Synthesis, characterization and crystal structure of the first trinuclear MFe₂(M = Cu and Ni) complexes based on nitroprusside

Three new complexes [Ni(H₂L)][Fe(CN)₅(NO)]₂ ± 6H₂O (1), [Ni(H₂L)][Fe(CN)₅(NO)]₂ ± 4H₂O (2) and [Cu(H₂L)][Fe-(CN)₅(NO)]₂ ± 4H₂O (3) (L = 3,10-bis(2-aminoethyl)-1,3,5, 8,10,12-hexaazacyclotetradecane) are prepared and characterized by IR, elemental analyses and single-crystal X-ray analyses, indicating that they are the first examples of trinuclear nitroprusside-bridged MFe₂ (M = Cu and Ni) complexes. In the three complexes, the central metal atoms (M) are all six-coordinated by the nitrogen atoms from the macrocyclic ligand and two cyano-bridges at the trans-positions to form distorted octahedral configurations. The axial N-M-N linkage is nearly vertical to the equatorial plane defined by four coordinating N atoms of macrocyclic ligand. The C ± N-Ni bond angle of 172.6° in complex 1 is apparently larger than those in complexes 2 and 3 (152.57° and 136.37°, respectively). The three complexes are all connected by hydrogen bonds into 3D networks. This study shows that the cyano-bridged trinuclear species could be generated via the control of the charge of the building blocks.