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

Abstract

The trans-[Cr(cyclam)(nic- O) 2]ClO 4 (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 d 3 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.