ic0517422_si_018.cif (15.77 kB)
Structural Diversity of the Oxovanadium Organodiphosphonate System: A Platform for the Design of Void Channels
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posted on 2006-04-17, 00:00 authored by Wayne Ouellette, Ming Hui Yu, Charles J. O'Connor, Jon ZubietaThe 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.
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layer structurenetwork substructurediphosphonate tether length5 PO 3cation increasesV 4 O 4OHtype 6 oxidesslab structurehydrothermal reactionsethylenediphosphonate ligandHFspacer length ntype 3type 1type 7 oxiden PO 32 PO 32 resultscharge balanceinterlamellar domainpolyhedral connectivitytype 2 oxidesNH 3vanadium sourceinterlamellar domainsalkyl chainsorganodiammonium cationsH 2 Ovanadium centerCH 2 CH 3diphosphonate ligandH 3 NRVoid Channelstypes 4V 2 O 2piperazinium cationsStructural Diversitytype 4 materialstype 1 oxides exhibitorganodiammonium component spillsoxides exhibit
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