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

A dynamic equilibrium has been found in CDCl3 between a neutral molecular square, [cis-Mo-2(DAniF)(2)](4)(O2CC6F4CO2)(4) ( 1) and triangle, [cis-Mo-2(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 H-1 and F-19 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 Delta G degrees for the conversion of three moles of squares to four moles of triangles is 21.0 kJ mol(-1). The conversion is enthalpically disfavored (Delta H degrees = 23.5 kJ mol(-1)), but entropically favored (Delta S degrees = 8.2 J K-1 mol(-1)).