Department of Chemistry, University of Houston, 136 Fleming Building, Houston, Texas 77204-5003, USA.
Inorg Chem. 2012 Jan 2;51(1):609-19. doi: 10.1021/ic2021403. Epub 2011 Dec 6.
Five new vanadium selenites, Ca(2)(VO(2))(2)(SeO(3))(3)(H(2)O)(2), Sr(2)(VO(2))(2)(SeO(3))(3), Ba(V(2)O(5))(SeO(3)), Sr(4)(VO(2))(2)(SeO(3))(4)(Se(2)O(5)), and Pb(4)(VO(2))(2)(SeO(3))(4)(Se(2)O(5)), have been synthesized and characterized. Their crystal structures were determined by single crystal X-ray diffraction. The compounds exhibit one- or two-dimensional structures consisting of corner- and edge-shared VO(4), VO(5), VO(6), and SeO(3) polyhedra. Of the reported materials, A(4)(VO(2))(2)(SeO(3))(4)(Se(2)O(5)) (A = Sr(2+) or Pb(2+)) are noncentrosymmetric (NCS) and polar. Powder second-harmonic generation (SHG) measurements revealed SHG efficiencies of approximately 130 and 150 × α-SiO(2) for Sr(4)(VO(2))(2)(SeO(3))(4)(Se(2)O(5)) and Pb(4)(VO(2))(2)(SeO(3))(4)(Se(2)O(5)), respectively. Piezoelectric charge constants of 43 and 53 pm/V, and pyroelectric coefficients of -27 and -42 μC/m(2)·K at 70 °C were obtained for Sr(4)(VO(2))(2)(SeO(3))(4)(Se(2)O(5)) and Pb(4)(VO(2))(2)(SeO(3))(4)(Se(2)O(5)), respectively. Frequency dependent polarization measurements confirmed that the materials are not ferroelectric, that is, the observed polarization cannot be reversed. In addition, the lone-pair on the Se(4+) cation may be considered as stereo-active consistent with calculations. For all of the reported materials, infrared, UV-vis, thermogravimetric, and differential thermal analysis measurements were performed. Crystal data: Ca(2)(VO(2))(2)(SeO(3))(3)(H(2)O)(2), orthorhombic, space group Pnma (No. 62), a = 7.827(4) Å, b = 16.764(5) Å, c = 9.679(5) Å, V = 1270.1(9) Å(3), and Z = 4; Sr(2)(VO(2))(2)(SeO(3))(3), monoclinic, space group P2(1)/c (No. 12), a = 14.739(13) Å, b = 9.788(8) Å, c = 8.440(7) Å, β = 96.881(11)°, V = 1208.8(18) Å(3), and Z = 4; Ba(V(2)O(5))(SeO(3)), orthorhombic, space group Pnma (No. 62), a = 13.9287(7) Å, b = 5.3787(3) Å, c = 8.9853(5) Å, V = 673.16(6) Å(3), and Z = 4; Sr(4)(VO(2))(2)(SeO(3))(4)(Se(2)O(5)), orthorhombic, space group Fdd2 (No. 43), a = 25.161(3) Å, b = 12.1579(15) Å, c = 12.8592(16) Å, V = 3933.7(8) Å(3), and Z = 8; Pb(4)(VO(2))(2)(SeO(3))(4)(Se(2)O(5)), orthorhombic, space group Fdd2 (No. 43), a = 25.029(2) Å, b = 12.2147(10) Å, c = 13.0154(10) Å, V = 3979.1(6) Å(3), and Z = 8.
五种新的钒硒酸盐，Ca(2)(VO(2))(2)(SeO(3))(3)(H(2)O)(2)，Sr(2)(VO(2))(2)(SeO(3))(3)，Ba(V(2)O(5))(SeO(3))，Sr(4)(VO(2))(2)(SeO(3))(4)(Se(2)O(5))，和 Pb(4)(VO(2))(2)(SeO(3))(4)(Se(2)O(5))，已被合成并表征。它们的晶体结构通过单晶 X 射线衍射确定。这些化合物表现出由角和边缘共享的 VO(4)、VO(5)、VO(6)和 SeO(3)多面体组成的一维或二维结构。在所报道的材料中，A(4)(VO(2))(2)(SeO(3))(4)(Se(2)O(5))(A = Sr(2+)或 Pb(2+))是非中心对称的(NCS)和极性的。粉末二次谐波产生(SHG)测量表明，Sr(4)(VO(2))(2)(SeO(3))(4)(Se(2)O(5))和 Pb(4)(VO(2))(2)(SeO(3))(4)(Se(2)O(5))的 SHG 效率约为 130 和 150×α-SiO(2)。对于 Sr(4)(VO(2))(2)(SeO(3))(4)(Se(2)O(5))和 Pb(4)(VO(2))(2)(SeO(3))(4)(Se(2)O(5))，分别获得了 43 和 53 pm/V 的压电电荷常数和-27 和-42 μC/m(2)·K 的热释电系数在 70°C 时。频率相关的极化测量证实，这些材料不是铁电体，即观察到的极化不能反转。此外，Se(4+)阳离子上的孤对电子可能被认为是立体活性的，这与计算结果一致。对于所有报道的材料，进行了红外、紫外-可见、热重和差热分析测量。晶体数据：Ca(2)(VO(2))(2)(SeO(3))(3)(H(2)O)(2)，正交晶系，空间群 Pnma(No.62)，a = 7.827(4)Å，b = 16.764(5)Å，c = 9.679(5)Å，V = 1270.1(9)Å(3)，Z = 4；Sr(2)(VO(2))(2)(SeO(3))(3)，单斜晶系，空间群 P2(1)/c(No.12)，a = 14.739(13)Å，b = 9.788(8)Å，c = 8.440(7)Å，β = 96.881(11)°，V = 1208.8(18)Å(3)，Z = 4；Ba(V(2)O(5))(SeO(3))，正交晶系，空间群 Pnma(No.62)，a = 13.9287(7)Å，b = 5.3787(3)Å，c = 8.9853(5)Å，V = 673.16(6)Å(3)，Z = 4；Sr(4)(VO(2))(2)(SeO(3))(4)(Se(2)O(5))，正交晶系，空间群 Fdd2(No.43)，a = 25.161(3)Å，b = 12.1579(15)Å，c = 12.8592(16)Å，V = 3933.7(8)Å(3)，Z = 8；Pb(4)(VO(2))(2)(SeO(3))(4)(Se(2)O(5))，正交晶系，空间群 Fdd2(No.43)，a = 25.029(2)Å，b = 12.2147(10)Å，c = 13.0154(10)Å，V = 3979.1(6)Å(3)，Z = 8。
