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.     

Syntheses, crystal structures, and magnetic properties of the oxalato-bridged mixed-valence complexes (FeII(bpm)3]2[FeIII2(ox)5].8H2O and FeII(bpm)3Na(H2O)2Fe(ox)(3).4H2O (bpm = 2,2'-bipyrimidine)

The preparation and crystal structures of two oxalato-bridged FeII-FeIII mixed-valence compounds, [FeII(bpm)3]2[FeIII2(ox)5].8H2O (1) and FeII(bpm)3Na(H2O)2FeIII(ox)(3).4H2O (2) (bpm = 2,2'-bipyrimidine; ox = oxalate dianion) are reported here. Complex 1 crystallizes in the triclinic system, space group P1, with a = 10.998(2) A, b = 13.073(3) A, c = 13.308(3) A, alpha = 101.95(2) degrees, beta = 109.20(2) degrees, gamma = 99.89(2) degrees, and Z = 1. Complex 2 crystallizes in the monoclinic system, space group P2(1)/c, with a = 12.609(2) A, b = 19.670(5) A, c = 15.843(3) A, beta = 99.46(1) degrees, and Z = 4. The structure of complex 1 consists of centrosymmetric oxalato-bridged dinuclear high-spin iron(III) [Fe2(ox)5]2- anions, tris-chelated low-spin iron(II) [Fe(bpm)3]2+ cations, and lattice water molecules. The iron atoms are hexacoordinated: six oxygen atoms (iron(III)) from two bidentate and one bisbidentate oxalato ligands and six nitrogen atoms (iron(II)) from three bidentate bpm groups. The Fe(III)-O(ox) and Fe(II)-N(bpm) bond distances vary in the ranges 1.967(3)-2.099(3) and 1.967(4)-1.995(3) A, respectively. The iron(III)-iron(III) separation across the bridging oxalato is 5.449(2) A, whereas the shortest intermolecular iron(III)-iron(II) distance is 6.841(2) A. The structure of complex 2 consists of neutral heterotrinuclear Fe(bpm)2Na(H2O)2Fe(ox)3 units and water molecules of crystallization. The tris-chelated low-spin iron(II) ([Fe(bpm)3]2+) and high-spin iron(III) ([Fe(ox)3]3-) entities act as bidentate ligands (through two bpm-nitrogen and two oxalato-oxygen atoms, respectively) toward the univalent sodium cation, yielding the trinuclear (bpm)2Fe(II)-bpm-Na(I)-ox-Fe(III)(ox)2 complex. Two cis-coordinated water molecules complete the distorted octahedral surrounding of the sodium atom. The ranges of the Fe(II)-N(bpm) and Fe(III)-O(ox) bond distances [1.968(6)-1.993(5) and 1.992(6)-2.024(6) A, respectively] compare well with those observed in 1. The Na-N(bpm) bond lengths (2.548(7) and 2.677(7) A) are longer than those of Na-O(ox) (2.514(7) and 2.380(7) A) and Na-O(water) (2.334(15) and 2.356(12) A). The intramolecular Fe(II)...Fe(III) separation is 6.763(2) A, whereas the shortest intermolecular Fe(II)...Fe(II) and Fe(III)...Fe(III) distances are 8.152(2) and 8.992(2) A, respectively. Magnetic susceptibility measurements in the temperature range 2.0-290 K for 1 reveal that the high-spin iron(III) ions are antiferromagnetically coupled (J = -6.6 cm-1, the Hamiltonian being defined as H = -JS1.S2). The magnitude of the antiferromagnetic coupling through the bridging oxalato in the magneto-structurally characterized family of formula [M2(ox)5](2m-10)+ (M = Fe(III) (1), Cr(III), and Ni(II)) is analyzed and discussed by means of a simple orbital model.     

New extended magnetic systems based on oxalate and iron(III) ions

A series of oxalate-bridged iron(III) complexes have been synthesized by the reaction of FeCl 3 with oxalic acid (H 2ox) and XCl, where X is a substituted univalent ammonium or an alkaline cation. We have obtained basically two different types of compounds by varying the nature and the shape of the counterion, with the dimensionality of the resulting product being strongly influenced by the counterion. Three-dimensional (3D) networks of oxo- and oxalato-bridged iron(III) ions of the general formula {X 2[Fe 2O(ox) 2Cl 2]. pH 2O} n have been obtained for X = Li (+) ( 1), Na (+) ( 2), and K (+) ( 3) with p = 4 and X = MeNH 3 (+) ( 4), Me 2NH 2 (+) ( 5), and EtNH 3 (+) ( 6) with p = 2. Similar 3D hydroxo- and oxalato-bridged iron(III) networks of the formula {X[Fe 2(OH)(ox) 2Cl 2].2H 2O} n resulted for X = EtNH 3 (+) ( 7a) and PrNH 3 (+) ( 8). Compound 7a undergoes a solid-to-solid transformation, leading to a new species of the formula {(H 3O)(EtNH 3)[Fe 2O(ox) 2Cl 2].H 2O} n ( 7b). Chainlike compounds of the formula {X 2[Fe 2(ox) 2Cl 4]. pH 2O} n [X = Me 2NH 2 (+)( 9, p = 1), Me 3NH (+) ( 10, p = 2), and Me 4N (+) ( 11, p = 0)] have been obtained for the bulkier alkylammonium cations. Magnetic susceptibility measurements in the temperature range 1.9-295 K show the occurrence of weak ferromagnetic ordering due to spin canting in the 3D networks 1- 8, with the value of the critical temperature ( T c) varying with the cation in the range 26 K ( 2) to 70 K ( 8) without significant structural modifications. The last three one-dimensional compounds exhibit the typical behavior of antiferromagnetically coupled chains of interacting spin sextets [ J = -8.3 ( 9), -6.9 ( 10), and -8.4 ( 11) cm (-1) with H = - J summation operator i S i S i+1 ].     

Oxalate-based soluble 2D magnets: the series [K(18-crown-6)]3[M(II)3(H2O)4{M(III)(ox)3}3] (M(III) = Cr, Fe; M(II) = Mn, Fe, Ni, Co, Cu; ox = C2O4(2-); 18-crown-6 = C12H24O6)

The synthesis and magnetic properties of the oxalate-based molecular soluble magnets with general formula [K(18-crown-6)] 3[M (II) 3(H 2O) 4{M (III)(ox) 3} 3] (M (III) = Cr, Fe; M (II) = Mn, Fe, Ni, Co, Cu; ox = C 2O 4 (2-)) are here described. All the reported compounds are isostructural and built up by 2D bimetallic networks formed by alternating M (III) and M (II) ions connected through oxalate anions. Whereas the Cr (III)M (II) derivatives behave as ferromagnets with critical temperatures up to 8 K, the Fe (III)M (II) present ferri- or weak ferromagnetic ordering up to 26 K.     

Structural analysis of the solid amorphous binuclear complexes of iron(III) and aluminum(III) with chromium(III)-DTPA chelator using energy dispersive X-ray diffraction

This paper is concerned with the structural data obtained for two amorphous binuclear complexes of iron(III) and aluminum(III) with chromium(III)-diethylentriaminepentaacetic acid (chromium(III)-DTPA, CrL(2)(-)) using the energy-dispersive X-ray diffraction technique. Fe(OH)CrL(H(2)O)(6) and Al(OH)CrL(H(2)O)(6) are binuclear complexes, the metals ions being bridged via oxygen atoms. The metal ions are all octahedrally coordinated.     

Synthesis, structure, and magnetic ordering of layered (2-D) V-based tris(oxalato)metalates

The reaction of K3[M(III)(ox)3].3H2O [M = V (1), Cr; ox = oxalate], Mn(II)/V(II), and [N(n-Bu)4]Br in water leads to the isolation of 2-D V-based coordination polymers, [[N(n-Bu)4][Mn(II)V(III)(ox)3]]n (2), [[N(n-Bu)4][V(II)Cr(III)(ox)3]]n (3), [[N(n-Bu)4][V(II)V(III)(ox)3]]n (4), and an intermediate in the formation of 4, [[N(n-Bu)4][V(II)V(III)(ox)3(H2O)2]]n.2.5H2O (4a), while 1-D [V(II)(ox)(H2O)2]n (5) is obtained by using Na2ox and [V(OH2)6]SO4 in water. The structures of 1-5 have been investigated by single crystal and/or powder X-ray crystallography. In 1, V(III) is coordinated with three oxalate dianions as an approximately D3 symmetric, trigonally distorted octahedron. 1 is paramagnetic [mu(eff) = 2.68 mu(B) at 300 K, D = 3.84 cm(-1) (D/k(B) = 5.53 K), theta = -1.11 K, and g = 1.895], indicating an S = 1 ground state. 2 exhibits intralayer ferromagnetic coupling below 20 K, but does not magnetically order above 2 K, and 3 shows a strong antiferromagnetic interaction between V(II), S = 3/2 and Cr(III), S = 3/2 ions (theta = -116 K) within the 2-D layers. 4 and 4a magnetically order as ferrimagnets at T(c)'s, taken as the onset of magnetization, of 11 and 30 K, respectively. The 2 K remanent magnetizations are 2440 and 2230 emu.Oe mol(-1) and the coercive fields are 1460 and 4060 Oe for 4 and 4a, respectively. Both 4 and 4a clearly show frequency dependence, indicative of spin-glass-like behavior. The glass transition temperatures were at 6.3 and 27 K, respectively, for 4 and 4a. 1-D 5 exhibits antiferromagnetic coupling of -4.94 cm(-1) (H = -2Jsigma(i=1)n.S(i-1) - gmu(B)sigma(i=0)(n)H.S(i)) between the V(II) ions.     

Influence of the Peripheral Ligand Atoms on the Exchange Interaction in Oxalato-Bridged Nickel(II) Complexes: An Orbital Model. Crystal Structures and Magnetic Properties of (H(3)dien)(2)[Ni(2)(ox)(5)].12H(2)O and [Ni(2)(dien)(2)(H(2)O)(2)(ox)]Cl(2)

Two nickel(II) complexes of formula (H(3)dien)(2)[Ni(2)(ox)(5)].12H(2)O (1) and [Ni(2)(dien)(2)(H(2)O)(2)(ox)]Cl(2) (2) (dien = diethylenetriamine and ox = oxalate dianion) have been synthesized and characterized by single-crystal X-ray diffraction. 1 crystallizes in the orthorhombic system, space group Abnn, with a = 15.386(4) ?, b = 15.710(4) ?, c = 17.071(4) ?, and Z = 4. 2 crystallizes in the monoclinic system, space group P2(1)/c, with a = 10.579(1) ?, b = 7.258(1) ?, c = 13.326(1) ?, beta = 93.52(3) degrees, and Z = 2. The structures of 1 and 2 consist of dinuclear oxalato-bridged nickel(II) units which contain bidentate oxalate (1) and tridentate dien in the fac-conformation (2) as terminal ligands. Both features, oxalato as a peripheral ligand and dien in the fac-conformation (instead of its usual mer-conformation), are unprecedented in the coordination chemistry of nickel(II). The nickel atom is six-coordinated in both compounds, the chromophores being NiO(6) (1) and NiN(3)O(3) (2). The Ni-O(ox) bond distances at the bridge (2.072(4) ? in 1 and 2.11(1) and 2.125(9) ? in 2) are somewhat longer than those concerning the terminal oxalate (2.037(5) and 2.035(3) ? in 1). Magnetic susceptibility data of 1 and 2 in the temperature range 4.2-300 K show the occurrence of intramolecular antiferromagnetic coupling with J = -22.8 (1) and -28.8 (2) cm(-)(1) (J being the parameter of the exchange Hamiltonian H = -JS(A).S(B)). The observed value of -J in the investigated oxalato-bridged nickel(II) complexes, which can vary from 22 to 39 cm(-)(1), is strongly dependent on the nature of the donor atoms from the peripheral ligands. This influence has been analyzed and rationalized through extended Hückel calculations.     

Dinuclear cyano complexes of cobalt(III) and Iron(III) containing noninnocent 1,2,4,5-tetrakis(2-pyridinecarboxamido)benzene bridging ligands

Two new dinucleating ligands 1,2,4,5-tetrakis(2-pyridinecarboxamido)benzene, H(4)(tpb), and 1,2,4,5-tetrakis(4-tert-butyl-2-pyridinecarboxamido)benzene, H(4)(tbpb), have been synthesized, and the following dinuclear cyano complexes of cobalt(III) and iron(III) have been isolated: Na(2)[Co(III)(2)(tpb)(CN)(4)] (1); [N(n-Bu)(4)](2)[Co(III)(2)(tbpb)(CN)(4)] (2); [Co(III)(2)(tbpb(ox2))(CN)(4)] (3); [N(n-Bu)(4)](2)[Fe(III)(2)(tpb)(N(3))(4)] (4); [N(n-Bu)(4)](2)[Fe(III)(2)(tpb)(CN)(4)] (5); [N(n-Bu)(4)](2)[Fe(III)(2)(tbpb)(CN)(4)] (6). Complexes 2-4 and 6 have been structurally characterized by X-ray crystallography at 100 K. From electrochemical and spectroscopic (UV-vis, IR, EPR, M?ssbauer) and magnetochemical investigations it is established that the coordinated central 1,2,4,5-tetraamidobenzene entity in the cyano complexes can be oxidized in two successive one-electron steps yielding paramagnetic (tbpb(ox1))(3)(-) and diamagnetic (tbpb(ox2))(2)(-) anions. Thus, complex 6 exists in five characterized oxidation levels: [Fe(III)(2)(tbpb(ox2))(CN)(4)](0) (S = 0); [Fe(III)(2)(tbpb(ox1))(CN)(4)](-) (S = (1)/(2)); [Fe(III)(2)(tbpb)(CN)(4)](2)(-) (S = 0); [Fe(III)Fe(II)(tbpb)(CN)(4)](3)(-) (S = (1)/(2)); [Fe(II)(2)(tbpb)(CN)(4)](4)(-) (S = 0). The iron(II) and (III) ions are always low-spin configurated. The electronic structure of the paramagnetic iron(III) ions and the exchange interaction of the three-spin system [Fe(III)(2)(tbpb(ox1))(CN)(4)](-) are characterized in detail. Similarly, for 2 three oxidation levels have been identified and fully characterized: [Co(III)(2)(tbpb)(CN)(4)](2)(-) (S = 0); [Co(III)(2)(tbpb(ox1))(CN)(4)](-) (S = (1)/(2)); [Co(III)(2)(tbpb(ox2))(CN)(4)](0). The crystal structures of 2 and 3 clearly show that the two electron oxidation of 2 yielding 3 affects only the central tetraamidobenzene part of the ligand.     

Complexes of chromium(III) with 2,3-dihydroxynaphthalene-6-sulfonic acid and 4,5-dihydroxynaphthalene-2,7-disulfonic acid in aqueous solution

The chromium(III) complex species formed, in acidic and basic solutions at 25.0+/-0.1 degrees C, between Cr(III) and 2,3-dihydroxynaphthalene-6-sulfonic acid (2,3-DHN-6-SA, H(2)L(2-)) and 4,5-dihydroxynaphthalene-2,7-disulfonic acid (4,5-DHN-2,7-DSA, H(2)L(-)) were determined. Over the acidic pH range, the coordination of 2,3-DHN-6-SA and 4,5-DHN-2,7-DSA to Cr(III) in 1 : 1 mole ratio occurs, and CrL and CrL(-) type complexes are formed. At near neutral pH, CrL(OH)(-) and CrL(OH)(2-) type hydroxo complexes are formed. The acid-dissociation constants of ligands and the formation constants of chromium(III) complexes were determined in 0.1 m KNO(3) ionic medium by potentiometric titration using the BEST computer program. Thus, the removing capacities of these ligands could be examined by calculating the equilibrium concentration of Cr(III) that exists in the discharge water of various industries since Cr(III) ions are the main pollutants present during waste water treatment in our city, Bursa.     

Synthesis, characterization, and chiral behavior of S-bridged Co(III)Pt(II)Co(III) trinuclear complexes composed of bis(thiolato)-type octahedral units cis(S)-[Co(aet)(2)(en)](+) and/or trans(N)-[Co(D-pen- N,O,S)(2)](-) (aet = 2-aminoethanethiolate, D-pen = D-penicillaminate)

A series of linear-type Co(III)Pt(II)Co(III) trinuclear complexes composed of C(2)-cis(S)-[Co(aet)(2)(en)](+) (aet = 2-aminoethanethiolate) and/or Lambda(D)-trans(N)-[Co(D-pen-N,O,S)(2)](-) (D-pen = D-penicillaminate) were newly prepared, and their chiral behavior, which is markedly different from that of the corresponding Co(III)Pd(II)Co(III) complexes, is reported. The 1:1 reaction of an S-bridged Co(III)Ni(II)Co(III) trinuclear complex, [Ni[Co(aet)(2)(en)](2)]Cl(4), with K(2)[PtCl(4)] in water gave an S-bridged Co(III)Pt(II)Co(III) trinuclear complex, [Pt[Co(aet)(2)(en)](2)]Cl(4) ([1]Cl(4)), while the corresponding 1:2 reaction produced an S-bridged Co(III)Pt(II) dinuclear complex, [PtCl(2)[Co(aet)(2)(en)]]Cl ([2]Cl). Complex [1](4+) formed both racemic (DeltaDelta/LambdaLambda) and meso (DeltaLambda) forms, which were separated and optically resolved by cation-exchange column chromatography. An optically active S-bridged Co(III)Pt(II)Co(III) trinuclear complex having the pseudo LambdaLambda configuration, Lambda(D)Lambda(D)-[Pt[Co(D-pen-N,O,S)(2)](2)](0) (Lambda(D)Lambda(D)-[3]), was also prepared by reacting Lambda(D)-trans(N)-K[Co(D-pen-N,O,S)(2)] with K(2)[PtCl(4)] in a ratio of 2:1 in water. Treatment of the racemic Delta/Lambda-[2]Cl with Lambda(D)-trans(N)-K[Co(D-pen-N,O,S)(2)] in a ratio of 1:1 in water led to the formation of LambdaLambda(D)- and DeltaLambda(D)-[Pt[Co(aet)(2)(en)][Co(D-pen-N,O,S)(2)]](2+) (LambdaLambda(D)- and DeltaLambda(D)-[4](2+)) and DeltaDelta(D)-[Pt[Co(aet)(2)(en)][Co(D-pen-N,S)(2)(H(2)O)(2)]](2+) (DeltaDelta(D)-[4'](2+)), besides trace amounts of Lambda(D)Lambda(D)-[3] and DeltaDelta- and DeltaLambda-[1](4+). These Co(III)Pt(II)Co(III) complexes were characterized on the basis of electronic absorption, CD, and NMR spectra, along with single-crystal X-ray analyses for DeltaDelta/LambdaLambda-[1]Cl(4), DeltaLambda-[1]Cl(4), and DeltaLambda(D)-[4]Cl(2). Crystal data: DeltaDelta/LambdaLambda-[1]Cl(4).6H(2)O, monoclinic, space group C2/c with a = 14.983(3) A, b = 19.857(4) A, c = 12.949(3) A, beta = 113.51(2) degrees, V = 3532(1) A(3), Z = 4; DeltaLambda-[1]Cl(4).3H(2)O, orthorhombic, space group Pbca with a = 14.872(3) A, b = 14.533(3) A, c = 14.347(2) A, V = 3100(1) A(3), Z = 4; DeltaLambda(D)-[4]Cl(2).6H(2)O, monoclinic, space group P2(1) with a = 7.3836(2) A, b = 20.214(1) A, c = 10.622(2) A, beta = 91.45(1) degrees V = 1682.0(4) A(3), Z = 2.     

Crystal structures and magnetic properties of two octacyanotungstate(IV) and (V)-cobalt(II) three-dimensional bimetallic frameworks

The synthesis, X-ray structures, and magnetic behavior of two new, three-dimensional compounds [W(IV)[(mu-CN)(4)Co(II)(H(2)O)(2)](2).4H(2)O](n) (1) and [[W(V)(CN)(2)](2)[(mu-CN)(4)Co(II)(H(2)O)(2)](3).4H(2)O](n) (2) are presented. Compound 1 crystallizes in the tetragonal system, space group I4/m with cell constants a = b = 11.710(3) A, c = 13.003(2) A, and Z = 4, whereas 2 crystallizes in the orthorhombic system, space group Cmca with cell constants a = 13.543(5) A, b = 16.054(6) A, c = 15.6301(9) A, and Z = 4. The structure of 1 shows alternating eight-coordinated W(IV) and six-coordinated Co(II) ions bridged by single cyanides in a three-dimensional network. The geometry of each [W(IV)(CN)(8)](4-) entity in 1 is close to a square antiprism. Its eight cyanide groups are coordinated to Co(II) ions which have two coordinated water molecules in trans position. The structure of 2 consists of alternating eight-coordinated W(V) and six-coordinated Co(II) ions linked by single cyanide bridges in a three-dimensional network. Each [W(V)(CN)(8)](3-) unit shows a geometry close to a square antiprism. Only six of its eight cyanide groups are coordinated to Co(II) ions while the other two are terminal. The Co(II) ion in 2 has the same CoN(4)O(2) environment as in 1. The magnetic behavior of 1 is that of magnetically isolated high spin Co(II) ions (S(Co) = 3/2), bridged by the diamagnetic [W(IV)(CN)(8)](3-) units (S(W(IV)) = 0). The magnetic behavior of 2, where the high spin Co(II) ions are bridged by the paramagnetic [W(V)(CN)(8)](3-) units [S(W(V)) = 1/2], is that of ferromagnetically coupled Co(II) and W(V) giving rise to an ordered ferromagnetic phase below 18 K. The magnetic properties of 1 are used as a blank to extract the parameters that are useful to analyze the magnetic data of compound 2.     

Oxalato-bridged dinuclear complexes of Cr(III) and Fe(III): synthesis, structure, and magnetism of [(C2H5)4N]4[MM'(ox)(NCS)8] with MM' = CrCr, FeFe, and CrFe

A new series of homo- and heterometallic oxalato-bridged dinuclear compounds of formulas [Et4N]4[MM'(ox)(NCS)8] ([Et4N]+ = [(C2H5)4N]+; ox = C2O4(2-)) with MM' = Cr(III)-Cr(III) (1), Fe(III)-Fe(III) (2), and Cr(III)-Fe(III) (3) is reported. They have been structurally characterized by infrared spectra and single-crystal X-ray diffraction. The three compounds are isostructural and crystallize in the orthorhombic space group Cmca with Z = 8, a = 16.561(8) A, b = 13.481(7) A, and c = 28.168(8) A for 1, a = 16.515(2) A, b = 13.531(1) A, and c = 28.289(4) A for 2, a = 16.664(7) A, b = 13.575(6) A, and c = 28.386(8) A for 3. The structure of 3 is made up of a discrete dinuclear anion [CrFe(ox)(NCS)8]4- and four disordered [Et4N]+ cations, each of them located on special positions. The anion, in a crystallographically imposed C2h symmetry, contains metal cations in distorted octahedral sites. The Cr(ox)Fe group, which is planar within 0.02 A, presents an intramolecular metal-metal distance of 5.43 A. Magnetic susceptibility measurements indicate antiferromagnetic pairwise interactions for 1 and 2 with J = -3.23 and -3.84 cm-1, respectively, and ferromagnetic Cr-Fe coupling with J = 1.10 cm-1 for 3 (J being the parameter of the exchange Hamiltonian H = -2JS1S2). The ESR spectra at different temperatures confirm the magnetic susceptibility data.     

Increasing the ordering temperatures in oxalate-based 3D chiral magnets: the series [Ir(ppy)2(bpy)][M(II)M(III)(ox)3] x 0.5 H2O (M(II)M(III) = MnCr, FeCr, CoCr, NiCr, ZnCr, MnFe, FeFe); bpy = 2,2'-bipyridine; ppy = 2-phenylpyridine; ox = oxalate dianion)

The synthesis, structure, and physical properties of a novel series of oxalate-based bimetallic magnets obtained by using the Ir(ppy)2(bpy)]+ cation as a template of the bimetallic [M(II)M(III)(ox)3]- network are reported. The compounds can be formulated as [Ir(ppy)2(bpy)][M(II)Cr(III)(ox)3] x 0.5 H2O (M(II) = Ni, Mn, Co, Fe, and Zn) and [Ir(ppy)2(bpy)]-[M(II)Fe(III)(ox)3] x 0.5 H2O (M(II) = Fe, Mn) and crystallize in the chiral cubic space group P4(1)32 or P4(3)32. They show the well-known 3D chiral structure formed by M(II) and M(III) ions connected through oxalate anions with [Ir(ppy)2(bpy)]+ cations and water molecules in the holes left by the oxalate network. The M(II)Cr(III) compounds behave as soft ferromagnets with ordering temperatures up to 13 K, while the Mn(II)Fe(III) and Fe(II)Fe(III) compounds behave as a weak ferromagnet and a ferrimagnet, respectively, with ordering temperatures of 31 and 28 K. These values represent the highest ordering temperatures so far reported in the family of 3D chiral magnets based on bimetallic oxalate complexes.     

Equilibrium studies on chromium(III) complexes of salicylic acid and salicylic acid derivatives in aqueous solution

The complexes of chromium(III) ion formed by salicylic acid, SA(H(2)L), and its derivatives (H(2)L): 5-nitrosalicylic acid (5-NSA), 5-sulphosalicylic acid (5-SSA) were investigated by means of potentiometry and spectroscopy, at 25 degrees C and in ionic strength of 0.1 M KNO(3) and 0.1 M KCl, respectively. Over the acidic pH range, the coordination of Cr(III) ion to SA and its derivatives in 1 : 1 mole ratio occurs, CrL(+) type complex is formed. In the excess of ligand, the coordination of the second ligand molecule is somewhat hindered; as a result CrL(HL) type complex occurs. Their existences were verified and their formation constants were determined. At near neutral pH, CrL(OH) and CrL(HL)(OH)(-) type hydroxo complexes formed by hydrolytic equilibria and their formation constants were also defined. The stabilities of Cr(III) complexes of SA and its derivatives decrease in the following order: SA>5-SSA>5-NSA. The formation constants of Cr(III) complexes of SA and its derivatives are in comparable ranges with the corresponding complexes of the 2,x-dihydroxybenzoic acid (2,x-DHBA) of Cr(III) ion. The stabilities of SA complexes for V(IV), Cr(III) and Fe(III) ions that have similar ionic radii, increase in the order VOL相似文献   

Chiral, Three-Dimensional Supramolecular Compounds: Homo- and Bimetallic Oxalate- and 1,2-Dithiooxalate-Bridged Networks. A Structural and Photophysical Study

In analogy to the [M(II)(bpy)(3)](2+) cations, where M(II) is a divalent transition-metal and bpy is 2,2'-bipyridine, the tris-chelated [M(III)(bpy)(3)](3+) cations, where M(III) is Cr(III) or Co(III), induce the crystallization of chiral, anionic three-dimensional (3D) coordination polymers of oxalate-bridged (&mgr;-ox) metal complexes with stoichiometries [M(II)(2)(ox)(3)](n)()(2)(n)()(-) or [M(I)M(III)(ox)(3)](n)()(2)(n)()(-). The tripositive charge is partially compensated by inclusion of additional complex anions like ClO(4)(-), BF(4)(-), or PF(6)(-) which are encapsulated in cubic shaped cavities formed by the bipyridine ligands of the cations. Thus, an elaborate structure of cationic and anionic species within a polymeric anionic network is realized. The compounds isolated and structurally characterized include [Cr(III)(bpy)(3)][ClO(4)] [NaCr(III)(ox)(3)] (1), [Cr(III)(bpy)(3)][ClO(4)][Mn(II)(2)(ox)(3)] (2), [Cr(III)(bpy)(3)][BF(4)] [Mn(II)(2)(ox)(3)] (3), [Co(III)(bpy)(3)][PF(6)][NaCr(III)(ox)(3)] (4). Crystal data: 1, cubic, P2(1)3, a = 15.523(4) ?, Z = 4; 2, cubic, P4(1)32, a = 15.564(3) ?, Z = 4; 3, cubic, P4(1)32, a = 15.553(3) ?, Z = 4; 4, cubic, P2(1)3, a = 15.515(3) ?, Z = 4. Furthermore, it seemed likely that 1,2-dithiooxalate (dto) could act as an alternative to the oxalate bridging ligand, and as a result the compound [Ni(II)(phen)(3)][NaCo(III)(dto)(3)].C(3)H(6)O (5) has successfully been isolated and structurally characterized. Crystal data: 5, orthorhombic, P2(1)2(1)2(1), a = 16.238(4) ?, b = 16.225(4) ?, c = 18.371(5) ?, Z = 4. In addition, the photophysical properties of compound 1 have been investigated in detail. In single crystal absorption spectra of [Cr(III)(bpy)(3)][ClO(4)][NaCr(III)(ox)(3)] (1), the spin-flip transitions of both the [Cr(bpy)(3)](3+) and the [Cr(ox)(3)](3)(-) chromophores are observed and can be clearly distinguished. Irradiating into the spin-allowed (4)A(2) --> (4)T(2) absorption band of [Cr(ox)(3)](3)(-) results in intense luminescence from the (2)E state of [Cr(bpy)(3)](3+) as a result of rapid energy transfer processes.     

Model Compounds for Iron Proteins. Structures and Magnetic, Spectroscopic, and Redox Properties of Fe(III)M(II) and [Co(III)Fe(III)](2)O Complexes with (&mgr;-Carboxylato)bis(&mgr;-phenoxo)dimetalate and (&mgr;-Oxo)diiron(III) Cores

A series of heterobimetallic complexes of the type [Fe(III)M(II)L(&mgr;-OAc)(OAc)(H(2)O)](ClO(4)).nH(2)O (2-5) and [{Fe(III)Co(III)L(&mgr;-OAc)(OAc)}(2)(&mgr;-O)](ClO(4))(2).3H(2)O (6) where H(2)L is a tetraaminodiphenol macrocyclic ligand and M(II) = Zn(2), Ni(3), Co(4), and Mn(5) have been synthesized and characterized. The (1)H NMR spectrum of 6 exhibits all the resonances between 1 and 12 ppm. The IR and UV-vis spectra of 2-5 indicate that in all the cases the metal ions have similar coordination environments. A disordered crystal structure determined for 3 reveals the presence of a (&mgr;-acetate)bis(&mgr;-phenoxide)-Ni(II)Fe(III) core, in which the two metal ions have 6-fold coordination geometry and each have two amino nitrogens and two phenolate oxygens as the in-plane donors; aside from the axial bridging acetate, the sixth coordination site of nickel(II) is occupied by the unidentate acetate and that of iron(III) by a water molecule. The crystal structure determination of 6 shows that the two heterobinuclear Co(III)Fe(III) units are bound by an Fe-O-Fe linkage. 6 crystallizes in the orthorhombic space group Ibca with a = 17.577(4) ?, b = 27.282(7) ?, c = 28.647(6) ?, and Z = 8. The two iron(III) centers in 6 are strongly antiferromagnetically coupled, J = -100 cm(-1) (H = -2JS(1).S(2)), whereas the other two S(1) = S(2) = (5)/(2) systems, viz. [Fe(2)(III)(HL)(2)(&mgr;-OH)(2)](ClO(4))(2) (1) and the Fe(III)Mn(II) complex (5), exhibit weak antiferromagnetic exchange coupling with J = -4.5 cm(-1) (1) and -1.8 cm(-1) (5). The Fe(III)Ni(II) (3) and Fe(III)Co(II) (4) systems, however, exhibit weak ferromagnetic behavior with J = 1.7 cm(-1) (3) and 4.2 cm(-1) (4). The iron(III) center in 2-5 exhibits quasi-reversible redox behavior between -0.44 and -0.48 V vs Ag/AgCl associated with reduction to iron(II). The oxidation of cobalt(II) in 4 occurs quasi-reversibly at 0.74 V, while both nickel(II) and manganese(II) in 3 and 5 undergo irreversible oxidation at 0.85 V. The electrochemical reduction of 6 leads to the generation of 4.     

Cr(III)(salen)Cl catalyzed asymmetric epoxidations: insight into the catalytic cycle

Intermediates of chromium-salen catalyzed alkene epoxidations were studied in situ by EPR, (1)H and (2)H NMR, and UV-vis/NIR spectroscopy (where chromium-salens were (S,S)-(+)-N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamino chromium(III) chloride (1) and racemic N,N'-bis(3,4,5,6-tetra-deuterosalicylidene)-1,2-cyclohexanediamino chromium(III) chloride (2)). High-valence chromium complexes, intermediates of epoxidation reactions, were detected and characterized by EPR and NMR. They are the reactive mononuclear oxochromium(V) intermediate (A) Cr(V)O(salen)L (where L = Cl(-) or a solvent molecule) and an inactive chromium-salen binuclear complex (B) which acts as a reservoir of the active species. The latter complex demonstrates an EPR signal characteristic of oxochromium(V)-salen species and (1)H NMR spectra typical for chromium(III)-salen complexes, and it is identified as mixed-valence binuclear L(1)(salen)Cr(III)OCr(V)(salen)L(2) (L(1), L(2) = Cl(-) or solvent molecules). The intermediates Cr(V)O(salen)L and L(1)(salen)Cr(III)OCr(V)(salen)L(2) exist in equilibrium, and their ratio can be affected by addition of donor ligands (DMSO, DMF, H(2)O, pyridine). Addition of donor additives increases the fraction of A over that of B. The same two complexes can be obtained with m-CPBA as oxidant. Reactivities of the Cr(V)O(salen)L complexes toward E-beta-methylstyrene were measured in DMF. The L(1)(salen)Cr(III)OCr(V)(salen)L(2) intermediate has been proposed to be a reservoir of the true reactive chromium(V) species. The chromium-salen catalysts demonstrate low turnover numbers (ca. 5), probably due to ligand degradation processes.     

Phenolate- and acetate (both mu(2)-1,1 and mu(2)-1,3 mode)-bridged face-shared trioctahedral linear Ni(II)(3), Ni(II)(2)M(II) (M = Mn, Co) complexes: ferro- and antiferromagnetic coupling

The complexes [(L)(2)Ni(II)(2)M(II)(mu(2)-1,3-OAc)(2)(mu(2)-1,1-OAc)(2)(S)(2)] x xMeOH [HL = N-methyl-N-(2-hydroxybenzyl)-2-aminoethyl-2-pyridine; M = Ni, S = MeOH, x = 6 (1); M = Mn, S = H(2)O, x = 0 (2); M = Co, S = MeOH, x = 6 (3)] have been synthesized. Crystal structures reveal that three octahedral MII ions form a linear array with two terminal moieties {(L)Ni(II)(mu(2)-1,3-OAc)(mu(2)-1,1-OAc)(MeOH/H(2)O)}(-) in a facial donor set and a central MII ion which is connected to the terminal ions via bridging phenolate and two types of bridging acetates. Magnetic measurements reveal that the Ni(II)(3) and Ni(II)(2)Co(II) centers are ferromagnetically and Ni(II)(2)Mn(II) center is antiferromagnetically coupled. An attempt has been made to rationalize the observed magneto-structural behavior.     

Structure, magnetism and optical properties of achiral and chiral two-dimensional oxalate-bridged anionic networks with symmetric and asymmetric ammonium cations

A series of two-dimensional (2D) oxalate-based compounds, namely [N(n-C4H9)4][M(II)Cr(III)(ox)3] (M(II) = Mn, Fe; ox = C2O4(2-)) and [N(C2H5)(n-C3H7)(n-C4H9)(n-C5H11)][M(II)M(III)(ox)(3)] ((M(II), M(III)) =(Mn, Cr), (Fe, Cr), (Mn, Fe)) were synthesised starting from racemic tris(oxalato)metalate: rac-[M(III)(ox)3]3- (M(III) = Cr, Fe). For Cr(III), the synthesis has been undertaken starting from resolved (Delta)- or (Lambda)-[Cr(III)(ox)3]3-. The natural circular dichroism measurements assess the enantioselectivity of the synthesis. X-Ray powder diffraction analysis has revealed that, when racemic reagents are used to synthesise Mn(II) containing compounds, a R3c achiral space group is found. In contrast a P6(3) chiral space group is found when starting from (Delta)- or (Lambda)-[Cr(III)(ox)3]3-. Surprisingly, whatever the optical purity of the starting building block, all Fe(II) containing compounds crystallise in the P6(3) chiral space group. The magnetic properties of the synthesised compounds confirm that these compounds are ferromagnets for M(III)= Cr. For M(II)= Mn, Theta ranges between 9 and 11 K and T(c) equals 6 K. For M(II)= Fe, Theta ranges between 14 and 16 K and Tc between 11 and 12 K. [N(C2H5)(n-C3H7)(n-C4H9)(n-C5H11)][Mn(II)Fe(III)(ox)3] is an antiferromagnet with Theta = - 107 K and T(N) = 29 K.     

Synthesis, crystal structures and magnetic properties of single and double cyanide-bridged bimetallic Fe2(III)Cu(II) zigzag chains

The bimetallic complexes [[Fe(III)(phen)(CN)4]2Cu(II)(H2O)2].4H2O (1), [[Fe(III)(phen)(CN)4]2Cu(II)].H2O (2) and [[Fe(III)(bipy)(CN)4]2Cu(II)].2H2O (3) and [[Fe(III)(bipy)(CN)4]2Cu(II)(H2O)2].4H2O (4) (phen = 1,10-phenanthroline and bipy = 2,2'-bipyridine) have been prepared and the structures of 1-3 determined by X-ray diffraction. The structure of 1 is made up of neutral cyanide-bridged Fe(III)-Cu(II) zigzag chains of formula [[Fe(III)(phen)(CN)4]2Cu(II)(H2O)2] and uncoordinated water molecules with the [Fe(phen)(CN)4]- entity acting as a bis-monodentate bridging ligand toward two trans-diaquacopper(II) units through two of its four cyanide groups in cis positions. The structure of 2 can be viewed as the condensation of two chains of 1 connected through single cyanide-bridged Fe(III)-Cu(II) pairs after removal of the two axially coordinated water molecules of the copper atom. The structure of 3 is like that of 2, the main differences being the occurrence of bipy (phen in 2) and two (one in 2) crystallization water molecules. The crystals of 4 diffract poorly but the analysis of the limited set of diffraction data shows a chain structure like that of 1 the most important difference being the fact that elongation axis at the copper atom is defined by the two trans coordinated water molecules. 1 behaves as a ferromagnetic Fe(III)2Cu(II) trinuclear system. A metamagnetic-like behavior is observed for 2 and 3, the value of the critical field (Hc) being ca. 1100 (2) and 900 Oe (3). For H > Hc the ferromagnetic Fe(III)2Cu(II) chains exhibit frequency dependence of the out-of-phase ac susceptibility signal at T < 4.0 K. The magnetic behavior of 4 corresponds to that of a ferromagnetically coupled chain of low spin iron(III) and copper(II) ions with frequency dependence of the out-of-phase susceptibility at T < 3.0 K. Theoretical calculations using methods based on density functional theory (DFT) have been employed to analyze and substantiate the exchange pathways in this family of complexes.