Boxes, helicates, and coordination polymers: A structural and magnetochemical investigation of the diverse coordination chemistry of simple pyridine-alcohol ligands

Abstract

A structurally diverse array of polynuclear complexes has been identified and structurally characterized from the reaction of 6-methylpyridine-2-methanol (1) with a range of cobalt(II) salts under a variety of reaction conditions. A tetranuclear cubane, [Co4(1-H)4Cl4(H 2O)3(CH3OH)], was isolated from the reaction of 1 with CoCl2·6H2O and NaOH in MeOH, and a tetranuclear double cubane, [Co4(1-H)6(NO 3)2], was isolated from the reaction of 1 with Co(NO 3)2·6H2O and NEt3 in MeOH. A bowl-shaped trinuclear complex, [Co3(1-H)3Cl 3(dmso)], which features a triply bridging dmso ligand, assembled upon mixing 1 and CoCl2·6H2O in dmso. A 1-D coordination polymer, [Co(1)2(SO4)]∞, where the sulfate ligands bridge "[Co(1)2]" units in a μ2:η1 fashion to build up the polymer structure, was isolated from the reaction of 1 with CoSO4·7H 2O. The reaction of the structurally related ligand 8-hydroxyquinaldine (2) with a mixture of CoCl2·6H 2O and Co(OAc)2·4H2O lead to the formation of the tetranuclear double cubane, [Co4(2-H) 6Cl2]. Temperature-dependent magnetic measurements have also been performed for these five complexes along with the hydrogen-bonded helicate [Co2(1)2(1-H)2]. The hydrogen bonds of the helicate mediate antiferromagnetic interactions between the cobalt(II) centers (J = -3.18(9) cm-1, g = 2.25(2)). The sulfate bridging ligands of [Co(1)2(SO4)]∞ are poor mediators of magnetic exchange. The Co(II) centers in the double-cubane complexes [Co4(1-H)6(NO3)2] and [Co4(2-H)6Cl2] are strongly antiferromagnetically coupled to each other at low temperature to give an S = 0 ground state. [Co4(1-H)4Cl4(H 2O)3(MeOH)] exhibits rather complicated magnetic behavior; however, we did not observe any evidence for single-molecule magnetism as was seen for structurally related complexes. © 2006 American Chemical Society.