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Subtle Structural Changes in Coordination Chains:  Influence of the Flexibility of the Precursor Ligands and of the Solvent

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posted on 05.09.2007, 00:00 by Cui-Juan Wang, Hai-Rui Ma, Yao-Yu Wang, Ping Liu, Li-Jun Zhou, Qi-Zhen Shi, Shie-Ming Peng
A novel flexible ligand dpap·2H2O (1) (dpap = 2,6-(N,N‘-di(4-pyridyl)amino)pyridine) and its five related coordination polymers {[Cu(dpap)(OAc)2]·CH3CN}n (2·CH3CN), {[Cu(dpap)(OAc)2]·0.25CH2Cl2}n (2·0.25CH2Cl2), {[Cu(dpap)(OAc)2]·CHCl3}n (2·CHCl3), {[Cu(dpap)(OAc)2]·0.5CH3OH}n (2·0.5CH3OH), and {[Cu(dpap)(maa)2]·2CH3OH}n (3·2CH3OH) (Hmaa = 2-methyl-acrylic acid) have been synthesized and structurally characterized by X-ray crystallography. The networks showed a lack of dependence on the nature of the counterion and solvent. Compound 2·CH3CN consists of uncoordinated guest CH3CN molecules and a one-dimensional (1D) zigzag chain. The diffusion in the CH2Cl2 solvent system results in a 1D helical chain of 2·0.25CH2Cl2, and that in CHCl3 system leads to a meso-helix chain [Cu(dpap)(OAc)2] motif of 2·CHCl3. The overall structure of 2·0.5CH3OH was found to be similar to that of 2·0.25CH2Cl2 despite the presence of different solvent molecules. The volumes of the channels are as follows:  2·CHCl3 > 2·0.25CH2Cl2 > 2·CH3CN > 2·0.5CH3OH. Using an maa group instead of an OAc- anion, we obtained polymer 3·2CH3OH, which displays a topological meso-helix chain.