混合价聚十五钒酸盐[V_(15)O_(36)Cl](NH_4)_3Na_7·30H_2O的合成与晶体结构

Synthesis and Crystal Structure of Mixed Valence Pentadecavanadate V_(15)O_(36)Cl](NH_4)_3Na_7·30H_2O

以XRD法确定制得的标题晶体属空间群D_(3A)~3,a=13.111,c=11.130。结构由帕特逊-极小函数法结合差值法解出,经精修得一致性因子R_w=0.0344。晶胞中坐落在6m2特殊位置上的是包合1个Cl^-的聚十五钒酸根[V_(15)O_(36)Cl]^(10-),配合键价法确认这是四价钒占主导地位的一类特种混合价同多酸根。

Using VOSO_4 or VOCl_2 as the starting materials, the title complex was prepared with additive agents NH2OH.HC1, NH2CH2COOH in the liquor with the final pH range of 8-9 controlled by NaOH.The title complex crystallizes in space group D3h3-P 62m with unit cell constants a= 13. 111 (7) A , c=11. 130(4)A and Z=1 for chemical formula (V15OMCl)(NH4)3Na7-30H2O. Those vanadium coordinates were derived by Patterson-minimum function method first and then the position parameters for the other non-hydrogen atoms were obtained by the Fourier difference techniques. Using 1084 independent reflections, the block-diagonal least-squares refinement for structural parameters gave final discrepency factor R and Rw being 0. 0353 and 0. 0344 respectively. X-ray structure analysis shows that in each unit cell two special positions with 3 symmetry are occupied by two (Na2(H2O)9)2+ groups and one 6m2 position is occupied by a chlorion-contained pentadecavanadate anion (V15O36Cl)10- in which there are 15 terminal-oxygen Oa, 3 bridged-oxygen Ob, 18 triple-linked Oc and three kinds of 15 Vanadium atoms. Carefully considering all the information of chemical bond parameters, hydrogen linking as well as the calculation results of bond-valence sum for all V and O atoms, we recognize that three V (3) atoms are in V (Ⅳ ) valence state and the rest 12 atoms of V (Ⅰ), V(Ⅱ) in IV-V mixed valence state. The average occupation ratio of V( Ⅴ ) for V(Ⅰ) and V(Ⅱ) is - 0. 25 which implies the pentadecavanadate group belongs to a special kind of poly-vanadate group in which the V(Ⅳ) plays the main part in holding the back-bone of the cluster and tolerates some extent V( Ⅴ) residing in.