Assembly reaction of 1,3-diamino-2-hydroxy-propane-N,N,N′,N′-tetraacetic acid (H5hdpta), sodium acetate and Cr3+ ion at pH 6.7 in aqueous solution leads to the formation of Na[Cr2(hdpta)(Ac)2] (1). Single crystal X-ray analysis show that 1 bears a 3D (4,4)-connected lon framework based on mononuclear Na+ nodes and dinuclear [Cr2(hdpta)(Ac)2]− complex ligands in which two Cr3+ ions are chelated by one hdpta5− and also bridged by two acetate auxiliary ligands. Further assemble of 1 with Gd3+ ions give rise to [Gd(NO3)3(H2O)4][Cr4Gd(hdpta)2(OH)4(H2O)5]·(NO3)·32H2O (2). The [Cr4Gd(hdpta)2(OH)4(H2O)5]+ cation of 2 exhibit a 1D chain structure based on [Cr4(hdpta)2(OH)4]2− complex ligands and mononuclear Gd3+ nodes. [Cr4(hdpta)2(OH)4]2− has a tetranuclear {Cr4} rectangular metal skeleton. Detailed synthesis experiments indicate heating is a simple and effective way to activate the inert Cr3+ ions to prepare oxygen-bridged Cr–Ln heterometallic compounds. Magnetic studies reveal that compound 2 shows overall antiferromagnetic interaction.
Graphical Abstract
Stepwise synthesis of a Cr–Na compound based on dinuclear {Cr2} unit and a Cr–Gd compound bearing tetranuclear {Cr4} unit are presented.