Pressure induced enhancement of the magnetic ordering temperature in rhenium(IV) monomers.

Materials that demonstrate long-range magnetic order are synonymous with information storage and the electronics industry, with the phenomenon commonly associated with metals, metal alloys or metal oxides and sulfides. A lesser known family of magnetically ordered complexes are the monometallic compounds of highly anisotropic d-block transition metals; the 'transformation' from isolated zero-dimensional molecule to ordered, spin-canted, three-dimensional lattice being the result of through-space interactions arising from the combination of large magnetic anisotropy and spin-delocalization from metal to ligand which induces important intermolecular contacts. Here we report the effect of pressure on two such mononuclear rhenium(IV) compounds that exhibit long-range magnetic order under ambient conditions via a spin canting mechanism, with Tc controlled by the strength of the intermolecular interactions. As these are determined by intermolecular distance, 'squeezing' the molecules closer together generates remarkable enhancements in ordering temperatures, with a linear dependence of Tc with pressure.

A Chiral, Photoluminescent, and Spin-Canted {Cu(I)Re(IV)2}n Branched Chain.

A new heteroleptic 1D Cu(I)-Re(IV) coordination polymer of the formula {Cu(I)Re(IV)Cl4(µ-Cl)(µ-pyz)[Re(IV)Cl4(µ-bpym)]}n·nMeNO2 (1; pyz = pyrazine, bpym = 2,2'-bipyrimidine) has been prepared through the Cu(I)-mediated self-assembly of two different Re(IV) metalloligands, namely, [ReCl5(pyz)](-) and [ReCl4(bpym)]. 1 consists of chiral branched chains with an overall rack-type architecture displaying photoemission and magnetic ordering. These results constitute a first step toward making new multifunctional magnetic materials based on mixed 3d-5d molecular systems.

Metamagnetic behaviour in a new Cu(II)Re(IV) chain based on the hexachlororhenate(IV) anion.

A new chloro-bridged heterobimetallic Cu(II)Re(IV) chain of formula {Cu(pyim)(Him)2ReCl6}n·MeCN (·MeCN) has been prepared and magnetostructurally characterised. Compound is the first example of the [Re(IV)Cl6](2-) anion acting as a metalloligand towards a paramagnetic metal ion.

Highly anisotropic rhenium(IV) complexes: new examples of mononuclear single-molecule magnets.

The rhenium(IV) complex (NBu4)2[ReBr4(ox)] (1) (ox = oxalate and NBu4(+) = tetra-n-butylammonium cation) has been prepared and its crystal structure determined by X-ray diffraction. The structure is made up of discrete [ReBr4(ox)](2-) anions and bulky NBu4(+) cations. Each [ReBr4(ox)](2-) anion is surrounded by six NBu4(+) cations, which preclude any significant intermolecular contact between the anionic entities, the shortest rhenium···rhenium distance being 9.373(1) Å. Variable temperature dc and ac magnetic susceptibility measurements and field-dependent magnetization experiments on polycrystalline samples of 1 reveal the occurrence of highly anisotropic magnetically isolated Re(IV) centers (S(Re) = 3/2), which exhibit slow relaxation of the magnetization at very low temperatures in a dc field. Ac measurements conducted on a polycrystalline sample of the complex (NBu4)2[ReCl4(ox)] (2) [compound isostructural to 1 whose structure and dc magnetic susceptibility study were previously reported in Tomkiewicz, A.; Bartczak, T. J.; Kruszynski, R.; Mrozinski, J. J. Mol. Struct. 2001, 595, 225] show a similar behavior, both complexes thus constituting new examples of mononuclear single-molecule magnets. High-frequency and -field electron paramagnetic resonance on polycrystalline samples of 1 and 2 and on single crystals of 2 allowed for the determination for the first time of the negative sign and confirmed a significant magnitude and rhombicity (E/D) of the zero-field splitting tensor of the [ReCl4(ox)](2-) and [ReBr4(ox)](2-) centers, originating from a combination of spin-orbit coupling and low molecular symmetry. D and E values of 1 and 2 were estimated through magnetization measurements and theoretically calculated through complete active space and density functional theory methodologies.

Ferromagnetic coupling and spin canting behaviour in heterobimetallic Re(IV)M(II/III) (M = Co(II/III), Ni(II)) species.

Three novel heterobimetallic Re(IV) compounds of formulae [ReBr(4)(µ-ox)M(4,7-Cl(2)phen)(2)]·CH(3)CN·CH(3)NO(2) [M = Co(II) (1) and Ni(II) (2)] and [ReBr(4)(ox)](3)[Co(III)(5,6-dmphen)(3)](2)·CH(3)CN·2CH(3)NO(2)·4H(2)O (3) [ox = oxalate, 4,7-Cl(2)phen = 4,7-dichloro-1,10-phenanthroline and 5,6-dmphen = 5,6-dimethyl-1,10-phenanthroline] have been synthesised and the structures of 1 and 3 determined by single crystal X-ray diffraction. Compound 1 is an oxalato-bridged Re(IV)Co(II) heterodinuclear complex where the [ReBr(4)(ox)](2-) unit acts as a bidentate ligand towards the [Co(4,7-Cl(2)phen)(2)](2+) entity, the separation between Re(IV) and Co(II) across the oxalate being 5.482(1) Å. Compound 3 is an ionic salt whose structure is made up of [Re(IV)Br(4)(ox)](2-) anions and [Co(III)(5,6-dmphen)(3)](3+) cations plus acetonitrile, nitromethane and water as solvent molecules. The magnetic properties of 1-3 were investigated in the temperature range 1.9-300 K. Relatively large ferromagnetic interactions between Re(IV) and M(II) through the bis(bidentate) oxalato occur in 1 and 2 [J(ReM) = +11.0 (1) and +12.2 cm(-1) (2), the Hamiltonian being defined as H = -J(ReM)S(Re)·S(M)] which are explained on the basis of orbital symmetry considerations. A behaviour typical of a magnetically diluted Re(IV) complex with a large and positive value of zero-field splitting for the ground level (D(Re) = +43 cm(-1)) is observed for 3 in the high temperature range, whereas it exhibits spin canting in the low temperature domain as well as magnetic ordering below ca. 4.8 K.

A heteropentanuclear oxalato-bridged [Re(IV)4Gd(III)] complex: synthesis, crystal structure and magnetic properties.

The compound (NBu(4))(5)[Gd(III){Re(IV)Br(4)(µ-ox)}(4)(H(2)O)]·H(2)O (1), with intramolecular antiferromagnetic coupling, is the first Re(iv) system incorporating a 4f ion.

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°.

First magnetostructural study on a heterodinuclear 2,2'-bipyrimidine-bridged complex.

The use of the [ReCl(4)(bpym)] precursor as a ligand toward the fully solvated nickel(II) metal ion affords the first example of a 2,2'-bipyrimidine-bridged Re(IV)-Ni(II) complex, [ReCl(4)(µ-bpym)NiBr(2)(H(2)O)(2)] (1), whose intramolecular ferromagnetic coupling has been substantiated from both experimental and theoretical studies.

Enhancing the magnetic coupling of oxalato-bridged Re(IV)2M(II) (M=Mn, Co, Ni, and Cu) trinuclear complexes via peripheral halide ligand effects.

Four heterotrinuclear Re(IV)(2)M(II) compounds of general formula (NBu(4))(2)[{Re(IV)Br(4)(µ-ox)}(2)M(II)(Him)(2)] [NBu(4)(+) = tetra-n-butylammonium cation, ox = oxalate, Him = imidazole; M = Mn (1), Co (2), Ni (3), and Cu (4)] have been synthesized by using the novel mononuclear complex [Re(IV)Br(4)(ox)](2-) as a ligand toward divalent first-row transition metal ions in the presence of imidazole. Compounds 1-4 are isostructural complexes whose structure contains discrete trinuclear [{Re(IV)Br(4)(µ-ox)}(2)M(II)(Him)(2)](2-) anions and bulky NBu(4)(+) cations. The Re and M atoms are six-coordinated: four peripheral bromo and two oxalate-oxygens (at Re), and two cis-coordinated imidazole molecules and four oxygen atoms from two oxalate ligands (at M), build distorted octahedral surroundings. Two peripheral [ReBr(4)(ox)](2-) units act as bidentate ligands through the oxalate group toward the central [M(II)(Him)(2)] fragment affording the trinuclear entities. The values of the intramolecular Re···M separation are 5.62(1) (1), 5.51(1) (2), 5.46(1) (3), and 5.55(1) Å (4). Magnetic susceptibility measurements on polycrystalline samples of 1-4 in the temperature range of 1.9-300 K show the occurrence of intramolecular antiferro- [J = -1.1 cm(-1) (1)] and ferromagnetic interactions [J = +3.9 (2), +19.7 (3), and +14.4 cm(-1) (4)], the Hamiltonian being defined as H = -J [S(M)(S(Re1) + S(Re2))]. The larger spin delocalization on the oxalato bridge in 1-4 when compared to the trinuclear Re(IV)(2)M(II) complexes with chloro instead of bromo as peripheral ligands (1'-4') accounts for the strengthening of the magnetic interactions in 1-4 [J = -0.35 (1'), +14.2 (3'), and +7.7 cm(-1) (4')]. An incipient frequency dependence of the out-of-phase ac signals of 3 at very low temperatures is reminiscent of a system with slow relaxation of the magnetization, a phenomenon characteristic of single-molecule magnet behavior.

New cyanide-bridged Mn(III)-M(III) heterometallic dinuclear complexes constructed from [M(III)(AA)(CN)4]- building blocks (M = Cr and Fe): synthesis, crystal structures and magnetic properties.

Three Mn(III)-M(III) (M = Cr and Fe) dinuclear complexes have been obtained by assembling [Mn(III)(SB)(H(2)O)](+) and [M(III)(AA)(CN)(4)](-) ions, where SB is the dianion of the Schiff-base resulting from the condensation of 3-methoxysalicylaldehyde with ethylenediamine (3-MeOsalen(2-)) or 1,2-cyclohexanediamine (3-MeOsalcyen(2-)): [Mn(3-MeOsalen)(H(2)O)(µ-NC)Cr(bipy)(CN)(3)]·2H(2)O (1), [Mn(3-MeOsalen)(H(2)O)(µ-NC)Cr(ampy)(CN)(3)][Mn(3-MeOsalen)(H(2)O)(2)]ClO(4)·2H(2)O (2) and [Mn(3-MeOsalcyen)(H(2)O)(µ-NC)Fe(bpym)(CN)(3)]·3H(2)O (3) (bipy = 2,2'-bipyridine, ampy = 2-aminomethylpyridine and bpym = 2,2'-bipyrimidine). The [M(AA)(CN)(4)](-) unit in 1-3 acts as a monodentate ligand towards the manganese(III) ion through one of its four cyanide groups. The manganese(III) ion in 1-3 exhibits an elongated octahedral stereochemistry with the tetradentate SB building the equatorial plane and a water molecule and a cyanide-nitrogen atom filling the axial positions. Remarkably, the neutral mononuclear complex [Mn(3-MeOsalen)(H(2)O)(2)]ClO(4) co-crystallizes with the heterobimetallic unit in 2. The values of the Mn(III)-M(III) distance across the bridging cyanide are 5.228 (1), 5.505 (2) and 5.265 Å (3). The packing of the neutral heterobimetallic units in the crystal is governed by the self-complementarity of the [Mn(SB)(H(2)O)](+) moieties, which interact each other through hydrogen bonds established between the aqua ligand from one fragment with the set of phenolate- and methoxy-oxygens from the adjacent one. The magnetic properties of the three complexes have been investigated in the temperature range 1.9-300 K. Weak antiferromagnetic interactions between the Mn(III) and M(III) ions across the cyanido bridge were found: J(MnM) = -5.6 (1), -0.63 (2) and -2.4 cm(-1) (3) the Hamiltonian being defined as H = -JS(Mn)·S(M). Theoretical calculations based on density functional theory (DFT) have been used to substantiate both the nature and magnitude of the exchange interactions observed and also to analyze the dependence of the magnetic coupling on the structural parameters within the Mn(III)-N-C-M(III) motif in 1-3.

Synthesis, crystal structure and magnetic properties of an oxalato-bridged Re(IV)Mo(VI) heterobimetallic complex.

The Re(IV)-Mo(VI) compound of formula (PPh(4))(2)[ReCl(4)(µ-ox)MoO(2)Cl(2)] (1) constitutes the first example of a heterodinuclear oxalato-bridged complex in the coordination chemistry of molybdenum.

Magneto-structural studies on heterobimetallic malonate-bridged M(II)Re(IV) complexes (M = Mn, Co, Ni and Cu).

The mononuclear Re(IV) compound of formula (PPh(4))(2)[ReBr(4)(mal)] (1) was used as a ligand to obtain the heterobimetallic species [ReBr(4)(µ-mal)Co(dmphen)(2)]· MeCN (2), [ReBr(4)(µ-mal)Ni(dmphen)(2)] (3), [ReBr(4)(µ-mal)Mn(dmphen)(2)] (4a), [ReBr(4)(µ-mal)Mn(dmphen)(H(2)O)(2)]·dmphen·MeCN·H(2)O (4b), [ReBr(4)(µ-mal)Cu(phen)(2)]·1/4H(2)O (5) and [ReBr(4)(µ-mal)Cu(bipy)(2)] (6) (mal = malonate dianion, dmphen = 2,9-dimethyl-1,10-phenanthroline, phen = 1,10-phenanthroline and bipy = 2,2'-bipyridine). The structures of 2 and 5 (single-crystal X-ray diffraction) are made up of neutral [ReBr(4)(µ-mal)M(AA)] dinuclear units [AA = dmphen with M = Co (2) and AA = phen with M = Cu (5)] where the metal ions are connected through a malonate ligand which exhibits simultaneously the bidentate [at the Re(IV)] and monodentate [at the M(II)] coordination modes. The carboxylate-malonate group in them adopts the anti-syn conformation with intramolecular ReM separation of 5.098(8) (2) and 4.947(2) Å (5). The magnetic properties of 1-6 were investigated in the temperature range 1.9-295 K. The magnetic behaviour of 1 is the expected for a magnetically isolated Re(IV) complex with a large value of the zero-field splitting (2D ca. -70 cm(-1)) whereas weak antiferromagnetic interactions between Re(IV) and M(II) are observed in the heterobimetallic compounds 2 (J = -0.63 cm(-1)), 3 (J = -1.37 cm(-1)), 4a (J = -1.29 cm(-1)), 5 (J = -1.83 cm(-1)) and 6 (J = -0.26 cm(-1)). Remarkably, 4b behaves as a ferrimagnetic chain with regular alternating Re(IV) and Mn(II) cations (J = -2.64 cm(-1)).

Heterotetranuclear oxalato-bridged Re(IV)3M(II) (M = Mn, Fe, Co, Ni, Cu) complexes: a new example of a single-molecule magnet (M = Ni).

The use of the mononuclear species (NBu(4))(2)[Re(IV)Cl(4)(ox)] (NBu(4)(+) = tetra-n-butylammonium cation; ox = oxalate dianion) as a ligand toward fully solvated divalent first-row transition-metal ions affords the tetranuclear complexes (NBu(4))(4)[{Re(IV)Cl(4)(mu-ox)}(3)M(II)] with M = Mn (1), Fe (2), Co (3), Ni (4), and Cu (5). Their structure is made up of discrete [{ReCl(4)(mu-ox)}(3)M](4-) anions and bulky NBu(4)(+) cations. The complexes 2-5 crystallize in the triclinic system with space group P1; 2 and 5 as well as 3 and 4 are isostructural. The Re and M atoms exhibit somewhat distorted ReCl(4)O(2) and MO(6) octahedral surroundings, with the oxalate groups adopting the bis-bidentate bridging mode. Magnetic susceptibility measurements on polycrystalline samples of 1-5 in the temperature range 1.9-300 K show the occurrence of intramolecular antiferromagnetic [J = -1.30 cm(-1) (1)] and ferromagnetic couplings [J = +1.62 (2), +3.0 (3), +16.3 (4), and +4.64 cm(-1) (5)], with the Hamiltonian being defined as H = -J[S(M)(S(Re1) + S(Re2) + S(Re3))]. Compound 4 is the first example of an oxalato-bridged heterometallic species that behaves as a single-molecule magnet with a ground-state spin S = (11)/(2) and D = -0.8(1) cm(-1), as shown by the study of its static and dynamic magnetic properties and a high-frequency electron paramagnetic resonance study on polycrystalline samples together with detailed micro-SQUID measurements on single crystals.

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).

X-ray structure of [ReCl4(mu-ox)Cu(pyim)2]: a new heterobimetallic Re(IV)Cu(II) ferrimagnetic chain.

A new heterobimetallic Re(IV)Cu(II) compound has been prepared and its crystal structure determined by single-crystal X-ray diffraction; magnetic susceptibility measurements show that this compound behaves as a ferrimagnetic chain with significant antiferromagnetic interactions between Re(IV) and Cu(II) metal ions.

Heterotrimetallic oxalato-bridged ReIV2MII complexes (M=Mn, Co, Ni, Cu): synthesis, crystal structure, and magnetic properties.

The use of the (NBu4)2[ReIVCl4(ox)] mononuclear species as a ligand toward divalent first row transition metal ions in the presence of imidazole affords the new trinuclear compounds of formula (NBu4)2[{ReIVCl4(mu-ox)}2MII(Him)2] [NBu4+=tetra-n-butylammonium cation, ox=oxalate dianion, Him=imidazole; M=Mn (1), Co (2), Ni (3), Cu (4)] whose preparation, crystal structures, and magnetic properties are reported. 1-4 are isostructural complexes which are made up of discrete trinuclear [{ReIVCl4(mu-ox)}2MII(Him)2]2- anions and bulky NBu4+ cations. The Re and M atoms exhibit somewhat distorted octahedral surroundings which are built by four chloro and two oxalate oxygens (Re) and two imidazole nitrogen and four oxalate oxygen atoms (M), the central M atom being linked to the two peripheral Re atoms through bis-bidentate oxalate. The values of the Re...M separation across bridging oxalate vary in the range 5.646(2) (M=Ni) to 5.794(2) A (M=Mn). Magnetic susceptibility measurements on polycrystalline samples of 1-4 in the temperature range 1.9-300 K show the occurrence of significant intramolecular antiferro- (1) and ferromagnetic (2-4) interactions. The nature and magnitude of the magnetic coupling in 1-4 are qualitatively understood through orbital symmetry considerations.

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.

Magnetic properties and molecular structures of binuclear (2-pyrazinecarboxylate)-bridged complexes containing Re(IV) and M(II) (M = Co, Ni).

Three novel Re(iv) compounds, the mononuclear complex Bu(4)N[ReBr(5)(Hpyzc)] (1) and the heterobimetallic complexes [ReBr(5)(mu-pyzc)M(dmphen)(2)].2CH(3)CN [M = Co (2), Ni (3)] (Hpyzc = 2-pyrazinecarboxylic acid, dmphen = 2,9-dimethyl-1,10-phenanthroline), have been synthesized and their crystal structures determined by single-crystal X-ray diffraction. The structure of 1 consists of [ReBr(5)(Hpyzc)](-) complex anions and tetrabutylammonium cations, Bu(4)N(+). The Re(iv) is surrounded by five bromide anions and a N-donor Hpyzc monodentate ligand, in a distorted octahedral environment. The structures of 2 and 3 consist of dinuclear units [ReBr(5)(mu-pyzc)M(dmphen)(2)], with the metal ions linked by a pyzc bridge ligand, being bidentate toward M(II) and monodentate toward Re(IV). The environment of Re(IV) is the same as in 1, whereas M(II) is six-coordinate, being surrounded by four nitrogen atoms of two bidentate dmphen ligands and one oxygen atom and one nitrogen atom of the pyzc anion. The magnetic properties of 1-3 were investigated in the temperature range 2.0-300 K. 1 shows the expected magnetic behavior for a mononuclear Re(IV) complex with a weak intermolecular antiferromagnetic coupling at low temperatures. The bimetallic complexes exhibit an intramolecular ferromagnetic coupling between Re(IV) and the M(II) ion (Co, Ni).

Synthesis, crystal structure and magnetic properties of novel heterobimetallic malonate-bridged MIIReIV complexes (M = Mn, Fe, Co and Ni).

Five novel ReIV-MII bimetallic complexes of formula [ReCl4(mu-mal)M(dmphen)2].MeCN [M = Co (1), Fe (2) and Ni (3)], [ReCl4(mu-mal)Ni(dmphen)(MeCN)2(H2O)].(MeCN)0.5(H2O)0.5 (4), and [ReCl4(mu-mal)Mn(dmphen)(H2O)2].dmphen.MeCN.H2O (5) (mal = malonate dianion, dmphen = 2,9-dimethyl-1,10-phenanthroline) have been synthesized, and the structures of 1, 2, 4, and 5 determined by single-crystal X-ray diffraction. The structures of 1 and 2 consist of neutral [ReCl4(mu-mal)M(dmphen)2] dinuclear units where the metal ions are linked through a malonate ligand which adopts simultaneously the bidentate (at ReIV) and monodentate (at MII) coordination modes. The bridging carboxylate-malonate group in them exhibits the anti-syn conformation. The rhenium atom is six-coordinated with four chloro atoms and two carboxylate-oxygens from a bidentate malonate group in a distorted octahedral environment. The M atom is five-coordinated being surrounded by four nitrogen atoms of two bidentate dmphen ligands and one oxygen atom of the malonato ligand. There are also ReIV(mu-mal)NiII dinuclear units in 4 with the same type of bridge, but the nickel atom is six-coordinated with one bidentate dmphen, two molecules of acetonitrile and one water molecule as peripheral ligands. Compound 5 is a neutral chain compound with regular alternating rhenium(IV) and manganese(II) ions. The [ReCl4(mal)]2- units in each chain act as bismonodenate ligands through two carboxylate-oxygen atoms toward [Mn(dmphen)(H2O)2]2+ entities. Variable-temperature magnetic measurements of 1-5 in the temperature range 2.0-300 K show the occurrence of weak antiferromagnetic interactions which are rationalized on the basis of the structural knowledge and simple orbital considerations. Very noticeable is compound 5, a ferrimagnetic chain with regular alternating ReIV and MnII cations.

Ligand design for heterobimetallic single-chain magnets: synthesis, crystal structures, and magnetic properties of MIICuII (M=Mn, Co) chains with sterically hindered methyl-substituted phenyloxamate bridging ligands.

Two new series of neutral oxamato-bridged heterobimetallic chains of general formula [MCu(L(x))(2)] m DMSO (m=0-4) (L(1)=N-2-methylphenyloxamate, M=Mn (1 a) and Co (1 b); L(2)=N-2,6-dimethylphenyloxamate, M=Mn (2 a) and Co (2 b); L(3)=N-2,4,6-trimethylphenyloxamate, M=Mn (3 a) and Co (3 b)) have been prepared by reaction between the corresponding anionic oxamatocopper(II) complexes [Cu(Lx)2](2-) with Mn(2+) or Co(2+) cations in DMSO. The crystal structures of [CoCu(L2)2(H2O)2] (2 b') and [CoCu(L3)2(H2O)2]4 H2O (3 b') have been solved by single-crystal X-ray diffraction methods. Compounds 2 b' and 3 b' adopt zigzag and linear chain structures, respectively. The intrachain Cu...Co distance through the oxamate bridge is 5.296(1) A in 2 b' and 5.301(2) A in 3 b', while the shortest interchain Co...Co distance is 5.995(5) A in 2 b' and 8.702(3) A in 3 b', that is, the chains are well isolated in the crystal lattice due to the presence of the bulky methyl-substituted phenyl groups. Although both Mn(II)Cu(II) and Co(II)Cu(II) chains exhibit ferrimagnetic behaviour with moderately strong intrachain antiferromagnetic coupling (-J(Mn,Cu)=24.7-27.9 cm(-1) and -J(Co,Cu)=35.0-45.8 cm(-1); H= Sigma -J(M,Cu)S(M,i)S(Cu,i)), only the Co(II)Cu(II) chains show slow magnetic relaxation at low temperatures (T(B)<3.5 K), which is characteristic of single-chain magnets (SCMs) because of the high magnetic anisotropy of the Co(II) ion. The blocking temperatures T(B) along this series of chains vary according to the steric hindrance of the aromatic substituent of the oxamate ligand in the series L(1)