Synthesis of Copper(II) Complexes with Maleic Acid

Abstract

Abstract Three copper(II) complexes with maleic acid, [Cu mal(H2O]) (I) (mal=C2H2(COO)2), [Cu(Hmal)2(H2O)4] (II) and [Cu2(Hmal)4]·H2mal·4EtOH (III) (EtOH=C2H5OH), were synthesized. Compound I was prepared from an aqueous solution of copper(II) sulfate pentahydrate and sodium hydrogenmaleate at room temperature as fine blue crystals. Compound II was prepared by adding little by little copper(II) hydroxide or copper(II) hydroxycarbonate to an aqueous solution of maleic acid at a temperature below 0°C in an ice-salt bath, obtaining light-blue powdered crystals. Compound III was prepared by heating a mixed alcoholic solution of maleic acid anhydride, copper(II) sulfate pentahydrate and sodium carbonate anhydride (3:1:1) in a flask with a reflux condenser for two hours. Fine bluish-green crystals were obtained. By using copper(II) hydroxide instead of copper(II) sulfate in the above preparation, a better yield can be obtained. The effective magnetic moments of I and II were 2.00 B. M. (20°C) and 1.97 B. M. (20°C), respectively, which are relatively close to the spin-only value of the divalent copper ion. On the other hand, the magnetic moment of III was subnormal, being 1.12 B. M. (18°C). The reflection spectrum of III gave a shoulder near 370 mμ, which is specific to green copper complexes. The product (IV) obtained by the thermal decomposition of I at 220°C and the product (V) obtained from II at 160°C, which are presumed to have the chemical formula [Cu-mal(H2O)0.1] and [Cu(Hmal)(mal)1⁄2], respectively, gave normal magnetic moments, 1.91 and 1.89 B. M. (20°C). However, product (VI), obtained by expelling the alcohol from III had a magnetic moment of 1.31 B. M. (17°C). Different from the corresponding copper(II) phthalate complexes, no green copper complexes having subnormal magnetic moments could be obtained through dehydration of the blue maleate complex I or the light-blue complex II having normal magnetic moments.