Reaction of thiamine diphosphate hydrochloride (H3TDPCl) with methylphenyltin(IV) dichloride in water. Molecular and crystal structures of the oxygen-capped cluster [{SnMe(HTDP)(OH)}(3)O](OH)center dot 21H(2)O, in which thiamine diphosphate coordinates via its terminal phosphate group

Reaction between thiamine diphosphate hydrochloride (H3TDPCl) and methylphe nyltin dichloride in water at pH ca. 5.6 afforded the title complex, which was studied by X-ray diffraction and IR and Raman spectroscopy in the solid state and by multinuclear NMR spectroscopy (H-1, C-13, P-31, and Sn-119) i n aqueous solution. The crystals of this compound are formed by the oxygen- capped cluster cation [{SnMe(HTDP)(OH)}(3)O](+), an OH- counterion, and wat er of crystallization. The cation has 3-fold symmetry, and the tin atom has coordination number 6 and a distorted octahedral coordination polyhedron. The HTDP- anion is bis-monodentate bridging between two Sn atoms via two of the oxygens belonging to the terminal phosphate of the ethyl diphosphate s ide chain [Sn-O 2.074(3), 2.100(5) Angstrom]. The thiamine moiety has F con formation, with torsion angles C(2) -N(3)-C(3,5')-C(5') = -5.8(11)degrees a nd N(3)-C(3,5')-C(5')-C(4') = -83.0(10)degrees and the ethyl diphosphate si de chain is folded back, directing the pyrimidine and thiazolium rings of t he three HTDP- anions away from the "missing" corner of the Sn3O4 core so t hat they form the walls of a "nest" with the core as its floor. Although th e diffraction data do not allow direct location of most of the hydrogen ato ms, indirect structural evidence suggests (i) that the OH- counterion lies inside the nest on the S-fold symmetry axis, (ii) that the remaining dissoc iable proton of the HTDP- anion forms a strong hydrogen bond between the py rimidine N(1') atom and the uncoordinated oxygen of the terminal phosphate of another HTDP- belonging to the same cluster, and (iii) that one of the o xygens of the nonterminal phosphate is hydrogen-bonded to one of the -OH gr oups that bridge between the Sn atoms. Features ii and iii are probably res ponsible for the folding of the ethyl diphosphate side chain. Hydrogen bond s involving the N(H-2)Hz group on the pyrimidine ring and the water molecul es of crystallization are also present. The multinuclear NMR results indica te that most of the structural features exhibited by the cluster in the sol id state remain in D2O solution. LR and Raman spectra are also discussed.