Abstract
The reaction of Co(NO3)(2)6H(2)O with N,N-diethanolamine (H(2)L1) in the presence of sodium acetate, using triethylamine as a base, leads to a tridecanuclear mixed-valent cobalt cluster [(Co9Co4III)-Co-II(OH)(6)(H2O)(2)(L1)(8)(OAc)(4)](NO3)(4)24H(2)O (1). Similar reaction with a newly designed hydroxy- and nitrogen-rich chelating ligand 2-[bis(pyridin-2-ylmethyl)amino]-2-(hydroxymethyl)propane-1,3-diol (H(2)L2) gives a mixed-valent Co-13 cluster [(Co7Co6III)-Co-II(OH)(12)(L2)(6)](NO3)(8)10H(2)O (2). The cobalt ions in both 1 and 2 are nearly coplanar, forming a novel shieldlike configuration for 1 and a unique hexagram structure for 2, both of which have not been observed for the polynuclear cobalt clusters. The magnetic susceptibility investigation showed that complexes 1 and 2 exhibited ferromagnetic coupling between Co-II ions. Further magnetic studies revealed a slight frequency dependence of 2, which suggests that 2 might be a single-molecule magnet.