Rhenium(V) complexes with benzimidazole (BzimH) and crystal structure of the hemiprotonated compound [ReO2(BzimH)(4)][ReO(OH)(BzimH)(4)](ReO4)(3)

trans-[ReO2(BzimH)(4)]I is generated by reacting ReO2I(PPh3)(2) with excess BzimH in methanol, but free Ligand is difficult to eliminate from the product. Pure samples of the trans-[ReO2(BzimH)(4)]BPh4 salt and of the protonated oxo-hydroxo form [ReO(OH)(BzimH),] (BF,), are isolated. Recrystallization of the dioxo complex in acetone-ether yields a pink solid. Red crystals suitable for X-ray diffraction are obtained by recrystallization of this solid in ethanol. The crystallographic study reveals a hemiprotonated [ReO2(BzimH)(4)][ReO(OH)(BzimH)(4)](ReO4)(3) phase (Acam, a = 10.794, b = 21.520, c = 27.196 Angstrom, R = 0.049). The O=Re=O fragments are parallel to one another along the unit cell c axis, forming layers of dimeric units consisting of one dioxo and one oxo-hydroxo species connected by a very short O-H ... O hydrogen bond of 2.44 Angstrom. The ReO4- anions form hydrogen bonds with ligand N-H groups. The complexes are characterized by solution (H-1 and C-13) and solid-state (C-13 CP-MAS) NMR, UV-VIS, and IR spectroscopies. H-1 NMR reveals that the benzimidazole protons in close proximity to the rhenium-oxo multiple bond or adjacent benzimidazole ligands are very sensitive to nonbonded magnetic effects.