Synthesis and characterization of rhenium(I) complexes based on O, N, N coordinating ligands: DFT/TDDFT studies on the electronic structures and spectral properties

Abstract

Mononuclear rhenium(I) complexes having fac-[Re(CO)3]+ moiety of general formula fac-[Re(CO)3(L)] have been synthesized in excellent yield by reacting [Re(CO)5Cl] with HL1 and HL2 in a ratio of 1:1 in methanol. Here L− is deprotonated form of 1-[(quinolin-8-ylimino)methyl]naphthalene-2-ol (HL1) and 1-[(quinolin-8-yl-diazenyl)]naphthalene-2-ol (HL2). The elemental analysis and ESI mass spectroscopic measurements ensure the formations of desired complexes. Molecular structures of fac-[Re(CO)3(L1)] and fac-[Re(CO)3(L2)] were confirmed by single-crystal X-ray diffraction. The complexes were also characterized by different spectroscopic techniques. A remarkable change in optical properties is observed in case of fac-[Re(CO)3(L2)] over fac-[Re(CO)3(L1)] where the ligands bearing a NN function (HL2) instead of coordinated CN function (HL1). The ground and excited-state geometries, NMR, absorption, and phosphorescence properties of Re(I) complexes were examined by DFT and TDDFT methods. The natural transition orbital (NTO) and spin density difference map analysis reveals the nature of excitations. The lowest lying triplet excited is associated with the 3MLCT excited state. The emission like transition is consistent with the strong 3MLCT character.