Elucidating the electronic structure of multiple bonded systems: Synthesis and characterization of bimetallic tungsten and ruthenium complexes

The following study is presented in two sections. In the first section variable-temperature magnetic and structural data of two pairs of diruthenium isomers (having an idealized D4h symmetry), one pair having axial ligands and the formula Ru2(DArF) 4Cl (where DArF is the anion of a diarylformamidine isomer, and Ar = p-anisyl or m-anisyl) and the other one being essentially identical but devoid of axial ligands and having the formula [Ru2(DArF) 4]BF4, show that the axial ligands have a significant effect on the electronic structure of the diruthenium core. Variable-temperature crystallographic and magnetic data as well as density functional theory (DFT) calculations unequivocally demonstrate the occurrence of π interactions between the p orbitals of the chlorine ligand and the π* orbitals in the Ru25+ cores. Electron paramagnetic resonance data show unambiguously that the unpaired electrons are in metal-based molecular orbitals. On the second section a triple bonded compound W2(TPG) 2Cl4, with a D2h symmetry at the core (where TPG is the anion of N,N’,N”- triphenylguanidine), was synthesized and structurally characterized by single-crystal x-ray crystallography, FT-IR, NMR and Raman spectroscopies, and electrochemical methods. The W–W distance in the solid state is 2.2612(4) Å, and the compound shows two one-electron reversible reductions at (E1/2) –0.73, and –1.04 V (vs Fc/Fc+). A one-electron reduction of the compound resulted in a complex with a bond order of 3.5, which was characterized by Raman and EPR spectroscopies (g = 1.83). The Raman shift of the W–W bond of both complexes are, 290, and 315 cm-1, respectively, consistent to the increase in bond order. DFT calculations were performed to aid in the assignment of the Raman shifts, and to help understand their electronic properties