EPR spectra from "EPR-silent" species: high-frequency and high-field EPR spectroscopy of pseudotetrahedral complexes of nickel(II)

High-frequency and high-field electron paramagnetic resonance (HFEPR) spectroscopy (using frequencies of approximately 90-550 GHz and fields up to approximately 15 T) has been used to probe the non-Kramers, S = 1, Ni(2+) ion in a series of pseudotetrahedral complexes of general formula NiL(2)X(2), where L = PPh(3) (Ph = phenyl) and X = Cl, Br, and I. Analysis based on full-matrix solutions to the spin Hamiltonian for an S = 1 system gave zero-field splitting parameters: D = +13.20(5) cm(-1), /E/ = 1.85(5) cm(-1), g(x) = g(y) = g(z) = 2.20(5) for Ni(PPh(3))(2)Cl(2). These values are in good agreement with those obtained by powder magnetic susceptibility and field-dependent magnetization measurements and with earlier, single-crystal magnetic susceptibility measurements. For Ni(PPh(3))(2)Br(2), HFEPR suggested /D/ = 4.5(5) cm(-1), /E/ = 1.5(5) cm(-1), g(x) = g(y) = 2.2(1), and g(z) = 2.0(1), which are in agreement with concurrent magnetic measurements, but do not agree with previous single-crystal work. The previous studies were performed on a minor crystal form, while the present study was performed on the major form, and apparently the electronic parameters differ greatly between the two. HFEPR of Ni(PPh(3))(2)I(2) was unsuccessful; however, magnetic susceptibility measurements indicated /D/ = 27.9(1) cm(-1), /E/ = 4.7(1), g(x) = 1.95(5), g(y) = 2.00(5), and g(z) = 2.11(5). This magnitude of the zero-field splitting ( approximately 840 GHz) is too large for successful detection of resonances, even for current HFEPR spectrometers. The electronic structure of these complexes is discussed in terms of their molecular structure and previous electronic absorption spectroscopic studies. This analysis, which involved fitting of experimental data to ligand-field parameters, shows that the halo ligands act as strong pi-donors, while the triphenylphosphane ligands are pi-acceptors.     

Electronic structure study of seven-coordinate first-row transition metal complexes derived from 1,10-diaza-15-crown-5: a successful marriage of theory with experiment

A detailed study of the electronic structure of seven-coordinate Mn(II), Co(II), and Ni(II) complexes with the lariat ether N,N'-bis(2-aminobenzyl)-1,10-diaza-15-crown-5 (L(1)) is presented. These complexes represent new examples of structurally characterized seven-coordinate (pentagonal bipyramidal) complexes for the Mn(II), Co(II), and Ni(II) ions. The X-ray crystal structures of the Mn(II) and Co(II) complexes show C(2) symmetries for the [M(L(1))](2+) cations, whereas the structures of the Ni(II) complexes show a more distorted coordination environment. The magnetic properties of the Mn(II) complex display a characteristic Curie law, whereas those of the Co(II) and Ni(II) ions show the occurrence of zero-field splitting of the S = 3/2 and 1 ground states, respectively. Geometry optimizations of the [M(L(1))](2+) systems (M = Mn, Co, or Ni) at the DFT (B3LYP) level of theory provide theoretical structures in good agreement with the experimental data. Electronic structure calculations predict a similar ordering of the metal-based beta spin frontier MO for the Mn(II) and Co(II) complexes. This particular ordering of the frontier MO leads to a pseudodegenerate ground state for the d(8) Ni(II) ion. The distortion of the C(2) symmetry in [Ni(L(1))](2+) is consistent with a Jahn-Teller effect that removes this pseudodegeneracy. Our electronic structure calculations predict that the binding strength of L(1) should follow the trend Co(II) approximately Mn(II) > Ni(II), in agreement with experimental data obtained from spectrophotometric titrations.     

Co-ordination compounds of diacetyldihydrazone and diacetylbis(monomethylhydrazone)

Summary Diacetyldihydrazone (DADH) forms only six-coordinate complexes with iron(II), cobalt(II), nickel(II) and zinc(II). In M(DADH)₂X₂ (M=Fe, X=Br or I; M=Co, X=I; M=Ni, X=Cl, Br or NCS) the ligand is chelating in the [M(DADH)₃]²⁺ cations, while in M(DADH)₂X₂ (M=Co, X=Cl or Br; M=Ni, X=Cl or Br) the ligand is probably bridging and bidentate. Diacetylbismonomethylhydrazone (DAMH), by contrast, forms predominantly tetrahedral complexes M(DAMH)X₂ (M=Fe or Co, X=Cl or Br; M=Ni, X=Br; M=Co, X=NCS; M=Zn, X=Cl, Br or NCS) and some octahedral complexes M(DAMH)₂X₂ (M=Co, X=NCS; M=Ni, X=Br). The i.r. spectra, electronic spectra and magnetic moments of the complexes are discussed.     

Density functional theory analysis of the interplay between Jahn-Teller instability, uniaxial magnetism, spin arrangement, metal-metal interaction, and spin-orbit coupling in Ca3CoMO6 (M = Co, Rh, Ir)

In the isostructural oxides Ca(3)CoMO(6) (M = Co, Rh, Ir), the CoMO(6) chains made up of face-sharing CoO(6) trigonal prisms and MO(6) octahedra are separated by Ca atoms. We analyzed the magnetic and electronic properties of these oxides on the basis of density functional theory calculations including on-site repulsion and spin-orbit coupling, and examined the essential one-electron pictures hidden behind results of these calculations. Our analysis reveals an intimate interplay between Jahn-Teller instability, uniaxial magnetism, spin arrangement, metal-metal interaction, and spin-orbit coupling in governing the magnetic and electronic properties of these oxides. These oxides undergo a Jahn-Teller distortion, but their distortions are weak, so that their trigonal-prism Co(n+) (n = 2, 3) ions still give rise to strong easy-axis anisotropy along the chain direction. As for the d-state split pattern of these ions, the electronic and magnetic properties of Ca(3)CoMO(6) (M = Co, Rh, Ir) are consistent with d(0) < (d(2), d(-2)) < (d(1), d(-1)) but not with (d(2), d(-2)) < d(0) < (d(1), d(-1)). The trigonal-prism Co(3+) ion in Ca(3)Co(2)O(6) has the L = 2 configuration (d(0))(1)(d(2), d(-2))(3)(d(1), d(-1))(2) because of the metal-metal interaction between adjacent Co(3+) ions in each Co(2)O(6) chain, which is mediated by their z(2) orbitals, and the spin-orbit coupling of the trigonal-prism Co(3+) ion. The spins in each CoMO(6) chain of Ca(3)CoMO(6) prefer the ferromagnetic arrangement for M = Co and Rh but the antiferromagnetic arrangement for M = Ir. The octahedral M(4+) ion of Ca(3)CoMO(6) has the (1a)(1)(1e)(4) configuration for M = Rh but the (1a)(2)(1e)(3) configuration for M = Ir, which arises from the difference in the spin-orbit coupling of the M(4+) ions and the Co···M metal-metal interactions.     

Perovskite-like Metal Formates with Weak Ferromagnetism and as Precursors to Amorphous Materials

Three isomorphous compounds M(CHOO)3[NH2(CH3)2] (M = Mn(1 x Mn), Co(2 x Co), Ni(3 x Ni)) have been synthesized in solvothermal conditions. Single-crystal X-ray diffraction shows that they are all crystallized in the trigonal space group R c with small differences in the lattice parameters. Bridged by the three-atom single-bridge CHOO-, M ions form a three-dimensional distorted perovskite-like structure with dimethylamine (DMA) cations located in the cages of the network. Based on the magnetic data, these three 3D compounds are weak ferromagnets with the critical temperature Tc = 8.5 K (1 x Mn), 14.9 K (2 x Co), and 35.6 K (3 x Ni), and for 2 x Co and 3 x Ni, spin reorientation might take place at 13.1 and 14.3 K, respectively. At 1.8 K, hysteresis loops can be observed for all three compounds with the coercivity field ca. 90 Oe (1 x Mn), 920 Oe (2 x Co), and 320 Oe (3 x Ni). The canting angles are estimated to be 0.08 degrees, 0.5 degrees, and 0.6 degrees for 1 x Mn, 2 x Co, and 3.Ni, respectively. The magnetic coupling between MnII ions in 1.Mn was estimated based on the model developed by Rushbrook and Wood for a Heisenberg antiferromagnet on a simple cubic lattice and the best fit gives J = -0.23 cm(-1). At the same time, according to molecular field theory of antiferromagnetism, the J values for compounds 1 x Mn, 2 x Co, and 3 x Ni were estimated to be -0.32 cm(-1), -2.3 cm(-1), and -4.85 cm(-1), respectively. The spin cant in these compounds may originate from the noncentrosymmetric character of the three-atom single-bridge CHOO-. Furthermore, amorphous materials 4 x Mn238, 5 x Mn450, 6 x Co320, and 7 x Ni300 were prepared from precursors 1-3 under an argon atmosphere at different temperatures according to the thermogravimetric analyses. As an interesting result, 5 x Mn450 was confirmed to be an amorphous form of Mn3O4 with a considerably large coercivity field HC = 4.1 kOe at 30 K compared to that value (250 Oe) for bulk Mn3O4.     

Synthesis and spectral studies on Co (II) and Ni (II) complexes with polyfunctional quinazoline-(3H)-4-ones

A series of complexes of Co(II) and Ni(II) with 2-(R)-3-(X)-substituted quinazoline-(3H)-4-ones, where R = methyl/phenyl and X = furalamino, uramino and thiouramino have been synthesised and characterised by analytical, conductivity, thermal and magnetic, infrared and electronic spectral data. Based on analytical and conductivity studies the stoichiometries of the complexes have been established. Conductivity data also show that all these complexes are non-electrolytes. Infrared spectral data indicate that all the ligands manifest neutral bidentate with both the metal ions. Geometries for the complexes have been proposed based on electronic spectral data. Various electronic spectral parameters have been calculated for all the complexes and relevant conclusions have been drawn with respect to the nature of bonds present in them.     

Electronic structure of A- and B-site doped lanthanum manganites: a combined X-ray spectroscopic study

The electronic properties of a series of colossal magnetoresistance (CMR) compounds, namely LaMnO3, La(1-x)Ba(x)(MnO3 (0.2 < or = x < or = 0.55), La(0.76)Ba(0.24)Mn(0.84)Co(0.16)O3, and La(0.76)Ba(0.24)Mn(0.78)Ni(0.22)O3, have been investigated in a detailed spectroscopic study. A combination of X-ray photoelectron spectroscopy (XPS), X-ray emission spectroscopy (XES), X-ray absorption spectroscopy (XAS), and resonant inelastic X-ray scattering (RIXS) was used to reveal a detailed picture of the electronic structure in the presence of Ba, Co, and Ni doping in different concentrations. The results are compared with available theory. The valence band of La(1-x)()Ba(x)MnO3 (0 < or = x < or = 0.55) is dominated by La 5p, Mn 3d, and O 2p states, and strong hybridization between Mn 3d and O 2p states is present over the whole range of Ba concentrations. Co-doping at the Mn site leads to an increased occupancy of the e(g) states near the Fermi energy and an increase in the XPS valence band intensity between 0.5 and 5 eV, whereas the Ni-doped sample shows a lower density of occupied states near the Fermi energy. The Ni d states are located in a band spanning the energy range of 1.5-5 eV. XAS spectra indicate that the hole doping leads to mixed Mn 3d-O 2p states. Furthermore, RIXS at the Mn L edge has been used to probe d-d transitions and charge-transfer excitations in La(1-x)Ba(x)MnO3.     

Coordination of metal ions by indolic acids. Complexes of indole-3-carboxylic,indole-3-acetic,indole-3-β-acrylic,indole-N-acetic and indole-N-methyl-2-carboxylic acids with some divalent metal ions

Complexes of formula M(L)₂·nH₂O [M=Co or Ni; L=indole-3-carboxylic (I3CH), indole-3-acetic (I3AH), indole-N-acetic (INAH), indole-N-methyl-2-carboxylic (INMH) and M=Co or Ni and Cu, L=indole-3-β-acrylic acids (I3βH)] were pepared and characaterized by i.r. and electronic spectroscopy and by susceptibility measurements and e.s.r. at room and low temperature. The cobalt and nickel complexes exhibit a distorted octahedral coordination except the Co(I3C)₂ complex for which a tetrahedral coordination was suggested. The Cu(I3β)₂·H₂O shows e.p.r. features that can be interpreted if the triplet state, S=1, depending on the temperature, is able to migrate through the crystal lattice of carboxylate dimers such as the copper(II) acetate monohydrate.     

Synthesis and Characterization of Cobalt(II), Nickel(II), and Zinc(II) Complexes with N,N ′-bis( Trans- Cinnamaldehyde)-1,2-Diiminoethane Ligand, (ca 2 en): Crystal and Molecular Structures of Co(ca 2 en)Cl 2 , Co(ca 2 en)Br 2 and Ni(ca 2 en)Br 2

A series of new complexes of the Schiff base obtained from trans- cinnamaldehyde and 1,2-diaminoethane (en) with the general formula of M(ca 2 en)X 2 (M = Co(II), Ni(II), Zn(II); X = Cl, Br, I, NCS, N 3 ; (ca 2 en) = N,N '-bis( trans- cinnamaldehyde)-1,2-diiminoethane) have been synthesized and characterized. The crystal structures of three pseudo -tetrahedral complexes, Co(ca 2 en)Cl 2 ( 1 ), Co(ca 2 en)Br 2 ( 2 ), and Ni(ca 2 en)Br 2 ( 5 ), were determined by X-ray diffraction. Crystal data for 1 , Co(ca 2 en)Cl 2 : monoclinic; space group P 2 1 / c ; a = 7.1925(14) Å, b = 20.327(4) Å, c = 14.029(3) Å; g =95.06(3)°; V = 2043.1(7) Å 3 ; Z = 4; and final R 1 = 0.0381 ( wR 2 = 0.0718) for 4653 independent reflections with I > 2 σ ( I ) and 226 parameters; 2 , Co(ca 2 en)Br 2 ; monoclinic, space group P 2 1 / c ; a = 7.3780(6) Å, b = 20.4372(17) Å, c = 14.1649(12) Å; g = 94.902(2)°; V = 2128.1(3) Å 3 ; Z = 4; and final R 1 = 0.0491 ( wR 2 = 0.1052) for 5858 independent reflections with I > 2 σ ( I ) and 227 parameters; 5 , Ni(ca 2 en)Br 2 : monoclinic, space group P 2 1 / c ; a = 7.2388(6) Å, b = 20.4651(16) Å, c = 14.2782(12) Å; g = 94.160(2)°; V = 2109.6(3) Å 3 ; Z = 4; R 1 = 0.0481 ( wR 2 = 0.0907) for 5914 independent reflections with I > 2 σ ( I ) and 227 parameters. The structures consist of discrete molecules in which the coordination polyhedra about the central metal ion are highly distorted tetrahedra with Cl(1)-Co-Cl(2), 115.51(3)°; N(1)-Co-N(2), 83.71(7)°; Br(1)-Co-Br(2), 114.58(4)°; N(1)-Co-N(2), 84.92(19)°; and Br(1)-Ni-Br(2), 125.23(3)°; N(1)-Ni-N(2), 85.11(15)° in 1 , 2 , and 5 , respectively. The stiryl groups are cis -endo with respect to the metal atom and the chelate ring is puckered. Utilization is made of electronic and vibrational spectra in structural diagnosis of other complexes.     

Spectroscopic studies on Mn(II), Co(II), Ni(II), and Cu(II) complexes with N-donor tetradentate (N4) macrocyclic ligand derived from ethylcinnamate moiety

Manganese(II), cobalt(II), nickel(II), and copper(II) complexes are synthesized with a novel tetradentate ligand, viz. 1,5,9,13-tetraaza-6,14-dioxo-8,16-diphenylcyclohexadecane (L) and characterized by the elemental analysis, molar conductance measurements, magnetic susceptibility measurements, mass, 1H NMR, IR, electronic, and EPR spectral studies. The molar conductance measurements of the complexes in DMSO correspond to be nonelectrolyte nature for Mn(II), Co(II), and Cu(II) whereas 1:2 electrolytes for Ni(II) complexes. Thus, these complexes may be formulated as [M(L)X(2)] and [Ni(L)]X(2), respectively (where M = Mn(II), Co(II), and Cu(II) and X = Cl- and NO(3-)). On the basis of IR, electronic, and EPR spectral studies an octahedral geometry has been assigned for Mn(II) and Co(II) complexes, square-planar for Ni(II) whereas tetragonal for Cu(II) complexes. The ligand and its complexes were also evaluated against the growth of bacteria and pathogenic fungi in vitro.     

Structures, physical properties, and chemistry of layered oxychalcogenides and oxypnictides

A series of layered oxychalcogenide and oxypnictide solids is described that contain oxide layers separated by distinct layers, which contain the softer chalcogenide (S, Se, Te) or pnictide (P, As, Sb, Bi) anions. The relationships between the crystal structures adopted by these compounds are described, and the physical and chemical properties of these materials are related to the structures and the properties of the elements. The properties exhibited by the oxychalcogenide materials include semiconductor properties, for example, in LaOCuCh (Ch = chalcogenide) and derivatives, unusual magnetic properties exhibited by the class Sr 2MO 2Cu 2-deltaS 2 (M = Mn, Co, Ni), and redox properties exhibited by the materials Sr 2MnO 2Cu 2 m-0.5 S m+1 ( m = 1-3) and Sr 4Mn 3O 7.5Cu 2Ch 2 (Ch = S, Se). Recent results in the oxychalcogenide area are reviewed, and some new results on the intriguing series of compounds Sr 2MO 2Cu 2-deltaS 2 (M = Mn, Co, Ni) are reported. Oxypnictides have received less recent attention, but this is changing: a new frenzy of research is underway following the discovery of high-temperature superconductivity (>40 K) in derivatives of the layered oxyarsenide LaOFeAs. The early results in this exciting new area will be reviewed.     

Spectroscopic characterization of tetradentate macrocyclic ligand: its transition metal complexes

Manganese(II), cobalt(II), nickel(II) and copper(II) complexes are synthesized with a novel tetradentate ligand viz. 1,3,9,11-tetraaza-4,8,12,16-tetraoxo-2,6,10,14-tetrathiacyclohexadecane (L) and characterized by the elemental analysis, molar conductance measurements, magnetic susceptibility measurements, electron impact mass, 1H NMR, IR, electronic and EPR spectral studies. The molar conductance measurements of the complexes in DMSO correspond to be nonelectrolytic nature for Mn(II), Co(II) and Cu(II) while 1:2 electrolytes for Ni(II) complexes. Thus these complexes may be formulated as [M(L)X2] and [Ni(L)]X2 (where M: Mn(II), Co(II), and Cu(II) and X = Cl- and NO3-). On the basis of IR, electronic and EPR spectral studies an octahedral geometry has been assigned for Mn(II) and Co(II) complexes, square-planar for Ni(II) whereas tetragonal for Cu(II) complexes. The ligand and its complexes were also evaluated against the growth of bacteria and pathogenic fungi in vitro.     

Magnetic properties and magnetic structures of synthetic natrochalcites, NaM(II)2(D3O2)(MoO4)2, M = Co or Ni

The magnetic properties and magnetic structures from neutron diffraction of two synthetic natrochalcites, NaM(II)2(H3O2)(MoO4)2, M = Co (1Co) or Ni (2Ni), are reported. They are isostructural (monoclinic C2/m) and consist of chains of edge-shared MO6 octahedra connected by mu-O from H3O2(-) and MoO4(2-). These chains form a three-dimensional network with O-H-O, O-Mo-O, and O-Na-O bridging 4, 3, and 4 metal ions, respectively. Both compounds behave as canted antiferromagnets but differ in their behaviors, 1Co showing a broad maximum (28 K) above the Neel transition (21 K) and the canting taking place at 13 K, some 8 K below T(N), while for 2Ni the canting takes place at T(N) (28 K). Analyses of the neutron powder diffraction data shed some light on the geometry of D3O2(-) and suggest antiferromagnetism with a propagation vector k = (0,0,0) with the moments within each chain being parallel but antiparallel to those in neighboring chains. The difference between 1Co and 2Ni is in the orientation of the moments; they are parallel to the chain axis (b-axis) for 1Co and perpendicular to it for 2Ni with a major component along the c-axis and a small one along the a-axis. The heat capacity data peak at 20.9(3) K (1Co) and 25.1(1) K (2Ni). The derived magnetic entropies, following correction of the lattice contribution using the measured data for the nonmagnetic Zn analogue, suggest S = 1/2 for 1Co but is lower than that expected for 2Ni (S = 1). In both cases, only ca. 60% of the entropy is found below the magnetic ordering temperature, suggesting considerable short-range correlations at higher temperatures. While the temperature at which the magnetic diffraction becomes observable coincides with that of at the peak in heat capacity, it is lower than T(N) observed by magnetization measurements in both cases, and there is evidence of short-range ordering in a narrow range of temperature (T(N) +/- 5 K).     

Synthesis, molecular and electronic structures of six-coordinate transition metal (Mn, Fe, Co, Ni, Cu, and Zn) complexes with redox-active 9-hydroxyphenoxazin-1-one ligands

A series of pseudo-octahedral metal (M = Mn, Fe, Co, Ni, Cu, Zn) complexes 4 of a new redox-active ligand, 2,4,6,8-tetra(tert-butyl)-9-hydroxyphenoxazin-1-one 3, have been synthesized, and their molecular structures determined with help of X-ray crystallography. The effective magnetic moments of complexes 4 (M = Mn, Fe, Co, and Ni) measured in the solid state and toluene solution point to the stabilization of their high-spin electronic ground states. Detailed information on the electronic structure of the complexes and their redox-isomeric forms has been obtained using density functional theory (DFT) B3LYP*/6-311++G(d,p) calculations. The energy disfavored low-spin structures of manganese, iron, and cobalt complexes have been located, and based on the computed geometries and distribution of spin densities identified as Mn(IV)[(Cat-N-SQ)](2), Fe(II)[Cat-N-BQ)](2), and Co(II)[Cat-N-BQ)](2) compounds, respectively. It has been shown that stabilization of the high-spin structures of complexes 4 (M = Mn, Fe, Co) is caused by the rigidity of the molecular framework of ligands 3 that sterically inhibits interconversions between the redox-isomeric forms of the complexes. The calculations performed on complex 4 (M = Co) predict that a suitable structural modification that might provide for stabilization of the low-spin electromeric forms and create conditions for the valence tautomeric rearrangement via stabilization of the low-spin electromer and narrowing energy gap between the low-spin ground state tautomer and the minimal energy crossing point on the intersection of the potential energy surfaces of the interconverting structures consists in the replacement of an oxygen in the oxazine ring by a bulkier sulfur atom.     

High spin Co(I): high-frequency and -field EPR spectroscopy of CoX(PPh3)3 (X = Cl, Br)

The previously reported pseudotetrahedral Co(I) complexes, CoX(PR(3))(3), where R = Me, Ph, and chelating analogues, and X = Cl, Br, I exhibit a spin triplet ground state, which is uncommon for Co(I), although expected for this geometry. Described here are studies using electronic absorption and high-frequency and -field electron paramagnetic resonance (HFEPR) spectroscopy on two members of this class of complexes: CoX(PR(3))(3), where R = Ph and X = Cl and Br. In both cases, well-defined spectra corresponding to axial spin triplets were observed, with signals assignable to three distinct triplet species, and with perfectly axial zero-field splitting (zfs) given by the parameter D = +4.46, +5.52, +8.04 cm(-1), respectively, for CoCl(PPh(3))(3). The crystal structure reported for CoCl(PPh(3))(3) shows crystallographic 3-fold symmetry, but with three structurally distinct molecules per unit cell. Both of these facts thus correlate with the HFEPR data. The investigated complexes, along with a number of structurally characterized Co(I) trisphosphine analogues, were analyzed by quantum chemistry calculations (both density functional theory (DFT) and unrestricted Hartree-Fock (UHF) methods). These methods, along with ligand-field theory (LFT) analysis of CoCl(PPh(3))(3), give reasonable agreement with the salient features of the electronic structure of these complexes. A spin triplet ground state is strongly favored over a singlet state and a positive, axial D value is predicted, in agreement with experiment. Quantitative agreement between theory and experiment is less than ideal with LFT overestimating the zfs, while DFT underestimates these effects. Despite these shortcomings, this study demonstrates the ability of advanced paramagnetic resonance techniques, in combination with other experimental techniques, and with theory, to shed light on the electronic structure of an unusual transition metal ion, paramagnetic Co(I).     

Modern spectroscopic techniques in the characterization of Schiff base macrocyclic ligand and its complexes with transition metals

Mn(II), Co(II), Ni(II), and Cu(II) complexes with a new azamacrocyclic tetradentate [N(4)] ligand i.e. 2,3,9,10-tetraphenyl;l,4,8,11-tetraazacyclotetradeca;1,3,8,10-tetraene (L) have been synthesized and characterized by elemental analysis, molar conductance measurements, magnetic susceptibility measurements, mass, (1)HNMR, IR, electronic and EPR spectral studies. On the basis of their non-electrolytic nature, the probable formula of the complexes is proposed to be [M(L)X(2)], where M=Mn(II), Co(II), Ni(II), and Cu(II), X=Cl(-) and NO(3)(-), in dimethylformamide (DMF). All the complexes are of high-spin type and found to have six coordinated, octahedral geometry for Mn(II), Co(II), and Ni(II) complexes, and tetragonal for Cu(II) complexes. Macrocyclic ligand and its complexes have also been screened against pathogenic bacteria and fungi in vitro as growth inhibiting agent.     

OXO CENTERED HETEROTRINUCLEAR TRANSITION METAL CAR- BOXYLATE COMPLEXES 5,~(57)Fe MOSSBAUER SPECTRA AND ELEC-TRON TRANSFER PROPERTIES OF COMPLEXES Fe_2MO(RCOO)_6L_3(M= Mn,Co,Ni)

<正> The 57Fe Mossbauer spectra of mixed-valence heterotrinuclear carboxylate complexes, [Fe2MO(OOCCH3)6Py3]. Py (M = Mn,Co,Ni,Py = Pyridine) and Fe2MO-(OOCCC13 )6THF3 (M = Mn, Co, Ni, THF = Tetrahydrofuran ) indicated that these Fe2M complexes are all valence-trapped on the 57Fe Mossbauer time scale (10-8s) both at 77 K and at room temperature. Expanding the PKS model to asymmetric tricenteral systems showed that intramolecular electron transfer in Fe2M complexes is difficult due to asymmetry of the Fe2MO(RCOO)6L3molecule and high potential-energy barrier.     

Homoleptic permethylpentalene complexes: "double metallocenes" of the first-row transition metals

The synthesis of the bimetallic permethylpentalene complexes Pn*2M2 (M = V, Cr, Mn, Co, Ni; Pn* = C8Me6) has been accomplished, and all of the complexes have been structurally characterized in the solid state by single-crystal X-ray diffraction. Pn*2V2 (1) and Pn*2Mn2 (3) show very short intermetallic distances that are consistent with metal-metal bonding, while the cobalt centers in Pn*2Co2 (4) exhibit differential bonding to each side of the Pn* ligand that is consistent with an eta(5):eta(3) formulation. The Pn* ligands in Pn*2Ni2 (5) are best described as eta(3):eta(3)-bonded to the metal centers. (1)H NMR studies indicate that all of the Pn*2M2 species exhibit D(2h) molecular symmetry in the solution phase; the temperature variation of the chemical shifts for the resonances of Pn*2Cr2 (2) indicates that the molecule has an S = 0 ground state and a thermally populated S = 1 excited state and can be successfully modeled using a Boltzmann distribution (DeltaH(o) = 14.9 kJ mol(-1) and DeltaS(o) = 26.5 J K(-1) mol(-1)). The solid-state molar magnetic susceptibility of 3 obeys the Curie-Weiss law with mu(eff) = 2.78 muB and theta = -1.0 K; the complex is best described as having an S = 1 electronic ground state over the temperature range 4-300 K. Paradoxically, attempts to isolate the "double ferrocene" equivalent, Pn*2Fe2, led only to the isolation of the permethylpentalene dimer Pn*2 (6). Solution electrochemical studies were performed on all of the organometallic compounds; 2-5 exhibit multiple quasi-reversible redox processes. Density functional theory calculations were performed on this series of complexes in order to rationalize the observed structural and spectroscopic data and provide estimates of the M-M bond orders.     

Electronic and magnetic structure of transition-metal carbodiimides by means of GGA+U theory

The electronic structures and magnetic properties of MNCN (M = Fe, Co, and Ni) have been investigated by density-functional theory including explicit electronic correlation through an ad hoc Coulomb potential (GGA+U). The results evidence CoNCN and NiNCN as type-II anti-ferromagnetic semiconductors (that is, intralayer ferromagnetic and interlayer anti-ferromagnetic), in accordance with experimental observations. Just like the prototype MnNCN, the MNCN phases, with M = Ni and Co, thus resemble the corresponding MO monoxides with respect to their magnetic and transport properties. By contrast, FeNCN remains (semi)metallic even upon applying a strong Coulomb correlation potential. This, most probably, is in contradiction with its observed optical transparency and expected insulating behavior and points toward a serious density-functional theory problem.