Synthesis and spectroscopic studies of diorganotin derivatives with 2-[(2,6-dimethylphenyl)amino]benzoic acid. Crystal and molecular structure of the first complexes of 2-[(2,6-dimethylphenyl)amino]benzoic acid. Crystal and molecular structures of 1,2 : 3,4-di-mu(2)-2-[(2,6-dimethylphenyl)amino]benzoato-O,O-1,3-bis-2-[(2,6-dimethylphenyl)amino]benzoato-O-1,2,4 : 2,3,4-di-mu(3)-oxo-tetrakis[di-butyltin(IV)] and bis-2-[(2,6-dimethylphenyl)amino]benzoato-di-n-butyltin(IV)