Second hyperpolarizabilities of singlet polycyclic diphenalenyl radicals: effects of the nature of the central heterocyclic ring and substitution to diphenalenyl rings

Adopting density functional theory and a hybrid exchange-correlation functional, the relationship between the second hyperpolarizability (gamma) and the diradical character has been investigated for diphenalenyl-based compounds containing different heterocyclic five-membered central rings (C(4)H(4)X, where X = NH, PH, O, S, CH(2), SiH(2), BH, GaH, C=O, C=S, and C=Se) or substituted by donor (NH(2))/acceptor(NO(2)) groups. It turns out that these structural modifications can tune the diradical character from 0.0 to 0.968 and lead to variations of gamma over more than 1 order of magnitude, demonstrating the controllability of gamma in this family of compounds. In particular, when the central ring is strongly aromatic, the diradical character is larger than 0.7, which is associated with pretty large gamma values except for almost the pure diradical case (y approximately 1). On the other hand, when the aromaticity decreases--or the antiaromaticity increases--the diradical character and the second hyperpolarizability get smaller. These relationships are correlated to structural (bond length alternation) and charge distribution (charge transfer between the phenalenyl rings and the central ring) properties, which account for the relative importance of the resonance diradical, zwitterionic, and quinoid forms. Therefore, the diradical character and the second hyperpolarizability can be controlled by the aromaticity of the ring while the paradigm of the enhancement of gamma for intermediate diradical character is globally verified. Then, upon introducing donor groups, the zwitterionic character increases, leading to closed-shell species and small second hyperpolarizabilities. In the case of substitution by acceptor groups, the charge transfer is reduced but the diradical character and the second hyperpolarizability hardly changes.     

Enhancement of second hyperpolarizabilities in open-shell singlet slipped-stack dimers composed of square planar nickel complexes involving o-semiquinonato type ligands

Using the spin-unrestricted hybrid density functional theory method, we have investigated the intermolecular interaction effects on the longitudinal static second hyperpolarizability (γ) of open-shell singlet slipped-stack dimers composed of singlet diradical square planar nickel complexes involving o-semiquinonato type ligands, Ni(o-C(6)H(4)X(2))(2) (where X = O, NH, S, Se, PH). For comparison, we have also examined the γ values of a closed-shell singlet slipped-stack dimer composed of closed-shell monomers Ni[o-C(6)H(4)S(NH(2))](2). It is found that for interplanar distance ranging between 3.0 and 5.0 ? the slipped-stack dimers with intermediate monomer diradical characters exhibit larger γ values per monomer (γ(dimer)/2) than those with large monomer diradical characters or than the closed-shell dimer. These results extend the domain of validity of the relationship found between γ and the diradical character for individual molecules. It also turns out that the ratio R = (γ(dimer)/2)/γ(monomer) increases upon decreasing the interplanar distance and that this increase is larger for intermediate diradical character than for the other cases. These phenomena have been analyzed by considering the γ density distributions of the dimers, demonstrating a significant field-induced third-order charge transfer between the monomers in the case of intermediate diradical character. The present results indicate that open-shell singlet slipped-stack aggregates composed of monomers with intermediate diradical characters constitute another mean for achieving highly efficient and tunable third-order nonlinear optical materials.     

Die massenspektrometrische Fragmentierung von NiII-Chelaten mit O-, N-, S-, Se-Donoratomen

Mass Spectrometric Fragmentation of Ni^II Chelates with O-, N-, S-, Se-Donor Atoms The mass spectra of 6Ni^II chelates having the same substituents but different donor atoms (sequence of ligand atoms ? C(X)? NH? C(Y)? ; X, Y = O, S, Se, NH; see formula (1)) are discussed. The fragmentation pattern of the (thio)benzoyl(thio, seleno)ureas are characterized by the abstraction of S or Se atoms. The appearence of small neutral molecules seems to be typical for the fragmentation of all complexes. The mass spectrum of the Ni^II chelate having a NiS₂Se₂ coordination sphere shows no molecular ion peak. The contents of molecular ions in the total ion stream correlates with the stability of the complexes.     

Origin of the enhancement of the second hyperpolarizability of singlet diradical systems with intermediate diradical character

The origin of the diradical character dependence of the second hyperpolarizability (gamma) of neutral singlet diradical systems is clarified based on the perturbation formula of gamma using the simplest diradical molecular model with different diradical characters, i.e., H2 under bond dissociation. The enhancement of gamma in the intermediate diradical character region turns out to originate from the increasing magnitude of the transition moment between the first and second excited states and the decrease of that between the ground and first excited states, respectively, with the increase in diradical character. This feature confirms that open-shell singlet conjugated molecules with intermediate diradical characters constitute a new class of third-order nonlinear optical systems, whose gamma values can be controlled by the diradical character in addition to the conjugation length.     

Influence of non-bridging donor atoms on the value of exchange interaction in binuclear Cu<Superscript>II</Superscript> complexes with bis-hydrazones based on 2,6-diformylphenol

The quantum chemical simulation of exchange interaction according to the broken symmetry approach was performed for a series of binuclear Cu^II complexes containing the asymmetric exchange moiety based on bis-hydrazones of 2,6-diformylphenol. The calculated values were compared between themselves and with the experimental values of the exchange parameter 2J for the binuclear copper(II) complexes with bis-hydrazones based on 2,6-diformylphenol in order to reveal the influence pattern of the nature of nonbridging donor atoms X (O, N, S, and Se) onto the exchange interaction. The strength of exchange interaction of the antiferromagnetic type depends significantly on the nature of nonbridging donor atoms, increasing in the series of X = O, NH, S, and Se.     

Theoretical evidence for the singlet diradical character of square planar nickel complexes containing two o-semiquinonato type ligands

Density functional theory and complete active space self-consistent field computations are applied to elucidate the singlet diradical character of square planar, diamagnetic nickel complexes that contain two bidentate ligands derived from o-catecholates, o-phenylenediamines, o-benzodithiolates, o-aminophenolates, and o-aminothiophenolates. In the density functional framework, the singlet diradical character is discussed within the broken symmetry formalism. The singlet-triplet energy gaps, the energy gained from symmetry breaking, the spin distribution in the lowest triplet state, and the form of the magnetic orbitals are applied as indicators for the singlet diradical character. Moreover, a new index for the diradical character is proposed that is based on symmetry breaking. All symmetry breaking criteria show that the complexes obtained from o-catecholates and o-benzodithiolates have the largest and the smallest singlet diradical character, respectively. The singlet diradical character should be intermediate for the complexes derived from o-phenylenediamines, o-aminophenolates, and o-aminothiophenolates. The diradical character of all complexes suggests the presence of Ni(II) central atoms. This is also indicated by the d-populations computed by means of the natural population analysis.     

Second hyperpolarizability (gamma) of singlet diradical system: dependence of gamma on the diradical character

The dependence of the second hyperpolarizability (gamma) on the diradical character (y) for singlet diradical systems is investigated using a model compound, the p-quinodimethane (PQM) molecule with different both-end carbon-carbon (C-C) bond lengths, by several ab initio molecular orbital and density functional theory methods. The diradical character based on UHF calculations indicates that at equilibrium geometry PQM is in a singlet ground state and primarily exhibits a quinoid structure, whereas the diradical character increases when increasing both-end C-C bond lengths. At the highest level of approximation, that is, using the UCCSD(T) method with the 6-31G+diffuse p (zeta = 0.0523) basis set, the longitudinal static gamma of PQM presents a maximum value for intermediate diradical character (y approximately 0.5) while the gamma values are larger for intermediate and large diradical character (y approximately 0.5-0.7) than for small diradical character (y < 0.2). This feature suggests that the gamma values of singlet diradical systems in the intermediate and somewhat strong correlation regimes are significantly enhanced as compared to those in the weak correlation regime. These results are substantiated by a complementary study of the variation in gamma upon twisted ethylene.     

Racemic monoperoxovanadium(V) complexes with achiral OO and ON donor set heteroligands: synthesis, crystal structure and stereochemistry of [NH3(CH2)2NH3][VO(O2)(ox)(pic)].2H2O and [NH3(CH2)2NH3][VO(O2)(ox)(pca)

Monoperoxovanadium(V) complexes, [NH3(CH2)2NH3][VO(O2)(ox)(pic)].2H2O (1) and [NH3(CH2)2NH3][VO(O2)(ox)(pca)] (2) [NH3(CH2)2NH3 = ethane-1,2-diammonium(2+), ox=oxalate(2-), pic=pyridine-2-carboxylate(1-), pca=pyrazine-2-carboxylate(1-)], were synthesized and characterized by X-ray analysis, IR and Raman spectroscopies. The five equatorial positions of the pentagonal bipyramid around the vanadium atoms are occupied by the eta2-peroxo ligand, two oxygen atoms of the ox, and the nitrogen atom of the pic or pca ligands, respectively. The oxo ligand and the oxygen atom of pic or pca are in the axial positions. Networks of X-HO (X=C, N or O) hydrogen bonds, and pi-pi interactions between aromatic rings in and anion-pi interactions in , determine the molecular packings and build up the supramolecular architecture. Three stereochemical rules for occupation of the donor sites in two-heteroligand [VO(O2)(L1)(L2)] complexes (L1, L2 are bidentate neutral or differently charged anionic heteroligands providing an OO, NN or ON donor set) are discussed. and crystallize as racemic compounds. The 51V NMR spectra proved that the parent complex anions of and partially decompose on dissolution in water to the monoperoxo-ox, -pic or -pca complexes.     

Determination of the acid/base properties of MgY and NH4Y molecular sieves by inverse gas chromatography

The surface characterization of MgY and NH(4)Y zeolites was performed using inverse gas chromatography (IGC). The adsorption thermodynamic parameters (the standard enthalpy (DeltaH degrees ), standard entropy change (DeltaS degrees ), and free energy change of adsorption (DeltaG degrees ), the dispersive component of the surface free energies (gamma(S)(d)), and the acid-base character of the surface of MgY and NH(4)Y zeolites were estimated using the retention time of different non-polar and polar probes at infinite dilution region. The specific free energy of adsorption (DeltaG(sp)), the specific enthalpy of adsorption (DeltaH(sp)), and the specific entropy of adsorption (DeltaS(sp)) of polar probes on MgY and NH(4)Y zeolites were determined. The values of the DeltaH(sp) were correlated with both the donor and acceptor numbers of the probes to quantify the acidic K(A) and the basic K(D) parameters of the zeolite surfaces. The values obtained for the K(A) and K(D) parameters indicated a basic character for the surface of MgY and NH(4)Y zeolites.     

Synthesis,crystal structures,and third-order nonlinear optical properties of a series of ferrocenyl organometallics

Three novel ferrocenyl complexes [Zn(4-PFA)(2)(NO(3))(2)](H(2)O) (1), [Hg(2)(OAc)(4)(4-BPFA)(2)](CH(3)OH) (2), and [Cd(2)(OAc)(4)(4-BPFA)(2)] (3) (4-PFA = [(4-pyridylamino)carbonyl]ferrocene, 4-BPFA = 1,1'-bis[(4-pyridylamino)carbonyl]ferrocene) were prepared, and complexes 1 and 2 were structurally characterized by means of X-ray single-crystal diffraction. In complex 1, the zinc(II) atom is coordinated at a distorted tetrahedral environment by two nitrogen atoms from two 4-PFA moieties and two oxygen atoms from two nitrate anions; [Zn(4-PFA)(2)(NO(3))(2)] units are linked by hydrogen bonds N-H.O and O-H.O forming one-dimensional chains. Complex 2 is a tetranuclear macrocycle compound consisting of two 4-BPFA moieties and two Hg atoms; [Hg(2)(OAc)(4)(4-BPFA)(2)] units form 1-D chains by hydrogen bonds N-H.O as complex 1. Some complexes with 1,1'-bisubstituted pyridine-containing ferrocene ligands have been described, but their crystal data are limited. Compound 2 is the first example of a macrocyclic pyridine-containing ferrocenyl complex. The third-order nonlinear optical (NLO) properties of 4-PFA, 4-BPFA, and complexes 1-3 were determined by Z-scan techniques. The results indicate that all the compounds exhibit strong self-focusing effect. The hyperpolarizability gamma values are calculated to be in the range 1.51 x 10(-)(28) to 3.12 x 10(-)(28) esu. The gamma values are nearly twice as large for complexes 1-3 as for their individual ligands, showing that the optical nonlinearity of the complexes is dominated by the ligands.     

Theoretical study on the second hyperpolarizabilities of phenalenyl radical systems involving acetylene and vinylene linkers: diradical character and spin multiplicity dependences

We have investigated the static second hyperpolarizabilities (gamma) of the singlet diradical systems with intermediate diradical character involving phenalenyl radicals connected by acetylene and vinylene pi-conjugated linkers, 1 and 2, using the hybrid density functional theory. For comparison, we have also examined the gamma values of the closed-shell and pure diradical systems with almost the same molecular size as 1 and 2. In agreement with our previous prediction of the diradical character dependence of gamma, it turns out that the gamma values of 1 and 2 are significantly enhanced compared to those of the closed-shell and pure diradical systems. In the present case, distinct differences in gamma values are not observed between the two pi-conjugated linkers, though the diradical character is found to depend on the kind of linker. Furthermore, we have investigated the spin multiplicity effect on gamma. Changing from the singlet to the triplet state, the gamma values of the systems with intermediate diradical character in the singlet state are quite reduced, though those of the pure diradical systems are hardly changed. Such spin multiplicity dependence of gamma is understood by considering the difference of diradical character between their singlet states together with the Pauli principle. The present results provide a possibility of a novel control scheme of gamma for phenalenyl radical systems involving pi-conjugated linkers by adjusting the diradical character through the change of the linked position of pi-conjugated linkers and the spin multiplicity.     

Versatility of heterocyclic thioamides in the construction of a trinuclear cluster [Cu3I3(dppe)3 (SC5H4NH)] and Cu(I) linear polymers {Cu6(SC5H4NH)6I6}n x 2nCH3CN and {Cu(I)6 (SC3H6N2)6X6}n (X = Br, I)

Reaction of copper(I) iodide with pyridine-2-thione (2-SC5H4NH) and 1,2-bis(diphenylphosphino)ethane (dppe) in a CH3CN-CHCl3 mixture yielded a triangular cluster, [Cu3I3(mu2-P,P-dppe)3 (eta1-SC5H4NH)], 1. Similar reaction with 2-SC5H4NH and a series of diphosphanes, Ph2P-X-Ph2P {X = -CH2- (dppm), -(CH2)3- (dppp), -(CH2)4- (dppb), -CH=CH- (dppen)}, gave a novel iodo-bridged hexanuclear Cu(I) linear polymer,{Cu6(mu3-SC5H4NH)4 (mu2-SC5H4NH)2 (I4)(mu-I)2-}n x 2nCH3CN, 2. Reactions of copper(I) iodide/copper(I) bromide with 1,3-imidazolidine-2-thione (SC3H6N2) in a CH3CN-CHCl3 mixture yielded hexanuclear Cu(I) linear chain polymers, [{Cu6(mu3-SC3H6N2)2 (mu2-SC3H6N2)4X2 (mu-X)4}n] (X = Br, 4; I, 5). In compound 1, two iodide atoms and one dppe form the dinuclear Cu(mu2-I)2 (mu2-dppe)Cu core, and two dppe ligands bridge this core with the third Cu(I) center coordinated to 2-SC5H4NH via the S atom. The chain polymer 2 has a centrosymmetric hexanuclear central core, Cu6S6I4 (mu-I)2--, formed by dimerization of six-membered trinuclear motifs, Cu3(mu2-SC3H6N2)3I3 via (mu3-S) bonding modes of the thione ligand, and has four terminal and two bridging iodine atoms in trans-orientations. Linear chains are separated by the nonbonded acetonitrile molecules. In 4 and 5, three copper(I) bromide or copper(I) iodide moieties and three SC3H6N2 ligands combined via bridging S donor atoms to form the six-membered trinuclear Cu3(mu2-SC3H6N2)3I3 cores which polymerized via S and X atoms in a side-on fashion to form linear chain polymers, [{Cu6(mu3-SC3H6N2)2 (mu2-SC3H6N2)4X2(mu-X)4}n]. The (mu3-S) modes of bonding of neutral heterocyclic thioamides are first examples, as are trinuclear cluster and linear polymers rare examples in copper chemistry.     

Multicomponent assembly of anionic and neutral decanuclear copper(II) phosphonate cages

A multicomponent synthetic strategy involving copper(II) ions, tert-butylphosphonic acid (t-BuPO(3)H(2)) and 3-substituted pyrazole ligands has been adopted for the synthesis of soluble molecular copper(II) phosphonates. The use of six different 3-substituted pyrazoles, 3-R-PzH [R = H, Me, CF(3), Ph, 2-pyridyl (2-Py), and 2-methoxyphenyl (2-MeO-C(6)H(4))] as ancillary ligands afforded nine different decanuclear cages, [Cu(5)(μ(3)-OH)(2)(O(3)P-t-Bu)(3)(3-R-Pz)(2)(X)(2)](2)·(Y) where R = H, X = t-BuPO(3)H, and Y = (Et(3)NH(+))(4)(solvent) (1); R = Me, X = 3-MePzH, and Y = solvent (2); R = Me, X = t-BuPO(3)H, and Y = (Et(3)NH(+))(4)(solvent) (3); R = CF(3), X = t-BuPO(3)H, and Y = (Et(3)NH(+))(4)(solvent) (4); R = Ph, X = 3-PhPzH, and Y = solvent (5); R = 2-Py, X = 0.5 MeOH, and Y = solvent (6); R = 2-Py, X = none, and Y = solvent (7); R = 2-Py, X = H(2)O, and Y = (Et(3)NH(+)·PF(6)(-))(2)(solvent) (8); R = 2-MeO-C(6)H(4), X = MeOH or 0.5:0.5 MeOH/H(2)O, and Y = solvent (9). Compounds 1-6, 8, and 9 were isolated using a direct synthetic method which involves the reaction of copper(II) salts and the ligands, while 7 was obtained from an indirect route involving the reaction of preformed copper-pyridylpyrazolate precursor complexes and t-BuPO(3)H(2). The decametallic compounds 1-9 possess a butterfly shaped core. The core of the cages 1, 3, and 4 are tetraanionic and contain more phosphonates than pyrazole ligands, while the other cages are neutral and contain more pyrazoles than phosphonate ligands. Compounds 1-6 have been studied by electrospray ionization-high-resolution mass spectrometry (ESI-HRMS). The decanuclear cage 6 was shown to be a good plasmid modifier.     

SELENIUM-CONTAINING HYDANTOINS

Abstract

The influence of the exo-chalcogen atoms on the hydantoin skeleton of the complete series of molecules NH C(=X) NH C(=Y)CMe₂ (X, Y = O, S, Se) has been studied from several points of view.     

Organophosphines in PtPCOX (X = N,Cl, S), PtPCNX (X = Cl,S, Br,I, As) and PtPCClX (X = S,I, As) derivatives: structural aspects

In this review are classified and analyzed structural parameters of almost 90 monomeric organoplatinum complexes with inner coordination spheres consisting of PtPCOX (X?=?N, Cl, S), PtPCNX (X?=?Cl, S, Br, I, As) and PtPCClX (X?=?S, I, As). These complexes crystallized in three crystal systems: orthorhombic (× 11), triclinic (× 32) and monoclinic (× 45). Distorted square planar arrangements about the Pt(II) atoms are provided by mono-, heterobi- and heterotridentate donor ligands. The chelating ligands create a wide variety of four-, five- and six-membered metallocyclic rings and the effects of both steric and electronic factors influence the L–Pt–L bite angles. There are wide variations in the trans-positions of the donor ligands. Two examples are classified as distortion isomers.     

Size dependences of the diradical character and the second hyperpolarizabilities in dicyclopenta-fused acenes: relationships with their aromaticity/antiaromaticity

Using long-range corrected density functional theory, the relationships between the electronic, magnetic, and nonlinear optical properties are drawn for two families of organic compounds, the dicyclopenta-fused acenes (DPAs) and the polyacenes (PAs), containing up to N = 12 fused rings. First, the longitudinal second hyperpolarizability (γ) of singlet DPAs is significantly enhanced with increasing system size, in comparison to PAs. This behavior is associated with an increase in the longitudinal spin polarization between the terminal five-membered rings of DPAs and is consistent with previous studies where γ is maximized for intermediate diradical character. The size dependence of the diradical character is also found to cause a hump in the γ/N evolution for singlet DPAs around N = 8. In fact, in the case of singlet PAs, the diradical characters y(0) and y(1), the various magnetic properties and the γ/N values vary monotonically with N, whereas for singlet DPAs, the shielding, the magnetizability, and the γ/N values exhibit extrema near N = 8 due to the appearance of transversal spin polarization in the middle six-membered rings in addition to the longitudinal spin polarization between the terminal five-membered rings. Moreover, it is shown that for singlet DPAs the longitudinal spin polarization (characterized by y(0)) is associated with the antiaromaticity (N ≤ 3) and the slight- or non-aromaticity (N ≥ 4) of the terminal five-membered rings, whereas the appearance of transversal spin-polarization (characterized by y(1)) is associated with the decrease in the aromaticity in the inner six-membered rings as shown for large PAs. Therefore, the exceptional behaviors in singlet DPAs for small N (N < 9) are caused by the increase in diradical character y(0) correlated with the anti-aromaticity or the slight-/non-aromaticity of terminal rings and the corresponding emergence of a global aromatic character. Such a relationship between the aromaticity/antiaromaticity and the diradical character is useful for designing real open-shell NLO molecules through the control of their diradical characters.     

Structure, bonding, electronic and energy aspects of a new family of early lanthanide (La, Ce and Nd) complexes with phosphoric triamides: insights from experimental and DFT studies

A new family of isostructural early lanthanide(III) complexes (LnXPA) of the general formula Ln(XPA)(2)Cl(3)(solv)(2), where Ln = La, Ce and Nd, XPA = (4-X-C(6)H(4)NH)P(O)(NC(4)H(8)O)(2), X = H, F, Cl and Br, and solv = H(2)O and CH(3)OH, is introduced. X-ray crystallography shows that the replacement of the coordinated water by a methanol molecule may reduce the symmetry level of the unit cell from the orthorhombic crystal system and the space group Fdd2 to monoclinic and C2/c. DFT calculations, at B3LYP, PBE and B3PW91 levels, have been carried out to get a better insight into the structural, electronic and energy aspects of the compounds. The large cation attraction energy (-ΔE) values in the range 269-273 kcal mol(-1), at the B3PW91/ECP/6-311+G** level for the model complexes XPA-La(3+) with stoichiometry 1 : 1, represent new ligands XPA as efficient complexant agents for lanthanides. The electronic nature of para substituent X has no significant effect on the Ln-ligand bonding and cation affinity of the ligands XPA. The results of atoms in molecules (AIM) analysis reveal a partial covalent contribution of the Ln-ligand interaction for the models XPA-La(3+) in the absence of counterions and coordinated solvents. In the real complexes LnXPA, a closed-shell Ln-ligand interaction is established. Increasing the charge difference between nitrogen and phosphorus atoms (by ~0.06 e) associated with a weakening of the Lp(O(P))→σ*(P-N) electronic delocalization (Lp(O(P)) being the lone pair of the phosphoryl oxygen atom) may lead to an increase in partial multiple bond character of the P-N bonds in coordinated ligands, agreeing with the increase in ν(P-N) and (2)J(PH) coupling constant values. The changes in electron density (ρ) and electronic energy density (H(r)) values confirm these structural reorganizations upon complexation.     

Spectroscopic techniques and cyclic voltammetry with synthesis: manganese(II) coordination stability and its ligand field parameters effect on macrocyclic ligands

Manganese(II) macrocyclic complexes are prepared with different macrocyclic ligands, containing cyclic skeleton bearing organic components which have different chromospheres like N, O and S donor atoms and stereochemistry. Thus, six macrocyclic ligands, were prepared and their capacity to retain the manganese(II) ion in solid as well as in aqueous solution was determined and characterized by elemental analyses, molar conductance measurements, magnetic susceptibility measurements, mass, (1)H NMR, IR, electronic spectral and cyclic voltammetric studies. The electronic spectrum of this system showed a dependence that may be consistent with the formation of stable complexes and coordination behaviour of the ions. ESR spectra of all the complexes are recorded in solid as well as solution, which show the oxidation state of the manganese(II). Spin Hamiltonian manganese(II), which can be defined as the magnetic field vector (H): H = gBeta(e)HS + D[S(2)(z) - 35/12] + E[S(2)(z) - S(2)(y)] + ASI + (1/6)a [S(4)(x) + S(4)(y) + S(4)(z) - 707/16] + (1/180)F[(35S(2)(z) - 475)/(2S(2)(z) + 3255/10)] Significant distortion of the manganese(II) ion in observed geometry is evident from the angle subtended by the different membered chelate rings and the angles spanned by trans donor atoms octahedral geometry. Cyclic voltammetric studies indicate that complexes with all ligands undergoes one electron oxidation from manganese(II) to manganese(III) followed by a further oxidation to manganese(IV) at a significantly more positive potential.     

Cl(3)V(mu-S(CH(3))(2))(3)VCl(3)(2)(-): a first-row,face-shared bioctahedral complex with multiple metal-metal bonding

Density functional theory calculations have been used to investigate the structure and bonding of the d(3)d(3) bioctahedral complexes X(3)V(mu-S(CH(3))(2))(3)VX(3)(2)(-) (X = F(-), Cl(-), OH(-), SH(-), NH(2)(-)). According to geometry optimizations using the broken-symmetry approach and the VWN+B-LYP combination of density functionals, the halide-terminated complexes have a V-V bond order of approximately 2, while complexes featuring OH(-), SH(-), or NH(2)(-) as terminal ligands exhibit full triple bonding between the vanadium atoms. The tendency toward triple bonding in the latter complexes is consistent with an increased covalency of the vanadium-ligand bonds, and the influence of bond covalency is apparent also in the tendency for V-V bond elongation in the complexes with OH(-) and NH(2)(-) terminal ligands. Detailed examination of the composition of molecular orbitals in all of the thioether-bridged V(II) complexes substantiates the conclusion that the strong antiferromagnetic coupling which we have determined for these complexes (-J > 250 cm(-)(1)) is due to direct bonding between metal atoms rather than superexchange through the bridging ligands. As such, these V(II) complexes comprise the first apparent examples of multiple metal-metal bonding in first-transition-row, face-shared dinuclear complexes and are therefore of considerable structural and synthetic interest.