Effect of Substituents in the Pentafluorobenzoate and 2,3,4,5- and 2,3,5,6-Tetrafluorobenzoate Anions on the Structure of Cadmium Complexes

Abstract

New cadmium 2,3,4,5-tetrafluorobenzoate (6HTfb) and 2,3,5,6-tetrafluorobenzoate (4Htfb) complexes, [Cd(6HTfb)(H₂O)₃]_n·(6HTfb)·2nH₂O (I), [Cd₃(Phen)₂(6HTfb)₆] (II, Phen = 1,10-phenanthroline), [Cd₂(Phen)₂(4Htfb)₄]_n·2nH₂O (III), and [Cd(Phen)₂(4Htfb)₂] (IV), were synthesized. Analysis of the obtained results and published data demonstrated that a decrease in the number of fluorine substituents is unfavorable for the formation of coordination polymers comprising stacked alternating fluorinated and non-fluorinated aromatic moieties. In the case of 2,4,5-trifluorobenzoate complex, a typical trivial structure of the binuclear cadmium complex with ligand-shielded metal core is formed. The synthesis of 2,3,4,5- and 2,3,5,6-tetrafluorobenzoate complexes produced an intermediate situation and demonstrated that the structure of complex formation products is affected by not only the number, but also the positions of fluorine substituents. Using quantum chemical calculations, it was shown that the formation of coordination polymers requires a molecular precursor with a Chinese lantern structure stable in solutions, while the formation of unusual flattened binuclear complexes with additionally coordinated water molecules requires doubly bridged binuclear complexes able to switch to a conformation with exposed coordinatively unsaturated metal centers.