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[Na6(H2O)12Ln2(dipic)6(NO3)]·18H2O (Ln = Ce (1), Pr (2), Nd (3), and Eu (5); dipicH2 = dipicolinic acid), were synthesized by a self-assembly process. The basic unit of these complexes contains (nearly) spherical octanuclear Na6Ln2 clusters. Such clusters can be constructed with or without the central nitrate ion as illustrated for the NaCe complex, [Na6(H2O)15Ce2(dipic)6]·21H2O (4), where the HNO3 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.