Magnetic Studies on Hexaiodorhenate(IV) Salts of Univalent Cations. Spin Canting and Magnetic Ordering in K₂[ReI₆] withT_c= 24 K

Abstract

The ionic salts of rhenium(IV) of formula (Cat)(2)[ReI(6)] with Cat = Li(+) (1), Na(+) (2), K(+) (3), Rb(+) (4), Cs(+) (5), NH(4)(+) (6), and AsPh(4)(+) (7) [AsPh(4)(+) = tetraphenylarsonium cation] have been synthesized, and the structures of two of them (namely, 3 and 6) were determined by single-crystal X-ray diffraction. 3 crystallizes in the monoclinic system, space group Pn, with a = 7.815(1) A, b = 7.874(1) A, c = 11.335(1) A, beta = 90.38(1) degrees, and Z = 2 whereas 6 crystallizes in the tetragonal system, space group P4/mnc, with a = 7.881(1) A, b = 7.881(1) A, c = 11.474(2) A, and Z = 2. The structures of 3 and 6 are made up of discrete [ReI(6)](2)(-) anions and K(+) (3) or NH(4)(+) (6) cations held together by electrostatic forces (3 and 6) and N-H.I hydrogen bonds (6). The rhenium(IV) cation in 3 and 6 is surrounded by six iodide ligands in an octahedral environment with the Re-I bond lengths varying in a very narrow range [2.704(3)-2.738(3) and 2.716(1)-2.722(2) A for 3 and 6, respectively]. The [ReI(6)](2)(-) anions in 6 describe a tetragonally distorted body-centered cubic structure. In 3, the arrangement of these units is similar but more distorted. The different arrangement of the anions in 3 and 6 accounts for the centrosymmetric (6) and non-centrosymmetric (3) structures observed. The magnetic properties of 1-7 were investigated in the temperature range 2.0-300 K. The magnetic behavior of 7 is that of a magnetically diluted Re(IV) complex with a large value of the zero-field splitting of the ground level (|2D| = 49.8 cm(-)(1)) whereas those of 1, 2, and 4-6 are typical of antiferromagnetically coupled systems with susceptibility maxima at 28 (1), 27 (2), 21 (4), 16 (5), and 20 K (6). In the case of compound 3, its magnetic behavior in the high-temperature range is parallel to that observed in the parent salts but below 24 K it is a weak ferromagnet with a canting angle of ca. 1.2 degrees.

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

“…5 and 6, respectively. At room temperature, the values of v M T are 5.14 (1) and 5.15 cm 3 mol À1 K (2), as expected for a pair of magnetically isolated high-spin Fe II (3d 6 , S = 2 with g = 2.2) and Re IV (5d 3 , S = 3/2 with g = 1.8) ions [14][15][16][17][18]. Upon cooling, the values of v M T decrease very slowly until ca.…”

“…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]. Hexahalorhenate(IV) salts of diamagnetic univalent cations, such as Ag I and alkali metal ions, show significant antiferromagnetic interactions, which are transmitted through these intermolecular Re-XÁ Á ÁX-Re pathways [14,15]. Remarkably, magnetic ordering due to spin canting was observed below 24 K in the case of the compound K 2 [ReI 6 ] [15], demonstrating the efficiency and strength of these through-space exchange interactions.…”

“…Hexahalorhenate(IV) salts of diamagnetic univalent cations, such as Ag I and alkali metal ions, show significant antiferromagnetic interactions, which are transmitted through these intermolecular Re-XÁ Á ÁX-Re pathways [14,15]. Remarkably, magnetic ordering due to spin canting was observed below 24 K in the case of the compound K 2 [ReI 6 ] [15], demonstrating the efficiency and strength of these through-space exchange interactions.…”

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

“…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 )).…”

“…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]. However, the isolation of mononuclear rhenate(IV) complexes with bulkier cations (even though they are paramagnetic [139]) cancels these intermolecular interactions, thereby allowing the estimation of magnetic anisotropy [119, 139-142, 146, 149-151, 153, 156, 158, 159, 168-171].…”