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、适宜的二磷酸酯配体与水的热液反应产生了一系列以中性的V−P−O网络作为重复结构基元的化合物。当{O3P(CH2)nPO3}4-二磷酸酯的连接链长度n为2−5时，可分离出1型金属-氧化物杂化物[V2O2(H2O){O3P(CH2)nPO3}]·xH2O。这类氧化物展现出典型的三维（3-D）“支柱”层状结构。当n增加到6−8时，遇到2-D“支柱”板状结构的2型氧化物[V2O2(H2O)4{O3P(CH2)6PO3}]。进一步将间隔延长至n=9时，提供了一种新的3-D结构，即3型，该结构通过支柱板的缩合形成V−P−O双层作为网络亚结构。当引入有机阳离子以平衡阴离子V−P−O网络中的电荷时，观察到4−7型的氧化物。对于间隔长度n=3，相同的3-D“支柱”层状氧化钒二磷酸酯框架在4型材料中容纳了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，其中一个由阳离子占据，另一个由结晶水占据。此外，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。当二磷酸酯连接链长度增加到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。这种氧化物具有2-D“支柱”网络或板状结构，其宏观形态与2型氧化物相似，且阳离子占据层间域。相反，将二磷酸酯连接链长度缩短至n=2，则导致3-D氧化钒有机磷酸盐结构类型7氧化物[H3N(CH2)5NH3][V3O3{O3P(CH2)2PO3}2]的形成。在这种情况下，乙二磷配体并未支撑V−P−O网络，而是与钒中心螯合，构建了7号复杂多面体连接性。用哌嗪阳离子替代4、5和7型简单烷基链提供了6型氧化物的2-D“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和热行为上，亦对此进行了讨论。