Angular Overlap Parameters Research Articles

Covalency parameters for nine-coordinated thorium acylpyrazolone complexes along with their synthesis and crystal features

This study discusses the synthesis and characterization of three thorium complexes with a general composition of [Th(L)4(EtOH)] demonstrated a nine-coordinated geometry in acylpyrazolone chemistry, a novel finding supported by single crystal evidence. A detailed analysis of complex [Th(L2)2(DMF)] was conducted, utilizing single-crystal X-ray diffraction data and Hirshfeld surface area analysis to investigate secondary interactions, exploring the planarity and bonding characteristics of the crystals. Covalency parameters such as the Nephelauxetic ratio, Sinha parameter, bonding parameter, and angular overlap parameter were calculated from electronic spectral data, revealing positive covalency and electron delocalization across the 5f orbital for all complexes. Notably, the presence of solvent bound to the 9th coordination site of the complex suggests potential changes in covalency across different solvents, thereby indirectly impacting chemical characteristics.

Synthesis and Structural Characterization of Some Lanthanide(III) Nitrate Complexes with a Mesogenic Schiff-Base, N,N’-di-4-(4’-heptadecyloxybenzoate) salicylidene-1,3-diaminopropane Derived from 2,4- dihydroxybenzaldehyde

Complexes of La(III), Pr(III), Nd(III), Sm(III), Gd(III) and Dy(III) with the Schiff-base, N,N′-di-4-(4’-heptadecyloxybenzoate)salicylidene-1,3-diaminopropane, (abbreviated as H2L) have been synthesized and characterized on the basis of elemental analyses, molar conductance, magnetic, electronic, infrared, 1H and 13C NMR spectral techniques. The nephelauxetic ratio (β), the bonding parameter (b1/2), Sinha’s parameter (%δ) and angular overlap parameter (η) have been calculated from the electronic spectra of Pr(III), Nd(III), Sm(III) and Dy(III) complexes. Infrared and NMR spectral data imply a bi-dentate bonding of the Schiff-base in its zwitterionic form (as LH2) to the Ln(III) ions through two phenolate oxygens, rendering the overall geometry around Ln(III) to distorted square antiprism. Polarized optical microscopy (POM) and differential scanning calorimetry (DSC) shows the liquid crystalline property of the ligand with a nematic (N) mesophase. Among the metal complexes, only that of the Gd(III) exhibits smectic B (SmB) and nematic (N) phases.

Magnetic Transitions in Iron Porphyrin Halides by Inelastic Neutron Scattering and Ab Initio Studies of Zero-Field Splittings.

Zero-field splitting (ZFS) parameters of nondeuterated metalloporphyrins [Fe(TPP)X] (X = F, Br, I; H₂TPP = tetraphenylporphyrin) have been directly determined by inelastic neutron scattering (INS). The ZFS values are D = 4.49(9) cm⁻¹ for tetragonal polycrystalline [Fe(TPP)F], and D = 8.8(2) cm⁻¹, E = 0.1(2) cm⁻¹ and D = 13.4(6) cm⁻¹, E = 0.3(6) cm⁻¹ for monoclinic polycrystalline [Fe(TPP)Br] and [Fe(TPP)I], respectively. Along with our recent report of the ZFS value of D = 6.33(8) cm⁻¹ for tetragonal polycrystalline [Fe(TPP)Cl], these data provide a rare, complete determination of ZFS parameters in a metalloporphyrin halide series. The electronic structure of [Fe(TPP)X] (X = F, Cl, Br, I) has been studied by multireference ab initio methods: the complete active space self-consistent field (CASSCF) and the N-electron valence perturbation theory (NEVPT2) with the aim of exploring the origin of the large and positive zero-field splitting D of the ⁶A₁ ground state. D was calculated from wave functions of the electronic multiplets spanned by the d⁵ configuration of Fe(III) along with spin–orbit coupling accounted for by quasi degenerate perturbation theory. Results reproduce trends of D from inelastic neutron scattering data increasing in the order from F, Cl, Br, to I. A mapping of energy eigenvalues and eigenfunctions of the S = 3/2 excited states on ligand field theory was used to characterize the σ- and π-antibonding effects decreasing from F to I. This is in agreement with similar results deduced from ab initio calculations on CrX₆³⁻ complexes and also with the spectrochemical series showing a decrease of the ligand field in the same directions. A correlation is found between the increase of D and decrease of the π- and σ-antibonding energies e(λ)(X) (λ = σ, π) in the series from X = F to I. Analysis of this correlation using second-order perturbation theory expressions in terms of angular overlap parameters rationalizes the experimentally deduced trend. D parameters from CASSCF and NEVPT2 results have been calibrated against those from the INS data, yielding a predictive power of these approaches. Methods to improve the quantitative agreement between ab initio calculated and experimental D and spectroscopic transitions for high-spin Fe(III) complexes are proposed.

Spectroscopic characterization of Lanthanoid derived from a hexadentate macrocyclic ligand: Study on antifungal capacity of complexes

Complexes of Ce(III), Nd(III), Sm(III) and Eu(III) were synthesized with NO-donor macrocyclic ligand, i.e. 3,5,13,15,21,22-hexaaza-2,6,12,16-tetramethyl-4,14-dithia-tricyclo[15.3.1.1(7-11)]docosane-1(21),2,5,7,9,11(22),12,15,17,19-decaene. The ligand was obtained by the condensation of 2,6-diacetylpyridine with thiourea and characterized by elemental analysis, mass, IR and 1H NMR spectral studies. All the complexes were characterized by elemental analyses, molar conductance measurements, magnetic susceptibility measurements, IR, mass, electronic spectral techniques and thermal studies. The ligand acts as a hexadentate and coordinated through four nitrogen atoms of azomethine groups and two nitrogen atoms of pyridine ring. The value of spectral parameters i.e. nephelauxetic effect (b), covalency factor (b1/2), Sinha parameter (δ%) and covalency angular overlap parameter (η) account for the covalent nature of the complexes. The macrocyclic ligand and its Lanthanoid were tested in vitro against two plant pathogenic fungi in order to assess their antifungal capacity.

4[N-Furfural)amino]antipyrine Semicarbazone의 질산 란탄(III) 배위화합물의 입체화학에 미치는 Picolines의 영향과 항박테리아 활성

4[N-(furfural)amino]antipyrine semicarbazone(FFAAPS)와 질산 란탄(III)이 형성하는 배위화합물의 입체화학에 미치는 <TEX>${\alpha}$</TEX>-, <TEX>${\beta}$</TEX>- 및 <TEX>${\gamma}$</TEX>-picolines의 영향을 연구하였다. 이들 배위화합물의 일반적 조성은 [Ln(FFAAPS)<TEX>$(NO_3)_3$</TEX>Pic] (Ln=La, Pr, Nd, Sm, Gd, Tb, Dy 또는 Ho 및 Pic=<TEX>${\alpha}$</TEX>-, <TEX>${\beta}$</TEX>- or <TEX>${\gamma}$</TEX>-picolines)이다. 모든 배위화합물은 원소분석, 분자량, 몰전기전도도, 자기수자율, 적외선 및 자외선 스펙트럼으로 특성을 조사하였다. 적외선 연구결과 FFAAPS는 N, N, O 주개를 갖는 중성 삼배위 리간드로 행동하는 반면, <TEX>${\alpha}$</TEX>-, <TEX>${\beta}$</TEX>- 또는 <TEX>${\gamma}$</TEX>-picoline는 헤테로 N-원자를 통하여 란탄(III) 이온에 배위된다. 질산 음이온은 이들 화합물에서 이배위로 결합한다. 자외선 스펙트럼 결과로부터 전자구름 퍼짐 효과(<TEX>${\beta}$</TEX>), covalence factor(<TEX>$b^{1/2}$</TEX>), Sinha parameter (<TEX>${\delta}%$</TEX>) 및 covalence angular overlap parameter(<TEX>${\eta}$</TEX>)를 계산하였다. 이들 착물의 열적성질을 열무게 분석법에 의해 연구하였다. 본 화합물에 있어서 란탄(III)의 배위수는 10으로 조사되었다. 기본 리간드인 FFAAPS와 착물의 항박테리아 선별조사 결과, 이들 착물은 중간 정도의 항박테리아 활성을 보였다. The effect of <TEX>${\alpha}$</TEX>-, <TEX>${\beta}$</TEX>- and <TEX>${\gamma}$</TEX>-picolines on the stereochemistry of the coordination compounds of lanthanide(III) nitrates derived from 4[N-(furfural)amino]antipyrine semicarbazone (FFAAPS) has been studied. The general composition of the present coordination compounds is [Ln(FFAAPS)<TEX>$(NO_3)_3$</TEX>Pic] (Ln=La, Pr, Nd, Sm, Gd, Tb, Dy or Ho and Pic=<TEX>${\alpha}$</TEX>-, <TEX>${\beta}$</TEX>- or <TEX>${\gamma}$</TEX>-picolines). All these coordination compounds have been characterized by elemental analyses, molecular weight, molar conductance, magnetic susceptibility, infrared and electronic spectra. The infrared studies suggest that the FFAAPS behaves as a neutral tridentate ligand with N, N, O donor while <TEX>${\alpha}$</TEX>-, <TEX>${\beta}$</TEX>- or <TEX>${\gamma}$</TEX>-picoline is coordinated to the lanthanide(III) ions via heterocyclic N-atom. Nitrates are bicovalently bonded in these compounds. From the electronic spectral data, nephelauxetic effect (<TEX>${\beta}$</TEX>), covalence factor (<TEX>$b^{1/2}$</TEX>), Sinha parameter (<TEX>${\delta}%$</TEX>) and the covalence angular overlap parameter (<TEX>${\eta}$</TEX>) have been calculated. Thermal stabilities of these complexes have been studied by thermogravimetric analysis. The coordination number of lanthanide(III) ions in the present compound is found to be ten. The antibacterial studies screening of the primary ligand FFAAPS and the complexes showed that the present complexes have moderate antibacterial activities.

Studies on the Effect of Various Anions and Pyridine on the Stereochemistry of Lanthanide(III) Coordination Compounds of 4[N-(2′-Hydroxy-1′-Naphthalidene)Amino] Antipyrine Thiosemicarbazone

In the present studies, the effect of pyridine on stereochemistry of the coordination compounds of lanthanide(III) derived from 4[N-(2′-hydroxy-1′-naphthalidene)amino] antipyrine thiosemicarbazone (HNAAPTS) has been studied. The general composition of the present complexes is LnX3·n(HNAAPTS)·Py (Ln = La, Pr, Nd, Sm, Gd, Tb, Dy, or Ho; X = NO3, n = 1, x = Cl, NCS or ClO4, n = 2, Py = pyridine). All the complexes were characterized by elemental analyses, molecular weight, molar conductance, magnetic susceptibilities, infrared and electronic spectral studies. The infrared studies reveal that the HNAAPTS behaves as a neutral tridentate (N, N, S), while pyridine is coordinated to metal ions via its nitrogen atom. Nitrates are bicovalently bonded, while thiocyanate is coordinated through a strong N-atom. Perchlorate ions are not coordinating in coordination sphere. From electronic spectral data, nephelauxetic effect (β), covalence factor (b½), Sinha parameter (δ%), and the covalence angular overlap parameter (η) have been calculated. Thermal stabilities of these complexes were studied by thermogravimetric analysis. In conclusion, the coordination number of lanthanides(III) in the present compounds is either seven or ten depending on the coordinating anions. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.

Lanthanide complexes derived from hexadentate macrocyclic ligand: Synthesis, spectroscopic and thermal investigation

The lanthanide complexes derived from (3,5,13,15-tetramethyl 2,6,12,16,21-22-hexaazatricyclo[15.3.I(1-17)I(7-11)]cosa-1(21),2,5,7,9,11(22),12,15,17,19-decane) were synthesized. The complexes were found to have general composition [Ln(L)X(2).H(2)O]X, where Ln=La(3+), Ce(3+), Nd(3+), Sm(3+) and Eu(3+) and X=NO(3)(-) and Cl(-). The ligand was characterized by elemental analyses, IR, Mass, and (1)H NMR spectral studies. All the complexes were characterized by elemental analyses, molar conductance measurements, magnetic susceptibility measurements, IR, Mass, electronic spectral techniques and thermal studies. The ligand acts as a hexadentate and coordinates through four nitrogen atoms of azomethine groups and two nitrogen of pyridine ring. The lanthanum complexes are diamagnetic while the other Ln(III) complexes are paramagnetic. The spectral parameters i.e. nephelauxetic ratio (beta), covalency factor (b(1/2)), Sinha parameter (delta%) and covalency angular overlap parameter (eta) have been calculated from absorption spectra of Nd(III) and Sm(III) complexes. These parameters suggest the metal-ligand covalent bonding. In the present study, the complexes were found to have coordination number nine.

Lanthanide complexes of tetradentate macrocyclic ligand Synthesis and spectroscopic investigation

In the present paper, the lanthanide complexes derived from (1,5,8,12-tetraaza-2,4,9,11-tetramethyl cyclotetraaza-1,4,8,11-tetraene) were synthesized. The general composition of the complexes is [Ln(L)X 2 .H 2 O]X, where Ln = La, Ce, Nd, Sm and Eu and X = NOj and Cl - . The ligand was characterized on the basis of elemental analyses, IR, Mass and 'H NMR spectral studies. All the complexes were characterized by elemental analyses, molar conductance measurements, magnetic susceptibility measurements, IR, Mass, electronic spectral techniques and thermal studies. The ligand acts as a tetradentate chelate and coordinates through four nitrogen atoms of azomethine groups. The lanthanum complexes are diamagnetic while the other Ln III complexes are paramagnetic due to the presence of 4f n unpaired electrons. The spectral parameters i.e. nephelauxetic effect (p), covalency factor (b 1/2 ), Sinha parameter (6%) and covalency angular overlap parameter (η) have been calculated from absorption spectra of Nd ΙΙΙ and Sm ΙΙΙ complexes. These parameters suggest the metal-ligand covalent bonding. In the present study, the complexes show the coordination number seven.

Studies on the Effect of Various Anions and Diphenyl Sulfoxide on the Stereochemistry of Lanthanide(III) Coordination Compounds of 4[N-(2′-hydroxy-1′-naphthalidene)amino] Antipyrinesemicarbazone

In the present studies the effect of diphenyl sulfoxide (DPSO) on the stereochemistry of the coordination compounds of lanthanides(III) derived from 4[N-(2′-hydroxy-1′-naphthalidene)amino]antipyrinesemicarbazone (HNAAPS) has been studied. The general composition of the present complexes is LnX3 · n (HNAAPS) · DPSO (Ln=La, Pr, Nd, Sm, Gd, Tb, Dy or Ho; X=NO3, n=1, X=NCS or ClO4, n=2). All these complexes were characterized by elemental analyses, molecular weight, molar conductance, magnetic susceptibility, infrared and electronic spectra. The infrared studies reveal that the HNAAPS behaves as a neutral tridentate (N, N, O), while DPSO is coordinated to the metal ion via its lone oxygen atom. Nitrates are bicovalently bonded, while thiocyanate is coordinated through strong N-atom. Perchlorato ions are not participating in coordination sphere. From electronic spectral data, nephelauxetic effect (β), covalence factor (b1/2), Sinha parameter ( δ%) and the covalence angular overlap parameter (η) have been calculated. XRD of two representative compounds were also investigated. Antibacterial properties of these complexes were also performed. Thermal stabilities of these complexes were studied by thermogravimetric analysis. In conclusion, the coordination number of lanthanides (III) in the present compounds is either seven or ten depending on the coordinating anions.

Coordination chemistry in two dimensions: the angular overlap model for actinyl complexes†

The angular overlap model has been applied to the study of actinyl coordination complexes AnO2L n (An = U, Np, Pu, Am; n = 4, 5, 6) using a 13-orbital sd5f7 manifold. After allowing for a triply bonded (σ + 2 ⊥ π) linear O≡An≡O substructure, a seven-orbital submanifold d3{dσ,dδ}f4{fδ,fϕ} remains for σ and π bonding to the ligands in the equatorial plane. The two fδ orbitals in this manifold cannot be used for σ bonding to the equatorial ligands leaving only a smaller five-orbital d3{dσ,dδ}f2{fϕ} manifold suitable for equatorial σ bonding. Pentagonal bipyramidal complexes of the type AnO2L5, which are known experimentally to be favored for monodentate L ligands, use this five-orbital submanifold most effectively to form σ bonds to all five equatorial ligands as indicated by the angular overlap parameters calculated for these orbitals. Hexagonal bipyramidal complexes of the type AnO2L6 are less favorable as formation of σ bonds to all six equatorial ligands (L) must necessarily either disturb the orbitals required for the linear O≡An≡O substructure or use high-energy actinide p orbitals. Angular overlap calculations on octahedral complexes of the type AnO2L4 show very uneven overlap between the orbitals in the d3{dσ,dδ}f2{fϕ} manifold with the four equatorial ligands. Thus the angular overlap model supports the experimental observation that the most favorable actinyl coordination geometry is the pentagonal bipyramidal AnO2L5 in the absence of ligands with special properties.

Crystal structure and colour of SrNiP2O7 and SrNi3(P2O7)2

The crystal structures of SrNiP 2 O 7 ( I ) and SrNi 3 (P 2 O 7 ) 2 ( II ) have been refined from single crystal data [( I ): P 2 1 / n , Z =4, a =5.2630(16), b =8.2605(10), c =12.6018(15) Å, β =90.224(19)°, 101 parameters, 1143 independent reflections, R / wR 2 =0.029/0.070; ( II ): P 2 1 / c , Z =2, a =7.4092(9), b =7.6594(8), c =9.4474(10) Å, β =112.216(9)°, 104 parameters, 1484 independent reflections, R / wR 2 =0.027/0.063]. SrNiP 2 O 7 belongs to the α -Ca 2 P 2 O 7 structure family with Ni 2+ ions occupying isolated square-pyramidal sites, d (Ni O) = 2.032 Å. SrNi 3 (P 2 O 7 ) 2 is isostructural to AM 3 (P 2 O 7 ) 2 (A = Ca, Pb and M = Fe, Co, Ni). Two crystallographically independent, slightly distorted [NiO 6 ] octahedra ( d (NiO) = 2.083 Å) share edges, thus forming chains along the b -axis ( d (NiNi) = 3.143 and 3.226 Å). The colours of SrNiP 2 O 7 (orange-red) and SrNi 3 (P 2 O 7 ) 2 (greenish-yellow) are significantly different. Reflectance spectra in the UV/VIS/NIR region are reported for SrNiP 2 O 7 , SrNi 3 (P 2 O 7 ) 2 , and the isotypic diphosphates CaNi 3 (P 2 O 7 ) 2 and BaNi 3 (P 2 O 7 ) 2 . Angular overlap parameters for the NiO interaction are derived. The shift in d -electron energies of Ni 2+ caused by the change in coordination from [NiO 5 ] ( C 4 v ) to [NiO 6 ] ( O h ) is reproduced nicely by the model calculations. Graphic

Synthesis, Characterization and Antibacterial Activity of Complexes of Lanthanide(III) Nitrates with 2-Chloro-10-[3-(Diethylamino)Propyl]-Phenothiazine

Fourteen new complexes of lanthanide(III) nitrates with 2-chloro-10-[3-diethylaminopropyl]phenothiazine (chlorproethazine) of the type [Ln(CPE)2(NO3)2]NO3 (where Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb. Dy. Ho, Er, Tm. Yb, Lu and CPE = chlorproethazine) have been synthesised and characterised on the basis of elemental analyses, magnetic moments, molar conductance measurements, IR, electronic spectra, TG and DTA. The analytical data suggest the Ln3+ ions are eight-coordinate. The nephelauxetic ratios (β), bonding parameters (b1/2), Sinha's parameters (δ%) and covalency angular overlap parameters (η) have been calculated for the Pr(III), Nd(III) and Er(III) complexes. The complexes have been screened for their antibacterial activities against four bacteria.

Ligand field properties of histidine on the sharp-line excitation spectrum of trans(imidazole)-bis( L-histidinato- O, N, N′)chromium( III) nitrate

Ligand field calculations have been performd based on the data from the absorption and low temperature sharp-line excitation spectra of trans(imidazole)-[Cr( L-his) 2]NO 3. The angular overlap parameters determined for imidazole nitrogen are 6233 cm −1 for e σNim and −549 cm −1 for e πNim . This indicates that the imidazole nitrogen is a weak σ-donor and its π-interaction can be interpreted by back-donation to the electron withdrawing empty molecular orbitals on the imidazole nitrogen.

Chelating Behaviour of 4[N-(Benzylidene)amino]-antipyrine Semicarbazone Towards Lanthanide Ions

Abstract A series of lanthanide(III) nitrate chelates of 4[N-(benzylidene)amino]antipyrine semicarbazone (BAAPS) with the general composition [Ln(BAAPS) (NO3)3] (Ln = La, Pr, Nd, Sm, Gd, Tb, Dy or Ho) have been synthesized in ethanol. All chelates were characterized on the basis of element analyses, conductance measurements, magnetic moments, infrared and electronic spectra. Their nephelauxetic ratios (β), covalency factors (b½), Sinha parameters (δ %) and angular overlap parameters (η) have been calculated for the Pr(III), Nd(III) and Sm(III) complexes, which indicate some covalent character of these complexes. Thermal stabilities of the complexes were also studied.

Synthesis and Spectral Investigation of Rare Earth (III) Complexes of Amido Acid Ligand Derived From 2,4-Dinitrophenylhydrazine

Abstract Fourteen rare earth(III) complexes REL3 -nH2O (where RE = Sc, n = 5; RE = Y, La, Ce, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, n = 6; RE = Pr, Nd, n = 4; HL = 1 -(N-carboxymethy1-N-pheny1)amino-acetyl-2′,4′-dinitrophenylhydrazine), have been synthesized and characterized by elemental analyses, conductance measurements, magnetic moments, IR, 1H NMR, electronic spectra, TG and DTA. Their nephelauxetic ratio (ß), bonding parameter (b½), Sinha's parameter (δ%) and covalency angular overlap parameter (δ%) have been determined for the Pr.3+, Nd3+and Er3+ complexes.

Magnetism of Pr3+-exchanged β″-alumina

The magnetic behaviour of polycrystalline Na+/Pr3+ - β″ - Al2O3 samples with various exchange rates has been studied. Magnetic measurements were recorded with a SQUID magnetometer in the temperature range 1.7–300 K at various field strengths. The data were interpreted by ligand-field calculations applying the angular overlap model (AOM). The calculations are based on angular overlap parameters obtained from optical investigations on Na+/Pr3+ - β - Al2O3.

Analysis of angular overlap parameters for the LaOX:Eu 3+(X = Cl, Br, I) series

The Angular Overlap Model (AOM) is applied to the LaOX:Eu 3+(X = Cl, Br, I) series involving σ, π, δ and φ effects based on the experimental energy levels. The calculations are made in two cases. (1) Consider oxygen and halogen having the same bond-length. (2) Consider the real structure. In both cases, the results show that for σ -bonding parameters, the values of e σ decrease with increasing charge number of halogen, i.e. Cl − > Br − > I −, this indicates that the bonding ability also decreases with this order. The absolute values of each parameter are much larger than zero—therefore they all must be included in a practical analysis. In the second case, the values of the e x parameter are negative, which means a “back-bonding” is formed, and this is profitable for the formation of α-bonding, usually referred to as “synergic effect”.

Analysis of angular overlap parameters for Eu 3+: Ln 2O 2S (LnLu, Y, Gd, La) crystal series

The angular overlap model (AOM) is applied to 4f 6 electron systems. The crystal field parameters are interpreted and covalency between 4f electrons and ligands is investigated based on the experimental energy levels. For Eu 3+:Ln 2O 2S (LnLu, Y, Gd, La) crystal series, we adopt two computational schemes. First of all, we assume that the distances to all ligands are equal, and then the distances to all ligands are divided into two groups, namely, oxygens as one group, sulfurs as the other. Of course, much information about covalency will be obtained from the latter case. Obviously, our results show that the covalency of LnO bonding is stronger than that of LnS bonding in line with much shorter bondlength for the former than that for the latter. The two schemes yield the same results, that is, for σ and π bonding, ligands are strong donors as well as σ, π effects are dominant over δ, φ effects.

Spectrochemical properties of noncubic transition metal complexes in solution. Part III. Mixed tetragonal distorted nickel(II) pyridine complexes in dimethyl sulphoxide

The electronic absorption spectra of the tetragonal Ni(py)4X2 complexes (py=pyridine and X=NCS−, Cl−, Br− or I−) in dimethyl sulphoxide (DMSO) solution have been measured at room temperature. The experimental curves were resolved by Gaussian analysis. The crystal field (CFM) and angular overlap (AOM) parameters were calculated by the Davidon-Fletcher-Powell method (gradient estimation). The assumed structures in solution are, for the iodide complex, [Ni(py)4(DMSO)2]I2 and for the others [Ni(py)4(DMSO)X]X (X=Cl−, Br−) and [Ni(py)4X2] (X=NCS−). A comparison of the spectra, ligand field parameters and stereochemistries in various solutions was made.

Spectrochemical properties of noncubic transition metal complexes in solutions—IV. Energy levels of tetragonal distorted chromium(III) complexes in aqueous solutions

Abstract A general method for the analysis of the d-d transition energies observed in the ligand field spectra of chromium(III) complexes with D 4 h or C 4υ symmetry is described and used to derive the crystal field and angular overlap parameters for the complexes of known stereochemistry. Examples are also presented. The spectrum of the diamminetetrakis(isothiocyanato)chromate(III) ammonium in aqueous solution is reported. The spectra of the miscellaneous systems have been studied theoretically using a crystal field model and an angular overlap model.