Structural diversity of Zn(ii)/Cd(ii) complexes based on bis(pyridyl) ligands with a long flexible spacer: From zero-dimensional binuclear, one-dimensional chain, two-dimensional layer, to three-dimensional frameworks

Abstract

Self-assembly of three bis(pyridyl) ligands with a long flexible spacer, 1,3-bis(2-pyridylaminomethyl)benzene (L1), 1,4-bis(2-pyridylaminomethyl)benzene (L2) and 1,4-bis(3-pyridylaminomethyl)benzene (L3), and group IIB metal salts (MX_n, M = Zn(II) and Cd(II), X = NO₃⁻, SO₄²⁻ and ClO₄⁻, n = 1 or 2) leads to the formation of seven metal–organic complexes, including zero-dimensional (0D) binuclear, one-dimensional (1D) chains , two-dimensional (2D) layer structures, and three-dimensional (3D) frameworks: [CdL1(SO₄)(H₂O)₃]₂ (1), [ZnL1(SO₄)]_n (2), [Cd(L2)_1.5(NO₃)₂]_n (3), [ZnL3(NO₃)₂]_n (4), [Cd(L3)₂(NO₃)₂]_n (5), [Zn(L3)₂]_n·2nClO₄ (6), and [Cd(L3)₃]_n·2nClO₄·2nH₂O (7), which have been characterized by elemental analysis, IR, PL, powder and single-crystal X-ray diffraction. Three flexible bis(pyridyl) ligands exhibit various trans-trans or cis-trans coordination modes, which results in diverse topological structures together with different anions and metal centers. Adjacent binuclear units in complex 1 linked by the sulfate-water tapes into a 2D supramolecular network. Complex 3 exhibits a 1D ladder chain structure, while complex 4 is a zig-zag chain structure. Complexes 2, 5 and 6 display (4,4) layer networks. Complex 7 is a 3D framework with pcu topology. The emission intensities of these complexes exhibit a regular change with different anions: SO₄²⁻ > ClO₄⁻ > NO₃⁻.