Transition Metal Ion Complexes Research Articles

Triplet electronic states in d(2) and d(8) complexes probed by absorption spectroscopy: a CASSCF/CASPT2 analysis of [V(H2O)6]3+ and [Ni(H2O)6]2+.

Octahedral complexes of transition metal ions with d(2) and d(8) electron configurations have triplet electronic states with identical T(2g), A(2g), T(1g)((3)F), and T(1g)((3)P) symmetry labels. CASSCF and CASPT2 calculations indicate the predominant electronic configurations for each triplet state. The two (3)T(1g) states show strong configuration mixing in the d(8) complex [Ni(H(2)O)(6)](2+), but much weaker mixing occurs between these states in the d(2) compound [V(H(2)O)(6)](3+). Calculated vibrational frequencies and equilibrium geometries for the triplet states are used to obtain theoretical absorption spectra that are in agreement with the experimental data.

The Intrinsic Stability of the Noble Gas-Coordinated Transition-Metal Complex Ions

Density-functional-theory and high-level ab initio calculations have been performed on the [AuXe4]2+ ion and some other hypothetical xenon-, krypton-, and argon-coordinated transition-metal complex cations in the gas phase. Geometry optimization at the QCISD(T) level using a (6s7p4d2f1g) basis set for Au and a (4s4p2d1f) set for Xe predicted Au-Xe bond lengths in good agreement with the AuXe4(2+)(Sb2F11-)2 crystal structure. The ligand-binding energies of the [AuXe4]2+, [AuXe4]3+, and [PtXe4]2+ ions were predicted to be 229, 565, and 233 kcal/mol, respectively, at the CCSD(T) level. It is found that higher-level correlation effects are important to obtain accurate geometry parameters. The calculated results also indicated that various trivalent, tetravalent, and hexavalent transition-metal complexes of xenon or krypton might also be intrinsically stable.

Bis-bipyridine hexa-aza-macrocycle complexes of zinc(II) and nickel(II) and the catalytic reduction of carbon dioxide

Aza-macrocyclic complexes have gained importance in catalysis for the activation of small molecules, like carbon dioxide. Bis-bipyridine hexa-aza-macrocycles efficiently co-ordinate as a tetradentate ligand, to give complexes of Zn(II), Ni(II) and other transition metal ions that are essentially planar. Spectroscopic, electrochemical and chemical characterizations of these systems are presented in this article. Electrochemical studies performed in a carbon dioxide atmosphere render preliminary information about its electrocatalytical reduction. Quantum chemical calculations are used to understand the origin of the manifested properties of both the ligands and the metal complexes. They show, in this case, the importance of delocalized π interactions, which are responsible for their different structural and electronic characteristics in protic and non-protic media.

A semi-empirical molecular orbital study of complex stabilities of hexadentate polyaminocarboxylate ligands and transition metal ion complexes

Semi-empirical molecular orbital calculations were performed in vacuo on a series of metal-hexadentate polyaminocarboxylate ligand complexes using the ZINDO/1 Hamiltonian. Stabilisation energies for the complexes were calculated by making use of isodesmic equations. The relative stabilities of several ethylenediamine- N, N, N′, N′-tetraacetic acid-transition metal complexes, and homologues thereof, are discussed first and compared with published stabilities of similar complexes based upon strain analyses carried out on isolated crystal structures. Second, after having established that the computational results are in good agreement with the published stabilities, a more comprehensive analysis of complex stabilities was carried out on ( S, S)-ethylenediamine- N, N′-disuccinic acid-transition metal complexes, and homologues thereof. Theoretical indications are that complex stabilities increase with an increase in the number of 6-membered rings formed upon complexation, i.e. complexation is favoured with an increase in the length of the side-chain ligators.

Synthesis, Characterization and Thermal Studies of Thiosemicarbazones of N-methyl-and N-ethylacetoacetanilide

Fourteen new complexes of several typical transition metal ions with two multidentate ligands. thiosemicarbazones of N-methyl-and N-ethylacetoacetanilide, have been synthesized. These complexes have the general formulae [MX3], [MY2], [MY], [MZ(H2O)3], [MZ(OH)(H2O)]2 or [MZ(H2O)], where M = Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Hg(II) or Ag(I) and X = bidentate monoanion, Y = tridentate monoanion and Z = tridentate dianion of the ligands. They have been characterized by elemental analyses, molar conductance and magnetic susceptibility measurements as well as electronic, infrared and 1H NMR spectral studies and thermogravimetric studies.

Transition Metal Ion Complexes of Schiff‐bases. Synthesis, Characterization and Antibacterial Properties

Some novel transition metal [Co(II), Cu(II), Ni(II) and Zn(II)] complexes of substituted pyridine Schiff-bases have been prepared and characterized by physical, spectral and analytical data. The synthesized Schiff-bases act as deprotonated tridentate for the complexation reaction with Co(II), Ni(II) and Zn(II) ions. The new compounds, possessing the general formula [M(L)2] where [M=Co(II), Cu(II), Ni(II) and Zn(II) and HL=HL1, HL2, HL3 and HL4] show an octahedral geometry. In order to evaluate the effect of metal ions upon chelation, the Schiff bases and their complexes have been screened for antibacterial activity against the strains such as Escherichia coli,Staphylococcus aureus, and Pseudomonas aeruginosa. The complexed Schiff bases have shown to be more antibacterial against one more bacterial species as compared to uncomplexed Schiff-bases.

Molecular and electronic structures of bis(pyridine-2,6-diimine)metal complexes [ML2](PF6)n (n = 0, 1, 2, 3; M = Mn, Fe, Co, Ni, Cu, Zn).

A series of mononuclear, octahedral first-row transition metal ion complexes mer-[M(II)L0(2)](PF6)2 containing the tridentate neutral ligand 2,6-bis[1-(4-methoxyphenylimino)ethyl]pyridine (L0) and a Mn(II), Fe(II), Co(II), Ni(II), Cu(II), or Zn(II) ion have been synthesized and characterized by X-ray crystallography. Cyclic voltammetry and controlled potential coulometry show that each dication (except those of Cu(II) and Zn(II)) can be reversibly one-electron-oxidized, yielding the respective trications [M(III)L0(2)]3+, and in addition, they can be reversibly reduced to the corresponding monocations [ML2]+ and the neutral species [ML2]0 by two successive one-electron processes. [MnL2]PF6 and [CoL2]PF6 have been isolated and characterized by X-ray crystallography; their electronic structures are described as [Mn(III)L1(2)]PF6 and [Co(I)L0(2)]PF6 where (L1)1- represents the one-electron-reduced radical form of L0. The electronic structures of the tri-, di-, and monocations and of the neutral species have been elucidated in detail by a combination of spectroscopies: UV-vis, NMR, X-band EPR, Mossbauer, temperature-dependent magnetochemistry. It is shown that pyridine-2,6-diimine ligands are noninnocent ligands that can be coordinated to transition metal ions as neutral L0 or, alternatively, as monoanionic radical (L1)1-. All trications are of the type [M(III)L0(2)]3+, and the dications are [M(II)L0(2)]2+. The monocations are described as [Mn(III)L1(2)]+ (S = 0), [Fe(II)L0L1]+ (S = 1/2), [Co(I)L0(2)]+ (S = 1), [Ni(I)L0(2)]+ (S = 1/2), [Cu(I)L0(2)]+ (S = 0), [Zn(II)L1L0]+ (S = 1/2) where the Mn(II) and Fe(II) ions are low-spin-configurated. The neutral species are described as [Mn(II)L1(2)]0, [Fe(II)L1(2)]0, [Co(I)L0L1]0, [Ni(I)L0L1]0, and [Zn(II)L1(2)]0; their electronic ground states have not been determined.

Structural correlations and conformational preference in edge-sharing binuclear d8 complexes with XR2 bridges. A theoretical study.

The binuclear complexes of d8 transition metal ions of the type [M2(mu-XR2)2L4] (where M = RhI, IrI, NiII, PdII, PtII, or AuIII; X = S, N, P, or As) appear in a variety of molecular conformations in which the coordination planes around the two metal atoms are sometimes coplanar, sometimes bent. For the bent compounds with asymmetric bridges, XR1R2, the substituents adopt different orientations relative to the metal framework and to each other. Ab initio theoretical studies on the different conformers of 30 representative complexes, complemented with a structural database analysis, have allowed the establishment of structural correlations in this family of compounds. The conformational choice results from a delicate balance of different interactions which are qualitatively analyzed, such as the changes in bond angles around the bridging atoms, the existence of weak metal...metal bonding in the bent structures, and steric interactions involving the terminal ligands and the substituents at the bridging atoms.

EPR investigations of bonding and activation of nitrogen oxides by surface complexes of transition metal ions

EPR spectroscopy has been used to investigate changes occurring at the molecular level during coordination and activation of NO and N2O small pollutant molecules on Cu/ZSM-5 and Mo/SiO2 catalysts, respectively. It is shown that the activation of nitric oxide occurs by formation of a bent η1{CuNO}11 surface adduct with rehybridization of the NO Orbitals. The spin Hamiltonian parameters of this species have been analyzed in detail, leading to a molecular and electronic picture of the complex. The mechanism along which N2O is decomposed upon interaction with surface Mo5+ species involves dissociative metal-to-ligand electron transfer. The reaction was monitored by EPR using naturally abundant and95Mo-enriched molybdenum. The dynamics of the N-O bond cleavage is discussed in terms of two-dimensional Morse potential energy surfaces. From the EPR parameters of the resultant O− radical, the spin density distribution and the stabilization energy were calculated.

Chromium(III): Extra nonlability of its 1:1 chelates of polycarbonylic ligands

Decomplexation rates of chromium(III) chelates of dicarbonylic and tricarbonylic ligands in aqueous solution have been evaluated. Results show an extreme nonlability of these metal complexes that does not depend on the chelating ligand structure. A more extensive analysis including structurally similar complexes of first-row transition metal ions [Ni(II), Co(II), and Cu(II)] shows decomplexation rate values at least 104 times higher than the rate constants of previously mentioned chromium metal complexes. Correlations between the decomplexation rate constants and the deprotonation capability of the enol tautomer suggest that the decomplexation rates of a structurally similar 1:1 chelate of quoted metal ions may be predicted from the ligand dissociation constant. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 178–183, 2000

Mono and trinuclear complexes of alpha-oximinoacetoacetylpyridine-4-phenylthiosemicarbazone.

Complexes of several transition metal ions with alpha-oximinoacetoacetyl pyridine-4-phenylthiosemicarbazone (H3OAPT) have been prepared. Attempts were made to elucidate their geometries by elemental analysis, molar conductance, magnetic measurements and by some spectroscopic (IR, ESR and electronic) techniques. All the investigated metal ions form mononuclear complexes except for CuII, which forms mononuclear and trinuclear complexes with its chloride and acetate salts, respectively. The IR spectra show that the ligand behaves as a mono or binegative tridentate. Moreover, it acts as a trinegative hexadentate in the trinuclear CuII complex. The protonation constants (logK1H = 9.9 and log K2H = 6.0), as well as the stability constants of the metal complexes, are determined by the pH-titration of H3OAPT and its metal(II) complexes against 0.01 M NaOH. CuII complexes possess square-planar stereochemistry while CoII and NiII have an octahedral one. The crystal field parameters of CoII and NiII complexes are evaluated.

Edge-Sharing Binuclear d8 Complexes with XR Bridges: Theoretical and Structural Database Study of their Molecular Conformation

Coplanar or bent? Binuclear complexes of d8 transition metal ions appear in a variety of molecular conformations in which the coordination planes around the two metal atoms can be coplanar or bent, and the substituents at the bridging atoms may adopt different orientations (see figure). Ab initio theoretical studies together with a structural database analysis provide a rationale for the experimentally observed structures.

Edge-Sharing Binuclear d8 Complexes with XR Bridges: Theoretical and Structural Database Study of their Molecular Conformation

Coplanar or bent? Binuclear complexes of d8 transition metal ions appear in a variety of molecular conformations in which the coordination planes around the two metal atoms can be coplanar or bent, and the substituents at the bridging atoms may adopt different orientations (see figure). Ab initio theoretical studies together with a structural database analysis provide a rationale for the experimentally observed structures.

Ligand displacement reactions of dimer and trimer pyridyl ligand/transition metal complexes

Ligand exchange reactions of pyridyl ligand/transition metal complexes are examined in a quadrupole ion trap mass spectrometer to evaluate the ability of multidentate ligands to displace other pyridyl ligands in complexes where the charge is highly delocalized and there is a great degree of ligand repulsions. Partially or fully coordinated transition metal ions in dimer or trimer species involving small mono- or bidentate pyridyl ligands undergo ligand displacement reactions with larger bi- and tridentate pyridyl ligands. Larger ligands with greater chelation abilities, such as 1,10-phenanthroline and 2,2′:6,2″-terpyridine, are often able to simultaneously displace two nonchelating ligands from a partially coordinated metal ion. However, the analogous reactions involving displacement of bidentate chelating ligands from more fully coordinated transition metal ion complexes are nearly quenched. In other cases, mixed-ligand dimer and trimer complexes are observed, indicating step-wise displacement of the initially complexed ligands.

Functionalized Derivatives of Benzo‐Crown Ethers. Part 4.Antifungal Macrocyclic Supramolecular Complexes of Transition MetalIons Acting as Lanosterol‐14‐α‐Demethylase Ihibitors

Poly- and mononuclear metal complexes of 2,3,11,12-bis[4-(10-aminodecylcarbonyl)]benzo-18- crown-6 (L) and Cu(II); Ni(II); Co(II) and Cr(III) have been synthesized and characterized by standard physico-chemical procedures. In the newly prepared complexes the crown moiety oxygen atoms of the macrocyclic host did not generally interact with metal ions, whereas the two amino groups of the ligand always did. Several of the newly synthesized compounds act as effective antifungal agents against Aspergillus and Candida spp., some of them showing activities comparable to ketoconazole, with minimum inhibitory concentrations in the range of 0.3−0.5 μg/mL. The mechanism of antifungal action of these coordination compounds is probably connected to an inhibition of lanosterol-14-α-demethylase, a metallo-enzyme playing a key role in sterol biosynthesis in fungi, bacteria and eukariotes.

Probing the structure of the human Ca 2+- and Zn 2+-binding protein S100A3: spectroscopic investigations of its transition metal ion complexes, and three-dimensional structural model

A large-scale procedure was developed for the anaerobic purification of the human recombinant Ca 2+- and Zn 2+-binding protein S100A3 for spectroscopic studies. S100A3 eluted as a non-covalently bound dimer (20.8 kDa). It contained 7.5±0.1 free thiol groups/monomer, and bound Ca 2+ with a K d of ≈4 mM, which corresponds to a tenfold increase in affinity compared to the aerobically purified protein. The transition metal ions Co 2+, Zn 2+ and Cd 2+ were used as spectroscopic probes to investigate the role of the 10 cysteine residues per monomer S100A3 in metal binding. Spectrophotometric titrations suggest the formation of dinuclear thiolate-bridged clusters consisting of a Me 2+(S Cys) 4 and a Me 2+(S Cys) 3(N His) site as described for zinc finger proteins. A three-dimensional structural model of S100A3 was proposed on the basis of the NMR structure of the structurally related rabbit S100A6 protein, and taking into account the structural influence of cysteine residues.

Matrix-assisted laser desorption/ionization mass spectrometry of noncovalent protein-transition metal ion complexes.

Transition metal ion complexes with proteins and peptides are important in many areas of analytical and biological chemistry. We used positive and negative ion MALDI-MS to detect complexes with Cu and Ni ions, and show that the specific and non-specific transition metal ion-peptide complexes can be distinguished by the use of different analytical protocols. The pH dependent stability of these complexes is also reflected in the MALDI data. We further show that triple complexes of peptides or protein with chelated metal ions can be detected efficiently and rapidly by MALDI mass spectrometry. Such triple complexes play an important role in metal chelate affinity chromatography, where histidine containing biopolymers in particular are thought to bind metal-ligand complexes, depending on the oxidation state of the metal and the number of unoccupied coordination sites of the ligand.

Study of Host‐Guest Complexation of Alkaline Earth Metal Ion, Aluminum Ion and Transition Metal Ions with Crown Ethers by Fast Atom Bombardment Mass Spectrometry

AbstractComplexations of crown ethers with alkali metal ions have been investigated extensively by FAB mass spectrometry over the past decade, but very little attention has been paid to reactions of crown ethers with other classes of metal ions such as alkaline earth metal ions, transition metal ions and aluminum ions. Although fast atom bombardment ionization mass spectrometry has proven to be a rapid and convenient method to determine the binding interactions of crown ethers with metal ions, problems in reliabilities for quantitative measurements of” binding strength for the host‐guest complexes have been described in the literature. Thus, in this paper, applications of FAB/MS for investigating the complexation of crown ethers with various classes of metal ions is discussed. Extensive fragmentations for neutral losses such as C2H4O or C2H4 molecules from the host‐guest complexes could be observed. The reason is attributed to the energetic bombardment processes of FAB occuring in the formation of these complexes. Complexes of cyclen with metal ions also show neutral losses of C2H4NH molecules leading to fragment ions. Transition metal ions usually form (Crown + MCl)+ type of ions, alkaline earth metal ions can form both (Crown + MCl)+ and (Crown + MOH)+ type of ions. But for aluminum ions, only (Crown + Al(OH)2)+ type of ions could he observed.

Laser-induced ESR shift of a paramagnetic transition metal complex ion [IrBr 6] 2−

Taking a paramagnetic transition metal complex ion [IrBr 6] 2− as an example, the laser-induced ESR shifts in oriented and unoriented samples have been studied and calculated. In oriented and unoriented systems the ESR shifts result from the contribution of the symmetric and antisymmetric polarizabilities. The shifts of the [IrBr 6] 2− complex ion are calculated to be of the order of 1∼10 kHz for a laser beam of 10 W cm −2. The factors affecting the magnitude of the laser-induced ESR shift are discussed. The results indicate that there should be observable ESR shifts in a molecular or radical paramagnetic system on applying linearly or circularly polarized light at a frequency near optical absorption.

Binary and ternary complexes of some inner transition metal ions with amino acids and acetyl acetone

The stability constants of the 1:1 and 1:2 (whenever possible) complexes formed between La 3+ , Ce 3+ , Th 4+ and the amino acid anions L-alaninate, L-phenylalaninate and L-histidinate were determined by potentiometric titration in aqueous solution (25±1 ○ C, I = 0.1 M KCl) and compared together with the constants previously determined. The various formation degree of the resulting M(L) and M(L) 2 were determined. In order to relate the formation degree of M(L) and M(L) 2 with the basicity of the amino acid anion (L - ), the acidity constants of the protonated amino acids, H 2 L + , were also measured. The main results of this work prove that Th 4+ ion forms the strongest complex with the studied amino acids. It is the only ion which forms a 1:2 complex. The heterocyclic ring of histidine plays a significant role in complexing with the studied metal ions as is clearly seen from the distribution of the degree of formation of the different complexes. The stability constants of the 1:1:1, 1:2:1 and 1:1:2 complexes formed between La 3+ , Ce 3+ , Th 4+ and the anions L-alaninate, L-phenylalaninate and L-histidinate together with the acetyl acetonate ion were also determined following the same experimental set up used in the study of the simple complexes. The mixed-ligand complexes turned out to be very much stronger than the simple ligand complexes. Formation of a mixed ligand complex can be considered as a type of senergism.