Group 15–azamacrocyclic chemistry. Reactions of 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane (L) with MCl3(M = As or Sb): crystal and molecular structures of [H2L][As4O2Cl10] and [H2L][Sb2OCl6]

Abstract

The reactions of MCl₃(M = As or Sb) and 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane (tetramethylcyclam, L) have been studied under controlled hydrolysis conditions as a route to anionic bridging chlorooxo arsenic- or antimony-(III) species. With M = As, the ionic complex [H₂L][As₄O₂Cl₁₀]1 has been isolated and characterised by an X-ray crystal-structure determination. The diprotonated tetraazamacrocyclic dications adopt an endodentate geometry with all four N–CH₃ groups positioned on the same side of the ring in an R,S,R,S[trans-(I)] configuration. The two protons are bonded to alternate nitrogen atoms and are involved in hydrogen bonding within the ring cavity. Each arsenic(III) centre of the tetranuclear µ₄-chloro-µ-oxo complex anion [As₄O₂Cl₁₀]^2– shows ψ-octahedral co-ordination geometry with an associated stereochemically active lone pair. With M = Sb, the ionic complex [H₂L][Sb₂OCl₆]2 has been isolated and its structure determined. The macrocyclic dications are again in an endodentate conformation with intramolecular hydrogen bonding across the ring cavity but in this case the N–CH₃ groups are directed in pairs to opposite sides of the ring in an R,R,S,S[trans-(III)] configuration. The antimony atoms of the binuclear µ-chloro-µ-oxo complex anion [Sb₂OCl₆]^2– have ψ-octahedral geometry with a stereochemically active lone pair. Both anions contain similar Cl₂MOMCl₂ primary units (mean As–Cl 2.21, Sb–Cl 2.43, As–O 1.77, Sb–O 1.94 Å) with Cl^– ions forming secondary M ⋯ Cl interactions (mean As ⋯ Cl 3.08, Sb ⋯ Cl 2.89 Å).