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)A 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–Clterminal 2.216(8), As–Clbridge 2.795(8)A]. 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 A 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–Clterminal 2.435(3), Sb–Clbridge 2.863(3)A]. Each of the antimony(III) centres is further associated with a unique chloride anion, Sb ⋯ Cl– 3.550(7)A, which, in turn, forms close contacts with the two protonated nitrogen atoms of the triazamacrocycle Cl ⋯ H–N 3.07, 3.02 A. 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 A. 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.