ARTICLE

DOI: 10.1002/zaac.200800384

Synthesis and Characterization of an Inorganic-Organic Hybrid Layered ZincPhosphite [(C2H3N3)Zn(HPO3)]

Xianchun Liu,[a] Yan Xing,*[a] Li Liu,[a] Shuyan Song,[a] Gaijuan Li,[a] and Ning Xu[a]

Keywords: Zinc; Solvothermal synthesis; Helical chains; Zinc phosphites; Crystal structure

Abstract. A inorganic-organic hybrid zinc phosphite(C2H3N3)Zn(HPO3) (1) has been prepared under solvothermalconditions in the presence of 1,2,4-triazole (trz) ligand.Its structurewas determined by single-crystal X-ray diffraction, and furthercharacterized by powder X-ray diffraction (XRD), FTIR spec-troscopy, elemental analysis, ICP analysis, thermogravimetricanalysis and fluorescent spectrum. It crystallizes in the monoclinic

IntroductionIn recent years many investigations of the design and syn-

thesis of inorganic-organic materials with helical structureshave been motivated by their rich structural chemistry andpotential applications in enantioselective separation, non-linear optics and catalysis [1�3]. To date, only a few ex-amples are reported to have helical characters [4�11]. Therational synthesis of inorganic-organic compounds contain-ing a helical array is still a challenging goal.

In the past decade, a number of interesting molecular,one-dimensional, layered, and three-dimensional zincphosphites have been produced [5, 6, 8, 9, 12�17]. How-ever, the occurrence of zinc phosphites having a helicalchain is still rare. For instance, a layered zinc phosphite[(C5H6N2)Zn(HPO3)], which consists of left-handed andright-handed helical chains has been synthesized in thepresence of 2-aminopyridine ligand [5]. Recently Yang et al.reported the syntheses of two 3D inorganic-organic hybridopen-framework zinc phosphites having infinite helical�Zn-O-P-chains [8, 9]. In the present work, we describethe solvothermal synthesis, crystal structure, thermal andphotoluminescent properties of a two-dimensional inor-ganic-organic hybrid zinc phosphite (C2H3N3)Zn(HPO3)with both left-handed and right-handed helical chains. It isbelieved that the organic amine templating molecules arevital for the formation of helical �Zn-O-P- chains.

* Dr. Y. XingTel: �86-431-86105529E-Mail: xingy202@nenu.edu.cn

[a] College of ChemistryNortheast Normal UniversityChangchun 130024, P. R. China

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system, space group P21/n, a � 7.5515(6) A, b � 9.1813(8) A, c �

10.0125(8) A, β � 111.267(1)°, V � 646.92(9) A3, Z � 4. The struc-ture consists of left-handed and right-handed helical chains thatare connected through bridging oxygen atoms to form a two-dimensional layer structure with 4.8-net. The compound exhibitsintense photoluminescence upon photo-excitation at 326 nm.

Experimental Section

Materials and Methods

All chemicals used during the course of this work were of reagentgrade and used as received from commercial sources withoutfurther purification. The X-ray powder diffraction (XRD) datawere collected on a Siemens D5005 diffractometer with Cu-Kαradiation (λ � 1.5418 A). Elemental analyses were performed on aPerkin-Elmer 2400 element analyzer. Inductively coupled plasma(ICP) analyses were carried out on a Perkin-Elmer Optima 3300DVspectrometer. Fourier transform infrared spectra (FT-IR) were re-corded within the 400-4000 cm�1 region on a Nicolet Impact 410FTIR spectrometer using KBr pellets. The thermalgravimetricanalyses (TGA) were performed on Perkin-Elmer TGA 7 thermo-gravimetric analyzer in the air with a heating rate of 10 °C min�1.Fluorescent spectrum was measured on a Fluorolog with a 400-Wxenon lamp as an excitation source at room temperature.

Synthesis

Large single crystal of compound 1 was synthesized using mildsolvothermal conditions and autogenous pressure. Typically, ZnO(0.246 g, 3 mmol), H3PO3 (0.738 g, 9 mmol), 1,2,4-triazole(trz)(0.414 g, 6 mmol) were dissolved in a volume of approximately 3 mlof a mixture of water, ethylene glycol (EG) (1:1v/v). The formedhomogenous gel with a pH of � 3 was sealed in a Teflon-linedstainless steel autoclave and heated at 120 °C for 7 days, followedby slow cooling down to room temperature. The pH of the mixturewas found to be critical for the successful synthesis of pure phase1. A higher or lower pH of the reaction mixture will result in anunknown phase together with 1. The resulting product, consistingof colorless block-like crystals was recovered by filtration, washedwith distilled water and dried in air. Inductively coupled plasma(ICP) spectrometric analysis gave the contents of Zn as 30.12 wt %(calcd. 30.49 wt %) and P as 14.05 % (calcd. 14.44 %), indicating aZn:P ratio of 1:1. Elemental analysis showed that the sample con-tained 11.31, 1.90 and 19.45 wt % of C, H and N, respectively, inwell accord with the expected values of 11.19, 1.86, and 19.58 wt %of C, H and N on the basis of the empirical formula given by the

X. Liu, Y. Xing, L. Liu, S. Song, G. Li, N. XuARTICLEsingle-crystal structure analysis. The infrared spectrum of 1 exhib-ited typical bands corresponding to the 1,2,4-triazole molecules(νC-H, νC-N, νN-N, νN-H 3000�3160, 1610�1400, 1210�1290 cm�1),whereas the bands at 1103, 998, 636 and 578 cm�1 are associatedwith the phosphite oxoanion. The band at 2406 cm�1 was associ-ated with the stretching vibrations of the P�H groups in phos-phite anions.

Crystal Structure Determination

A suitable single crystal of as-synthesized compound with thedimensions of 0.20�0.18�0.08 mm was selected for single-crystalX-ray diffraction analysis. The intensity data were collected on aSiemens SMART CCD diffractometer using graphite-mono-chromatic MoKα radiation (λ � 0.71073 A). Data processing wasaccomplished with the SAINT processing program [18]. The struc-tures were solved by direct methods with the SHELXTL 97software package [19]. The zinc and phophorus atoms were firstlocated, and the carbon, nitrogen, and oxygen atoms were foundin the final difference Fourier maps. The H atoms in the P-H groupwere found in Fourier difference maps and the remaining H atomswere placed geometrically and refined using a riding model. All

Table 1. Crystal data and structure refinement for 1.

Empirical formula C2 H4 N3 O3 P ZnFormula weight 214.44Temperature 293(2) KWavelength 0.71073 ACrystal system monoclinicSpace group P21/na /A 7.5515(6)b /A 9.1813(8)c /A 10.0125(8)β /° 111.267(1)Volume /A3 646.92(9)Z 4Dcalc /mg · m�3 2.202Absorption coefficient (mm�1) 3.989F(000) 424Crystal size /mm 0.20 � 0.18 � 0.08θ range /° 2.93�28.28Limiting indices �9 � h � 8

�11 � k � 11�13 � l � 11

Reflections collected 3869Reflections unique 1537 [R(int) � 0.0289]Refinement method Full-matrix least-squares on F2

Data / restraints / parameters 1537 / 0 / 95Goodness-of-fit on F2 1.009Final R indices [I>2σ(I)] R1 � 0.0281, wR2 � 0.0633R indices (all data) R1 � 0.0389, wR2 � 0.0673Largest diff. peak and hole /e · A�3 0.415 and �0.452

Table 2. Selected bond lengths /A and angles /° for 1.

Zn(1)-O(1) 1.9018(19) P(1)-O(1) 1.492(2)Zn(1)-O(2)#1 1.924(2) P(1)-O(2) 1.499(2)Zn(1)-O(3)#2 1.961(2) P(1)-O(3) 1.521(2)Zn(1)-N(1) 2.003(2) P(1)-H(1A) 1.35(3)

O(1)-Zn(1)-O(2)#1 99.89(10) O(1)-P(1)-O(2) 111.67(12)O(1)-Zn(1)-O(3)#2 103.65(9) O(1)-P(1)-O(3) 112.00(13)O(2)#1-Zn(1)-O(3)#2 106.79(11) O(2)-P(1)-O(3) 112.59(13)O(1)-Zn(1)-N(1) 122.54(10) O(1)-P(1)-H(1A) 107.1(11)O(2)#1-Zn(1)-N(1) 111.27(9) O(2)-P(1)-H(1A) 108.2(11)O(3)#2-Zn(1)-N(1) 111.23(9) O(3)-P(1)-H(1A) 104.8(11)

Symmetry transformations used to generate equivalent atoms:#1 �x�1/2,y�1/2,�z�3/2 #2 x�1/2,�y�1/2,z�1/2

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non-hydrogen atoms were refined anisotropically. Crystal and ex-perimental data are listed in Table 1. Selected bond lengths andangles are listed in Table 2. Crystallographic information of thecompound has been deposited with the Cambridge Crystallo-graphic Data Center as supplementary publication numberCCDC-692235. Copies of the data can be obtained free of chargeon application to CCDC, 12 Union Road, Cambridge CB2 1EZ,UK (Fax: (�44)-1223-336-033; E-mail: deposit@ccdc.cam.ac.uk).

Results and Discussion

The agreement between the experimental and simulatedXRD patterns based on single-crystal X-ray solution indi-cated the phase purity of the as-prepared sample (Fig. 1).

Figure 1. Simulated and experimental powder X-ray diffractionpatterns.

Figure 2. Asymmetric unit of 1 (50 % thermal ellipsoids) showingthe atomic labeling scheme.

Layered Zinc Phosphite [(C2H3N3)Zn(HPO3)]

Figure 3. Representation of the 4.8-net sheet in 1. Color code: Zn: green; P: yellow; O: red; C: grey; N: blue.

Structure analysis reveals that 1 crystallizes in the mono-clinic space group P21/n. As shown in Figure 2, the asym-metric unit of compound 1 contains 10 independent non-hydrogen atoms, including one zinc atom, one phosphorusatom, three oxygen atoms, two carbon atoms and three ni-trogen atoms. The zinc atom is tetrahedrally coordinated,bonded to three oxygen atoms [Zn-O(av.)1.931(3) A] andone nitrogen atom [Zn-N1.999(3) A] from the templatemolecule. The Zn-N bond corresponds to a direct link be-tween zinc and the 1,2,4-triazole template in a monodentatefashion. The O-Zn-O bond angles are in the range of99.87(14)-106.85(16)°, and O-Zn-N bond angles are in therange 111.26(14)-122.46(14)°. The phosphorus atom sharesthree oxygen atoms with adjacent Zn atom [P-O: 1.488(3)�1.519(3) A], with the forth ligand being a terminal P-H bond[1.32(4) A]. The O-P-H and the O-P-O bond angles are in therange of 101.9(18)-112.56(19)°, indicating a pseudo pyramids

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of HPO32�. As shown in Figure 3, the connectivity of the

strictly alternating ZnO3N and HPO3 units in 1 results in theneutral zinc phosphite layers. Zinc tetrahedral and phos-phorus pseudo-tetrahedral are connected to form 4-rings and8-rings. Each 4-ring has two up and two down vertices, thusboth the Zn-N and P-H bonds point into the inter-layer re-gion. The non-protonated 1,2,4-triazole molecules reside alter-nately above and below the layer. Within each layer of 1, bothleft-handed and right-handed helical chains can be extractedfrom the layer structure as reported previously for 4.82 rings[5, 8]. The central axis of each helical chain is a twofold screwaxis along the [010] direction. A view of the left-handed andright-handed helical chains is shown in Figure 4. Figure 5shows the packing of the layers. It can be seen that the layerexhibits a puckered pattern.

In order to examine the thermal stability of 1, thermal-gravimetric analysis (TGA) under air atmosphere was car-

X. Liu, Y. Xing, L. Liu, S. Song, G. Li, N. XuARTICLE

Figure 4. A view of the left-handed and right-handed helical chainsalong the [010] direction exhibited by 1.

Figure 5. Packing of the puckered layers of 1.

ried out. TG analysis for 1 reveals a total weight loss of33.35 wt % in the region 120�860 °C. This is in good agree-ment (calcd. weight loss � 32.18 wt %) with a process in-volving the loss of all the organic species.

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The fluorescent spectrum of the title compound wasmeasured in solid state at room temperature. On excitationat 326 nm, the compound displays a strong fluorescent em-ission band centered at 392 nm. The free 1,2,4-triazoleligand shows emission band at about 421 nm [20]. Thefluorescent emission band of 1 is blue-shifted relative to theligand. The strong emission of 1 can be assigned as ligand-to-metal charge transfer.

In summary, a new layered inorganic-organic hybrid zincphosphite have been synthesized solvothermally. The under-standing of the role of the organic ligand could be import-ant in terms of rational synthesis and properties of helicalinorganic-organic hybrid materials.

AcknowledgementThis work was supported by Training Fund of NENU’S ScientificInnovation Project (No.NENU-STC07004) and the Analysis andTesting Foundation of Northeast Normal University.

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4887.Received: June 26, 2008

Accepted: September 4, 2008