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Dynamic equilibrium between cyclic oligomers. Thermodynamic and structural characterization of a square and a triangle.

Cotton FA, Murillo CA, Yu R

Department of Chemistry and Laboratory for Molecular Structure and Bonding, P. O. Box 3012, Texas A and M University, College Station, Texas 77842-3012, USA. cotton@tamu.edu

A dynamic equilibrium has been found in CDCl(3) between a neutral molecular square, [cis-Mo(2)(DAniF)(2)](4)(O(2)CC(6)F(4)CO(2))(4) (1) and triangle, [cis-Mo(2)(DAniF)(2)](3)(O(2)CC(6)F(4)CO(2))(3) (2) (DAniF = the anion of N,N'-di-p-anisylformamidine). The two components have been crystallographically characterized and solution studies by (1)H and (19)F NMR spectra of the concentration- and the temperature-dependence of the equilibrium have been performed. The conversion of three moles of molecular squares 1 to four moles of molecular triangles 2 has an equilibrium constant of 1.98(7) x 10(-4) at 23.7 degrees C. At this temperature, the DeltaG(0) for the conversion of three moles of squares to four moles of triangles is 21.0 kJ mol(-1). The conversion is enthalpically disfavored (DeltaH(0) = 23.5 kJ mol(-1)), but entropically favored (DeltaS(0) = 8.2 J K(-1) mol(-1)).

Published 9 August 2006 in Dalton Trans.
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