Oxalato Bridge Research Articles

Syntheses and crystal structures of three novel oxalate coordination compounds: Rb2Co(C2O4)2·4H2O, Rb2CoCl2(C2O4) and K2Li2Cu(C2O4)3·2H2O.

Single crystals of three novel transition-metal oxalates, dirubidium di-aqua-dioxalatocobalt(II) dihydrate or dirubidium cobalt(II) bis-(oxalate) tetra-hydrate, Rb2[Co(C2O4)2(H2O)2]·2H2O, (I), catena-poly[dirubidium [[di-chlorido-cobalt(II)]-μ-oxalato]] or dirubidium cobalt(II) dichloride oxalate, {Rb2[CoCl2(C2O4)]} n , (II), and poly[dipotassium [tri-μ-oxalato-copper(II)dilithium] dihydrate] or dipotassium dilithium copper(II) tris-(oxalate) dihydrate, {K2[Li2Cu(C2O4)3]·2H2O} n , (III), have been grown under hydro-thermal conditions and their crystal structures determined using single-crystal X-ray diffraction. The structure of (I) exhibits isolated octa-hedral [Co(C2O4)2(H2O)2] units, whereas (II) consists of trans chains of Co2+ ions bridged by bidentate oxalato ligands and (III) displays a novel tri-periodic network of Li+ and Cu2+ ions linked by oxalato bridging ligands.

Sonochemical synthesis, crystal structure and catalase interaction of a new 2D coordination polymer based on isoniazid and oxalato bridges

A new Mn(II) complex based on oxalato (ox2−) and isoniazid (INH), formulated as [Mn(µ-ox)(µ-NIH (N,O)) (µ-NIH (N)Cl]n (1) has been synthesized under sonochemical irradiation. The molecular structure of complex 1 was studied by elemental analysis, Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), differential thermal analysis (DTA), vibrating sample magnetometer (VSM), and single-crystal X-ray diffraction (SC-XRD). This complex belongs to a monoclinic system with space group P21/c. X-ray crystallography data revealed Mn(II), adopts a distorted octahedral geometry formed by two nitrogen atoms, three oxygen atoms, and one chloride anion. The results of VSM revealed that in the applied magnetic field up to 15,000 Oe, complex 1 is a weak ferromagnet. The interaction of complex 1 with bovine liver catalase (BLC) was investigated by spectroscopic methods. The enzymatic function of BLC decreased to 45.6% when the concentration of the complex was 6.0 × 10−6 M. Fluorescence results revealed that the combination of BLC with the complex is subjected to static quenching mechanism (Kb = 1.73 and 0.38 × 105 M−1at 300 and 310 K, respectively). The interaction process was spontaneous, exothermic, and enthalpy-driven, with a major role of Van der Waals and hydrogen bond forces. UV-Vis, 3D, and synchronous fluorescence measurements indicated the changes in the microenvironment residues of BLC in the presence of complex 1. In conclusion, the above complex can interact with catalase and so inhibit its catalytic activity for the decomposition of hydrogen peroxide.

Supramolecular architectures of metal-oxalato coordination polymers bearing N-tethered adenine nucleobases

Reactions of N-methylated adenine (9-methyladenine and 3-methyladenine) with water-soluble oxalato complexes in the presence of potassium oxalate yields a series of oxalato-bridged complexes with the nucleobases as pendant ligands whose crystal structures and magnetic properties are reported herein. The complexes [M2(µ-ox)2(9Meade)3]n [M(II) = Zn (1), Cu (2); where ox = oxalato and 9Meade = 9-methyladenine] are composed of infinite corrugated one-dimensional chains in which two types of metal(II) centres are sequentially bridged by asymmetric bis-bidentate oxalato ligands and their coordination polyhedra are filled by N7-coordinated 9-methyladenine molecules giving rise to two different chromophores: an octahedral N2O4 donor set with the nucleobase moieties in trans-arrangement, and square based pyramidal NO4 coordination polyhedra. The cohesiveness of their supramolecular 3D architectures is achieved by means of an extensive network of non-covalent interactions including a short contact between the minor groove N3 site of the model 9-methyladenine and the oxalato bridging ligand from a neighbouring chain. This unconventional interaction between the lone pair of the pyrimidinic nitrogen atom of the nucleobase and the π-system of the oxalate anion has been analysed and discussed in the light of available structural data for analogous systems. The compounds {[M(µ-ox)(H2O)(3Meade)]·H2O}n [M(II) = Zn (3), Co (4) and Mn (5); where 3Meade = 3-methyladenine], and {[Cu(µ-ox)(3Meade)2]·4H2O}n (6) are comprised of zig–zag metal-oxalato chains, with the oxalato adopting a symmetric bis-bidentate coordination mode. The octahedral environment of the metals is completed in a cis-arrangement by one water molecule and the imidazole N7 donor site of a 3-methyladenine ligand for 3–5, and by two N7-coordinated nucleobases for 6. The crystal packing of the chains leads to the presence of channels with dimensions of 5 × 10 Å for 6, and 4 × 6 Å for 3–5 which are occupied by crystallization water molecules. The non-covalent interactions of the nucleobases among them and with the metal-oxalato framework have been studied in detail as well as the magnetic interactions mediated by the bridging oxalato ligand.

Magneto-structural correlations in asymmetric oxalato-bridged dicopper(II) complexes with polymethyl-substituted pyrazole ligands

Two oxalato-bridged dinuclear copper(II) complexes, [{Cu(Hdmpz)3}2(μ-ox)](ClO4)2·2H2O (1) and [{Cu(Htmpz)3}2(μ-ox)](ClO4)2·2H2O (2) (Hdmpz = 3,5-dimethyl-1H-pyrazole and Htmpz = 3,4,5-trimethyl-1H-pyrazole), have been synthesized and structurally and magnetically characterized. The crystal structures of 1 and 2 consist of asymmetric bis-bidentate μ-oxalatodicopper(II) complex cations with two short [Cu–O = 1.976(2) (1) and 1.973(2) Å (2)] and two long copper–oxygen bonds [Cu–O = 2.122(2) (1) and 2.110(2) Å (2)]. The environment at each CuII ion in 1 and 2 is closer to the trigonal bipyramidal geometry than to the square pyramidal [τ = 0.633 (1) and 0.711 (2)]. The magnetic properties of 1 and 2 show moderate antiferromagnetic coupling between the CuII ions through the oxalato bridge [J = −129 (1) and 161 cm−1 (2); H = −JS1 · S2 with S1 = S2 = SCu = ½]. A thorough magneto-structural analysis has been carried out for the family of asymmetric μ-oxalatodicopper(II) complexes with different terminal ligands to determine the influence on the sign and strength of the magnetic coupling of subtle structural factors, such as the trigonal distortion of the metal geometry and the lengthening or the asymmetry of the metal-oxalato bond distances.

Dinuclear copper(II) complexes with ethylenediamine derivative and bridging oxalato ligands: solvatochromism and density functional theory studies

Two oxalato-bridged copper(II) complexes of formula, [Cu2(L1)2(µ-ox)](NO3)2·H2O, 1 and [Cu2(L2)2(µ-ox)](NO3)2·H2O, 2 (ox = oxalato dianion, L1 = N,N-dimethyl,N′-benzylethane-1,2-diamine, L2 = N,N-diethyl,N′-benzylethane-1,2-diamine), have been synthesized and characterized by elemental analyses, spectroscopic (IR, UV–Vis) data and molar conductance measurements. The crystal structure of complex 1 was determined by X-ray diffraction analysis, revealing two centrosymmetric dinuclear units. The first consists of a [Cu2(L1)2(µ-ox)(NO3)2] molecule, in which each Cu(II) center is in a square-pyramidal environment, providing two nitrogen atoms from the diamine-chelating ligands plus two oxygen atoms from the oxalate in the basal plane and an oxygen of the nitrate group in the axial position. The second unit [Cu2(L1)2(µ-ox)(H2O)2](NO3)2 has a similar structure, but the apical sites are occupied by water ligands and the nitrate anions are free from coordination. Both complexes are solvatochromic. Their solvatochromism was investigated with different solvent parameter models using SPSS/PC and DFT methodology. The solvatochromic behaviors of the complexes were also explored by TD-DFT in ethanol and acetonitrile solvents. The calculated visible absorption spectra were in accord with the experimental results.

New dinuclear copper complexes incorporating bis(imidazolyl) based ligands and bidentate–monodentate oxalate bridges. Crystal structure and magnetic properties of [Cu2(BIM)2(C2O4)2]·4H2O and [Cu2(BIK)2(C2O4)2] (BIM = bis(2-imidazolyl)methane), BIK = bis(2-imidazolyl)ketone). Exploring magneto-structural correlations

This paper reports the synthesis, X-ray crystal structure and magnetic characterization of two novel copper(II) dinuclear compounds including bis(imidazolyl) ligands and oxalate anions, [Cu2(BIM)2(C2O4)2]·4H2O (1) (BIM=bis(2-imidazolyl)methane) and [Cu2(BIK)2(C2O4)2] (2) (BIK=bis(2-imidazolyl)ketone). The oxalate anion acts as bidentate–monodentate in both cases, although it exhibits different coordination bridging modes: whereas in compound 1 a μ1,1,2-oxalato is observed, a μ1,2,3-oxalato is found in compound 2. In both cases, the 3D framework is held together by a combination of H-bonding and aromatic-aromatic interactions provided by the convenient structural features of BIM and BIK ligands and oxalate. EPR spectra are indicative of an essentially dx2-y2 ground state for the copper(II) ions in both compounds. Magnetic susceptibility measurements reveal the existence of weak antiferromagnetic exchange interactions between the copper(II) ions (2J=−0.33(1)cm−1 for compound 1 and 2J=−1.45 (1)cm−1 for compound 2. Finally, the reported values of the singlet–triplet gap are compared with those observed in related copper(II) compounds with bidentate–monodentate out-of-plane oxalato bridges.

Ascorbic acid decomposition into oxalate ions: a simple synthetic route towards oxalato-bridged heterometallic 3d-4f clusters.

Two types of oxalato-bridged heterometallic 3d-4f dodeca- and hexanuclear compounds have been obtained by connecting six bi- and, respectively, trinuclear moieties through oxalato bridges arising from the slow decomposition of the L-ascorbic acid.

Synthesis, crystal structure and magnetic properties of H2tppz[ReCl6] and [Cu(bpzm)2(μ-Cl)ReCl3(μ-ox)Cu(bpzm)2(μ-ox)ReCl3(μ-Cl)]n.

Two new Re(iv) compounds of formulae H2tppz[ReCl6] (1) and [Cu(bpzm)2(μ-Cl)ReCl3(μ-ox)Cu(bpzm)2(μ-ox)ReCl3(μ-Cl)]n (2) [tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine and bpzm = bis(pyrazolyl-1-yl)methane] have been prepared and their crystal structures determined by X-ray diffraction on single crystals. Compound 1 is a mononuclear species whose structure consists of octahedral hexachlororhenate(iv) anions and diprotonated H2tppz(2+) cations which are arranged in the unit cell as alternating anionic and cationic layers, held together by electrostatic forces. The structure of 2 is made up of alternating [Cu(1)(bpzm)2](2+) and [(ox)ReCl3(μ-Cl)Cu(2)(bpzm)2(μ-Cl)ReCl3(ox)](2-) entities interlinked by oxalate bridges to afford a neutral heterobimetallic chain. The oxalate group adopts the didentate (at Re)/monodentate (at Cu) bridging mode. The magnetic behavior of 1 and 2 has been investigated over the temperature range 1.9-295 K. 1 is a magnetically diluted Re(iv) complex, the relatively large value of the zero-field splitting of the ground level [D = -15.8(2) cm(-1)] accounting for the variation of χMT in the low temperature range. Weak intrachain ferromagnetic interactions between Re(iv) and Cu(ii) through oxalate (J1 = +0.15 cm(-1)) and single chloro (J2 = +4.9 cm(-1)) bridges occur in 2 which are obscured by the large zero-field splitting of the Re(iv) ion (DRe = 42 cm(-1)). In addition, interchain antiferromagnetic interactions are also involved in 2 which are responsible for the metamagnetic behavior observed, the value of the critical dc magnetic field (Hc) being 20 kOe.

Self-assembly of Schiff-base palladacycle-based discrete pseudo-macrocycles: Evidence for hemilability of oxalate ligand

Bis-bidentate tetra-coordinated oxalato bridged binuclear Schiff-base palladacycles [Pd{C,N-κ2-(4-R)C6H3CHNC6H3-2,6-i-Pr2]2(μ-η2-η2-C2O4) (R = H; OMe) were synthesized. Reactions of μ-oxalato bridged Schiff-base palladacycles [Pd{C,N-κ2-(4-R)C6H3CHNC6H3-2,6-i-Pr2]2(μ-η2-η2-C2O4) (R = H; OMe) with 1,4-bis(diphenylphosphino)butane (dppb) and 1,4-bis(diphenylphosphino)pentane (dppp) generated discrete pseudo-macrocycles with 1,1′-bicoordinated oxalato bridge. Unexpectedly, μ-oxalato bridged Schiff-base palladacycle [Pd(C,N-κ2-C6H4CHNC6H3-2,6-i-Pr2)]2(μ-η2-η2-C2O4) reacted with PPh3 to form unusual bidentate/monodentate tri-coordinated oxalato bridged binuclear cyclopalladated complex [Pd(C,N-κ2-C6H4CHNC6H3-2,6-i-Pr2)(PPh3)](μ-η2-η1-C2O4)[Pd(C-κ1-C6H4CHNC6H3-2,6-i-Pr2)(PPh3)].

Absence of a magnetic interaction in a dinuclear copper complex? The case of a crossed axial–equatorial oxalate coordination mode

A simple and easy preparation of the hydrogen oxalate ligand (HOOCCOO)−, with only one deprotonated carboxylic function, is described. 13C NMR spectroscopy furnishes a straightforward characterization of this interesting ligand. This ligand coordinates in its monodeprotonated form to a CuII complex with a free coordination position, yielding a complex that presents a very weak antiferromagnetic interaction. In a subsequent step, the second deprotonation allows the isolation of an oxalato-bridged dinuclear CuII complex, which is characterized by structural determination, the copper ions being pentacoordinate in an equivalent centrosymmetry-related environment. DFT calculations show that the magnetic interaction through the oxalato bridge is strictly equal to 0cm−1, demonstrating that the singlet and triplet states of this oxalato-bridged dinuclear CuII complex have the same energy. This dinuclear complex presents a rhombic EPR spectrum, with three well-defined g values, at room temperature as well as at 100K.

A Two-Dimensional Oxamate- and Oxalate-Bridged CuIIMnII Motif: Crystal Structure and Magnetic Properties of (Bu4N)2[Mn2{Cu(opba)}2ox

A new compound of formula (Bu4N)2[Mn2{Cu(opba)}2ox] (1) [Bu4N(+) = tetra-n-butylammonium cation, H4opba = 1,2-phenylenebis(oxamic acid), and H2ox = oxalic acid] has been synthesized and magneto-structurally investigated. The reaction of manganese(II) acetate, [Cu(opba)](2-), and ox(2-) in dimethyl sulfoxide yielded single crystals of 1. The structure of 1 consists of heterobimetallic oxamato-bridged Cu(II)Mn(II) chains which are connected through bis-bidentate oxalate coordinated to the manganese(II) ions to afford anionic heterobimetallic layers of 6(3)-hcb net topology. The layers are interleaved by n-Bu4N(+) counterions. Each copper(II) ion in 1 is four-coordinate in a square planar environment defined by two amidate-nitrogen and two carboxylate-oxygen atoms from the two oxamate groups of the obpa ligand. The manganese(II) ion is six-coordinate in a somewhat distorted octahedral surrounding that is built by two oxalate-oxygen and four carbonyl-oxygen atoms from two [Cu(opba)](2-) units. The magnetic properties of 1 in the temperature range 1.9-300 K correspond to those expected for the coexistence of intralayer antiferromagnetic interactions of the type copper(II)-manganese(II) across oxamato and manganese(II)-manganese(II) through oxalato bridges plus a weak spin canting in the very low temperature domain. Simulation of the magnetic data through quantum Monte Carlo methodology reveals the magnitude of the intralayer magnetic interactions [J(CuMn) = -32.5(3) cm(-1), and J(MnMn) = -2.7(3) cm(-1)], their values being within the range of those previously observed in lower nuclearity systems.

Syntheses, crystal structures, circular dichroism, and magnetic properties of chiral dinuclear and polymeric nickel(II) compounds

Chiral dinuclear nickel(II) complexes, [Ni(LR,R)(C2O4)Ni(LR,R)](ClO4)2·4CH3CN (3) and [Ni(LS,S)(C2O4)Ni(LS,S)](ClO4)2·4CH3CN (4) and chiral polymeric compounds, [Ni(LR,R)(CrO4)]n·2H2O·CH3CN (5) and [Ni(LS,S)(CrO4)]n·2H2O·CH3CN (6) have been synthesized and characterized (LR,R/S,S=1,8-di((R/S)-α-methylbenzyl)-1,3,6,8,10,13-hexaazacyclotetradecane). These chiral compounds were characterized by X-ray crystallography, circular dichroism, and molecular magnetism. The nickel(II) ions in 3 and 4 have a distorted octahedral geometry by coordination with four nitrogens of a macrocyclic ligand with chiral pendents in a folded conformation and two oxygens of an oxalate ion in the cis positions. The nickel(II) ions in 5 and 6 have a distorted octahedral geometry by coordination with four nitrogens of a macrocyclic ligand in a planar conformation and two oxygens of two chromate ions in the axial positions. Complexes 3 and 4 show strong antiferromagnetic interactions [3: g=2.36, J/kB=−29.9K (−20.8cm−1); 4: g=2.18, J/kB=−25.5K (−17.7cm−1)], while 5 and 6 exhibit weak antiferromagnetic couplings [5: g=2.25, J/kB=−1.20K (−0.83cm−1); 6: g=2.25, J/kB=−0.68K (−0.47cm−1)]. The former complexes occur strong antiferromagnetic interactions via the oxalato bridges within the nickel(II) dimers, the latter compounds are weak antiferromagnetic interactions through the chromate ions within the 1D polymers. The circular dichroism (CD) spectrum of 3 has exhibited two negative peaks at 336 and 533nm, and that of 4 has displayed an enantiomeric pattern. The CD spectrum of 5 has appeared a negative absorption above ca. 550nm, while that of 6 has shown an enantiomeric pattern in the same wavelength region.

Theoretical Insights into the Ferromagnetic Coupling in Oxalato-Bridged Chromium(III)-Cobalt(II) and Chromium(III)-Manganese(II) Dinuclear Complexes with Aromatic Diimine Ligands

Two novel heterobimetallic complexes of formula [Cr(bpy)(ox)(2)Co(Me(2)phen)(H(2)O)(2)][Cr(bpy)(ox)(2)]·4H(2)O (1) and [Cr(phen)(ox)(2)Mn(phen)(H(2)O)(2)][Cr(phen)(ox)(2)]·H(2)O (2) (bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline, and Me(2)phen = 2,9-dimethyl-1,10-phenanthroline) have been obtained through the "complex-as-ligand/complex-as-metal" strategy by using Ph(4)P[CrL(ox)(2)]·H(2)O (L = bpy and phen) and [ML'(H(2)O)(4)](NO(3))(2) (M = Co and Mn; L' = phen and Me(2)phen) as precursors. The X-ray crystal structures of 1 and 2 consist of bis(oxalato)chromate(III) mononuclear anions, [Cr(III)L(ox)(2)](-), and oxalato-bridged chromium(III)-cobalt(II) and chromium(III)-manganese(II) dinuclear cations, [Cr(III)L(ox)(μ-ox)M(II)L'(H(2)O)(2)](+)[M = Co, L = bpy, and L' = Me(2)phen (1); M = Mn and L = L' = phen (2)]. These oxalato-bridged Cr(III)M(II) dinuclear cationic entities of 1 and 2 result from the coordination of a [Cr(III)L(ox)(2)](-) unit through one of its two oxalato groups toward a [M(II)L'(H(2)O)(2)](2+) moiety with either a trans- (M = Co) or a cis-diaqua (M = Mn) configuration. The two distinct Cr(III) ions in 1 and 2 adopt a similar trigonally compressed octahedral geometry, while the high-spin M(II) ions exhibit an axially (M = Co) or trigonally compressed (M = Mn) octahedral geometry in 1 and 2, respectively. Variable temperature (2.0-300 K) magnetic susceptibility and variable-field (0-5.0 T) magnetization measurements for 1 and 2 reveal the presence of weak intramolecular ferromagnetic interactions between the Cr(III) (S(Cr) = 3/2) ion and the high-spin Co(II) (S(Co) = 3/2) or Mn(II) (S(Mn) = 5/2) ions across the oxalato bridge within the Cr(III)M(II) dinuclear cationic entities (M = Co and Mn) [J = +2.2 (1) and +1.2 cm(-1) (2); H = -JS(Cr)·S(M)]. Density functional electronic structure calculations for 1 and 2 support the occurrence of S = 3 Cr(III)Co(II) and S = 4 Cr(III)Mn(II) ground spin states, respectively. A simple molecular orbital analysis of the electron exchange mechanism suggests a subtle competition between individual ferro- and antiferromagnetic contributions through the σ- and/or π-type pathways of the oxalato bridge, mainly involving the d(yz)(Cr)/d(xy)(M), d(xz)(Cr)/d(xy)(M), d(x(2)-y(2))(Cr)/d(xy)(M), d(yz)(Cr)/d(xz)(M), and d(xz)(Cr)/d(yz)(M) pairs of orthogonal magnetic orbitals and the d(x(2)-y(2))(Cr)/d(x(2)-y(2))(M), d(xz)(Cr)/d(xz)(M), and d(yz)(Cr)/d(yz)(M) pairs of nonorthogonal magnetic orbitals, which would be ultimately responsible for the relative magnitude of the overall ferromagnetic coupling in 1 and 2.

Enhancing the Magnetic Coupling of Oxalato-Bridged ReIV2MII (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 Ĥ = -J [Ŝ(M)(Ŝ(Re1) + Ŝ(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.

Unexpected magnetic topology in the heterobimetallic [Re IVBr 4(μ-ox)Cu II(bpy) 2] compound

A novel oxalato-bridged rhenium(IV)-copper(II) compound, namely [Re IVBr 4(μ-ox)Cu II(bpy) 2] ( 1), has been obtained by reacting (PPh 4) 2[ReBr 4(ox)] with Cu(CF 3SO 3) 2 and 2,2′-bpy in CH 3CN, and its crystal structure determined by single-crystal X-ray diffraction. Intermolecular Br⋯Br interactions and nonbonding Cu⋯Br type contacts between the heterobimetallic dinuclear units lead to a two-dimensional supramolecular structure. Compound 1 behaves magnetically as a [Re IVCu II] 2 tetranuclear species with weak antiferromagnetic interactions through the oxalato bridge and intermolecular Br⋯Br contacts.

Low-Dimensional Copper(II) Complexes with the Trinucleating Ligand 2,4,6-Tris(di-2-pyridylamine)-1,3,5-triazine: Synthesis, Crystal Structures, and Magnetic Properties†

The preparation and structural characterization of three new copper(II) complexes of formula [Cu(3)(dipyatriz)(2)(H(2)O)(3)](ClO(4))(6) x 2 H(2)O (1), {[Cu(4)(dipyatriz)(2)(H(2)O)(2)(NO(3))(2)(ox)(2)](NO(3))(2) x 2 H(2)O}(n) (2), and [Cu(6)(dipyatriz)(2)(H(2)O)(9)(NO(3))(3)(ox)(3)](NO(3))(3) x 4 H(2)O (3) [dipyatriz = 2,4,6-tris(di-2-pyridylamine)-1,3,5-triazine and ox = oxalate] are reported. The structure of 1 consists of trinuclear units [Cu(3)(dipyatriz)(2)(H(2)O)(3)](6+) and uncoordinated perchlorate anions. The two dipyatriz molecules in 1 act as tris-bidentate ligands with the triazine cores being in a quasi eclipsed conformation. Each copper atom in 1 exhibits a distorted square pyramidal geometry CuN(4)O with four pyridyl-nitrogen atoms from two dipyatriz ligands building the basal plane and a water molecule occupying the axial position. The values of the intratrimer copper-copper separation are 8.0755(6) and 8.3598(8) A. Compound 2 exhibits a layered structure of copper(II) ions which are connected through bis-bidentate dipyatriz ligands and bidentate/outer monodentate oxalato groups. The copper atoms in 2 exhibit six- [Cu(1)N(4)O(2)] and five-coordination [Cu(2)N(2)O(3)]. A water molecule and three pyridyl-nitrogen atoms [Cu(1)] and two pyridyl-nitrogen plus two oxalate-oxygen atoms [Cu(2)] define the equatorial plane whereas either an oxalate-oxygen and a pyridyl-nitrogen [Cu(1)] or a nitrate-oxygen [Cu(2)] fill the axial positions. The copper-copper separation through the bridging oxalato is 5.6091(6) A whereas those across dipyatriz vary in the range 7.801(1)-9.079(1) A. The structure of compound 3 contains discrete cage-like hexacopper(II) units [Cu(6)(dipyatriz)(2)(H(2)O)(9)(NO(3))(3)(ox)(3)](3+) where two trinuclear [Cu(3)(dipyatriz)](6+) fragments are connected by three bis-bidentate oxalate ligands, the charge being balanced by three non-coordinated nitrate anions. The values of the intracage copper-copper distance are 5.112(3)-5.149(2) A (across oxalato) and 7.476(2)-8.098(2) A (through dipyatriz). Magnetic susceptibility measurements of polycrystalline samples of 1-3 in the temperature range 1.9-295 K show the occurrence of a weak antiferromagnetic interaction across dipyatriz in 1 [J = -0.08(1) cm(-1), the Hamiltonian being defined as (wedge)H = -J ((wedge)S(1).(wedge)S(2) + (wedge)S(1) x (wedge)S(3) + (wedge)S(2) x (wedge)S(3))] and weak ferro- (2) and strong antiferromagnetic (3) interactions through the oxalato bridge in 2 [J = +0.45(2) cm(-1)] and 3 [J = -390(1) cm(-1)]. The use of the dipyatriz-containing copper(II) species as a building block to design homo- and heterometallic magnetic compounds is analyzed and discussed.

First binuclear Cr(III)–Mn(III) oxalato-bridged complexes: Synthesis, crystal structures and magnetic properties

Two Cr(III)–Mn(III) binuclear complexes, with the general formula [{Mn(H 2O)(valen)}{Cr(AA)(C 2O 4) 2}] · 3H 2O, have been obtained by assembling [Mn((H 2O)(CH 3CN)(valen)] + and [Cr(AA)(C 2O 4) 2] − ions [H 2valen is a bicompartmental Schiff-base proligand, resulting from the 2:1 condensation of 3-methoxysalicyladehyde with ethylenediamine; AA = 2,2′-bipyridine (bipy) 1; 1,10-phenahroline (phen) 2]. In the two compounds the [Cr(AA)(C 2O 4) 2] − ions coordinate through one oxalato oxygen atom into one apical position of the manganese(III) ions, which exhibit an elongated octahedral stereochemistry. The other apical position is occupied by an aqua ligand. The intramolecular distances between the metal centers are 5,329 and 5.442 Å, for 1 and 2, respectively. The packing of the molecules in the crystal (the interactions at the supramolecular level) are governed by the self-complementarity of the {Mn(valen)(H 2O)} moieties. The aqua ligand of one moiety is hydrogen bonded to the oxygen atoms from the { O 2 O 2 ′ } compartment of a second complex yielding head-to-teal dimeric species. The magnetic properties of the two complexes have been investigated and reveal weak antiferromagnetic interactions mediated by the oxalato bridge (2 J = −2.12, and −2.02 cm −1 for 1 and 2, respectively). The zero-field-splitting effects for the two metal ions have been taken into account.

Rhenium(IV)–copper(II) heterobimetallic complexes: Synthesis, crystal structure and magnetic properties

Two Re(IV)–Cu(II) heterometallic complexes {(CuL α)[ReCl 4(ox)]} n (where L α = N-meso-5,12-Me 2-7,14-Et 2-[14]-4,11-dieneN 4), 1, and (CuL β)[ReCl 4(ox)] (L β = N-rac-5,12-Me 2-7,14-Et 2-[14]-4,11-dieneN 4 N-rac-5,12-Me 2-7,14-Et 2-[14]-4,11-dieneN 4), 2, were synthesized. The [CuL 2+] macrocyclic cation is coordinated from above and below by [ReCl 4(ox)] 2− units through the chloro-ligands and creates a chloro-bridged heterometallic Re IV–Cu II one-dimensional zig-zag chain. Compound 2 can be viewed as a heterobimetallic dinuclear unit, in which the Re(IV)-Cu(II) centers are linked by an oxalato bridge. The magnetic behavior of 1 and 2 has been investigated over the temperature range 1.8–300 K. Compound 1 behaves like a ferrimagnetic {Re(IV)–Cu(II)} bimetallic, one-dimensional chain with intrachain antiferromagnetic coupling. Compound 2 shows a weak antiferromagnetic interaction within the [Re(IV)–Cu(II)] unit along with a strong single-ion anisotropy, D(Re) = −63 cm −1.

Synthesis, Characterization, and Norbornene Polymerization Behavior of the Half-Sandwich Complexes [Cp*3M3(μ3-L)Cl3] and [Cp*M(2-SPyH)Cl2] (M = Ir, M = Rh, [L]3−= 1,3,5-Triazine-2,4,6-trithiolato, 2-SPy = 2-Pyridinethione)

The trinuclear complexes [Cp*3M3(μ3-L)Cl3] (3a, M = Ir; 3b, M = Rh; [L]3− = 1,3,5-triazine-2,4,6-trithiolato) have been synthesized via the reactions of the bridging oxalato complexes [Cp*2M2(μ-C2O4)Cl2] (2a, M = Ir; 2b, M = Rh) with the trisodium salt of 1,3,5-triazine-2,4,6-trithiol (Na3L), respectively. The reactions of half-sandwich iridium and rhodium complexes [Cp*MCl(μ-Cl)]2 with 2-pyridinethione gave the corresponding mononuclear complexes [Cp*M(2-SPyH)Cl2] (4a, M = Ir; 4b, M = Rh). All complexes have been characterized by elemental analyses and NMR and IR spectroscopy. The molecular structures of 3a,b and 4a,b have been determined by X-ray crystallography. The trinuclear iridium complex 3a shows catalytic activities for the polymerization of norbornene in the presence of methylaluminoxane (MAO) as cocatalyst.

Polyfunctional Inorganic−Organic Hybrid Materials: An Unusual Kind of NLO Active Layered Mixed Metal Oxalates with Tunable Magnetic Properties and Very Large Second Harmonic Generation

Mixed M(II)/M(III) metal oxalates, as "stripes" connected through strong hydrogen bonding by para-dimethylaminobenzaldeide (DAMBA) and water, form an organic-inorganic 2D network that enables segregation in layers of the cationic organic NLO-phore trans-4-(4-dimethylaminostyryl)-1-methylpyridinium, [DAMS+]. The crystalline hybrid materials obtained have the general formula [DAMS]4[M2M'(C2O4)6].2DAMBA.2H2O (M = Rh, Fe, Cr; M' = Mn, Zn), and their overall three-dimensional packing is non-centrosymmetric and polar, therefore suitable for second harmonic generation (SHG). All the compounds investigated are characterized by an exceptional SHG activity, due both to the large molecular quadratic hyperpolarizability of [DAMS+] and to the efficiency of the crystalline network which organizes [DAMS+] into head-to-tail arranged J-type aggregates. The tunability of the pairs of metal ions allows exploiting also the magnetic functionality of the materials. Examples containing antiferro-, ferro-, and ferri-magnetic interactions (mediated by oxalato bridges) are obtained by coupling proper M(III) ions (Fe, Cr, Rh) with M(II) (Mn, Zn). This shed light on the role of weak next-nearest-neighbor interactions and main nearest-neighbor couplings along "stripes" of mixed M(II)/M(III) metal oxalates of the organic-inorganic 2D network, thus suggesting that these hybrid materials may display isotropic 1D magnetic properties along the mixed M(II)/M(III) metal oxalates "stripes".