Cobalt coordination polymers regulated by in situ ligand transformation

Abstract

A series of cobalt(II) coordination polymers {[Co(L₁)₂(H₂O)₂]·4H₂O·2DMF}_n (1; HL₁ = 4-(3,5-(dicyano-2,6-dipyridyl)dihydropyridyl)benzoic acid; DMF = N,N-dimethylformamide), {[Co(L_1a)₂(H₂O)₂]·2H₂O}_n (2, HL_1a = 4-(3,5-dicyano-terpyridyl)benzoic acid), and [Co₃(μ₃-OH)₂(L_1a)₂(TP)(H₂O)₂]_n (3, TPA = terephthalic acid) are reported, in which the conformation of the primary ligand L₁⁻ has been regulated by in situ oxidative dehydrogenation into L_1a⁻ in different solvent systems. Single crystal structural analyses reveal that compound 1 exhibits a 4⁴-sql coordination layer structure constructed from cobalt centres and parent L₁⁻ ligands; compound 2 is constructed from Co²⁺ cations doubly connected by L_1a⁻ anions, which are generated in situ through oxidative dehydrogenation of L₁⁻; while compound 3 features a rod-packing 3D network with a pcu-type topology, in which cobalt–oxygen chain units are interconnected by L_1a⁻ and TP²⁻ mixed ligands. The formation mechanism of L_1a⁻ ligand via an in situ oxidative dehydrogenation reaction has been briefly discussed. This current study confirms that in situ ligand transformation is viable for controlled coordination polymer assembly, and is also adaptable to a more complexed ligand system.