Recognition of topological isomerism: synthesis, structure, and magnetic properties of two pentanuclear high-spin molecules of the type [NiI(N-N)2]3[FeIII(CN)6]2.
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abstract
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) A, b = 24.895(5) A, c = 24.522(5) A, beta = 98.68(3) degrees, V = 11787(4) A(3), and Z = 4. The pi-pi interactions between the tmphen ligands provide the closest intermolecular contacts of 3.37 A leading to large intermolecular M...M distances (> 8.68 A). 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)(H(2)O)][[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) A, b = 17.607(4) A, c = 18.057(4) A, alpha = 94.58(3) degrees, beta = 103.29(3) degrees, gamma = 95.18(3) degrees, V = 4065(2) A(3), and Z = 2. The pi-pi interactions of 3.29 A between the bpy ligands are the closest intermolecular contacts, and the intermolecular M...M separations are greater than 7.76 A. 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'[(S(Fe(2)).S(Ni(3)))] + D[S(Ni(1))(z)(2) + S(Ni(2))(z)(2) + S(Ni(3))(z)(2)]. No evidence for long-range magnetic ordering was observed for crystalline samples of 1 or 2.
