Cyanide-Bridged Fe-Fe and Fe-Co Molecular Squares: Structures and Electrochemsitry of [Fe_4~II (#mu#-CN)_4(bpy)_8] (PF_6)_4 centre doe 4H_2O, [Fe_2~IICo_2~II (#mu#-CN)_4 (bpy)_8] (PF_6)_4 centre dot 3CHCl_3 centre dot 2CH_3CN, and [Fe_2~IICo_2~III (

摘要

Cyanide-bridged iron-iron and iron-cobalt molecular squares of [Fe_4~II(#mu#-CN)_4(bpy)_8] (PF_6)_4 centre dot 4H_2O (1), [Fe_2~II Co_2~II (#mu#-CN)_4(bpy)_8] (PF_6)_4 centre dot 3CHCl_3 centre dot 2CH_3CN (2), and [Fe_2~IICo_2~III(#mu#-CN)_4(bpy)_8] (PF_6)_6 centre dot 2CHCl_3 centre dot 4CH_3NO_2 (3) (bpy = 2,2-dipyridine) were prepared. X-ray structure analyses for 1-3 were performed and their electrochemistry was studied. In 1-3, four metal ions are bridged by cyanide groups to form tetranuclear macrocycles ("molecular squares"). Each metal ion in the square is six-coordinate; four of the coordination sites are occupied by the nitrogen atoms of two of bpy ligands and the remaining cis coordination sites are occupied by cyanide-carbon or cyanidenitrogen atoms. In 1, Fe-C (cyanide) (1.899(4)-1.927(4) A) and Fe-N (cyanide) (1.929(4)-1.950(4) A) distances are typical of low-spin e~(2+) ions. In 2, Fe-C(cyanide) and Co~(2+)-N (cyanide) bond lengths are in the range 1.919(5)-1.963(5) A and 1.850(5)-2.017(50 A, respecitvley; in contrast, shorter bond lengths are observed for the metal to cyanide-carbon and cyanide-nitrogen (1.878(7)-1.893(7) A) in 3. As a result, the molecular squares in 1, 2, and 3 have sides of 4.947(1)-4.986(1) A, 5.001(1)-5.053(1) A, and 4.910(1)-4.918(1) A, respectively. Magnetic sussceptibility measurements revealed that Fe~(2+) and Co~(3+) ions in 1 and 3 are diamagnetic, while the highspin Co~(2+) ions in 2 are weakly coupled through the low-spin Fe~(2+) ions. Cyclic voltammograms of the squares are presented, and the electrochemically generated mixed-valent speices [Fe_2~IIFe_2~II(#mu#-CN)_4(bpy)_8]~(6+) was discussed in terms of the intervalence transfer band.