Absorption spectra of first-row transition metal complexes of bacteriochlorins: a theoretical analysis

A theoretical study on a family of divalent transition metal bacteriochlorin complexes (M-BC, where M = Mn, Fe, Co, Ni Cu, and Zn) has been carried out to elucidate their potentialities as active molecules in photodynamic therapy (PDT). To draw a complete picture of their electronic properties, both for the ground and excited states, these complexes have been studied by the means of density functional theory (DFT). The time-dependent DFT (TDDFT) approach was used to interpret the electronic spectra, while solvent effects were taken into account by explicitly considering both two water molecules coordinated to the central metal atom and the contribution from the solvent bulk. Particular attention has been devoted to the analysis of the so-called Q bands, since these can be particularly important for medical applications. Metal substitution and environment (solvent) effects have been analyzed, and good agreement is found between computed and available UV-vis spectra. These theoretical data, especially those relative to the metallobacteriochlorins not yet completely characterized at the experimental level, could give some hints for future medical applications.     

Extended network thiocyanate- and tetracyanoethanide-based first-row transition metal complexes

Linear chain thiocyanate complexes of M(NCS)(2)(OCMe(2))(2) (M = Fe, Mn, Cr) composition have been prepared and structurally, chemically, and magnetically characterized. Fe(NCS)(2)(OCMe(2))(2) exhibits metamagnetic-like behavior, and orders as an antiferromagnet at 6 K. The Mn and Cr compounds are antiferromagnets with T(c) of 30 and 50 K, respectively, with J/k(B) = -3.5 (-2.4 cm(-1)) and -9.9 K (-6.9 cm(-1)), respectively, when fit to one-dimensional (1-D) Fisher chain model (H = -2JS(i)·S(j)). Co(NCS)(2) was prepared by a new synthetic route, and powder diffraction was used to determine its structure to be a two-dimensional (2-D) layer with μ(N,S,S)-NCS motif, and it is an antiferromagnet (T(c) = 22 K; θ = -33 K for T > 25 K). M(NCS)(2)(OCMe(2))(2) (M = Fe, Mn) and Co(NCS)(2) react with (NBu(4))(TCNE) in dichloromethane to form M(TCNE)[C(4)(CN)(8)](1/2), and in acetone to form M[C(4)(CN)(8)](OCMe(2))(2) (M = Fe, Mn, Co). These materials possess μ(4)-[C(4)(CN)(8)](2-) that form 2-D layered structural motifs, which exhibit weak antiferromagnetic coupling. Co(TCNE)[C(4)(CN)(8)](1/2) behaves as a paramagnet with strong antiferromagnetic coupling (θ = -50 K).     

Theoretical study of first-row transition metal porphyrins and their carbonyl complexes

The equilibrium geometry, relative energies, normal mode frequencies, and electron and spin density distributions for first-row transition metal porphyrins M(P) (M is a transition metal in the oxidation state +2, P = C₂₀H₁₂N₄) and their five-and six-coordinate carbonyl complexes M(P)CO and M(P)(CO)(AB) (AB = CO, CN^?, CS) in different spin states have been calculated by the density functional theory B3LYP method with the 6-31G and 6-31G* basis sets. The energies of binding of the CO group to M(P) molecules D(M-CO) have been estimated. The calculated properties change as a function of the metal, the number of carbonyl groups (shown for Fe(P) as an example), and the multiplicity. Calculations show that, for five-coordinate complexes M(P)CO with M = Ti and V, high-spin states and significant D(M-CO) energies are typical. For Fe(P)CO, a singlet with a small D(M-CO) energy is preferable. For Cr(P)CO and Mn(P)CO (which also have small D(M-CO) energies), the states with different spins, which strongly differ in geometry and electronic structure, are close in energy, within 0.1–02. eV. The energy of binding of CO to M(P)CO (M = Cr, Mn, Fe) is considerably higher than the energy of binding of CO to M(P), which is evidence that the transformation of five-coordinate metalloporphyrins into six-coordinate ones is energetically favorable. The behavior of the D(M-CO) energies is interpreted using a qualitative model that considers not only the effects of participation (or nonparticipation) of “active” $ d_{x^2 - y^2 } The equilibrium geometry, relative energies, normal mode frequencies, and electron and spin density distributions for first-row transition metal porphyrins M(P) (M is a transition metal in the oxidation state +2, P = C₂₀H₁₂N₄) and their five-and six-coordinate carbonyl complexes M(P)CO and M(P)(CO)(AB) (AB = CO, CN⁻, CS) in different spin states have been calculated by the density functional theory B3LYP method with the 6-31G and 6-31G* basis sets. The energies of binding of the CO group to M(P) molecules D(M-CO) have been estimated. The calculated properties change as a function of the metal, the number of carbonyl groups (shown for Fe(P) as an example), and the multiplicity. Calculations show that, for five-coordinate complexes M(P)CO with M = Ti and V, high-spin states and significant D(M-CO) energies are typical. For Fe(P)CO, a singlet with a small D(M-CO) energy is preferable. For Cr(P)CO and Mn(P)CO (which also have small D(M-CO) energies), the states with different spins, which strongly differ in geometry and electronic structure, are close in energy, within 0.1–02. eV. The energy of binding of CO to M(P)CO (M = Cr, Mn, Fe) is considerably higher than the energy of binding of CO to M(P), which is evidence that the transformation of five-coordinate metalloporphyrins into six-coordinate ones is energetically favorable. The behavior of the D(M-CO) energies is interpreted using a qualitative model that considers not only the effects of participation (or nonparticipation) of “active” , and , d _xz , and d _yz AO in bonding of M to the P ring and axial ligands, but also the fraction of the total bond energy consumed for the preparation (promotion) of those “valence states” of the M(P) molecules that are realized in M(P)CO and M(P)(CO)(AB) complexes. For the series of compounds Fe(P)(CO)₂ − Fe(P)(CO)(CS) − Fe(P)(CS)₂ − Fe(P)(CO)(CN⁻) in the singlet, triplet, and ionized states, the trans influence of axial ligands in low-spin metalloporphyrins is shown to follow the same qualitative scheme as is typical of octahedral transition metal complexes: in mixed-ligand complexes (as compared to the symmetric ones), the stronger bond becomes shorter and even stronger, while the weaker bond becomes longer and even weaker. It is assumed that the same scheme will persist for more complicated low-spin six-coordinate metalloporphyrins in the states with the vacant AO and occupied d _xz and d _xz AOs involved in bonding with both axial ligands with the filled shell. Original Russian Text ? O.P. Charkin, A.V. Makarov, and N.M. Klimenko, 2008, published in Zhurnal Neorganicheskoi Khimii, 2008, Vol. 53, No. 5, pp. 781–794.     

UV photoelectron spectra of first-row transition metal hydridocarbonyl and hydridotrifluorophosphine complexes

The He(I) photoelectron spectrum of FeH₂(PF₃)₄ is reported, and the bands are assigned and compared with those of the analogous carbonyl complex. Molecular obrital energies for the MH σ-bonding orbitals, metal-3 d orbitals and metal-phosphorus σ-bonding orbitals for the hydridocarbonyl and hydridotrifluorophosphine complexes MnHL₅, FeH₂L₄ and CoHL₄ (L CO and PF₃) are compared and correlations discussed.     

Pyridazine- versus pyridine-based tridentate ligands in first-row transition metal complexes

A series of first-row transition metal complexes with the unsymmetrically disubstituted pyridazine ligand picolinaldehyde (6-chloro-3-pyridazinyl)hydrazone (PIPYH), featuring an easily abstractable proton in the backbone, was prepared. Ligand design was inspired by literature-known picolinaldehyde 2-pyridylhydrazone (PAPYH). Reaction of PIPYH with divalent nickel, copper, and zinc nitrates in ethanol led to complexes of the type [Cu(II)(PIPYH)(NO(3))(2)] (1) or [M(PIPYH)(2)](NO(3))(2) [M = Ni(II) (2) or Zn(II) (3)]. Complex synthesis in the presence of triethylamine yielded fully- or semideprotonated complexes [Cu(II)(PIPY)(NO(3))] (4), [Ni(II)(PIPYH)(PIPY)](NO(3)) (5), and [Zn(II)(PIPY)(2)] (6), respectively. Cobalt(II) nitrate is quantitatively oxidized under the reaction conditions to [Co(III)(PIPY)(2)](NO(3)) (7) in both neutral and basic media. X-ray diffraction analyses reveal a penta- (1) or hexa-coordinated (2, 3, and 7) metal center surrounded by one or two tridentate ligands and, eventually, κ-O,O' nitrate ions. The solid-state stoichiometry was confirmed by electron impact (EI) and electrospray ionization (ESI) mass spectrometry. The diamagnetic complexes 5 and 6 were subjected to (1)H NMR spectroscopy, suggesting that the ligand to metal ratio remains constant in solution. Electronic properties were analyzed by means of cyclic voltammetry and, in case of copper complexes 1 and 4, also by electron paramagnetic resonance (EPR) spectroscopy, showing increased symmetry upon deprotonation for the latter, which is in accordance with the proposed stoichiometry [Cu(II)(PIPY)(NO(3))]. Protic behavior of the nickel complexes 2 and 5 was investigated by UV/vis spectroscopy, revealing high π-backbonding ability of the PIPYH ligand resulting in an unexpected low acidity of the hydrazone proton in nickel complex 2.     

Approximate STO functions for the first-row transition metal atoms

Slater type orbital (STO) basis sets for the atoms Sc-Zn have been derived using a technique based on the distance between subspaces. The accuracy for several properties of these basis sets has been tested. Basis sets studied are of both single- and double-zeta sizes, although this technique can be generalized for any size. Uniform quality criteria through the series of atoms Sc-Zn are difficulty to establish due to the varying number of d electrons. A comparative study at the atomic level of the quality of STO basis sets (both the two new basis sets and Clementi's basis sets) for the first-row transition elements has been carried out. Results show that the new basis sets provide better simulation for several properties. Molecular calculations on compounds with these atoms using a Gaussian expansion fitted according to the new values of optimized STOs are also included. The results obtained are similar to those reported when STO-3G basis set is used.     

A periodic walk: a series of first-row transition metal complexes with the pentadentate ligand PY5

A series of transition metal complexes derived from the pentadentate ligand PY5, 2,6-(bis-(bis-2-pyridyl)methoxymethane)pyridine, illustrates the intrinsic propensity of this ligand to complex metal ions. X-ray structural data are provided for six complexes (1-6) with cations of the general formula [M(II)(PY5)(Cl)](+), where M = Mn, Fe, Co, Ni, Cu, Zn. In complexes 1-4 and 6, the metal ions are coordinated in a distorted-octahedral fashion; the four terminal pyridines of PY5 occupy the equatorial sites while the axial positions are occupied by the bridging pyridine of PY5 and a chloride anion. Major distortions from an ideal octahedral geometry arise from displacement of the metal atom from the equatorial plane toward the chloride ligand and from differences in pyridine-metal-pyridine bond angles. The series of complexes shows that M(II) ions are consistently accommodated in the ligand by displacement of the metal ion from the PY5 pocket, a tilting of the axial pyridine subunit, and nonsymmetrical pyridine subunit ligation in the equatorial plane. The displacement from the ligand pocket increases with the ionic radius of M(II). The axial pyridine tilt, however, is approximately the same for all complexes and appears to be independent of the electronic ground state of M(II). In complex 5, the Cu(II) ion is coordinated by only four of the five pyridine subunits of the ligand, resulting in a square-pyramidal complex. The overall structural similarity of 5 with the other complexes reflects the strong tendency of PY5 to enforce a distorted-octahedral coordination geometry. Complexes 1-6 are further characterized in terms of solution magnetic susceptibility, electrochemical behavior, and optical properties. These show the high-spin nature of the complexes and the anticipated stabilization of the divalent oxidation state.     

Formation constants and thermodynamic functions for some bivalent transition metal complexes with p-sulphono-salicylidene-sulphanilamide

No potentiometric work on complex formation with the Schiff-base p-sulphono-salicylidene-sulphanilamide (p-SUSASUD) has appeared. This paper describes potentiometric studies of complex formation by Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) with the Schiff-base ligand, p-sulphono salicylidene-sulphanilamide in aqueous medium at a constant ionic strength (μ = 0.1 M KNO₃). The metal ligand stability constants and thermodynamic parameters like ΔG, ΔH, ΔS and thermodynamic stabilization energy (δH) have been determined at 30 ± 1°C.     

Valence 4p functions for the first-row transition metal atoms

For the valence 4p orbitals of the first-row transition metal atoms Sc through Zn, Gaussian-type basis functions are developed referring to excited 3d ^m 4s ¹4p ¹ electronic configurations. Molecular tests of the present work 4p sets are performed for the Cu atom, the diatomic Cu₂ molecule, and Cu₉ and Cu₁₃ clusters, and the results are compared with those from two literature sets. Received: 17 January 2000 / Accepted: 30 May 2000 / Published Online: 11 September 2000     

Synthesis, thermal and spectral studies of first-row transition metal complexes with Girard P reagent-based ligand

A new series of first-row transition metal complexes with 1-acetylpyridinium chloride-4-benzoyl thiosemicarbazide (H2GPBzIT) have been prepared and characterized by elemental analysis, spectroscopic and magnetic measurements. The proton-ligand ionization constants were determined potentiometrically using Irving-Rossotti technique. The stability constants of complexes were also calculated and were found in agreement with the sequence of stability constants of Irving and Williams. Thermal stability and degradation kinetics have been measured using thermogravimetric analyzer. Kinetic parameters were obtained for each stage of thermal degradation of complexes using Coats-Redfern method.     

The hapticity of octafluorocyclooctatetraene in its first-row mononuclear transition metal carbonyl complexes: effect of perfluorination

The iron tricarbonyl complex of octafluorocyclooctatetraene was synthesized by Hughes and co-workers and shown by X-ray crystallography to have a trihapto–monohapto structure (η^3,1-C₈F₈)Fe(CO)₃ in contrast to the tetrahapto structure (η⁴-C₈H₈)Fe(CO)₃ formed by the non-fluorinated cyclooctatetraene. This difference has stimulated a comprehensive density functional theoretical study of the octafluorocyclooctatetraene metal carbonyl complexes (C₈F₈)M(CO) _n (n = 4, 3, 2, 1 for M = Ti, V, Cr, Mn, and Fe; n = 3, 2, 1 for M = Co, Ni) for comparison with their hydrogen analogues (C₈H₈)M(CO) _n . In most such systems, the substitution of fluorine for hydrogen leads to relatively small changes in the preferred structures. However, for the iron carbonyl derivatives (C₈X₈)Fe(CO)₃ (X = H, F), the difference observed experimentally has been confirmed by theory with (η^3,1-C₈F₈)Fe(CO)₃ and (η⁴-C₈H₈)Fe(CO)₃ being the lowest energy structures by 4 and 14 kcal/mol, respectively. The ligand exchange reactions C₈H₈ + (C₈F₈)M(CO) _n  → C₈F₈ + (C₈H₈)M(CO) _n are predicted to be exothermic for almost all of the systems considered, with the (η^3,1-C₈X₈)Fe(CO)₃ system being the main exception. This suggests that the C₈F₈ ligand generally bonds more weakly to transition metals than the C₈H₈ ligand in accord with the electron-withdrawing effect of the ligand fluorine atoms.     

About the calculation of exchange coupling constants in polynuclear transition metal complexes

The application of theoretical methods based on the density functional theory with hybrid functionals provides good estimates of the exchange coupling constants for polynuclear transition metal complexes. The accuracy is similar to that previously obtained for dinuclear compounds. We present test calculations on simple model systems based on H. He and CH(2). He units to compare with Hartree-Fock and multiconfigurational results. Calculations for complete, nonmodeled polynuclear transition metal complexes yield coupling constants in very good agreement with available experimental data.     

Broken symmetry approach to calculation of exchange coupling constants for homobinuclear and heterobinuclear transition metal complexes

The application of broken symmetry density functional calculations to homobinuclear and heterobinuclear transition metal complexes produces good estimates of the exchange coupling constants as compared to experimental data. The accuracy of different hybrid density functional theory methods was tested. A discussion is presented of the different methodological approaches that apply when a broken symmetry wave function is used with either Hartree–Fock or density functional calculations. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 1391–1400, 1999     

Structure and bonding in first-row transition metal dicarbide cations MC2+

A theoretical study of the first-row transition metal dicarbide cations MC2+ (M=Sc-Zn) has been carried out. Predictions for different molecular properties that could help in their eventual experimental detection have been made. Most MC2+ compounds prefer a C2v symmetric arrangement over the linear geometry. In particular, the C2v isomer is specially favored for early transition metals. Only for CuC2+ is the linear isomer predicted to be the global minimum, although by only 1 kcal/mol. In all cases the isomerization barrier between cyclic and linear species seems to be very small (below 2 kcal/mol). The topological analysis of the electronic density shows that most C2v isomers are T-shaped structures. In general, MC2+ compounds for early transition metals have larger dissociation energies than those formed by late transition metals. In most cases the dissociation energies for MC2+ compounds are much smaller than those obtained for their neutral analogues. An analysis of the bonding in MC2+ compounds in terms of the interactions between the valence orbitals of the fragments helps to interpret their main features.     

Spectrophotometric studies,stability constants and thermodynamics for complexes ofo-hydroxyacetophenone isobutyroylhydrazone with some bivalent transition metal ions

Summary The u.v. spectra ofo-hydroxyacetophenone isobutyroylhydrazone (HAIBuH) were investigated in pure organic solvents as well as in Britton Robinson buffer solutions of varyingpH values. The interaction ofHAIBuH with Co(II), Ni(II) and Cu(II) were studied spectrophotometrically. The optimumpH favouring the formation of the highly coloured complexes are 8.5, 8.0 and 7.5 for Co(II), Ni(II) and Cu(II), respectively. The stoichiometries of these complexes were determined and indicated the formation of 1:2 (metal:ligand) complexes of Co(II) and Ni(II) and a 1:1 complex of Cu(II). The dissociation constantspK ^H ofHAIBuH and the overall stability constants log of their complexes were determined at different temperatures (293, 303 and 313 K). The corresponding thermodynamic parameters (G, H and S) in 20% (v/v) ethanol-water mixture were derived and discussed.

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Spektrophotometrische Untersuchungen, Stabilitätskonstanten und Thermodynamik der Komplexe vono-Hydroxyacetophenonisobutyroylhydrazon mit einigen bivalenten Übergangsmetallionen

Zusammenfassung Die UV-Spektren vono-Hydroxyacetophenon-isobutyroylhydrazon (HAIBuH) wurden in reinen organischen Solventien und in Britton-Robinson-Pufferlösungen von verschiedenempH gemessen. Die Wechselwirkung vonHAIBuH mit Co(II), Ni(II) und Cu(II) wurde spektrophotometrisch untersucht. Die optimalenpH-Werte zur maximalen Ausbildung der starkgefärbten Komplexe sind 8.5, 8.0 bzw. 7.5 für Co(II), Ni(II) bzw. Cu(II). Für die Stöchiometrien wurde ein Metall: Ligand-Verhältnis 1:2 für Co(II) und Ni(II) und 1:1 für Cu(II) bestimmt. Die DissoziationskonstantenpK ^H vonHAIBuH und die Gesamtstabilitätskonstanten log der Komplexe wurden bei verschiedenen Temperature bestimmt (293, 303 und 313 K) und die entsprechenden thermodynamischen Parameter (G, H und S) in 20% (v/v) Ethanol-Wasser-Mischung errechnet und diskutiert.

     

Density functional study of ammonia activation by late first-row transition metal cations

Density functional theory (DFT) in its B3LYP implementation is used to investigate the reaction of ammonia with the late (Co(+), Ni(+), and Cu(+)) first-row transition metal cations in both high- and low-spin states. The potential energy surfaces (PES's) leading to three different exit channels are closely examined. The binding energies for the reaction products are calculated and compared with the corresponding experimental values. A comparison with our earlier works covering the reactivity of the Sc-Fe series of cations is made in order to underline similarities and differences of the reaction mechanisms as well as to establish trends along the row.     

Tetracyanomanganate(II) and its salts of divalent first-row transition metal ions

The first known paramagnetic, tetrahedral cyanide complex, [Mn(II)(CN)(4)](2)(-), is formed by the photoinduced decomposition of [Mn(IV)(CN)(6)](2)(-) in nonaqueous solutions or by thermal decomposition in the solid state. In acetonitrile or dichloromethane, photoexcitation into the ligand-to-metal charge transfer band (lambda(max) = 25 700 cm(-1), epsilon = 3700 cm(-1) M(-1)) causes the homolytic cleavage of cyanide radicals and reduction of Mn(IV). Free cyanide in dichloromethane leads to the isolation of polycyanide oligomers such as [C(12)N(12)](2)(-) and [C(4)N(4)](-), which was crystallographically characterized as the PPN(+) salt C(40)H(30)N(5)P(2): monoclinic space group = I2/a, a = 18.6314(2) A, b = 9.1926(1) A, c = 20.8006(1), beta =106.176(2) degrees, Z = 4]. In the solid state Mn(IV)-CN bond homolysis is thermally activated above 122 degrees C, according to differential scanning calorimetry measurements, leading to the reductive elimination of cyanogen. The [Mn(II)(CN)(4)](2-) ion has a dynamic solution behavior, as evidenced by its concentration-dependent electronic and electron paramagnetic spectra, that can be attributed to aggregation of the coordinatively and electronically unsaturated (four-coordinate, 13-electron) metal center. Due to dynamics and lability of [Mn(II)(CN)(4)](2-) in solution, its reaction with divalent first-row transition metal cations leads to the formation of lattice compounds with both tetrahedral and square planar local coordination geometries of the metal ions and multiple structural and cyano-linkage isomers. alpha-Mn(II)[Mn(II)(CN)(4)] has an interpenetrating sphalerite- or diamond-like network structure with a unit cell parameter of a = 6.123 A (P43m space group) while a beta-phase of this material has a noninterpenetrating disordered lattice containing tetrahedral [Mn(II)(CN)(4)](2-). Linkage isomerization or cyanide abstraction during formation results in alpha-Mn(II)[Co(II)(CN)(4)] and Mn(II)[Ni(II)(CN)(4)] lattice compounds, both containing square planar tetracyanometalate centers. alpha-Mn(II)[Co(II)(CN)(4)] is irreversibly transformed to its beta-phase in the solid state by heating to 135 degrees C, which causes a geometric isomerization of [Co(II)(CN)(4)](2)(-) from square planar (nu(CN) = 2114 cm(-1), S = (1)/(2)) to tetrahedral (nu(CN) = 2158 cm(-1), S = (3)/(2)) as evidenced by infrared and magnetic susceptibility measurements. Mn(II)[Ni(II)(CN)(4)] is the only phase formed with Ni(II) due to the high thermodynamic stability of square planar [Ni(II)(CN)(4)](2)(-).     

Divalent transition metal complexes

4-(4-ethoxy-phenylhydrazono)-1-phenyl-3-methyl-1H-pyrazolin-5(4H)-one (5a) (H-EMPhP) as ligand and its Cu(II), Co(II) and Ni(II) complexes 4(a-c) were synthesized and characterized by their thermal and spectral properties. The azocoupling product (H-EMPhP), able of azo-hydrazone tautomerism 5(a-d), act as a bidentate ligand involving in coordination the azogroup nitrogen of its common anion (7) and the oxygen atom that is bound to the pyrazole ring of the mentioned anion (7).     

Binding of some first-row transition metal ions by a poly(iminoethylene)dithiocarbamate copolymer

The binding of the transition metal ions VO²⁺, Fe²⁺, Fe³⁺, CO²⁺, Co³⁺, Ni²⁺ and Cu²⁺ by a poly(iminoethylene) dithiocarbamate copolymer has been investigated by uptake studies and physical measurements (electronic, IR, and ESR spectra and magnetic susceptibility). Metal ions may be bound by both the dithiocarbamato and amino groups of the co-polymer. Binding to nitrogen (in addition to binding to sulphur) increases in the order FE(II)<Ni(II)<Cu(II) and accounted for increasing metal ion uptake by the copolymer in the same order. Factors which determine the relative uptake of the metal ions by the copolymer are discussed.     

Stability constants of 2-mercaptohistamine metal complexes

Summary Stability constants of 2-mercaptohistamine (2-MH) with a number of transition metal ions were determined by a potentiometric titration method and the coordination mode of (2-MH) metal complexes were thereby characterized. With Mn^II, Fe^ll, Co^II, and Ni^II, coordination occurred through both the imidazole-nitrogen and amino groups, while with Zn^II, Cd^II, Pb^II, and Hg^II, both thiolate and amino groups, contribute to the coordination. in the 2-MH copper complex, polymer formation is suggested on the basis of visible absorption and e.p.r. spectra.