The first examples of dirhenium(III,II) paramagnetic complexes with bridging diphenylphosphinomethane and 2-mercaptopyridine ligands: A collective experimental and theoretical studies

2-mercaptopyridine (H-pySH), 5-chloro-2-mercaptopyridine (Cl-pySH) and 5-trifluoromethyl-2-mercaptopyridine (F3C-pySH) ligands react with the multiply-bonded paramagnetic dirhenium(III,II) complex [Re-2(mu-O2CCH3)Cl-4(mu-dppm)(2)] (1) [dppm is Ph2PCH2PPh2] in refluxing ethanol to afford the paramagnetic substitution products of the type [Re-2(mu-dppm)(2)(mu-R-pyS)(2)Cl-2]Cl (2(R)) [R = H, Cl, CF3]. These are the first examples of paramagnetic dirhenium complexes that contain the bridging mercaptopyridine ligand. These complexes have very similar spectral (UV-vis, IR, EPR) and electrochemical properties which are also reported. The identity of 2(H) and 2(CF3) has been established by single-crystal X-ray structure determination (ReRe distance similar to 2.29 & Aring;). The electronic structures and optical properties of the complexes are scrutinized by density functional theory (DFT) and time-dependent DFT studies. DFT calculation shows that the highest occupied molecular orbital (HOMO) corresponds to a delta* interaction between the d-orbitals of rhenium atoms and pi* interaction between the sulphur atoms and the rhenium centers whereas the lowest unoccupied molecular orbital (LUMO) is the Re-2 pi* based orbital.