COMPLEXATION EQUILIBRIA AND STRUCTURES OF DIMETHYLTIN(IV) COMPLEXES WITH N-METHYLIMINODIACETATE, PYRIDINE-2,6-DICARBOXYLATE, ETHYLENEDIAMINE-N,N'-DIACETATE AND ETHYLENEDIAMINE-N,N,N',N'-TETRAACETATE

The complexation equilibria of the dimethyltin(IV) ion with N-methylim inodiacetate (mida), pyridine-2,6-dicarboxylate (pdc), ethylenediamine -N,N'-diacetate (edda) and ethylenediamine-N,N,N',N'-tetraacetate (edt a) have been investigated in aqueous solution at 25.0 degrees C and I= 0.1 mol dm(-3) ((H,Na)NO3) by potentiometric measurements. The overall stability constants beta(pqr) for [(SnMe(2))(p)H(q)L(r)]((2p+q-nr)+) (n=2 for L=mida, pdc, edda; n=4 for L=edta) defined as ]((2p+q-nr)+)][ SnMe(2)(2+)](-p)[H+](-q)[L(n-)](-r) are evaluated as follows: log beta (1-11)=2.53(3), log beta(101)=9.625(4) and log beta(112)=20.73(4) for L=mida; log beta(101)=10.533(6), log beta(111)=12.65(5) and log beta(1 12)=17.69(3) for L=pdc; log beta(101)=12.412(8), log beta(111)=15.75(3 ), log beta(112)=24.12(4) and log beta(122)=30.87(4) for L=edda; log b eta(2-21)=4.75(1), log beta(2-11)=10.44(2) and log beta(201)=15.41(2) for L=edta. The crystal structures of [SnMe(2)(mida)(H2O)]. H2O, [SnMe (2)(pdc) (H2O)]. H2O, [SnMe(2)(edda)] and [(SnMe(2))(2)(edta) (H2O)(2) ]. H2O have been determined by X-ray crystal structure analyses. The m ida and pdc complexes have a dimeric structure which consists of disto rted pentagonal-bipyramidal tin units with two methyl groups in the ax ial position. The edda complex has a distorted octahedral monomer stru cture with two methyl groups in the cis position. The edta complex con sists of a polymer structure with spanning edta ligands in which each tin unit has a geometry quite analogous to those of the mida and pdc c omplexes. The preference in geometry of the dimethyltin(IV) complexes is discussed in terms of the effects of the bound ligands. The dimethy ltin(IV) complexes formed in aqueous solution have been characterized on the basis of the molecular structures in the crystals and the value s of the stability constants and pK(a).