Effect of benzoic acid substituents and additional functional groups of ancillary ligands in modulating the nuclearity and aggregation behavior of transition metal carboxylates

Abstract

Structural modulation of transition metal carboxylates has been studied by employing different auxiliary ligands in the reactions of metal acetates with substituted benzoic acids. A series of neutral transition metal benzoates [Cu(tbba)2(imH)2] (1), [Cu(tipba)2(2,4,6-collidine)2] (2), [Co(tbba)2(dmpH)2] (3), [Co(tipba)2(imH)2] (4), [M(tmba)2(pymeH)2] (M = Cu (5), Co (6) and Zn (7)), [Zn(tmba)2(pydmeH2)] (8), [Cu2(tmba)2(pydmeH2)2][(tmba)2(tmbaH)2] (9) and [Zn2(dmp)2(tbba)2(dmpH)2] (10) have been isolated as products from the reaction between the respective metal acetates and substituted benzoic acids (acids used: 4-tert-butylbenzoic acid (tbbaH), 2,4,6-triisopropylbenzoic acid (tipbaH), 2,4,6-trimethylbenzoic acid (tmbaH)) and N-donor auxiliary ligands (imidazole (imH), 3,5-dimethylpyrazole (dmpH), 2,4,6-collidine, 2-pyridinemethanol (pymeH), and pyridine-2,6-dimethanol (pydmeH2)). The new complexes have been characterized by both analytical and spectroscopic methods. The molecular structures of 1–10 have further been established by single crystal X-ray diffraction studies. The complexes 1–8 are mononuclear, while compounds 9 and 10 have been found to be dinuclear due to the role of benzoic acid in 9 and pyrazolate anion as bridging ligand in 10. The geometry around the metal ion is square-planar in 1 and 2, tetrahedral in 3, 4 and 10, octahedral in 5–7 and 9 and trigonal-bipyramidal in 8. Complexes with ligands that contain additional functional groups such as >NH and –OH are involved in hydrogen bonding interactions. These weak interactions lead to the formation of 1-D linear polymers or 2-D sheets.