Structural studies on organotin(iv) complexes formed with ligands containing {s,n,o} donor atoms

Journal of Radioanalytical and Nuclear Chemistry, Vol. 252, No. 3 (2002) 523–530 Structural studies on organotin(IV) complexes formed with ligands
containing {S,N,O} donor atoms
A. Szorcsik,1 L. Nagy,2* K. Gajda-Schrantz,1 L. Pellerito,3 E. Nagy,1 F. T. Edelmann4
1 Biocoordination Research Group of Hungarian Academy of Sciences, Department of Inorganic and Analytical Chemistry, Szeged University, H-6701 Szeged, Hungary 2Department of Inorganic and Analytical Chemistry, Szeged University, H-6701 Szeged, Hungary 3 Department of Inorganic Chemistry, University of Palero, Palermo, Italy 4 Department of Chemistry, Otto-von-Guericke University,Universitätplatz 2, Geb. M D-39106 Magdeburg, Germany A number of complexes of ligands containing {O,N,S} donor atoms (2,3,4,6-tetra-O-acetyl-β-D-thioglucopyranoside, 1-thio-β-D-glucose, 2-aminomercaptopurine, 4-amino-2-mercaptopyrimidine and 2-amino-6-mercaptopurine-9-D-riboside) with di-n-butyltin(IV) oxide, diphenyltin(IV)oxide, tribenzyltin(IV) chloride, and trimethyltin(IV) chloride were prepared in the solid state. It was found that the complexes contain theorganotin(IV) moiety and the ligand in a ratio of 1:1 or 2:1. The FTIR and Raman spectra clearly demonstrated that the organotin(IV) moietiesreact with the {S} atom of the ligands, while di-n-butyltin(IV) oxide is coordinated to the deprotonated hydroxy group. In several cases, the basicpart of the ligands also participates in complex formation. Comparison of the experimental Mössbauer ∆ values with those calculated on the basisof the pqs concept revealed that the organotin(IV) moiety has trigonal-bipyramidal geometry, and in certain cases tetrahedral geometry too. Someof the complexes contain the organotin(IV) cation in two different surroundings.
Introduction
Experimental
Organotin(IV) compounds are known to exert therapeutic effects on various tumor cells,1 but little isknown concerning their mode of action. In previous The ligands and the starting organotin(IV) papers, we have discussed the coordination chemistry of compounds Bu2SnO, Bu2SnCl2 and (CH3)3Cl were Et2Sn(IV),2 n-Bu2Sn(IV)3,4 and Bz2Sn(IV)5 with non- Sigma and Fluka products of analytical purity and were protected carbohydrates, flavonoids6 and 2-polyhydroxy- used without further purification. The schematic alkylthiazolidine-4-carboxylic acids (PHTAc).7 structures of the ligands used are shown in Fig. 1.
symmetry and local structure of the complexes have been Ph2SnO was prepared by the hydrolysis of Ph2SnCl2 in determined by Mössbauer and FTIR spectroscopy2–7 and alkaline media. Bz3SnCl was prepared as follows: a by EXAFS.8 The complex formation equilibria and mixture of 20 g (0.17 mol) fat-free Sn powder and solution structures of Et2Sn(IV)2+ complexes of 150 cm3 water was refluxed. The suspension was stirring PHTAc,7 N-D-gluconylamino acids8 and L-cysteine and intensively and 18.2 cm3 (0.16 mol) BzCl was added its derivatives,9 or of Me2Sn(IV)2+ complexes of drop wise drop. The reaction was continued for 5 hours, carbohydrates,10 DNA fragments,11 hydroxycarboxylic until most of the Sn had reacted. The product acids and their thioanalogues,12–13 have also been precipitated on cooling of the solution. The solid was filltered off, and the Bz3SnCl was extracted with In order to obtain more information on the molecular acetone, using a Soxhlet apparatus. The product thus basis of the interactions between organotin(IV) cations obtained was recrystallized from ethyl acetate.
and biologically important molecules containing {S}donor atom(s) (among them oligopeptides or Preparation of the complexes from organotin(IV) oxide glycopeptides), we have prepared several complexes ofthiol-containing carbohydrates and their adenosine Bu2SnO complexes: equimolar amounts of Bu2SnO derivatives in the solid state. The bonding sites of the and the ligand were suspended or dissolved in dry organotin(IV) species were studied by means of FTIR methanol and the mixture was refluxed for 4 hours.
and Raman spectroscopy, while the geometry of the Some complexes precipitated rapidly from the mixture, complexes formed was investigated by Mössbauer while others were obtained after removal of the solvent Comments: The complex 1a was obtained after
evaporation of the solvent. In the case of 8a, the
solubility of the ligand is low. The solution was
evaporated to half volume and the solid was crystallized.
In the case of 7a the complex precipitated.
0236–5731/2002/USD 17.00 Akadémiai Kiadó, Budapest 2002 Akadémiai Kiadó, Budapest Kluwer Academic Publishers, Dordrecht A. SZORCSIK et al.: STRUCTURAL STUDIES ON ORGANOTIN(IV) COMPLEXES precipitated and filtered off. The preparation modes andconditions, together with the physical data on thecomplexes, are shown in Table 1.
Comments: 2b was obtained by evaporation of the
solution. 8b is an oily material. Ligand 7 was not
dissolved completely either. In the case of 9b a mixture
of the ligand and NaOMe was refluxed for 30 minutes,
after which Me3SnCl was added to the solution.
Mössbauer spectroscopy: The 119Sn Mössbauer spectra were measured at liquid nitrogen temperaturewith a multichannel analyzer [TAKES Mod. 269,Ponteranica, Bergamo (Italy)] and the followingWissenschaftliche Elektronik system [MWE, München(Germany)]: an MR250 driving unit, an FG2 digitalfunction generator and an MA250 velocity transducer,moved at linear velocity, constant acceleration, in atriangular waveform.
The organotin(IV) samples were maintained at liquid nitrogen temperature in a model NDR-1258-MD Cryoliquid nitrogen cryostat (Cryo Industries of America,Inc., Atkinson, NH, USA) with a Cryo sample holder.
The temperature of 77.3±0.1 K was controlled with amodel ITC 502 temperature controller OxfordInstruments, Oxford, England. The multichannel Fig. 1. Structures of the studied complexes calibration was performed with an enriched iron foil[57Fe = 95.2%, thickness 0.06 mm, Dupont, MA USA, atroom temperature, by using a 57Co-Pd source (10 mCi, The complex 1b was prepared from Ph2SnO. The
Ritverc GmbH, St. Petersburg, Russia], while the zero starting material did not dissolve completely. After point of the Doppler velocity scale was determined at addition of the ligand, some solid precipitated, and was room temperature, through the absorption spectra of filtered off. After the reaction was completed, the natural CaSnO3 (119Sn = 0.5 mg/cm2) and a CaSnO3 compound was obtained by evaporation of the solvent.
source (10 mCi, Ritverc GmbH, St. Petersburg, Russia).
The resulting 5.105 count spectra were refined with appropriate software to obtain the isomer shift, δ, the nuclear quadrupole splitting, ∆ (mm.s–1), and the width The starting organotin(IV) compound was refluxed at half-height of the resonant peaks, Γ (mm.s–1).
for 30 minutes in methanol. The ligand was then added The FTIR spectra of the ligands and the complexes in in 1:1 ratio, and the solution was boiled for 2 hours.
KBr pellets were measured on BioRad Digilab Division FTS-40 and FTS-65A instruments in the range precipitated, the amount of precipitate increased after 4000–200 cm–1. The FT Raman spectra were recorded cooling and filtration of the solution (2a’). Evaporation
with a BioRad Digilab Division FT Raman spectrometer of all the solvent yielded the solid 2a.
from liquid and solid samples contained in glass cells.
Relevant vibration bands are reported in Table 3.
A mixture of the ligand and NaOMe in 10% excess was refluxed for 30 minutes in methanol. During this To determine the steric arrangement of the time, the acidic groups of the ligand were deprotonated coordination sphere in the organotin(IV) compounds, the and methanol was formed. The organotin(IV) compound experimental ∆ values were calculated on the basis of a was then added in 1:1 molar ratio and the reflux was simple but general molecular orbital model, according to continued for 2 hours. In methanolic solution, the pqs concept for the possible symmetries of tetra-, penta- and hexa-coordinated Sn(IV) binding involving 3Sn(IV)+ reacts with the deprotonated donor groups and the complex is formed together with NaCl, which is A. SZORCSIK et al.: STRUCTURAL STUDIES ON ORGANOTIN(IV) COMPLEXES Table 1. Numbering of the compounds prepared and the compositions of the starting solutions Composition of starting reaction solution 2,3,4,6-tetra-O-acetyl-β-D-thioglucopyranose : Bu2SnO 2:1 2,3,4,6-tetra-O-acetyl-β-D-thioglucopyranose : Ph2SnO 2:1 1-thio-β-D-glucose-Na-salt dihydrate : Bz3SnCl 1:1 1-thio-β-D-glucose-Na-salt dihydrate : Me3SnCl 1:1 4-amino-2-mercaptopyrimidine : Bu2SnO 2:1 4-amino-2-mercaptopyrimidine : Me3SnCl 1:1 2-amino-6-mercaptopurine-9-D-riboside hydrate : Me3SnCl 1:1 2-amino-6-mercaptopurine-9-D-riboside hydrate : Me3SnCl : Bu2SnO 1:1:1 Table 2. Partial quadrupole splitting (pqs) values of the functional The pqs values of the different functional groups groups used in the calculations (in mm.s–1) used in our calculations are given in Table 2.
Results and discussion
{Alk}tba = –0.94 {O–}tba = –0.21{Alk}tbe = –1.13 {O–}tbe = –0.09{Alk}oct = –1.03 {O–}oct = –0.27 {Ph}tetr = –1.26 {OH}tetr = –0.40{NH2R}tetr = –0.795 {S–Ph}tetr = –0.55 The IR and Raman data are consistent with the formation of well-defined compounds with the The characteristic vibration spectroscopic data on the ligand and complexes are collected in Table 3. Some {H2O}tba = 0.18 {S–}oct = –0.56{H2O}tbe = 0.43 {H2O}oct = 0.20 2,3,4,6-tetra-O-acetyl-β-D-thioglucopyranose *b: bidentate; m: monodentate, tetr: tetrahedral structure, tba: trigonal-bypiramidal structure in axial position, tbe: trigonal-bypiramidal In the spectrum of the ligand, the strong, well- equatorial position, oct: octahedral structure.
developed band at 2584 cm–1 is assigned to ν(SH) (Fig.
2). The –C=O band of the acetate group is found at1742 cm–1. In the spectrum of the complex formed withBu2SnO (L: metal ratio = 2:1), the strong –C=Ostretching vibration (1741.2 cm–1) and the n-Bu groupand sugar ring skeleton (3050–2800 cm–1) anddeformation (1480–400 cm–1) bands remains. However, ν(SH) disappears, and a new band is observed at359 cm–1, relating to the Sn-S bond. Similar changesoccured for the complex formed with Ph2SnO, in an L:Mratio of 2:1.
These data unambiguously support the coordination of the deprotonated –SH group, by replacement of the{O} atom from the organotin(IV) oxide.
These complexes probably have a monomeric tetrahedral structure, because two –S– groups arecoordinated to the central Sn atom together with two n-Bu groups. Oligomerization, which is characteristic forthe carbohydrate-organotin(IV) complexes can notoccur,1b because all of the alcoholic hydroxy groups areprotected by the acetate groups.
1-Thio-β-D-glucose Na-salt dihydrate In the spectrum of the ligand, the characteristic thioglucopyranose (1) and their complex (1a)
stretching vibration frequencies of alcoholic the hydroxy A. SZORCSIK et al.: STRUCTURAL STUDIES ON ORGANOTIN(IV) COMPLEXES groups are in the range 3520–3100 cm–1. These bands are imposed into a broad line. The latter reflects thehydrogen-bonding network between the hydroxy groups.
The spectrum of the ligand contains strong and sharp bands at 3335.1 and 3112.9 cm–1, indicating the 3000–2800 cm–1, while the deformation vibration of the presence of a protonated amino group, and confirming sugar ring can be found in the range 1600–500 cm–1.
the zwitterion character of the ligand. This wasconfirmed by the absence of ν(SH) in both the IR andthe Raman spectra.
1-Thio-β-D-glucose Na-salt dihydrate :Bz3SnCl 1:1 complex The deformation bands of the amino group are well developed, and the characteristic vibration of thepyrimidine ring is observed between 1650 and In a consequence of the coordination, the structure of the ligand spectrum is rearranged. Two important bands(characteristic of the alcoholic hydroxy and the Bzgroups) appear in the spectrum, together with a new 4-Amino-2-mercaptopyrimidine : Bu2SnO 2 : 1 complex band of the Sn–S bond at 332.6 cm–1, supportingcomplex formation. The deprotonation and coordination In the spectrum of this complex, the positions of of the alcoholic hydroxy groups, and consequently the ν(NH3 ), δ(NH3 ) and the ring vibration were oligomerization of the complex is ruled out, because, in unchanged as compared with those for the ligand, which the spectrum of the complex, the ν(OH) (a 3400 cm–1) rules out the coordination of the amino group and the bands remain almost unchanged and a new ν(Sn–O) band ia not observed in the range of 460–495 cm–1.
The ν(Sn–S) band at 348.5 cm–1 in the Raman spectrum of the complex clearly shows the coordination Accordingly, it seems that in the in 1:1 complex the central Sn atom is tetra-coordinated by three Bz groupsand one {S} atom, and probably has a tetrahedralstructure. In the 1:1 complex of 1-thio-β-D-glucose Na- 2-Amino-6-mercaptopurin-9-D-riboside hydrate salt dihydrate and Me3SnCl, the observed phenomena were almost the same as discussed above; the ν(Sn–S) In the spectrum of the ligand, the ν(OH), ν(NH3 ), band appears at 340–370 cm–1, indicating the formation ν(CH2) and ν(CH) bands appeared in the interval 3500–2780 cm–1, while the range 1640–1500 cm–1contains the δ(NH + band of the –SH group is not observed in the IR and Raman spectra, indicating the zwitterion form of thecompound.
The spectrum of the ligand contains bands in the range 3287–3130 cm–1 characteristic for the protonatedamino group. ν(SH) does not appear, and consequently 2-Amino-6-mercaptopurine-9-D-riboside hydrate : this group is deprotonated and is in zwitterion form. In the range of 1665–1480 cm–1, the deformation bands ofthe amino group appear, and the skeleton bands of the In the mixed metal complex, the presence of the alcoholic hydroxy groups is confirmed by the broad andintensive bands in the higher wavenumber range, due tothe hydrogen-bonds. These bands overlap intensively the 2-Aminomercaptopurine: Bu2SnO 2 : 1 complex The coordination of the {N} atom is shown by the large shift (20–30 cm–1) in the deformation band of the characteristic bands for Bu2Sn(IV) moieties [ν(CH3) and group, together with shifts in the skeleton 2)] in the range 2960–2800 cm–1. The bands of the amino group are shifted by 3–6 cm–1, towards the lowerwavenumber, which clearly shows the coordination ofthe {N} atom. The coordination of the {S} atom is ruled out, because of the absence of the Sn–S band in theRaman spectrum.
The experimental Mössbauer parameters determined by computer evaluation of the spectra measured at liquidnitrogen temperature are presented in Table 4.
2-Aminomercaptopurine: Me3SnCl 1 : 1 complex The same can be said as in the case of the A. SZORCSIK et al.: STRUCTURAL STUDIES ON ORGANOTIN(IV) COMPLEXES Table 3. Assignements of characteristic IR and Raman vibrations for ligands and complexes studied Table 4. Experimental and calculated Mössbauer parameters of the complexes studied 1a. 2,3,4,6-Tetra-O-acetyl-β-D-tio-glucopyranose:Bu2SnO = 2:1
1b. 2,3,4,6-Tetra-O-acetil-β-D-thio-glucopyranose:Ph2SnO = 2:1
2a. 1-Thio-β-D-glucose Na-salt dihydrate: Bz3SnCl = 1:1
2b. 1-Thio-β-D-glucose Na-salt dihydrate: Me3SnCl =1:1
7a. 2-Aminomercaptopurine: Bu2SnO = 2:1
8a. 4-Amino-2-mercaptopyrimidine: Bu2SnO = 2:1
9b. 2-Amino-6-mercaptopurine-9-D-riboside hydrate:
tetr: tetrahedral, tbp: trigonal-bypiramidal, oct: octahedral.
A. SZORCSIK et al.: STRUCTURAL STUDIES ON ORGANOTIN(IV) COMPLEXES –S- and protonated alcoholic hydroxy groups are
coordinated. However, the positions of the three Bz
groups are different: in 2a(1) all three are equatorial,
while in 2a(2) two of the three are axial and one is
equatorial. The proposed structures are depicted in
Fig. 4.
The complex 2b. was prepared with the same ligand
by using Me3SnCl. Two species was again detected.
2b(2) has a simple regular tetrahedral structure,
involving coordination by three Me and one –S- groups.
In the second complex the donor atoms are in a trigonal-
bipyramidal arrangement: besides three Me groups, one
deprotonated and one protonated OH groups are also
coordinated. The deprotonation of the –OH group is
probably due to the crystal water content of the starting
ligand, which causes partial hydrolysis of the
organotin(IV) cation. In this reaction Me3SnOH is
formed, which is reacts with the ligand –OH to
replacement one water molecule.
The existence of the two species with different structures is confirmed by the Raman measurements. TheSn–S vibration appears at a 350 cm–1, splitted into two,indicating the different bonding modes.
Fig. 3. Experimental Mössbauer spectra mesured at liquid nitrogen temperature of 2a. (a) and 9b. (b) complexes All these spectra exhibit IS and ∆ which clearly indicate
the presence of Sn(IV) species. Most of the spectra
exhibit a superposition of two doublets (Fig. 3).
Exceptions are the samples 1a and 1b. This suggests the
presence of nonequivalent Sn environments within the
compounds. Consequently, the spectra were decomposed
into two doublets, the inner and the outer two lines being
taken together.
For structural elucidation based on the Mössbauer parameters, the pqs concept was used. All possiblearrangements of tetra- penta- and hexacoordinated Snwere taken into account. The chemical natures of theligands (the possible donor atoms determined by FTIRand Raman spectroscopic methods) were alsoconsidered.
The measured and calculated Mössbauer ∆ values agree relativelly well. Accordingly, the complexes 1a
and 1b have tetrahedral structures: besides the two n-Bu
groups, two –S– groups are coordinated to the central Sn
atom.
The complex 2a has two trigonal-bipyramidal
Fig. 4. The proposed structure of complexes studied structural isomers [2a(1) and (2)]. In both species the
A. SZORCSIK et al.: STRUCTURAL STUDIES ON ORGANOTIN(IV) COMPLEXES In the cases of purine, pyrimidine-containing ligands, and consequently they are situated regularly around the the Mössbauer measurements indicated the formation of central Sn atoms. At the same time, the larger Bz groups two structural isomers. The complexes 7a. has a trigonal-
make a larger distortion within the tetrahedron, where bipyramidal structure, and 8a. an octahedral structure,
the bond angle is ca. 104° (complex 2a.). A similar
with the possible donor atom arrangements shown in Fig.
observation was reported in ref. 20 for the organotin(IV) 4. These observations are in line with the literature data: compounds formed with silasesquioxanes.
in studies on the coordination of organotin(IV) moietiesby thiol S and heterocyclic N, diorganotin(IV)complexes of 2-mercaptopyridine (HSPy), R2Sn(SPy)2 Conclusions
and R2SnCl(SPy), were characterized in the solid stateand in solution15. The structure of the latter complex Bu2Sn(IV), Ph2(IV)2+, Benz3(IV)+ and Me3Sn(IV)+ (R = Ph) was determined by X-ray diffraction. With the complexes were prepared in the solid state with ligands bidentate ligand SPy, Sn forms a four-membered chelate containing –SH and/or –OH, –NH2 donor groups.
ring with a short N-Sn-N bite angle of 64.8(1)°, leading The coordination sites on the ligands were measured to a heavily distorted trigonal-bipyramidal environment by means of FTIR and Raman spectroscopy. It was around the Sn. The related complexes have analogous found that in every case (when available) the –S– groups structures. The compounds R2Sn(SPy)2 involve distorted of the ligands (beside the other groups) were coordinated octahedra with R in trans positions, and the S- and N- to the organotin(IV) moieties, being the most acidic.
donor atoms in cis positions. The solid-state molecular The Raman spectra of the thiol-containing ligands structures are retained in chloroform solution.
revealed the ν(S–H) band, which disappeared on The solid-state structures of the complexes complex formation, indicating formation of the Sn–S bond. This was confirmed by the appearance of ν(Sn–S) 2SnHal(SPym) (R = i-Pr, n-Bu, i-Bu, t-Bu, Cy, Ph, SPym = 2-mercaptopyrimidine) are of trigonal- bipyramidal type, but distorted, with the angles C-Sn-C In the cases of purine, pyrimidine and ligands larger than 120° for the R2Sn(IV)2+ and Cy2Sn(IV)2+ containing a nucleoside skeleton, the Raman spectra do derivatives. The complexes R2Sn(Spyr)2 have trans-R2 not exhibit the ν(S–H) vibration. The ligand is in the octahedral, or possibly skew-trapezoidal structures, with cis-S,S and cis-N,N atoms in the equatorial plane. The complex Me2SnCl(SPym) could be assumed to be a frequencies, indicating some kind of interaction between monomeric, trigonal-bipyramidal species with the angle the donor group and the organotin(IV) moieties. This C-Sn-C around 134–145°, or a monodimensional was confirmed by Mössbauer spectroscopic The local environments of the central Sn(IV) atoms Finally, ligand 9 was reacted with two types of
were determined by Mössbauer spectroscopic measure- ments. On the basis of the pqs calculation, the local ribose part of the molecule, leading to the formation of structrures were proposed for the complexes.
the tetrahedrally coordinated species 9b(2).
Our results demonstrate that, in the mixed 2-amino-6- In some cases, the differences between the calculated mercaptopurine-9-D-riboside hydrate: Me3SnCl: and measured ∆ values are larger than the experimental Bu2SnO = 1:1:1 system, the Bu2SnO reacts with the D- error. This can be explained by the knowledge that the ribose moiety of the ligand. Although we did not find calculated value is given for the ideal structure with a any FTIR or Raman spectroscopic evidence for the 120° C-Sn-C bond angle for examples of the trigonal- coordination of Me3Sn(IV)+ to the –SH group of the bypiramidal arrangements, or 109° for the tetrahedral ligand, the Mössbauer measurements showed the structure. A distortion of 5–10° results in a formation of a complex coordinated by three Me, one 0.2–0.41 mm–1 larger measured ∆ value than that RNH2 and –S– groups [9b.(1)].
calculated for the ideal structure18,19 for di- andtriorganotin(IV) complexes formed with antibiotics reported by Pellerito. For the present complexes, thisconsideration means that the angles C-Sn-C are between One of us (L.N.) would like to thank the DAAD for providing a 125 and 130°. This is in agreement with the results of the fellowship to Germany. This work was supported financially by theHungarian Research Foundation (OTKA T032067 and T029554), by the Foundation for Development of Research and Education at The 2b. complex was prepared from Me3SnCl. The
Universities, FKFP 0015/1999, Hungary), by the Ministero della pqs calculation indicated that the complex has a Ricerca Scientifica e Tecnologica (M.U.R.S.T., Rome) and by theUniversitá di Palermo, Palermo, Italy.
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