Metamagnetism in tetrachlorobis(N-phenylacetamidine)rhenium(IV)

Magnetic anisotropy in two- to eight-coordinated transition–metal complexes: Recent developments in molecular magnetism

“…Many hexa-coordinated metal complexes exhibit magnetic anisotropies [4,12,22,[108][109][110][111][112][113][114][115][116][117][118][119][120][121][122] and a few recent studies have demonstrated possible SMM-type behavior by the mono-nuclear complexes. It should be recalled that the first reported SMM was a polynuclear complex that incorporated hexa-coordinated Mn II/III ions in a slightly distorted O h geometry [123][124][125][126].…”

“…However, the most interesting cases involved Re IV metal ions with octahedral geometry in a series of complexes (Fig. 27), which can be categorized as: (i) hexahalorhenates(IV) [119,[139][140][141][142][143][144][145][146] (79), and I (80)) [139], (ii) pentahalorhenates(IV) with one labile coordination site [147,148] such as (NH 2 Me 2 )[Re IV X 5 (DMF)] (where X = Cl (81) and Br (82)) [147], (iii) tetrahalorhenates(IV) with cis-blocking chelating organic ligands [110,[149][150][151][152][153][154][155][156] such as (NBu 4 ) 2 [Re(ox)X 4 ] (where ox = oxalate, X = Cl (83) and Br (84) For a hexa-coordinated 3d 3 ion with ideal O h geometry, significantly high first-order SOC and thus large magnetic anisotropy will be obtained from the triply degenerate ground state (involving d xy , d xz , and d yz orbitals) if Jahn-Teller distortion, which inevitably breaks the degeneracy and minimizes the SOC, is not present. In octahedral complexes, Jahn-Teller distortion splits the lowest lying triply degenerate d orbitals, thereby leading to two sets of orbitals, i.e., d xy and (d xz , d yz ), irrespective of whether the nature of the distortion is compression (where the energy order is d xy < (d xz , d yz )) or elongation (where the energy order is d xy > (d xz , d yz )).…”

“…Due to their high magnetic anisotropy, efficient magnetic exchange coupling ability, redox stability, and geometric rigidity, rhenates (mainly the halo-/pseudohalorhenates) have been used extensively as building units in the construction of polymetallic magnetic complexes [163][164][165][166]. Neutron diffraction experiments [110,167] and spin density distribution studies [156] have shown that the ligands coordinated with the Re IV ion in these mononuclear complexes possess considerable amounts of spin density, which promotes efficient intermolecular Re IV •••X•••Re IV interactions (where X is a spin carrier) in the solid state. Hence, quantifying the magnetic anisotropy of these complexes in magnetic studies appears to be quite tricky because of intermolecular magnetic superexchange interactions, even when the Re IV centers are separated by diamagnetic species in a crystal lattice [140,144,[146][147][148]157].…”

Magneto-structural studies on heterobimetallic malonate-bridged MIIReIV complexes (M = Mn, Co, Ni and Cu)

“…General Flores 2124, Montevideo, Uruguay. E-mail: ckremer@fq.edu.uy 2,9-dimethyl-1,10-phenanthroline) which exhibits a well defined dinuclear structure; 1c (ii) the family of tetranuclear compounds NBu 4 [{ReCl 4 (m-ox)} 3 M¢] (M¢ = Mn, Fe, Co, Ni and Cu; NBu 4 + = tetra-n-butylammonium), one of them (M¢ = Ni) behaving as a single molecule magnet; 1e,1g (iii) the chain compounds [ReCl 4 (mox)Cu(bipy) 2 ] (bipy = 2,2¢-bipyridine) and [ReCl 4 (m-ox)Cu(pyim) 2 ] (pyim = 2-(2-pyridyl)imidazole) with regular alternating Re(IV) and Cu(II) ions. 1a,1g Their crystal structures show that although the preferred coordination mode of the bridging oxalato is the bis-bidentate mode, the rarer bidentate/monodentate (outer or inner) coordination mode can also occur depending mainly on the nature and arrangement of the auxiliary ligands around the M or M¢ atoms.…”

Hexakis(diethylacetamide)iron(II) hexahalorhenate(IV) ionic salts: X-ray structures and magnetic properties

“…Re IV is a 5d 3 ion with a ground electronic state 4 A 2g , with three unpaired electrons (t 2g 3 configuration), and its high value of the spin-orbit coupling constant (k $ 1000 cm À1 for the free ion) accounts for the high magnetic anisotropy that Re IV compounds exhibit [9]. Polarized neutron diffraction studies and density functional theory calculations performed on Re IV systems have revealed strong spin delocalization from the Re IV centre onto the peripheral atoms of the ligands of its complexes [10][11][12][13]. This fact accounts for the significant intermolecular magnetic interactions existing between spin densities on neighbouring molecules, which are generally mediated through Re-XÁ Á ÁX-Re contacts (X = halogen atom) in the crystal lattice of these systems [6].…”