Ligand Field Parameters Research Articles

The role of NiO on the structural and optical properties of sodium zinc borate glasses

Abstract Nickel-doped sodium zinc borate (NZB) glasses of composition [15 ZnO – (65 – x) B2O3 –x NiO – 20 Na2O], where (x = 0.0, 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 mol %), were prepared following the melt quenching technique. The effect of NiO additives on the structural and optical properties of NZB glasses has been studied by a set of complementary techniques. The amorphous nature of the prepared samples was verified by both X-ray diffraction pattern analysis (XRD) and scanning electron microscopy (SEM). Additional structural information and physically relevant parameters such as density, molar volume, inter ionic distance, the average Boron–Boron separation, and ion concentration, have been calculated. Furthermore, the optical basicity and electronic polarizability of the system were empirically determined. Boron structural units and both Ni2+ and Zn2+ specific vibrations were identified using FTIR spectroscopy. The direct comparison of the vibrational spectra of all samples showed a slight reduction in N4 ratio, from 32% to 29%, with increasing NiO content. The detailed deconvolution process of optical spectra revealed specific absorption bands characteristic for Ni2+ ions, in the visible and NIR regions, preferentially occupying octahedral sites. Ligand field parameters such as crystal field and Racah parameters were estimated, and the covalent nature between Ni2+ ions and the surrounding ligand is indicated from the nephelauxetic effect. The optical band gap energy as calculated from Tauc's model was observed to decrease from 3.88 to 3.49 eV with increasing NiO content, while the refractive index follows the opposite behavior. Urbach energy values and metallization criterion factor confirmed the semiconductor character of the present Ni-doped NZB glasses.

Comparative Study of the Thermal Stabilities of the Experimentally Known High-Valent Fe(IV) Compounds Fe(1-norbornyl)4 and Fe(cyclohexyl)4.

The high stability of the experimentally known homoleptic 1-norbornyl derivative (nor)4Fe of iron in the unusual +4 oxidation state is a consequence of the high reaction barriers of the singlet or triplet potential surfaces constrained by the global dispersion attraction and the great steric demands of the norbornyl groups. The much more limited stability of the corresponding cyclohexyl derivative (cx)4Fe may result from the conical intersection between the singlet potential surface and the quintet spin potential surface arising from the weaker dispersion attraction and the reduced steric effect of the cyclohexyl groups relative to the 1-norbornyl groups. In contrast, the high stability of the likewise experimentally known (cx)4M (M = Ru or Os) structures results from the larger ligand field splitting (Δ) of the d-orbital energies for the second and third-row transition metals ruthenium and osmium relative to that of the first-row transition metal iron. The cyclohexyl derivative (cx)4Fe is predicted to be reactive toward carbon monoxide to insert CO into up to two Fe-C bonds. However, the dispersion effect as well as the much larger size of the 1-norbornyl substituents prevents similar reactivity of (nor)4Fe with carbon monoxide.

How the Ligand Field in Lanthanide Coordination Complexes Determines Magnetic Susceptibility Anisotropy, Paramagnetic NMR Shift, and Relaxation Behavior.

ConspectusComplexes of lanthanide(III) ions are being actively studied because of their unique ground and excited state properties and the associated optical and magnetic behavior. In particular, they are used as emissive probes in optical spectroscopy and microscopy and as contrast agents in magnetic resonance imaging (MRI). However, the design of new complexes with specific optical and magnetic properties requires a thorough understanding of the correlation between molecular structure and electric and magnetic susceptibilities, as well as their anisotropies. The traditional Judd–Ofelt–Mason theory has failed to offer useful guidelines for systematic design of emissive lanthanide optical probes. Similarly, Bleaney’s theory of magnetic anisotropy and its modifications fail to provide accurate detail that permits new paramagnetic shift reagents to be designed rather than discovered.A key determinant of optical and magnetic behavior in f-element compounds is the ligand field, often considered as an electrostatic field at the lanthanide created by the ligands. The resulting energy level splitting is a sensitive function of several factors: the nature and polarizability of the whole ligand and its donor atoms; the geometric details of the coordination polyhedron; the presence and extent of solvent interactions; specific hydrogen bonding effects on donor atoms and the degree of supramolecular order in the system. The relative importance of these factors can vary widely for different lanthanide ions and ligands. For nuclear magnetic properties, it is both the ligand field splitting and the magnetic susceptibility tensor, notably its anisotropy, that determine paramagnetic shifts and nuclear relaxation enhancement.We review the factors that control the ligand field in lanthanide complexes and link these to aspects of their utility in magnetic resonance and optical emission spectroscopy and imaging. We examine recent progress in this area particularly in the theory of paramagnetic chemical shift and relaxation enhancement, where some long-neglected effects of zero-field splitting, magnetic susceptibility anisotropy, and spatial distribution of lanthanide tags have been accommodated in an elegant way.

Superatomic Ligand-Field Splitting in Ligated Gold Nanoclusters.

Gold nanoclusters are attractive because of their electronic and optical properties. Many theoretical models have been proposed to explain their electronic structures through an electron-counting approach. However, subtle features may not be well explained by electron-counting rules. In this work, we have discovered a unique example of ligand-controlled skeletal bonding in two recently reported gold nanoclusters with very similar compositions and geometries. We have shown that the superatomic orbitals of the common kernel of the two clusters undergo different ligand-field splitting because of the different ligand-field strengths in the two clusters. Such a difference is clearly revealed by constructing the Jellium orbitals via an orbital alignment process, and a subsequent localization of the Jellium orbitals allows us to obtain localized bonding models. Finally, on the basis of localized bonding models, we predict the existence of a ligated gold cluster with a [Au32]4+ kernel.

Correlating Electronic Structure and Magnetic Anisotropy in Actinide Complexes [An(COT)2], AnIII/IV = U, Np, and Pu.

The electronic structures and magnetic anisotropies for compounds [An(COT)2] (An = UIII/UIV, NpIII/NpIV and PuIII/PuIV, COT = cyclooctatetraene) are characterized using scalar relativistic density functional theory calculations and second-order perturbation theory based on a complete active space self-consistent field reference including spin-orbit coupling. The degree of participation of 5f orbitals in actinide-ligand bonding and the associated metal-ligand covalency is found to trend as U > Np ≥ Pu for both the tetra-positive and tripositive An complexes. A spin-Hamiltonian analysis indicates only weak single-molecule magnet (SMM) characteristics for [U(COT)2]- and [Np(COT)2] complexes and no significant SMM behavior for the other complexes. The weak SMM behavior in [U(COT)2]- and [Np(COT)2] is attributed to a subtle interplay between local symmetry and ligand-field splitting. Such a result suggests that magnetic anisotropy in 5f3 ions can be modulated in general by electrostatic ligand field design. In particular, σ-donor ligands oriented 180 degrees relative to one another will have a maximal influence on the 5f-orbital ligand field splitting, while π donors like cyclopentadiene and COT generate ligand field influences that have more acute angles associated with corresponding atoms on the individual ligands. These observations rationalize the differences in SMM characteristics for [U(BcMe)3] (BcMe- = dihydrobis(methylimidazolyl)borate) and [U(BpMe)3] (BpMe- = dihydrobis(methylpyrazolyl)borate) and indicate strategies to design new actinide-based SMMs with high magnetic relaxation barriers.

A Vanadium(III) Complex with Blue and NIR-II Spin-Flip Luminescence in Solution.

Luminescence from Earth-abundant metal ions in solution at room temperature is a very challenging objective due to the intrinsically weak ligand field splitting of first-row transition metal ions, which leads to efficient nonradiative deactivation via metal-centered states. Only a handful of 3dn metal complexes (n ≠ 10) show sizable luminescence at room temperature. Luminescence in the near-infrared spectral region is even more difficult to achieve as further nonradiative pathways come into play. No Earth-abundant first-row transition metal complexes have displayed emission >1000 nm at room temperature in solution up to now. Here, we report the vanadium(III) complex mer-[V(ddpd)2][PF6]3 yielding phosphorescence around 1100 nm in valeronitrile glass at 77 K as well as at room temperature in acetonitrile with 1.8 × 10-4% quantum yield (ddpd = N,N'-dimethyl-N,N'-dipyridine-2-ylpyridine-2,6-diamine). In addition, mer-[V(ddpd)2][PF6]3 shows very strong blue fluorescence with 2% quantum yield in acetonitrile at room temperature. Our comprehensive study demonstrates that vanadium(III) complexes with d2 electron configuration constitute a new class of blue and NIR-II luminophores, which complement the classical established complexes of expensive precious metals and rare-earth elements.

Generation of two-dimensional spectrochemical series in tetrahedral complexes

The physical properties of metal complexes that exist in many places are due to the ligand field splitting and electronic configuration of the d-orbital of the central transition metal, so changing the ligand field splitting of the d-orbital allows to control the physical properties. The arrangement of metals and ligands in order of the ligand field splitting is called a spectrochemical series. There is already a spectrochemical series only in the case of octahedral hexa-coordination complexes, but no equivalent index is shown for any other symmetry such as tetrahedral tetra-coordination complexes. In this study, we have investigated the creation of spectrochemical series in tetrahedral tetra-coordinated metal complexes. As a result, it is possible to accurately grasp the ligand field splitting of a tetrahedral tetra-coordinated metal complex, and to more effectively apply energy for expressing a spin crossover phenomenon in which the magnetism reversibly changes.

Effect of Molecular Distortion of Ligand Field Splitting in Five-Coordinated Metal Complex

Metal complex indicates the significant physical properties such as magnetism, electrical conductivity and an optical property due to the electronic interaction between the ligand molecule and the central metal ion. We have evaluated the magnetism of the metal complex by controlling the ligand field splitting, which is the energy splitting of the d-orbitals. The magnetic phenomenon of such compounds are realized as a result of the electronic state based on the transition metal coordination complexes, and which can be switched between high spin (HS) and low spin (LS), that is called a spin-crossover (SCO) phenomenon. Our group have been investigated the way how to control the spin state according to the concept of a molecular distortion. The five-coordinated metal complex ML5 has been experimentally confirmed to be a molecular distortion called the Berry pseudorotation (BPR). In the BPR process, both the axial and equatorial ligands can move at the same rate of increasing the angle between the other axial or equatorial ligands in five-coordinated metal complex. The classical BPR mechanism changes its molecular symmetry between two independent trigonal bipyramidals (TBPs) of D3h symmetry via a square pyramidal (SP) of C4v symmetry. The distortion parameters in the five-coordinated metal complexes τ5 are proposed in order to represent the distortion of the BPR process quantitatively. In this work, we predicted the possibility of the SCO phenomenon in intramolecular exchange mechanism through the BPR process in a five-coordinated metal complexes.

The magnetism change by Jahn-Teller distortionin octahedral hexa-coordinate complex

Metal complexes exhibit significant physical properties such as electrical conductivity, magnetism and optical properties. They can be controlled by changing the ligand field splitting of the d-orbital of the central metal ion. We have investigated the reversible spin crossover (SCO) phenomenon by changing the ligand field splitting in six-coordinated metal complexes ML6. In this study, we focused on the change of the spin states by uniaxial Jahn-Teller distortion in the case of an octahedral hexa-coordinated metal complexes ML6, involving two types of different ligand molecules. In addition, we have used DV-Xα and DVME methods in order to calculate the electronic states. In order to reproduce the effect of the Jahn-Teller distortion in the calculation, a uniaxial anisotropic distortion has been applied into the octahedral hexa-coordinate metal complex. The purpose of this research is to study the mechanism and phenomenon of the spin state changing by discussing the calculated electronic states of the spin crossover phenomenon.

Spin Crossover in 3D Metal Centers Binding Halide-Containing Ligands: Magnetism, Structure and Computational Studies

The capability of a given substance to change its spin state by the action of a stimulus, such as a change in temperature, is by itself a very challenging property. Its interest is increased by the potential applications and the need to find sustainable functional materials. 3D transition metal complexes, mainly with octahedral geometry, display this property when coordinated to particular sets of ligands. The prediction of this behavior has been attempted by many authors. It is, however, made very difficult because spin crossover (SCO), as it is called, occurs most often in the solid state, where besides complexes, counter ions, and solvents are also present in many cases. Intermolecular interactions definitely play a major role in SCO. In this review, we decided to analyze SCO in mono- and binuclear transition metal complexes containing halogens as ligands or as substituents of the ligands. The aim was to try and find trends in the properties which might be correlated to halogen substitution patterns. Besides a revision of the properties, we analyzed structures and other information. We also tried to build a simple model to run Density Functional Theory (DFT) calculations and calculate several parameters hoping to find correlations between calculated indices and SCO data. Although there are many experimental studies and single-crystal X-ray diffraction structures, there are only few examples with the F, Cl, Br and series. When their intermolecular interactions were not very different, T1/2 (temperature with 50% high spin and 50% low spin states) usually increased with the calculated ligand field parameter (Δoct) within a given family. A way to predict SCO remains elusive.

XANES spectroscopic studies at L3 edge of 79Au in its various chemical forms

The systematic X-ray absorption near edge structure (XANES) investigation at Au L3-edge was made on Au in metallic form and its compounds in various definite oxidation states, viz., Au(OH)3, AuCl, AuCl3, HAuCl4, AuI and AuBr3. The spectra have been recorded with linearly polarized photon beam from 2.5 GeV INDUS-2 Synchrotron source. All XANES spectra were deconvoluted to configure the energy positions of bound and continuum state transitions. With respect to the reference metallic Au, the absorption edge of the Au-compounds shifts towards higher energies with increasing valency of the absorbing atom. The origin of different shifts is found to be dependent on the charge transfer mechanism between Au and ligands in the measured spectra at Au L3-edge. The shifts in the absorption energies have also correlated to an increase in the ligand field strength. The absorption edge energy and area of the white-line peaks for the Au-compounds with Au in +3 oxidation state increase systematically in the spectrochemical series as AuBr< AuCl< HAuCl4< Au(OH)3, which indicates hybridization of d-orbitals and increasing tendency of ligand atom to attract electrons. Theoretical simulations are in line with this trend and the Au-series demonstrates that energy shifts in XANES spectra of Au(III) compounds can be understood in terms of crystal field theory.

Absorption spectra, ligand field parameters and g factors of Cr3+ doped α-Al2O3 laser crystal: ab initio calculations

In this paper we present, in the unified frame, the results of the ab initio investigations of absorption spectra, ligand field parameters and g factors for three valence chromium doped α-Al2O3 crystal. Our calculations are based on a new methodology applied to a cluster [CrO6]9− embedded in an extended point charge field of host matrix ligands. After the differential functional theory optimization of the doped crystal, a vibrational theoretical spectroscopic study based on infrared spectroscopy has been employed in order to confirm the stability of the optimized doped crystal structure. The ab initio energy calculation of the electronic states and corresponding wave functions of Cr3+ are documented from the complete active space self-consistent field. The improved energy states from the N-electron valence second order perturbation theory, second order dynamic correlation dressed complete active space (DCD-CAS2), difference dedicate configuration interaction with three degrees of freedom (MRDDCI3) and spectroscopy-oriented configuration interactions, were analyzed. Based on the ab initio ligand field theory procedure we extracted ligand field parameters and spin–orbit coupling constant which were used to recalculate the energy levels of the studied system. In addition, g factors for the ground state 4A2 of Cr3+ ion in corundum are calculated taking into account the full configuration interaction. The results obtained are discussed and the comparisons with measured values from literature show a reasonable agreement, which justifies and recommend this new route of investigation.

Improvement of Ab Initio Ligand Field Theory by Means of Multistate Perturbation Theory.

Over the last few years, ab initio ligand field theory (AILFT) has evolved into an important tool for the extraction of ligand field models from ab initio calculations. The inclusion of dynamic correlation on top of complete active space self-consistent field (CASSCF) reference functions, which is important for accurate results, was so far realized at the level of second-order N-electron valence state perturbation theory (NEVPT2). In this work, we introduce two alternative methods for the inclusion of dynamic correlation into AILFT calculations, the second-order dynamic correlation dressed complete active space method (DCD-CAS(2)) and the Hermitian quasi-degenerate NEVPT2 (HQD-NEVPT2). These methods belong to the class of multistate perturbation theory approaches, which allow for the mixing of CASSCF states under the effect of dynamic correlation (state-mixing). The two new versions of AILFT were tested for a diverse set of transition-metal complexes. It was found that the multistate methods have, compared to NEVPT2, an AILFT fit with smaller root mean square deviations (rmsds) between ab initio and AILFT energies. A comparison of AILFT excitation energies with the experiment shows that for some systems, the agreement gets better at the multistate level because of the smaller rmsds. However, for some systems, the agreement gets worse, which could be attributed to a cancellation of errors at the NEVPT2 level that is partly removed at the multistate level. An investigation of trends in the extracted ligand field parameters shows that at the multistate level, the ligand field splitting Δ gets larger, whereas the Racah parameters B and C get smaller and larger, respectively. An investigation of the reasons for the observed improvement for octahedral CrIII halide complexes shows that the possibility of state-mixing relaxes constraints that are present at the NEVPT2 level and that keep Δ and B from following their individual preferences.

New Analysis Model for the Determination of Racah and Crystal-Field Splitting Parameters: Verification and Case Studies

The Racah parameters in conjunction with the Tanabe—Sugano energy-level diagram are widely used as a means of describing the effects of electron—electron repulsion within the metal complexes in coordination chemistry. A determination of the excitation energy levels in the 3d3-configuration ions (Mn4+, Cr3+, etc.) is possible from a set of Racah parameters (B and C) and crystal-field splitting parameter (Dq), and vice versa. The Tanabe—Sugano diagram promises that the zero-phonon line 2Eg energies, E(2Eg)ZPL, over B of the Mn4+ and Cr3+ ions should be nearly crystal field independent, since they are practically parallel to the horizontal axis in the whole range of Dq/B variation. However, the experimental E(2Eg)ZPL plots showed a gradual increase with increasing Dq/B, in disagreement with the Tanabe—Sugano diagram. Therefore, a new analysis model assuming the Racah parameter ratio of C/B ∼ 4.7 has been recently proposed [ECS J. Solid State Sci. Technol., 8, R164 (2019); 8, R183 (2019)]. However, the new model has been used without rigorous validation. The present study focused on this problem and analyzed the luminescence properties of LiBaF3:Cr3+ and LaGaO3:Mn4+ phosphors. More generalized expressions were proposed for analyzing the various kinds of phosphors at an optional ratio of C/B = r.

Analysis of the Fe 2p XPS for hematite α Fe2O3: Consequences of covalent bonding and orbital splittings on multiplet splittings.

The origins of the complex Fe 2p X-Ray Photoelectron Spectra (XPS) of hematite (α-Fe2O3) are analyzed and related to the character of the bonding in this compound. This analysis provides a new and novel view of the reasons for XPS binding energies (BEs) and BE shifts, which deepens the current understanding and interpretation of the physical and chemical significance of the XPS. In particular, many-body effects are considered for the initial and the final, 2p-hole configuration wavefunctions. It is shown that a one-body or one-configuration analysis is not sufficient and that the many-body, many-determinantal, and many-configurational character of the wavefunctions must be taken into account to describe and understand why the XPS intensity is spread over an extremely large number of final 2p-hole multiplets. The focus is on the consequences of angular momentum coupling of the core and valence open shell electrons, the ligand field splittings of the valence shell orbitals, and the degree of covalent mixing of the Fe(3d) electrons with the O(2p) electrons. Novel theoretical methods are used to estimate the importance of these various terms. An important consequence of covalency is a reduction in the energy separation of the multiplets. Although shake satellites are not considered explicitly, the total losses of intensity from the angular momentum multiplets to shake satellites is determined and related to the covalent character of the Fe-O interaction. The losses are found to be the same for Fe 2p1/2 and 2p3/2 ionization.

Spectroscopic Properties, Magnetic Behaviours and Hirshfeld Surface Analysis of Ag[Cr(1,3-pdta)]·3H2O

The presence of various functional groups present in Ag[Cr(1,3-pdta)]·3H2O (1,3-pdta = 1,3-propanediaminetetraacetate) was confirmed by FT-IR spectral results. The electronic spectral properties and magnetic behaviours were also described. The results of our calculations yielded the crystal field splitting and Racah parameters of Dq = 1969 cm-1, B = 594 cm-1 and C = 3250 cm-1. Hirshfeld surface analysis by three-dimensional (3D) molecular surface contours and two-dimensional (2D) fingerprint plots were performed to visualize, explore and quantify the intermolecular interactions in the crystal lattice. Hirshfeld surface contours and 2D fingerprint maps revealed that the crystal packing is dominated by H···O/O···H and H···H contacts. The strong hydrogen-bonding interactions are linked with O–H···O consisting the highest fraction of 63.4% followed by these of the H···H type contributing 25.5%. Other very weak contacts of Ag···O/O···Ag, C···H/H···C, O···O, Ag···H/H···Ag and O···C/C···O are present in the title compound.

Tailoring Spin–Orbit Coupling by Aligned Earth-Abundant Metals for Extending Lifetime of Charge-Transfer Excited State

The long charge-transfer excited state (CTES) lifetime of organometal complexes make them very promising in the applications of photovoltaic, photocatalysis and photosensor. Employing the spin–orbit coupling (SOC) of noble metals for achieving long-lived CTES are often essential to guarantee high performance. There is much interest in replacing these noble metals with non-noble metals due to low cost and environmental friendliness. However, despite the exploration of advanced molecular designs, it is failing to access a long-lived CTES of earth-abundant metal-containing complexes by the SOC effect. Because weak ligand field splitting of non-noble metals causes rapid deactivation of CTES. Here, the SOC of orderly aligned non-noble metals on a layered double hydroxide (LDH) nanosheet is enhanced through the Rashba effect caused by breaking of the inversion symmetry. Taking porphyrins-Pd (Pd-TCPP) as a model chromophore, a series of (LDHs/Pd-TCPP)n films are fabricated, and a high polar distortion (alinged P...

Elucidating the Electronic Structure and Magnetic and Conducting Properties of μ-Oxo Mn-phthalocyanine [MnPc(CN)]2O Complex

The μ-oxo phthalocyanine dimer complex [Mn(Pc)(CN)]2O has been characterized as the first single-component molecular conductor exhibiting magnetoresistance at room temperature. Herewith, we report a detailed study of the electronic structure and the magnetic and conducting properties of this μ-oxo MnPc dimer complex. A combined strategy of wave-function-based quantum chemistry calculations on the complex and plane-wave-based periodic calculations on the crystal has been employed together with semiclassical Boltzmann transport theory calculations. Our results provide information about the ligand field parameters of the Mn ions, clarify their spin states on the [Mn(Pc)(CN)]2O complex, and explain the temperature dependence of both the magnetic susceptibility and the effective magnetic moment, taking into account the presence of excited low-lying states with S = 2 and weak intermolecular magnetic interactions, as key ingredients of the magnetic behavior. The analysis of the density of states of the low-spin and high-spin density functional theory + U magnetic solutions and their respective temperature dependence of the electric resistivity give some clues about the conducting properties and the negative magnetoresistance reported for this system.

X-ray absorption fine structure spectroscopic study of (NH4)2ReF6

The (NH4)2ReX6 (X = F, Cl, Br, I) salts have been investigated by x-ray absorption fine structure spectroscopy. The Re-F distance determined by EXAFS in (NH4)2ReF6 (i.e., 1.95 A) is in good agreement with the one determined by single crystal x-ray diffraction in A2ReF6 salts (A = K, Rb, Cs). The XANES studies of (NH4)2ReX6 (X = F, Cl, Br, I) indicates that the positions of the absorption edge and of the white line are shifted to higher energy when moving from I to F. These shifts have been explained in terms of the crystal field splitting parameter and covalent charge carried by the Re atoms. Calculations of the XANES spectra of the ReX62− (X = F, Cl, Br, I) anions at the Re-L3 edge have been performed and the calculated shifts and intensity of the white lines reproduce well the experimental observations.

Density Functional Theory (DFT)-Based Bonding Analysis Correlates Ligand Field Strength with 99Ru Mössbauer Parameters of Ruthenium-Nitrosyl Complexes.

We applied density functional theory calculations to ruthenium-nitrosyl complexes, which are known to exist in high-level radioactive waste generating during reprocessing of spent nuclear fuel, to give a theoretical correlation between 99Ru Mössbauer spectroscopic parameters and ligand field strength for the first time. The structures of the series of complexes, [Ru(NO)L5] (L = Br-, Cl-, NH3, CN-), were modeled based on the corresponding single-crystal X-ray coordinates. The comparisons of the geometries and total energies between the different spin states suggested that the singlet spin state of [Ru(II)(NO+)L5] complexes were the most stable. This result was supported by the benchmark calculations of the 99Ru Mössbauer isomer shift (δ) and quadrupole splitting (ΔEQ) values. The calculated results of both the δ and ΔEQ values reproduced the experimental results by reported previously and increased in the order of L = Br-, Cl-, NH3, CN-. Finally, we estimated the ligand field strength (Δo) based on molecular orbitals, assuming C4v symmetry and showed the increase of Δo values in that order, being consistent with well-known spectrochemical series of ligands. The increase attributes to the strengthening of the abilities of σ-donor and π-acceptor of the L-ligands to the Ru atom, resulting in the increase of the δ values. Furthermore, the increase of the σ-type donation into Ru dx2-y2 orbital and the π-type back-donation from Ru dxz, dyz orbitals in that order caused the decrease of the electron density along the Ru-NO axis, resulting in the increase of the ΔEQ values. This study is expected to contribute to the ligand design for the ruthenium-nitrosyl complexes, leading to the drug design for NO carrier and the decontamination of radioactive ruthenium from the ecological system, as well as the recovery of platinum-group metals from high-level radioactive waste.