Synthesis, characterization, and crystal structures of two new divalent metal complexes of N,N′-bis(phosphonomethyl)-1,10-diaza-18-crown-6:: A hydrogen-bonded 1D array and a 3D network with a large channel

Reaction of N,N'-bis(phosphonomethyl)-1,10-diaza-18-crown-6 (H4L) with copper(II) acetate in 1:1 ethanol/water mixed solvents afforded a new crystal-engineered supramolecular metal phosphonate, Cu(H2L) (complex 1). By reaction of the same ligand with cadmium(II) nitrate in a 2:1 (M/L) ratio in methanol, a cadmium(11) complex with a 3D network structure was isolated, Cd-2.75(L)(H2O).1.5NO(3).7H(2)O.MeOH (complex 2). The copper(II) complex crystallized in the monoclinic space group P2(1)/c, with a = 10.125(4), b = 14.103(6), and c = 14.537(6) Angstrom, beta = 91,049(8)degrees, V = 2075.4(16) Angstrom(3), and Z = 2. The Cu(II) ions in complex 1 are 6-coordinated by two phosphonate oxygen atoms, two nitrogen, and two oxygen atoms from the crown ether ring. Their coordination geometry can be described as Jahn-Teller-distorted octahedral, with elongated Cu-O(crown) distances (2.634(4) and 2.671(4) Angstrom for Cu(1) and Cu(2), respectively). The other two crown oxygen atoms remain uncoordinated. Neighboring two Cu(H2L) units are further interlinked via a pair of strong hydrogen bonds between uncoordinated phosphonate oxygen atoms, resulting in a one-dimensional supramolecular array along the a axis. The cadmium(11) complex is tetragonal, P4(2)/n (No. 86) with a = 20.8150(9) and c = 18.5846(12) Angstrom, V = 8052.0(7) Angstrom(3), and Z = 8. Among four cadmium(II) atoms in an asymmetric unit, one is 8-coordinated by four chelating phosphonate groups, the second one is 8-coordinated by 6 coordination atoms from a crown ring and two oxygen atoms from two phosphonate groups, the third Cd(II) atom is octahedrally coordinated by three aqua ligands and three phosphonate oxygen atoms from three phosphonate groups, and the fourth one is 6-coordinated by four aqua ligands and two oxygen atoms from two phosphonate groups in a distorted octahedral geometry. These cadmium atoms are interconnected by bridging phosphonate tetrahedra in such a way as to form large channels along the c direction, in which the lattice water molecules, methanol solvent, and nitrate anions reside. The effect of extent of deprotonation of phosphonic acids on the type of complex formed is also discussed.