Non-covalently aggregated zinc and cadmium complexes derived from substituted aromatic carboxylic acids: Synthesis, spectroscopy, and structural studies

Mononuclear zinc carboxylates [Zn(L)(2,2′-bpy)2](ClO4)(nH2O) (1–4) (LH = 3-aminobenzoic acid (3-abaH) (1), salicylic acid (saH2) (2), 3,5-diisopropylsalicylic acid (dipsaH2) (3), and 3-methyl-2-thiophenecarboxylic acid (3-Me-2-TCAH) (4)) and cadmium carboxylates [Cd(tipba)(2,2′-bpy)2](tipbaH) (5) (tipaH = 2,4,6-triisopropylbenzoic acid), [Cd(2,2′-bpy)2(2-TCA)(ClO4)] (6) (2-TCAH = thiophene-2-carboxylic acid) and [{Cd(2,2′-bpy)2(3-Me-2-TCA)}{Cd(2,2′-bpy)2(3-Me-2-TCA)(H2O)}](ClO4)2 (7) have been synthesized from the reaction of the metal precursor complex [M(OAc)(2,2′-bpy)2](ClO4)(H2O) (M = Zn and Cd) with the respective aromatic carboxylic acid in methanol at ambient conditions. Complexes 1–7 have been characterized with the aid of elemental analysis and FT-IR, UV–Vis, fluorescence, 1H NMR spectroscopic methods and further analyzed by single-crystal X-ray diffraction studies. The carboxylate groups show chelating and monodentate coordination behavior in these complexes. While the cadmium ion in 6 is heptacoordinated, the structure of 5 reveals a coordination number of eight with square antiprismatic geometry. Hydrogen bonding patterns in 1–4 and 7 result in a 1-D polymeric structure while 5 is a 2-D layer structure and 6 is a 3-D polymeric structure.