THE EPR SPECTRA OF TETRADENTATE SCHIFF BASE COMPLEXES OF COPPER (II) I. N,N'-Bis-(acetylacetone) ethylenediimine and N,N'-Bis-(1,1,1-trifluoroacetylacetone) ethylenediimine

Abstract

The EPR spectrum of N, N'-bis-(acetylacetone)ethylenediimino Cu(II), [Cu-en(acac)₂], and N, N'-bis-(1,1,1-trifluoroacetylacetone)ethylenediimino-Cu(II), [Cu-en(tfacac)₂], have been studied in doped single crystals of the corresponding Ni(II) chelate. The parameters in the usual doublet spin-Hamiltonian are found to be: Cu[en(acac)₂], g_z =2.183 ± 0.003, g_x =2.047 ± 0.004, g_y =2.048 ± 0.004, A_z =204.8 × 10^?4cm^?1, A_x =31.5 × 10^?4cm^?1, A_y =27.1 × 10^?4 cm^?1, A_zN= 12.8 × 10^?4 cm^?1 and A_xN =A_yN =14.3 × 10^?4 cm^?1: Cu[en(tfacac)₂], g_z =2.192 ± 0.002, g_x =2.048 ± 0.004, g_y =2.046 ± 0.004, A_z =200.8 × 10^?4 cm^?1, A_x =31.1 × 10^?4 cm^?1, A_y =28.3 × 10^?4 cm^?1, A_zN =12.8 × 10^?4 cm^?1 and A_xN =A_yN =14.6 × 10^?4 cm^?1. These parameters are related to coefficients in the molecular orbitals of the complex. It is found that the α-bonding is quite covalent and there is significant in-plane σ-bonding. From the nitrogen hyperfine structure it is determined that the hybridization on the nitrogen is sp².     

THE PHOTOEXCITED TRIPLET STATE OF TETRAPHENYL CHLORIN, MAGNESIUM TETRAPHENYL PORPHYRIN AND WHOLE CELLS OF CHLAMYDOMONAS REINHARDI. A LIGHT MODULATION-EPR STUDY

Abstract— The photoexcited triplet states of frozen solutions of tetraphenyl chlorin (TPC), magnesium tetraphenyl porphyrin (MgTPP) and whole cells of Chlamydomonas reinhardi have been studied by light modulation-EPR spectroscopy. The porphyrins were chosen to be studied as model compounds for chlorophyll molecules, From EPR spectra the zero field splitting parameters (ZFS) were calculated. For TPC, |D| = 0.0364 ± 0.0002 cm^-1, |E| = 0.0063 ± 0.0002 cm^-1. For MgTPP, |D| = 0.0310 ± 0.0002 cm^-1. For chloroplasts, |D| = 0.0280 ± 0.0004 cm^-1, |E| = 0.0032 ± 0.0004 cm^-1. In all compounds studied, except MgTPP, electron spin polarization (ESP) was observed. From the analysis of the kinetic curves at each canonical orientation we evaluated the spin lattice relaxation rate W, the depopulation rate constants k_p, and the ratio between the population rate constants, A_p, at zero magnetic field. For TPC in ethanol-toluene (5:1) k_x= (0.70 ± 0.10) × 10³ s^-1, k_y= (0.40 ± 0.07) × 10³ s^-1, k_x= (0.24 ± 0.05) × 10³ s^-1; A_x:A_y:A_z? 1.0:0.6:0.4; W= (2.60 ± 0.40) × 10³ s^-1. For MgTPP, only the total decay rate constant, k_T, was calculated: (1.5 ± 0.2) × 10 s^-1 in n-octane and (4.8 ± 0.8) × 10 s^-1 in ethanol. The results for TPC and MgTPP are compared to those reported previously for chlorophyll. It is concluded that the dynamics of the photoexcited triplet state in chlorophylls are mainly governed by the chlorin macrocycle. From the EPR spectrum and ZFS parameters of chloroplasts, we propose that both chlorophyll a and chlorophyll b are the main constituents of the EPR spectrum. From the analysis of the kinetic curves we obtain separately the kinetic parameters for chlorophylls a and b, k^a_x= (1.30 ± 0.20) × 10³ s^-1, k^a_y;= (0.85 ± 0.15) × 10³ s^-1k^a_x= (0.32 ± 0.05) × 10³ s^-1; A^a_x:A^a_y:A^a_z? 1.0:0.7:0.2; W^a= (1.20 ± 0.20) × 10³ s^-1; k^b_x= (0.56 ± 0.09) × 10³ s^-1, k^b_y= (0.30 ± 0.04) × 10³ s^-1, k^b_z= (0.06 ± 0.01) × 10³ s^-1; A^b_x:A^b_y:A^b_x? 1.0:0.6:0.1; W^b= (5.00 ± 0.80) × 10³ s^-1. These results are very close to those found separately for chlorophyll a and chlorophyll b oligomers in vitro.     

Spin polarization in the lowest triplet state of chlorophyll

Chlorophyll-b in glassy solution has a spin-polarized lowest triplet state at and above 77 K. The magnitude of the effect is different for MTHF and ethanol as solvents, in contrast to what is found for the porphin free base. Chlorophyll-a does not exhibit spin-polarization under identical conditions as for chlorophyll-b. Zero-field parameters are found to be:chlorophyll-a (MTHF) D = (281 ± 6) × 10^?4 cm^?1; E = (39 ± 3) × 10^?4 cm^?1;chlorophyll-b (MTHF) D = (289 ± 4) × 10^?4 cm^?1; E = (49 ± 3) × 10^?4 cm^?1,From ESR signal kinetics it follows that for chlorophyll-b, population and depopulation mainly involve the spin level y?, describing a spin moving in a plane perpendicular to the molecular plane:P_y ? P_x ? P_z; k_x = 240 ± 40 s^?1; k_y = 600 ± 120 s^?1; k_z ? 75 s^?1,where P_i and k_i denote populating and decay rates. Thus, the kinetic scheme for the chlorophyll triplet is different from that of porphyrins with heavier metal ions, but very similar to that of the porphin free base. The spin-lattice relaxation time is found to be anisotropic and shorter than the decay rates of individual spin levels. Nevertheless, spin polarization can be observed, essentially because the ESR signal amplitude depends on population differences.     

EPR and optical absorption studies of Cu2+ doped bis (glycinato) Mg (II) monohydrate single crystals

Electron paramagnetic resonance (EPR) study of Cu²⁺ doped bis (glycinato) Mg (II) monohydrate single crystals is carried out at room temperature. Copper enters the lattice substitutionally and is trapped at two magnetically inequivalent sites. The observed spectra are fitted to a spin-Hamiltonian of rhombic symmetry with the following values of the parameters: Cu²⁺ (I), g_x = 2.1577 ± 0.0002, g_y = 2.2018 ± 0.0002, g_z = 2.3259 ± 0.0002, A_x = (87 ± 2) × 10^?4 cm^?1, A_y = (107 ± 2) × 10^?4 cm^?1, A_z = (141 ± 2) × 10^?4 cm^?1; Cu ²⁺ (II), g_x = 2.1108 ± 0.0002, g_y = 2.1622 ± 0.0002, g_z = 2.2971 ± 0.0002, A_x = (69 ± 2) × 10^?4 cm^?1, A_y = (117 ± 2) × 10^?4 cm^?1and A_z = (134 ± 2) × 10^?4 cm^?1. The ground state wave function of the Cu²⁺ ion in this lattice is evaluated to be predominantly |x² ? y². The g-factor anisotropy is also calculated and compared with the experimental value. With the help of the optical absorption study, the nature of bonding in the complex is discussed.     

Ion exchange properties of β-eucryptite (LiAlSiO4): EPR investigation on copper-doped single crystals

Investigation of the ion exchange properties of β-eucryptite (LiAlSiO₄) single crystals indicates that it is impossible to substitute Li⁺ by other bigger univalent cations such as Na⁺, K⁺, or Ag⁺. On the contrary, Li⁺ exchange by bivalent cations, Cu²⁺ or Mn²⁺, is very easy. For a general orientation of the crystal with respect to the magnetic field, the EPR spectrum of Cu²⁺ ions in β-eucryptite consists of 12 sharp lines partially superimposed on a broad line. The sharp lines are attributed to isolated copper ions in the conducting channels. Cu²⁺ lies in sixfold coordinated Li″ sites, but not in the fourfold coordinated Li″ sites. The corresponding spin Hamiltonian parameters at T = 140 K are found to be: g_x = 2.362, g_y = 2.340, g_z = 1.990; ∥A_x∥ = 85 × 10^?4cm^?1, ∥A_y∥ = 71 × 10^?4cm^?1, ∥A_z∥ = 203 × 10^?4 cm^?1. The broad line is attributed to clusters of Cu²⁺ located in neighboring Li″ sites.     

Determination of the population,depopulation and the anisotropic spin lattice relaxation rates in the photoexcited triplet state of phenazine. A light modulation-EPR study

The photoexcited triplet state of phenazine in toluene glasses at 35 K is investigated by light modulation-EPR spectroscopy. From the transient EPR spectra and the kinetics in the three canonical orientations (p = x, y, z) the rate parameters are determined. Thus, the depopulation rate constants k_p, the anisotropic spin lattice relaxation rate constants W_p, and the ratios between the population constants A_p are calculated: k_x = (2.2 ± 0.3) × 10² s^?1, k_y = (0.21 ± 0.04) × 10² s^?1, k_z = (0.06 ± 0.03) × 10² s^?1, W_x = (8.6 ± 0.9) × 10³ s^?1, W_y = (11.0 ± 1.0) × 10³ s^?1, W_z = (14.0 ± 1.4) × 10³ s^?1, and A_x: _Ay:A_z ≈ 1:0.04:0.02. It is concluded therefore that the in-plane spin state |τ_x > is the active one.     

ESR STUDY OF IRRADIATED PENTACYANONITROSYL COBALTATE (II)

Abstract

An ESR study of γ-irradiated pentacyanonitrosyl cobaltate (II) shows the presence of two paramagnetic species. One, with g∥ =2.005, g∥ =2.172, A∥ 81.3 and A∥ =-26.2 × 10^?4 cm^?1, is the well-known d ⁷ species Co(CN)₅ ^3-. The second shows g∥<g∥ and much lower ⁵⁹Co hyperfine interactions. The ESR parameters are shown to be consistent with those predicted for the species [Co(CN)₅ NO]^4- with C _S symmetry, a bent Co–N–O bond, and a d ₇ configuration with the odd electron in an a' orbital formed by mixing the cobalt d _x –y ² and d _z ² orbitals. Theoretical arguments are advanced to show that, in general, small metal hyperfine splittings in low symmetry ions do not necessarily establish that the unpaired electron is in a ligand-dominated orbital.     

Paramagnetic resonance of interstitial mo5+ in a tio2 lattice

Paramagnetic absorption of Mo⁵⁺ has been studied in a polycrystalline TiO₂ rutile lattice, The g tensor (g_x = 1.897, g_y = 1.920, g_z = 1.857) and the hyperfine tensor (A_x = 32.7, (A_y = 51.2, (A_z = 58.5 (in 10^?4 cm^?1)) are in agreement with those expected for an nd¹ ion in an interstitial position.     

KINETICS OF FORMATION AND STABILITY CONSTANTS OF MONO AND BIS l-TYROSINE COMPLEXES OF Cu(II), Co(II), AND Ni(II)

Abstract

The kinetics and stability constants of l-tyrosine complexation with copper(II), cobalt(II) and nickel(II) have been studied in aqueous solution at 25° and ionic strength 0.1 M. The reactions are of the type M(HL)^(3-n)+ _n-1 + HL- ? M(HL)^(2-n)+_n(k_n, forward rate constant; k_-n, reverse rate constant); where M=Cu, Co or Ni, HL^? refers to the anionic form of the ligand in which the hydroxyl group is protonated, and n=1 or 2. The stability constants (K_n=k_n/k_-n) of the mono and bis complexes of Cu²⁺, Co²⁺ and Ni²⁺ with l-tyrosine, determined by potentiometric pH titration are: Cu²⁺, log K₁=7.90 ± 0.02, log K₂=7.27 ± 0.03; Co²⁺, log K₁=4.05 ± 0.02, log K₂=3.78 ± 0.04; Ni²⁺, log K₁=5.14 ± 0.02, log K₂=4.41 ± 0.01. Kinetic measurements were made using the temperature-jump relaxation technique. The rate constants are: Cu²⁺, k₁=(1.1 ± 0.1) × 10⁹ M ^?1 sec^?1, k_-1=(14 ± 3) sec^?1, k₂=(3.1 ± 0.6) × 10⁸ M ^?1 sec^?1, k^?2=(16 ± 4) sec^?1; Co²⁺, k₁=(1.3 ± 0.2) × 10⁶ M ^?1 sec^?1, k_-1=(1.1 ± 0.2) × 10² sec^?1, k₂=(1.5 ± 0.2) × 10⁶ M ^?1 sec^?1, k_-2=(2.5 ± 0.6) × 10² sec^?1; Ni²⁺, k₁=(1.4 ± 0.2) × 10⁴ M ^?1 sec^?1, k_-1=(0.10 ± 0.02) sec^?1, k₂=(2.4 ± 0.3) × 10⁴ M ^?1 sec^?1, k_-2=(0.94 ± 0.17) sec^?1. It is concluded that l-tyrosine substitution reactions are normal. The presence of the phenyl hydroxyl group in l-tyrosine has no primary detectable influence on the forward rate constant, while its influence on the reverse rate constant is partially attributed to substituent effects on the basicity of the amine terminus.     

The relaxation spectra of nickel(II) and cobalt(II) arginine complexes

The temperature-jump method has been used to determine the nickel(II)- and cobalt(II)-arginine complexation kinetics. In the pH range studied, the neutral form of the ligand, HL, is the attacking, as well as the complexed, ligand species. The reactions reported on are of the type where n = 1, 2, 3 and M is Ni or Co. At 25° and ionic strength 0.1M the association rate constants are: for nickel(II) k₁ = 2.3 × 10³(±20%), k₂ = 2.4 × 10⁴(±20%), k₃ = 3.5 × 10⁴(±40%) M^?1 sec^?1; for cobalt(II) k₁ = 1.5 × 10⁵(±20%), k₂ = 8.7 × 10⁵(±20%), k₃ = 2.0 × 10⁵(±40%) M^?1 sec^?1. Arginine binds to metal ions less well than homologous chelating agents due to the electrostatic repulsion arising from the positively charged terminus of the zwitterion. Kinetically, the effect appears in the association rate constants with nickel reactions more strongly influenced than cobalt.     

The features of the Cu2+-entry into the structure of tourmaline

EPR and optical absorption spectra of Cu²⁺ ion were investigated in natural elbaites from Brazil and Zambia and in synthetic olenite single crystal. In elbaite from Zambia, the content of Cu²⁺ ions was found to be about 0.006 pfu, whereas in Brazilian elbaite the amount of this ion can approach up to 0.2 pfu. The rose color of elbaite from Zambia is mainly due to optical absorption at 515 nm related to Mn³⁺ ions. The blue color of Brazilian elbaite is related to Cu²⁺ absorption bands at 695 nm and 920 nm. Spin Hamiltonian parameters of Cu²⁺ calculated from the angular dependence of the EPR spectra are: g _x = 2.054, g _y = 2.092, g _z = 2.374; A _x = 27.8·10^?4 cm^?1, A _y = 59.3·10^?4 cm^{? 1}, A _z = 133.2·10^?4 cm^?1. We propose that Cu²⁺ ions enter into Y octahedra with common edges; the symmetry of these Y octahedra is lowered because of local disorder induced by occupancy of the Y site by cations of very different size and charge, such as Li⁺, Al³⁺, and Cu²⁺.     

Beiträge zum thermischen Verhalten und zur Kristallchemie von wasserfreien Phosphaten. XV. Darstellung,Kristallstruktur und Eigenschaften von Kupfer(II)-ultraphosphat CuP4O11 (≙ Cu2P8O22)

Synthesis, Crystal Structure, and Properties of Copper(II) Ultraphosphate CuP₄O₁₁ CuP₄O₁₁ was synthesised from Cu₂P₄O₁₂ and P₄O₁₀ (500°C, sealed silica ampoules) using iodine and a few mg of CuP₂ or phosphorus as mineraliser. Chemical transport reactions in a temperature gradient 600 → 500°C led to the formation of well developed, colourless, transparent crystals with edge-lengths up to 5 mm (deposition rate m ≈? 2 mg/h). The crystal structure of copper(II) ultraphosphate (C1 ; Z = 8; a = 13.084(3) Å, b = 13.024(2) Å, c = 10.533(2) Å, α = 89.28(2)°, β = 118.42(2)°, γ = 90.30(2)°) has been determined and refined from X-ray data obtained from a pseudo-merohedrally twinned crystal (twin element two-fold rotation axis // b; volume ratio: 17/3; 3063 independent reflections with 2θ ? 53.4°; 291 variables; conventional residual (based on F) R1 = 0.038, wR2 = 0.101 (based on F²), GooF = 1.10). The crystal structure of CuP₄O₁₁ is built from four crystallographically independent ten-membered polyphosphate rings of very similar conformation. These rings are linked to form two-dimensional nets parallel (?2 0 1) planes. There is a close topological relationship between these nets and those formed in polyphosphides CdP₄ and CuP₂. Copper on two crystallographic sites (Cu₂P₈O₂₂) is coordinated by oxygen thus forming elongated [CuO₆] octahedra (d_eq(Cu? O) ≈? 1.96 Å; d_ax(Cu? O) ≈? 2.34 Å). The crystal g-tensor of CuP₄O₁₁ has been determined from powder samples to g₁ = 2.09, g₂ = 2.24, g₃ = 2.36. These values are in good agreement with molecular g-values from calculations within the framework of the angular overlap model on the two independent CuO₆ octahedra (Cu²⁺(1): g_x = 2.09, g_y = 2.10, g_z = 2.52; Cu²⁺(2): g_x = 2.08, g_y = 2.11, g_z = 2.52) assuming exchange coupling. The observed broad absorption band (7000 cm^?1 to 13000 cm^?1) from powder reflectance measurements (4000–28000 cm^?1) and the bulk magnetic susceptibility of μ_exp = 1.99 μ_B is also reproduced nicely by this calculations.     

Kinetics of the reactions of acenaphthene and acenaphthylene and structurally-related aromatic compounds with OH and NO3 radicals,N2O5 and O3 at 296 ± 2 K

The kinetics of the atmospherically important gas-phase reactions of acenaphthene and acenaphthylene with OH and NO₃ radicals, O₃ and N₂O₅ have been investigated at 296 ± 2 K. In addition, rate constants have been determined for the reactions of OH and NO₃ radicals with tetralin and styrene, and for the reactions of NO₃ radicals and/or N₂O₅ with naphthalene, 1- and 2-methylnaphthalene, 2,3-dimethylnaphthalene, toluene, toluene-α,α,α-d₃ and toluene-d₈. The rate constants obtained (in cm³ molecule^?1 s^?1 units) at 296 ± 2 K were: for the reactions of O₃; acenaphthene, <5 × 10^?19 and acenaphthylene, ca. 5.5 × 10^?16; for the OH radical reactions (determined using a relative rate method); acenaphthene, (1.03 ± 0.13) × 10^?10; acenaphthylene, (1.10 ± 0.11) × 10^?10; tetralin, (3.43 ± 0.06) × 10^?11 and styrene, (5.87 ± 0.15) × 10^?11; for the reactions of NO₃ (also determined using a relative rate method); acenaphthene, (4.6 ± 2.6) × 10^?13; acenaphthylene, (5.4 ± 0.8) × 10^?12; tetralin, (8.6 ± 1.3) × 10^?15; styrene, (1.51 ± 0.20) × 10^?13; toluene, (7.8 ± 1.5) × 10^?17; toluene-α,α,α-d₃, (3.8 ± 0.9) × 10^?17 and toluene-d₈, (3.4 ± 1.9) × 10^?17. The aromatic compounds which were observed to react with N₂O₅ and the rate constants derived were (in cm³ molecule^?1 s^?1 units): acenaphthene, 5.5 × 10^?17; naphthalene, 1.1 × 10^?17; 1-methylnaphthalene, 2.3 × 10^?17; 2-methylnaphthalene, 3.6 × 10^?17 and 2,3-dimethylnaphthalene, 5.3 × 10^?17. These data for naphthylene and the alkylnaphthalenes are in good agreement with our previous absolute and relative N₂O₅ reaction rate constants, and show that the NO₃ radical reactions with aromatic compounds proceed by overall H-atom abstraction from substituent-XH bonds (where X = C or O), or by NO₃ radical addition to unsaturated substituent groups while the N₂O₅ reactions only occur for aromatic compounds containing two or more fused six-membered aromatic rings.     

TETRAETHYLPHYROPHOSPHITE AS A BRIDGING LIGAND IN A BIMETALLIC RUTHENIUM(II) - RUTHENIUM(II) COMPLEX

Abstract

The complex μ-TEPP-trans-bis[P(OEt)₃Ru(NH₃)₄]₂(PF₆)₄ has been prepared and characterized by microanalysis, vibrational and electronic spectroscopy (λ_max=299 nm, ?=6.4 × 10² M^?1 cm^?1; λ_max=262 nm, ?=8.6 × 10² M^?1 cm^?1), and cyclic voltammetry (E°'=+0.64 V versus S.C.E., 25°, μ=0.10 M NaCf₃COO, C_H+=1 × 10^?3 M). In aqueous solutions, ([H⁺] > 1 × 10^?4 M), the binuclear species undergoes hydrolysis yielding the mononuclear species trans-(Ru(NH₃)₄P(OEt)₃(H₂O)]²⁺ with a specific rate constant of 2.4 × 10^?5 sec^?1 at 25° δH^#=84.5 kJ mol^?1; δS^#=?49.4 J mol^?1 K^?1.     

Octahedral copper(II) carboxylate complex: synthesis,structural description,DNA-binding and anti-bacterial studies

Self-assembly of CuSO₄, para-methyl-2-phenyl acetate and 1,10-phenanthroline afforded good-quality crystalline complex in quantitative yield. The complex was characterized by FTIR and UV-visible spectroscopy, electrochemistry, and powder and single-crystal XRD studies. Its structure was found to possess axially elongated octahedral symmetry with CuO₄N₂ chromophore. Its purity was assessed by powder XRD spectrum. Absorption study yielded a broad band corresponding to ²E_g→²T_2 g transition. Electrochemical solution study indicated diffusion-controlled irreversible electron transfer process corresponding to Cu(II)/Cu(I) redox couple with diffusion coefficient = 7.89(±0.1)×10^?9 cm²s^?1. Results of spectroscopic techniques support each other. Complex exhibited excellent DNA-binding ability through UV-visible spectroscopy and cyclic voltammetry yielding K_b values 1.399 × 10⁴ M^?1 and 5.81 × 10³ M^?1, respectively. The complex exhibited significant activity against bacterial strains Escherichia coli, Micrococcus luteus and Staphylococcus aureus and good activity against Bacillus subtilis. These preliminary studies impart good biological relevance on the synthesized complex.     

Single crystal electron spin resonance of bis(tetraphenylphosphonium) bis(quinoxaline-2,3-dithiolato)oxovanadate(IV) as a pure compound and diluted in the isomorphous molybdenum(IV) compound

Single crystal e.s.r. spectra at room temperature and Q-band frequencies on [PPh₄]₂ [(Mo/V)O(qdt=₂] (qdt = quinoxaline-2,3-dithiolate) containing ca 3% vanadium gave the spin-Hamiltonian parameters g₁ = 1.977 ± 0.001, g₂ = 1.985 ± 0.001, g₃ = 1.987 ± 0.001, A₁ = (−38.5 ± 0.3) × 10⁻⁴, A₂ = (−45.1 ± 0.3) × 10⁻⁴, A₃ = (−133.2 ± 0.3) × 10⁻⁴ cm⁻¹, and Q′ = −(0.15±0.05) × 10⁻⁴ cm⁻¹. The g and A tensor axes are not coincident. The principal values of the g and A tensors have been analysed via an angular overlap treatment. Proton spin-flip transitions were observed in the spectra at X-band frequencies. Single crystal e.s.r. spectra of undiluted [PPh₄]₂ [VO(qdt)₂] at both X- and Q-band frequencies are interpreted in terms of a two-dimensional weak exchange model with J₀ = −48 ± 2G (ferromagnetic).     

THE EPR SPECTRUM OF COPPER-DOPED SINGLE CRYSTALS OF GLYCYLGLYCINE

Abstract

The EPR Spectrum of Cu(II)-doped into a single crystal of α-glycylglycine is reported. The results show that there are several magnetically non-equivalent sites, only two of which were strong enough to be analysed. The values parameters in the spin Hamiltonian deduced from the data are: g _z =2.242 ± 0.003, g _x =2.062 ± 0.005, g _y =2.044 ± 0.005, A _z =162.8 ± G, A _x =32.6 ± 2.0 G, A _y =21.6 ± 2.0 G. The Cu(II) environment seems to be square planar and involving four ligand molecules, each molecule forming one bond with the copper. The nitrogens are located in the trans position. The bonding is chiefly in-plane [sgrave]-bonding.     

A five-coordinate copper(II) perchlorate complex with tris(N-methylbenzimidazol-2-ylmethyl)amine and salicylate

A five-coordinate copper(II) complex with the tripod ligand tris(N-methylbenzimidazol-2-ylmethyl)amine (Mentb) and salicylate, with the composition [Cu(Mentb) (salicylate)](ClO₄) · 2DMF, was synthesized and characterized by elemental and thermal analyses, electrical conductivity, IR and UV-Vis spectral measurements. The crystal structure of the complex has been determined by single-crystal X-ray diffraction. The Cu(II) is five-coordinate with four N atoms from the Mentb ligand and an O atom of the monodentate salicylate ligand. The N₄O donors are in a distorted trigonal-bipyramid geometry. Cyclic voltammograms indicate a quasireversible Cu²⁺/Cu⁺ couple. The X-band EPR spectrum of the complex confirms the trigonal-bipyramidal structure with g_∥ < g _⊥ and a very small value of A_∥ (41 × 10^?4 cm^?1).     

Synthesis,crystal structure and properties of a novel copper(II) complex with tripod ligand tris(1H-benzimidazol- 2-ylmethyl)amine

A five-coordinate copper complex with the tripod ligand tris(1H-benzimidazol-2-ylmethyl)amine (ntb), of composition [Cu(ntb)(H₂O)] (C1O₄)₂?·?C₅H₄N₂O₃?·?H₂O (C₅H₄N₂O₃?=?4-nitropyridine-N-oxide), was synthesized and characterized by means of elemental analyses, electrical conductivities, thermal analyses, IR, and U.V. The crystal structure of the copper complex has been determined by single-crystal X-ray diffraction, and shows that the Cu^II is bonded to a tris(1H-benzimidazol-2-ylmethyl)amine (ntb) ligand and a water molecule through four N atoms and one O atom, giving a distorted trigonal–bipyramidal coordination geometry with approximate C ₃ molecular symmetry. Cyclic voltammograms of the copper complex indicate a quasi-reversible Cu⁺²/Cu⁺ couple. Electron spin resonance data confirm a trigonal-bipyramidal structure and with g ₂?<?g _ζ and a very small value of A ₂ (20?×?10^?4?cm^?1).     

STRUCTURAL,MAGNETOCHEMICAL, SPECTRAL AND THERMAL PROPERTIES OF TRANS-TETRAKIS(1,2-DIAZOLE) BISBROMOMANGANESE(II)

Abstract

The crystal structure of trans-tetrakis(1,2-diazole)bisbromomanganese(II) was solved by direct methods using single-crystal X-ray (Mo-Kα) diffractometer data and refined to R = 0.054 for 1270 unique reflections with I > 2Δ(I). The compound crystallized from water as almost colourless, monoclinic prisms in space group C2/c (No. 15) with unit cell dimensions a = 14.208(2), b = 9.454(1), c = 15.015(3)Å,β = 118.68(1)°, Z = 4. The structure is formed from [(C₃H₄N₂)₄(Br)₂Mn] molecular units held together through stacking of the 1.2-diazole rings approximately in the b-direction and weak van der Waals forces and hydrogen bonds. The coordination sphere around the Mn²⁺ ion is weakly distorted octahedral with two pairs of trans-positioned 1,2-diazole molecules at distances Mn-N(1) = 2.246(7) and Mn-N(3) = 2.229(6) Å, respectively, in the basal plane and the Br^? ions occupying the apical positions at a distance Mn-Br(1) = 2.729(1)Å. The angles Br(1)-Mn-N(1), Br(1)-Mn-N(3) and N(1)-Mn-N(3) are 91.2(1). 89.6(1) and 87.8(2)°. respectively. The 1,2-diazole rings are practically planar, but slightly tilted (N(1) and N(3) containing rings are at angles of 89.9(3) and 86.4(3)° with respect to the basal coordination plane). The molecular units form columns in the b-direction. The molar magnetic susceptibilities, corrected for diamagnetism by Pascals constants, at 93–303 K show the compound to be of high-spin complex type with a Curie-Weiss equation X'_M = 4.30/(T-3.3) and the reflectance spectrum in accordance with this shows only a very weak shoulder at 23500 cm^?1 corresponding to the ⁶A_1g ± ⁴T_2g transition for the Mn²⁺ ion. The infrared spectrum shows an Mn-Br band at 715 and Mn-N bands at 680, 600 and 580 cm^?1. The thermogravimetric (TG) curve shows the complex to release the 1,2-diazole molecules in two steps in accordance with the structure.