SYNTHESIS AND STRUCTURE OF μ2-OXO-BIS [(PENTAFLUOROPROPIONATO)-TRIS(5-BROMO-2- METHOXYPHENYL)ANTIMONY]

The synthesis of μ2-oxo-bis[(pentafluoropropionato)tris(5-bromo-2-methoxyphenyl)antimony] (1) has been curried out by the oxidative addition reaction of tris(5-bromo-2methoxyphenyl)antimony with pentafluoropropionic acid in the presence of hydrogen peroxide at an equimolar ratio of reactants. The compound is characterized by IR spectroscopy and X-ray diffraction analysis. According to X-ray diffraction data, there are two types of crystallographically independent molecules with slightly different geometrical parameters in the crystal. The antimony atoms in each molecule are linked by the bridging oxygen atom (the SbOSb angle is 167.6(7)°). The trigonal bipyramidal coordination of antimony atoms is distorted; the axial OSbO angles are 175.9(4)°, 174.5(4)° for Sb(1) and Sb(2) atoms, respectively. The sums of valence CSbC angles in the equatorial planes are 359.6(6)° and 356.4(6)°. The mean values of the Sb(1)–C and Sb(2)–C bond lengths are 2.12(2) Å, the Sb–O(μ2) distances are 1.89(1), 1.98(1) Å. The carboxylate ligands in each molecule are monodentate. The distances between the antimony atoms and the corresponding terminal oxygen atoms are 2.22(1), 2.39(1) Å, the Sb···O=C distances are 3.38(2), 3.71(1) Å. The d(Sb···O=C)/d(Sb–О) ratios, which can be used to estimate the asymmetry of the ligand related to metal atom coordination, are 1.67 and 1.41. In crystal 1 there are such contacts as Sb···OMe (2.88(1)–3.16(1), 3.01(1)–3.20(1) Å), hydrogen bonds involving halogen atoms H···F (2.16, 2.50, 2.58 Å), H···Br (2.92, 2.96, 3.04 Å) and carbonyl oxygen atoms H···О (2.43, 2.59 Å), as well as halogen···halogen F···F interactions (2.70, 2.71 Å).

The present work is related to the study of the interaction of tris(5-bromo-2methoxyphenyl)antimony with pentafluoropropionic acid in the presence of hydrogen peroxide at 1:1:1 molar ratio of the reactants and the structure determination of the reaction product.
X-ray diffraction analysis of crystalline substance 1 was performed on a Bruker D8 QUEST automatic four-circle diffractometer (Mo K  -emission,  0.71073 Å, graphite monochromator).
Data collection and editing, unit-cell parameters refinement, and correction for absorption were carried out in SMART and SAINT-Plus software [18]. All calculations aimed at solving and refining the structure of compound 1 were performed in SHELXL/PC software [19]. Structure 1 was determined by direct methods and refined with the least squares method in the anisotropic approximation for nonhydrogen atoms. Selected bond lengths and bond angles of 1 are summarized in Table 1. Crystal

Results and Discussion
It has been found that the oxidative addition reaction of tris(5-bromo-2-methoxyphenyl)antimony with pentafluoropropionic acid in the presence of hydrogen peroxide at 1:1:1 molar ratio with the formation of binuclear organic antimony compound 1 with μ 2 -bridging oxygen atom: 2 (5-Br-2-MeOС 6 Н 3 ) 3  In the IR spectrum of compound 1 there are bands at 521 cm -1 , characterizing the Sb-C vibrations [20], and at 440 cm -1 due to the Sb-O vibrations [21]. The intense absorption band at 1719 cm -1 characterizes the carbonyl group C=O stretching vibrations, the band at 1375 cm -1 does it for the C-F bonds. The absorption bands at 1169 cm -1 and 1283 cm -1 correspond to vibrations of the C Ar -Br and C Ar -OMe bonds, respectively.

Conclusion
The oxidative addition reaction of tris(5-bromo-2-methoxyphenyl)antimony with pentafluoropropionic acid at 1:1 molar ratio in the presence of hydrogen peroxide leads to formation of the binuclear compound with a bridging oxygen atom, the structural organization of which is due to hydrogen bonds and contacts with halogen atoms.