Structural Diversity of the Oxovanadium Organodiphosphonate System: A Platform for the Design of Void Channels

The hydrothermal reactions of a vanadium source, an appropriate diphosphonate ligand, and water in the presence
of HF provide a series of compounds with neutral V−P−O networks as the recurring structural motif. When the
{O3P(CH2)nPO3}4- diphosphonate tether length n is 2−5, metal−oxide hybrids of type 1, [V2O2(H2O){O3P(CH2)nPO3}]·xH2O, are isolated. The type 1 oxides exhibit the prototypical three-dimensional (3-D) “pillared” layer architecture.
When n is increased to 6−8, the two-dimensional (2-D) “pillared” slab structure of the type 2 oxides [V2O2(H2O)4{O3P(CH2)6PO3}] is encountered. Further lengthening of the spacer to n = 9 provides another 3-D structure, type
3, constructed from the condensation of pillared slabs to give V−P−O double layers as the network substructure.
When organic cations are introduced to provide charge balance for anionic V−P−O networks, oxides of types 4−7
are observed. For spacer length n = 3, a range of organodiammonium cations are accommodated by the same
3-D “pillared” layer oxovanadium diphosphonate framework in the type 4 materials [H3N(CH2)nNH3][V4O4(OH)2
{O3P(CH)3PO3}2]·xH2O [n = 2, x = 6 (4a); n = 3, x = 3 (4b); n = 4, x = 2 (4c); n = 5, x = 1 (4d); n = 6,
x = 0.5 (4e); n = 7, x = 0 (4f)] and [H3NR]y[V4O4(OH)2 {O3P(CH)3PO3}2]·xH2O [R = −CH2(NH3)CH2CH3, y =
1, x = 0 (4g); R = −CH3, n = 2, x = 3 (4h); R = −CH2CH3, y = 2, x = 1 (4i); R = −CH2CH2CH3, y = 2, x
= 0 (4j); cation = [H2N(CH2CH3)2], y = 2, x = 0 (4k)]. These oxides exhibit two distinct interlamellar domains,
one occupied by the cations and the second by water of crystallization. Furthermore, as the length of the cation
increases, the organodiammonium component spills over into the hydrophilic domain to displace the water of
crystallization. When the diphosphonate tether length is increased to n = 5, structure type 5, [H3N(CH2)2NH3][V4O4(OH)2(H2O){O3P(CH2)5PO3}2]·H2O, is obtained. This oxide possesses a 2-D “pillared” network or slab structure,
similar in gross profile to that of type 2 oxides and with the cations occupying the interlamellar domain. In contrast,
shortening the diphosphonate tether length to n = 2 results in the 3-D oxovanadium organophosphonate structure
of the type 7 oxide [H3N(CH2)5NH3][V3O3{O3P(CH2)2PO3}2]. The ethylenediphosphonate ligand does not pillar V−P−O
networks in this instance but rather chelates to a vanadium center in the construction of complex polyhedral
connectivity of 7. Substitution of piperazinium cations for the simple alkyl chains of types 4, 5, and 7 provides the
2-D pillared layer structure of the type 6 oxides, [H2N(CH2CH2)NH2][V2O2{O3P(CH)nPO3H}2] [n = 2 (6a); n = 4
(6b); n = 6 (6c)]. The structural diversity of the system is reflected in the magnetic properties and thermal behavior
of the oxides, which are also discussed.

以钒源、适宜的二膦酸配体及水在氢氟酸存在下发生的 hydrothermal reactions 为基础，生成了一系列以中性 V−P−O 网络（作为反复出现的结构母题）为特征的化合物。当 {O3P(CH2)nPO3}4- 二膦酸桥连长度 n 为 2−5 时，可分离出类型 1 的金属-氧化物杂化物 [V2O2(H2O){O3P(CH2)nPO3}]·xH2O。类型 1 的氧化物呈现出典型的三维（3-D）“支柱”层状结构。当 n 增至 6−8 时，遇到类型 2 的氧化物，表现为二维（2-D）“支柱”板状结构 [V2O2(H2O)4{O3P(CH2)6PO3}]。进一步延长间隔至 n = 9，可得到另一种三维结构，类型 3，由支柱板状结构的缩合形成，网络亚结构为 V−P−O 双层。引入有机阳离子以平衡阴离子 V−P−O 网络的电荷，观察到类型 4−7 的氧化物。对于间隔长度 n = 3，相同的三维“支柱”层状氧化钒二膦酸盐框架在类型 4 材料中容纳了一系列有机双铵阳离子 [H3N(CH2)nNH3][V4O4(OH)2 {O3P(CH)3PO3}2]·xH2O [n = 2, x = 6 (4a); n = 3, x = 3 (4b); n = 4, x = 2 (4c); n = 5, x = 1 (4d); n = 6, x = 0.5 (4e); n = 7, x = 0 (4f)] 和 [H3NR]y[V4O4(OH)2 {O3P(CH)3PO3}2]·xH2O [R = −CH2(NH3)CH2CH3, y = 1, x = 0 (4g); R = −CH3, n = 2, x = 3 (4h); R = −CH2CH3, y = 2, x = 1 (4i); R = −CH2CH2CH3, y = 2, x = 0 (4j); 阳离子 = [H2N(CH2CH3)2], y = 2, x = 0 (4k)]。这些氧化物表现出两个不同的层间域，一个被阳离子占据，另一个则被结晶水占据。随着阳离子长度的增加，有机双铵成分溢出到亲水域，取代结晶水。当二膦酸桥连长度增至 n = 5 时，得到结构类型 5 的氧化物 [H3N(CH2)2NH3][V4O4(OH)2(H2O){O3P(CH2)5PO3}2]·H2O。此氧化物具有二维“支柱”网络或板状结构，宏观形态与类型 2 氧化物相似，且阳离子占据层间域。相反，将二膦酸桥连长度缩短至 n = 2，导致类型 7 氧化物的三维氧化钒有机膦酸盐结构。在此例中，乙二醇膦酸配体并未支撑 V−P−O 网络，而是与钒中心螯合，构建了 7 的复杂多面体连通性。以哌嗪阳离子替换类型 4、5 和 7 的简单烷基链，提供了类型 6 氧化物的二维“支柱”层状结构 [H2N(CH2CH2)NH2][V2O2{O3P(CH)nPO3H}2] [n = 2 (6a); n = 4 (6b); n = 6 (6c)]。该系统的结构多样性体现在氧化物的磁性质和热行为上，亦有所论述。