Two magnetic subsystems in bimetallic [Co(C5H5NO6)][COCl4]

Abstract
The specific heat and susceptibility of the title compound and of [Co(C5H5NO)6][ZnCl4], which are isostructural and monoclinic, have been measured. Two magnetic subsystems are present in the Co/Co compound, the Co2+ ions on octahedral positions exhibiting antiferromagnetic ordering at Tc = 0.95(1) K, the Co2+ ions on tetrahedral positions remaining paramagnetic down to at least 0.04 K. The paramagnetic ions experience two different molecular fields from the ordered Co2+ ions.