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Dalton Trans., 2006, 3900 - 3905, DOI: 10.1039/b604928a
Dynamic equilibrium between cyclic oligomers. Thermodynamic and structural characterization of a square and a triangle
F. Albert Cotton, Carlos A. Murillo and Rongmin Yu
A dynamic equilibrium has been found in CDCl3 between a neutral molecular square, [cis-Mo2(DAniF)2]4(O2CC6F4CO2)4 ( 1) and triangle, [cis-Mo2(DAniF)2]3(O2CC6F4CO2)3 ( 2) (DAniF = the anion of N,N
-di-p-anisylformamidine). The two components have been crystallographically characterized and solution studies by 1H and 19F 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) × 10–4 at 23.7 °C. At this temperature, the 
G0 for the conversion of three moles of squares to four moles of triangles is 21.0 kJ mol–1. The conversion is enthalpically disfavored (H0 = 23.5 kJ mol–1), but entropically favored (S0 = 8.2 J K–1 mol–1).
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