Crystal structure and spectroscopic properties of trans-bis(nicotinato)(1,4,8,11-tetraazacyclotetradecane)chromium(III) perchlorate

The trans-[Cr(cyclam)(nic-O)2]ClO4 (cyclam = 1,4,8,11-tetraazacyclotetradecane; nic-O = O-coordinated nicotinate) has been prepared and structurally characterized by single-crystal X-ray diffraction at 150 K. The chromium atom is in a tetragonally compressed octahedral environment with four N atoms of the macrocyclic ligand in equatorial positions and two O-bonded nicotinates in trans axial positions. The macrocyclic cyclam adopts the centrosymmetric trans-III configuration with six- and five-membered chelate rings in chair and gauche conformation, respectively. The IR and visible spectral properties are consistent with the result of X-ray crystallography. The resolved band maxima of the electronic d–d spectrum are fitted with secular determinant for quartet state energy of d3 configuration in tetragonal field including configurational interaction. It is found that the nitrogen atoms of the cyclam ligand are a strong σ-donors and that O-bonded nicotinato group has strong σ- and π-donor characteristics toward the chromium(III) ion.