Synthesis, crystal structure and magnetic properties of a novel heterobimetallic rhenium(IV)-dysprosium(III) chain.

The use of the mononuclear rhenium(IV) precursor [ReBr5 (H2 pydc)](-) (H2 pydc=3,5-pyridinedicarboxylic acid) as a metalloligand towards dysprosium(III) afforded the first heterobimetallic Re(IV) -Dy(III) complex. Crystal structures and static and dynamic magnetic properties of both rhenium-containing species are reported herein. The 5d-4f compound shows an extended 1D structure and the AC magnetic measurements reveal frequency dependence at low temperature suggesting slow relaxation of the magnetization.

Nickel(II) complexes with methyl(2-pyridyl)ketone oxime: synthesis, crystal structures and DFT calculations.

The synthesis and structural characterization of the three novel nickel(II) complexes [Ni(OOCPh)(2)(mpkoH)(2)] (1), [Ni(NO(3))(2)(mpkoH)(2)] (2) and [Ni(mpkoH)(3)](NO(3))(2)·½H(2)O (3·½H(2)O), with mpkoH=methyl(2-pyridyl)ketone oxime is reported. Geometry optimization and population analyses were performed by means of DFT calculations for the previously mentioned compounds as well as for [NiCl(2)(mpkoH)(2)] (4). Electronic UV-vis spectra were also simulated in the TD-DFT framework to assign the origin of the absorption bands and in doing so, to have a clear picture of the absorptive features of the coordination compounds under investigation.

New family of thiocyanate-bridged Re(IV)-SCN-M(II) (M = Ni, Co, Fe, and Mn) heterobimetallic compounds: synthesis, crystal structure, and magnetic properties.

The heterobimetallic complexes of formula [(Me(2)phen)(2)M(µ-NCS)Re(NCS)(5)]·CH(3)CN [Me(2)phen = 2,9-dimethyl-1,10-phenanthroline and M = Ni (1), Co (2), Fe (3), and Mn (4)] have been prepared, and their crystal structures have been determined by X-ray diffraction on single crystals. Compounds 1-4 crystallize in the monoclinic C2/c space group, and their structure consists of neutral [(Me(2)phen)(2)M(µ-NCS)Re(NCS)(5)] heterodinuclear units with a Re-SCN-M bridge. Each Re(IV) ion in this series is six-coordinated with one sulfur and five nitrogen atoms from six thiocyanate groups building a somewhat distorted octahedral environment, whereas the M(II) metal ions are five-coordinated with four nitrogen atoms from two bidentate Me(2)phen molecules and a nitrogen atom from the bridging thiocyanate describing distorted trigonal bipyramidal surroundings. The values of the Re···M separation through the thiocyanate bridge in 1-4 vary in the range 5.903(1)-6.117(3) Å. The magnetic properties of 1-4 as well as those of the parent mononuclear Re(IV) compounds (NBu(4))(2)[Re(NCS)(6)] (A1) (NBu(4)(+) = tetra-n-butylammonium cation) and [Zn(NO(3))(Me(2)phen)(2)](2)[Re(NCS)(5)(SCN)] (A2) were investigated in the temperature range 1.9-300 K. Weak antiferromagnetic interactions between the Re(IV) and M(II) ions across the bridging thiocyanate were found in 1-4 [J = -4.3 (1), -2.4 (2), -1.8 (3), and -1.2 cm(-1) (4), the Hamiltonian being defined as H = -JS(Re)·S(M)]. The magnetic behavior of A2 is that of a magnetically diluted Re(IV) complex with a large and positive value of the zero-field splitting for the ground level (D(Re) = +37.0 cm(-1)). In the case of A1, although its magnetic behavior is similar to that of A2 in the high-temperature range (D(Re) being +19.0 cm(-1)), it exhibits a weak ferromagnetism below 3.0 K with a canting angle of 1.3°.

Pentachloro(pyrazine)rhenate(IV) complex as precursor of heterobimetallic pyrazine-containing Re(IV)2M(II) (M = Ni, Cu) species: synthesis, crystal structures and magnetic properties.

Three novel Re(IV) mononuclear complexes of formulae NBu4[ReC15(pyz)] (1), NH2Me2[ReCl5(pyz)] (2) and NH4[ReCl5(pyz)].0.75H2O (3), (pyz being pyrazine; NBu4+ = tetra-n-butylammonium cation, NH2Me2+ = dimethylammonium cation and NH4+ = ammonium cation), were synthesized by ligand substitution reaction from [ReCl6]2- anion and pyrazine in N,N-dimethylformamide (DMF). In addition, two new heterobimetallic compounds, the salt namely [ReCl5(pyz)]2[Ni(cyclam)](4) (cyclam = 1,4,8,11-tetraazacyclotetradecane) and the heterotrinuclear [{ReCl5(mu-pyz)}2Cu(DMF)4] (5) complex, were prepared by using as precursor 1 and 3, respectively. Compounds 1-5 were characterized by single-crystal X-ray diffraction. 1-3 are made up of discrete [ReCl5(pyz)]- anions and NBu4 (1), NH2Me2+ (2) and NH4+ (3) cations. [ReCl5(pyz)]- unit interacts toward Ni(II) (4) and Cu(II) (5) metal ions through different modes. In 4 two [ReCl5(pyz)]- anions weakly interact with a [Ni(cyclam)]2+ cation through chloro atoms, while compound 5 is a heterotrinuclear pyrazine-bridged Re(IV)2Cu(II) complex made up of [ReCl5(pyz)]- anions and [Cu(DMF)4]2+ cations. The magnetic properties of 1-5 were investigated in the temperature range 1.9-300 K. The magnetic behaviour of 1 is that of a magnetically diluted Re(IV) complex with a large value of zero-field splitting of the ground state (/2D/ is ca. 18.8(1) cm(-1)), whereas those of 2 and 3 are typical of antiferromagnetically coupled systems exhibiting susceptibility maxima at 10 (2) and 12 K (3). Compound 4 shows antiferromagnetic interactions between Re(IV) metal ions, Ni(II) being diamagnetic (because of its square-planar geometry), while 5 exhibits a ferromagnetic coupling between Re(IV) and Cu(II) metal ions across the pyrazine bridges with a J(ReCu), value of +11.8(1) cm(-1).

A novel series of rhenium-bipyrimidine complexes: synthesis, crystal structure and electrochemical properties.

Four novel rhenium complexes of formula [ReCl(4)(bpym)] (1), [ReBr(4)(bpym)] (2) PPh(4)[ReCl(4)(bpym)] (3) and NBu(4)[ReBr(4)(bpym)] (4) (bpym = 2,2'-bipyrimidine, PPh(4) = tetraphenylphosphonium cation and NBu(4) = tetrabutylammonium cation), have been synthesized and their crystal structures determined by single-crystal X-ray diffraction. The structures of 1 and 2 consist of [ReX(4)(bpym)] molecules held together by van der Waals forces. In both complexes the Re(iv) central atom is surrounded by four halide anions and two nitrogen atoms of a bpym bidentate ligand in a distorted octahedral environment. The structures of 3 and 4 consist of [ReX(4)(bpym)](-) anions and PPh(4)(+) () or NBu(4)(+) (4) cations. The coordination sphere of the Re(iii) metal ion is the same as in 1 and 2, respectively. However, whereas the Re-X bonds are longer the Re-N bonds are shorter than in 1 and 2. This fact reveals that the bpym ligand forms a stronger bond with Re(iii) than with Re(iv) resulting in a stabilisation of the lower oxidation state. [ReX(4)(bpym)] complexes are easily reduced, chemically and electrochemically, to the corresponding [ReX(4)(bpym)](-) anions. A voltammetric study shows that the electron transference is a reversible process characterized by formal redox potentials of +0.19 V (1) and +0.32 V (2) vs. NHE, in acetonitrile as solvent.

Rhenium(IV)-copper(II) heterobimetallic complexes with a bridge malonato ligand. Synthesis, crystal structure, and magnetic properties.

The Re(IV) complex [ReCl4(mal)]2-, in the form of two slightly different salts, (AsPh4)1.5(HNEt3)0.5[ReCl4(mal)] (1a) and (AsPh4)(HNEt3)[ReCl4(mal)] (1b), and the Re(IV)-Cu(II) bimetallic complexes [ReCl4(mu-mal)Cu(phen)2].CH3CN (2), [ReCl4(mu-mal)Cu(bpy)2] (3), and [ReCl4(mu-mal)Cu(terpy)] (4) (mal=malonate dianion, AsPh4=tetraphenylarsonium cation, HNEt3=triethylammonium cation, phen=1,10-phenanthroline, bpy=2,2'-bipyridine and terpy=2,2':6',2' '-terpyridine) have been synthesized and the structures of 1a, 1b, 2, and 3 determined by single-crystal X-ray diffraction. The structures of 1a and 1b are made up of discrete [ReCl4(mal)]2- anions and AsPh4+ and HNEt3+ cations, held together by electrostatic forces and hydrogen bonds. The Re(IV) atom is surrounded by four chloride anions and a bidentate malonate group, in a distorted octahedral environment. The structure of 2 consist of neutral dinuclear units [ReCl4(mu-mal)Cu(phen)2], with the metal ions united through a bridge carboxilato. The environment of Re(IV) is nearly identical to that in the mononuclear complex, and Cu(II) is five coordinate, being surrounded by four nitrogen atoms of two bidentate phen ligands and one oxygen atom of the malonato ligand. In 3, there are also dinuclear units, [ReCl4(mu-mal)Cu(bpy)2], but the Cu(II) ions complete a distorted octahedral coordination by binding with the free malonato oxygen atom of a neighbor unit, resulting in an infinite chain. The magnetic properties of 1-4 were also investigated in the temperature range 2.0-300 K. The magnetic behavior of 1a and 1b is as expected for a Re(IV) complex with a large value of the zero-field splitting (2D ca. 110 cm(-1)). For the bimetallic complexes, the magnetic coupling between Re(IV) and Cu(II) is antiferromagnetic in 2 (J=-0.39 cm(-1)), ferromagnetic in 4 (J=+1.51 cm(-1)), and nearly negligible in 3 (J=-0.09 cm(-1)).

Magnetic studies on hexahalorhenate(IV) salts of ferrocenium cations [Fe(C5R5)2]2[ReX6] (R = H, CH3; X = Cl, Br, I).

The hexahalorhenate(IV) salts of formula [Fe(C5H5)2]2[ReX6], with X = Cl (1), Br (2), and I (3), and [Fe(C5Me5)2]2[ReX6], with X = Cl (4), Br (5), and I (6) ([Fe(C5Me5)2]+ = decamethylferrocenium cation), have been synthesized and the structures of 1, 2, and 4 determined by single-crystal X-ray diffraction. 1, 2, and 4 crystallize in the orthorhombic system, space groups Pbca (1 and 2) and Ibam (4), with a = 14.099(2) A, b = 16.125(2) A, and c = 22.133(15) A, for 1, a = 14.317(3) A, b = 16.848(3) A, and c = 22.099(2) A for 2, and a = 15.8583(5) A, b = 15.9368(5) A, and c = 16.9816(6) A for 4. The three structures are made up of discrete [ReX6]2- anions and ferrocenium cations held together by electrostatic forces. There are anion-anion contacts in 1 and 2 but only through one direction. The [ReX6]2- octahedra are arranged along the y axis forming chains of Re and X atoms, -Re-X...X-Re-X...X-Re-, where the intermolecular X...X distances are shorter than the van der Waals distances. A somewhat greater separation between the anions occurs in 4. The magnetic properties of 1-6 were investigated in the temperature range 2.0-300 K. 1, 2, 4, and 5 exhibit an antiferromagnetic coupling between the anions, whereas a ferromagnetic coupling between anions and cations is the dominant interaction in 3. 6 behaves as a magnetically isolated compound, its susceptibility being the simple addition of the independent contributions of the uncoupled paramagnetic cations and anions.

Magnetic studies on hexaiodorhenate(IV) salts of univalent cations. Spin canting and magnetic ordering in K2[ReI6] with Tc = 24 K.

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.

Heterobimetallic oxalato-bridged M(II)Re(IV) complexes (M = Mn, Fe, Co, Ni): synthesis, crystal structure, and magnetic properties.

Four rhenium(IV)-M(II) bimetallic complexes of formula [ReCl(4)(mu-ox)M(dmphen)(2)].CH(3)CN with M = Mn (1), Fe (2), Co (3), and Ni (4) (ox = oxalate anion, dmphen = 2,9-dimethyl-1,10-phenanthroline) have been synthesized and the crystal structures of 1 and 3 determined by single-crystal X-ray diffraction. 1 and 3 are isostructural and crystallize in the monoclinic system, space group P2(1)/c, with a = 16.008(4) A, b = 12.729(2) A, c = 18.909(5) A, beta = 112.70(2) degrees, and Z = 4 for 1 and a = 15.998(4) A, b = 12.665(2) A, c = 18.693(5) A, beta = 112.33(2) degrees, and Z = 4, for 3. The structure of 1 and 3 is made up of neutral [ReCl(4)(mu-ox)M(dmphen)(2)] bimetallic units (M = Mn (1), Co (3)) and acetonitrile molecules of crystallization. M(II) and Re(IV) metal ions exhibit distorted octahedral coordination geometries being bridged by a bis(bidentate) oxalato ligand. The magnetic behavior of 1-4 has been investigated over the temperature range 2.0-300 K. A very weak antiferromagnetic coupling between Re(IV) and Mn(II) occurs in 1 (J = -0.1 cm(-)(1)), whereas a significant ferromagnetic interaction between Re(IV) and M(II) is observed in 2-4 [J = +2.8 (2), +5.2 (3), and +5.9 cm(-)(1) (4)].

Synthesis, Crystal Structure, and Magnetic Properties of Tetraphenylarsonium Tetrachloro(oxalato)rhenate(IV) and Bis(2,2'-bipyridine)tetrachloro(&mgr;-oxalato)copper(II)rhenium(IV).

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.