Synthesis, structure, optical and magnetic properties of [CrL(X)3], {L=4′-(2-pyridyl)-2,2′:6′,2"-terpyridine;: X = Cl-, N3-, NCS-}

Three complexes of composition [CrL(X)(3)], where L = 4'-(2-pyridyl)-2,2':6',2 ''-terpyridine and X = Cl-, N-3(-), NCS- are synthesized. They are characterized by IR, UV-Vis, fluorescence, EPR spectroscopic, and X-ray crystallographic studies. Structural studies reveal that the Cr(III) ion is coordinated by three N atoms of L in a meridional fashion. The three anions occupy the other three coordination sites completing the mer-N3Cl3 (1) and mer-N3N3 (2 and 3), distorted octahedral geometry. The Cr-N2 has a shorter length than the Cr-N1 and Cr-N3 distances and the order Cr-N(NCS-) < Cr-N(N-3(-)) < Cr-Cl is observed. They exhibit some of the d-d transitions in the visible and intra-ligand transitions in the UV regions. The lowest energy d-d transition follows the trend [CrLCl3] < [CrL(N-3)(3)] < [CrL(NCS)(3)] consistent with the spectrochemical series. In DMF, they exhibit fluorescence having pi -> pi* character. All the complexes show a rhombic splitting as well as zero-field splitting (zfs) in X-band EPR spectra at 77 K. (C) 2008 Elsevier Ltd. All rights reserved.