Compounds of the 16-membered macrocyclic tetraamine (4RS,12RS)-2,2,4,10,10,12-hexamethyl-1,5,9,13-tetraazacyclohexadecane with cobalt(II), nickel(II), copper(II) and zinc(II); structural and molecular mechanics studies

The cyclic tetraamine compound (4RS,12RS)-(2,2,4,10,10,12-hexamethyl-1,5,9, 13-tetraazacyclohexadecane) nickel(II) perchlorate, [Ni(L-1)] (ClO4)(2), ha s been prepared by reduction of the imine functions of (2,4,4,10,12,12-hexa methyl-1,5,9,13-tetraazacyclohexadeca-1,9-diene) nickel(II) by catalytic hy drogenation, or by NaBH4 in acetonitrile/methanol. The ligand L-1 was isola ted, after reaction with acid, as the salt [(L-1)H-4](ClO4)Cl-3.H2O. Compou nds with cobalt(II), copper( II), and zinc(II) were prepared from this, and the structures of [M(L-1)] (ClO4)(2), M = Co, Ni and Cu, and [Cu(L-1)] [Zn Cl4], determined by X-ray diffraction: [Co(C18H40N4)] (ClO4)(2), orthorhomb ic, Pn2(1)/a, a 8.644(3), b 14.869(8), c 19.541(7), Z4, R-1 0.062 for 99 re flections with I > 2 sigma (I); [Ni(C18H40N4)] (ClO4)(2), monoclinic, C2/c, a 11.780(4), b 12.580(4), c 16.930(3), beta 90.14( 4)degrees, Z4, R-1 0.06 7 for 1644 reflections with I > 2 sigma (I); [Cu(C18H40N4)] (ClO4)(2), mono clinic, C2/c, a 11.508(7), b 13.17(2), c 16.83(1), beta 92.37(5)degrees, Z4 , R-1 0.114 for 2366 reflections with I > 2 sigma (I); [Cu(C18H40N4)] [ZnCl 4], monoclinic, P2(1)/n, a 9.392(3), b 14.915(6), c 17.591(7), beta 95.94(3 )degrees, Z4, R-1 0.041 for 2301 reflections with I >2 sigma (I). All have the C-rac, 1RS,4SR,5RS,9RS,12RS,13SR, configuration with N-H groups alterna ting on opposite sides of the molecular 'plane' around the ring. All have f lattened tetrahedral coordination geometry, with the quartet ground state c obalt(II) cation most twisted and the copper(II) tetrachlorozincate, perchl orate and singlet ground state nickel(II) complex cations progressively mor e flattened. The macrocycles have overall saddle-like conformations with ch elate rings tilted alternately to opposite sides of the molecular 'plane'. The compounds all have both trimethyl-substituted chelate rings in chair co nformations. The unsubstituted chelate rings both have chair conformations for the cobalt(II) compound, both have twist-boat conformations for the nic kel(II) and copper(II) perchlorate salts and have one chair and one twist-b oat conformation for the copper(II) tetrachlorozincate salt. Mean M-N dista nces ( ) and trans-N-M-N angles {N(1)-M-N(9), N(5)-M-N(13) (degrees)} are: Co, 1.99, 130.3(5), 115.5(5); Ni, 1.93, 163.6(4), 155.8(4); Cu (ClO4), 1.99 , 155.0(6), 143.8(7); Cu (ZnCl4) 2.00, 146.6(2), 135.0(2). The influence of axial interactions with counter ions, hydrogen bonding and other lattice i nteractions on the structures adopted are discussed. Strain energies for th e possible configurations/conformations of coordinated L-1 have been calcul ated by molecular mechanics and related to the observed structures.