Hybrid Organic–Inorganic Polyoxometalates: Functionalization of VIV/ VV Nanosized Clusters to Produce Molecular Capsules

Functionalization of polyoxovanadate clusters using phosphonate and arsonate ligands results in molecular capsules (see structure; green V, purple P, red O, black C). Through the use of extended homologous ligands, these hybrid organic-inorganic capsules can be successively elongated into tubular molecules.

Homo-and heteropolymetallic 3-(2-pyridyl)pyrazolate manganese and rhenium complexes

fac-[MBr(CO)(3)(pypzH)] (M = Mn, Re; pypzH = (3-(2-pyridyl) pyrazole) complexes are prepared from fac[ MBr(CO)(3)(NCMe)(2)] and pypzH. The result of their deprotonation depends on the metallic substrate: the rhenium complex affords cleanly the bimetallic compound [fac-{Re(CO)(3)(mu(2)-pypz)}] 2 (mu(2)-pypz = mu(2)-3-(2pyridyl-. 1N) pyrazolate-2. 1N), which was crystallographically characterized, whereas a similar manganese complex was not detected. When two equivalents of pyridylpyrazolate are used, polymetallic species [fac-M(CO) 3(mu(2)-pypz)(mu(3)-pypz) M'] (mu(3)-pypz = mu(3)-3-(2-pyridyl-kappa N-1) pyrazolate-1 kappa 2N, N: 2. 1N:; M = Mn, M' = Li, Na, K; M = Re, M' = Na) are obtained. The crystal structures of the manganese carbonylate complexes were determined. The lithium complex is a monomer containing one manganese and one lithium atom, whereas the sodium and potassium complexes are dimers and reveal an unprecedented coordination mode for the bridging 3-(2-pyridyl) pyrazolate ligand, where the nitrogen of the pyridyl fragment and the nitrogen-1 of pyrazolate are chelated to manganese atoms, and each nitrogen-2 of pyrazolate is coordinated to two alkaline atoms. The polymetallic carbonylate complexes are unstable in solution and evolve spontaneously to [fac-{Re(CO) 3(mu(2)-pypz)}](2) or to the trimetallic paramagnetic species [MnII(mu(2)-pypz) 2{fac-{MnI(CO) 3(mu(2)-pypz)}(2)}]. The related complex cis-[MnCl2(pypzH)(2)] was also synthesized and structurally characterized. The electrochemical behavior of the new homo-and heteropolymetallic 3-(2-pyridyl) pyrazolate complexes has been studied and details of their redox properties are reported.

The design, synthesis and characterization of new building blocks for the preparation of molecule-based magnetic materials /

Two new families of building blocks have been prepared and fully characterized and their coordination chemistry exploited for the preparation of molecule-based magnetic materials. The first class of compounds were prepared by exploiting the chemistry of 3,3'-diamino-2,2'-bipyridine together with 2-pyridine carbonyl chloride or 2-pyridine aldehyde. Two new ligands, 2,2'-bipyridine-3,3'-[2-pyridinecarboxamide] (Li, 2.3) and N'-6/s(2-pyridylmethyl) [2,2'bipyridine]-3,3'-diimine (L2, 2.7), were prepared and characterized. For ligand L4, two copper(II) coordination compounds were isolated with stoichiometrics [Cu2(Li)(hfac)2] (2.4) and [Cu(Li)Cl2] (2.5). The molecular structures of both complexes were determined by X-ray crystallography. In both complexes the ligand is in the dianionic form and coordinates the divalent Cu(II) ions via one amido and two pyridine nitrogen donor atoms. In (2.4), the coordination geometry around both Cu11 ions is best described as distorted trigonal bipyramidal where the remaining two coordination sites are satisfied by hfac counterions. In (2.5), both Cu(II) ions adopt a (4+1) distorted square pyramidal geometry. One copper forms a longer apical bond to an adjacent carbonyl oxygen atom, whereas the second copper is chelated to a neighboring Cu-Cl chloride ion to afford chloride bridged linear [Cu2(Li)Cl2]2 tetramers that run along the c-axis of the unit cell. The magnetic susceptibility data for (2.4) reveal the occurrence of weak antiferromagnetic interactions between the copper(II) ions. In contrast, variable temperature magnetic susceptibility measurements for (2.5) reveal more complex magnetic properties with the presence of ferromagnetic exchange between the central dimeric pair of copper atoms and weak antiferromagnetic exchange between the outer pairs of copper atoms. The Schiff-base bis-imine ligand (L2, 2.7) was found to be highly reactive; single crystals grown from dry methanol afforded compound (2.14) for which two methanol molecules had added across the imine double bond. The susceptibility of this ligand to nucleophilic attack at its imine functionality assisted via chelation to Lewis acidic metal ions adds an interesting dimension to its coordination chemistry. In this respect, a Co(II) quaterpyridine-type complex was prepared via a one-pot transformation of ligand L2 in the presence of a Lewis acidic metal salt. The rearranged complex was characterized by X-ray crystallography and a reaction mechanism for its formation has been proposed. Three additional rearranged complexes (2.13), (2.17) and (2.19) were also isolated when ligand (L2, 2.7) was reacted with transition metal ions. The molecular structures of all three complexes have been determined by X-ray crystallography. The second class of compounds that are reported in this thesis, are the two diacetyl pyridine derivatives, 4-pyridyl-2,6-diacetylpyridine (5.5) and 2,2'-6,6'-tetraacetyl-4,4'-bipyridine (5.15). Both of these compounds have been designed as intermediates for the metal templated assembly of a Schiff-base N3O2 macrocycle. From compound (5.15), a covalently tethered dimeric Mn(II) macrocyclic compound of general formula {[Mn^C^XJCl-FkO^Cl-lO.SFbO (5.16) was prepared and characterized. The X-ray analysis of (5.16) reveals that the two manganese ions assume a pentagonal-bipyramidal geometry with the macrocycle occupying the pentagonal plane and the axial positions being filled by a halide ion and a H2O molecule. Magnetic susceptibility data reveal the occurrence of antiferromagnetic interactions between covalently tethered Mn(II)-Mn(II) dimeric units. Following this methodology a Co(II) analogue (5.17) has also been prepared which is isostructural with (5.16).

Chelated fluoroboron cations : synthesis and multinuclear nmr studies

The preparation of chelated difluoroboron cations (DD)BF2+, where DD is a saturated polydentate tertiary-amine or polydentate aromatic ligand, has been systematically studied by using multinuclear solution and solid state nuclear magnetic resonance spectroscopy and fast atom bombardment mass spectrometry. Three new methods of synthesis of (DD)BF2+ cations are reported, and compared with the previous method of reacting a chelating donor with Et20.BF3. The methods most effective for aromatic donors such as 1,1O-phenanthroline are ineffective for saturated polydentate tertiary-amines like N,N,N' ,Nil ,Nil-pentamethyldiethylenetriamine. Polydentate tertiary-amine donors that form 5-membered rings upon bidentate chelation were found to chelate effectively when the BF2 source contained two leaving groups (a heavy halide and a Lewis base such as pyridine =pyr or isoxazole =ISOX), i.e., pyr.BF2X (X = CI or Br), ISOX.BF2X and (pyr)2BF2+. Those that would form 6membered rings upon chelation do not chelate by any of the four methods. Polydentate aromatic ligands chelate effectively when the BF2 source contained a weak Lewis base, e.g., ISOX.BF3, ISOX.BF2X and Et20.BF3. Bidentate chelation by polydentate tertiaryamine and aromatic donors leads to nmr parameters that are significantly different then their (D)2BF2+ relatives (D =monod~ntate t-amines or pyridines). The chelated haloboron cations (DD)BFCI+, and (DD)BFBr+ were generated from D.BFX2 adducts for all ligands that form BF2+ cations above. In addition, the (DD)BCI2+ and (DD)BBr2+ cations were formed from D.BX3 adducts by the chelating aromatic ligands, except for the aromatic ligand 1,8-bis(dimethylamino)naphthalene, which formed only the (DD)BF2+ cation, apparently due to its extreme steric hindrance. Chelation by a donor is a two-step reaction. For polydentate tertiary-amine ligands, the two rates appear to be very dependent on the two possible leaving groups on the central boron atom. The order of increasing ease of displacement for the donors was: pyr < Cl < Br < ISOX. The rate of chelation by polydentate aromatic ligands appears to be dependent on the displacement of the first ligand from the boron. The order of increasing ease of displacement for the donors was: pyr < CI < ISOX ~ Br < Et20.

Transition Metal Complexes of Schiff Bases with Azide and Thiocyanate as Coligands:Spectral and Structural Investigations

Metallo-organic chemistry,incorporating the frontiers of both inorganic and organic chemical aspects,is a topic of utility concern.The first exploration of coordinated metal complexes dates back to the ninettenth century,during the days of Alfred Werner.Thereafter,inorganic chemistry witnessed a great outflow of coordination compounds,with unique structural characteristics and diverse applicatons.The diversity in structures exhibited by the coordination complexes of multidentate ligands have led to their usage as sensors,models for enzyme mimetic centers,medicines etc.The liganda chosen are of prime importance in determining the properties of coordination compounds.Schiff bases are compounds obtained by the condensation of an aidehyde or ketone with an amine.The chemical properties of Schiff bases and their complexes are widely explored in recent years owing to their pharmacological activity,their catalytic activities and so on.On the other hand pseudohalides like azide and thiocyanate are versatile candidates for the construction of dimeric or polymeric complexes having excellent properties and diverse applications.So a combination of the Schiff bases and the pseudohalogens for the synthesis of metal complexes can bring about interesting results.An attempt into this area is the besis of this Ph.D theis.

Ligation properties of N4-phenylsemicarbazones towards transition metals: Synthesis and spectral studies

Semicarbazones and their transition metal complexes have been receiving considerable attention because of their biological relevance and applications in the field of analysis and in the field of organic NLO materials. Their structural diversity also attracted inorganic chemists. A good deal of work has been reported on the synthesis and structural investigation of semicarbazones and their complexes. This is due partially to their capability of acting as multidentate, NO, NNO, ONO and ONNO donors with the formation of either mono or bi or polynuclear complexes. Their chemistry and pharmacological applications have been extensively investigated. Appreciable biological applications as well as diverse stereochemistry of their metal complexes prompted us to synthesize two new tridentate ONO donor N4-phenyl semicarbazones derived from 2-hydroxy-4-methoxyacetophenone and 2-hydroxy-4-methoxybenzophenone and their transition metal complexes. These ketones were selected since they can provide a further binding site from phenolic–OH and can thus increase the denticity. Introduction of heterocyclic bases like 1,10-phenanthroline, 2,2′-bipyridine, 4,4′-dimethyl- 2,2′-bipyridine and 4-picoline and some pseudohalides like azide and thiocyanate ion can result in mixed ligand metal chelates with different geometries in coordination compounds In the present study, oxovanadium(IV), manganese(II), cobalt (II/III), nickel(II), copper(II) and zinc(II) complexes of 2-hydroxy-4- methoxyacetophenone-N4-phenylsemicarbazone (H2ASC) and 2-hydroxy-4- methoxybenzophenone-N4-phenylsemicarbazone (H2BSC) were synthesized and characterized.

Studies on Transition Metal Chelates of some Tridentate Aroylhydrazones

The ability of aroylhydrazones to bind with transition metals is a developing area of research interest and the coordinating properties of hydrazones can be tuned by the appropriate choice of parent aldehyde or ketone and the hydrazide. So in the present work we selected four different aroylhydrazones as principal ligands. Introduction of heterocyclic bases like 1,10-phenanthroline, 2,2′-bipyridine, 3-picoline and pyridine leads to the syntheses of mixed ligand metal chelates which can cause different bonding modes, spectral properties and geometries in coordination compounds. The importance of aroylhydrazones and their complexes in various fields and their interesting coordinating properties stimulate our interest in the investigation of transition metal chelates with four different aroylhydrazones. The aroylhydrazones selected are 4-benzyloxy-2-hydroxybenzaldehyde-4-nitrobenzoylhydrazone dimethylformamide monosolvate, 5-bromo-2-hydroxy-3-methoxybenzaldehyde nicotinoylhydrazone dihydrate methanol monosolvate, 4-diethylamino-2- hydroxybenzaldehyde nicotinoylhydrazone monohydrate and 2-benzoylpyridine- 4-nitrobenzoylhydrazone. The selection of 4-benzyloxy-2-hydroxybenzaldehyde- 4-nitrobenzoylhydrazone was based on the idea of developing ligands having D-π-A general structure, so that the proligand and metal complexes exhibit NLO activity. Hence it is interesting to explore the coordinating capabilities of the synthesized hydrazones and to study the NLO activity of hydrazones and some of the metal complexes.

Systematic studies on 3d-3d and 3d-4f multimetallic complexes with interesting magnetic and/or luminescent properties

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Synthesis, crystal structures, magnetic properties and catecholase activity of double phenoxido-bridged penta-coordinated dinuclear nickel(II) complexes derived from reduced Schiff-base ligands: mechanistic inference of catecholase activity

Three double phenoxido-bridged dinuclear nickel(II) complexes, namely [Ni-2(L-1)(2)(NCS)(2)] (1), [Ni-2(L-2)(2)(NCS)(2)] (2), and [Ni-2(L-3)(2)(NCS)(2)] (3) have been synthesized using the reduced tridentate Schiff-base ligands 2-[1-(3-methylamino-propylamino)-ethyl]-phenol (HL1), 2-[1-(2-dimethylamino-ethylamino)-ethyl]-phenol (HL2), and 2-[1-(3-dimethylarnino-propylamino)-ethyl]-phenol (HL3), respectively. The coordination compounds have been characterized by X-ray structural analyses, magnetic-susceptibility measurements, and various spectroscopic methods. In all complexes, the nickel(II) ions are penta-coordinated in a square-pyramidal environment, which is severely distorted in the case of 1 (Addison parameter tau = 0.47) and 3 (tau = 0.29), while it is almost perfect for 2 (tau = 0.03). This arrangement leads to relatively strong antiferromagnetic interactions between the Ni(II) (S = 1) metal centers as mediated by double phenoxido bridges (with J values of -23.32 (1), -35.45 (2), and -34.02 (3) cm(3) K mol(-1), in the convention H = -2JS(1)S(2)). The catalytic activity of these Ni compounds has been investigated for the aerial oxidation of 3,5-di-tert-butylcatechol. Kinetic data analysis following Michaelis-Menten treatment reveals that the catecholase activity of the complexes is influenced by the flexibility of the ligand and also by the geometry around the metal ion. Electrospray ionization mass spectroscopy (ESI-MS) studies (in the positive mode) have been performed for all the coordination compounds in the presence of 3,5-DTBC to characterize potential complex-substrate intermediates. The mass-spectrometry data, corroborated by electron paramagnetic resonance (EPR) measurements, suggest that the metal centers are involved in the catecholase activity exhibited by the complexes.

Perspectives for Novel Mixed Diruthenium-Organic Drugs as Metallopharmaceuticals in Cancer Therapy

Ruthenium compounds have been actively studied as metallodrugs for cancer therapy. Representatives of ruthenium-based antitumor drugs are the classes of ruthenium(III)-chlorido-(N-ligand)complexes, including the drugs namely NAMI-A and KP1019 in clinical trials, and ruthenium(II)-arene organometallics, with some compounds currently undergoing advanced preclinical testing. An alternative approach for tumor-inhibiting metallodrugs is the coordination of metal ions to organic pharmaceuticals. The combination of antitumor-active ruthenium ion with biologically-active pro-ligands in single compounds can result in the enhancement of activity, for example through synergistic effects. In the present article, some developments in the ruthenium-based antitumor drugs field are briefly highlighted and recent studies on mixed diruthenium-organic drugs as metallopharmaceuticals in cancer therapy are described. Novel organic pharmaceuticals-containing diruthenium(II, III)complexes have shown promising antitumor activity for C6 rat glioma - a model for glioblastoma multiforme (GBA).

Photoluminescence study of new lanthanide complexes with benzeneseleninic acids

New lanthanide complexes with benzeneseleninic (ABSe) and 4-chloro-benzeneseleninic (ABSeCl) acids have been synthesized and characterized by elemental analysis, infrared and UV-visible spectroscopies. The emission spectra of the trivalent europium complexes presented the typical electronic (5)D(0) -> (7)F(j) transitions of the ion (J = 0-4). The ground-state geometries of the europium complexes have been calculated by using the Sparkle/AM1 model. From these results, the 4f-4f intensity parameters and energies of the ligand singlet and triplet excited states have been obtained. The lower emission quantum yield for the [Eu(ABSe)(3)(H(2)O)(2)](H(2)O)(2) compound, as compared to the [Eu(Al(3)SeCl)(3)(H(2)O)(2)] one, can be associated to the higher numbers of water molecules, in the first and second coordination spheres, that contribute to the luminescence quenching. The [Eu(Al(3)Se)(3)(H(2)O)(2)](H(2)O)(2) complex presents an intermediate state whose energy difference with respect to the first excited singlet state is resonant with three phonons from the water molecules, favouring a multiphonon relaxation process from the singlet state followed by a fast internal conversion process; this effect is less pronounced in the complex with the ABSeCl ligand. The luminescence decay curves of the gadolinium complexes indicate that the level responsible for the intramolecular energy transfer process has a triplet character for both compounds. The nephelauxetic effect in these compounds was investigated under the light of a recently proposed covalency scale based on the concept of overlap polarizability of the chemical bond. (C) 2009 Elsevier B.V. All rights reserved.

Desenvolvimento de um novo complexo macrocíclico do sistema cobalto cyclam

In this work were synthesized and studied the spectroscopic and electrochemical characteristics of the coordination compounds trans-[Co (cyclam)Cl2]Cl, trans- Na[Co(cyclam)(tios)2], trans-[Co(en)2Cl2]Cl and trans-Na[Co(en)2(tios)2], where tios = thiosulfate and en = ethylenediamine. The compounds were characterized by: Elemental Analysis (CHN), Absorption Spectroscopy in the Infrared (IR), Uv-Visible Absorption Spectroscopy, Luminescence Spectroscopy and Electrochemistry (cyclic voltammetry). Elemental Analysis (CHN) suggests the following structures for the complex: trans- [Co(cyclam)Cl2]Cl.6H2O and trans-Na[Co(cyclam)(tios)2].7H2O. The electrochemical analysis, when compared the cathodic potential (Ec) processes of the complexes trans- [Co(cyclam)Cl2]Cl and trans-[Co(en)2Cl2]Cl, indicated a more negative value (-655 mV) for the second complex, suggesting a greater electron donation to the metal center in this complex which can be attributed to a greater proximity of the nitrogen atoms of ethylenediamine in relation to metal-nitrogen cyclam. Due to the effect of setting macrocyclic ring to the metal center, the metal-nitrogen bound in the cyclam are not as close as the ethylenediamine, this fact became these two ligands different. Similar behavior is also observed for complexes in which the chlorides are replaced by thiosulfate ligand, trans-Na[Co(en)2(tios)2] (-640 mV) and trans-Na[Co(cyclam)(tios)2] (-376 mV). In absorption spectroscopy in the UV-visible, there is the band of charge transfer LMCT (ligand p d* the metal) in the trans-Na[Co(cyclam)(tios)2] (350 nm, p tios  d* Co3+) and in the trans-Na[Co(en)2(tios)2] (333 nm, p tios d* Co3+), that present higher wavelength compared to complex precursor trans- [Co(cyclam)Cl2]Cl (318 nm, pCl  d* Co3+), indicating a facility of electron density transfer for the metal in the complex with the thiosulfate ligand. The infrared analysis showed the coordination of the thiosulfate ligand to the metal by bands in the region (620-635 cm-1), features that prove the monodentate coordination via the sulfur atom. The νN-H bands of the complexes with ethylenediamine are (3283 and 3267 cm-1) and the complex with cyclam bands are (3213 and 3133 cm-1). The luminescence spectrum of the trans-Na[Co(cyclam)(tios)2] present charge transfer band at 397 nm and bands dd at 438, 450, 467, 481 and 492 nm.

Estudo teórico QTAIM e DFT dos compostos de coordenação: efeito quelato, titanocenos e ligação química

This work is a study of coordination compounds by quantum theory of atoms in molecules (QTAIM), based on the topological analysis of the electron density of molecular systems, both theoretically and experimentally obtained. The coordination chemistry topics which were studied are the chelate effect, bent titanocene and chemical bond in coordination complexes. The chelate effect was investigated according to topological and thermodynamic parameters. The exchange of monodentate ligands on polydentate ligands from same transition metal increases the stability of the complex both from entropy and enthalpy contributions. In some cases, the latter had a higher contribution to the stability of the complex in comparison with entropy. This enthalpic contribution is explained according to topological analysis of the M-ligand bonds where polidentate complex had higher values of electron density of bond critical point, Laplacian of electron density of bond critical point and delocalization index (number of shared electrons between two atoms). In the second chapter, was studied bent titanocenes with bulky cyclopentadienyl derivative π-ligand. The topological study showed the presence of secondary interactions between the atoms of π-ligands or between atoms of π-ligand and -ligand. It was found that, in the case of titanocenes with small difference in point group symmetry and with bulky ligands, there was an nearly linear relationship between stability and delocalization index involving the ring carbon atoms (Cp) and the titanium. However, the titanocene stability is not only related to the interaction between Ti and C atoms of Cp ring, but secondary interactions also play important role on the stability of voluminous titanocenes. The third chapter deals with the chemical bond in coordination compounds by means of QTAIM. The quantum theory of atoms in molecules so far classifies bonds and chemical interactions in two categories: closed shell interaction (ionic bond, hydrogen bond, van der Waals interaction, etc) and shared interaction (covalent bond). Based on topological parameters such as electron density, Laplacian of electron density, delocalization index, among others, was classified the chemical bond in coordination compounds as an intermediate between closed shell and shared interactions

Complexos metálicos de cobalto, níquel e cobre com a Pirazina-2-carboxamida e 4- hidrazida ácida piridincarboxílica: síntese e caracterização

This work involved the synthesis, characterization and proposing the molecular structure of coordination compounds involving ligands pyrazine-2-carboxamide (PZA) and 4- hydrazide acidic pyridine carboxylic (INH) and metals of the first transition series (M = Co2+, Ni2+ and Cu2+). For the characterization of the compounds used were analytical techniques such as infrared absorption spectroscopy average (FT-IR) molar conductivity measurements, CHN elemental analysis, EDTA Complexometric, measurement of melting point, X-ray diffraction by powder method, Thermogravimetry (TG) and Differential Thermal Analysis (DTA) and Simultaneous Differential Scanning Calorimetry (DSC). The absorption spectra in the infrared region suggested that the ligand coordination to the metal center occurs through the carbonyl oxygen atom and nitrogen alpha pyrazine ring to those complexes formed with PZA. For INH complexes with metal-ligand coordination is through the carbonyl oxygen and nitrogen of the terminal hydrazide grouping. The conductivity measurements of the complexes in aqueous solution they suggest to all behavior of the type 1:2 electrolytes, and conduct of non-electrolytes in acetonitrile. The results obtained by CHN elemental analysis and EDTA Complexometric allowed to infer the stoichiometry of the compounds synthesized. For all of the complexes obtained was possible to record the melting points, neither of which melted near the melting temperature of the free ligands. The X-ray diffraction showed that the complexes of pyrazinamide exhibited diffraction lines, suggesting that these compounds are crystalline, while compounds of isoniazid, with the exception of cobalt, exhibited diffraction lines, indicating that they are crystalline. The results from the TG-DTA and DSC allowed information regarding the dehydration and thermal decomposition of these complexes

Síntese e caracterização de compostos de coordenação homolépticos e heterolépticos com o ligante ácido kójico

The present work has as main objective to contribute to the coordination chemistry of the ligand kojic acid, with the synthesis and characterization of the homoleptic compounds [Al(kj)3], [Fe(kj)3], [Fe(kj)2], [Cu(kj)2] e [Ru(kj)3], and the new heteroleptic complexes, trans- K2[Fe(kj)2(CN)2] and trans-Na2[Ru(kj)2(CN)2]. The obtained compounds were characterized by vibrational spectroscopy in the infrared region (IV) and Electronic spectroscopy in the ultraviolet and visible region (Uv-Vis). The infrared results indicated the coordination of the bidentate ligand kojic acid, due to reductions in the values of the stretching frequencies of the carbonyl and double bonds, compared to the free ligand for all complexes obtained. The presence of new vibrational modes indicated the change of symmetry of the molecules in the new compounds synthesized. Additionally, the presence of vibrational modes assigned to metal-oxygen also contributed to confirm the ligand coordinating to the metal ions. Through this technique, was also possible to perform correlations of the numbers of vibrational modes, in the region 1400-900 cm-1 and the compounds geometry. The heteroleptic compounds exhibited υC≡N in 2065 and 2053 cm-1, respectively, for the trans-K2[Fe(kj)2(CN)2] and trans-Na2[Ru(kj)2(CN)2], indicating coordination of the cyano ligand to metal ions FeII e RuII. Comparing the obtained values with literature data was possible to identify the complex isomerism as trans. In relation to the results of electronic spectroscopy, studies of pH variation of kojic acid provided information on the distribution of electron density in the molecule, showing characteristic spectral profile of kojic ion and its protonated form (Hkj, kojic acid), with two bands at 215 and 269 nm, or deprotonated (kj-), with bands at 226 and 315 nm. The electronic spectra obtained for all complexes in aqueous medium, in the ultraviolet region, exhibited variations of the energies assigned to kojic acid intraligand transitions while in the visible region, only transitions assigned to charge transfer of iron and ruthenium complex have been identified