Hydrothermal Synthesis and Crystal Structure of a Three-dimensional Compound {Mn(H_2O)_4(VO)_2(PO_4)_2}_n

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1 INTRODUCTION Current research interest is focused on the designof structures built up from octahedral and tetrahedralbuilding blocks[1]. During the wide investigations intransition-metal phosphates for many years, a num-ber of new mixed transition-metal phosphates havebeen reported[2]. A great number of manganese phos-phates were largely discovered as minerals[1]. On theother hand, many vanadium phosphates have alsobeen prepared recently partly because of their poten-tial applications in catalysis[3]. The fact that both Mnand V can exhibit (through electrochemical methods)mixed valency will make these compounds serve aspotential battery materials[4]. Single crystals of Ni-(VO)2(PO4)2?3H2O and Co(VO)2(PO4)2?4H2O were obtained by hydrothermal reactions[5]. Up to now, the attempts to grow crystals of Mg, Mn and Zn com- n pounds have made successes[5]. In this paper we re- l port the hydrothermal synthesis and crystal structure n of a new three-dimensional network constructed by - the layers of vanadium phosphorous oxide and they e are further connected by [Mn(H2O)4]2+ cations. - e 2 EXPERIMENTAL o - 2. 1 Synthesis n A mixture of Mn(OAc)2?2H2O (1 mmol), Na2VO3 s) (2.5 mmol) and H3PO4 (5.194 mmol) was placed in a s Teflon vessel which was filled with 18 mL H2O - (final pH = 1.5) and enclosed in a stainless steele bomb. The reaction vessel was maintained at 160 ℃under autogenous pressure for 2 days before slowly (I > 2σ(I)) and GOF = 1.056 based on 154 observedcooling to room temperature at the rate of 4.3 ℃/h. reflections and 16 parameters for compound 1.Then brown prism crystals of the title compound sui-table for X-ray diffraction study were isolated. IR 3 RESULTS AND DISCUSSION(KBr pellet) (cm-1): 3400(s), 3142(s), 2727(w),1682(s), 1620(s), 1369(s), 1336(w), 1001(w), 980(s), 3. 1 Structure description820(m), 777(m), 577(m). Anal. Calcd. for {Mn(H2O)4- The crystallographic data for compound 1 are(VO)2(PO4)2}n 1: H, 1.79; Mn, 12.19; V, 22.60%. listed in Table 1. The atomic coordinates, thermalFound: H, 1.77; Mn, 12.24; V, 22.61%. parameters and selected bond distances are given in2. 2 Crystal structure determination Tables 2, 3 and 4, respectively. As shown in Fig. 1a, A suitable crystal of 1 was glued on a glass fiber the Mn2+ cation is six-coordinated by two oxygenand mounted on a Siemens SMART CCD diffracto- atoms (Mn–O, 2.126(15) ?) from two neighboringmeter equipped with a graphite-monochromated Mo- [(VO)2(PO4)2]n 2n- sheets and four coordinated waterKα radiation (λ = 0.71073 ?). Crystallographic data molecules (Mn–O, 2.051(17) ?), exhibiting a slightlywere collected at room temperature and corrected for distorted octahedral geometry. Each V4+ cation isLorentz and polarization effects, and the empirical also five-coordinated including one V=O (1.601(16)absorptions were corrected by SADABS program[6]. ?) and four V–O (1.970(7) ?), assuming a distortedThe structure was solved by direct methods as well square pyramidal geometry. As shown in Fig. 1b, theas successive difference Fourier synthesis, and re- 2D mosaic layers are constructed by the vanadiumfined by full-matrix least-squares with anisotropic phosphorous oxide, [(VO)2(PO4)2]n 2n- , but they arethermal parameters for all non-hydrogen atoms. The not isolated.final refinement gave R = 0.0577, wR(F2) = 0.1298 a) b) c) Fig. 1. a) Asymmetric unit for compound 1; b) [(VO)2(PO4)2]n 2n-2D sheet viewed along the c axis; c) 3D network constructed from the vanadium phosphorous oxide layers which are further connected by [Mn(H2O)4]2+ cations viewed along the a axis Table 1. Summary of Crystal Data and Structure Refinements Formula Mn(H2O)4(VO)2(PO4)2 Formula weight 450.82 Temperature 293(2) K Wavelength 0.71073 ? Crystal system Tetragonal system Space group I4/mmm Unit cell dimensions a=6.251(3) c=13.410(9) ?

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