Azamacrocyclic stabilisation of the halogenocations MX3+ where M = Ge or Sn and X = Cl or Br. Synthesis and molecular structures of [GeCl3(L1)]+2[H3O]+Cl–3·MeCN, [SnCl3(L1)]+2[SnCl6]2–·4MeCN, [GeBr3(L2)]+2[MeNH3]+Br–3·MeCN and [SnBr3(L2)]+2[SnBr6]2– where L1 = 1,4,7-trimethyl-1,4,7-triazacyclononane and L2 = 1,3,5-trimethyl-1,3,5-triazacyclohexane

Abstract

Treatment (1∶1 in acetonitrile) of the reaction systems MCl₄–1,4,7-trimethyl-1,4,7-triazacyclononane (L¹) and MBr₄–1,3,5-trimethyl-1,3,5-triazacyclohexane (L²), where M^IV = Ge or Sn, provided ionic compounds featuring the trihalogenocationic species [MX₃(Lⁿ)]⁺ rather than direct adduct formation [MX₄(Lⁿ)]. Crystal structure determinations (X-ray diffraction) confirmed an ionic formulation for each of the four products isolated, viz. [GeCl₃(L¹)]⁺₂[H₃O]⁺Cl^–₃·MeCN 1, [SnCl₃(L¹)]⁺₂[SnCl₆]^2–·4MeCN 2, [GeBr₃(L²)]⁺₂[MeNH₃]⁺Br^–₃·MeCN 3, and [SnBr₃(L²)]⁺₂[SnBr₆]^2– 4. Ligand attachment to M^IV, both for L¹ and L², is terdentate N-donor (η³) throughout and the resulting six-co-ordinate cations [MX₃(Lⁿ)]⁺ show the anticipated fac-octahedral metal geometry. Individual M–N bond distances within each cation are the same, viz. mean values 2.113(2) 1, 2.244(8) 2, 2.142(7) 3, 2.311(6) Å 4, reflecting a uniform central location of the MX₃⁺ unit over the ring cavity. The ‘cone angle’ N_ring–M–N_ring values (mean) for compounds 3 64.3(3) and 4 59.7(2)° involving L² are conspicuously smaller, ca. 20°, than those for compounds 1 82.90(8) and 2 79.1(3)° involving L¹ as a reflection of the insistent steric demands of the more compact six-membered triazacyclohexane ligand.