Self-assembly, structures, magnetic properties and solution behaviors of six mixed-valence cobalt clusters

The introduction of multidentate chelating ligands and secondary small inorganic anions into a variablevalence cobalt synthesis system led to the formation of six novel mixed-valence cobalt clusters, namely, [(Co2Co2III)-Co-II (mdea)(2)(OH)(2)(2,2'-bipy)(2)(CH3CN)(4)]center dot 4ClO(4)center dot 2H(2)O (SD/Co1), [(Co2Co2III)-Co-II(dmhmp)(6)(CH3CN)(4)]center dot 4ClO(4) center dot 4CH(3)CN (SD/Co2), [(CoCo4III)-Co-II (mdea)(4)(N-3)(4)(piv)(2)] (SD/Co3), [(Co2Co2Na)-Co-II-Na-III(mdea)(2)(N-3)(piv)(8)] (SD/Co4), [(Co4Co2III)-Co-II (dea)(2)(Hdea)(4)(piv)(4)]center dot 2piv (SD/Co5), and [(Co2Co2III)-Co-II(mdea)(2)(dmpea)(2)(OH)(2)(CH3CN)(2)(H2O)(2)]center dot 4ClO(4) center dot 2H(2)O (SD/Co6) (H(2)dea = diethanolamine, H(2)mdea = N-methyldiethanolamine, 2,2'-bipy = 2,2'-bipyridine, Hdmhmp = 3,5-dimethyl-1-(hydroxymethyl)-pyrazole, Hpiv = pivalic acid and dmpea = 1-(3,5- dimethyl-1H- pyrazol-1-yl)-ethanimine). Among them, compounds SD/Co1, SD/Co2 and SD/Co6 have a similar cationic tetranuclear core motif {Co4O6} consisting of two Co-III and two Co-II mixed-valence ions. Compound SD/Co3 has two similar neutral pentanuclear {Co5O8} clusters co-crystallized in one asymmetric unit that each contains four Co-III ions and one Co-II ion. Compound SD/Co4 consists of a bimetallic pentanuclear calyx-like {Co4Na} skeleton including two Co-III and two Co-II ions, while compound SD/Co-5 has a cationic hexanuclear rod- like cluster {Co6O8} consisting of two Co-III and four Co-II ions. In addition, the highresolution electrospray ionization mass spectrometry (HRESI-MS) technique was introduced to detect their solution behaviors and reveal their evolutional processes. Magnetic measurements indicated that these cobalt clusters show distinct magnetic behaviors at low temperature.