Syntheses, crystal structures, and properties of two Cd–Fe heterobimetallic compounds with bridging en and dien ligands

Abstract

From the system Cd(II)–L–[Fe(CN)6]4−, complexes [{Cd(en)}2{Fe(CN)6}] (1) and [{Cd(H2O)(dien)}2{Fe(CN)6}] ⋅ 4H2O (2) were prepared and characterized. The same products were also isolated from mother liquors containing [Fe(CN)6]3− in which Fe(III) was reduced to Fe(II) upon irradiation. By the combination of IR and Mössbauer spectroscopy, the presence of the low-spin state (S = 0) for Fe(II) was corroborated in both 1 and 2. The Cd(II) and Fe(II) in both complexes are linked by bridging cyano ligands forming a 3-D crystal structure of 1 and a 1-D ribbon-like structural motif in 2. The bidentate en in 1 links two pentacoordinated Cd(II), while in 2 the dien ligand exhibits a rare chelating-bridging bonding mode completing the hexacoordination of Cd(II) and enhancing the dimensionality of the formed structure to 2-D. Fe(II) in both structures exhibits octahedral coordination by cyano bridging in 1 whereas in 2 two cyano ligands are terminal. Water of crystallization and the coordinated water in 2 are involved in hydrogen bonds. Dehydration in 2 is a one-step process with a minimum on the DTA curve at 92°C.