Synthesis, Crystal Structure, and Magnetic Properties of Tetraphenylarsonium Tetrachloro(oxalato)rhenate(IV) and Bis(2,2‘-bipyridine)tetrachloro(μ-oxalato)copper(II)rhenium(IV)

Abstract

Two new rhenium(IV) compounds of formula (AsPh(4))(2)[ReCl(4)(ox)] (1) and [ReCl(4)(&mgr;-ox)Cu(bipy)(2)] (2) (AsPh(4) = tetraphenylarsonium cation, ox = oxalate anion, and bipy = 2,2'-bipyridine) have been synthesized and their crystal structures determined by single-crystal X-ray diffraction. 1 and 2 crystallize in the monoclinic system, space groups P2(1)/c and P2(1)/n, respectively, with a = 22.250(5) Å, b = 11.245(3) Å, c = 19.089(4) Å, beta = 96.59(2) degrees, and Z = 4 for 1 and a = 9.421(2) Å, b = 16.909(4) Å, c = 16.179(4) Å, beta = 93.97(2) degrees, and Z = 4 for 2. The structure of 1 is made up of [ReCl(4)(ox)](2)(-) anions and AsPh(4)(+) cations held united by electrostatic forces. Rhenium(IV) is hexacoordinate, with two oxygens of a chelating ox and four chlorine atoms building a distorted octahedron around the metal atom. There is no contact between the [ReCl(4)(ox)](2)(-) anions, the shortest Re.Re and Cl.Cl distances being 10.345 and 7.209 Å, respectively. This anionic complex is coordinated to a [Cu(bipy)(2)](2+) cation in 2, through one oxalate-oxygen, giving a neutral heterometallic dinuclear unit. The Cu(II) ion shows a very distorted five-coordinated geometry, four bipy-nitrogens occuping the equatorial positions and the oxygen atom the apical one. The basal plane geometry is distorted toward the tetrahedron, the dihedral angle between the mean planes of the two bipy ligands is 37.6(2) degrees. These [ReCl(4)(&mgr;-ox)Cu(bipy)(2)] units are arranged in such a way that a chlorine atom of one of them points toward the copper atom of the neighboring one, forming helicoid chains. The intrachain Re.Cu distances through chloro and oxalato bridges are 4.658 and 4.798 Å, respectively. The magnetic behavior of 1 and 2 has been investigated over the temperature range 1.8-300 K. 1 is a magnetically diluted Re(IV) complex, the great value of zero-field splitting of the ground level (D = 60 cm(-)(1)) accounting for the variation of chi(M)T with T in the low-temperature range. 2 behaves as a ferrimagnetic chain, with weak antiferromagnetic interactions between Re(IV) and Cu(II) through oxalato and single chloro bridges.

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 )).…”

“…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].…”

Synthesis, Crystal Structure and Magnetic Properties of Heteropolynuclear ReIVMII Complexes Based on the Robust [ReCl5(pyzCOO)]2– Unit (pyzCOO = 2‐pyrazinecarboxylate)

“…[10] Also, the diffuse character of 5d orbitals allows a significant degree of spin delocalization onto the ligands, which accounts for the strength of the magnetic interactions between Re IV centres or between Re IV and other paramagnetic ions at large distances. [11,12] All the reported Re IV M II/III polynuclear compounds were prepared by the rational "complex as ligand" approach in which a fully solvated or a pre-formed partially blocked first-row transition-metal ion M II/III was allowed to react with a Re IV mononuclear species, such as [ReX 4 (ox)] 2-(X = Cl, Br) [12][13][14] or trans-[ReCl 4 (CN) 2 ] 2-. [4a] This synthetic strategy, based on the bridging ability of oxalate or cyanide ligands together with their known capacity to mediate magnetic interactions between paramagnetic centres, has led to a remarkable diversity of crystal structures, nuclearity and magnetic properties.…”

“…[4a] This synthetic strategy, based on the bridging ability of oxalate or cyanide ligands together with their known capacity to mediate magnetic interactions between paramagnetic centres, has led to a remarkable diversity of crystal structures, nuclearity and magnetic properties. Besides the two examples mentioned in the first paragraph, several other di-, [15][16][17] tri- [18] and tetranuclear complexes [15b] as well as one-dimensional (1D) compounds [12,16,19,20] have also been described. Up to now, two heterobimetallic Re IV compounds with heavier 4d or 4f metals have also been synthesized, namely (PPh 4 ) 2 [21] and the pentanuclear (NBu 4 ) 5 [Gd III {Re IV Br 4 (μ-ox)} 4 (H 2 O)]·H 2 O.…”

Synthesis, Crystal Structure and Magnetic Properties of a Novel Heterobimetallic Rhenium(IV)–Dysprosium(III) Chain

“…Additionally,t he greater diffuseness of its magnetic orbitals causes al arge degree of spin delocalization on the peripheral ligandst hat leads to as trengthening of the magnetic interactions. [8] All of these features have been described in mono-a nd polynuclear Re IV -based species, someo ft hem show magnetic ordering, SMM and SCM behavior. [9][10][11][12][13] Recently,t he first Re IV -4fm ixed compound was reported, with the isotropic Gd III ion as the lanthanide element.…”