ANALYSIS OF THE CONCENTRATION-DEPENDENCE OF NUCLEAR MAGNETIC-RESONANCE PARAMETERS BY MEANS OF CHEMICAL-EQUILIBRIA - ELUCIDATION OF THE COMPLEX-FORMATION BETWEEN DIMETHYLTIN DICHLORIDE AND PYRIDINE BASE IN SOLUTION

A procedure for the analysis of the concentration dependence of NMR parameters on chemical equilibria, utilizing the Davidon-Fletcher-Powell method of optimization, is described in detail for (1) A + B = AB, (2) A + 2B = AB2, and (3) A + B = AB (K1), AB + B = AB2 (K2). The procedure is applied to the Me2SnCl2 + 2,2′-bipyridine and Me2SnCl2 + pyridine systems in CHCl2CHCl2, and the coexistence of 1:1 Me2SnCl2-pyridine and 1:2 Me2SnCl2-pyridine complexes is proven in the latter system. Little has been reported about the former complex. Determination of K1 and K2 in the Me2SnCl2 + pyridine system is successful by using 2J(SnH) data (K1 = 16.6 ± 1.9 dm3 mol-1 and K2 = 4.44 ± 0.24 dm3 mol-1), when the J of the 1:2 complex is taken as that of the tin compound in a large excess of pyridine, whereas only rough estimates of K1 and K2 are available when this J is also regarded as a variable parameter in the calculation. The formation constant of the 1:1 complex in the Me2SnCl2 + 2,2′-bipyridine system is 4500 ± 320 dm2 mol-1 in CHCl2CHCl2, about twice as large as that reported in CH3CN, and reflects much weaker solvation by CHCl2CHCl2 than by CH3CN. © 1979 American Chemical Society.