Controlled assemblies of hepta- and trideca-CoII clusters by a rational derivation of salicylalde schiff bases: microwave-assisted synthesis, crystal structures, ESI-MS solution analysis and magnetic properties

Hydrothermal reaction of Co(ClO4)(2)center dot 6H(2)O with 2-ethoxy-6-(iminomethyl) phenol (Heimp) or 3-ethoxysalicylaldoxime (H(2)eosa) leads to the formation of two completely different Co-II complexes [Co-7(eimp)(6)(OMe)(6)]center dot 2ClO(4) (1) and [Co-13(eosao)(8)(Heosao)(6)(ClO4)(4)]center dot H2O (2). Compound 1 is a disc-like heptanuclear Co-II cluster with all the eimp(-) ligands displaying the eta(1): eta(2): eta(1): mu(2) binding mode. Compound 2 is a butterfly-like nano-tridecanuclear Co-II cluster and the oximation of iminomethyl group results in its complicated binding modes. Four of the six Heosao(-) ligands adopt the eta(1): eta(2): eta(1): mu(2) mode and the other two take the eta(1) : eta(2) : eta(1) : eta(1) : mu(3) fashion, while eight eosao(2-) ligands are in the eta(2): eta(1): eta(2): mu(4), eta(1): eta(3): eta(1): eta(2): mu(5) manner. Microwave heating during the synthetic process will dramatically improve the reaction rate and yield of 1, which however, is not valid for the formation of 2. Electrospray ionization mass spectrometry (ESI-MS) solution analysis was performed, which reveals a ligand substitution reaction of the core bridge for 1. For 2, the result of ESI-MS indicates that the Co-13 cluster still exists in solution, and maintains a conformation similar to that observed in the crystal structure. Magnetic studies show that 1 exhibits a dominated ferromagnetic coupling between the Co-II ions below 30 K, while 2 is a typical antiferromagnetic system.