Synthesis and characterization of heptacoordinated tin(IV) complexes. X-ray crystal structure of [nBu2Sn(dappt)]·(Me 2CO)0.5 [H2dappt = 2,6-diacetylpyridine bis(4-phenylthiosemicarbazone)]

摘要

The chelating properties of 2,6-diacetylpyridine bis(thiosemicarbazones) have been investigated and six different coordination modes have been discovered so far. [Ph2Sn(daptsc)]?·2DMF1 (H2daptsc = 2,6-diacetylpyridine bis (thiosemicarbazone), which was obtained from Ph2SnO in DMF (N,N-dimethylformamide), crystallizes in a regular PBP geometry with the dianion daptsc2- in the pentagonal plane and the two phenyl groups in the axial positions. Similarly, in [nBu2Sn(H2daptsc)]Cl 2?·MeNO22 the Sn(IV) atom is heptacoordinated in a distorted PBP configuration, with the five SNNNS donor atoms of the H2daptsc in the pentagonal plane. In [Ph2Sn(Hdaptsc)]Cl3 the Sn(IV) atom is heptacoordinated and also has a PBP geometry, where only one of the H2daptsc arms has undergone deprotonation. A fourth coordination mode was reported for [Zn2(daptsc)2]?·2MeOH?·H 2O4, where each of the two fully deprotonated ligands, daptsc2-, are coordinated to two Zn(II) atom in a distorted octahedral geometry. The dinuclear complex [Zn2(daptsc)2]?·MeOH?·H 2O4, crystallized from MeOH solution, possesses one octahedral and one tetrahedral Zn(II) atoms. Finally, spectroscopic and X-ray studies showed that bis(thiosemicarbazones) can also behave as tetradentate dianionic ligands, forming square-planar complexes with Ni(II), Cu(II) and Pd(II) in the sixth coordination mode5. In this case, the metal ion is coordinated through the pyridine nitrogen, the thiolate sulfur, the azomethine nitrogen and the thioimide nitrogen atom. The other sulfur atom remains in the thione form and does not coordinate. Since both Sn(IV)6 and thiosemicarbazones7 have significant pharmacological activity, some crystal structures of organotin(IV) complexes with 4-substituted thiosemicarbazones have already been discussed6. We report in this work the preparation and characterization of new heptacoordinated organotin(IV) complexes with the ligand 2,6-diacetylpyridine bis(4-phenylthiosemicarbazone), whose structure is shown below.     Experimental Materials All solvents were purified and dried according to standard procedures. 2,6-diacetylpyridine (Aldrich) and the organotin halides (Aldrich) were used without further purification. IR spectra were recorded on a Nicolet 5ZDX-FT spectrophotometer in the 4000-400 cm-1 range using KBr pellets. 119Sn M??ssbauer spectra were recorded using a constant acceleration spectrometer moving a CaSnO3 source at room temperature. The samples were analyzed at 85K. The spectra were computer-fitted, assuming Lorentzian lines shapes. X-ray diffraction data were collected at room temperature using an Enraf-Nonius CAD-4 automatic diffractometer, with a graphite monocromated MoKa radiation obtained in a fine focus sealed tube (see Table 1).     Preparation of H2dappt and its Sn(IV) complexes The pale yellow 2,6-diacetylpriridine bis(4-phenylthiosemicarbazone), H2dappt, was prepared by refluxing a 2:1 molar mixture of 4-phenylthiosemicarbazide8 with 2,6-diacetylpyridine in absolute EtOH. The Sn(IV) complexes were obtained by the following procedure: 0.097 g (0.21 mmol) of H2dappt were dissolved by refluxing a 1:1 molar mixture of MeOH/Me2CO (10 mL) for 10 min. To this solution was added 0.22 mmol of the appropriate organotin(IV) species, dissolved in 2 mL of MeOH, and the resulting mixture was refluxed for about 1 h. Cooling the solution and slow evaporation of the solvent led to the appearance of crystalline products with yields on the order of 60%. The microanalyses were performed with a Perkin Elmer 2400C analyzer, giving for C, H and N the following results. H2dappt. Anal. Found: C, 59.05; H, 4.82; N, 21.24. Calcd. for C23H23N7S2 : C, 59.87; H, 4.99; N, 21.26%. 1. MeSnCl(dappt)], m.p. 157 ?oC (dec.). Anal. Found: C, 47.22; H, 3.68, N, 15.51. Calcd. for C24H24ClN7S2 Sn: C, 45.85, H, 3 85, N, 15.59%. 2. [Me2Sn(dappt)], m.p. 231-234 ?oC. Anal. Found: C, 48.60; H, 4.39, N, 15.97. Calcd. for C25H27N7S2 Sn: C, 49.36; H, 4.47; N, 16.12%. 3. [nBu2Sn(dappt)]?·(Me 2CO)0.5, m.p. 238-241 ?oC. Anal. Found: C, 53.58; H, 5.64, N, 13.53. Calcd. for C32.5H42N7O0.5 S2Sn: C, 52.77; H, 5.48; N, 14.13%. 4. [Ph2Sn(dappt)], m.p.134 ?oC (dec.). Anal. Found: C, 48.03; H, 3.71; N, 9.24. Calcd. for C35H31N7S2 Sn: C, 49.11; H, 3.74; N, 8.53%.   Results and Discussion Crystal and molecular structure of [nBu2Sn(dappt)]?· (Me2CO)0.5 (3). The ORTEP drawing of the molecular structure of di-n-butyl[2,6-diacetylpyridine bis(4-phenylthiosemicarbazone)]tin(IV) acetone solvate, [nBu2Sn(dappt)]?· (Me2CO)0.5 (3), is shown in Figure 1. Crystal structure parameters and conditions of data collection are given in Table 1. Selected bond distances and angles are presented in Table 2.       All non hydrogen atoms were refined with anisotropic displacement parameters with the exception of those of the n-butyl groups and those of the solvate molecule. For the latter, greater freedom for thermal displacements was observed in accord with their low steric