Recognition of topological isomerism:: Synthesis, structure, and magnetic properties of two pentanuclear high-spin molecules of the type [NiII(N-N)2]3[FeIII(CN)6]2

The syntheses, structures, and magnetic properties of two pentanuclear cyanide-bridged compounds are reported. The trigonal bipyramidal molecule {[Ni(tmphen)(2)](3)[Fe(CN)(6)](2)}.14H(2)O, (1)(.)14H(2)O (tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline) crystallizes in the space group P2(1)/c (No. 14) with unit cell parameters a = 19.531(4) Angstrom, b = 24.895(5) Angstrom, c = 24.522(5) Angstrom, beta = 98.68(3)degrees, V = 11787(4) Angstrom(3), and Z = 4. The pi-pi T interactions between the tmphen ligands provide the closest intermolecular contacts of 3.37 Angstrom leading to large intermolecular (MM)-M-... distances (> 8.68 Angstrom). The dc magnetic susceptibility of 1 indicates a ferromagnetically coupled S 4 ground state best fit to the parameters g = 2.23, J = +4.3 cm(-1), and D-Ni = +8.8 cm(-1) for the Hamiltonian H = -2J [(S-Fe(1) + S-Fe(2))-(S-Ni(1) + S-Ni(2) + S-Ni(3))] + D[S-Ni(1)z(2) + S-Ni(2)z(2) + S-Ni(3)z(2)]. The extended square molecule [Ni(bpy)(2)(H2O)]{[Ni(bpy)(2)](2)[Fe(CN)(6)](2)}.12H(2)O, (2).12H(2)O (bpy = 2,2'-bipyridine) crystallizes in the space group P1 (No. 2) with unit cell parameters a = 13.264(3) Angstrom, b = 17.607(4) Angstrom, c = 18.057(4) Angstrom, alpha = 94.58(3)degrees, beta = 103.29(3)degrees, gamma = 95.18(3)degrees, V = 4065(2) Angstrom(3), and Z = 2. The pi-pi interactions of 3.29 Angstrom between the bpy ligands are the closest intermolecular contacts, and the intermolecular (MM)-M-... separations are greater than 7.76 Angstrom. The dc magnetic susceptibility data for 2 are also in accord with an S 4 ground state arising from intramolecular ferromagnetic coupling. The data were best fit to the parameters g 2.25, J = J' = +3.3 cm(-1), and D-Ni = +5.8 cm(-1) for the Hamiltonian H = -2J[(S-Fe(1) + S-Fe(2)).(S-Ni(1) + S-Ni(2))] - 2J'[((SFe(2)SNi(3))-S-.)] + D[S-Ni(1)z(2) + S-Ni(2)z(2) + S-Ni(3)z(2)]. No evidence for S long-range magnetic ordering was observed for crystalline samples of 1 or 2.