Interaction of 1,3-Adamantanediacetic Acid (H(2)ADA) and Ditopic Pyridyl Subunits with Cobalt Nitrate under Hydrothermal Conditions: pH Influence, Crystal Structures, and Their Properties

A systematic investigation of the pH influence on the interaction between 1,3-adamantanediacetic acid (H(2)ADA), 1,3-bis(4-pyridyl)propane (bpp)/4,4'-dipyridine (4,4'-bipy), and cobalt nitrate under hydrothermal conditions has resulted in a series of coordination polymers with different composition and dimensionality, namely [Co(HADA)(2)(bpp)](n) (1), {[Co(ADA)(bpp)- (CH OH)]center dot H O (2). [Co-2(ADA)(2)(bpp)](n) (3). [Co(HADA)(2)(4,4'-bipy)(H2O)(2)](n) (4). and [Co(ADA)(4,4'-bipy)(0.5)](n) (5). These neutral polymeric complexes exhibit structural and dimensional diversity due to various coordination modes of the flexible H(2)ADA ligand. X-ray structural analysis reveals that 1 and 4 are one-dimensional (1-D)chains. The chain of complex 1 is directed by bpp, in which HADA located at both sides of the chain. Compared with the case of 1, the 1-D linear chain is composed of 4,4'-bipy and Co(II) ions in 4. Complexes 2, 3, and 5 show different 2-D networks. In 2, the final structure is formed via the linkage of Co-bpp chains by ADA. Complex 3 is composed of 1-D looped chains in which there are two kinds of (Co(2)ADA(2)] metallomacrocycles, and the chains are further connected by bpp to form the 2-D structure. The building block represents a one-dimensional chain consisting of [Co(2)ADA(2)] units linked by 4,4'-bipy in 5. Five new coordination modes of H(2)ADA are observed; among them, the bridging modes have proven that H(2)ADA call be used as in effective bridging ligand for metal-organic complexes, especially for metal organic layered structures (MOLS). It has also been found that the structure formation of the complexes is mainly governed by the pH value of the solution. The other effect is probably the flexibility of the pyridyl-containing ligands optimizing their position within file complexes. The TG, XRPD data of synthesized complexes and the magnetic properties For 3 and 5 have also been investigated.