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

A ligand 5-(4 H -1,2,4-triazol-4-yl)benzene-1,3-dicarboxylic acid (H 2 L) with N- and O-donors was successfully applied to construct a series of coordination complexes [Cu 3 (μ 3 -OH) 2 (HL) 4 ] n ( 1 ), [Co(HL) 2 (H 2 O) 4 ]·3H 2 O ( 2 ), [Ni(HL) 2 (H 2 O) 4 ]·3H 2 O ( 3 ), [Mn(HL) 2 ] n ( 4 ), {[Cu 2 (L) 2 (μ-OH 2 ) 2 ]·3H 2 O} n ( 5 ), {[Co 2 (L) 2 (μ-OH 2 ) 2 ]·3H 2 O} n ( 6 ), {[Ni 2 (L) 2 (μ-OH 2 ) 2 ]·3H 2 O} n ( 7 ), and {[Mn(L)(μ-OH 2 )]·2H 2 O} n ( 8 ) under hydrothermal conditions. By adjusting the reaction pH, H 2 L ligand is partially deprotonated to give HL – form in 1 – 4 and completely deprotonated to afford L 2– 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 (4 2 .6 5 .8 3 ) 2 (4 2 .6 6 .8 6 .10)(4 2 .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 (4 2 .6) 2 (4 4 .6 2 .8 8 .10). Complexes 5 – 7 are isostructural and display (4,5)-connected 3D frameworks with Point (Schläfli) symbol of (4 2 .5 2 .6 2 )(4 2 .5 3 .6 2 .7 3 ), and 8 is a binodal (4,6)-connected 3D net with the Point (Schläfli) symbol of (3.5 4 .6)(3 2 .5 6 .6 6 .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 μ 3 -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 .