Synthesis and characterisation of a series of tetra- and octa-copper(II) complexes with macrocyclic ligands

Abstract

A Series of seven tetracopper(II) and three octacopper(II) complexes has been synthesised using the tetranucleating macrocyclic ligands H₄L¹ and H₄L²{13,26-dimethyl- and 13,26-di-tert-butyl-3,9,17,23-tetraazatetracyclo[23.3.1.1^11,15]triaconta-1(29),2,9,11,13,15(30),16,23,25,27-decaene-6,20,29,30-tetraol}. Four representative complexes have been structurally characterised by single-crystal X-ray diffraction studies: [Cu₄(µ₄-OH)L²][NO₃]₃·2H₂O, 3·2H₂O, monoclinic, a= 10.384(2), b= 18.515(5), c= 11.264(2)Å, β= 107.48(2)°, [{Cu₄(µ₅-O)L¹(ClO₄)}₂][ClO₄]₂·2H₂O, 7·2H₂O, triclinic, a= 11.497(4), b= 12.714(3), c= 13.546(4)Å, α= 102.92(2), β= 113.15(2), γ= 100.36(3)°; [{Cu₄(µ₅-O)L²(ClO₄)}₂][ClO₄]₂·CH₃OH, 9·CH₃OH, monoclinic, a= 15.778(5), b= 17.384(8), c= 15.392(5)Å, β= 109.54(3)°; [Cu₄(µ-N₃)₂L²(N₃)₂]·2CH₃OH, 10·2CH₃OH, monoclinic, a= 8.559(3), b= 18.719(6), c= 13.485(7)Å, β= 97.29(4)°. The tetranuclear complexes contain planar Cu₄(µ₄-OH) cores but the hydroxo donor can be replaced by two azido ligands to form 10, in which the four copper(II) atoms are no longer coplanar. In non-protic solvents, or with added base, the tetracopper(II) complexes dimerise with loss of the hydroxo proton to form octacopper(II) complexes which contain two Cu₄-(µ₅-O) units.