Dihydroxybenzoic acids as polydentate ligands in phenylantimony (V) complexes

Highlights

• Reactions of pentaphenylantimony with 2,5- and 2,6-dihydroxybenzoic acids proceeds involving the carboxyl group.

• Interaction of pentaphenylantimony with 2,3-dihydroxybenzoic acid proceeds involving hydroxyl groups.

• The crystals 1 and 2 are formed of the [Ph₄Sb]⁺ cations and carboxylate anions.

• The five-membered metallocycle is present in the complex anion in 3.

• The structure of 1 and 2 can be considered as a resonance hybrid of salt-like and covalent forms.

Abstract

The compounds Ph₄Sb[O(O)CC₆H₃(OH)₂-2,5] (1), Ph₄Sb[O(O)CC₆H₃(OH)₂-2,6] (2) and [Ph₄Sb]⁺[Ph₄Sb(O₂C₆H₃CO₂H)]⁻(3) were obtained through the interaction of pentaphenylantimony with 2,5-; 2,6- and 2,3-dihydroxybenzoic acids in toluene. The structure of synthesized compounds and the coordination type of antimony atoms in 1, 2 and 3 depend on the location of hydroxyl groups in the benzene ring. The antimony atoms in 1 and 2 have distorted trigonal-bipyramidal coordination, through to different degrees. The antimony atom in the anion of compound 3 is hexacoordinated with [C₄O₂]⁻ surroundings. The compounds 1,2 and 3 have been characterized by elemental analysis, IR- and NMR-spectroscopy, X-ray analysis.

Introduction

Organoantimony compounds are of practical relevance due to their biological and catalytic activity [1], [2], [3], [4], [5]. The specificity of the particular compound properties is conditioned by the nature of its ligands which are bonded to the central antimony atom [5], [6], [7], [8]. Synthesis of novel organoantimony derivatives with polyfunctional ligands makes in possible to expand the range of compounds with useful properties [9], [10], [11].

The reactions between pentaphenylantimony and polyfunctional organic compounds are of interest due to the formation of antimony complexes with different structural functions of the ligands [9], [12], [13]. On the other hand, any reaction with pentaphenylantimony is a distinctive indication of hydrogen atom mobility for organoantimony compounds with different functional groups [14], [15], [16]. Thus, the interaction between pentaphenylantimony and sulfosalicylic acid begins with substitution of the hydrogen atom located in the sulfo group. The carboxyl group is involved in reaction with an excess of pentaphenylantimony; the hydroxyl group does not take part in the reaction [17]. During the reaction between pentaphenylantimony and salicylaldoxime, the oximate group is reactive; the hydroxyl group does not take part in the reaction [18]. The interaction of pentaphenylantimony with salicylic and 5-bromosalicylic acids proceeds without involving the hydroxyl group, regardless of the mole ratio [19], [20]. Interaction between pentaphenylantimony and 2,4-dihydroxybenzoic acid proceeds involving the carboxyl and para-hydroxyl groups, independently of the mole ratio [21].

It should be noted that dihydroxybenzoic acids are biologically-active compounds with different properties [22], [23], [24]. For this reason studying reactions between pentaphenylantimony and other dihydroxybenzoic acids and establishing the structural features is of interest.

In continuation of the study of dihydroxybenzoic acids organoantimony derivatives, the reactions between pentaphenylantimony, and 2,3-, 2,5- and 2,6- dihydroxybenzoic acids have been carried out, the structural features of the products of reactions Ph₄Sb[O(O)CC₆H₃(OH)₂–2,5], Ph₄Sb[O(O)CC₆H₃(OH)₂–2,6] and [Ph₄Sb]⁺[Ph₄Sb(O₂C₆H₃CO₂H)]⁻ have been determined.