The preparations, X-ray structures, and magnetic characterizations are presented for two new pentadecanuclear cluster compounds: [Ni(II)(Ni(II)(MeOH)(3))(8)(mu-CN)(30)(M(V)(CN)(3))(6)].xMeOH.yH(2)O (M(V) = Mo(V) (1) with x = 17, y = 1; M(V) = W(V) (2) with x = 15, y = 0). Both compounds crystallize in the monoclinic space group C2/c, with cell dimensions of a = 28.4957(18) A, b = 19.2583(10) A, c = 32.4279(17) A, beta = 113.155(6) degrees, and Z = 4 for 1 and a = 28.5278(16) A, b = 19.2008(18) A, c = 32.4072(17) A, beta = 113.727(6) degrees, and Z = 4 for 2. The structures of 1 and 2 consist of neutral cluster complexes comprising 15 metal ions, 9 Ni(II) and 6 M(V), all linked by mu-cyano ligands. Magnetic susceptibilities and magnetization measurements of compounds 1 and 2 in the crystalline and dissolved state indicate that these clusters have a S = 12 ground state, originating from intracluster ferromagnetic exchange interactions between the mu-cyano-bridged metal ions of the type Ni(II)-NC-M(V). Indeed, these data show clearly that the cluster molecules stay intact in solution. Ac magnetic susceptibility measurements reveal that the cluster compounds exhibit magnetic susceptibility relaxation phenomena at low temperatures since, with nonzero dc fields, chi"(M) has a nonzero value that is frequency dependent. However, there appears no out-of-phase (chi"(M)) signal in zero dc field down to 1.8 K, which excludes the expected signature for a single molecule magnet. This finding is confirmed with the small uniaxial magnetic anisotropy value for D of 0.015 cm(-1), deduced from the high-field, high-frequency EPR measurement, which distinctly reveals a positive sign in D. Obviously, the overall magnetic anisotropy of the compounds is too low, and this may be a consequence of a small single ion magnetic anisotropy combined with the highly symmetric arrangement of the metal ions in the cluster molecule.

Reaction of tris(oxalato)chromium(III) complexes, [Cr III (ox) 3 ] 3-(ox 2-) C 2 O 4 2-), with salts of the trivalent rare earth ions, Ln) La, Ce, Pr, and Nd, generates the polymeric 3d-4f coordination solids with stoichiometries [Ln III Cr III (ox) 3 (H 2 O) 4 ] 2 ‚nH 2 O, n varies from 12 to 7. Results of single-crystal structural analyses of two representative compounds within the isostructural series are discussed. Crystal data: [La III Cr III (ox) 3 (H 2 O) 4 ] 2 ‚ 12H 2 O (1), monoclinic, space group C2, a) 36.080(8) Å, b) 10.906(1) Å, c) 10.935(2) Å,) 105.55(1)°, Z) 4; [Ce III Cr III (ox) 3 (H 2 O) 4 ] 2 ‚12H 2 O (2), monoclinic, space group C2, a) 36.075(6) Å, b) 10.887(1) Å, c) 10.913(2) Å,) 105.65(1)°, Z) 4. X-ray powder diffraction established the isostructurality within the series, and from thermal gravimetry analyses, the number of water molecules of crystallization for the conditioned, polycrystalline samples was determined. The crystal structures assume extended molecular arrays based on two types of symmetrically independent molecular chains with a ladder-type motif. Therein, the metal ions are mutually bridged by three oxalate ligands; thus, the tris-chelated Cr(III) ion has a slightly distorted octahedral environment, whereas the tris-chelated Ln(III) ion is 10-coordinated with four additional water molecules in its coordination sphere. Two other compounds of the same stoichiometry, involving the Eu(III) and Tb(III) ions, are presented. A preliminary study of the magnetic properties of the structurally characterized compounds is reported.

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