Ligand Field Spectra Research Articles

Ab Initio Study of Vibronic and Magnetic 5f-to-5f and Dipole-Allowed 5f-to-6d and Charge-Transfer Transitions in [UX6]n- (X = Cl, Br; n = 1, 2).

The absorption spectra of the octahedral [UX6]n- (X = Cl, Br; n = 1, 2) complexes in the near-infrared (NIR) and UV-vis spectral regions were studied theoretically, using a relativistic restricted active space second-order perturbation theory (RASPT2) wavefunction framework, with the spin-orbit (SO) coupling treated by state interaction, in conjunction with Kohn-Sham density functional theory calculations for determining the vibrational normal modes. The electric-dipole-allowed ligand-to-metal charge-transfer (LMCT) and 5f-to-6d transitions, and the electric-dipole-forbidden 5f-to-5f ligand field (LF) transitions, are thereby obtained within the same theoretical framework. For the 5f-to-5f LF transitions, the observed absorption intensity is mostly due to vibronic coupling with low-energy electric-dipole-allowed transitions, but in some cases, the magnetic dipole intensity of the purely electronic transition has comparable intensity to the vibronic transitions. Experimental LF spectra of 5f2 open-shell systems have been reported decades back, but ab initio calculations of their vibronic intensity have not yet been reported in the literature. Although the LF spectra for the 5f2 systems can be assigned in detail, based on the calculations, the spectra are very complex and the underlying electronic states are strongly multiconfigurational. Therefore, the usefulness of the LF spectra beyond serving as a "fingerprint" of the LF and the metal oxidation state appears to be limited.

Calculation of Dipole-Forbidden 5f Absorption Spectra of Uranium(V) Hexa-Halide Complexes.

Restricted-active-space wave function calculations including spin-orbit coupling, in combination with Kohn-Sham density functional calculations of vibrational modes, were used to determine the vibronic and electronic absorption intensities of the near-infrared electric dipole-forbidden 5f-5f transitions of representative uranium(V) hexa-halide complex ions. The agreement with experimentally assigned vibronic and electronic transitions measured for powder or solution samples of salts of the complex ions is reasonable overall and excellent for the experimentally best-resolved E5/2u → E5/2u' bands. The intensity of the vibronic transitions may be borrowed from ligand-to-metal charge-transfer excitations as well as 5f-to-6d metal-centered transitions. Magnetically allowed electronic transitions contribute to the two lower-frequency bands of the ligand-field spectrum.

Measurement of the Ligand Field Spectra of Ferrous and Ferric Iron Chlorides Using 2p3d RIXS.

Ligand field spectra provide direct information about the electronic structure of transition metal complexes. However, these spectra are difficult to measure by conventional optical techniques due to small cross sections for d-to-d transitions and instrumental limitations below 4000 cm-1. 2p3d resonant inelastic X-ray scattering (RIXS) is a second order process that utilizes dipole allowed 2p to 3d transitions to access d-d excited states. The measurement of ligand field excitation spectra by RIXS is demonstrated for a series of tetrahedral and octahedral Fe(II) and Fe(III) chlorides, which are denoted Fe(III)-Td, Fe(II)-Td, Fe(III)-Oh, and Fe(II)-Oh. The strong 2p spin-orbit coupling allows the measurement of spin forbidden transitions in RIXS spectroscopy. The Fe(III) spectra are dominated by transitions from the sextet ground state to quartet excited states, and the Fe(II) spectra contain transitions to triplet states in addition to the spin allowed 5Γ → 5Γ transition. Each experimental spectrum is simulated using a ligand field multiplet model to extract the ligand field splitting parameter 10Dq and the Racah parameters B and C. The 10Dq values for Fe(III)-Td, Fe(II)-Td, and Fe(III)-Oh are found to be -0.7, -0.32, and 1.47 eV, respectively. In the case of Fe(II)-Oh, a single 10Dq parameter cannot be assigned because Fe(II)-Oh is a coordination polymer exhibiting axially compressed Fe(II)Cl 6 units. The 5T → 5E transition is split by the axial compression resulting in features at 0.51 and 0.88 eV. The present study forms the foundation for future applications of 2p3d RIXS to molecular iron sites in more complex systems, including iron-based catalysts and enzymes.

Synthesis, structural characterization, superoxide dismutase and antimicrobial activities studies of copper (II) complexes with 2-(E)-(2-(2-aminoethylamino) methyl)-4-bromophenol and (19E, 27E)-N1, N2-bis (phenyl (pyridine-2-yl)-methylene)-ethane-1, 2-diamine as ligands

Three new copper (II) complexes, [Cu(L)(H2O)]ClO4 (1), [Cu(L1)(ClO4)]+ (2) and [Cu(L1)]2+ (3), where HL=2-(E)-(2-(2-aminoethylamino)methyl)-4-bromophenol, L1 =(19E, 27E)-N1,N2-bis(phenyl(pyridine-2-yl)-methylene)-ethane-1, 2-diamine, have been synthesized and characterized by using various physic-chemical and spectroscopic methods. The solid-state structures of 1 and 2 were determined by single crystal X-ray crystallography. Infrared spectra, ligand field spectra and magnetic susceptibility measurements agree with the observed crystal structures. The molecular structure of copper complexes showed that the ligands occupies the basal plane of square pyramidal geometry with the H2O of 1 or the ClO4 of 2 occupying the remaining apical position. Complexes 1 and 2 crystallize in the monoclinic system of the space group P21/c, a=10.5948(6)Å, b=19.6164(11)Å, c=8.6517(5)Å, α=90°, β=108.213(2)°, γ=90° and Z=4 for 1, a=9.5019(3)Å, b=11.3 801(3)Å, c=25.3168(14)Å, α=90°, β=100.583(4)°, γ=90°, and Z=4 for 2. The synthesized Schiff base (HL/L1) was behaves as tetradentate ON3/N4 ligands with donor groups suitable placed for forming 2 or 3 five membered chelate rings. Copper (II) complexes display X-band EPR spectra in 100% DMSO at 77K giving g||>g⊥>2.0023 indicating dx2–y2 ground state. The half-wave potential values for Cu (II)/Cu (I) redox couple obtained in the reaction of the copper (II) complexes with molecular oxygen and superoxide radical (O2−) electronegated in DMSO are in agreement with the SOD-like activity of the copper (II) complexes. In vitro antimicrobial activities of the complexes against the two bacteria (Escherichia coli, Salmonella typhi) and the two fungi (Penicillium, Aspergillus sp.) have been investigated comparing with the Schiff base ligands.

Synthesis, electrochemical, structural, spectroscopic and biological activities of mixed ligand copper (II) complexes with 2-{[(Z)-(5-bromo-2-hydroxyphenyl)methylidene]amino}benzoic acid and nitrogenous bases

Three new copper (II) complexes viz. [Cu(L1)(bipy)]⋅2H2O 1, [Cu(L1)(dmp)]⋅CH3CN 2, [Cu(L1)(phen)] 3 where L1H2=2-{[(Z)-(5-bromo-2-hydroxyphenyl)methylidene]amino}benzoic acid, bipy=2,2′-bipyridine; dmp=2,9-dimethyl 1,10-phenanthroline, phen=1,10-phenanthroline have been synthesized and characterized by physic-chemical and spectroscopic methods. The solid-state structures of 1 and 2 were determined by single crystal X-ray crystallography, which revealed distorted square pyramidal geometry. In solid-state structure, 1 is self-assembled via intermolecular π…π stacking and the distances between centroids of aromatic ring is 3.525Å. L1H2 is a diprotic tridentate Schiff base ligand having ONO donor site. Infrared spectra, ligand field spectra and magnetic susceptibility measurements agree with the observed crystal structures. The EPR spectra of these complexes in frozen DMSO solutions showed a single at g ca. 2. The trend in g-value (g||>g⊥>2.0023) suggests that the unpaired electron on copper (II) has dx2-y2 character. Copper (II) complexes 1–3 yielded an irreversible couple corresponding to the Cu (II)/Cu (I) redox process. Superoxide dismutase activity of all these complexes has been revealed to catalyze the dismutation of superoxide (O2-) and IC50 values were evaluated and discussed. Antimicrobial and antifungal activities of these complexes were also investigated.

Synthesis, spectroscopy and magnetism of fluoridoborate transition metal complexes with aminoflavone ligand (3-af). X-ray crystal structure of [Cu(BF4)2(3-af)2] and [Zn(BF4)(3-af)2](BF4)·CH3C(O)OEt

The compounds of general formula M(BF4)2(3-af)2 3H2O where M=Ni(II), Co(II) and Cu(BF4)2(3-af)2, [Zn(BF4)(3-af)2](BF4)·CH3C(O)OEt with 3-aminoflavone (3-af) have been synthesized and characterized. The crystal structure of copper and zinc complexes has been determined by X-ray diffraction method. The complexes have been characterized by infrared, ligand field spectra and magnetic measurements. These mononuclear complexes are tetragonal, [4+2] coordinated (Cu, Ni and Co) and penta-coordinated (Zn). The ligand acts as N,O-chelate. The results of the magnetic studies of complexes in 1.8–300K range indicate a very weak intermolecular interaction between magnetic centers. The magnetic behavior of cobalt and nickel complexes indicates an important orbital contribution via spin–orbit coupling. From X-ray powder-diffraction patterns, the complexes of Ni(II) (2) and Co(II) (3) were found not to be isomorphous.

Solid-state transition metal chemistry with imidazol-2-yl-methyl[N-(n-butyl)amino]-diphenylphosphine oxide (2-izmape). Crystal structure of the [Cu(2-izmape)2](ClO4)2 complex

The complexes of general formula [Cu(2-izmape)2](ClO4)2, [M(2-izmape)2(ClO4)2], M=Ni and Co, with imidazol-2-yl-methyl[N-(n-butyl)amino]-diphenylphosphine oxide (2-izmape) ligand have been synthesized and characterized. In particular, the crystal structure of copper complex has been determined. The complexes have been characterized by infrared, ligand field spectra and magnetic measurements. These mononuclear complexes are 4+2 coordinated (Cu) and 6-coordinated (Ni and Co). The ligand acts as N,N,O′-chelate (Cu) and N,N-chelate (Ni, Co). The results of the magnetic studies of complexes in the range of 1.8–300K indicate the copper centers are magnetically isolated. For Ni and Co complexes a very weak intermolecular ferromagnetic interaction is suggested. The magnetic behavior of cobalt and nickel complexes indicates an important orbital contribution in magnetic properties via spin-orbit.

Synthesis, spectroscopic, electrochemical, magnetic properties and super oxide dismutase activity of nickel (II) complexes with unsymmetrical Schiff base ligands

s: Five new mixed-ligand nickel (II) complexes; viz; [Ni (BHM)(PMDT)]1; [Ni(BHM)(dien)] 2; [Ni(BHM)(L 1 )]3; [Ni(BHM)(L 2 )] 4, [Ni(BHM)(L 3 )] 5; where H2BHM= N ’ -(1E)-(5-bromo-2-hydroxyphenyl) methylidene] benzoylhydrazide, PMDT= N,N,N’,N, ” N ” -Pentamethyldiethylenetriamine; dien= diethylenetriamine; L 1 = N,Ndimethyl-N’ (Pyrid-2-yl-methyl) ethylenediamine; L 2 = N-methyl-N’-(pyrid-2ylmethyl)ethylenediamine; L 3 = N,N-dimethyl-N’-(6-methyl)pyrid-2-ylmethyl) ethylenediamine, have been synthesized and characterized by using elemental analyses, FAB (fast atomic bombardment), magnetic measurements, electronic absorption , conductivity measurements, cyclic voltammetry (CV) and IRspectroscopy . All the complexes yielded an irreversible couple that can be assigned to a Ni II → Ni I redox process. Infrared spectra, ligand field spectra and magnetic susceptibility measurements agree with the observed octahedral environment. H2BHM is a diprotic tridentate Schiff base ligand (ONO donor atom) whereas L 1 -L 3 possessing N3 coordination sites. The SOD activities have been measured using alkaline DMSO as a source of superoxide radical (O2 – ) and nitro blue tetrazolium (NBT) as O2 – scavenger.

Synthesis, Characterization, and Spectroscopic Characteristics of Chromium(6+) and -(4+) Silicalite-2 (ZSM-11) Materials

The systematic incorporation of Cr ions into a phase-pure silicalite-2 lattice was accomplished through hydrothermal synthesis using 3,5-dimethylpiperidinium as a templating agent. The Cr ions, after calcination to remove the template, were in the 6+ oxidation state, with their incorporation into the lattice verified by the systematic expansion of the unit cell as a function of Cr loading. The structures of these materials as revealed by electronic spectroscopy and X-ray absorption near-edge spectroscopy (XANES) were consistent with the dioxo structure typically exhibited by Cr(6+) in an amorphous silica matrix. These materials were highly luminescent, with the emission spectra showing an unusually well-resolved vibronic structure characteristic of an emissive site with little inhomogeneous broadening. The site was reduced under flowing CO to Cr(4+), as characterized by XANES. The reduction of Cr from 6+ to 4+ resulted in unit-cell volumes that are systematically smaller than those observed with Cr(6+), even though the ionic radius of Cr(4+) is larger. This is attributed to the fact that the Cr(6+) site is not a simple metal ion but a significantly larger [CrO(2)](2+) unit, requiring a larger lattice expansion to accommodate it. Through analysis of the XANES preedge and assignment of the ligand-field spectrum of the Cr(4+) ions, it is possible to establish isomorphic substitution into the silicalite lattice.

Jahn–Teller-distorted dimeric anions in (cat)[Mn 2F 8(H 2O) 2]·2H 2O (cat = pipzH 2, dabcoH 2) and (dabcoH 2) 2[Mn 2F 8(H 2PO 4) 2

Using biprotonated dabco (1,4-diazabicyclo[2.2.2]octane) or pipz (piperazine) as counter cations, mixed-ligand fluoromanganates(III) with dimeric anions could be prepared from hydrofluoric acid solutions. The crystal structures were determined by X-ray diffraction on single crystals: dabcoH 2[Mn 2F 8(H 2O) 2]·2H 2O ( 1), space group P2 1, Z = 2, a = 6.944(1), b = 14.689(3), c = 7.307(1) Å, β = 93.75(3)°, R 1 = 0.0240; pipzH 2[Mn 2F 8(H 2O) 2]·2H 2O ( 2), space group P 1 ¯ , Z = 2, a = 6.977(1), b = 8.760(2), c = 12.584(3) Å, α = 83.79(3), β = 74.25(3), γ = 71.20(3)°, R 1 = 0.0451; (dabcoH 2) 2[Mn 2F 8(H 2PO 4) 2] ( 3), space group P2 1/ n, Z = 4, a = 9.3447(4), b = 12.5208(4), c = 9.7591(6) Å, β = 94.392(8)°, R 1 = 0.0280. All three compounds show dimeric anions formed by [MnF 5O] octahedra (O from oxo ligands) sharing a common edge, with strongly asymmetric double fluorine bridges. In contrast to analogous dimeric anions of Al or Fe(III), the oxo ligands (H 2O ( 1, 2) or phosphate ( 3)) are in equatorial trans-positions within the bridging plane. The strong pseudo-Jahn–Teller effect of octahedral Mn(III) complexes is documented in a huge elongation of an octahedral axis, namely that including the long bridging Mn–F bond and the Mn–O bond. In spite of different charge of the anion in the fluoride phosphate, the octahedral geometry is almost the same as in the aqua-fluoro compounds. The strong distortion is reflected also in the ligand field spectra.

Spectral, structural, and superoxide dismutase activity of some octahedral nickel(II) complexes with tri-tetradentate ligands

Three nickel(II) complexes, [Ni(L1)2] ⋅ 3H2O (1), [Ni(L2)2](ClO4)2 (2), and [Ni(L3)(bipy)](ClO4)2 (3), where L1 = N′-[phenyl(pyridin-2-yl)methylidene]furan-2-carbohydrazide, L2 = 2,6-bis[N,N′-(4-methoxyphenyl)ethanimidoyl]pyridine, and L3 = N-(methoxy-phenyl-pyridin-2-yl-methyl)-N-(phenyl-pyridin-2-yl-methylene)-ethane-1,2-diamine, have been synthesized and characterized by physico-chemical and spectroscopic methods. The solid-state structures of 1–3 were determined by single crystal X-ray crystallography, which revealed distorted octahedral geometry. In solid-state structure, 3 is self-assembled via intermolecular π ··· π stacking and intramolecular CH(methyl) ··· π(phenyl) non-covalent interactions. Infrared spectra, ligand-field spectra, and magnetic susceptibility measurements agree with the observed crystal structures. These complexes have also been revealed to catalyze effectively the dismutation of superoxide () in alkaline dimethyl superoxide-nitro blue tetrazolium assay.

The Ho(III) as structural probe for high temperature ionic liquids: RCl 3 (R = rare earth)

The electronic absorption spectra of the f ← f transitions of Ho 3+ as a probe cation doped in solid and liquid YCl 3 and TbCl 3 have been measured from room temperature to above the melting point of both compounds. In the same temperature range Raman spectroscopy has been utilized to characterize all phases present. Emphasis is given on the Ho 3+ ligand field spectra of the 5G 6 ← 5I 8 hypersensitive transition and their similarities with the known spectra of holmium chloro-elpasolite. Smooth spectral changes with nearly invariant molar absorptivities (between 30 and 40 L mol −1 cm −1) are observed upon melting YCl 3 and α-TbCl 3 which indicate that most probably the Ho 3+ is in 6-fold distorted octahedral coordination in both compounds and both phases. Drastic spectral changes are observed alongside the α-TbCl 3 to β-TbCl 3 phase transition where the coordination is altered from six to eight and the molar absorptivity quadruples. The spectra of liquid Y(Ho)Cl 3 and Tb(Ho)Cl 3 are correlated to the spectra of liquid La(Ho)Cl 3 and Gd(Ho)Cl 3 and are attributed to the ligand field states of Ho 3+ in distorted octahedral geometries. In conjunction with the molar volumes of all RCl 3 (R = rare earth) liquids which are invariant and independent of R and with Raman spectroscopic measurements for the same systems, a common possible structure of the rare earth chloride liquids is deduced and proposed.

Modeling the Vibronic Spectra of Transition Metal Complexes: The Ligand-Field Spectrum of [PtCl4]2−

A framework for calculating the intensity distribution and vibrational fine structure in the polarized ligand-field spectrum of transition metal complexes using the Herzberg-Teller approach is introduced and used to model the spectrum of the [PtCl4]2- ion. The model uses geometries, vibrational frequencies, and transition moments generated using density functional calculations on the ground and excited states, which arise from spin-allowed reorganization of the d electrons. The model predicts the whole spectral trace, including the polarization, the difference in the frequency of the electronic origin, the band maximum and the vertical transition energy, and the temperature dependence of the band intensities and the frequencies of the band maxima. Excitation to the 1A2g state is accompanied by a vibrational progression in the breathing mode of the excited state, as observed experimentally. Excitation to both the 1B1g and 1Eg states is accompanied by a loss of planarity and extended vibrational progressions in two modes, and the resulting spectra are inherently of low resolution.

Synthesis, spectroscopy and magnetism of novel metal complexes of 3-aminoflavone (3-af). X-ray crystal structure of 3-af and [Cu(3-af) 2(NO 3) 2

The synthesis and characterization of four new complexes with the bioactive ligand 3-aminoflavone (3-af) are reported. The complexes of general formula [M(3-af) 2(H 2O) 2](NO 3) 2 · nH 2O], where M = Co(II), Ni(II), and Zn(II), and n = 0, 2, 0, respectively, and [Cu(3-af) 2(NO 3) 2] compound were prepared and studied. In particular, to investigate the binding in detail, the crystal structures of the free ligand (3-af) and [Cu(3-af) 2(NO 3) 2] ( 1) were determined. The new coordination compounds were identified and characterized by elemental analysis, magnetic measurements, and infrared and ligand-field spectra. The crystal structure of the Cu(II) complex reveals that the ligand acts as a N, O-bidentate chelate ligand forming a five-membered ring with the copper(II) ion. The copper(II) ion is octahedrally surrounded by the two amino nitrogens and two carbonyl oxygens from two chelating organic ligands in trans arrangement. Two molecules of coordinated nitrate anions occupy axial positions. The spectral and magnetic properties are in accordance with the structural data of the copper(II) compound. From X-ray powder-diffraction patterns and IR spectra, the complexes of nickel(II) ( 2) and cobalt(II) ( 3) were found to be mutually isomorphous. The results of the spectroscopic studies suggest a mononuclear structure of 2 and 3 complexes. The variable-temperature (1.8–300 K) magnetic susceptibility data of 2 indicate a weak ferromagnetic interaction. The magnetic behavior of complex 3 is characteristic of cobalt(II) systems with an important orbital contribution via spin–orbit-coupling and also suggests a weak ferromagnetic interaction.

The Ho3+ Hypersensitive Transitions as Structural Probes for Molten Rare-Earth Ahlorides

The electronic absorption spectra of the f ← f transitions of Ho3+ in solid and molten Cs2NaHoCl6 elpasolite and in Y(Ho)Cl3 have been measured from room temperature up to above the melting point of both compounds. Emphasis is given on the ligand field spectra of the 5G6 ← 5I8 hypersensitive transition. Smooth spectra changes are observed upon melting the solids. In conjuction with Raman spectroscopic measurements the absorption spectra are attributed to HoCl 3− 6 octahedra in distorted geometries. The spectra of molten Y(Ho)Cl3 are correlated to the elpasolite spectra as well as with the spectra of La(Ho)Cl3 and Gd(Ho)Cl3 to deduce the possible structure of the host rare-earth chlorides.

Visible light absorption of binuclear TiOCo II charge-transfer unit assembled in mesoporous silica

Grafting of Co II(NCCH 3) 2Cl 2 onto mesoporous Ti–MCM-41 silica in acetonitrile solution affords binuclear Ti–O–Co II sites on the pore surface under complete replacement of the precursor ligands by interactions with anchored Ti centers and the silica surface. The Co II ligand field spectrum signals that the Co centers are anchored on the pore surface in tetrahedral coordination. FT-infrared action spectroscopy using ammonia gas adsorption reveals Co–O–Si bond modes at 831 and 762 cm −1. No Co oxide clusters are observed in the as-synthesized material. The bimetallic moieties feature an absorption extending from the UV into the visible to about 600 nm which is attributed to the Ti IV–O–Co II → Ti III–O–Co III metal-to-metal charge-transfer (MMCT) transition. The chromophore is absent in MCM-41 containing Ti and Co centers isolated from each other; this material was synthesized by grafting Co II onto a Ti–MCM-41 sample with the Ti centers protected by a cyclopentadienyl ligand. The result indicates that the appearance of the charge-transfer absorption requires that the metal centers are linked by an oxo bridge, which is additionally supported by XANES spectroscopy. The MMCT chromophore of Ti–O–Co II units has sufficient oxidation power to serve as visible light electron pump for driving multi-electron transfer catalysts of demanding uphill reactions such as water oxidation.

Initial use of di-2-pyridyl ketone oxime in chromium carboxylate chemistry: Triangular [formula omitted] compounds and unexpected formation of a carboxylate-free dichromium(II,II) complex

A systematic investigation of the [Cr 3O(O 2CCMe 3) 6(H 2O) 3](O 2CCMe 3)/(py) 2CNOH [(py) 2CNOH = di-2-pyridyl ketone oxime] reaction system is described, involving the determination of the influence of the Cr III:(py) 2CNOH ratio, the temperature and the presence of counterions on the identity of the reaction products. As a consequence, complexes [Cr 2{(py) 2CNO} 4] · 2H 2O ( 1 · 2H 2O), [Cr 3OCl(O 2CCMe 3) 4{(py) 2CNO} 2] · 2Me 2CO ( 2 · 2Me 2CO) and [Cr 3O(O 2CCMe 3) 4{(py) 2CNO} 2(H 2O)](NO 3) · H 2O · 0.5Me 2CO ( 3 · H 2O · 0.5Me 2CO) have been isolated and structurally characterized by single-crystal X-ray studies. (py) 2CNO − behaves as a N, N′-bidentate chelating and/or N, N′, O-tridentate bridging ligand binding through one 2-pyridyl and the oximate nitrogen atoms, and/or the oximate oxygen atom. 1 is a relatively stable air-stable dinuclear Cr(II) complex with no metal–metal bonding arising, from the ligand-assisted reduction of the ‘basic carboxylate’ Cr(III) triangle. The structures of 2 and 3 consist of similar neutral and cationic triangles of Cr III ions, respectively, centered by a triply bridging oxo ligand and with two edge-bridging oximate groups from the two 2.1110 (py) 2CNO − ligands. Variable-temperature magnetic susceptibility studies and EPR data for 2 reveal an antiferromagnetically-coupled system with an S T = 3/2 ground state. Solid-state IR and ligand field spectra of 2 are briefly discussed in terms of its structure.

Spectral studies on cobalt(II), nickel(II) and copper(II) complexes of naphthaldehyde substituted aroylhydrazones

A series of new coordination complexes of cobalt(II), nickel(II) and copper(II) with two new aroylhydrazones, 2-hydroxy-1-naphthaldehyde isonicotinoylhydrazone (H 2L 1) and 2-hydroxy-1-naphthaldehyde-2-thenoyl-hydrazone (H 2L 2) have been synthesized and characterized by elemental analysis, conductance measurements, magnetic susceptibility measurements, 1H NMR spectroscopy, IR spectroscopy, electronic spectroscopy, EPR spectroscopy and thermal analysis. IR spectra suggests ligands acts as a tridentate dibasic donor coordinating through the deprotonated naphtholic oxygen atom, azomethine nitrogen atom and enolic oxygen atom. EPR and ligand field spectra suggests octahedral geometry for Co(II) and Ni(II) complexes and a square planar geometry for Cu(II) complexes.

Mo2(CN)11]:5- A Detailed Description of Ligand-Field Spectra and Magnetic Properties by First-Principles Calculations

An ab initio multiconfigurational approach has been used to calculate the ligand-field spectrum and magnetic properties of the title cyano-bridged dinuclear molybdenum complex. The rather large magnetic coupling parameter J for a single cyano bridge, as derived experimentally for this complex by susceptibility measurements, is confirmed to a high degree of accuracy by our CASPT2 calculations. Its electronic structure is rationalized in terms of spin-spin coupling between the two constituent hexacyano-monomolybdate complexes. An in-depth analysis on the basis of Anderson's kinetic exchange theory provides a qualitative picture of the calculated CASSCF antiferromagnetic ground-state eigenvector in the Mo dimer. Dynamic electron correlations as incorporated into our first-principles calculations by means of the CASPT2 method are essential to obtain quantitative agreement between theory and experiment.

Magnetic Anisotropy of [Mo(CN)7]4- Anions and Fragments of Cyano-Bridged Magnetic Networks

Quantum chemistry calculations of CASSCF/CASPT2 level together with ligand field analysis are used for the investigation of magnetic anisotropy of [Mo(CN)7]4- complexes. We have considered three types of heptacyano environments: two ideal geometries, a pentagonal bipyramid and a capped trigonal prism, and the heptacyanomolybdate fragment of the cyano-bridged magnetic network K2[Mn(H2O)2]3[Mo(CN)7]2.6H2O. At all geometries the first excited Kramers doublet is found remarkably close to the ground one due to a small orbital energy gap in the ligand field spectrum, which ranges between a maximal value in the capped trigonal prism (800 cm(-1)) and zero in the pentagonal bipyramid. The small value of this gap explains (i) the axial form of the g tensor and (ii) the strong magnetic anisotropy even in strongly distorted complexes. Comparison with available experimental data for the g tensor of the mononuclear precursors reveals good agreement with the present calculations for the capped trigonal prismatic complex and a significant discrepancy for the pentagonal bipyramidal one. The calculations for the heptacyanomolybdate fragment of K2[Mn(H2O)2]3[Mo(CN)7]2.6H2O give g(perpendicular)/g(parallel) approximately 0.5 and the orientation of the local anisotropy axis close to the symmetry axis of an idealized pentagonal bipyramid. These findings are expected to be important for the understanding of the magnetism of anisotropic Mo(III)-Mn(II) cyano-bridged networks based on the [Mo(CN)7]4- building block.