Reaction of antimony(III) halides with Lewis bases

Abstract

The reaction of antimony (III) halides, SbX 3, with Lewis bases has been studied calorimetrically in 1.2-dichloroethane solution. The O-donors, Ph 3PO, Me 2SO and pyridine- N-oxide, form 1:1 adducts mostly of high stability but with small enthalpies of formation. Phosphines also form 1:1 adducts, though PBu 3 gives both SbCl 3PBu 3 and SbCl 3(PBU 3) 2: diphosphines are unidentate but some of the complex diphosphine (SbCl 3) 2 is formed when SbCl 3 is in excess. Aromatic amines form 1:1 adducts of moderate stability (100 < K < 2500 1 mole −1) with rather large enthalpies of formation, mostly about 100 kJ mole −1. Heterocyclic bases form very stable 1:1 adducts ( K < 10 3 1 mole −1) with enthalpies of formation around 90 kJ mole −1; a second molecule of base can also be added with K 2 < K 1 and -Δ H 2 < - Δ H 1 - Enthalpies of formation of adducts with 2,2′-bipyridine and 1,10-phenanthroline are less than those of 1:1 adducts with pyridine. Aliphatic amines and 2,4,6-trimethylpyridine form adducts of the type SbX 3B 3 of very high stability with enthalpies of formation about 250 kJ mole −1. There is some evidence that in these adducts the base is coordinated to halogen rather than antimony.