Synthesis, 119 Sn Mo¨ssbauer spectroscopic studies and X-ray crystal structure determination of new seven-coordinate diorganotin(IV) complexes with S,N,N,N,S-pentadentate Schiff bases derived from 2,6-diacetylpyridine of S-methyl- and S-benzyldithiocarbazates Gerima´rio F. de Sousa* and Viviane A. da S. Falcomer Instituto de Quı´mica, Universidade de Brası´lia, 70919-970 Brası´lia, DF, Brazil Yvonne P. Mascarenhas and Javier Ellena Instituto de Fı´sica de Sa ˜o Carlos, Universidade de Sa ˜o Paulo, 13560-970 Sa ˜o Paulo, SP, Brazil Jose´ D. Ardisson Laborato ´rio de Fı´sica Aplicada, Centro de Desenvolvimento da Tecnologia Nuclear, 30123-970 Belo Horizonte, MG, Brazil Jesu´s Valde´s-Martı´nes and Simo´n Herna´ndez-Ortega Instituto de Quı´mica, Universidad Nacional Auto ˆnoma de Me´xico, Circuito Exterior, Ciudad Universitaria, Coyaca ´n, 04510 DF, Me´xico Received 19 April 2006; accepted 25 April 2006 Abstract The reactions of the ligands 2,6-diacetylpyridine bis(S-methyldithiocarbazate)] (H 2 dapmdtc) and 2,6-diacetylpyridine bis(S-benzyldithiocarbazate)] (H 2 dapbdtc) with R 4-m SnCl m (R = Me, n Bu, Ph; and m=2) led to the formation of six seven-coordinate diorganotin(IV) complexes, which were studied by microanalysis, i.r., n.m.r ( 1 H, 119 Sn) and Mo¨ ssbauer spectroscopies. The X-ray structures determination of complexes [Me 2 Sn(dapmdtc)], [Me 2 Sn(dapbdtc)] and [Ph 2 Sn(dapbdtc)] revealed the presence of neutral seven-coordinated complexes. The structures consist of monomeric units in which the Sn(IV) atom exhibits distorted pentagonal bipyramidal (PBP) geometry, with the S,N,N,N,S-donor systems of the ligands lying in the equatorial plane and organic groups in the apical positions. A correlation between Mo¨ssbauer and X-ray data based on the point-charge model is discussed. Introduction Metal complexes of S,N,N,N,S-pentadentate Schiff base ligands derived from S-alkyldithiocarbazates com- prise an important class of compounds because of their interesting physical chemistry properties [1, 2] and potentially relevance in biological systems [3–6]. In this context, a number of 3d-metal complexes have been extensively studied by X-ray structural analysis and a number of other spectroscopic techniques [7, 8]. How- ever, pentadentate agents derived from S-alkyldithio- carbazates have not received much attention and the first organotin(IV) complex of this class of ligands was recently reported by Ali and collaborators [9]. This paper is an extension of research programs devoted to the investigation of the coordination modes of bis(semicarbazones) and bis(thiosemicarbazones) with organotin(IV) compounds as well as to the chemi- stry and structures of five-, six- and seven-coordinate organotin(IV) derivatives [10–12]. The ligands shown below were chosen since they have the potential to form seven-coordinated tin(IV) compounds. Further- more, these ligands that contain a HNC=S moiety, are capable of thioketo-thioenol tautomerism, and can coordinate to a metal atom through nitrogen or through sulfur, or simultaneously through nitrogen and sulfur [13]. H 2 dapmdtc; R = _ CH 3 H 2 dapbdtc; R = _ CH 2 Ph N N C N CH 3 C N H 3 C N C S C S H S H S R R * Author for correspondence: E-mail: gfreitas@unb.br Transition Metal Chemistry (2006) 31:753–759 Ó Springer 2006 DOI 10.1007/s11243-006-0059-4