Copper(II) environments in some macrobicycle complexes at room and low temperatures: Some novel binuclear chloro-bridged systems

Single crystal X-ray studies are recorded for five copper(II) complexes of macrobicyclic ligands. In both [Cu(sar)][ZnCl ₄] (295, 170 K) determinations ('sar' = 3,6,10,13,16,19-hexaazabicyclo[6.6.6]icosane) and [Cu(NH ₃) ₂sar]Cl ₄•6H ₂O (295 K), the ligand encapsulates the copper atom by coordinating through all six nitrogen atoms, though distortions of the primary coordination sphere from an octahedral array are both marked and quite different in the two cases. [Cu(sar)] ²⁺ undergoes a relatively facile detachment of one ligand strand in acid solution, giving a species with a different bound-N configuration to that of the reactant and which may be crystallised in various forms. In the solid of composition Cu(ClO ₄) ₂•2HClO ₄•1/ 2HCl•H ₂O•sar (295 K) the complex present is binuclear '[(sarH)CuClCu(sarH ₂)](ClO ₄) ₆•2H ₂O', with the linear CuClCu array comprising the apical bonds of a pair of square-pyramidal ClCuN ₄ components. In mononuclear [Cu(sarH ₂)(ONO ₂)](NO ₃) ₃•3H ₂O (295 K) two of the ligand strings coordinate in a quasi-square-planar array, with an approach of an anionic oxygen atom to one of the remaining opposed axial coordination sites. In the crystalline complex formed between copper(II) triflate (Cu(tfs) ₂; 'tfs' = F ₃CSO ₃ ^-) and the expanded macrobicycle Me ₅tricosaneN ₆ (Me ₅tricosaneN ₆ ≡ fac-1,5,9,13,20-pentamethyl-3,7,11,15,18,22-hexaazabicyclo[7.7.7]tricosane), the ligand, despite the lack of any protonation, is found (295, 150 K) to be bound in a quinquedentate form, with one triflate-O occupying the sixth coordination site about the metal, in the mononuclear complex [Cu(Me ₅tricosaneN ₆)(O-tfs)](tfs). This contrasts with the perchlorate counterpart wherein all nitrogen atoms are coordinated within an encapsulating cage. Graphical Abstract: Structural studies of Cu(II) complexes of macrobicyclic hexamines characterise the ready displacement of some of the N-donor atoms from the coordination sphere of the metal. [Figure not available: see fulltext.]