Synthesis and structure of bis(tetraphenylantimony) 2,6-pyridinedicarboxylate toluene solvate

At interaction of pentaphenylantimony with 2,6-pyridinedicarboxylic acid (mole ratio 1:1 or 2:1) in a toluene solution, bis (tetraphenylantimony) 2,6-pyridinedicarboxylate toluene solvate (1) has been obtained for the first time (yield 72%, colorless crystals, m.p. 170 °C). The compound 1 has been characterized by IR-spectroscopy, elemental and X-ray analysis. The absorption band of a carbonyl group with the frequency 1620 cm-1 is present in the IR-spectrum, shifting towards the area of low-frequency oscillations in comparison with the spectrum of the acid (1701 cm-1). According to the data of X-ray analysis the unit cell crystallographic parameters of compound 1: triclinic syngony, the symmetry group P; a = 12.494(5), b = 13.788(5); c = 16.684(6) Å; V = 2550.5(16) Å3; Z = 2; ρ(calc.) = 1.455 g/сm3. The Sb(1) and Sb(2) atoms in a molecule have a distorted trigonal-bipyramidal coordination in different degrees. The CSb(1)O and CSb(2)O axial angles equal 178.41(10)° and 176.75(11)°, the CSb(1)C and CSb(2)C equatorial angles vary in the ranges 111.58(14)-125.24(13)°) and 103.44(13)-146.5(11)°. The Sb(1,2)-O bond lengths equal 2.301(2), 2.310(2) Å. The Sb(1,2)-Ceqv equatorial bonds (2.105(3)-2.112(3) Å and 2.140(3)-2.162(3) Å) are shorter than the Sb(1,2)-Cax axial one (2.177(3), 2.162(3) Å). The bidentate binding of carboxylate ligands is weak (the distance Sb(1)∙∙∙O(2) equals 3,263(4) Å) it has been proved by significant difference in the lengths of single (С-О 1.288(3), 1.261(4) Å) and double bonds (С=О 1.226(3), 1.236(4) Å) in the carboxylate groups. The pypidine ring nitrogen atom coordinates to the antimony atom (the distance Sb(2)∙∙∙N equals 2.947(3) Å).