Cyano-bridged Fe(II)-Cu(II) bimetallic assemblies: honeycomb-like and pentanuclear structures

A 2D honeycomb-like compound Fe(CN)₆{Cu(apn)}₃]_n(ClO₄)_2n(H₂O)_4n (1) (apn=N-(3-aminopropyl)-1,3-propanediamine) and a pentanuclear compound Fe(CN)₆{Cu(dmen)₂}₄](ClO₄)₄ (2) (dmen=N,N-dimethylethylenediamine) have been prepared and characterized. In the synthesis, the use of ferricyanide or ferrocyanide yielded identical products due to reduction of Fe(III) ion to Fe(II) in water. For 1, all cyanide groups of ferrocyanide are bonded to six Cu(II) ions of which two symmetry-related Cu atoms are linked to nitrogen atoms of cyanide ligands bound to the neighboring Fe(II) center, resulting in the honeycomb structure. The variations of the geometries around Cu(II) centers are between ideal trigonal bipyramidal and square pyramidal structures, which may arise from the relative structural arrangements of flexible apn ligands. For 2, all the Cu(II) ions can be seen as square pyramidal geometries composed of basal least-squares planes from four dmen nitrogen atoms and apical nitrogen atoms from cyanide bridge. The Cu-NC angle around Cu centers in 2 is 127.9(7)°, much acuter than that of 1, which is presumably associated with steric interactions between the bulky methyl groups of the dmen ligands on the neighboring Cu ions. Both compounds exhibit very weak antiferromagnetic interactions in the low temperature range.