Linear and cyclic tetranuclear copper(I) complexes containing anions of N,N'-bis(pyrimidine-2-yl)formamidine |
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Authors: | Chan Zhi-Kai Wu Ying-Yann Chen Jhy-Der Yeh Chen-Yu Wang Chih-Chieh Tsai Yi-Fang Wang Ju-Chun |
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Institution: | Department of Chemistry, Chung-Yuan Christian University, Chung-Li, Taiwan R.O.C. |
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Abstract: | The reaction of Kpmf (pmf = anion of N,Nprime or minute]-bis(pyrimidyl-2-yl)formamidine, Hpmf) with CuSCN afforded the complexes KCu4(pmF)3(SCN)2], 1, and Cu(4)(pmf)4, 2. Reaction of 1 with (n-Bu)4N]PF6 in THF gave the complex (n-Bu)4N]Cu4(pmf)3(SCN)2], 3. Their structures were characterized by X-ray crystallography. Complexes 1 and 3 are the first linear tetranuclear complexes containing only Cu(I) atoms, while complex 2 is cyclic. The four Cu(I) atoms of complexes 1 and 3 are helically bridged by three tetradentate pmf- ligands. The Cu4(pmf)3(SCN)2]- anions of 1 show weak interactions with adjacent K(THF)5]+ cations through the sulfur atoms, forming infinite chains which are subjected to a series of intermolecular pi-pi interactions. In complex 2, the pmf- ligands are coordinated to the copper atoms in bidentate fashion through the two central amine nitrogen atoms, leaving the pyrimidine nitrogen atoms uncoordinated. Unexpected fluxional behaviors were observed for complexes 1 and 3 in solution. By the DNMR analysis, the free energy of activation (DeltaGc(not equal)) for the exchange is 12.8 kcal mol(-1) at 278 K (T(c)), and the rate constant of exchange (K(c)) is 470 s(-1) for 1. The DeltaGc(not equal) and Kc are 12.6 kcal mol(-1) at 273 K and 433 s(-1), respectively, for 3. |
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