Stereodynamics and degenerate ligand exchange in solutions of tetracoordinate chelate complexes of nontransition metals

Минкин, Владимир И.; Nivorozhkin, L. E.; Korobov, M. S.

doi:10.1070/rc1994v063n04abeh000085

Cited by 47 publications

(23 citation statements)

References 106 publications

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“…Structure 15 with C 2 sym metry corresponds to a minimum while structure 16 is a TS of the enantiomerization proceeding by the diagonal twist mechanism with a calculated barrier of 9.7 kcal mol -1 ; this is in good agreement with experimentally observed values. 2 As in the previous case, TS 17 of the reaction proceeding by the dissociation mechanism lies much higher on the energy scale (barrier height is 35.3 kcal mol -1 ).…”

Section: Resultsmentioning

confidence: 94%

Effect of ligand environment on the mechanism of enantiomerization of BeII, ZnII, and CuII bischelate complexes

Starikov

Minyaev

2009

Russ Chem Bull

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The effect of ligand environment on the mechanism of enantiomerization of Be II , Zn II , and Cu II bischelate aminovinylketonate complexes was studied by the B3LYP/6 311++G (d,p) method. Substituents at the nitrogen atom (R = H, Me, Pr i ) significantly affect the mechanism of enantiomerization. In the beryllium complexes, the diagonal twist mechanism is changed to the dissociation mechanism. In the zinc complexes, only the diagonal twist mechanism is realized. The barrier to reaction monotonically increases with the size of the substituent. In the copper complexes, the effect of substituents manifests itself in the change in the relative stabilities of different forms. At R = H, the square planar form is more stable, while the tetrahedral configuration is favorable at R = Pr i . For the Cu II complex with R = Me, the energy difference between two forms is less than 1 kcal mol -1 , which leads to stabilization of the square planar structure in the solid state, whereas the tetrahedral form is more stable in solution.Key words: mechanism of enantiomerisation, chelate complex, ligands, quantum chemical calculations.Stereochemically nonrigid compounds with donor acceptor bonds are valuable objects for the design of novel polyfunctional materials with variable properties, which can be used as molecular switches, magnetically active structures or systems with nonlinear optical properties. 1 Among the best studied classes of such compounds, there are four coordinate bischelate complexes of main group and transition metals, which can undergo rapid enantio merization in solutions. 2,3Possible inversion based mechanisms of intramolecu lar rearrangements in four coordinate chelate complexes are shown in Scheme 1. Intramolecular enantiomerization can follow three pathways involving diagonal twist via cis form 2a or trans form 2b or the M-N bond rupture formation via structure 3 (here, the coordination number of the central atom decreases).Complexes of the main group metals are most stable in tetrahedral form, whereas for some transition metal complexes planar forms are energetically more favorable.The aim of this work is to perform a quantum chemi cal study on the mechanism and energy characteristics of intramolecular enantiomerization of bischelate amino vinylketonate complexes of Be II , Zn II , and Cu II (see struc *Dedicated to Academician I. I. Moiseev on the occasion of his 80th birthday. ture 1а in Scheme 1) and to elucidate the effect of the nature of the central atom M and the substituent R at the nitrogen atom on the mechanism of this reaction. Calculation ProcedureCalculations were carried out in the framework of the density functional theory (B3LYP/6 311++G(d,p) method) using the Gaussian 03 program. 4 To locate stationary points on the potential energy surfaces (PES), full geometry optimization of molecular structures and the force constant calculations were performed. Structures corresponding to energy minima on the PES were located by the steepest descent method (motion along a gradient line) from a saddle ...

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Section: Resultsmentioning

confidence: 94%

Effect of ligand environment on the mechanism of enantiomerization of BeII, ZnII, and CuII bischelate complexes

Starikov

Minyaev

2009

Russ Chem Bull

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“…The complexes of transition d 8 metals (Ni 2+ , Pd 2+ , and Pt 2+ ) are characterized by the polyvariant configurations (cis and trans planar and pseudo tet rahedral) of the coordination mode MN 2 Y 2 (Y = O, S), depending primarily on the nature of the central metal atom, the choice of ligating donor atoms, and struc tural regularities of the ligands. The transition from the O containing (Y = O) to S containing (Y = S) complexes is accompanied by basic changes in the configuration of the coordination mode MN 2 Y 2 and related properties of the complexes [1][2][3][4][5][6]. Therefore, complexes based on bifunctional donor systems capa ble of accomplishing one of two variants of the coordi nation mode MN 2 O 2 (a) or MN 2 S 2 (b), depending on the metal atom, are of special interest.…”

Section: Introductionmentioning

confidence: 99%

“…Considerable attention is given to experimental studies of the molecular structures and spectral, mag netic, and other physical properties of chelate com plexes of transition and nontransition metals with Schiff bases (coordination modes MN 2 Y 2 (Y = O, S)) [1][2][3][4]. The complexes of transition d 8 metals (Ni 2+ , Pd 2+ , and Pt 2+ ) are characterized by the polyvariant configurations (cis and trans planar and pseudo tet rahedral) of the coordination mode MN 2 Y 2 (Y = O, S), depending primarily on the nature of the central metal atom, the choice of ligating donor atoms, and struc tural regularities of the ligands.…”

Section: Introductionmentioning

confidence: 99%

Quantum-chemical model for the formation of the coordination mode structure of Be(II), Ni(II), Pd(II), Pt(II), and Hg(II) bis(chelate) complexes with polydentate azomethine ligands

Kharabayev

Starikov

2015

Russ J Coord Chem

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The competitive coordination for the formation of the coordination mode (MN 2 O 2 or MN 2 S 2 ) of Be(II), Ni(II), Pd(II), Pt(II), and Hg(II) bis(chelate) complexes based on thioindanone derivatives of aro matic azomethines is studied using the density functional theory methods. The dependences of the relative stability of the complexes on the properties of the central metal atom and ligating donor atoms are qualita tively consistent with Pearson's principle of hard and soft acids and bases. The dependences of the MN 2 Y 2 (Y = O, S) coordination mode configuration on the nature of the metal atom, donor atoms, and specific fea tures of the ligand structure are explained on the basis of the calculated data obtained for the azomethine bis(chelates) of d 8 metals (Ni 2+ , Pd 2+ , and Pt 2+ ).

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“…Rearrangements in such ligands result from electrocyclic rearrangement and spin exchange occurs not due to spin crossover effects but rather configurational isomerization. We should note that a definite advantage of configurational modulation of the spin state is the extremely high rate of spin-forbidden rearrangements equal or greater than the rate of electronic transitions [12].…”

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confidence: 99%

Quantum-chemical modeling of metal coordination compounds with photoswitchable magnetic properties controlled by ligand rearrangements

2011

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The complexation of chromenes with transition metal ions was studied using the B3LYP*/6-311++G (d,p) method. We are the first to show that transformation of the spin state of a transition metal complex through an LD LISC mechanism can be achieved by means of configurational isomerization of the metal-chelate coordination site induced by ligand rearrangement.The search for bistable structures, whose magnetic properties can be controlled by variation of the temperature of medium or pressure or by irradiation, is a prominent area of research in the chemistry of coordination compounds [1-4]. The major mechanisms responsible for such behavior of molecular magnetics are spin crossover [5], valence tautomerism [2, 6], and configurational isomerism [7]. Ligand-driven light-induced spin change (LD LISC) based on the insertion of photoisomerizing fragments, whose transformations alter the ligand field strength, thereby altering the magnetic properties, holds considerable interest in the quest for efficient molecular switches and energy-independent magnetic molecular memory [1,8].The LD LISC effect related to cis-trans ligand isomerization was first discovered for octahedral trans-stabilized Fe(II) complexes with thiocyanate counter-ions [8]. The insertion of a photochromic fragment into a transition metal complex capable of crossover is a promising pathway for obtaining photocontrolled polyfunctional materials [1,4,5,8,9]. A series of Fe(II) and Fe(III) complexes displaying LD LISC effect due to photoinduced cis-trans rearrangement of styryldipyridine [10]

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Stereodynamics and degenerate ligand exchange in solutions of tetracoordinate chelate complexes of nontransition metals

Cited by 47 publications

References 106 publications

Effect of ligand environment on the mechanism of enantiomerization of BeII, ZnII, and CuII bischelate complexes

Effect of ligand environment on the mechanism of enantiomerization of BeII, ZnII, and CuII bischelate complexes

Quantum-chemical model for the formation of the coordination mode structure of Be(II), Ni(II), Pd(II), Pt(II), and Hg(II) bis(chelate) complexes with polydentate azomethine ligands

Quantum-chemical modeling of metal coordination compounds with photoswitchable magnetic properties controlled by ligand rearrangements

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