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, |θCW|, 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 |θCW| 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 M¨ossbauer 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 Tc molecular magnets