INTERACTION OF PENTAPHENYLANTIMONY WITH ACETYLENEDICARBOXYLIC ACID. MOLECULAR STRUCTURE OF BIS(TETRAPHENYLANTIMONY) ACETYLENEDICARBOXILATE

Bis(tetraphenylantimony) acetylenedicarboxilate (1) has been synthesized by the interaction of pentaphenylantimony with acetylenedicarboxylic acid (mole ratio 2:1 or 1:1) in toluene. In molecule 1 the acid anion has the bridging role and bonds Ph4Sb fragments. The antimony atoms have distorted trigonal bipyramidal coordination with the oxygen atom in the axial position. The Sb–O bond lengths are 2.287(4) and 2.389(4) Å, the Sb–C bond lengths are 2.110(7)2.179(6) Å and 2.108(6)2.165(6) Å.


Introduction
It is known that the interaction of pentaarylantimony with dicarboxylic acid can give two types of compounds: acidic tetraarylantimony carboxilates and bis(tetraarylantimony) carboxilates [14]. According to the X-ray diffraction data, the coordination of antimony atoms in these types of molecules is significantly different. In the first case there is a tendency of the Ar 4 Sb fragment to the transformation into the tetrahedric configuration, which is accompanied by increase of the distance between the antimony atom and the oxygen atom of the monodentate carboxylic ligand, which has the bond of coordinating character [13].
In binuclear bis(tetraarylantimony) carboxilates the antimony atom has a slightly distorted trigonal bipyramidal coordination [SbC 4 O]. As a rule, the bridging carboxilyc ligand has anisobidental type of coordination caused by intramolecular interactions Sb···O=С between the antimony atoms and carbonyl oxygen atoms [2, 46]. Only oxalate ligand is coordinated to the antimony atom almost symmetrically, thus the antimony atom coordination transforms into the octahedral one [7].
In the continuation of our research of organoantimony dicarboxylic acid derivatives the reactions of pentaphenylantimony with acetylenedicarboxylic acid have been studied. The product structure has been determined by the X-ray diffraction analysis.

Experimental
Interaction of pentaphenylantimony with acetylenedicarboxylic acid. А) A mixture of 0.200 g (0.394 mmol) of pentaphenylantimony and 0.022 g (0.197 mmol) of acetylenedicarboxylic acid in 5 mL of toluene was kept in a sealed glass ampoule at room temperature for 24 h. The solution was concentrated, the crystals were filtered off and dried. The substance was isolated as 0.173 g (90 %) of colorless crystals 1 with T dec = 178 С. IR spectra were recorded in KBr pellets on the IR Fourier-transform spectrometer Bruker Tensor 27.
The X-ray diffraction analyses of crystal 1 was performed on the Bruker D8 Quest diffractometer (Mo K  -radiation,  = 0.71073 Å, graphite monochromator). The data collection and editing as well as the refinement of unit cell parameters and the absorption accounting were carried out using SMART and SAINT Plus program packages [8]. All calculations for the structure determination and refinement were carried out using the SHELXTL/PC [9] and OLEX2 [10] programs packages. The structures were determined by the direct method and refined by least-squares method calculations in anisotropic approximation for non-hydrogen atoms. Selected crystallographic data and structure refinement results for compounds I and II are given in Table 1, and selected bond lengths and bond angles are listed in Table 2.

Results and Discussion
We have found that the reaction of pentaphenylantimony with dicarboxylic acid (mole ratio 2:1 or 1:1) proceeds in toluene solution at room temperature with the substitution of hydrogen atoms in two carboxyl groups and the formation of bis(tetraphenylantimony) acetylenedicarboxilate (1). The yield of compound 1 is up to 90%:

Ph 5 Sb + HOC(O)СС(O)COH  Ph 4 SbOС(О)ССH + PhH + CO 2
The yield of tetraphenylantimony propiolate isolated from the reaction mixture is 76%. Its IR spectrum, melting point and parameters of crystal cell correspond to the similar characteristics of the compound synthesized from pentaphenylantimony and propiolic acid [11]. Bis(tetraphenylantimony) carbonate (Ph 4 Sb) 2 СО 3 is the second product of this reaction with the yield about 10%. This product has been identified by its melting point and IR spectrum. As shown by X-ray diffraction, the obtained bis(tetraphenylantimony) carbonate has triclinic modification described in the paper [12].
The structural organization of the crystal is formed with the participation of weak hydrogen bonds of (Ph)CHO(=C) type.

Conclusions
Thus, the interaction between pentaphenylantimony with acetylenedicarboxylic acid has the specific feature: under mild conditions both carboxylic groups react. We did not succeed in isolation of acidic tetraphenylantimony carboxilate. Even short-duration heating of reaction mixture is accompanied by the decarboxylation of a carboxyl group in the acid and the formation of tetraphenylantimony propiolate.
In the bis(tetraphenylantimony) acetylenedicarboxilate molecule the carboxylate groups are characterized by the monodental type of the bond.