Crystal Structures of Manganese and Cobalt Dichloride Monohydrate and Deuteration Effects on Magnetic Behavior

This
work reports the long sought crystal structures of the title members
of the intriguing series of 3d transition metal dichloride monohydrates.
The double chain structure which results from rearrangement of the
well-known pseudo-octahedral coordination geometry and single chains
in the corresponding metal chloride dihydrate is extremely unusual.
MnCl2·H2O and CoCl2·H2O each crystallize in orthorhombic space group Pnma with Z = 4 and lattice parameters a = 9.0339(1), 8.8207(3); b = 3.68751(5), 3.5435(1); c = 11.5385(2), 11.2944(4) all in Å and for Mn, Co,
respectively. Results are reported also for both fully deuterated
systems; the structures remain the same with lattice parameter changes
typically much less than 0.1%. Various magnetic properties of MnCl2·D2O and CoCl2·D2O are reported. For the latter, there are no apparent differences,
qualitatively or quantitatively, from the previously measured properties
of CoCl2·H2O. Interestingly, for the former
some differences with respect to MnCl2·H2O are apparent, principally a lower Tmax = 3.10(10) K about which a broad antiferromagnetic maximum is centered,
and a larger value χmax = 0.336(3) emu/mol. However,
antiferromagnetic ordering appears to occur at essentially the same
2.18(2) K. Results of fits to susceptibilities of MnCl2·D2O and CoCl2·D2O are
compared with those obtained before for MnCl2·H2O and CoCl2·H2O. Structural considerations
serve to rationalize the physical properties, especially the lower
dimensional magnetism of monohydrates.