Synthesis and structural and magnetic characterisation of cobalt(ii) complexes of mixed phosphonate-antimonate ligands

The polynucleating oxygen donor ligands, [(SbAr)4O 2(PhPO3H)4(PhPO3)4] 1 and [(SbAr)2O(HO3PtBu)6] 2, based on condensation of p-chlorophenylstibonic acid (ArSbO3H2) and phosphonic acids, were used to prepare polymetallic cobalt(ii) complexes. Reaction of 1 with cobalt acetate under solvothermal conditions produces three different types of polymetallic cobalt complexes. With LiOMe/pyridine as base in MeOH a dinuclear cobalt cage, [Co2(SbAr)4O 4(O3PPh)4(OMe)4py2] 3, is formed, with four Sb(ii) and two Co(ii) centres bridged by μ3- oxides and phosphonates. The pyridine in the structure can be replaced by 3-picoline 4, 4-picoline 5, quinoline 6, 1,2-diazole 7, 4-phenylpyridine 8, 4-ethyl pyridine 9 and methanol 10. Using pyrazine (pyz) instead of pyridine under the same conditions a polymer, [Co2(SbAr)4O 4(O3PPh)4(OMe)4(C4H 4N2)]n11, is formed. A similar 1D-polymer forms with 4,4′-bipyridyl-ethylene 12 in place of pyrazine. With Et 3N/pyridine as base in MeCN a tetranuclear cobalt cage, [Co 4(SbAr)5O9(O3PPh) 6(py)4] 13, with five Sb(ii) centres forming a "bowtie" and bridging to four Co(ii) centres by phosphonates and μ3-oxides, is formed. The reaction of 2 with cobalt acetate using LiOMe/pyridine as base in methanol, under solvothermal conditions, produces a dinuclear Co(ii) complex, [Co2(SbAr)2(O3P tBu)3O2(OMe)2(py)2] 14, with two CoII and two Sb centres at the vertices of a distorted tetrahedron. Magnetic measurements on selected number of these cobalt cages are reported. © 2010 The Royal Society of Chemistry.