SYNTHESIS AND SPECTROSCOPIC CHARACTERIZATION OF SOME NEW HYDROGENOXALATO ORGANOTIN (IV) COMPLEXES

The synthesis and spectroscopic studies (infrared and Mössbauer) of new hydrogenoxalato derivatives and adducts containing SnRn (R=Me, Ph; n=2, 3) residues are reported. Based on their spectroscopic data dimeric and polymeric structures containing hexacoordinated or pentacoordinated Sn are suggested, the hydrogenoxolate anion behaving as a monocoordinating or a monochelating ligand. In two studied adducts, supramolecular architectures may be obtained when extra hydrogen bonds involving the free NH groups are considered.


Compounds synthesis
The studied compounds (A, B, C, D) were obtained as white precipitates. All the precipitates were stirred around two hours before being filtered.
The analytical data reported in Table 1, have allowed to suggest the following formulae:  Elemental analyses have been obtained at the ICMCB-Bordeaux University (France) with a CHNS: Flash EA 1112 Thermofisher. Infrared spectra have been recorded at the CRPP-Bordeaux University (France) using a Nicolet 6700 FT-IR spectrophotometer on diamond. Mössbauer spectra were recorded at the ICMCB-Bordeaux (France) on a liquid helium cryostat with a HALDER spectrometer.
Infrared abbreviations: br (broad); sh (shoulder) vs (very strong); s (strong); m (medium); w (weak). Mössbauer abbreviations: Δ (quadrupole splitting); (isomer shift); (full width at half-height). The chemicals were purchased from Aldrich Company-Germany without any further purification. For A and B, the absence of a band assigned to sSnC2 on the infrared spectra of these two derivatives allows to conclude to linear SnMe2 and SnPh2 groups. The asSnC2 vibration is located respectively at 585 cm -1 and at 284 cm -1 on the infrared spectra. The broad absorptions around 3300 cm -1 on the infrared spectra of these two compounds attributed to H indicate the existence of hydrogen bonds.
The value of the quadrupole splitting of (B) (=4.45 mm . s -1 ) greater than the one of SnPh2Cl2 (=2.89mm . s -1 ) [12] is in agreement with a transcoordinated SnPh2 group and a trans octahedral environment around tin atom [13]. The structure resulting from these spectroscopic data is an infinite chain structure with a transcoordination of the SnR2 group, an octahedral environment around tin center and a chelating hydrogenoxalate anion ( Figure  1).   For D, the broad absorption at 3277 cm -1 on the infrared spectrum attributed to νOH of the hydroxyl group of the oxyanion indicates the existence of hydrogen bonds.
Based on the spectroscopic data we propose for this compound a dimeric structure containing octahedral tin centres with a monochelating anion and transcoordinated SnPh2 residues. By analogy with the complex (C), this complex can be considered as two anions [HC2O4SnPh2Cl2]connected by NH...O hydrogen bonds via [ + H2N(C4H8)NH2 + ] and a dimerization through acetic acid hydrogen bonds types (Figure 3). In (C) and (D) the free NH groups may be considered involved in extra hydrogen bonds leading to supramolecular architectures.

CONCLUSIONS
The studied compounds have dimeric and infinite chain structures, the environment around the tin atoms being octahedral or trigonal bipyramidal, the hydrogenoxalate anion behaving as a monocoordinating or monochelating ligand. The use of diamines has allowed us to isolate two adducts containing dications H3N(CH2)2NH3(HC2O4)2 . 2SnMe3Cl and C4N2H12(HC2O4)2 . 2SnPh2Cl2 whose proposed structures contain hydrogen bonds between the cations and the oxyanions (in these two last adducts, considering extra hydrogen bonds involving the free NH groups may lead to supramolecular architectures).