STRUCTURE-FUNCTION-RELATIONSHIPS IN THE INTERACTION OF ZINC(II) AND CADMIUM(II) WITH AN EXTENDED RANGE OF 16-MEMBERED TO 19-MEMBERED MACROCYCLES INCORPORATING OXYGEN, NITROGEN, AND SULFUR DONOR ATOMS

The interaction of zinc(II) and cadmium(II) with a series of potentially quinquedentate macrocycles incorporating nitrogen, oxygen, and/or sulfur donor atoms is reported. These ligands form part of an extended array in which a systematic variation in donor atom pattern and ring size is present (and against which structure-function relationships arc more clearly seen). Stability constants for the 1:1 (metal:ligand) complexes have been determined in 95% methanol (l = 0.1 M, NEt4ClO4) at 25-degrees-C. The factors influencing the stabilities of individual zinc(II) and cadmium(II) complexes are discussed in the light of a range of crystallographic and other data. The X-ray structures of five complexes, isolated during the study, are reported. [Zn(L1)](ClO4)2 crystallized in the monoclinic space group P2(1)/c, with a = 12.766(2) angstrom, b = 9.127(2) angstrom, c = 20.975(4) angstrom, beta = 97.90(2)-degrees, and Z = 4. All five donor atoms of the macrocycle are coordinated to the zinc cation, which exhibits a distorted trigonal bipyramidal geometry. [Zn(CH3C6H4SO3)(L1)]CH3C6H4SO3 crystallized in the monoclinic space group P2(1)/c with a = 9.655(2) angstrom, b = 13.605(3) angstrom, c = 26.721(5) angstrom, beta = 97.94(2)-degrees, and Z = 4. The zinc atom is six coordinate with a distorted octahedral geometry made up of all five donor atoms of the N4O macrocyclic ligand and an oxygen atom, O(11), of a coordinated 4-toluene sulfonate anion, trans to N(2b). [Cd(ClO4)(L3)(CH3OH)]ClO4 crystallized in the triclinic space group P1BAR, a = 14.204(2) angstrom, b = 10.892(2) angstrom, c = 9.268(2) angstrom, a = 109.85(2)-degrees, beta = 108.19(2)-degrees, gamma = 97.12(2)-degrees, and Z = 2. The coordination sphere approximates a pentagonal bipyramid with the donor atoms of the macrocycle in the equatorial positions while the axial sites are occupied by O(1) of a perchlorate anion and O(11) of a coordinated methanol molecule. [Zn(NO3)(L15)(H2O)]ClO4.C2H5OH crystallized in the monoclinic space group P2(1)/c (nonstandard setting P2(1)/n) with a = 26.654(5) angstrom, b = 10.819(2) angstrom, c = 10.691(2) angstrom, beta = 95.12(2)-degrees, and Z = 4. The zinc atom is six coordinate with the complex cation exhibiting a distorted-octahedral geometry comprising the three nitrogen donor atoms of the O2N3 macrocyclic ligand [namely, N(la), N(1b) and N(1c)] in a facial arrangement, a water molecule trans to N(1c), and O(1) and O(2) of a chelating bidentate nitrate anion. [Cd-(NO3)2(L15)]2.2C2H5OH, crystallized in the monoclinic space group P2(1)/c with a = 9.228(4) angstrom, b = 14.008(3) angstrom, c = 22.235(3) angstrom, beta = 97.21(2)-degrees, and Z = 2. In contrast to the above zinc complex, this species is binuclear with the two cadmium ions separated by 4.17 A and linked by two single oxygen (from nitrate) bridges across a centre of inversion; each Cd-O(bridging) distance is 2.474(5) angstrom. The cadmium atoms are seven coordinate with coordination of each being completed by the three nitrogens of the macrocyclic ligand and a bidentate nitrate ion.