Density Functional Theory Studies of the Binding of Molecular Oxygen with Schiff's Base Complexes of Cobalt

Transition Metal Complexes of Thiosemicarbazides, Thiocarbohydrazides, and Their Corresponding Carbazones with Cu(I), Cu(II), Co(II), Ni(II), Pd(II), and Ag(I)-A Review

This review focuses on some interesting and recent applications of transition metals towards the complexation of thiosemicarbazides, thiocarbohydrazides, and their corresponding carbazones. We started the review with a description of the chosen five metals, including Cu[Cu(I), Cu(II], Co(II), Ni(II), Pd(II), and Ag(I) and their electronic configurations. The stability of the assigned complexes was also discussed. We shed light on different routes describing the synthesis of these ligands. We also reported on different examples of the synthesis of Cu(I), Cu(II), Co(II), Ni(II), Ag(I), and Pd(II) of thiosemicarbazide and thiocarbohydrazide complexes (until 2022). This review also deals with a summary of the fruitful use of metal complexes of thiosemicarbazones and thiocarbazones ligands in the field of catalysis. Finally, this recent review focuses on the applications of these complexes related to their biological importance.

Influence of the Lewis basicity hardness of crystallization solvents on the coordination sphere of the complex [Co(3,5-dinitrobenzoate-O,O′)2]: crystallographic and theoretical analysis

Crystal growth of [Co(DNB)2] in different solvents is a thermodynamic process favored by ΔErecrys (kcal mol−1) where mono/trinuclear molecules are obtained. Closeness of HOMO orbitals of solvents to the SOMOs orbitals of Co(ii) ions guide the process.

Preparation of organocobalt(iii) complexes via O2 activation

The coupling of selective C-H activation with O₂ activation is an important goal for organic synthesis. New experimental and computational results, along with the results from experimental work accumulated over many decades, now unequivocally link O₂ activation with C-H activation by the classic Co(salen) complexes. A common holistic mechanistic framework can rationalise the formation of ostensibly diverse peroxo, superoxo, organo and alkoxide complexes of Co^III(salen). DFT calculations show that cobalt(iii)superoxo, dicobalt(iii)peroxo and cobalt(iii)hydroperoxo complexes are all viable intermediates as participants in hydrogen atom transfer reactions, whereas a Co(iv)oxo intermediate is unlikely. The reaction conditions will determine the pathway followed and all pathways are initiated through the initial formation of a superoxo complex, Co^III(salen)(O₂˙)(MeOH) (EPR: g = 2.025, A = 19 G). Organo and alkoxide ligands are derived from solvent media and the trends in reactivity reveal that combination of the pK_a and BDE of the C-H of the respective solvent substrates are important. These data explain why landmark, structurally characterized, μ₂-η¹,η²-peroxide and η¹-superoxide Co(salen)-O₂ adducts were predominantly isolated from solvents with high C-H pK_a values (DMSO, DMF, DMA).

Reaction of N, N 1 -phenylenebis(salicyalideneiminato)cobalt(III) and l-cysteine in mixed aqueous medium: kinetics and mechanism

The redox kinetics involving the reaction of N, N'-phenylenebis(salicyalideneiminato)cobalt(III) ([CoSalophen]+) and l-cysteine (LSH) was studied using pseudo-first order approach under the following conditions, [H+] = 1.0 × 10-3 mol/dm3, μ = 0.1 C2 mol/dm3 (NaCl), λmax = 470 nm and T = 27 ± 1 °C in DMSO: H2O; 1:4 v: v medium. The redox reaction was 1st order in both [CoSalophen+] and [LSH], with the overall 2nd order. Hydrogen ion concentration effect revealed the activeness of both the protonated and deprotonated form of the reductant, positive Brønsted-Debye salt effect and was also ion catalyzed. There was no evidence suggesting an intermediate complex of significant stability in the reaction. Free radical was detected to take part and as such the reasonable mechanistic pathway for the reaction is suggested to be outer-sphere, hence proposed.

Synthesis, Spectroscopy and Electrochemistry of Cobalt(III) Schiff Base Complexes

Three Co(III) complexes of the type [Co(chel)(PBu3)]ClO4.H2O, (chel = 5-BrSalen, 5-MeOSalen and 4-MeOSalen), were synthesised and characterised by elemental analysis, IR, UV-Vis and 1H NMR spectroscopy. In their electronic spectra, the absorptions between 550 and 750 nm of these complexes are attributable to the lowest d–d transition. The axial ligands affect this transition through a σ-intraction with the dz2 orbital and the equatorial ligands affect it by π-interaction with populated d-orbitals. On the basis of an electronic structural model, in which the dz2 orbital is populated in forming cobalt(II), it is suggested that equatorial ligand substitution affects the reduction potentials less than axial ligand substitution.

Observation of novel oxygen⋯oxygen interaction in supramolecular assembly of cobalt(iii) Schiff base complexes: a combined experimental and computational study

Structural features of two newly synthesized mononuclear cobalt(iii) complexes have been examined by DFT calculations.

How molecular oxygen binds to bis[trifluoroacetylacetonato(-1)]cobalt(II)--ab initio and density functional theory studies

Cobalt(II) diketonate complexes, such as bis[trifluoroacetylacetonato(-1)]cobalt(II) [Co(tfa)(2)], catalyze the aerobic oxidation of alkenols into functionalized tetrahydrofurans. To gain insight into activation of triplet dioxygen by Co(tfa)(2) in a protic solvent, as used in oxidation catalysis, the electronic structure of aquabis[trifluoroacetylacetonato(-1)]cobalt(II)--Co(tfa)(2)(H(2)O)--and the derived dioxygen adduct were characterized using ab initio (CASSCF, NEVPT2) and density functional theory (BP86, TPSSh, B3LYP) methods. The ground state of Co(tfa)(2)(H(2)O) is a high-spin, quartet state. As dioxygen approaches the cobalt atom, the quartet state couples with a triplet dioxygen molecule and forms a sextet, a quartet, and a doublet spin state with the high-spin state being the lowest in energy. At the equilibrium Co-O(2) distance of 1.9 Å, Co(tfa)(2)(H(2)O)(O(2)) has a doublet superoxo Co(III) ground state with the unpaired electron residing on the oxygen moiety, in a nearly unchanged O(2)π* orbital.

{2,2'-[1,1'-(Ethane-1,2-diyldinitrilo)-diethyl-idyne]diphenolato}bis-(pyrrolidine)cobalt(III) perchlorate p-xylene hemisolvate

In the mononuclear title complex, [Co(C(18)H(18)N(2)O(2))(C(4)H(9)N)(2)]ClO(4)·0.5C(8)H(10), the Co(III) ion has a slightly distorted octa-hedral coordination geometry. In the Me-salen ligand, the benzene rings are almost parallel, making a dihedral angle of 0.48 (13)°, but the torsion angle along the central C-C bond is 41.1 (2)°·The pyrrolidine rings are in slightly distorted chair conformations. The N atoms of the pyrrolidine axial ligands are involved in N-H⋯O hydrogen bonds with the perchlorate anions, and these hydrogen bonds connect the ionic species into infinite chains along the b axis. Some relatively short C-H⋯π inter-actions are also present in the crystal structure and C-H⋯O inter-actions occur. The guest solvent p-xylene mol-ecule lies on a special position at the inversion centre.

Unambiguous determination of the adsorption geometry of a metal--organic complex on a bulk insulator

Individual molecules of Co-Salen, a small chiral paramagnetic metal--organic Schiff base complex, were deposited on NaCl(001) and subsequently imaged with noncontact atomic force microscopy employing Cr coated tips in a cryogenic ultrahigh vacuum environment. Images were obtained in which both the position and orientation of the adsorbed molecules and the atomic structure of the surface are resolved simultaneously, enabling the determination of the exact adsorption site. Density functional theory calculations were used to identify the ionic sublattice resolved with the Cr tip and also to confirm the adsorption site and orientation of the molecule on the surface. These calculations show that the central Co atom of the molecule physisorbs on top of a Cl ion and is aligned along 110-directions in its lowest energy configuration. In addition, a local energy minimum exists along 100-directions. Due to the chirality of the molecule, two mirror symmetric configurations rotated by approximately +/-5 degrees away from these directions are energetically equivalent. The resulting 16 low energy configurations are observed in the experimental images.

{(+)-(1R,2R)-1,2-Diphenyl-2,2'-[ethane-1,2-diylbis(nitrilo-methyl-idyne)]-di-phenol-ato}dipyridine-cobalt(III) perchlorate sesquihydrate

In title complex, [Co(C(28)H(22)N(2)O(2))(C(5)H(5)N)(2)]ClO(4)·1.5H(2)O, the Co(III) ion is in a slightly distorted octa-hedral coordination environment with the pyridine ligands in a trans arrangement. In addition to the cation and anion, the asymmetric unit also contains three half-occupancy solvent water mol-ecules and all components are connected via inter-molecular O-H⋯O hydrogen bonds.

Synthesis, structure and spectroscopic behaviors of a five- and six-coordinated tri-cobalt(II) cluster: [(CoL)2(OAc)2Co].2C2H5OH

A tri-nuclear cobalt(II) cluster, [(CoL)2(OAc)2Co].2C2H5OH, has been synthesized by the reaction of cobalt(II) acetate tetrahydrate with a novel Salen-type bisoxime chelating ligand, 3,3'-dimethoxy-2,2'-[ethylenedioxybis(nitrilomethylidyne)]diphenol (H2L), and characterized by elemental analyses, IR spectra, TG-DTA and molar conductances. UV-vis spectroscopic titration in methanol solution clearly indicated the exclusive formation of the 3:2 [Co3L2]2+ cluster. The single-crystal X-ray diffraction determination of the Co(II) cluster shows that there are two acetate ions coordinate to three cobalt(II) ions through Co-O-C-O-Co bridges, and quadruple mu-phenoxo oxygen atoms from two [CoL] chelates also coordinate to cobalt(II) ions. Interestingly, different conformational central ions: five- and six-coordinated geometries were found in the cluster.

[(-)-(1S,2S)-N,N'-Bis(2-oxidobenzyl-idene)-1,2-diphenyl-ethane-1,2-diamine]-bis-(pyridine)cobalt(III) perchlorate methanol hemisolvate hemihydrate

In the title compound, [Co(C(28)H(22)N(2)O(2))(C(5)H(5)N)(2)]ClO(4)·0.5CH(4)O·0.5H(2)O, each Co(III) ion is coordinated by the tetra-dentate N,N'-bis-(2-oxidobenzyl-idene)-1,2-diphenyl-ethane-1,2-diamine ligand [Co-N = 1.900 (3) and 1.903 (3) Å; Co-O = 1.885 (3) and 1.891 (3) Å] and two pyridine ligands [Co-N = 1.967 (4) and 1.977 (3) Å] in a distorted octa-hedral geometry. The packing of the cations and anions forms voids of 258 Å(3), which are filled by methanol and solvent water mol-ecules with half occupancies. O-H⋯O hydrogen bonds between solvent molecules, perchlorate anions and water molecules, and between water molecules and O atoms of the ligand, help to consolidate the crystal packing.

Activation of molecular oxygen and its use in stereoselective tetrahydrofuran-syntheses from delta,epsilon-unsaturated alcohols

Bishomoallylic alcohols (pent-4-en-1-ols) underwent efficient oxidative cyclizations, if treated with O(2) and bis{2,2,2-trifluoromethyl-1-[(1R,4S)-1,7,7-trimethyl-2-(oxo-kappaO)bicyclo[2.2.1]hept-3-yliden]ethanolato-kappaO}cobalt(ii) in solutions of 2-propanol at 60 degrees C. Ring closures occurred diastereoselectively and afforded 2,3-trans- (96% de), 2,4-cis- (approximately 60% de), and 2,5-trans-substituted (>99% de) (phenyl)tetrahydrofur-2-ylmethanols as major components. Formation of bicyclic compounds and a 2,3,4,5-substituted oxolane was feasible as exemplified by syntheses of oxabicyclo[4.3.0]nonylmethanols and a derivative of natural product magnosalicin in 61-72% (90-99% de). The effectiveness of tetrahydrofuran synthesis was critically dependent on (i) solvent, (ii) reaction temperature, (iii) initial cobalt concentration, (iv) chain length between hydroxyl and vinyl groups, and (v) substitution at reacting entities. A sequence is proposed for rationalizing observed selectivities.

Synthesis, NMR, DFT and antimicrobial studies of Zn(II) complexes with N-benzyloxycarbonyl-S-alanine

In this study, the first complexes of Zn(II) with the N-benzyloxycar- bonyl-S-alaninato ligand (N-Boc-S-ala) were synthesized. The new complexes were characterized by elemental analysis, conductometric measurements, IR, 1H-NMR, 13C-NMR and 2D-NMR spectroscopy. On the basis of the experimental data, tetrahedral geometry of the Zn(II) complexes was proposed. A very good agreement between the NMR and DFT calculated data was obtained. Investigation of antimicrobial activity of the newly synthesized complexes was also performed. It was established that [Zn(N-Boc-S-ala)2] was selective and acts only on Candida albicans.

Theoretical studies on vibrational spectra of some halides of group IVB elements

The vibrational spectra of group IVB elements halides MX4 (M=Ti(IV), Zr(IV), Hf(II); X=F, Cl, Br and I), have been investigated by ab initio RHF, MP2 and density functional theory B3LYP method with LanL2DZ basis sets. The optimized geometries, calculated vibrational frequencies and Far-IR intensities of MX4 are evaluated via comparison with experimental data. The vibrational frequencies, calculated by these methods, are compared to each other. The results indicate that B3LYP method is more reliable than RHF and MP2 methods for the frequencies calculations for these compounds. With this method, some vibrational frequencies of M2X6(2+)(M=Ti(IV), Zr(IV) and Hf(II); X=F, Cl, Br and I) are also predicted.

Synthesis, characterization, and single crystal X-ray structures of [CoIII(acacen)(thioacetamide)2]ClO4 and [CoIII((BA)2en)(thioacetamide)2]PF6 — Solvatochromic properties of [CoIII(acacen)(thioacetamide)2]ClO4

The trans-[CoIII(acacen)(ta)2]ClO4 (1) and trans-[CoIII((BA)2en)(ta)2]PF6 (2) complexes, where H2acacen = bis(acetylacetone)ethylenediimine, H2(BA)2en = bis(benzoylacetone)ethylenediimine, and ta = thioacetamide, have been synthesized by a solid-state method, and characterized by elemental analyses, IR, UV–vis, and 1H NMR spectroscopy. The crystal and molecular structures of 1 and 2 were determined by X-ray crystallography. Both compounds crystallize in the monoclinic space group P2/n. The ClO4 and PF6 ions are both disordered, ClO4 on a twofold axis in 1 and PF6 on an inversion center in 2. Also bridging N-CH2-CH2-N is disordered in both compounds. The octahedral coordination of Co(III) is slightly distorted in both cases. The thioacetamide ligands are S-bonded and occupy the axial position. The IR, UV–vis, and 1H NMR spectra of the two complexes and their solvatochromic properties are also discussed. The longest wavelength absorption that appears at 517 nm for 1 and at 528 nm for 2 in chloroform is solvent dependent, and is assigned as a metal-mediated ligand-to-ligand charge transfer (LLCT).Key words: solid-state synthesis, thioactamide, Co(III) (Schiff base), crystal structure, solvatochromism, metal-mediated LLCT.

Reactions of d0 Group 4 Amides with Dioxygen. Preparation of Unusual Oxo Aminoxy Complexes and Theoretical Studies of Their Formation

Reactions of d0 amides M(NMe2)4 (M = Zr, 1; Hf, 2) with O2 have been found to yield unusual trinuclear oxo aminoxide complexes M3(NMe2)6(mu-NMe2)3(mu3-O)(mu3-ONMe2) (M = Zr, 3; Hf, 4) in high yields. Tetramethylhydrazine Me2N-NMe2 was also observed in the reaction mixtures. Crystal structures of 3 and 4 have been determined. Density functional theory calculations have been performed to explore the mechanistic pathways in the reactions of model complexes Zr(NR2)4 (R = H, 5; Me, 1) and [Zr(NR2)4]2 (R = H, 5a; Me, 1a) with triplet O2. Monomeric and dimeric reaction pathways in the formation of the Zr complex 3 are proposed.

Syntheses, characterization and study of the use of cobalt (II) Schiff-base complexes as catalysts for the oxidation of styrene by molecular oxygen

Schiff-Base complexes of bis-5-phenylazosalicylaldehyde ethylenediimine and bis-5-phenylazosalicylaldehyde-O-phenylenediimine ligands with Co(II) (I and II) have been synthesized and characterized by their IR spectra and elemental analyses. These complexes catalyze the oxidation of styrene in the presence of dioxygen and excess pyridine. The effect of the reaction conditions on the oxidation of styrene was studied by varying solvent, nature and amount of the catalyst and substrate. The catalytic behavior of the studied complexes was shown to be dependent on the conditions applied. In all reactions, acetophenone and 1- phenylethanol were the only observed products.

Magnetic ordering in a mononuclear cobalt(ii) complex containing a Schiff-base pentadentate ligand

A mononuclear cobalt(II) complex CoL5, containing the pentadentate O2N3 salen-type Schiff-base ligand H2L5=N,N[prime or minute]-bis(3-tert-butyl-2-hydroxy-5-methylbenzylidenyl)-1,7-diamino-4-methyl-4-azaheptane, exhibits magnetic ordering at 4 K as proven by ac magnetic susceptibility (both in- and out-of-phase), magnetization, field-cooled magnetization and zero-field cooled magnetization measurements.

Characterization of Ground and Low-Lying Excited States of CoO4: A Combined Matrix Isolation and DFT Study

The nature of the reaction products between CoO(2) and molecular O(2), isolated in rare gas matrices, have been investigated using IR absorption spectroscopy. In this paper, we report on the vibrational spectrum of the CoO(4) molecule in its ground and first low-lying excited states. Isotopic substitutions using (16)O(2) and (18)O(2) precursors, as well as (16)O(2) + (18)O(2) and (16)O(2) +( 16)O(18)O + (18)O(2) mixtures in either excess argon or neon, enable demonstration of C(2)(v)() and C(s)() structures for the respective states. CoO(4) is formed following molecular diffusion by complexation of ground-state CoO(2) by an O(2) molecule. The molecule is first formed in the excited state and then spontaneously relaxes to the ground state after remaining in the dark. The kinetics of relaxation can be fitted to a first-order exponential decay with an excited-state lifetime estimated around 23 +/- 2 min in argon and 15 +/- 2 min in neon, indicative of a slow, spin-forbidden process. Population of the excited state is induced by photons around 4250 +/- 250 cm(-1). Experimental results are compared to density functional theory (DFT) calculations at the BPW91/6-311G(3df) level. Electronic and geometrical optimizations were carried out starting from the ground-state precursors (i.e., (3)Sigma(g)(-) for O(2) and (2)Sigma(g)(+) for CoO(2)). Calculations predict a (2)A(2) (C(2)(v)()) ground state and a (4)A' (C(s)()) first excited state 0.37 eV above, close to the 4250 +/- 250 cm(-1) experimental excitation energy. The transition pathway is found to involve two supplementary states with crossed potential energy surfaces (PESs): a (2)B(1) excited state, 0.48 eV above the ground state, reached first through an adiabatic transition with a photon around 4800 cm(-1), and a (4)B(1) transition state into which the system relaxes before finally attaining the (4)A' (C(s)()) excited state. Harmonic frequencies and absolute intensities are also calculated and compared with the experimental data, indicating however that the DFT underestimates the internuclear distances for both configurations. Force and interaction constants were obtained with a semiempirical harmonic force-field potential calculation. They were then used in an empirical rule of plot linking force constants and internuclear distances in order to obtain an estimate of the Co-O bond lengths for each state and are compared to the DFT predictions.

Ab initio and density functional theory studies on vibrational spectra of palladium (II) and platinum (II) complexes of methionine and histidine: effect of theoretical methods and basis sets

The vibrational spectra of methionine and histidine-containing palladium (II) and platinum (II) complexes, cis-M(Met)X2 and cis-M(His)X2 (M = Pd and Pt; X = F, Cl, Br and I; Met = methionine, His = histidine), have been systematically investigated by ab initio Restricted Hartree-Fock (RHF) and density functional B3LYP methods with LanL2DZ and SDD basis sets. The geometries of cis-Pd(Met)Cl2, cis-Pt(Met)Cl2, cis-Pd(His)Cl2 and cis-Pt(His)I2 optimized and vibrational frequencies and IR intensities of cis-M(Met)Cl2 and cis-M(His)Cl2 (M = Pd and Pt) calculated are evaluated via comparison with the experimental values. The vibrational frequencies calculated show that the methods, rather than basis sets, affect the accuracy of the calculation. The best results that can reproduce the experimental ones are obtained at B3LYP level without any scale factor used. The vibrational frequencies of cis-M(Met)X2 and cis-M(His)X2 (M = Pd and Pt; X = F, Br and I) that have not yet been experimentally reported are predicted.