Generation and spectroscopic characterization of new 18+δ electron complexes. Relationship between the stability of 18+δ electron organometallic complexes and their ligand reduction potentials

The relationship between the electrochemical reduction potential of a ligand and the ability of that ligand to form a kinetically inert 18+δ complex in a reaction with a 17-electron radical was investigated. (18+δ complexes are 19-electron adducts in which the unpaired electron is primarily located on a ligand orbital.) To probe the relationship, a series of 18+δ complexes was generated by irradiating the Cp′₂Mo₂(CO)₆, Cp₂Fe₂(CO)₄ and Co₂(CO)₈ dimers in the presence of a series of bidentate phosphorus ligands. (Irradiation of the dimers formed 17-electron metal radicals by photolysis of the metal-metal bonds.) These experiments showed that bidentate phosphorus ligands with reduction potentials more positive than −1 volt (versus SCE) formed long-lived 18+δ complexes (in THF or CH₂Cl₂ solutions at 23 °C), while ligands with potentials more negative than −1 V formed reactive 18+δ complexes. The inability to detect 18+δ complexes in the latter case is attributed to kinetic factors: the 18+δ complexes are powerful reductants and they readily initiate a chain disproportionation of the dimers by electron transfer. Analogous experiments with bidentate nitrogen ligands did not produce any detectable 18+δ complexes. In this case, the undetectability of the 18+δ complexes is probably thermodynamic in origin: the hard nitrogen ligands and soft metal centers form adducts that are unstable with respect to metal-nitrogen bond cleavage. 18+δ complexes are the subject of increasing interest, especially as models for their more reactive 19-electron-complex counterparts. These results provide some guidelines for the design of 18+δ complexes that can be synthesized, isolated and characterized for such studies.     

Relationship between pKa of 8-quinolinol derivatives and a π-donor ability of the 8-quinolinolato oxygen in linear nitrosylruthenium(II) complexes

The relationship between the pK_a of 8-quinolinol derivatives {8-quinolinol (Hqn), 2-methyl- (H2-Meqn), 2,4-dimethyl- (H2,4-diMeqn), 5-chloro- (H5-Clqn) and 5,7-dichloro-8-quinolinols (H5,7-diClqn)} and a π-donor ability of the 8-quinolinolato oxygens has been investigated by the identification of the structures of the major products, [RuCl(QN)(QN′)NO] (HQN=8-quinolinol derivative; HQN′=different 8-quinolinol derivatives), obtained by the reaction of [RuCl₃(QN or QN′)NO]⁻ with HQN′ or HQN. The results obtained clearly showed that the oxygen of the 8-quinolinol derivative that has a higher pK_a predominantly coordinates in the trans position to the NO ligand and is a better π-electron donor. The order of the π-electron donor ability for the oxygen of the 8-quinolinol derivatives is as follows: H2-Meqn≥H2,4-diMeqn>Hqn≥H5-Clqn>H5,7-diClqn, almost agreeing with the magnitude of the pK_a values of the corresponding 8-quinolinols. The structures of cis-1 [RuCl(5,7-diClqn)₂NO] and cis-1 [RuCl(5,7-diClqn)(2-Meqn)NO] were determined by X-ray diffraction.     

Dissociative phosphine exchange for cyclopentadienylmolybdenum(III) systems. Bridging the gap between Werner-like coordination chemistry and low-valent organometallic chemistry

Several phosphine exchange processes on 17-electron CpMoCl₂(PR₃)₂ systems have been investigated. The exchange of two PPh₃ ligands with either two PMe₃ ligands or with Ph₂PCH₂PPh₂ (dppe) is complete within a few minutes at −80 °C. Equally fast is the exchange of two PEt₃ ligands with two PMe₃ ligands. On the other hand, the exchange of two PEt₃ ligands with dppe is much slower ( to a few hours at r.t.), with excess dppe accelerating the exchange and free PEt₃ retarding it. The self-exchange reaction of PMe₃ is extremely slow (less than 25% exchange at r.t. in 6 h at r.t.) and an analysis of the initial rate of this reaction shows a two-term rate law with one [PMe₃]-dependent and one independent term. Finally, PMe₃ self-exchange on Cp^*MoCl₂(PMe₃)₂ proceeds over one order of magnitude faster than for the corresponding Cp system, with a substantially [PMe₃]-independent rate law. All these data are indicative of a dominant dissociative exchange mechanism involving rupture of the Mo---PR₃ bond in the slow step and formation of a 15-electron intermediate. The rate of phosphine dissociation qualitatively correlates with the Mo---P distance in the 17-electron starting complex. Only for the Cp---MoCl₂(PMe₃)₂ system is phosphine dissociation sufficiently slowed down so that the alternative associative exchange pathway becomes competitive. Possible reasons for a low activation barrier in these dissociative exchanges are discussed.     

Second sphere coordination behavior of aquo and amine ligands bound to a η-benzeneruthenium(II) cation

The bis(oxazoline) ligand, 2,2-bis[4(R)-phenyl-1,3-oxazolon-2-yl]propane (bpop), was introduced to the η⁶-benzenemthenium(II) moiety on treatment with [Ru(η⁶-C₆H₆)Cl₂]₂ to give [Ru(η⁶-C₆H₆)(bpop)Cl]⁺. Aquo and amine complexes [Ru(η⁶-C₆H₆)(bpop)(L)]²⁺ (L = H₂O (1), NH₂R; R = H (2) , Me (3) , and n-Bu (4) ) were prepared by treating the chloride complex with AgBF₄ in the presence of L. X-ray structure determinations of 1 and 3 were carried out. Both complexes possessed a three-leg piano stool structure with the N or O donors located at the three comers of a pseudo octahedron. The aquo complex 1 exhibited a dynamic NMR feature in which two magnetically nonequivalent oxazoline parts observed at lower temperatures were interchanged with each other at higher temperatures. This observation was ascribed to the formation of a C₂-symmetric 16-electron intermediate via Ru-OH₂ cleavage, which is slower in acetone than in dichloromethane owing to more effective solvation by acetone around hydrogens of the coordinated water molecule. The two diastereotopic N-hydrogens of 4 underwent deuterium exchange with CD₃OD with greatly different rates from each other owing to different energy of NHO (D) (CD₃) interaction. Carboxylate and sulfonate ions (A⁻) formed second sphere complexes with 4 by means of NHA⁻ hydrogen bonding, as evidenced by continuous shift of NH₂ resonances with increasing amounts of the anions added.     

Measurement of the oxidation-reduction potentials for two-electron and four-electron reduction of lipoamide dehydrogenase from pig heart.

The oxidation-reduction potential, E2, for the couple oxidized lipoamide dehydrogenase/2-electron reduced lipoamide dehydrogenase has been determined by measurement of equilibria of these enzyme species with lipoamide and dihydrolipoamide or with oxidized and reduced azine dyes. E2 is -0.280 V at pH 7, and deltaE2/deltapH is -0.06 V in the pH range 5.5 to 7.6. Values for E1, the oxidation-reduction potential for the couple 2-electron reduced enzyme/4-electron reduced enzyme, were obtained from measurements of the extent of dismutation of 2-electron reduced enzyme to form mixtures containing oxidized and 4-electron reduced enzyme. E1 is -0.346 V at pH 7, and deltaE1/deltapH is -0.06 V in the pH range 5.7 to 7.6. Spectra of oxidized enzyme and 4-electron reduced enzyme do not show variations with pH over this range, but the spectrum of the 2-electron reduced enzyme is pH-dependent, with the molar extinction at 530 nm changing from 3250 M-1 cm-1 at pH 8 to 2050 M-1 cm-1 at pH 5.2. The pH-dependent changes which are observed in the absorption properties of the 2-electron reduced enzyme are consistent with the disappearance of a charge transfer complex between an amino acid side chain and the oxidized flavin at the lower pH values, with the apparent pK of the side chain at pH 5. It has been suggested that the 530 nm absorbance of 2-electron reduced enzyme is due to a charge transfer complex between thiolate anion and oxidized flavin, and we propose that the thiolate anion is stabilized by interaction with a protonated base. The thermodynamic data predict that the amount of 4-electron reduced enzyme formed when the enzyme is reduced by excess NADH will be pH-dependent, with the greatest amounts seen at low pH values. These data support earlier evidence (Matthews, R.G., Wilkinson, K.D., Ballou, D,P., and Williams, C.H., Jr. (1976) in Flavins and Flavoproteins (Singer, T.P., ed) pp. 464-472; Elsevier Scientific Publishing Co., Amsterdam) that the role of NAD+ in the NADH-lipoamide reductase reaction catalyzed by lipoamide dehydrogenase is to prevent accumulation of inactive 4-electron reduced enzyme by simple reversal of the reduction of 2-electron reduced enzyme by NADH.     

Potentiometric analysis of Escherichia coli cytochromes in the optical absorbance range of 500 nm to 700 nm.

The oxidation-reduction potentials of Escherichia coli cytochromes have been studied by a recently described technique for automated electrodic potentiometry (Hendler, R.W., Songco, D., and Clem, T.R. (1977) Anal. Chem. 49, 1908-1913; Hendler, R.W. (1977) Anal. Chem. 49, 1914-1918), where entire spectra are recorded at a series of solution potentials. New techniques for resolution of the spectra versus voltage data have been applied. The results indicate that a 1-electron transport chain conducts electrons from substrate to cytochrome d, which is the cytochrome oxidase. Cytochrome d contains several components which appear to increase electron transfer first to a 2-electron stage and then to a 4-electron stage for the final reduction of a molecule of oxygen to 2 molecules of water.     

Electrophilic abstractions on Os(H)2X(NO)L2: selective access to new unsaturated cationic Os(II) hydrides

Nitrosylation of Os(H)₃ClL₂ (L = P¹Pr₃) affords the known Os(H)₂Cl(NO)L₂ (2). Soft electrophiles (Ag⁻, Na⁻) react with complex 2 by chloride abstraction to ultimately yield truly 16-electron dihydride Os(H)₂(NO)(P¹Pr₃)₂⁻ (4a), characterized by variable-temperature NMR. Complex 4a reversibly binds H₂, forming Os(H)₂(H₂)(NO)(P¹Pr₃)⁻ with an unusually high barrier for intramolecular hydride exchange. Under kinetic conditions, protonation of 2 with strong acids follows the selectivity for chloride abstraction. Thermodynamically, protonation at the hydride is preferred, quantitatively producing cationic OsHCl(NO)L₂⁺, isolated and characterized by X-ray diffraction as the BAr₄^F− salt (7) (Ar^F=3,5−(CF₃)₂C₆H₃). Structures of isoelectronic OsHCl(NO)(PH₃)₂ and OsHCl(CO)(PH₃)₂ were optimized with ab initio DFT (Becke3LYP) methods and compared to show the greater unsaturation of the metal in the cationic species. Both complexes, 4a and 7, are highly electrophilic and reversibly coordinate dichloromethane in solution. The observed reactivity patterns of the synthesized unsaturated hydrides are rationalized in terms of the determining influence of the ‘push-pull’ π-stabilization of the metal center.     

The Escherichia coli alkylation response protein AidB is a redox partner of flavodoxin and binds RNA and acyl carrier protein

Microorganisms are exposed to a wide variety of exogenous and endogenous chemical agents that alkylate DNA. Escherichia coli cells exhibit an adaptive response that recognizes and repairs alkylated DNA lesions using Ada, AlkA, and AlkB enzymes. Another alkylation response protein, the DNA-binding flavoprotein AidB, was proposed to repair DNA or protect it from chemical alkylating agents, but direct evidence for its role is lacking. Here, AidB was shown to form tight complexes with both flavodoxin and acyl carrier protein. In addition, electron transfer between 1-electron and 2-electron reduced flavodoxin to oxidized AidB was observed, although with very small rate constants. AidB was found to bind to RNA, raising the prospect that the protein may have a role in protection of RNA from chemical alkylation. Finally, the reagent N-methyl-N′-nitro-N-nitrosoguanidine was eliminated as a direct substrate of the enzyme.     

The electronic structure of the electron-reservoir complex CpFe(hexamethylbenzene) revisited: a regular metal-centered SOMO

While all the available experimental and theoretical data on 19-electron electron reservoir complexes of the general type (η⁵-C₅R₅)Fe(η⁶-arene) (R = H, Me) agree for a SOMO participation of Fe being larger than that of the Cp and arene ligands, recent DFT calculations disagree on only one compound, namely CpFe(HMB) (HMB = hexamethylbenzene). The reported calculations show clearly that CpFe(HMB) is not an exception and has iron-based SOMO, like all the members of the (η⁵-C₅R₅)Fe(η⁶-arene) (R = H, Me) family.     

Silicon-containing carbene complexes 16. Intramolecular agostic stabilization versus nucleophilic addition to the 16-electron carbene complex (CO)4(L)W=C(NMe2)SiPh2Me

The 16-electron complex (CO)₄W=C(NMe₂)SiPh₂Me (1) was photochemically prepared from (CO)₅W=C- (NMe2)SiPh₂Me. Reactions with selected nucleophiles, having different ligand properties, were performed to test the strength of the intramolecular agostic interaction of one of the phenyl groups, by which 1 is stabilized. The stable complexes cis-(CO)₄LW=C(NMe₂)SiPh₂Me were formed with L=P(OMe)₃, P(OEt)₃ or 2,6-Me₂C₆H₃NC. The substituted complexes had no tendency for ligand elimination. Addition of acetonitrile or pyridine to an ether solution of 1 resulted in the formation of cis-(CO)₄(MeCN)W=C(NMe₂)SiPh₂Me or cis-(CO)₄(C₅H₅N)- W=C(NMe₂)SiPh₂Me, respectively. These reactions were reversed on evaporation of the solutions. No reaction was observed with triethylamine.     

Quantifying the energetic contributions of desolvation and π-electron density during translesion DNA synthesis

This report examines the molecular mechanism by which high-fidelity DNA polymerases select nucleotides during the replication of an abasic site, a non-instructional DNA lesion. This was accomplished by synthesizing several unique 5-substituted indolyl 2'-deoxyribose triphosphates and defining their kinetic parameters for incorporation opposite an abasic site to interrogate the contributions of π-electron density and solvation energies. In general, the K(d, app) values for hydrophobic non-natural nucleotides are ～10-fold lower than those measured for isosteric hydrophilic analogs. In addition, k(pol) values for nucleotides that contain less π-electron densities are slower than isosteric analogs possessing higher degrees of π-electron density. The differences in kinetic parameters were used to quantify the energetic contributions of desolvation and π-electron density on nucleotide binding and polymerization rate constant. We demonstrate that analogs lacking hydrogen-bonding capabilities act as chain terminators of translesion DNA replication while analogs with hydrogen bonding functional groups are extended when paired opposite an abasic site. Collectively, the data indicate that the efficiency of nucleotide incorporation opposite an abasic site is controlled by energies associated with nucleobase desolvation and π-electron stacking interactions whereas elongation beyond the lesion is achieved through a combination of base-stacking and hydrogen-bonding interactions.     

One-dimensional polymeric chlorocadmate(II) systems of N-methylpiperazinium and N,N′-dimethylpiperazinium compounds: synthesis, structural and thermal properties

The chlorocadmate(II) systems of (H₂me₂pipz)[Cd₂Cl₆(H₂O)₂] (1) and (H₂mepipz)₂[Cd₃Cl₁₀(H₂O)] (2) (L = me₂pipz = N,N′-dimethylpiperazine; L′ = mepipz = N-methylpiperazine) were prepared and their structural and thermal properties investigated. Compound 1 is monoclinic, space group P2₁/c, A = 7.664(1), B = 7.472(4), C = 15.347(1) Å, β = 99.468(7)°, Z = 2, R = 0.024. The crystal structure consists of organic cations and infinite one-dimensional chains of [CdCl₃(H₂O)]_n³⁻ anions. Each Cd atom is octahedrally surrounded by bridged and terminal chlorine atoms and by a water molecule, which is in trans position with respect to the terminal chlorine atom. Inter- and intrachain hydrogen bond interactions between the terminal chlorine atoms and the water molecules contribute to the crystal packing. Compound 2 is orthorhombic, space group Cmc2₁, A = 15.286(3), B = 13.354(3), C = 13.154(3) Å, R = 0.023. The crystal structure consists of organic dications and infinite chains of [Cd₂Cl₆(CdCl₄H₂O]_n⁴⁻ units running along the [001] axis. Each unit is formed of regularly alternate six-coordinated Cd atoms, one of them linking one pentacoordinated Cd atom which completes its coordination througha water molecule. A strong hydrogen bond interaction involving the organic dication and the inorganic chain contributes to the crystal packing. Differential hydrogen bond interaction involving the organic dication and the inorganic chain contributes to the crystal packing. Differential scanning calorimetry measurements did not show the presence of any structural phase transitions. The structures are compared with those of (H₂pipz)[Cd₂Cl₆(H₂O)₂] (3), (H₂mepipz)[Cd₂Cl₆(H₂O)₂]·H₂O (4) and (H₂mepipz)[Cd₂Cl₆] (5) (L = pipz = piperazine, L′ = mepipz = N-ethylpiperazine).     

Regio- and stereoselective dimerization of 1-alkynes catalyzed by an Os(II) complex

The complex [(PP₃)OsH(N₂)]BPh₄ is a catalyst precursor for the regio- and stereoselective dimerization of HCCR (R=Ph, SiMe₃) to (Z)-1,4-disubstituted-but-3-en-l-ynes (PP₃=P(CH₂CH₂PPh₂)₃). In the presence of H₂O or C₂H₅OH, the catalytic reaction with HCCSiMe₃ selectively gives but-3-en-l-ynyl-trimethyisilane. A detailed study under different experimental conditions, the detection of some intermediates, and the use of isolated complexes in independent reactions, taken altogether, permit mechanistic conclusions which account for the observed products. A key-role is played by (vinylidene)σ-alkynyl complexes which transform into η³-butenynyl derivatives via intramolecular C---C bond formation. The Os(II) η³-butenynyl complexes are likely reagents in the rate determining step of the catalytic cycle, and produce free (Z)-1,4-disubstituted-but-3-en-l-ynes upon σ-bond metathesis reaction with HCCR. The 16-electron fragments [(PP₃)OsX]⁺ (X = H, Cl, CCR) are capable of promoting the 1-alkyne to vinylidene tautomerism. In particular, the (vinylidene)hydride [(PP₃)OsH{C=C(H)-SiMe₃}]BPh₄ has been isolated and properly characterized. Since the stoichiometric reaction of the latter compound with HCCSiMe₃ gives vinyltrimethylsilane, the formation of (vinylidene)hydride species is suggested to be an effective step, alternative to 1-alkyne insertion, in the reduction of 1-alkynes to alkenes assisted by hydrido metal complexes.     

Electrospray mass spectrometric investigation of the relative ligand properties of EPh3 ligands (E=P, As, Sb or Bi) towards Ag and Cu

Electrospray mass spectrometry (ESMS) has been used to investigate the relative ligand properties of the triphenylpnictogen ligands EPh₃ (E=P, As, Sb and Bi) towards silver(I) and copper(I) ions. It is found that the preferred species formed increase in coordination number from two for PPh₃ in [Ag(PPh₃)₂]⁺ to four for SbPh₃ in [Ag(SbPh₃)₄]⁺, consistent with the decreasing donor ligand ability and increasing metal –E bond length in the series PPh₃–AsPh₃–SbPh₃. With BiPh_3, the spectra were complex, suggesting considerable decomposition. These studies also suggest that silver(I) and copper(I) ions will have widespread utility in the characterisation of tertiary stibine ligands, as has been described previously for phosphines and arsines. These studies demonstrate the power of the ESMS technique in determining the donor properties of a related series of ligands, and this information is of significance in coordination chemistry.     

Simple synthesis of organo-iron complexes from iron-sandwich raw materials using visible light

Piano-stool organo-iron complexes [CpFeL₁L₂L₃]⁺ bearing a variety of ligands (Cp = η⁵-C₅H₅, L = neutral 2-electron ligand) can be readily synthesized by visible photolysis of any member of the family of [FeCp(arene)][PF₆] sandwich complexes (arene = η⁶-arene) including those in which the arene is mono-, bis or trisubstituted. A short review is provided for these reactions and processes and their applications in organo-iron synthesis.     

Synthesis, spectroscopy, electrochemistry and thermal study of vanadyl unsymmetrical Schiff base complexes

The new tetradentate unsymmetrical N₂O₂ Schiff base ligands and VO(IV) complexes were synthesised and characterized by using IR, UV-Vis and elemental analysis. The electrochemical properties of the vanadyl complexes were investigated by means of cyclic voltammetry. The oxidation potentials are increased by increasing the electron-withdrawing properties of functional groups of the Schiff base ligands according to the trend of MeO < H < Br < NO₂. The thermogravimetry (TG) and differential thermoanalysis (DTA) of the VO(IV) complexes were carried out in the range of 20-700 °C. The complexes were decomposed in two stages. Also decomposition of synthesised complexes is related to the Schiff base characteristics. The thermal decomposition of the studied reactions was first order.     

Synthesis, crystal structures and magnetic properties of transition metal–azide complexes coordinated with pyridyl nitronyl nitroxides

Two novel complexes Co(N₃)₂(PNN)₄ (I) and Mn(N₃)₂(PNN)₂(CH₃OH)(C₂H₅OH) (II) (PNN=2-(p-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3–oxide) were synthesized and characterized by infrared spectra, elemental analyses and UV–Vis techniques. The crystal structures of both complexes have been determined by X-ray diffraction analysis. Complex I is a neutral five-spin system and adopts a centrosymmetric tetragonally compressed octahedral coordination geometry in which Co(II) ion is coordinated to four radicals through the nitrogen atoms of the pyridine rings and two azide anions occupying the axial positions. Complex II is a neutral three-spin system in which Mn(II) ion is bound to two azide anions, two alcohol molecules and two radicals through the nitrogen atom of pyridine rings, and shows one-dimensional chain structure via hydrogen bonds (d_ON=2.78 Å). The magnetic properties for complexes I and II have been investigated in the temperature range 2–300 K. A theoretical model has been developed for complex I and the magnetic behaviors for both complexes have been discussed in detail.     

Isolation of a thermodynamically unfavorable [Ni(DACO)2] complex and its isomer: syntheses, characterization, crystal structures and theoretical study (DACO=1,5-diazacyclooctane)

Two Ni^II complexes of 1,5-diazacyclooctane (DACO), [Ni(DACO)₂]Br₂ (I) and [Ni(DACO)₂]Br·ClO₄ (II) have been newly synthesized and characterized. Single crystal X-ray diffraction analysis of DACO and both Ni^II complexes reveals that DACO takes boat/chair conformation in the solid state and its Ni^II complexes. In complex I, Ni^II ion is at the center of symmetry, which is four-coordinated by nitrogen donors of DACO. However, in complex II, an unexpected coordination mode of [M(DACO)₂]²⁺ (M=Cu^II and Ni^II) was found, in which two DACO ligands are related to each other by a mirror plane and the coordination sphere of Ni^II is a distorted planar geometry. Furthermore, complexes I and II form quite different packing patterns (macrocycle or chain) through hydrogen bonds, which may be a key role to stabilize the crystals. The results of theoretical calculation indicate that complex I has thermodynamic stability, while II has chemical stability. Therefore, both of them have the probability to be obtained from different reaction processes or conditions.     

Ultraviolet radiation, evolution and the π-electron system

Ultraviolet radiation is an important natural mutagen. Because of the energetic characteristics, the carbon compounds most susceptible to UV absorbance are those that contain π-electron systems. The π-electron configuration is most commonly represented in organic chemistry within aromatic ring structures. An analysis of a wide range of biochemically important processes shows that the susceptibility of this system lies at the heart of almost all UV radiation effects on life. Its disruption accounts for UV radiation-induced damage in nucleic acids, proteins and lipids. However, throughout the evolution of the biosphere, life has also used the UV absorbance of π-electron containing compounds to screen out UV radiation, turning their UV absorbance into a protection mechanism. Although UV radiation effects can be analyzed in terms of organism physiology, a more reductionist analysis shows the π-electron system to be the common chemical determinant in the evolution of UV radiation damage effects and protection strategies in organisms. It reveals an interesting evolutionary story.     

Synthesis, characterization and cytotoxic activity of palladium (II) dithiocarbamate complexes with α,ω-diamines

The polymeric [PdCl(dithiocarbamate)]_n complexes, in which the ligand ion is dimethyldithiocarbamate (DMDT), pyrrolidine dithiocarbamate (PyDT, (CH₂)₄NCS₂⁻) and sarcosine ethyl ester dithiocarbamate (ESDT, EtO₂CCH₂N(CH₃)CS₂⁻), have been reacted with chelating diamines, like ethylenediamine (en) or 1,3-diaminopropane (dap) and long chain diamines, like 1,4-diaminobutane (dab) or 1,7-diaminoheptane (dah). The reaction products depend on either diamine chain length or molar ratio. By operating at PdCl(dithiocarbamate)/diamine molar ratio 1:1 chelating diamines yielded the ionic [Pd(dithiocarbamate)(diamine)]Cl species (diamine = en or dap), whereas with long chain diamines species of the type [Pd(dithiocarbamate)(diamine)]_nCl_n (diamine = dab or dah) were obtained, in which each Pd(dithiocarbamate)⁺ unit binds to the NH₂ group of two different molecules, in a network of bridging diamines. At molar ratio 1:0.5, the long chain diamines yielded the binuclear [Pd₂Cl₂(dithiocarbamate)₂(diamine)] complexes (diamine = dab or dah), whereas exchange reactions take place generally in the presence of en or dap. The reaction trend is described on the basis of IR and proton NMR spectra. The new dithiocarbamate complexes were preliminarily tested for their cytotoxicity on human cancer cells.