Organometallic polymers with the backbone consisting of ferrocene and bimetallic tetracarboxylates

The tetranuclear compounds Mo₂(O₂CCF₃)₄ (FPA)₂ (1), Rh₂(O₂CCH₃)₄ (FPA)₂ (2), and Rh₂(O₂CCF₃)₄ (FPA)₂ (3) (FPA = ferrocenyl-4-pyridylacetylene) have been synthesized by the reaction of bimetallic tetraacetates with FPA in a 1:2 stoichiometry. They have been investigated as models of oligomeric and polymeric complexes of analogous composition. UV/Vis absorption spectroscopy and cyclic voltammetry indicate that Rh₂(O₂CCF₃)₄ possesses the strongest inductive effect of the three bimetallic tetracarboxylates examined in this study. Complex 1 was additionally characterized by single crystal X-ray analysis, revealing a Mo-Mo distance of 214.22(3) pm, which is elongated in comparison to Mo₂(O₂CCF₃)₄ [209.0(4) pm], and a Mo-N distance of 250.4(2) pm. Oligomers with backbones consisting of 1,1′-bis(4-pyridylethynyl)ferrocene (BPEF) and bimetallic tetracarboxylates, [M₂(O₂CR)₄(BPEF)]_n (M = Mo, R = CF₃, 4; M = Rh, R = CH₃, 5; M = Rh, R = CF₃, 6), have been prepared by treating the bimetallic tetracarboxylates with BPEF in a 1:1 molar ratio. The terminal groups and the number of repeating units have been estimated by elemental analyses. The oligomeric complexes 5 and 6 are insoluble in all common solvents. Complex 4 dissolves in strongly coordinating donor solvents due to replacement of the BPEF ligands by solvent molecules.