High-Spin Molecules:  Synthesis, X-ray Characterization, and Magnetic Behavior of Two New Cyano-Bridged Ni^II₉Mo^V₆and Ni^II₉W^V₆Clusters with aS= 12 Ground State

Abstract

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.

Theoretical study of the exchange coupling substituting MoV with WV in four cyano-bridged M′9M6 (M′ = MnII or NiII; M = MoV or WV) systems

“…Our calculated J ap and J eq values of Ni 9 Mo 6 and Ni 9 W 6 are on the order of 16 cm −1 coinciding with the experimental values. 6 From Table 1, the obtained J ap or J eq of models MnMo 6 , MnW 6 , NiMo 6 , NiW 6 , MnMo 3 , MnW 3 , NiMo 3 and NiW 3 calculated using different spin configurations are not consistent. Therefore, it is necessary to calculate a few more spin configurations than what is needed by pairwise exchange models for polynuclear systems.…”

A high-spin cyanide-bridged Mo6Mn9 cluster: crystal structure and magnetism

“…Following the pioneering work of Kahn's group [13][14][15], these flexible species may be used as versatile synthons to construct a variety of architectures or networks with novel topological structures and interesting magnetic properties. For example, M V -Mn II [16][17][18][19][20][21][22][23][24][25][26], M VMn III , [27,28], and M V -Cu II [29][30][31][32][33][34][35][36][37][38][39][40], bimetallic assemblies with a variety of extended structures, have been obtained; a few polynuclear clusters with M 6 V Mn 9 II type (M = Mo and W) have been reported as well [41][42][43][44][45][46] …”

Three novel octacyanomolybdate(IV)–M(II) [M = Mn and Cu] bimetallic assemblies: crystal structures and magnetic properties

“…Recently bimetallic octacyanometallates have attracted much attention because of their interesting structure and magnetic properties [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. The [M(CN) 8 ] 3-,4-(M = Mo, W, and Nb) units exhibit various geometrical structures such as square antiprism, dodecahedron, bicapped trigonal prism, and cyanide group is a kind of good bridging building bloke for transition metals complexes.…”