Search for Combinations of Monocarboxylic Acids to Obtain Mixed-Anion Complexes of Cadmium and Zinc

The possibility of obtaining mixed-anion complexes of cadmium and zinc with various combinations of monocarboxylic acid anions was studied. When pentafluorobenzoate (Pfb), benzoate (Bz) anions, and 1,10-phenanthroline (Phen) were combined in the composition of the compounds, crystals of previously described homoanion compounds were formed. When 2,3,5,6-tetrafluoro-4-(trifluoromethyl)phenylacetate (Tfpha) or 3,5-dinitrobenzoate (Dnb) anions were used instead of pentafluorobenzoate, mixed-anion compounds [Cd2(Phen)2(Tfpha)2(Bz)2] (I), [Cd3(Phen)2(Dnb)3(Bz)3][Cd3(Phen)2(Dnb)4.5(Bz)1.5] (II), [Zn3(Phen)2(Dnb)4(Bz)2]·2(C6H6) (III), and [ZnCd2(Phen)2(Dnb)5(Bz)]·3(C6H6)·(MeOH) (IV) were isolated. According to X-ray diffraction data, in the structures of compounds II and IV, some anion positions are simultaneously occupied by Bz and Dnb anions in different ratios. The compounds [Cd2(Phen)2(Dnb)2(Pha)2] (V) and [Zn(H2O)(Phen)(Dnb)(Pha)]·MeCN (VI, Pha = phenylacetate anion) demonstrate that mixed-anion complexes can also form when conformationally flexible phenylacetate and sterically more rigid 3,5-dinitrobenzoate anions are combined on zinc and cadmium ions. The synthesized compounds I–VI were characterized by X-ray diffraction analysis (CCDC nos. 2443227, 2443228, 2443229, 2443230, 2443231, and 2443232, respectively), IR spectroscopy, and CHN analysis. The structures and crystal packings of the obtained complexes were analyzed in detail. It was found that the main contribution to the stabilization of the crystal packings arises from NO2···π, π···π, C–H···F, and N–O···π interactions.