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Inorganics 2015, 3(2), 194-218; doi:10.3390/inorganics3020194

Single-Crystal to Single-Crystal Reversible Transformations Induced by Thermal Dehydration in Keggin-Type Polyoxometalates Decorated with Copper(II)-Picolinate Complexes: The Structure Directing Role of Guanidinium

1
Departamento de Química Inorgánica, Facultad de Ciencia y Tecnología, Universidad del País Vasco UPV/EHU, P. O. Box 644, Bilbao 48080, Spain
2
Servicios Generales de Investigación SGIker, Universidad del País Vasco UPV/EHU, P. O. Box 644, Bilbao 48080, Spain
3
BCMaterials, Parque Científico y Tecnológico de Bizkaia, Edificio 500, Derio 48160, Spain
*
Authors to whom correspondence should be addressed.
Academic Editors: Greta Ricarda Patzke and Pierre-Emmanuel Car
Received: 13 April 2015 / Accepted: 19 May 2015 / Published: 27 May 2015
(This article belongs to the Special Issue Polyoxometalates)
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Abstract

Three new hybrid inorganic-metalorganic compounds containing Keggin-type polyoxometalates, neutral copper(II)-picolinate complexes and guanidinium cations have been synthesized in bench conditions and characterized by elemental analysis, infrared spectroscopy and single-crystal X-ray diffraction: the isostructural [C(NH2)3]4[{XW12O40}{Cu2(pic)4}]·[Cu2(pic)4(H2O)]2·6H2O [X = Si (1), Ge (3)] and [C(NH2)3]8[{SiW12O40}2{Cu(pic)2}3{Cu2(pic)4(H2O)}2]·8H2O (2). The three compounds show a pronounced two-dimensional character owing to the structure-directing role of guanidinium. In 1 and 3, layers of [{XW12O40}{Cu2(pic)4}]n4n hybrid POM chains and layers of [Cu2(pic)4(H2O)] complexes and [C(NH2)3]+ cations pack alternately along the z axis. The hydrogen-bonding network established by guanidinium leads to a trihexagonal tiling arrangement of all copper(II)-picolinate species. In contrast, layers of [C(NH2)3]+-linked [{SiW12O40}2{Cu(pic)2}3]n8n double chains where each Keggin cluster displays a {Cu2(pic)4(H2O)} moiety pointing at the intralamellar space are observed in 2. The thermal stability of 13 has been studied by thermogravimetric analyses and variable temperature powder X-ray diffraction. Compounds 1 and 3 undergo single-crystal to single-crystal transformations promoted by reversible dehydration processes and the structures of the corresponding anhydrous phases 1a and 3a have been established. Despite the fact that the [Cu2(pic)4(H2O)] dimeric complexes split into [Cu(pic)2] monomers upon dehydration, the packing remains almost unaltered thanks to the preservation of the hydrogen-bonding network established by guanidinium and its associated Kagome-type lattice. Splitting of the dimeric complexes has been correlated with the electron paramagnetic resonance spectra. View Full-Text
Keywords: polyoxometalates; crystal-to-crystal transformations; guanidinium polyoxometalates; crystal-to-crystal transformations; guanidinium
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Pache, A.; Reinoso, S.; Felices, L.S.; Iturrospe, A.; Lezama, L.; Gutiérrez-Zorrilla, J.M. Single-Crystal to Single-Crystal Reversible Transformations Induced by Thermal Dehydration in Keggin-Type Polyoxometalates Decorated with Copper(II)-Picolinate Complexes: The Structure Directing Role of Guanidinium. Inorganics 2015, 3, 194-218.

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