High-spin-Verbindungen: ein Cyano-verbrückter molekularer MnMo-Cluster mitS=51/2-Grundzustand sowie ferromagnetischer Intercluster-Ordnung bei tiefen Temperaturen

A multitechnique approach has allowed the first experimental determination of single-ion anisotropies in a large iron(III)-oxo cluster, namely [NaFe6(OCH3)12(pmdbm)6ClO4 (1) in which Hpmdbm = 1,3-bis(4-methoxyphenyl)-1,3-propanedione. High-frequency EPR (HF-EPR). bulk susceptibility measurements, and high-field cantilever torque magnetometry (HF-CTM) have been applied to iron-doped samples of an isomorphous hexagallium(III) cluster [NaGa6(OCH3)12-(pmdbm)6]ClO4, whose synthesis and X-ray structure are also presented. HF-EPR at 240 GHz and susceptibility data have shown that the iron(III) ions have a hard-axis type anisotropy with DFe = 0.43(1) cm(-1) and EFe = 0.066(3) cm(-1) in the zero-field splitting (ZFS) Hamiltonian H = DFe[S2(z) - S(S + 1)/3] + Fe[S2(x) - S2(y)]. HF-CTM at 0.4 K has then been used to establish the orientation of the ZFS tensors with respect to the unique molecular axis of the cluster, Z. The hard magnetic axes of the iron(III) ions are found to be almost perpendicular to Z, so that the anisotropic components projected onto Z are negative, DFe(ZZ)= -0.164(4) cm(-1). Due to the dominant antiferromagnetic coupling, a negative DFe(ZZ) value determines a hard-axis molecular anisotropy in 1, as experimentally observed. By adding point-dipolar interactions between iron(III) spins, the calculated ZFS parameter of the triplet state, D1 = 4.70(9) cm(-1), is in excellent agreement with that determined by inelastic neutron scattering experiments at 2 K, D1 = 4.57(2) cm(-1). Iron-doped samples of a structurally related compound, the dimer [Ga2(OCH3)2(dbm)4] (Hdbm = dibenzoylmethane), have also been investigated by HF-EPR at 525 GHz. The single-ion anisotropy is of the hard-axis type as well, but the DFe parameter is significantly larger [DFe = 0.770(3) cm(-1). EFe = 0.090(3) cm(-1)]. We conclude that, although the ZFS tensors depend very unpredictably on the coordination environment of the metal ions, single-ion terms can contribute significantly to the magnetic anisotropy of iron(III)-oxo clusters, which are currently investigated as single-molecule magnets.

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Binuclear Complexes as Building Blocks for Polynuclear Complexes with High-Spin Ground States: Synthesis and Structure of a Tetranuclear Nickel Complex with anS=4 Ground State

Kersting

Steinfeld

Siebert

2001

Chem. Eur. J.

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The coordinatively unsaturated dinickel(II) complex [(L2)Ni2](BPh4)2 (2), where (L2)2- represents the dianionic form of the 'N4S2' ligand N,N'-bis(2-thio-3-aminomethyl-5-tert-butylbenzyl)propane-1,3-diamine), has been investigated with respect to its ability to function as a building block for the preparation of polynuclear nickel complexes with a high-spin ground state. Treatment of 2 with pyridazine (pydz) followed by addition of two equivalents of NH4SCN afforded the dinuclear mupyridazine complex [(L2)Ni2(mu-pydz)(NCS)2] (4). The reaction of 2 with pyridazine and NaN3 in a 1:1:1 molar ratio gave the tetranuclear nickel(II) complex [[(L2)Ni2(mu-pydz)(N3)]2](BPh4)2 (5). Both complexes have been characterized by X-ray crystallography and variable-temperature magnetic susceptibility studies. In complex 4 two fac(SCN)N2Ni(II) units are linked by two thiophenolate sulfur atoms and a mu-pydz ligand to give a (SCN)N2Ni(mu-S)2(mu-pydz)NiN2(NCS) core structure with a pseudoconfacial bioctahedral geometry. The two NCS- groups occupy opposite coordination sites, each is in a cis position to the pydz bridge. Analyses of the susceptibility data indicate the presence of an intramolecular ferromagnetic exchange interaction between the two Ni(II) (S = 1) ions. Complex 5 is composed of two binuclear [(L2)Ni2(mu-pydz)]2+ subunits which are linked by two azide ions to give a rectangular array of four six-coordinate Ni(II) ions. The binuclear [(L2)Ni2(mu-pydz)]2+ fragments in 4 and 5 are isostructural. Analyses of the susceptibility data of 5 reveal ferromagnetic exchange interactions between the Ni(II) ions of the binuclear subunit as well as for the mu(1,3)N3-bridged Ni(II) ions. Thus, compound 4 has an S = 2 ground state, whereas in 5 it is S = 4.

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High-spin-Verbindungen: ein Cyano-verbrückter molekularer MnMo-Cluster mitS=51/2-Grundzustand sowie ferromagnetischer Intercluster-Ordnung bei tiefen Temperaturen

Cited by 45 publications

References 25 publications

High-Nuclearity Chromium–Nickel–Cyanide Clusters: An Open Cr8Ni5(CN)24 Cage and aC3-Symmetric Cr10Ni9(CN)42 Cluster Incorporating Three Forms of Cyanonickelate

High-Nuclearity Chromium–Nickel–Cyanide Clusters: An Open Cr8Ni5(CN)24 Cage and aC3-Symmetric Cr10Ni9(CN)42 Cluster Incorporating Three Forms of Cyanonickelate

Single-Ion versus Dipolar Origin of the Magnetic Anisotropy in Iron(III)-Oxo Clusters: A Case Study

Binuclear Complexes as Building Blocks for Polynuclear Complexes with High-Spin Ground States: Synthesis and Structure of a Tetranuclear Nickel Complex with anS=4 Ground State

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