Alkaline-earth (Mg-Ba) coordination networks built around the tris(dipicolinato)cerate(3 < sup > - < /sup > ) ion: Highly hydrated networks that survive dehydration

Abstract

Alkaline-earth (AE)/cerium(III)-based heterometallic coordination compounds of the biologically important ligand dipicolinic acid (dipicH2), namely [Mg(H2O)6]2[Ce(dipic)3][Ce(dipic)2(H2O)3]·2H2O (1), [Ca3(H2O)12Ce2(dipic)6]·6H2O (2), [Sr3(H2O)16Ce2(dipic)6]·4H2O (3) and [Ba2(H2O)7Ce(dipic)3NO3]·H2O (4), have been obtained by the reduction of an aqueous solution of (NH4)2Ce(NO3)6·6H2O in the presence of dipicH2 and alkaline-earth oxides or carbonates. This series demonstrates the role of AE ions in controlling the topology of coordination networks based on the [Ce(dipic)3]3- anion. Compound 1 is a zero-dimensional ionic compound, the crystal structure of compound 2 is based on a mixed four-connected 3D network, compound 3 presents ladder-shaped chains running along a crystallographic axis, and layers of squeezed CeBa6 pentagonal pyramids interconnected by nitrates generate a mixed five- and six-connected network in 4. A thermal analysis showed that all four compounds exhibit reversible water-uptake capacity and the basic nature of the frameworks could be intact up to at least 120 °C.