Syntheses and structures of copper(i) complexes based on CunXn (X = Br and I; n = 1, 2 and 4) units and bis(pyridyl) ligands with longer flexible spacer

Abstract

Self-assembly of four bis(pyridyl) ligands with longer flexible spacer: 1,4-bis(3-pyridylaminomethyl)benzene (L1), 1,4-bis(2-pyridylaminomethyl)benzene (L2), 1,3-bis(3-pyridylaminomethyl)benzene (L3) and 1,3-bis(2-pyridylaminomethyl)benzene (L4), and CuX (X = Br and I) leads to the formation of eight [Cu_nX_n]-based (X = Br and I; n = 1, 2, and 4) complexes, [Cu₂I₂L1(PPh₃)₄] (1), [Cu₄Cl₂Br₂(L4)₂(PPh₃)₆]·(CH₃CN)₂ (2), [Cu₂I₂(L3)₂] (3), {[Cu₂Br₂L2(PPh₃)₂]·(CH₂Cl₂)₂}_n (4), [CuIL1]_n·nCH₂Cl₂ (5), [CuIL1]_n (6), [CuIL4]_n (7) and [Cu₂I₂L4]_n (8), which have been synthesized and characterized by elemental analysis, IR, TG, powder and single-crystal X-ray diffraction. Structural analyses show that the eight complexes possess an increasing dimensionality from 0D (1–3) to 1D (4) to 2D (5–8), in which 1 and 2 contain a CuX unit, 2–7 contain a Cu₂X₂ unit and 8 contains a Cu₄X₄ unit. Such evolvement indicates that the conformation of flexible bis(pyridyl) ligands and the participation of triphenylphosphine (PPh₃) as a second ligand take an essential role in the framework formation of the Cu(I) complexes. Moreover, a pair of symmetry-related L3 ligands in complex 3 coordinate to the rhomboid Cu₂I₂ dimer to form “handcuff-shaped” dinuclear structures, which are further joined together through intermolecular N–H⋯I hydrogen bonds to furnish a 2D (4,4) layer. Although complexes 5 and 6 exhibit a similar 2D (4,4) layer constructed from L1 ligand bridging [Cu₂I₂]_n units, the different packing fashion of the layers leads to the formation of 3D porous frameworks of 5 and dense 3D frameworks of 6. The “twisted-boat” conformation of the Cu₄I₄ tetramer unit in complex 8 has not been reported so far.