Hydrothermal Syntheses, Structures And Properties Of 4, 5-Imidazoledicarboxylic Acid Complexes

Syntheses of coordination polymers, metallacycles and hydrogen-bonded metal-organic networks are currently of considerable interest in coordination and supramolecular chemistry. The coordination chemistry of 4,5-Imidazole-dicarboxylic acid (H3IDC) remains largely unexplored although it is rather simple and has a great potential for coordinative interaction and hydrogen bonding. It can be successively deprotonated to generate H2IDC-, HIDC2- and IDC3-, which should assume various coordinative and hydrogen-binding modes, and hence a large diversity of molecular or supramolecular architectures should be expected. To our knowledge, only three dinuclear complexes of H3IDC have been reported in literature. In this thesis, we report ten transition metal complexes of this interesting ligand, which are synthesized by hydrothermal methods and characterized by means of IR spectra, thermalgravimetric analyses(TGA), elemental analyses, ICP, single crystal X-ray structural analyses, variable-temperature and variable-field magnetic measurements. The main three parts are as follows.(1) Five mononuclear complexes, trans-[M(H2IDC-)2(H2O)2] (M = Mn(II) (1), Zn(II) (2), Co(II) (3) and Cd(II) (4)) in which molecular units coordinated by two water molecules and two H2IDC- ions in u1-2 mode as supramolecular tectons resulting in 3D architectures via hydrogen-bonding, are hydrothermally synthesized and structurally characterized. We have obtained three isostructural complexes (1, 2, and 3) under different reaction conditions and discussed their exotic hydrogen bonding patterns. Two supramolecular isomers of Cd(II) (4 and 5) are reported, their isomeric phenomena due to the formation of hydrogen bonding C-H O and the included crystallization water molecules in 5, which were testified by TGA.(2) Three coordination polymers bridged by HIDC2-, which can be divided into two species resultant from the selectivity of the hydrogen atom deprotonatedsecondly. Two 1D polymers of Cd(HIDC2-)(H2O)2 (6) and Ni(HIDC2-) (1,10-phen) (9) are linked by bis(bidentate) HIDC2- in u2- 4 mode whose second deprotonated hydrogen atom is that attached to the secondary amine group on the imidazole ring. Although bridged by the same linker, 6 and 9 result in different topologies (quasi-linear chains in 6 and sawtooth-shaped in 9) due to different coordination geometry around metal ions (trans in 6 and cis in 9). One 2D (4,4) wave-like net of Mn(II) (7) is bridged by HIDC2- in u3- 5 mode in which two hydrogen atoms of carboxylic group have been removed.(3) Two heterometallic species containing tetranuclear molecular squares or octanuclear molecular cubes with IDC3- (8 and 10). 8 is a heterometallic complex, Na2[CoII2CoIII2(IDC3-)4(bipy)4]-12H2O (bipy = 2,2'-bipyridine), in which mixed-valence tetranuclear squares with the imidazoledicarboxylate (IDC3-) ions as linkers are tethered into a unique spiral chain through disodium units. The terminated cobalt ions as an angular unit, alternately [Co(bipy)]3- and [Co(bipy)]2-, joined the linear unit IDC3- into an exactly co-planar square Co4. More interestingly, when terminal ligands are removed, the octahedral transition metal ions Ni(II) acting as angular units directly, combine the same linear linker IDC3- in the same mode as that in 8 into an original cubic cage of [Nig (IDC3-)12]20- Na5[Ni2(IDC3-)3] 11H2O (10), and there exist strong antiferromagnetic interactions between Ni(II) ions.