Spherical octanuclear clusters in a Na-Ln-dipic system - encapsulation of a nitrate ion and incorporation of water nonamers and dodecamers

Abstract

A series of heterometallic Na/4f polynuclear cluster complexes, viz. H[Na < inf > 6 < /inf > (H < inf > 2 < /inf > O) < inf > 12 < /inf > Ln < inf > 2 < /inf > (dipic) < inf > 6 < /inf > (NO < inf > 3 < /inf > )]·18H < inf > 2 < /inf > O (Ln = Ce (1), Pr (2), Nd (3), and Eu (5); dipicH < inf > 2 < /inf > = dipicolinic acid), were synthesized by a self-assembly process. The basic unit of these complexes contains (nearly) spherical octanuclear Na < inf > 6 < /inf > Ln < inf > 2 < /inf > clusters. Such clusters can be constructed with or without the central nitrate ion as illustrated for the NaCe complex, [Na < inf > 6 < /inf > (H < inf > 2 < /inf > O) < inf > 15 < /inf > Ce < inf > 2 < /inf > (dipic) < inf > 6 < /inf > ]·21H < inf > 2 < /inf > O (4), where the HNO < inf > 3 < /inf > is replaced with three water molecules. The crystals of these compounds contain a large number of lattice water molecules which are assembled as high-symmetry water nonamers or dodecamers, both based on a central chair-shaped hexamer. The thermal properties and reversible water uptake as well as the solid-state photoluminescence of the Eu(iii) analog are discussed.