Interplay of bipyridine and 4,4′-diaminodiphenylmethane ligands in crystal design of cadmium-based coordination polymers: Structures and unusual photoluminescence quenching

Abstract

Starting from Cd(ClO4)2·2H2O, four positively charged coordination polymers were prepared and characterized by IR spectroscopic and single-crystal X-ray diffraction methods. The obtained crystalline solids included one-dimensional coordination polymers, {[Cd(dadpm)(2,2′-bpy)2](ClO4)2}n (1), and {[Cd(dadpm)(2,2′-bpy)2](ClO4)2·0.5(H2O)}n (2), and two-dimensional coordination polymers, {[Cd(4,4′-bpy)2(H2O)2](ClO4)2(dadpm)2}n (3), and {[Cd(4,4′-bpy)2(H2O)2](ClO4)2(4,4′-bpy)0.5(dadpm)·EtOH}n (4) (dadpm = 4,4′-diaminodiphenylmethane, 2,2′-bpy = 2,2′-bipyridine; 4,4′-bpy = 4,4′-bipyridine). The similar one-dimensional coordination backbones in 1 and 2 were originated from the mononuclear Cd(II) coordination cores with the N6 distorted octahedral geometries going from two terminal bidentate-chelate 2,2′-bpy and two bidentate-bridging dadpm ligands that mediated the successive metal atoms in coordination chains. The charge-balanced perchlorate anions were located in the interchain space complemented by water molecules in 2. The coordination chains were interconnected into H-bonded networks via NH(NH2)⋯O hydrogen bonds. The 2D coordination polymers 3 and 4 comprised the same positively charged square-grid infinite networks {[Cd(4,4′-bpy)2(H2O)2]2+}n with sql topology and with cadmium atom in the N4O2 tetragonally distorted octahedral coordination geometry as a single node. The charge-compensated ClO4− anions and the dadpm molecules were located in the interlayer space in 3 being complemented by the 4,4′-bpy and EtOH molecules in 4. The solid-state photoluminescence in all reported coordination polymers was significantly attenuated and redistributed along the spectrum in comparison with the pure dadpm which revealed the dual emission in the form of a strong narrow signal in the ultraviolet and a weak signal in the yellow regions of spectrum.