Inorganica Chimica Acta 362 (2009) 3421–3426

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Inorganica Chimica Acta

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Two new supermolecular structures of organic–inorganic hybrid compounds:[Zn(phen)(SO4)(H2O)2]n and [Cu(phen)(H2O)2] � SO4 (phen = 1,10-phenanthroline)

Xin Hu a,*, Jixi Guo b, Cong Liu a, Han Zen a, Yongjiang Wang a, Weijun Du a

a College of Life Science and Chemistry, Xinjiang Normal University, No. 102 Xinyi Road, Urumqi 830054, Chinab Institute of Applied Chemistry, Xinjiang University, Urumqi 830046, China

a r t i c l e i n f o a b s t r a c t

Article history:Received 13 March 2008Received in revised form 2 March 2009Accepted 6 March 2009Available online 16 March 2009

Keywords:Crystal structureFluorescenceOrganic–inorganic hybridPhenSupramolecular structure

0020-1693/$ - see front matter � 2009 Published bydoi:10.1016/j.ica.2009.03.011

* Corresponding author. Tel.: +86 991 4332683.E-mail address: huxin@xjnu.edu.cn (X. Hu).

Two new organic–inorganic hybrid compounds [Zn(phen)(SO4)(H2O)2]n (1) and [Cu(phen)(H2O)2] � SO4

(2) have been prepared by conventional aqueous solution synthesis and characterized by single-crystalX-ray diffraction, IR spectroscopy, thermal gravimetric analysis (TGA) and fluorescent spectroscopy. Incompound 1, the sulfate group adopts bidentate mode to coordinate with two Zn(II) ions to form one-dimensional polymer. The one-dimensional polymers are further linked together via the intermolecularhydrogen-bonding and p–p stacking interactions to form a 3D supramolecular framework. Compound 2is build up of discrete [Cu(phen)(H2O]2+ cations and SO4

2� anions to form a three-dimensional frameworkvia hydrogen-bonding and p–p stacking interactions. Furthermore, the luminescent properties of both 1and 2 were studied. The complexes 1 and 2 excited at 280 nm wavelength produced characteristic lumi-nescence features, arising maybe due to the p–p transitions.

� 2009 Published by Elsevier B.V.

1. Introduction

The field of novel organic–inorganic hybrid compounds designhas attracted great attention owing to not only their intriguingstructural motifs but also their potential applications in catalysis,medicine, host guest chemistry and the promising photo-, electro-and magnetic materials [1–8]. In such materials, functionality canbe introduced from either the inorganic species or the organicbuilding blocks. Furthermore, the combination of them is expectedto produce cooperative effects so as to initiate or enhance the prop-erties [9–12]. Recently much research has focused on the synthesisof inorganic–organic hybrid frameworks using such as PO4

3�,ClO4

�, NO3� and SO4

2� and derivative ions as bridging [13–17],which play significant roles in the assembly of small-molecularcomponents, and can be used as cross-linking agents to increasedimensionality in addition to structural complexity. Organic spe-cies, on the other hand, with versatile binding modes and featurescan be used to adjust the channel size, transfer energy or electron,enhance spin-orbital coupling as well as impart chemical reactivityor chirality [18,19]. Therefore, many hybrid materials have beensynthesized using rigid organic building blocks in the past decade.In this paper, we present the synthesis and the structural charac-terization of two new organic–inorganic hybrid supramolecularcompounds based on sulfate and 1,10-phenanthroline, [Zn(phen)-(SO4)(H2O)2]n (1) and [Cu(phen)(H2O)2] � SO4 (2).

Elsevier B.V.

2. Experimental

2.1. Materials and methods

All reagents were purchased from commercial sources and usedas received. Elemental analyses of carbon, hydrogen and nitrogenwere performed on a PE-2400 analyzer. IR spectra were recordedon a BRUKER EQUINOX-55 spectrophotometer within 400–4000 cm�1 using the samples prepared as pellets with KBr. Ther-mal analyses were carried out on a NETZSCH STA 449C instrumentwith a heating rate of 5 �C min�1 in an atmosphere of flowing air.The crystal structures were performed using Bruker Smart 1000CCD and SHELXTL-97 crystallographic software package of molecularstructures. The fluorescence behaviors of the complexes were stud-ied using a HITACHI F-4500 Fluorescence Spectrophotometer witha Xe arc lamp as the light source at room temperature. The slitwidth for excitation and emission was 2.5 nm, and the scan speedwas1200 nm min�1.

2.2. Synthesis and characterization

2.2.1. Synthesis of compound 1A mixture of ZnCl2 (1 mmol), Na2SO4 (1 mmol), NaOH (1 mmol),

1,10-phenanthroline (1 mmol) and isonicotinic acid (1 mmol) weredissolved in 60 ml C2H5OH/H2O (v/v 1:1) at 90 �C with continuousstirring. The resulting solution was filtered and the filtrate waskept at room temperature for several days, forming crystals of 1.Yields based on Zn: 48%. Anal. Calc. for [Zn(phen)(SO4)(H2O)2]n:

Table 2Selected bond lengths (Å) and angles (�) for compounds 1 and 2.

Compound 1Zn–O(1) 2.0603(11) Zn–N 2.1148(11)Zn–O(1i) 2.0603(11) Zn–Ni 2.1148(11)Zn–O(2) 2.2368(10) Zn–O(2i) 2.2368(10)O(1)–Zn–O(1i) 96.20(6) O(1i)–Zn–O(2i) 92.78(4)O(1i)–Zn–Ni 92.75(5) O(1)–Zn–O(2i) 88.08(4)O(1)–Zn–Ni 170.56(5) Ni–Zn–O(2i) 88.49(4)O(1i)–Zn–N 170.56(5) O(1i)–Zn–O(2) 88.08(4)O(1)–Zn–N 92.75(5) N–Zn–O(2i) 90.52(4)N–Zn–Ni 78.49(7) N–Zn–O(2) 88.49(4)Ni–Zn–O(2) 90.52(4) O(2i)–Zn–O(2) 178.72(5)O(1)–Zn–O(2) 92.78(4) O(2ii)–S–O(2) 110.60(9)O(2ii)–S–O(3ii)

Compound 2Cu–O(1) 1.9679(11) Cu–N 2.0034(12)Cu–O(1i) 1.9679(11) Cu–Ni 2.0034(12)O(1)–Cu–Ni 173.78(5) O(1)–Cu–O(1i) 93.92(7)N–Cu–Ni 81.83(7) O(1i)–Cu–N 173.78(5)O(1i)–Cu–Ni 92.14(5) O(1)–Cu–N 92.14(5)O(2ii)–S–O(3ii) 109.54(7)

Symmetry codes for: (1) (i) �x, y, 0.5 � z; (ii) �x, y, 1.5 � z; (2) (i) �x, y, 0.5 � z; (ii)�x, y, 1.5 � z.

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C, 38.16; H, 3.20; N, 7.42. Found: C, 37.87; H, 3.18; N, 7.15%. IR for 1(KBr cm�1) 3448(br), 1519(m), 1427(m), 1196(s), 1105(s), 852(m),725(m), 619(m).

2.2.2. Synthesis of compound 2Compound 2 was prepared similarly to compound 1, by using

Cu(OAc)2 � H2O (1 mmol), NaOH (1 mmol), Na2SO4 (1 mmol),1,10-phenanthroline (1 mmol) and isonicotinic acid (1 mmol).The resulting solution was filtered and the filtrate was kept atroom temperature for several days, forming crystals of 2. Yieldsbased on Cu: 34%. Anal. Calcd for [Cu(phen)(H2O)2] � SO4 (2): C,38.35; H, 3.22; N, 7.45. Found: C, 38.43; H, 3.22; N, 7.20%. IR for2 (KBr cm�1) 3449(br), 1516(m), 1424(m), 1146(s), 1106(s),853(m), 720(m), 620(m).

2.3. X-ray crystallography

Suitable single crystals of the complexes 1 and 2 were mountedon a Bruker Smart 1000 CCD diffractometer equipped with graph-ite monochromated Mo Ka (k = 0.71073 Å) radiation. Empiricalabsorption corrections were applied. The unit cell parameters weredetermined by least square refinements of reflections in bothcases. The structures were solved by direct method and refinedby full-matrix least squares on F2. All non-hydrogen atoms wererefined anisotropically. Hydrogen atoms were located from the dif-ference map, and then added geometrically. All calculations wereperformed using SHELXTL-97 program package [20,21]. Crystal dataand experimental details for compounds 1 and 2 are contained inTable 1. Selected bond distances and angles are listed in Table 2.

3. Results and discussion

3.1. Structural description of [Zn(phen)(SO4)(H2O)2]n (1)

The molecular structure of 1 is shown in Fig. 1. The central me-tal ions are not coordinated to the isonicotinic acid moleculars. Se-

Table 1Crystal data and structure refinement parameters for 1 and 2.

Compounds 1 2

Empirical formula C12H12N2O6SZn C12H12N2O6SCuFormula weight 377.67 375.84Crystal system monoclinic monoclinicT (K) 293(2) 293(2)Wavelength (Å) 0.71073 0.71073Space group C2/c C2/ca (Å) 15.1333(9) 14.8533(13)b (Å) 14.1365(8) 13.8176(12)c (Å) 6.6942(4) 7.0140(6)a (�) 90.00 90b (�) 103.4400(10) 108.565(2)c (�) 90.00 90V (Å3) 1392.88(14) 1364.6(2)Z 4 4Absorption coefficient (mm�1) 1.945 1.786Crystal size (mm) 0.20 � 0.20 � 0.15 0.40 � 0.10 � 0.10h Range for data collection (�) 2.77–33.32 2.89–33.25Reflections collected/unique 6617 6471Limiting indices �16 6 h 6 23 �13 6 h 6 23

�15 6 k 6 21 �19 6 k 6 21�10 6 l 6 10 �10 6 l 6 10

Rint 0.0207 0.0187Dcalc (g cm�3) 1.801 1.829Data/restraints/parameters 2614/2/110 2521/2/109F(0 0 0) 768 764Goodness-of-fit on I 1.058 1.095Final R indices [I > 2h(I)] R1 = 0.0323 R1 = 0.0353

xR2 = 0.0852 xR2 = 0.0913R indices (all data) R1 = 0.0357 R1 = 0.0323

xR2 = 0.0874 xR2 = 0.0897

Fig. 1. View of the molecular structure of complex 1 (30% probability ellipsoids).

lected bond distances and angles are listed in Table 2. Zn(II) ion issix-coordinated by two nitrogen atoms (NB, N0AB) from one phenligand and four oxygen atoms from two water molecules(O1B,O1AB) and l2-SO4

2� anions(O2B, O2AB). In the complex, atomsO1B, O1AB, NB and N0AB form the equatorial plane around Zn(II)ion and the axial positions are occupied by O2B and O2AB. Themean plane deviation formed by the four equatorial atoms is about0.0592 Å. The zinc ion deviation 0.0000 Å from the equatorial planeindicates that it lies in the plane. The average Zn–O distance2.1486 Å is longer than the Zn–N distances 2.1148 Å. The bond an-gle of O(2B)–Zn–O(2AB) is 178.72� deviated from ideal value 180�.Consideration of the bands and angles around the central metal ionindicate that the Zn cation is located in the center of a distortedoctahedron.

Fig. 2. The polymeric chain structure of compound 1 showing the C–H���O hydrogen bonds (viewing along c-axis). For clarity only hydrogen-bonding atoms and p–pinteractions atoms are given.

X. Hu et al. / Inorganica Chimica Acta 362 (2009) 3421–3426 3423

In complex 1, the three-dimensional (3D) supramolecular archi-tecture is built up by means of intermolecular H-bonding and p–pstacking interactions. The sulfate groups adopts l2-bridging modeto coordinate with two Zn(II) ions to form 1D coordination polymeralong the b-axis, as shown in Fig. 2. The neighboring polymers arelinked via hydrogen bonds between the equatorial plane coordi-nated water molecules (O1, O1A) and the sulfate oxygen atoms(O3, O3A) to form double one-dimensional chains structures(O(1)–H(1HO)� � �O(3i): 0.833(9), 1.813(10) and 2.6363(15) Å,170(2)�; O(1)–H(1BO)� � �O(3ii): 0.825(10), 1.899(11) and2.7037(15) Å, 164.9(2)�, (i) x, y, �1 + z; (ii) x, �y, �0.5 + z). Further-

Fig. 3. The crystal packing of complex 1 showing supramolecular sheet formed by

more, these chains are assembled by the intermolecular p–p stack-ing interactions between the phen ligand rings of adjacentmolecules are also observed in an offset parallel way in the latticewith an inter-plane distance of 3.372 Å (Fig. 2). These latter arelinked to each other by H-bonding interactions between O(3) andthe C(2) atoms developing along the c axial (C(2)–H(2)� � �O(3):0.93, 2.45, 3.281(2) Å and 149�) (Fig. 3). Both the hydrogen-bond-ing and p–p stacking interactions connect adjacent polymers andextend them into three-dimensional network. Therefore, both ofH-bonding and p–p stacking interactions play critical role to thestability of the crystal lattice.

H-bonding along b axial. For clarity only hydrogen-bonding atoms are given.

Fig. 4. View of the molecular structure of complex 2 (30% probability ellipsoids).

Fig. 5. The crystal packing of complex 2 showing 2D supramolecular sheet formed bybonding atoms and p–p interactions atoms are given.

Fig. 6. TGA curve

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3.2. Structural description of [Cu(phen)(H2O)2] � SO4 (2)

The crystal structure of 2 consists of discrete [Cu(phen)(H2O]2+

cations and SO42� anions. The perspective view of 2 is shown in

Fig. 4 and the selected bond distances and angles are listed in Table2. The coordination geometry around the copper(II) center could bedescribed as a square planar environment. The copper(II) ion iscoordinated by two nitrogen atoms (Cu–N = 2.0034(12) Å, Cu–N(0A) = 2.0034(12) Å) and two oxygen atoms (Cu–O(1) = 1.9679(11) Å, Cu–O(1A) = 1.9679(11) Å) from two water molecules. It isnoteworthy that the oxygen atom of SO4

2� group is not coordi-nated to copper(II) ions. But in the crystal packing of complex 2,two oxygen atoms (O1, O1A) from SO4

2� anions locate at the equa-torial axial positions of the Cu(II) ion (Cu–O(2) = 2.465 Å, Cu–O(2A) = 2.465 Å) forming the expanded octahedral geometry(Fig. 5). In this compound, copper–oxygen bond distances of unco-ordinated SO4

2� ligand are longer than that of coordinated SO42�

ligand usually in the range of 1.962–2.238 Å [22–26].Among the compound 2, the tetrahedral SO4

2� groups can formhydrogen-bonding interactions with various hydrogen-bondingdonor molecules in different directions to enhance crystal stabilityand improve water solubility. Furthermore, the electronegativesulfate group SO4

2� can also act as counter anion that balancesthe charge on frameworks when neutral ligands are employed.The supramolecular structure of 2 is dominated by strong hydro-gen bonds in which the coordinated water ligands act as donorsand the sulfate anions act as acceptors (O(1)–H(1AO)� � �O(3):

H-bonding and p–p interactions (viewing along c-axis). For clarity only hydrogen-

s of 1 and 2.

X. Hu et al. / Inorganica Chimica Acta 362 (2009) 3421–3426 3425

0.825(14), 1.784(13) and 2.6072(16) Å, 176(3)�; O(1A)–H(1BO)� � �O(3): 0.820(16), 1.855(15) and 2.6673(16) Å, 171(2)�).At the same time, the intermolecular C–H���O hydrogen bondsformed between the sulfate anions and the phen ligands (C(6)–H(6)� � �O(2A): 0.930, 2.530 and 3.282 Å, 143.2�; C(6A)–H(6)� � �O(2): 0.930, 2.530 and 143.2�). These interactions connectthe cations and anions into two-dimensional (2D) supermolecule.The 2D supermolecule is further extended into a three-dimen-sional (3D) structure through C(2)–H(2)� � �O(3) hydrogen bonds(C(2)–H(2)� � �O(3): 0.93, 2.53 and 3.349(3) Å, 147�) between thesulfate anions and the phen ligands. In the crystal structural pack-ing diagram of 2, the [Cu(phen)(H2O] � SO4 complex molecules arefurther stabilized by p–p stacking interactions, since the inter-pla-nar phen–phen distances of neighboring complex molecules are3.529 Å which is larger than compound 1 (see Fig. 5).

3.3. Thermal analyses

TGA was carried out for polycrystalline samples of compounds 1and 2 in the temperature range 26–700 �C (Fig. 6). For 1, thedecomposition of the mixed ligand complex undergoes in threestages. Degradation of two water molecules takes place in the firststage between 70 and 188 �C with a mass loss of 8.74% (calculated:9.57%). The residue at the first stage was found to may be[Zn(phen)(SO4)]n and the second stage between 380 and 548 �Ccorresponds to decomposition of the remaining SO4

2� anion. Theobserved mass loss is 26.90% which is roughly consistent withthe theoretical value of 25.43%. With heating, the decompositionof the phen ligand was followed. The third stage, which occurs inthe temperature range 548–670 �C, the observed mass loss(47.66%) is coincide with the calculated value (47.71%). The finalresidue, estimated as zinc oxide, has the observed mass 21.80%as against the calculated value of 21.55%. For 2, in the first stage be-tween 90 and 180 �C, the water molecules degrade with a 8.34%mass loss (calculated: 9.59%). The second stage is related to thedecomposition of the SO4

2� anion in the temperature range of290–370 �C, weight constancy is attained at around 480 �C.

3.4. Fluorescent properties

Inorganic–organic hybrid coordination polymers have beeninvestigated for fluorescence properties and for potential applica-tions as luminescent materials, such as light-emitting diodes(LEDs) [27–29]. The photoluminescence properties of complexes

Fig. 7. The solid-state fluorescence spectra of compounds 1 and 2 under irradiationof 280 nm at room temperature.

1 and 2 were studied in the solid state at room temperature. Themeasurements were carried out under the same experimental con-ditions and excited at a wavelength of 280 nm. As shown in Fig. 7,both compounds display a broad emission band in the blue lightregion (maximal emission peaks at 400 and 450 nm, respectively,for 1 and 2), which may be attributed to intra-ligand pL—p�L transi-tions emission from the 1,10-phenanthroline [30]. The relativeintensities of the two emission bands were slightly different fromeach other and the fluorescence of compound 2 is slight red-shiftcompared to that of compound 1. The red-shift of the emission en-ergy from the compound 2 to the compound 1 may be related tothe pL—p�L transitions emission in the complex is weaker whichled to the obvious decrease of fluorescence intensity.

4. Conclusion

In this paper, two organic–inorganic hybrid compounds con-taining SO4

2� anion and phen moiety supramolecular complexeshave been synthesized and characterized for the first time. TheSO4

2� groups in complexes 1 and 2 are used as counter anions.But the SO4

2� anion in 1 adopts bidentate mode to coordinate withmetal ions and the complex displays one-dimensional polymer. Inthe case of 2, the uncoordinated SO4

2� groups are presented. Sucheffects of the counter anions may provide the prospect of synthe-sizing new organic–inorganic hybrid transition metal supramolec-ular complexes by the modification of inorganic ligands and theorganic ligands. The two compounds exhibit a broad fluorescentemission bands, and they may be used as fluorescent materials.It is believed that more and more hybrid compounds with goodluminescent property can be developed.

5. Supplementary material

CCDC 672036 and 672037 contain the supplementary crystallo-graphic data for this paper. These data can be obtained free ofcharge from The Cambridge Crystallographic Data Centre viawww.ccdc.cam.ac.uk/data_request/cif.

Acknowledgments

This work was supported by the Scientific Research Foundationin Xinjiang Educational Institutions (XJEDU2007S24) and theYoung Scholar Science Foundation of Xinjiang Normal University.

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