Magnetism of a 3-D network of trigonal Co6 clusters

Hydrothermal treatment of a mixture of SrCl2, Na2ox (ox = oxalate) and CoCl2 affords pink prismatic crystals of NaSr3Co6(OH)6(ox)6Cl(H2O)7 (1). X-ray structure determination reveals 1 to be composed of [Co6(OH)6]6+ clusters that are linked together by oxalate anions into a 3-D pseudo-face-centred-cubic structure. This anionic network is well defined. The framework is charge balanced by sodium, strontium and chloride ions, for which we see some positional disorder. Magnetic studies show that 1 is dominated by antiferromagnetic interactions, most likely associated with the hydroxide bridges between d7 Co(II) centres. Compound 1 remains a paramagnet all the way down until ∼10 K, where it undergoes a magnetic phase transition to an ordered spin canted magnetic ground state. The high |θ|/Tc ratio is most likely due to a combination of low magnetic dimensionality and to a geometrically frustrated network topology. Comparisons are drawn between the structure and magnetism of 1 and related compounds including Ba4Fe6(OH)6(ox)6Br2(H2O)4 (2).

Despite local cation disorder in the complex oxalate NaSr3Co6(OH)6(ox)6Cl(H2O)7 low temperature magnetisation measurements reveal a long-range magnetically ordered ground state.Figure optionsDownload as PowerPoint slide