Angular Overlap Parameters Research Articles

The vibronic structure of mixed-ligand osmium(iv) complexes

Mixed-ligand osmium(iv) complexes, OsCl5X2- and cis-OsCl4X2- 2, with X = Br or I, are optically investigated by recording the 10 K absorption spectra of the caesium and tetrabutylammonium salts in KBr pellets and the 10–20 K emission spectra of complexes doped in Cs2SnCl6, both in the energy region between 5000 and 17 000 cm-1. The measured peaks (origins and vibronics) are due to zero-phonon and vibronic transitions respectively within the (t2g)4 subshell configuration, which gives rise to a maximum of 15 energy levels at low symmetry. From the well-resolved absorption and emission spectra the d-level energies can be obtained for many of the split states that are expected in the region considered. For an assignment to symmetry types, selection rules for electric dipole transitions are applied, comparing peak intensities in the spectra. Ligand-field calculations using angular overlap parameters support these assignments, which must, however, be considered as partially tentative.

The electronic structure of tris(bipyridine)chromium(III) perchlorate

The sharp-line excitation spectrum of [Cr(bpy) 3] (ClO 4) 3·HbpyClO 4 (bpy=2,2′-bipyridine) revealed an unusually large 2E g splitting of 165 cm −1, which was attributed to an extensive π interaction of the bipyridine with the Cr(III) d orbitals. Ligand field calculations based on the exact geometric positions of the coordinated nitrogen atoms yielded values for the angular overlap parameters of −2283 cm −1 for e π and 342 cm −1 for e ππ. The latter represents the extent of phase coupling between the two nitrogen atoms in a bipyridine molecule. These values lead to an interpretation of the π interaction in terms of two strongly electron-withdrawing empty bipyridine molecular orbitals of different symmetry type.

Synthetic and structural studies of some trivalent lanthanide metal complexes ofo-hydroxyacetophenone (N-benzoyl)glycyl hydrazone

o-Hydroxyacetophenone (N-benzoyl)glycyl hydrazone (o-HABzGH) forms complexes of the types [M(o-HABzGH)Cl2(H2O)2]Cl and [M(o-HABzGH-2H)OH(H2O)2], where M = Y(III), Gd(III), Tb(III) and Dy(III). The complexes have been characterized by elemental analyses, molar conductance, magnetic susceptibility, infrared, electronic,1H NMR and13C NMR spectral techniques. The nephelauxetic ratio (β), covalency (δ), bonding parameter (b 1/2) and angular overlap parameter (η) have been calculated from Dy(III) complexes. Infrared and NMR spectral studies show thato-HABzGH acts as a neutral bidentate ligand in the adduct complexes and as a dinegative tridentate one in the neutral complexes. A coordination number of six has been proposed for the metal ion in all the complexes.

Synthesis and Spectral Studies of Lanthanide Metal Complexes of Acetone (N-Benzoyl)Glycyl Hydrazone

Abstract Acetone (N-benzoyl)glycyl hydrazone (BzAGH) has been found to react with trivalent lanthanide metal ions to form complexes of the type [Ln(BzAGH)Cl(H2O)3]Cl2 where Ln = La(III), Pr(III), Nd(III), Sm(III), Eu(III), Gd(III), Tb(III) and Dy(III). The complexes have been characterized by elemental analyses, molar conductance, magnetic, electronic, IR, 1H NMR and 13C NMR spectral techniques. Molar conductance studies in 0.001 M MeOH solutions indicate a 2:1 electrolytic behaviour of all the complexes. The nephelauxetic ratio, the bonding parameter, the Sinha's parameter and the covalency angular overlap parameter have been calculated from the electronic spectra of the Pr(III), Nd(III) and Sm(III) complexes. The IR and 1H NMR spectral studies reveal that BzAGH acts as a neutral bidentate chelating ligand in the complexes.

Coordinated lanthanide metal complexes ofN-benzoylglycine hydrazide

N-benzoylglycine hydrazide (BzGH) reacts with trivalent lanthanide metal ions forming complexes of the type [Ln(BzGH)2Cl(H2O)2]Cl2·nH2O, where Ln=LaIII, PrIII, NdIII, SmIII, EuIII, GdIII, TbIII, DyIII, or YIII;n=1 or 2. The structures of the complexes have been studied by conductance, magnetic, electronic, i.r.,1H n.m.r. and13C n.m.r. spectral techniques. The nephelauxetic ratio, the bonding parameter, Sinha's parameter and the covalency angular overlap parameter have been calculated from the electronic spectra of PrIII, NdIII and SmIII complexes. Seven-coordination is proposed in the NdIII complex. The i.r. and1H n.m.r. spectral data suggest bidentate BzGH in all the complexes.

On the coordination sphere geometry of trisacetylacetonato metal(III) complexes of the first transition series rationalized by orbital phase coupling effects

The directional contribution of π-bonding effects leading to distortions of chelate complexes from higher symmetry is investigated on the basis of orbital phase coupling introduced into the angular overlap model. For first row transition group acetylacetonates the increase of oxygen-oxygen bites compared to closed shell compounds is well explained from calculated bite angles given in terms of angular overlap parameters. These are derived for the chromium and cobalt compounds from trigonal band splittings in the polarized absorption and CD spectra. Phase coupling effects, in these cases, are found to produce larger distortions than possible Jahn-Teller forces active in the ground and the excited states.

The distance dependence of the parameters of the angular overlap model

Calculations are made of the distance dependence of the σ and π diatomic overlap integrals for various metal d x and f x fluoro and chloro systems, whence are derived the derivative quantities, ∂ρ π/∂ R and ∂ρ π/∂ R, which represent the variation with distance, R, of the Angular Overlap parameters, ρ σ and ρ π. For all systems the results indicate that the alternative evaluation of the derivative terms via an electrostatic model yields only modest agreement for the σ quantities and substantially underestimates the π terms. For f x species the predicted R dependence of the ρ σ parameters is compared with the limited available experimental data.

Angular overlap parameters for ruthenium(II) complexes

Approximate Angular Overlap Model e π parameters have been obtained for a number of ligands L by comparison of the t 2g(Ru) → π *(bpy) transition energies in [Ru(bpy) 2L 2] complexes. The filled t 2g subshell of Ru(II) limits the effects of otherwise strongly π-donating ligands.

Über das magnetische Verhalten von Cs2ASmF6 (A = Na, K, Rb)

AbstractThe magnetic behaviour of Cs2NaSmF6, Cs2KSmF6 and Cs2RbSmF6 has been studied in the temperature range between 3.0 and 251.3 K. The magnetic data are interpreted by means of a previously developed model in which the influence of the crystal field is theoretically described by the angular overlap model. The angular overlap parameter eπ (R) is determined for given ratio eπ (R)/eπ (R). As basis the 66 state functions of the ground term 6H as well as the 108 state functions of the sextet terms 6H and 6F are used. The dependence of the angular overlap parameters eπ (R) and eπ (R) on the basis is investigated. The energy. The energy values of the crystal‐field levels of the two lowest states 6H5/2 and 6H7/2 are calculated.

The assessment of the crystal field parameters for f n-electron systems by the angular overlap model. rare-earth ions M 3+ in Cs 2NaMCl 6

Experimental crystal field parameters of trivalent rare-earth ions (M 3+) in cubic Cs 2NaMCl 6 elpasolites are fitted in terms of the angular overlap model accounting for σ and π bonding. The transferability of the angular overlap parameters from one system to another is tested.

Tetrahedral complexes of nickel(II): electronic spectra, γ and π bonding, andthe electroneutrality principle

Angular overlap and intereclectron repulsion parameters for 13 `tetrahedrally' co-ordinated complexes of nickel(II) are critically compared and shown to descibe distributions of valence electron density in γ abd π bond network which consistently reflect the operation of the electroneutrality principle. The a.o.m. and inerelectron repulsion parameters were derived from analyses of spectra and magnetic properties, five of which are reported for the first time.

Is the angular overlap model chemically significant?

Recent comments on the transferability of angular overlap parameters and a criticism of the practice of setting eδ≈ 0 are discussed, and arguments in favour of eδ≈ 0 are presented. It is emphasised that the angular overlap model is a sub-division of ligand-field theory, qualitatively distinct from molecular-orbital theory.

The magnetic, spectral, and structural properties of trans-tetra-amminedinitronickel(II)

The structural (295 and 130 K), magnetic, and spectral properties of trans-[Ni(NH3)4(NO2)2] are reported. The crystal structure of the compound has been determined by single-crystal X-ray diffraction methods at 295 and 130 K. Crystals are monoclinic, space group C2/m, Z= 2, with a= 1 062.1(4)[1 062.8(4)], b= 681.2(4)[688.7(2)], c= 591.2(3)[597.4(3)] pm, and β= 114.83(3)[114.80(3)]° where the 295 K values are in square parentheses. Diffractometry has provided significant Bragg intensities for 900 (130 K) and 1 264 (295 K) independent reflections and the structures have been refined by full-matrix least-squares methods to R 0.028 (130 K) and 0.051 (295 K). The molecule has a rectangular, almost square [N–Ni–N = 87.5(1)°] plane of ammonia molecules accurately perpendicular to the axis containing the trans-nitrite groups. The molecules are bound together by a fairly simple but strong hydrogen-bonding arrangement. The structure at 130 K is essentially the same as at 295 K. The Ni–N bond lengths, corrected for librational motions, are Ni–N(H3) 210.9 (211.1) and Ni–N(O2) 214.2 (215.2) pm where the 295 K values are in parentheses. The magnetic susceptibility follows a Curie–Weiss law with θ=–5.5 K between 10 and 300 K, but departs from this below 10 K to become independent of temperature below 3 K. The data fit the theory for the ground 3A2g term with zero-field splitting represented by D= 15.2 K(10.4 cm–1). This zero-field splitting, together with some limited data about the solid-state spectra, is reproduced by a ligand-field treatment with angular-overlap parameters eσ(NH3)= 3 700, eσ(NO2)= 12 000, eπ(NO2)= 5 700 cm–1. The i.r. spectrum, including that of the deuteriated compound, is largely interpreted along conventional lines, but shows a band at 1 850 cm–1. This band probably arises from strong hydrogen bonding involving one of the ammine hydrogen atoms in particular. This same hydrogen atom is also involved in an anomalously long N–H bond, and has large thermal parameters.

Über das magnetische Verhalten von Cs2MHoF6 (M = Na, K, Rb)

Abstract The magnetic behaviour of CS2MHoF6 (M = Na, K, Rb) has been studied in the temperature range between 3.2 and 251.3 K. The magnetic data are interpreted by means of a previously developed model in which the influence of the crystal field is theoretically described by the angular overlap model. Values of the angular overlap parameters eσ(R) and eπ(R) cannot be determined unequivocally. The energy values of the crystal-field levels of the 5I8 ground state are calculated.

Magnetische Eigenschaften der Normaltemperaturform von CsYbO2

Abstract The magnetic behaviour of the normal-temperature form of CsYbO2 has been studied in the temperature range between 2.8 and 251.3 K. Besides at temperatures below about 12 K the magnetic data are well interpreted by means of a model in which the influence of the crystal field is theoretically described by the angular overlap model and the influence of magnetic interaction by the molecular field model. By this the transferability of the angular overlap parameters from one compound to another is tested. The energy values of the crystal-field levels of the 2F7/2 ground state are calculated.

Angular overlap investigation on unsymmetrical transition metal complexes

A ligand field model based on an angular overlap parameterization is applied to the study of the electronic structure of unsymmetrical cobalt(II) and nickel(II) complexes. Angular overlap parameters are obtained by fitting the spectral frequencies of the compounds and their transferability between different chromophores is investigated. The effects on the spectra due to the geometrical distortions of the chromophores from idealized symmetries are examined. Applications of the model to the study of the connection existing between spin state and coordination geometry in series of complexes are reported.

Chemical significance of normalised spherical harmonic(NSH) hamiltonian and angular overlap parameters in some five- and six-coordinated trivalent chromium complexes with terdentate benzoyl hydrazones

The five- and six-coordinate chromium(III) complexes derived from benzoylhydrazine and salicylaldehyde (BSH), o-hydroxyacetophenone (BAH), o-hydroxypropiophenone (BPH), o-hydroxybutyrophenone (BBH) and 2-hydroxy-1-naphthaldehyde (BNH) having the general formulae [Cr(L)X] 2 and [Cr(L) 2] Cl (XCl, Br or NO 3) are described. The complexes have been characterised by elemental analyses and by electrical conductance, magnetic and spectral (electronic and IR) measurements. The five-coordinated complexes are dimeric having phenolic oxygen bridges as revealed by ▪ ring vibrations in the IR. spectra at 730–745 cm −1. The v(M-X) values are consistent with five-coordinate geometry of the complexes. The low magnetic moments of five-(2.95–3.25 BM) and six-coordinate (3.80–3.90 BM) complexes have been explained in terms of antiferromagnetic exchange coupling and low symmetry components. The electronic spectra of six-coordinate complexes are consistent with tetragonal geometry of the molecule while five-coordinate complexes appear to have trigonal bipyramidal shape. Various ligand field parameters viz. Ds, Dt, Dq L and Dq Z have been evaluated and in turn have been used to calculate NSH parameters, viz. DS, DT, DQ, DQ, L and DQ Z and the degree of distortion in terms of (DT/DQ)(0.156–0.185). The electronic spectra of six-coordinate complexes have also been interpreted in terms of McClure's semi-empirical molecular orbital and orbital angular overlap model and the parameters d σ , d π , e′ σL , e′ πL , e′ σZ , e′ πZ and the ratio ( e′ σZ / e′ πZ ) pertaning to these theories have been calculated. An attempt has been made to correlate these parameters with each other and to find out their chemical significance.

Low-temperature ligand-field and far-infrared spectra of trans-dichlorotetrakis(5-methylpyrazole)nickel(II) and trans-dibromotetrakis(5-methylpyrazole)nickel(II)

Polarized crystal spectra (10 K) and far-infrared spectra (80 K) have been recorded for Ni(MPZ) 4X 2 (MPZ = 5-methylpyrazole; X = Cl, Br). Reasonable assignments have been made in terms of D 4h symmetry. The significance of the various calculated ligand field and orbital angular overlap parameters is discussed.

A non-empirical appraisal of the angular-overlap model for transition-metal complexes

Non-empirical SCF molecular-orbital calculations of the d-orbital energies in the complexes [MnF6–iCli]k–(i= 1–6) and distorted [MnF6]k–(k= 2 or 4) have been made within a valence-electron approximation. These energies have been shown to be accurately modelled by a one-electron angular-overlap Hamiltonian. The angular-overlap parameters for Cl and F have a relationship which is similar to that determined from experiment for some chromium(III) complexes.

Über des magnetische Verhalten von Cs2MYbF6 (M = Na, K, Rb) und Cs2NaYbBr6 / On the Magnetic Behaviour of Cs2MYbF6 (M = Na, K, Rb) and Cs2NaYbBr6

Abstract The magnetic behaviour of Cs2MYbF6 (M = Na, K, Rb) and Cs2NaYbBr6 has been studied in the temperature range between 3.5 and 251.3 K. The magnetic data are interpreted by means of a previously developed model in which the influence of the crystal field is theoretically described by the angular overlap model. The obtained values of the angular overlap parameter eσ(R) for the individual compounds are discussed and compared with each other. The energy values of the crystal-field levels of the 2F7/2 ground state are calculated.