Different coordination modes of tetradentate Schiff bases in monomeric and dimeric oxorhenium(V) complexes

The reactions of the tetradentate amine-phenol type Schiff bases H₂sal₂en (1,2-ethylenebis(salicylideneimine) and H₂sal₂mp (1,2-benzylenebis(salicylideneimine)) with trans-ReOCl₃(PPh₃)₂] or (n-Bu₄N)ReOCl₄] in air gave the products (µ-O)ReO(sal₂en)]₂ (1) and ReOCl(sal₂mp)] (2), respectively. X-ray and spectroscopic studies have shown that 1 contains the linear O=Re–O–Re=O grouping, with the four donor atoms of sal₂en^2? coordinating in the square plane cis to the oxo ions. In 2, a cis oxo-chloro arrangement is observed with a phenolic oxygen being coordinated trans to the oxo group. The terminal Re=O bond lengths in 1 and 2 are 1.709(4) and 1.683(3)?Å, respectively.