Synthesis, Structures, and Characterization of Metal-Organocarboxylate Compounds
Reticular synthesis of metal-organic hybrid compounds deals with the interaction of two primary building components, namely metal connectors and organic linkers, to build structures for specific applications. This work focuses on studying the role of linear aromatic dicarboxylates as bridging linkers for the formation of magnetic and chiral framework materials. A series of dicarboxylate-bridged nickel (II) cluster compounds were synthesized and their magnetic properties investigated. The compounds Ni3(1,4-BDC)3(DMF)2(DMA)2 (3-1) and Ni3(1,4-BDC)3(DMF)4 (3-2) [1,4-BDC = terephthalate, DMF = N,N’-dimethylformamide, and DMA = dimethylamine] have layered structures whereas Ni3(2,6-NDC)3(DMF)2(DMA)2 (3-3) [2,6-NDC = naphthalate], Ni3(3-O)(4,4’-BPDC)3(DMA)3 (3-4) [4,4’-BPDC = 4,4’-biphenyldicarboxylate], and Ni4(3-O)(1,4-NDC)4(DMF)2(DMA)2 (3-5) [1,4-NDC = 1,4-naphthalenedicarboxylate] have three- dimensional frameworks. An isoreticular series of chiral frameworks, Ni2O(Asp)(1,4-BDC)0.5 (4-1) [Asp= aspartate, Ni2O(Asp)(1,4-NDC)0.5 (4-2), Ni2O(Asp)(2,6-NDC)0.5 (4-3) and Ni2O(Asp)(4,4’-BPDC)0.5 (4-4) were also prepared. These compounds are built from homochiral chains of [Ni2O(L-Asp)(H2O)2] connected by the aromatic dicarboxylate ligands. The compounds contain channels parallel to the chains with dimensions that depend on the lengths of the rigid dicarboxylate linkers. The sensitivity of the synthesis of compound 4-1 toward several parameters such as pH, reaction time, and solvent system was studied. Coordination compounds were also synthesized by the reaction of metal cations with a new ligand meso-1,4-phenylenebis(hydroxyacetic acid) (H2L). Four new compounds, Ni2L2•(H2O)4 (5-1), CoL•H2O (5-2), ZnL•H2O (5-3), and PbL (5-4) were prepared in single crystal form and characterized by X-ray crystallography and IR spectroscopy. In the final section, films of metal-organic compounds were grown on carboxylate-functionalized gold (Au) surfaces as an initial attempt towards developing functional metal-organic materials for device applications. Zinc terephthalate (MOF-5) crystals were deposited on top of Au substrates that were functionalized with self-assembled monolayers (SAMs) with COOH- terminal groups. Nucleation of MOF-5 crystals was induced by pretreatments with Zn2+ solutions. The kinetics of crystal growth was investigated by analysis of optical images of the films at different periods of crystallization to determine the particle size distribution. The procedure used to grow MOF-5 films on Au surfaces functionalized with SAMs was also used in the preparation of manganese formate and lanthanum formate films.