The stepwise formation of mixed-metal coordination networks using complexes of 3-cyanoacetylacetonate

Abstract

The complexes [Cu(L¹)₂] 1, [Fe(L¹)₃] 3 and [Al(L¹)₃] 4 [L¹ = CH₃C(O)C(CN)C(O)CH₃] have been prepared for use as metallo-ligands in mixed-metal coordination networks. Surprisingly, the nature of the copper precursor is important in the synthesis of 1, with the reaction between Cu(NO₃)₂·3H₂O, HL¹ and NEt₃ giving [Cu₆(µ₃-OMe)₄(µ-OMe)₂(L¹)₆] 2 instead of the anticipated 1, which was obtained with CuCl₂·2H₂O under the same conditions. Compound 1 reacts with AgNO₃ to form [Cu(L¹)₂·AgNO₃]_∞5, the structure of which contains one-dimensional chains in which Ag⁺ ions bridge between molecules of 1. These chains are cross-linked into ladders by bridging nitrates. The product obtained from the reaction of 3 and AgNO₃ is crucially dependent on the solvent used. The reaction in methanol–acetone gives [Fe(L¹)₃·AgNO₃]_∞6, {[Fe₂(µ-OMe)₂(L¹)₄·2AgNO₃]·CH₃C(O)CH₃}_∞7 and [Fe₂(µ-OMe)₂(L¹)₄·AgNO₃]_∞8. Compounds 6 and 8 both have one-dimensional chain structures, whereas 7 has a two-dimensional layer structure. The reaction in methanol gives 6 and 8 as the major products and, in addition, small quantities of {[AgFe₂(µ-OMe)₂(L¹)₄]OH·0.4H₂O]_∞9. Compound 9 has a three-dimensional structure based on doubly interpenetrated PtS nets. Compounds 7–9 contain Fe₂(µ-OMe)₂(L¹)₄ dimers, but the coordination properties of the dimers differ, with all the cyanides coordinated in 7 and 9 but one uncoordinated in 8. The orientation of the cyanide groups depends on the relative chirality of the iron centres. A transmetallation reaction occurs between 4 and AgNO₃ to give [Ag(L¹)]_∞10, which has a two-dimensional layer structure. Compounds 2, 3 and 5–10 have been characterised by X-ray crystallography.