Me2CO: 19.2

21 5.19

14 4.67

21 4.52

17 4.87

22 5.24

205 4.71

181 4.65

15 4.61

12 4.41

"All values for acetone solutions.

i

.$

t.g.

0 I I I 0 200 400 600

Temperature (~

d.t.g.

Figure 1. T.g.a. and d.t.g, curves of complex (2).

7 5 E

N

2 -

1 0

0 0

0

0

0

0000 O 0 0 O 0 0 0 0 0 0 0 0

00

e e e e

I I I 1 oo 200 300

T (K)

Figure 2. The variation of zuT versus Tfor complex (5).

in MeOH and acetone but the electronic spectrum of the acetone solution shows the split band corresponding to a pseudotetrahedral configuration.

The magnetic moment of complex (5) at 300K is 5.24 B.M. and the plot ofzTversus Tbetween 6 and 291 K (Figure 2) is typical for an octahedral cobalt(II) complex (18). The i.r. data appear to indicate that it contains nitrogen- bonded thiocyanate (19) and n i t rogen-su lphur -donor bidentate triazine. Accordingly, complex (5) is formulated as [Co(NCS)z(taz)2]. In acetone solution, complex (5) behaves as a nonelectrolyte but the electronic spectrum of this blue solution shows that a tetrahedral complex is

present, probably [Co(NCS)2(taz)2], where taz is r/1 through nitrogen only,

The i.r. spectra of complexes (6)-(8) indicate that they contain bidentate ni trogen-sulphur-donor triazine, with two H20 molecules completing the hexacoordination of cobalt, and their vis. absorption maxima are consistent with the presence of a [CON28202] chromophore. The presence of free perchlorate, tetrafluoroborate and nitrate in the respective compounds is shown by bands at 1140, 1120 and 1380 cm - 1, respectively(2O). Complexes (6) and (7) are soluble in acetone, where they behave as 1:2 electrolytes, but the acetone solution of (8) is nonconduc-

234 Tetrahydrotriazine Co" complexes Transition Metal Chemistry, 19 (1994) 230 234

ring, which may be attributed to replacement of the axial H 2 0 molecules by nitrate ions. This is supported by the vis. spectrum of the solution, since the absorption maximum at 19.9 x 103cm -1 in the solid state is shifted to 19.0 x 10 3 cm 1.

The i.r. spectrum of complex (9) indicates that the triazine acts as monodentate nitrogen-donor ligand (no band is found around 1340 c m - 1). The vis. spectrum of the solid sample shows an absorption band at 19.6 x 10 3 c m - 1, characteristic of octahedral coordination. Furthermore, the vis. spectrum of the acetone solution is almost coincident with that in the solid state and the solution is nonconduc- ting. Consequently, the structure represented in Scheme 1 is assigned to complex (9). Two i.r. bands from chelating bidentate nitrate ~2~ should be observed at ca. 1450 and 1300cm -1 but unfortunately both spectral regions are obscured by strong absorptions of the taz ligand.

Acknowledgements

The authors thank the Direcci6n General de Educaci6n y Universidad de la Comunidad Aut6noma de Murcia, Spain, for financial support.

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(Received 22 February 1993) T M C 2977