Vibronic Coupling Parameters Research Articles

Polaronic Mechanism of Vibronic Localization in Mixed-Valence Cation Radicals with a Non-Conjugated Chromophore on the Bridge

In quest of a controllable intramolecular electron transfer (ET) across a bridge, we study the cation-radical form of the parent 1,4-diallyl-butane (I) and its derivatives (II)-(VI). In these mixed-valence (MV) compounds, the bridge of variable length connecting allyl redox sites can be either saturated (-CH2 CH2-) (I, III, and V) or unsaturated, modified by the π-spacer (-HC═CH-) (II, IV, and VI). Ab initio calculations for the charge delocalized transition structure and for fully optimized localized form of 1,ω-diallyl cation radicals I-VI allowed us to estimate the potential barriers for ET between the terminal allyl groups, vibronic coupling, and ET parameters. The ET barrier in all compounds with the π-fragment on the bridge is shown to be higher with respect to that in the systems with a saturated bridge. We propose a model based on the concept of a specific polaronic effect of the spacer. Charge localization at an allyl group creates an electric field polarizing the π-fragment and the bridge as a whole. The induced dipole moment interacts with the localized charge giving rise to the additional vibronic stabilization in a self-consistent manner without an appreciable change of localized charge. Utilization of this spacer-driven polaronic effect is expected to provide a route to a controllable ET in bridged MV compounds.

Controllable Electron Transfer in Mixed-Valence Bridged Norbornylogous Compounds: Ab Initio Calculation Combined with a Parametric Model and Through-Bond and Through-Space Interpretation.

In the context of a computationally guided approach to the controllable electron transfer in mixed-valence (MV) systems, in this article, we study the electron transfer (ET) in the series of oxidized norbornadiene C7H8 (I) and its polycyclic derivatives, C12H12 (II), C17H16, (III), C27H24 (IV), and C32H28 (V), with variable lengths of the bridge connecting redox sites. The work combines an ab initio CASSCF evaluation of the electronic structure of systems I-V with the parametric description in the framework of the biorbital two-mode vibronic model. The model involves coupling with the "breathing" mode and intercenter vibration modulating the distances between the redox fragments. The ab initio calculations were performed for two types of optimized structures of I-V: (a) charge-localized global minimum (Cs) and (b) symmetric configuration (C2v) with the delocalized charge. This allows one to estimate the potential barrier separating charge-localized configurations as well as vibronic coupling parameters and the electron transfer integral. Along with the adiabatic approach, the quantum-mechanical analysis of the vibronic levels has been applied to precisely estimate the quantum effect of tunneling splitting. We estimate the "through-space" and "through-bond" contributions to the parameters interrelated with the charge transfer (CT). The through-space effect proves to be a major factor of ET at a short distance between the redox centers, whereas the through-bond contribution is dominant at a long distance. Vibronic coupling under the condition of through-space ET leads to the localization of the positive charge on the π-chromophore, while the through-bond component of ET results in compensating σ-shifts and subsequent charge delocalization over the bridge. The limitations of the parametric approach were discussed in the context of the two components contributing to the ET. Particularly, the bridge polarization in the course of through-bond ET proves to be beyond the basis of the employed parametric model.

Multimode two-dimensional vibronic spectroscopy. II. Simulating and extracting vibronic coupling parameters from polarization-selective spectra.

Experimental demonstrations of polarization-selection two-dimensional Vibrational-Electronic (2D VE) and 2D Electronic-Vibrational (2D EV) spectroscopies aim to map the magnitudes and spatial orientations of coupled electronic and vibrational coordinates in complex systems. The realization of that goal depends on our ability to connect spectroscopic observables with molecular structural parameters. In this paper, we use a model Hamiltonian consisting of two anharmonically coupled vibrational modes in electronic ground and excited states with linear and bilinear vibronic coupling terms to simulate polarization-selective 2D EV and 2D VE spectra. We discuss the relationships between the linear vibronic coupling and two-dimensional Huang-Rhys parameters and between the bilinear vibronic coupling term and Duschinsky mixing. We develop a description of the vibronic transition dipoles and explore how the Hamiltonian parameters and non-Condon effects impact their amplitudes and orientations. Using simulated polarization-selective 2D EV and 2D VE spectra, we show how 2D peak positions, amplitudes, and anisotropy can be used to measure parameters of the vibronic Hamiltonian and non-Condon effects. This paper, along with the first in the series, provides the reader with a detailed description of reading, simulating, and analyzing multimode, polarization-selective 2D EV and 2D VE spectra with an emphasis on extracting vibronic coupling parameters from complex spectra.

First principles study of the vibronic coupling in positively charged [formula omitted

Vibronic coupling parameters for C60+ were derived via DFT calculations with hybrid B3LYP and CAM-B3LYP functional, based on which the static Jahn-Teller effect were analyzed. The global minima of adiabatic potential energy surface (APES) shows a D5d Jahn-Teller deformation, with stabilization energies of 110 and 129 meV (with B3LYP and CAM-B3LYP respectively), which are two times larger than that in C60-, suggesting the crucial role of the dynamical Jahn-Teller effect. Present results enable us to assess the actual situation of dynamical Jahn-Teller effect in C60+ and excited C60 in combination with the established parameters for C60-.

Dynamical Jahn‐Teller effect in the first excited

AbstractJahn‐Teller effect of C60 monoanion in the first electronically excited states was theoretically investigated. The orbital vibronic coupling parameters for t1g next lowest unoccupied molecular orbitals were derived from the Kohn‐Sham orbital levels calculated using a frozen phonon approach with both hybrid B3LYP and CAM‐B3LYP functionals, which take long‐range interaction correction into consideration. With these coupling parameters, the vibronic states of first excited were derived by exactly diagonalizing dynamical Jahn‐Teller Hamiltonian. The results showed that dynamical Jahn‐Teller effects are more significant in the first excited than those in the ground electronic states. This work also clarified that CAM‐B3LYP gives results closer to experimental data than B3LYP.

Pseudo Jahn–Teller origin tracking for symmetry breaking in halogenabenzene: How can a bird fly?

AbstractThe cyclic iodabenzene molecule (CH)5I was first introduced and characterized as planar configuration and zwitterionic valence structure by Glukhovtsev in 1991. Recently, it caused researchers' great interest due to the theoretical discovery of a stable bird‐like structure by Hoffmann et al. in 2017 which has similar electronic structure and charge distribution as well‐known Meisenheimer complex C6H. Inspired by this, we continue to tell the halogenabenzene story by revealing the origin of the bird‐like structure and understanding how the electronic behavior affects the geometrical symmetry for a molecule. By combining the Pseudo Jahn–Teller effect (PJTE) theory with the ab initio calculations for halogenabenzenes (CH)5X (X = F, Cl, Br, I) and C6H, it is illustrated that the vibronic coupling of 1A1 ground state and 1B1 excited states with C2v planar structure along the out‐of‐plane b1 distortion triggers the symmetry breaking of planar configuration to form a preferred bird‐like structure. This interpretation can be also applied to explain their different stabilization energies by analyzing numerically the energy gaps of coupled electronic states and PJTE vibronic coupling parameters. Taking use of the PJTE formulation above, we also tracked the origin of restoring to be planar for (CH)5X2+ cation, as well as their isoelectronic species (CH)5O+ and (CH)5N, and suggests an effective strategy to stabilize the planar configuration for halogenabenzenes.

Luminescent spectroscopy and structural properties of Ce3+-doped low-temperature X1–Y2SiO5 material prepared by polymer-assisted sol–gel method

Cerium (Ce3+)-doped monoclinic X1–Y2SiO5 (YSO)-type oxyorthosilicates powders were prepared by monomer and polymer-assisted sol–gel method. The present work aims to study the influence of ethylene glycol (EG) monomer, polyethylene glycol (PEG) polymer and polyvinyl alcohol (PVA) polymer, as fuels and nucleating agents for the crystallization, on structural and luminescence properties of the Ce3+ (xCe = 0.01)-doped Y2SiO5. The X-ray diffraction technique, field emission scanning electron microscopy, Fourier transform infrared spectroscopy and steady photoluminescence have been used to characterize the samples. It is found that the types of fuels affect the phase purity and luminescent characteristics of phosphors. All samples exhibit intense violet-blue asymmetric emission band in the range of 370–540 nm with a maximum intensity centered at around 420 nm assigned to the 5d → 4f (2F5/2, 2F7/2) interconfigurational transitions of Ce3+ ion in YSO nanomaterial. Finally, the vibronic coupling parameters are estimated and discussed.

Geometry, Electronic Structure, and Pseudo Jahn-Teller Effect in Tetrasilacyclobutadiene Analogues.

We revealed the origin of the structural features of a series of tetrasilacyclobutadiene analogues based on a detailed study of their electronic structure and the pseudo Jahn-Teller effect (PJTE). Starting with the D4h symmetry of the Si4R4 system with a square four-membered silicon ring as a reference geometry, and employing ab initio calculations of energy profiles along lower-symmetry nuclear displacements in the ground and several excited states, we show that the ground-state boat-like and chair-like equilibrium configurations are produced by the PJT interaction with appropriate excited sates. For Si4F4 a full two-mode b1g−b2g adiabatic potential energy surface is calculated showing explicitly the way of transformation from the unstable D4h geometry to the two equilibrium C2h configurations via the D2h saddle point. The PJTE origin of these structural features is confirmed also by estimates of the vibronic coupling parameters. For Si4R4 with large substituents the origin of their structure is revealed by analyzing the PJT interaction between the frontier molecular orbitals. The preferred chair-like structures of Si4R4 analogues with amido substituents, and heavier germanium-containing systems Ge4R4 (potential precursors for semiconducting materials) are predicted.

Localization-Delocalization in Bridged Mixed-Valence Metal Clusters: Vibronic PKS Model Revisited.

Here we describe a new vibronic model of mixed valence (MV) dimer inspired by the conventional Piepho, Krausz, and Schatz (PKS) approach. We attempted to partially lift the main restriction of the PKS model dealing with the vibronically independent moieties of a MV molecule. The refined version of the PKS model in which the bridging ligands are included deals with the three main interactions: electron transfer (integral t0) related to the high-symmetric ligand configuration, on-site vibronic coupling (parameter υ) arising from the modulation of the crystal field on the metal sites by the breathing displacements of their nearest ligand surroundings, and intercenter vibronic coupling (parameter ζ) describing the dependence of the electron transfer on ligand positions in the course of their breathing movement. We apply the modified model to the analysis of the adiabatic potentials and electronic density distributions in the minima of their lower sheets for the cases of one-electron MV dimer with long and short bridges and for the two-electron MV dimer exhibiting a valence disproportionation effect. The inclusion of the intercenter interaction in addition to the conventional PKS coupling is shown to produce a strong effect on the degree of localization in MV dimers and, in particular, on the assignments to the Robin and Day classes and on the conditions of stabilization of valence disproportionated states in bielectron transfer systems.

Novel Effect Induced by Pseudo-Jahn-Teller Interactions: Broken Cylindrical Symmetry in Linear Molecules.

It is shown that in linear molecules the pseudo-Jahn-Teller (PJT) interaction of a Σ or Π term with a Δ term induces a bending instability that is angular dependent, reducing the symmetry of the adiabatic potential energy surface from expected D∞h to D4h and C∞v to C2v or C4v. This spontaneously broken cylindrical symmetry (BCS) emerges from the solution of the vibronic coupling equations of the PJT effect (PJTE) problems (Σ+Δ)⊗w, (Π+Δ)⊗w, (Π+Σ+Δ)⊗w, and (Δ+Δ)⊗w, where w includes linear, quadratic, and fourth order vibronic coupling terms, and it is confirmed by ab initio calculations for a series of triatomic molecules with ground or excited Δ terms. The BCS is due to the angular symmetry of the electronic wave functions of the Δ term, ∼cos 2φ, and ∼sin 2φ, split by the fourth order vibronic coupling, which in overlap with the other symmetry wave functions of the Σ or Π term provides for the periodical symmetry of the added covalency that facilitates the bending. The mechanism of this PJT-induced BCS effect is discussed in detail; the numerical values of the vibronic coupling parameters for the molecules under consideration were estimated by means of combining separate ab initio calculations of some of them with a procedure fitting the analytical expressions to ab initio calculated energy profiles. It is also shown that the bending of linear molecules in Δ states, similar to Π states, is exclusively a PJT (not Renner-Teller) effect. The BCS revealed in this paper illustrates again the predicting power of the PJTE.

A theoretical analysis of chemical bonding, vibronic coupling, and magnetic anisotropy in linear iron(ii) complexes with single-molecule magnet behavior

The electronic structure and magnetic anisotropy of six complexes of high-spin FeII with linear FeX2 (X = C, N, O) cores, Fe[N(SiMe3)(Dipp)]2 (1), Fe[C(SiMe3)3]2 (2), Fe[N(H)Ar′]2 (3), Fe[N(H)Ar*]2 (4), Fe[O(Ar′)]2 (5), and Fe[N(t-Bu)2]2 (7) [Dipp = C6H3-2,6-Pri2; Ar′ = C6H3-2,6-(C6H3-2,6-Pri2)2; Ar* = C6H3-2,6-(C6H2-2,4,6-Pri2)2; Ar# = C6H3-2,6-(C6H2-2,4,6-Me3)2], and one bent (FeN2) complex, Fe[N(H)Ar#]2 (6), have been studied theoretically using complete active space self-consistent field (CASSCF) wavefunctions in conjunction with N-Electron Valence Perturbation Theory (NEVPT2) and quasidegenerate perturbation theory (QDPT) for the treatment of magnetic field and spin-dependent relativistic effects. Mossbauer studies on compound 2 indicate an internal magnetic field of unprecedented magnitude (151.7 T) at the FeII nucleus. This has been interpreted as arising from first order angular momentum of the 5Δ ground state of FeII center (J. Am. Chem. Soc. 2004, 126, 10206). Using geometries from X-ray structural data, ligand field parameters for the Fe-ligand bonds were extracted using a 1 : 1 mapping of the angular overlap model onto multireference wavefunctions. The results demonstrate that the metal–ligand bonding in these complexes is characterized by: (i) strong 3dz2–4s mixing (in all complexes), (ii) π-bonding anisotropy involving the strong π-donor amide ligands (in 1, 3–4, 6, and 7) and (iii) orbital mixings of the σ–π type for Fe–O bonds (misdirected valence in 5). The interplay of all three effects leads to an appreciable symmetry lowering and splitting of the 5Δ (3dxy, 3dx2−y2) ground state. The strengths of the effects increase in the order 1 < 5 < 7 ∼ 6. However, the differential bonding effects are largely overruled by first-order spin–orbit coupling, which leads to a nearly non-reduced orbital contribution of L = 1 to yield a net magnetic moment of about 6 μB. This unique spin–orbital driven magnetism is significantly modulated by geometric distortion effects: static distortions for the bent complex 6 and dynamic vibronic coupling effects of the Renner–Teller type of increasing strength for the series 1–5.Ab initio calculations based on geometries from X-ray data for 1 and 2 reproduce the magnetic data exceptionally well. Magnetic sublevels and wavefunctions were calculated employing a dynamic Renner–Teller vibronic coupling model with vibronic coupling parameters adjusted from the ab initio results on a small Fe(CH3)2 truncated model complex. The model reproduces the observed reduction of the orbital moments and quantitatively reproduces the magnetic susceptibility data of 3–5 after introduction of the vibronic coupling strength (f) as a single adjustable parameter. Its value varies in a narrow range (f = 0.142 ± 0.015) across the series. The results indicate that the systems are near the borderline of the transition from a static to a dynamic Renner–Teller effect. Renner–Teller vibronic activity is used to explain the large reduction of the spin-reversal barrier Ueff along the series from 1 to 5. Based upon the theoretical analysis, guidelines for generating new single-molecule magnets with enhanced magnetic anisotropies and longer relaxation times are formulated.

Theoretical analysis and quantification of the absorption spectra of uranyl complexes with structurally-related tridentate ligands

A semi-empirical model of vibronic coupling was developed in the present work to provide a quantitative analysis of partially resolved vibronic structure in uranyl absorption spectra. The studied uranyl complexes share a similar structure but bear different electric charges in the equatorial ligands. Their optical absorption spectra exhibit the common characteristics of charge transfer vibronic transitions of uranyl complexes but fine structures arising from specific vibrational modes are obscured. Accordingly, in application of the Franck-Condon principle of vibronic coupling, our model takes a mode-degenerate approximation. The absorption spectra of uranyl in various ligand environments were calculated and fitted to the experimental data. The semi-empirical approach enabled quantitative evaluation of the electronic energy levels, vibrational frequencies, and vibronic coupling strength. Moreover, the expansion of the U=O bond in the excited states was calculated from the values of the vibronic coupling parameters determined in simulation of the experimental spectra. The calculated results agree very well with the experimentally observed trends in thermodynamic binding constants and structural parameters. A theoretical interpretation is given to the dependence of the U=O bond expansion on the charges carried by the uranyl ligand complexes.

Luminescence and Spectroscopic Properties of Yellow-Emitting Carbonitride Phosphors and Their Application in White LEDs

A series of yellow-emitting carbonitride phosphors with compositions of was synthesized by using exothermic solid-state metathesis reactions. The wavelength of the broad band yellow emission was tunable, varying from 570 to 577 nm. The photoluminescence (PL) intensity enhanced with increasing dopant content and was optimized at 3 mol % under excitation at 415 nm. We analyzed the 5d energy levels of in a capped trigonal prismatic complex and estimated the vibronic coupling parameters and Stokes shifts. To understand the thermal quenching behavior, the temperature-dependent PL for was investigated. To demonstrate its potential application, we fabricated a warm white light-emitting diode (LED) using , pumped with a 420 nm GaInN LED chip, and the electroluminescence data were also presented.

Low-Energy Bands of Ferrocene−Ferrocenium Dimers: Bandshape Analysis with a Four-Level Two-Mode Vibronic Coupling Configuration Interaction (VCCI) Model Including Asymmetry

Ferrocene-ferrocenium dimers exhibit a double-peak intervalence charge-transfer (IVCT) band in the NIR/MIR region, which is analyzed in terms of a four-level, two-mode vibronic coupling configuration interaction (VCCI) scheme. Besides providing satisfactory fits of the measured spectra, the model also gives electronic and vibronic coupling parameters as well as CI mixing coefficients. A temperature-dependent asymmetry of the potential is introduced in order to describe the temperature dependence of the solid-state spectra and account for complementary Mossbauer data, which indicate a temperature-driven electron localization-delocalization transition in the singly bridged radical cations. The VCCI model is also successfully applied to the doubly bridged Fe(II)-Fe(III) bisfulvalenide dimer, which exhibits a double-peak IVCT transition as well. The VCCI analysis reveals that all dimers have a one-minimum potential in the ground state, leading in the absence of asymmetry to class III behavior (electron delocalization). If electron localization corresponding to class II characteristics occurs, it is due to an asymmetric (but still one-minimum) potential and not, as usual, to a double-minimum potential, explaining the class II-III borderline behavior observed for these systems.

Vibronic coupling parameters and Stokes shift in thiogallate phosphors

This article is devoted to the problem of the electron–vibrational interaction in 4f–5d optical transitions and the calculation of the Stokes shift in thiogallate materials. Usually 4f–5d transitions give rise to the broad vibronic bands whose shape-function have been described and found, including terms corresponding to the emission (absorption) from both ground and first excited levels. This approximation can be applied not only at low temperatures, but at high temperatures also, including room temperature, when the most photoluminescence (PL) measurements are carried out. We estimate vibronic coupling parameters and make the fitting of experimental data for Ba, Ca and Sr thiogallates. The peculiarity of Stokes shift is discussed. The theoretical results are in good agreement with the experimental data.

Electron–vibrational interaction in 4f–5d optical transitions in Ba, Ca, Sr thiogallates doped with Eu 2+ ions

This study is devoted to the problem of the electron–vibrational interaction in 4f–5d optical transitions. We analyze the room temperature experimental data on the vibronically assisted broad bands arising from the 4f–5d transitions in Ba, Ca, and Sr thiogallates doped with Eu 2+ ions. An approximate simple expression is given for the shape function of the broad vibronic bands with allowance for the terms corresponding to the emission (absorption) from both ground and first excited vibrational levels. We estimate the vibronic coupling parameters and the Stokes shifts for these systems. The theoretical results are in a good agreement with the experimental data.

A vibronic model for the absorption spectra ofCr2+ ionsin CdSexS1−x

In the present paper we report a vibronic model for the absorption bands of theCr2+ ion inCdSe and CdSe0.6S0.4 crystals. For the most probable impurity clusters,CrSe4,CrSe3S,CrSeS3 and CrSe2S2, the crystal field splittings and the vibronic coupling parameters are estimated with the aid ofthe exchange charge model of the crystal field accounting for the exchange and covalence effects.On this basis the transitions responsible for the formation of the optical bands arising from theCrSe4,CrSe3S,CrSeS3 and CrSe2S2 species are determined and the profiles of the absorption bandscorresponding to these species are calculated. The total spectrum of theCdSe0.6S0.4:Cr2+ crystal is obtained by summation over partial spectra arising fromall mentioned species. The profiles of the absorption bands inCdSe:Cr2+ and CdSe0.6S0.4:Cr2+ calculated on the basis of the numerical solution of the dynamical vibronic problems proveto be in quite good agreement with the experimental data.

DFT-Based Studies on the Jahn−Teller Effect in 3d Hexacyanometalates with Orbitally Degenerate Ground States

The topology of the ground-state potential energy surface of M(CN)(6) with orbitally degenerate (2)T(2g) (M = Ti(III) (t(2g)(1)), Fe(III) and Mn(II) (both low-spin t(2g)(5))) and (3)T(1g) ground states (M = V(III) (t(2g)(2)), Mn(III) and Cr(II) (both low-spin t(2g)(4))) has been studied with linear and quadratic Jahn-Teller coupling models in the five-dimensional space of the epsilon(g) and tau(2g) octahedral vibrations (Tg[symbol: see text](epsilon(g)+tau(2g)) Jahn-Teller coupling problem (T(g) = (2)T(2g), (3)T(1g))). A procedure is proposed to give access to all vibronic coupling parameters from geometry optimization with density functional theory (DFT) and the energies of a restricted number of Slater determinants, derived from electron replacements within the t(2g)(1,5) or t(2g)(2,4) ground-state electronic configurations. The results show that coupling to the tau(2g) bending mode is dominant and leads to a stabilization of D(3d) structures (absolute minima on the ground-state potential energy surface) for all complexes considered, except for [Ti(CN)(6)](3-), where the minimum is of D(4h) symmetry. The Jahn-Teller stabilization energies for the D3d minima are found to increase in the order of increasing CN-M pi back-donation (Ti(III) < V(III) < Mn(III) < Fe(III) < Mn(II) < Cr(II)). With the angular overlap model and bonding parameters derived from angular distortions, which correspond to the stable D(3d) minima, the effect of configuration interaction and spin-orbit coupling on the ground-state potential energy surface is explored. This approach is used to correlate Jahn-Teller distortion parameters with structures from X-ray diffraction data. Jahn-Teller coupling to trigonal modes is also used to reinterpret the anisotropy of magnetic susceptibilities and g tensors of [Fe(CN)(6)](3-), and the (3)T(1g) ground-state splitting of [Mn(CN)(6)](3-), deduced from near-IR spectra. The implications of the pseudo Jahn-Teller coupling due to t(2g)-e(g) orbital mixing via the trigonal modes (tau(2g)) and the effect of the dynamic Jahn-Teller coupling on the magnetic susceptibilities and g tensors of [Fe(CN)(6)](3-) are also addressed.

Pseudorotation in fullerene anions

Jahn-Teller (JT) problems are often characterised by an adiabatic potential energy surface (APES) containing either a set of isoenergetic wells or a trough of equivalent-energy points, which may be warped by higher-order coupling terms or anisotropic effects. In all three cases, the JT effect will be dynamic. Either tunnelling between the wells or rotation (of a distortion) around the trough will restore the original symmetry of the system. This motion is referred to as pseudorotation. It should be possible to observe a JT system in a distorted geometry if measurements are made on a sufficiently short timescale. In various cubic systems, this timescale has been calculated to be the order of picoseconds. Such timescales are accessible using modern methods of ultrafast spectroscopy. Measurements of pseudorotation rates can lead to important information on the strength and nature of the JT coupling present. We will present analytical calculations that allow the rate of pseudorotation to be determined in terms of the vibronic coupling parameters. We will show how these results can be applied to E ⊗ e systems and then to the more complicated system applicable to C 60 - anions. This is of particular interest because of the high icosahedral symmetry of fullerene ions and also because of the many potential uses of materials containing these ions. We conclude by outlining experiments that should be capable of measuring pseudorotation in C 60 anions.

Effects of vibronic interaction in cyano-bridged clusters containing Mn(III) and Mn(II) ions

The effects of vibronic interaction in the formation of the barrier for magnetization reversal in the cyanide-based binuclear Mn(III)–CN–Mn(II) clusters containing octahedrally coordinated Mn(III) and Mn(II) ions were examined. Along with the orbitally dependent superexchange between the Mn(II) and Mn(III) ions the model includes an axial component of the crystal field, spin–orbit coupling and vibronic interaction operating within the ground 3 T 1 ( t 2 4 ) term of the low-spin Mn(III) ion. The vibronic coupling parameters for the Mn(III) ion in the octahedral surrounding of six carbon ions have been evaluated in the framework of the exchange charge model of the crystal field accounting for the exchange and covalence effects. The dominating role of the tetragonal vibrations for the 3T 1 term of a single Mn(III) ion was demonstrated. The ability of the investigated complex to act as a Single-Molecule Magnet was analyzed as a function of both the temperature and the strength of vibronic coupling with the tetragonal vibrations. Very strong vibronic interaction strongly facilitates tunneling through the barrier, i.e., suppresses the barrier for magnetization reversal and prevents from long life time of magnetization.