Stabilization of a helical water chain in a metal-organic host of a trinuclear schiff base complex

Abstract

Three heterometallic trinuclear Schiff base complexes, [{CuL¹(H₂O)}₂Ni(CN)₄]•4H₂O (1), [{CuL²(H₂O)} ₂Ni(CN)₄] (2) and [{CuL³(H₂O)} ₂Ni(CN)₄] (3) (HL¹ = 7-amino-4-methyl-5-azahept-3-en-2-one, HL² = 7-methylamino-4-methyl-5-azahept-3-en-2-one, and HL³ = 7-dimethylamino-4-methyl-5-azahept-3-en-2-one), were synthesized. All three complexes were characterized by elemental analysis, IR and UV spectroscopies and thermal analysis. Two of them (1 and 3) were also characterized by single crystal X-ray crystallography. Complex 1 forms a hydrogen-bonded one-dimensional metal-organic framework that stabilizes a helical water chain into its cavity, but when any of the amine hydrogen atoms of the Schiff base are replaced by methyl groups, as in L² and L³, the water chain vanishes, showing explicitly the importance of the host−guest H-bonding interactions for the stabilization of a water cluster.