Characterization of diorganotin(IV) complexes with captopril. The first crystallographically authenticated metal complex of this anti-hypertensive agent.

Abstract Diorganotin(IV) complexes R 2 Sn(cap) (capH 2 = N -[( S )-3-mercapto-2-methylpropionyl]- l -proline; R=Me, Et, n -Bu and t -Bu) were prepared and characterised. The FTIR and Raman spectra demonstrated that the organotin(IV) moieties interact with the {S} atom of the ligand, while the other coordination sites are the carboxylate and the amide –CO groups. Mossbauer Δ data showed that the diorganotin(IV) compounds adopt slightly distorted trigonal-bipyramidal (tbp) geometry. A single-crystal X-ray study was performed on the compound Me 2 Sn(cap): the Sn atom is five-coordinated in a distorted tbp environment, with two {O} atoms in the axial positions and the {S} and two {C} atoms in the equatorial (eq) plane. Each cap ligand coordinates to two different Sn atoms, and infinite zigzag chains are formed, directed parallel to each other and to the b axis of the unit cell. NMR (CDCl 3 ) of the Me 2 Sn(IV) and n -Bu 2 Sn(IV) complexes indicated the presence of different oligomeric species.