Cyano-bridged FeIII2CuII3 and FeIII4NiII4 complexes:: Syntheses, structures, and magnetic properties

Two tricyanometallate precursors, (Bu4N)[(Tp(4Bo))Fe(CN)(3)]center dot H2O center dot 2MeCN (1) and (Bu4N)[(pzTp)Fe(CN)(3)] (2) [Bu4N+ = tetrabutylammonium cation; Tp(4Bo) = tris(indazolyl)hydroborate; pzTp = tetrakis(pyrazolyl)borate], with a low-spin Fe-III center have been synthesized and characterized. The reactions of 1 or 2 with [Cu(Me(3)tacn)(H2O)(2)](ClO4)(2) (Me(3)tacn = N,N',N' '-trimethyl-1,4,7-triazacyclononane) afford two pentanuclear cyano-bridged clusters, [(Tp(4Bo))(2)(Me(3)tacn)(3)Cu3Fe2(CN)(6)](ClO4)(4)center dot 5H(2)O (3) and [(pzTp)(2)(Me(3)tacn)(3)Cu3Fe2(CN)(6)](ClO4)(4)center dot 4H(2)O (4), respectively. Assembly reactions between 2 and [Ni(phen)(CH3OH)(4)](ClO4)(2) (phen = 1,10-phenanthroline) or Zn(OAc)(2)center dot 2H(2)O afford a molecular box [(pzTp)(4)(phen)(4)Ni4Fe4(CH3OH)(4)(CN)(12)](ClO4)(4)center dot 4H(2)O (5) and a rectangular cluster [(pzTp)(2)Zn2Fe2(OAc)(2)(H2O)(2)(CN)(6)] (6). Their molecular structures were determined by single-crystal X-ray diffraction. In complexes 1 and 2, the central Fe-III ions are coordinated by three cyanide carbon atoms and three nitrogen atoms of Tp(4Bo-) or pzTp(-). Both complexes 3 and 4 show a trigonal-bipyramidal geometry, in which [(L)Fe(CN)(3)](-) units occupy the apical positions and are linked through cyanide to [Cu(Me(3)tacn)](2+) units situated in the equatorial plane. Complex 5 possesses a cubic arrangement of eight metal irons linked through edge-spanning cyanide bridges, while complex 6 shows Zn2Fe2(CN)(4) rectangular structure, in which Fe-III and Zn-II ions are alternately bridged by the cyanide groups. Intramolecular ferromagnetic couplings are observed for complexes 3-5, and they have S = (5)/(2), (5)/(2), and 6 ground states and appreciable magnetic anisotropies with negative D values equal to -0.49, -2.39, and -0.39 cm(-1), respectively.