Since 1976, numerous studies have been carried out on layered metal phosphonates due to their potentially useful properties such as ion exchange, catalysis, and heterogeneous catalyst supports [1]. Zn and Cu vinylphosphonates belong to this type of layered materials, where the vinyl groups point toward the interlayer region. However, Pb(O₃PCH=CH₂) shows a new 3D porous structure with the vinyl groups projecting into the channels [2]. In all of them, the presence of the vinyl function may be used for coordination of catalytically active species or for investigation of further organic reactions within a confined region. In this respect, the orientation/alignment of the vinyl groups within the structure may have an important effect on the reactivity [3].

In the present work, we report the synthesis and structural characterization of several divalent transition metal phosphonates containing unsaturated groups: M(O₃PCH=CH₂)^.H₂O (M=Co, Ni and Cd) and M(O₃P-C(C₆H₅)=CH₂)^.H₂O (M=Co and Cd). These materials have been prepared by hydrothermal procedure and structurally characterized by laboratory X-ray powder diffraction. Dehydration processes in these materials were also studied. Both families of compounds show layered frameworks. M(O₃PCH=CH₂)^.H₂O (M=Co, Ni and Cd) compounds crystallize in orthorhombic unit cells and they are isostructural to the reported Zn derivative [1]. M(O₃P-C(C₆H₅)=CH₂)^.H₂O (M=Co and Cd) crystallize in monoclinic unit cells and their crystal structures have been solved following an ab initio methodology and refined by the Rietveld method. The attached figure shows the layered structure of cadmium vinylphenylphosphonate. The reactivity of these materials, under UV radiation, will be also reported.

Layered framework of Cd(O₃P-C(C₆H₅)=CH₂)^.H₂O

References

[1] D.A. Knight, V. Kim, R.J. Butcher, B.A. Harper and T.L. Schull, J. Chem. Soc., Dalton Trans., 2002, 824-826.
[2] G.B. Hix,A. Turnerm K, Vahter, B.M. Kariuki, Microporous Mesoporous Mater. 2007, 99, 62-69.
[3] B. Menaa, B.M. Kariuki and I.J. Shannon, New J. Chem., 2002, 26, 906-909.

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