New Heptacoordinated Organotin(IV) Complexes Derivatives of 2,6-diacetylpyridinebis(2-furanoylhydrazone), H2dapf, and 2,6-diacetylpyridinebis(2-thenoylhydrazone), H2dapt: Crystal and Molecular Structure of [Me2Sn(Hdapt]Br.H2O

Abstracts

The reaction of the ligands H2dapf and H2dapt, with R4-mSnXm (m = 2, 3; R = Me, Ph and X = Cl, Br) led to the formation of eight new heptacoordinated organotin(IV) complexes, which were studied by microanalysis, IR, NMR and Mössbauer spectroscopy to investigate their structural properties. The methyl derivative [Me2Sn(Hdapt)]Br.H2O was also studied by single crystal X-ray diffraction. It crystallizes in the monoclinic system, space group P2(1)/c, with a = 21.920(3), b = 7.4470(5), c = 16.805(2) Å, beta = 110.18(1)º, Z = 4. The structure determination revealed a monocationic complex of Sn(IV) in a distorted bipyramidal geometry [Me2Sn(Hdapf)]+, with Br- as counter ion and one molecule of water helping the crystal packing. Mössbauer parameters of the complex [Me2Sn(Hdapf)]2[Me2SnCl4] have evidenced two Sn(IV) sites, as observed in the crystal structure determination. Also a correlation between Mössbauer and X-ray data based on the point-charge model is discussed.

hydrazone complexes; heptacoordinated organotin(IV) complexes

As reações dos ligantes H2dapf e H2dapt, com R4-mSnXm (m = 2, 3; R = Me, Ph e X = Cl, Br) resultaram na formação de oito novos complexos organoestânicos heptacoordenados, os quais foram estudados por análise elementar, espectroscopias no IV, RMN de ¹H e Mössbauer, para investigar suas propriedades estruturais. O derivado metilado, [Me2Sn(Hdapt)]Br.H2O, foi também caracterizado por difração de raio X por monocristais. O complexo cristaliza no sistema monoclínico e grupo de espaço P2(1)/c, com a = 21.920(3), b = 7.4470(5), c = 16.805(2) Å, beta = 110.18(1)º e Z = 4. A determinação estrutural revelou um complexo monocatiônico de Sn(IV), [Me2Sn(Hdapf)]+, numa geometria bipiramidal trigonal, na qual o Br- está como contra-íon e uma molécula de água ajuda o empacotamento cristalino. Os parâmetros Mössbauer para o complexo [Me2Sn(Hdapf)]2 [Me2SnCl4] evidenciaram dois sítios de Sn(IV), como observado pela determinação da estrutura cristalina. Também uma correlação entre os dados de Mössbauer e de raio X, baseada no modelo carga-ponto, é discutida.

Article

New Heptacoordinated Organotin(IV) Complexes Derivatives of 2,6-diacetylpyridine bis (2-furanoylhydrazone), H₂dapf, and 2,6-diacetylpyridine bis (2-thenoylhydrazone), H₂dapt. Crystal and Molecular Structure of [Me₂Sn(Hdapt)]Br.H₂O

Gerimário F. de Sousa ^a, *, Maria B.P. Mangas ^a , Regina H.P. Francisco ^b , Maria T. do P. Gambardella ^b , Ana M.G.D. Rodrigues ^b , Anuar Abras ^c

^a Instituto de Química,ICC, Universidade de Brasília, 70919.900 Brasília - DF, Brazil

^b Instituto de Química de São Carlos, IQSC, Universidade de São Paulo, 13560.250 São Carlos - SP, Brazil

^c Departamento de Física, ICEx, Universidade Federal de Minas Gerais, 30123.970 Belo Horizonte - MG, Brazil

As reações dos ligantes H₂dapf e H₂dapt, com R_4-mSnX_m (m = 2, 3; R = Me, Ph e X = Cl, Br) resultaram na formação de oito novos complexos organoestânicos heptacoordenados, os quais foram estudados por análise elementar, espectroscopias no IV, RMN de ¹H e Mössbauer, para investigar suas propriedades estruturais. O derivado metilado, [Me₂Sn(Hdapt)]Br.H₂O, foi também caracterizado por difração de raio X por monocristais. O complexo cristaliza no sistema monoclínico e grupo de espaço P2₁/c, com a = 21.920(3), b = 7.4470(5), c = 16.805(2) Å, b = 110.18(1)º e Z = 4. A determinação estrutural revelou um complexo monocatiônico de Sn(IV), [Me₂Sn(Hdapf)]⁺, numa geometria bipiramidal trigonal, na qual o Br^- está como contra-íon e uma molécula de água ajuda o empacotamento cristalino. Os parâmetros Mössbauer para o complexo [Me₂Sn(Hdapf)]₂ [Me₂SnCl₄] evidenciaram dois sítios de Sn(IV), como observado pela determinação da estrutura cristalina. Também uma correlação entre os dados de Mössbauer e de raio X, baseada no modelo carga-ponto, é discutida.

The reaction of the ligands H₂dapf and H₂dapt, with R_4-mSnX_m (m = 2, 3; R = Me, Ph and X = Cl, Br) led to the formation of eight new heptacoordinated organotin(IV) complexes, which were studied by microanalysis, IR, NMR and Mössbauer spectroscopy to investigate their structural properties. The methyl derivative [Me₂Sn(Hdapt)]Br.H₂O was also studied by single crystal X-ray diffraction. It crystallizes in the monoclinic system, space group P2₁/c, with a = 21.920(3), b = 7.4470(5), c = 16.805(2) Å, b = 110.18(1)º, Z = 4. The structure determination revealed a monocationic complex of Sn(IV) in a distorted bipyramidal geometry [Me₂Sn(Hdapf)]⁺, with Br^- as counter ion and one molecule of water helping the crystal packing. Mössbauer parameters of the complex [Me₂Sn(Hdapf)]₂[Me₂SnCl₄] have evidenced two Sn(IV) sites, as observed in the crystal structure determination. Also a correlation between Mössbauer and X-ray data based on the point-charge model is discussed.

Keywords: hydrazone complexes; heptacoordinated organotin(IV) complexes

Introduction

The chelating properties of 2,6-diacetylpyridinebis(hydrazones) have been investigated towards several organotin chlorides, R_4-mSnCl_m (m = 2, 3). It has been found that these ligands act as pentadentate and coordinate to Sn (IV) through the two enolate oxygen atoms, the two azomethine nitrogens and the pyridil nitrogen^1,2,3. However, the nature of coordination depends on the metal ion, the pH of the medium, the reaction conditions, and also the nature of the hydrazone⁴. For instance, the pentadentate hydrazone can remain protonated as in the compound [MeSnCl(H₂dapsc)]²⁺, H₂dapsc = 2,6-diacetylpyridinebis(semicarbazone)², it can be deprotonated as in the complex [Et₂Sn(dapt)], H₂dapt = 2,6-diacetylpyridinebis(2-thenoylhydrazone)¹, or partially protonated as in the monocation [Me₂Sn(Hdapf)]⁺, H₂dapf = 2,6-diacetylpyridinebis(2-furanoylhydrazone)³. Single crystal X-ray diffraction studies have shown that in all three modes of complexation, the Sn(IV) atom exhibits a nearly pentagonal bipyramidal coordination geometry with equatorial plane defined by the ONNNO donor set of the hydrazone ligand. The present work deals with the preparation and characterization of eight new complexes with the ligands 2,6-diacetylpyridinebis(2-furanoylhydrazone), H₂dapf, and 2,6-diacetylpyridinebis(2-thenoylhydrazone), H₂dapt, whose structures are shown below. These two ligands were chosen since they have the potential to form pentacoordinated or higher coordinated Sn(IV) complexes. Furthermore, different possibilities of binding to the metal in the enolate or ketone forms make this study extremely interesting. The complexes formed were studied by microanalysis, IR, ¹H-NMR, Mössbauer spectroscopy and crystal X-ray diffraction.

Experimental

Synthesis

The ligands H₂dapf and H₂dapt were prepared according to the literature⁵, using EtOH as solvent. The Sn(IV) complexes were prepared by the following method. The methanol solution of the organotin(IV) derivative was added to the hot methanol solution of appropriate hydrazone in a 1/1 mol ratio. The resulting mixture was refluxed for 1 h and filtered to form a clear solution and allowed to stand at room temperature. After cooling and slow evaporation of the solvent, crystalline products were formed with yields about 60%, which did not melt below 250 °C. Crystals, which were suitable for X-ray analysis, were isolated only for the complexes 2 and 7. The structure of 2 was determined previously³. The microanalysis were performed with a Perkin Elmer 2400C analyser, giving for C, H and N the following results.

1. [MeSnCl(dapf)]. Anal. Calcd. for (C₂₀H₁₈ClN₅O₂Sn): C, 43.90; H, 3.32; N, 12.81. Found: C, 43.40; H, 2.90; N, 12.72%.

2. [Me₂Sn(Hdapf)]₂[Me₂SnCl₄]. Anal. Calcd. for (C₂₃H₂₈Cl₄N₅O₂Sn₂): C, 39.31; H, 3.67; N, 10.41. Found: C, 38.72; H, 3.39; N, 10.62%.

3. [Me₂Sn(Hdapf)]Br. Anal. Calcd. for (C₂₁H₂₂BrN₅O₂Sn): C, 41.53; H, 3.62; N, 11.54. Found: C, 40.25; H, 3.87; N, 11.40%.

4. [Ph₂Sn(dapf)]. Anal. Calcd. for (C₃₁H₂₅N₅O₂Sn): C, 57.26; H, 3.11; N, 10.77. Found: C, 58.57; H, 2.93; N, 10.50%.

5. [MeSnCl(dapt)]. Anal. Calc.d for (C₂₀H₁₈ClN₅O₂Sn): C, 41.52; H, 3.11; N, 12.10. Found: C, 40.73; H, 2.93; N,12.11%.

6. [Me₂Sn(Hdapt)]₂[Me₂SnCl₄]. Anal. Calcd. for (C₂₃H₂₈Cl₄N₅S₂Sn₂): C, 37.51; H, 3.58; N, 9.94%. Found: C, 37.07; H, 3.44; N, 9.77%.

7. [Me₂Sn(Hdapt)]Br.H₂O. Anal. Calcd. for (C₂₁H₂₂BrN₅S₂Sn): C, 38.25; H, 3.61; N, 10.62%. Found: C, 38.55; H, 3.41, N, 10.33%.

8. [Ph₂Sn(dapt)]. Anal. Calcd. for (C₃₁H₂₅N₅S₂Sn): C, 54.55; H, 3.66; N, 10.26. Found: C, 53.81; H, 3.49; N, 9.87%.

Infrared spectra were recorded on a Nicolet 5ZDX-FT spectrophotometer in the 4000-400 cm^-1 range using KBr pellets. Due to poor solubility of the complexes, it was possible to perform ¹H NMR spectra only for the complexes 2, 3, 6 and 7 in CDCl₃, using a 250 MHz Bruker spectrometer. Chemical shifts are relative to internal tetramethylsilane. ¹¹⁹Sn Mössbauer spectra were measured using a constant acceleration spectrometer moving a CaSnO₃ source at room temperature. The isomer shift values are given with respect to this source. The samples were measured at liquid nitrogen temperature and all spectra were computer fitted assuming Lorentzian line shapes. X-ray diffraction data were collected at room temperature using an Enraf-Nonius CAD-4 automatic diffractometer, with a graphite monocromated MoK_a radiation (l = 0.71073 Å), obtained in a fine focus sealed tube.

X-ray structure determination of [Me ₂ Sn(Hdapt)]Br.H ₂ O

The unit cell of the complex 7 was determined by a least-squares fit of settings for 25 strong reflections, with 10° £ q £ 18°. Intensity measurements were carried out up to 27°, using w/2q scan mode. A yellow, prismatic, single-crystal with dimensions: 0.2 x 0.15 x 0.3 mm was used. During the data collection the intensity decay was checked through the measurement of 3 standard reflections every 120 min and a correction factor was applied (average value = 0.9976). Absorption corrections were also taken into account according to an empirical method, y scan⁶. The maximum and minimum transmission factors were respectively 0.9964 and 0.7905. The crystal data and structure refinement parameters are given in Table 1.

The structure was solved by heavy-atom method. The refinement on (F(hkl))² through iterative full-matrix least-squares calculations including all data was done, and weights w = 1/[S²(F²_obs) + (0.0817P)² + 10.9505P] where P = (F²_obs + 2 F²_calc)/3 were assigned to them⁷. The observed criterion was used only for calculating R factor for observed reflections. The refinement process was applied until convergence (mean value of shift/esd = 0.000) and the maximum, minimum and average peaks of electronic density residues were 2.80, -2.34 and 0.14 e Å^-3, respectively. These peaks are high. The most positive is 0.44 Å from C132 and the negative is 0.50 Å from S135. Anisotropic displacement parameters were assigned to non-H atoms, with exception of one of the thiophene rings (C131, C132, C133, C134, S135). The rings have different behaviors during the refinement process, one of them is close to the bromide and the water molecule. The other one has a greater volume to occupy in the crystal structure. Due to this, the model was refined with isotropic temperature parameters for the atoms of this thiophene ring. Consequently, the highest peak and the deepest hole in the residual eletronic density are close to these atoms. Several attempts to refine them anisotropicaly and/or including disorder effects were done, without any success.

The H-atom positions were calculated and refined as riding atoms, except HN1, HO3A and HO3B, whose fractional atomic coordinates were determined in a difference Fourier map, calculated after convergence of the model with all other atoms and refined. An isotropic displacement parameter was applied to all H-atoms, using values 20% greater than the equivalent temperature factor of the corresponding C-atom.

Results and Discussion

Crystal structure of [Me ₂ Sn(Hdapt)]Br.H ₂ O

The structure determination revealed the presence of a complex cation of tin(IV), trans-dimethyl[2,6-diacetylpyridinebis(2-thenoylhydrazone]tin(IV), with bromide as counter ion. A water molecule helps the packing mode.

The metal is heptacoordinated, showing a distorted pentagonal bipyramidal geometry, with the pentahapto ligand, Hdapt^-, at the equatorial plane and two methyl groups at the axial positions. The major ligand is planar, except for the thiophene rings, which make dihedral angles of 27.4(1)° and 11.4(3)°, respectively, with the equatorial plane. Table 2 contains the fractional atomic coordinates and the equivalent isotropic displacement parameters. Table 3 contains selected bond distances and angles. Figure 1 shows the molecule with labeled atoms.

During the reaction the proton from one of the azomethine groups leaves the molecule. The other, HN1, remains in the structure. As a consequence, differences between bond distances and angles around the metal can be observed, O1 atom is in a keto form and O2 is an enolate, which has greater basicity (Table 3).

This fact was also observed in the structures of other complexes, in which a similar ligand loses one proton, such as in [Ph₂Sn(Hdaptsc)]Cl⁸ [H₂daptsc = 2,6-diacetylpyridinebis(thiosemicarbazone)] with distances Sn-S: 2.592(1) and 2.703(1) Å; Sn-N: 2.348(4), 2.353(4) and 2.491(4) Å; [Me₂Sn(Hdapf)]₂[Me₂SnCl₄]³ [H₂dapf = 2,6-diacetylpyridinebis(furanoylhydrazone)] with distances Sn-O: 2.227(4) and 2.474(4) Å; Sn-N: 2.246(4), 2.263(5), and 2.314(4) Å; and [MeSnCl(Hdaptsc)]Cl.MeOH² with distances Sn-S: 2.527(2) and 2.633(2) Å, Sn-N: 2.288(6), 2.328(6), and 2.430(6) Å. On the other hand, when both protons, from the two arms of the molecule remain attached or leave it, the observed values of the homologue bond distances and angles are similar, reflecting a higher symmetry for these complexes. Two examples of the first case are: [MeSnCl(H₂dapsc)]Cl₂.2H₂O², with distances Sn-O: 2.177(6) and 2.180(6) Å; Sn-N: 2.252(7), 2.262(6) and 2.284(7) Å; [ClSnCl(H₂dapsc)]Cl₂.2H₂O⁹ with distances Sn-O: 2.127(5) and 2.123(6) Å; Sn-N: 2.259(6), 2.260(7), and 2.272(7) Å. Examples of the second case are: [PhSnPh(daptsc)].2DMF¹⁰, with distances Sn-S: 2.593(1) and 2.603(1) Å, Sn-N: 2.368(3), 2.421(4) and 2.427(4) Å; [EtSnEt(dapt)]¹ with distances: Sn-O: 2.251(13) and 2.285(14) Å, Sn-N: 2.300(16), 2.306(17) and 2.356(16) Å.

In the crystal packing, pairs of [Me₂Sn(Hdapt)] Br.H₂O are observed. These pairs are built by H-interactions through the proton from the azomethine groups, the water molecules and the bromide. This can be seen in Fig. 2. The H-bond distances and angles are N1-O3: 2.889(8), HN1-O3: 2.24(7), N1-HN1-O3: 166(9)°, O3-Br: 3.294(7), O3-HO3A: 0.58(10), O3-HO3B: 0.78(9), Br-HO3A: 2.86(12) Å, HO3-O3-HO3B: 109(9)°, O3-HO3A-Br: 134(14)°.

Infrared spectroscopy

The main vibrational bands of the ligands H₂dapf and H₂dapt, and their complexes are shown in Table 4. The disappearance of the n(NH) and n(CO) bands in complexes 1, 4, 5 and 8, derived from the most acidic organotin precursors, namely MeSnCl₃ and Ph₂SnCl₂, is a consequence of the double deprotonation of the ligands, indicating that these groups are involved in the formation of deprotonated complexes via enolisation. On the other hand, the IR spectra of complexes 2, 3, 6 and 7, obtained with the same ligands and the less acidic precursors Me₂SnCl₂ and Me₂SnBr₂ in this region are different, showing that the n(CO) band shifts to lower frequencies, which is indicative of bonding of the carbonyl oxygen to the metal atom.

The position of the n(NH) absorption shifted to smaller frequencies in complexes 2 and 3, is probably due to the hydrogen bond in which the N-H group is involved being weaker than in free ligands. The N5-HN5 distance³ of 0.82(6)° found in complex 2 is longer than the N1-HN1 distance of 0.67(7)° found here in complex 7. The IR results suggest that deprotonation may not occur upon complexation with Me₂SnX₂ (X = Cl, Br). However, the structure determined by X-ray diffraction of the complexes 2 and 7, shows that partial deprotonation of the ligands indeed take place.

It is seen from Table 4 that [n(CO) + n(CN)], d(CH)_aryl and d(CH)_alkyl absorption bands have shifted to higher frequencies in all the complexes. This is due to a greater rigidity shown by these groups. Similar results can be found in the literature^1,3,11.

¹ H-NMR spectroscopy

Table 5 shows the ²J(^117,119Sn, ¹H) coupling constants only for the ionic complexes 2, 3, 6 and 7, obtained from the partial deprotonation of H₂dapf and H₂dapt. The neutral complexes 1, 4, 5 and 8, resulting from the double deprotonation showed poor solubility in CDCl₃ and in other usual solvents. The observed Sn-H coupling constants are in the range characteristic of heptacoordinated organotin(IV) complexes¹¹. ²J values are very close for the heptacoordinated complexes 2, 3, 6 and 7, suggesting similar structures for these species. The same can be concluded for the anionic hexacoordinated counter ions in 2, 6 and 9.

Mössbauer spectroscopy

¹¹⁹Sn Mössbauer spectroscopy was performed on all eight complexes, giving the results in Table 5, which includes parameters from the literature for comparison. Some of the spectra are shown in Fig. 3.

All the complexes present one heptacoordinated Sn(IV) site, except 2 and 6 which show the presence of two different Sn(IV) sites in a 2:1 ratio. The most abundant site corresponds to a monocationic complex with heptacoordinated Sn(IV), in a distorted pentagonal bipyramidal geometry, and the other site corresponds to the hexacoordinated Sn(IV) which is a dianionic complex acting as counter ion. This conclusion is in accordance with single crystal X-ray analysis³ of the complex 2.

The isomer shift (d) of the complex 1 (0.68 mm/s) and 5 (0.65 mm/s) are lower than that of the parent acid MeSnCl₃¹⁴ (1.20 mm/s). The same is true for the heptacoordinated site of 2 (1.29 mm/s) and 6 (1.25 mm/s), 3 (1.31 mm/s) and 7 (1.25 mm/s), and 4 (1.01 mm/s) and 8 (1.03 mm/s) compared to their parent acids Me₂SnCl₂¹⁴ (1.49 mm/s), Me₂SnBr₂¹⁵ (1.59 mm/s) and Ph₂SnCl₂¹⁴ (1.32 mm/s), respectively.

Isomer shifts decrease on complexation, as a result of rehybridization to higher coordination for Sn atoms in the complexes, indicating lower s-electron density at the Sn nucleus in the complexes as compared to the parents acids. This can be attributed to a greater involvement of d-orbitals, which now take part in the Sn(IV) hybridization scheme, thus reducing the weight of s-orbitals in the overall hybridization of the metal^16,17. This conclusion is consistent with that observed for the Sn-H coupling constants, i.e., an increase in the coordination number produces an increase in ²J values^1,11 (Table 5). Similar results have been reported for a great variety of other Sn(IV) compounds^1,18,19.

The complexes of the same Sn(IV) precursor with different ligands, i.e., 1 and 5, 2 and 6, 3 and 7, and 4 and 8, have very similar isomer shifts. This is in accordance to the fact that the only difference between the ligands is in the 5-member ring, which has oxygen in H₂dapf and sulfur in H₂dapt. Since this difference is outside of the coordination sphere of the Sn atom, no sensible change in the s-electron density of Sn(IV) nucleus is expected.

From Table 5 it can be seen that, except for the complex 7, the same conclusion is true for the quadrupole splittings. The difference between complex 3 (D = 4.01 mm/s) and 7 (D = 3.80 mm/s) may be related to the presence of a H₂O molecule in 7.

On the other hand, the complexes of the same ligand with different Sn(IV) precursors show that the inverse dependence of the isomer shift values with the electronegativity of the substituents is quite reasonable^18-21. This behavior can be seen either for the complexes of H₂dapf or H₂dapt. Complexes 1, 2 (monocationic), 3 and 4 have the same ligand H₂dapf in the equatorial plane and different axial groups. Going from 1 to 2, chloride was replaced by a less electronegative Me group, which accounts for higher d of 2 compared to 1. Complexes 2 and 3 have the same axial groups, therefore the same d is observed. Now going from 3 to 4, Me is replaced by a more electronegative group Ph, leading to a decrease in d.

The Mössbauer parameters d and D obtained for the dianionic complexes 2 and 6 are in agreeement with similar species, complexes 10, 11 and 12 (Table 5).

Quadrupole splitting (D) values, presented in Table 5, are not sufficient to characterize a Sn(IV) complex as either tetra-, penta-, hexa-, or heptacoordinated¹. However, a successfulr correlation between quadrupole splitting and the structure of different coordinated Sn(IV) using, either simple point-charge approach^10,22-24 or a more elaborate hybridization treatment²⁵, has been reported. According to these models, one assumes that L, a parameter [L], is assigned to each ligand, which makes a fixed and independent contribution to the quadrupole splitting.

For Sn(IV) complexes containing SnR₂ moiety, such a quadrupole splitting is dominated by highly covalent Sn-C bonds, and one can show by ignoring the contribution of the other ligands, that D is given by^22,23,

where [R] denotes the partial quadrupole splitting of the group R and q is the R-Sn-R angle. Eq. (1) has been satisfactorily applied to four-, five- and six-coordinated Sn(IV) compounds, using appropriate values of [R] for each coordination number^21,22,24. Although little Mössbauer and structural data are available in the literature for heptacoordinated Sn(IV) compounds, the existing data have shown a reasonable and consistent behavior for Eq. (1)^1,9,23.

Considering the complexes 2 and 7 whose structure were determined by single crystal X-ray diffraction, the [Me] can be estimated. Inserting the values D = 3.96 mm/s and q = 166° ³ for the heptacoordinate site of complex 2 and D = 3.80 mm/s and q = 164.9° of 7 into Eq. (1) we get [Me] = -1.01 mm/s and [Me] = -0.98 mm/s, respectively. These values agree within 4% with [alkyl] = -0.97 mm/s reported for heptacoordinate Sn(IV) complexes embodyng pentacoordinate ligands¹. Now using the value [Me] = 1.00 mm/s (average of -1.01 and -0.98 mm/s) and D = 4.01 mm/s of complex 3 and D = 3.94 mm/s for the heptacoordinate Sn(IV) of complex 6, Eq. (1) allows us to predicte for the Me-Sn-Me angle q = 180º and q = 169° for the complexes 3 and 6, respectively. The later value is in excellent agreement with q = 166° found for complex 2.

The Ph-Sn-Ph angle for the phenyl derivatives, complexes 4 and 8, can be also predicted through Eq. (1) and appropriate values of [Ph].

Combining Mössbauer and structural data for the heptacoordinate complex [Ph₂Sn(Hdaptsc)]Cl⁸ [H₂dapstc = 2,6-acetylpyridinebis(thiosemicarbazone)], i.e., D = 3.13 mm/s) and q = 167.9°, we found [Ph] = -0.80 mm/s, which agrees very well with a previous reported¹ value [Ph] = -0.78 mm/s. Inserting D = 3.22 mm/s 4 and D = 3.24 mm/s 8 and [Ph] = -0.80 mm/s into Eq. (1) we get q = 180º for both complexes.

Finally the predicted Me-Sn-Me angles for the hexacoordinate Sn(IV) sites of complexes 2 and 6, namely [Me₂SnCl₄]^2- can be estimated using [Me] = -1.03 mm/s for hexacoordinate species^21,22. Inserting D = 4.11 mm/s 2 and D = 3.99 mm/s 6 together with [Me] = -1.03 mm/s into Eq. (1) we obtained q = 175° (X-ray diffraction: 180°) and q = 163°, respectively for Me-Sn-Me angle of complexes 2 and 6.

The correlation between Mössbauer and X-ray structural data, using a simple point-charge model, gave values for [Me] and [Ph] in excellent agreement with earlier reported values. We think that this correlation is important considering the poor number of published structural data for heptacoordinate complexes as compared to penta- and hexacoordinate species.

Concluding, eight new heptacoordinated organotin(IV) complexes of the ligands H₂dapf and H₂dapt were obtained, which were investigated by means of microanalysis, IR, ¹H-NMR, Mössbauer spectroscopy and X-ray diffraction.

The crystallographic data were deposited at the Cambridge Crystallographic Data Centre under the number CCDC114597.

Acknowledgments

The authors are greateful for finantial support from CNPq, CAPES, FINEP, FAPEMIG and FAPESP in Brazil, as well as for a CNPq scholarship to M.B.P.M.

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Publication Dates

• Publication in this collection
  23 Oct 2002
• Date of issue
  1999

History

• Received
  09 Nov 1998