Natural bond orbital analysis and density functional study of linear and bent oxo-bridged dimers of rhenium(V)

The calculations using the density functional theory (DFT) method were done on two diamagnetic oxo-bridged dinuclear rhenium complexes: [{Re(O)Br2(3,5-Me2pzH)2}2(μ-O)] (1) with a linear ORe-O-ReO core and [{Re(O)Br(3,5-Me2pzH)}2(μ-O)(μ-3,5-Me2pz)2] (2) with a bent Re2O3 unit (pzHmonodentate N-pyrazole and pzbidentate N,N′-pyrazole ligand). The optimized geometries of 1 and 2 agree with the X-ray structures. The MO sequence is almost the same for 1 with a linear ORe-O-ReO core and 2 with a bent Re2O3 unit. The bending of Re2O3 unit in 2 is a consequence of steric congestion introduced by two coordinated 3,5-dimethylopyrazole bridging ligands. Additional information about binding in the complexes 1 and 2 was obtained by NBO analysis.