pH Dependent Structural Diversity of Metal Complexes with 5-(4H-1,2,4-Triazol-4-yl)benzene-1,3-dicarboxylic Acid

A ligand 5-(4H-1,2,4-triazol-4-yl)benzene-1,3-dicarboxylic acid (H2L) with N- and O-donors was successfully applied to construct a series of coordination complexes [Cu3(μ3-OH)2(HL)4]n (1), [Co(HL)2(H2O)4]·3H2O (2), [Ni(HL)2(H2O)4]·3H2O (3), [Mn(HL)2]n (4), {[Cu2(L)2(μ-OH2)2]·3H2O}n (5), {[Co2(L)2(μ-OH2)2]·3H2O}n (6), {[Ni2(L)2(μ-OH2)2]·3H2O}n (7), and {[Mn(L)(μ-OH2)]·2H2O}n (8) under hydrothermal conditions. By adjusting the reaction pH, H2L ligand is partially deprotonated to give HL– form in 1–4 and completely deprotonated to afford L2– form in 5–8. The structural analyses revealed that complex 1 is a three-dimensional (3D) (3,3,5,6)-connected framework with Point (Schläfli) symbol of (4.6.8)2(42.65.83)2(42.66.86.10)(42.6)2, while 2 and 3 are discrete mononuclear complexes which are extended by hydrogen bonds to form 3D frameworks. The (3,6)-connected 3D framework of 4 is defined as a metal–organic replica of anatase (ant) net with Point (Schläfli) symbol of (42.6)2(44.62.88.10). Complexes 5–7 are isostructural and display (4,5)-connected 3D frameworks with Point (Schläfli) symbol of (42.52.62)(42.53.62.73), and 8 is a binodal (4,6)-connected 3D net with the Point (Schläfli) symbol of (3.54.6)(32.56.66.9). The results revealed that the reaction pH and the metal center play important role in determining the structures of the complexes. Magnetic studies indicate that the mixed μ3-hydroxo and triazolyl bridges in 1 and the double syn–syn carboxylate bridges in 4 mediate antiferromagnetic interactions. The alternating triazolyl and water bridges show alternating ferro- and antiferromagnetic interactions in 5 but antiferromagnetic interactions in 6 and 7. The mixed triazolyl and water bridges show antiferromagnetic interactions in 8.