Magnetic interaction between manganese (2+) atoms through aquo bridges and bifurcated cyano groups

The magnetic interaction between adjacent manganese atoms through aquo double bridges in Mn₂[M(CN)₆]·xH₂O where x ≤ 8 and 2 and M ≤ Fe, Ru, Os, was studied. Through these bridges a relatively weak antiferromagnetic interaction is established with an estimated Curie-Weiss temperature, _CW|, close to 4 K and a super exchange constant, |J|, of 0.27 cm^-1. When these materials are dehydrated the antiferromagnetic interaction between the Mn atoms undergoes a dramatic increase, with estimated values for |_CW| and |J| of 61 K and 4.11 cm^-1, respectively. Such reinforcement in the magnetic interaction is accompanied by a shift of 32 cm^-1 for the ν (CN) vibration towards the low frequency region while for the iron compound the Mössbauer spectrum, initially a single line, becomes a quadrupole splitting doublet of relatively low isomer shift (δ) value. The Curie constant of the involved Mn atoms shows a negative correlation with the observed shifts in ν (CN) and δ on dehydration. From the observed magnetic behaviour and the spectroscopic data a double coordination of an N end of the CN ligand to two Mn atoms is proposed. Such strong magnetic interaction through the N atom of the CN ligand could be used as a prototypical bridge to obtain high T_c molecular magnets.