Ternary copper(II) malonato complexes with alkali metals: K₂Cu(mal)₂ · 3H₂O, Rb₂Cu(mal)₂ · H₂O, Cs₂[Cu(H₂O)₂(mal)₂] 2H₂O

Abstract

Reactions of copper(II) chloride and malonic acid with the corresponding alkali metal carbonate in the presence of imidazole in aqueous methanol at pH = 4.2–6.0 yielded K2Cu(mal)2 · 3H2O (1), Rb2Cu(mal)2 · H2O (2) and Cs2[Cu(H2O)2(mal)2] · 2H2O (3) (H2mal = malonic acid). In 1, octahedrally coordinated Cu atoms are interlinked by malonate anions to generate 2D [Cu(mal)4/2]2– anionic layers, between which the K+ cations are sandwiched. The 1D anionic [Cu(mal)(mal)2/2]2– chain in 2 is generated from square pyramidally coordinated Cu atoms bridged by malonate anions and is held together by Rb+ cations. The cesium compound consists of Cs+ cations and trans-[Cu(H2O)2(mal)2]2– anions with Cu atoms octahedrally coordinated. Diminution in dimensionality from the 2D [Cu(mal)4/2]2– anionic layer in 1 through the 1D anionic [Cu(mal)(mal)2/2]2– chain in 2 to trans-[Cu(H2O)2(mal)2]2– anions in 3 could be attributed to the replacement of the smaller alkali cation by the larger one. IR spectroscopic, magnetic and thermal data are discussed.