Controlled hydrolysis reactions of the Group 15 element–azamacrocyclic complexes MCl3L (M = As, Sb or Bi; L = 1,4,7-trimethyl-1,4,7-triazacyclononane). Formation and crystal structures of [AsCl2L][As2OCl5], [H2L]2[Sb2OCl6]Cl2, [HL]I and [H2L]2[Sb2Cl9]Cl·MeCN·H2O

Abstract

Reactions of MCl₃(M = As, Sb or Bi) and 1,4,7-trimethyl-1,4,7-triazacyclononane (Me₃[9]aneN₃= L) gave the respective 1 : 1 adducts as white-yellow microcrystalline solids which were characterised by microanalytical and spectroscopic (IR and ¹H NMR) data. Addition of water to AsCl₃L under controlled stoichiometry in acetonitrile solution led to the formation of the white crystalline salt [AsCl₂L][As₂OCl₅]1. A crystal structure determination revealed the cation as five-co-ordinate with ψ-octahedral metal geometry featuring a cis-AsCl₂⁺ unit co-ordinated to the three donor nitrogen atoms of the ligand (fac) and a stereochemically active lone pair occupying the sixth site [As–Cl 2.462(7), 2.520(7) and As–N 2.18(2), 2.12(2), 2.10(2)Å with the latter directly opposite to the lone pair]. The anion is made up of a dinuclear (µ-oxo) Cl₂As–O–AsCl₂ unit with a single Cl^– anion linked symmetrically to the two separate arsenic atoms [mean As–Cl_terminal 2.216(8), As–Cl_bridge 2.795(8)Å]. Controlled hydrolysis of SbCl₃L in acetonitrile solution provided colourless needle crystals of [H₂L]₂[Sb₂OCl₆]Cl₂2 as identified by X-ray diffraction studies. The structure of the dication shows protonation of two of the three nitrogen atoms with strong intramolecular hydrogen bonding N–H ⋯ N 2.70–2.85 Å involving the third amine centre. This is the first structural characterisation of the diprotonated form of L. The structure of the accompanying chlorooxoantimony(III) anion can be described as a single (µ-oxo) Cl₂Sb–O–SbCl₂ unit linked to two chloride ions via secondary Sb ⋯ Cl bonding involving the two metal centres [mean Sb–Cl_terminal 2.435(3), Sb–Cl_bridge 2.863(3)Å]. Each of the antimony(III) centres is further associated with a unique chloride anion, Sb ⋯ Cl^– 3.550(7)Å, which, in turn, forms close contacts with the two protonated nitrogen atoms of the triazamacrocycle Cl ⋯ H–N 3.07, 3.02 Å. Treatment of L and SiMe₃I in acetonitrile solution provided yellow needle crystals of [HL]I 3. X-Ray (diffraction) crystallographic characterisation revealed a monoprotonated ring (L) in which the single proton is bonded directly to one nitrogen atom and to the remaining two via intramolecular hydrogen N–H ⋯ N 2.71 Å. The product isolated from the reaction of L and SiCl₄ in the presence of antimony(V) chloride as halide abstractor in acetonitrile was identified by a crystal structure determination as [H₂L]₂[Sb₂Cl₉]Cl·MeCN·H₂O 4. The structure reveals two [H₂L]⋯Cl moieties which have dimensions similar to those found for 2. Conformational analyses have been carried out on free L and its mono-, di- and tri-protonated forms and the results are consistent with the experimental conformations observed in this work and elsewhere.