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.

在氢氟酸存在下，钒源、合适的双磷酸配体与水的热液反应生成一系列以中性V−P−O网络为重复结构母体的化合物。当{O3P(CH2)nPO3}4-双磷酸 tether 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。此类氧化物展现出典型的三维（3-D）“支柱”层状结构。当 n 增加至 6−8 时，遇到类型 2 的二维（2-D）“支柱”板状结构氧化物[V2O2(H2O)4{O3P(CH2)6PO3}]。进一步将间隔延长至 n = 9，则提供另一种三维结构，即类型 3，该结构通过支柱板状结构的缩合形成V−P−O双层作为网络子结构。引入有机阳离子以平衡阴离子V−P−O网络电荷时，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”层状氧化钒双磷酸框架在类型 4 材料中可容纳一系列有机二铵阳离子[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种不同的层间域，其中一域被阳离子占据，另一域则由结晶水占据。随着阳离子长度的增加，有机二铵成分溢出到亲水域中，取代结晶水。当双磷酸 tether 长度增加到 n = 5 时，获得结构类型 5，[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，其总体轮廓与类型 2 氧化物相似，且阳离子占据层间域。相比之下，将双磷酸 tether 长度缩短至 n = 2，则导致类型 7 氧化物的三维氧化钒有机磷化物结构[H3N(CH2)5NH3][V3O3{O3P(CH2)2PO3}2]。在此情况下，乙二磷酸配体并未支撑V−P−O网络，而是螯合到钒中心，构建了7号复杂多面体连接性。以哌嗪阳离子替代类型 4、5 和 7 中的简单烷基链，提供类型 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反映在氧化物的磁性质和热行为上，这些特性亦有所讨论。