Kinetic studies of the reduction of hexaaquacobalt(III) perchlorate by a cobaloxime, [Co(dmgBF2)2(H2O)2]

The reaction of with Co(dmgBF₂)₂(H₂O)₂ in 1.0 M HClO₄/LiClO₄ was found to be first-order in both reactants and the [H⁺] dependence of the second-order rate constant is given by k_2obs = b/[H⁺], b at 25 °C is 9.23 ± 0.14 × 10² s⁻¹. The [H⁺] dependence at lower temperatures shows some saturation effect that allowed an estimate of the hydrolysis constant for as K_a = 9.5 × 10⁻³ M at 10 and 15 °C. Marcus theory and the known self-exchange rate constant for Co(OH₂)₅OH^2+/+ were used to estimate an electron self-exchange rate constant of k₂₂ = 1.7 × 10⁻⁴ M⁻¹ s⁻¹ for .     

Kinetic studies of tris(2,2′-bipyridine)iron(III) perchlorate with cobaloxime, [Co(dmgBF2)2(H2O)2]

The kinetics of the reduction of by Co(dmgBF₂)₂(H₂O)₂ in 0.041 M HNO₃/NaNO₃ was found to be first-order in both the oxidizing and reducing agents and the second-order rate constant is given by k_obs = k₁ + k₂K[Cl⁻], with k₁=1.59 × 10⁶ M⁻¹ s⁻¹and k₂K = 1.83 × 10⁸ M⁻² s⁻¹, at 25 °C. The term that is first-order in [Cl⁻] is attributed to the formation of an ion-pair between and Cl⁻. For k₁, the activation parameters ΔH* and ΔS* are 2.22 ± 0.02 kcal mol⁻¹ and −22.7 ± 0.8 cal mol⁻¹ K⁻¹, respectively. The self-exchange rate constant of k₂₂ ≈ 8.7 × 10⁻³ M⁻¹ s⁻¹ for was estimated using Marcus theory and the known self-exchange rate constant for .     

Solvent exchange, solvent interchange, aquation and isomerisation reactions of cis- and trans-[Co(tmen)2(NCMe)2] in water, Me2SO and MeCN: kinetics and stereochemistry

The synthesis and characterisation of cis- and trans-[Co(tmen)₂(NCCH₃)₂](ClO₄)₃ are described. Solvolysis rates have been measured by both ¹H NMR spectroscopy and UV-Vis spectrophotometry in dimethyl sulfoxide at 298.2 K. The cis isomer undergoes solvolysis by consecutive first-order reactions, k₁=5.61 × 10⁻⁴ and k₂=5.35 × 10⁻⁴ s⁻¹, each with steric retention. The measured solvolysis rate (single step reaction) for the trans isomer is k=1.54 × 10⁻⁵ s⁻¹. The solvent exchange rates have been measured by ¹H NMR spectroscopy in CD₃CN at 298.2 K: k_ex(cis)=k_ct + k_cc=2.0 × 10⁻⁵ and k_ex(trans)=k_tc + k_tt=4.56 × 10⁻⁶ s⁻¹. From these data, the measured cis-trans isomerisation rate (1.71 × 10⁻⁶ s⁻¹) and equilibrium position in CH₃CN (17% trans), the steric course for substitution in the exchange processes has been determined: trans reactant - 69% trans product; cis reactant - 99% cis product. Aquation rates for cis- and trans-[Co(tmen)₂(NCCH₃)₂](ClO₄)₃ have also been determined spectrophotometrically and by NMR; k_cis=1.3 × 10⁻⁴ and k_trans=2.7 × 10⁻⁵ s⁻¹. In both cases the steric course for the primary aquation step is indeterminate because the subsequent steps are faster. Where data are available, the [Co(tmen)₂X₂]ⁿ⁺ complexes are found to be consistently much more reactive than their [Co(en)₂X₂]ⁿ⁺ analogues.     

Kinetics study of the substitution reaction of fac-[Fe(CN)2(CO)3I] with PPh3

Substitution reaction of fac-[Fe^II(CN)₂(CO)₃I]⁻ with triphenylphosphine (PPh₃) produced mono phosphine substituted complex cis-cis-[Fe^II(CN)₂(CO)₂(PPh₃)I]⁻. Crystal structure of the product showed that carbonyl positioned trans- to iodide was replaced by PPh₃. The substitution reaction was monitored by quantitative infrared spectroscopic method, and the rate law for the substitution reaction was determined to be rate = k[[Fe^II(CN)₂(CO)₂(PPh₃)I]⁻][PPh₃]. Transition state enthalpy and entropy changes were obtained from Eyring equation k = (k_BT/h)exp(−ΔH^≠/RT + ΔS^≠/R) with ΔH^≠ = 119(4) kJ mol⁻¹ and ΔS^≠ = 102(10) J mol⁻¹ K⁻¹. Positive transition state entropy change suggests that the substitution reaction went through a dissociative pathway.     

Activation parameters in flash photolysis studies of Mo(CO)6

Reported is a combined time-resolved optical (TRO) and infrared (TRIR) spectroscopic investigation of the flash photolysis of Mo(CO)₆ in cyclohexane solution. TRIR studies using 308 nm excitation led to transient bleaching of the strong ν_CO band at 1987 cm⁻¹ of Mo(CO)₆ and appearance of new bands at 1931 and 1964 cm⁻¹ attributed to Mo(CO)₅(Sol). Using a high pressure/variable temperature flow cell, the kinetics of back reaction with CO (k_CO) to regenerate the hexacarbonyl was studied over the P_CO range 1-20 atm and at five temperatures. These data gave k_CO=4.6±0.2×10⁶ M⁻¹ s⁻¹ (298 K) and the activation parameters kJ/mol and J mol⁻¹ K⁻¹ from which an interchange mechanism was proposed. The analogous species seen in the TRO experiment displayed a transient absorbance at 420 nm and analogous kinetics properties although at lower P_CO self-trapping with Mo(CO)₆ (to give Mo₂(CO)₁₁) is a competitive process. The Mo(CO)₅(Sol) transient could also be trapped by ⁿPrBr (k_RBr=5.3±0.7×10⁷ M⁻¹ s⁻¹).     

Optical and EPR spectra of the thionitrosyl complex [Cr(OH2)5(NS)]

The green thionitrosyl complex [Cr(OH₂)₅(NS)]²⁺ was isolated in solution by the hydrolysis of [Cr(NCCH₃)₅(NS)]²⁺. The optical absorption spectra of both compounds are dominated by a band with vibrational progression around 600 nm assigned as a {d_yz,zx, π^∗(NS)} → {π^∗(NS), d_yz,zx}^∗ transition. The optical data indicate that the NS ligand is a weaker π-acceptor than the NO ligand. The EPR parameters of [Cr(OH₂)₅(NS)]²⁺ were determined: g_iso, g_∥ and g_⊥: 1.96515, 1.92686(5) and 1.986860(8); A_iso(⁵³Cr), A_∥(⁵³Cr) and A_⊥(⁵³Cr): 25.3 × 10⁻⁴, 38 × 10⁻⁴ and 18.5 × 10⁻⁴ cm⁻¹; A_iso(¹⁴N), A_∥(¹⁴N) and A_⊥(¹⁴N): 6.5 × 10⁻⁴, 2.81 × 10⁻⁴ and 8.346(12) × 10⁻⁴ cm⁻¹.     

Decarbonylation of As2Co2(CO)6, a binuclear cobalt carbonyl derivative of diarsenic

The structures and relative energies of the As₂Co₂(CO)_n (n = 6, 5, 4) derivatives are predicted by density functional theory to be analogous to those of the corresponding H₂C₂Co₂(CO)_n derivatives. Thus As₂Co₂(CO)₆ is predicted to have three carbonyls on one cobalt atom eclipsed relative to the three carbonyls on the other cobalt atom. The corresponding As₂Co₂(CO)₆ structure with a staggered rather than eclipsed arrangement of the Co(CO)₃ units is a transition state rather than a genuine minimum. For As₂Co₂(CO)₅ the structure in which an equatorial group is removed from the As₂Co₂(CO)₆ structure and a singly bridged As₂Co₂(CO)₄(μ-CO) structure are predicted to have essentially the same energies, within <2 kcal/mol. A higher energy As₂Co₂(CO)₅ structure by 9 ± 2 kcal/mol is derived from the As₂Co₂(CO)₆ structure by removal of an axial carbonyl group. The two unbridged As₂Co₂(CO)₅ structures correspond to those observed experimentally in the photolysis of As₂Co₂(CO)₆ in Nujol matrices at low temperatures. In such photolysis experiments the higher energy isomer is produced initially and then converted to the lower energy isomer upon annealing. A singly bridged structure was found for As₂Co₂(CO)₄. The analogous structure was not observed in the previous work with H₂C₂Co₂(CO)₄. However, such a H₂C₂Co(CO)₃(μ-CO) structure is found here for the acetylene complex. This singly bridged structure is predicted to lie 1.9 kcal/mol below the H₂C₂Co₂(CO)₄4-1S structure by the BP86 method but 3.5 kcal/mol above the latter by the B3LYP method. In addition to the singly bridged As₂Co₂(CO)₄ structure, the same six unbridged structures were located for As₂Co₂(CO)₄ that were previously found for H₂C₂Co₂(CO)₆.     

Structural characterization, electrochemistry, and spectroelectrochemistry of trans-dioxorhenium(V) complex with 4-methoxypyridine, [ReO2(4-MeOpy)4]PF6, and characterization of [ReO2(4-MeOpy)4] generated electrochemically

Crystal structure of [ReO₂(4-MeOpy)₄][PF₆] (4-MeOpy = 4-methoxypyridine) complex has been examined by the single crystal X-ray analytical method. This complex shows a trans-dioxo geometry (average Re-O bond length = 1.766(2) Å) and its equatorial plane is occupied by four 4-MeOpy molecules (average Re-N bond length = 2.156(4) Å). Electrochemical reaction of [ReO₂(4-MeOpy)₄]⁺ in CH₃CN solution containing tetra-n-butylammonium perchlorate as a supporting electrolyte has been studied using cyclic voltammetry at 24 °C. Cyclic voltammograms show one redox couple around 0.65 V (E_pa) and 0.58 V (E_pc) [versus ferrocene/ferrocenium ion redox couple, (Fc/Fc⁺)]. Potential differences between two peaks (ΔE_p) at scan rates in the range from 0.01 to 0.10 V s⁻¹ are 65 mV, which is almost consistent with the theoretical ΔE_p value (59 mV) for the reversible one electron transfer reaction at 24 °C. The ratio of anodic peak currents to cathodic ones is 1.04 ± 0.03 and the (E_pa + E_pc)/2 value is constant, 0.613 ± 0.001 V versus Fc/Fc⁺, regardless of the scan rate. Spectroelectrochemical experiments have also been carried out by applying potentials from 0.40 to 0.77 V versus Fc/Fc⁺ with an optically transparent thin layer electrode. It was found that the UV-visible absorption spectra show clear isosbestic points at 228, 276, and 384 nm, and that the electron stoichiometry is evaluated as 1.03 from the Nernstian plot. These results indicate that the [ReO₂(4-MeOpy)₄]⁺ complex is oxidized reversibly to the [ReO₂(4-MeOpy)₄]²⁺ complex. Furthermore, it was clarified that the [ReO₂(4-MeOpy)₄]²⁺ in CH₃CN has the characteristic absorption bands at 236, 278, 330, 478, and 543 nm and their molar absorption coefficients are 4.3 × 10⁴, 4.5 × 10³, 1.0 × 10⁴, and 6.1 × 10³ M⁻¹ cm⁻¹ (M = mol dm⁻³), respectively.     

The cyanocarbanion (C[C(CN)2]3) as monodentate ligand: Synthesis, structure and magnetic properties of [Mn2(bpym)3(tcpd)2(H2O)2] (tcpd = (C[C(CN)2]3) and bpym = 2,2′-bipyrimidine)

One-pot reaction between MnCl₂·4H₂O, K₂tcpd (tcpd²⁻ = [C₁₀N₆]²⁻ = (C[C(CN)₂]₃)²⁻ = 2-dicyanomethylene-1,1,3,3-tetracyanopropanediide anion) and 2,2′-bipyrimidine (bpym = C₈H₆N₄) in aqueous solution yields the new compound [Mn₂(bpym)₃(tcpd)₂(H₂O)₂] (1). The molecular structure of 1 consists of a centrosymmetrical binuclear complex which includes unprecedented unidentate tcpd ligands with two bidentate and a bis-chelate bpym units. Examination of the intermolecular distances reveals that the dinuclear units are held together by hydrogen bonds involving coordinated water molecules and two nitrile groups of the tcpd ligand, giving rise to a 2D structure overall. Variable-temperature magnetic susceptibility data show the occurrence of slight antiferromagnetic coupling (J = −0.58 cm⁻¹) between the Mn(II) ions through bridging bpym (the exchange Hamiltonian being defined as ).     

Electrochemical reduction properties of A-frame compounds and crystal structure of Pd2(dppm)2(Me)2(Br) dimer

Two series of A-frame complexes, [Pd₂(dppm)₂(R)₂(μ-X)]⁺ (R = Me and X = Cl, Br, I, H; R = Mes and X = Br, I), were investigated by cyclic voltammetry (CV). The 2-electron reduction potentials for the first series increase from I (−1.10), Br (−1.17), Cl (−1.25) to H (−1.65 V versus SCE, in CHCl₃), as well as in the second series; Br (−1.35) and I (−1.38 V versus SCE, in THF). The nature of the LUMO where the electron reduction takes place is qualitatively addressed by DFT on the corresponding model complexes [Pd₂(H₂PCH₂PH₂)₂(R)₂(μ-X)]⁺. The LUMO and (LUMO + 1) of the halide derivatives exhibit the presence of Pd d_x²-y² atomic orbitals interacting in an anti-bonding fashion with the n-donor orbitals of X⁻, P, and Me⁻, explaining in part the observed reactivity upon reduction. The X-ray structure of [Pd₂(dppm)₂(Me)₂(μ-Br)]⁺ compound exhibits the typical A-frame structure with a Pd?Pd non-bonding distance of 3.036(1) Å, and long Pd-Br bonds of 2.5623(5) and 2.5793(5) Å.     

Mechanism and biological implications of the NO release of cis-[Ru(bpy)2L(NO)](n+) complexes: a key role of physiological thiols

Nitric oxide (NO) has a critical role in several physiological and pathophysiological processes. In this paper, the reactions of the nitrosyl complexes of [Ru(bpy)₂L(NO)]ⁿ⁺ type, where L = SO₃²⁻ and imidazole and bpy = 2,2′-bipiridine, with cysteine and glutathione were studied. The reactions with cysteine and glutathione occurred through the formation of two sequential intermediates, previously described elsewhere, [Ru(bpy)₂L(NOSR)]ⁿ⁺ and [Ru(bpy)₂L(NOSR)₂] (SR = thiol) leading to the final products [Ru(bpy)₂L(H₂O)]ⁿ⁺ and free NO. The second order rate constant for the second step of this reaction was calculated for cysteine k₂(SR⁻) = (2.20 ± 0.12) × 10⁹ M^− 1 s^− 1 and k_2(RSH) = (154 ± 2) M^− 1 s^− 1 for L = SO₃²⁻ and k₂(SR⁻) = (1.30 ± 0.23) × 10⁹ M^− 1 s^− 1 and k₂(RSH) = (0.84 ± 0.02) M^− 1 s^− 1 for L = imidazole; while for glutathione they were k₂(SR⁻) = (6.70 ± 0.32) × 10⁸ M^− 1 s^− 1 and k₂(RSH) = 11.8 ± 0.3 M^− 1 s^− 1 for L = SO₃²⁻ and k₂(SR⁻) = (2.50 ± 0.36) × 10⁸ M^− 1 s^− 1 and k₂(RSH) = 0.32 ± 0.01 M^− 1 s^− 1 for L = imidazole. In all reactions it was possible to detect the release of NO from the complexes, which it is remarkably distinct from other ruthenium metallocompounds described elsewhere with just N₂O production. These results shine light on the possible key role of NO release mediated by physiological thiols in reaction with these metallonitrosyl ruthenium complexes.     

Robust anionic building blocks [M(malonate)2(H2O)2] for crystal engineering of inorganic-organic hybrid materials

One-pot reactions of transition metal (Cu^II, Ni^II, Co^II, or Cd^II) salt with malonic acid (H₂mal) in the presence of mesocyclic diamine generate three supramolecular complexes and a coordination polymer. [Cu(mal)₂(H₂O)₂](H₂O)₂(H₂DACH) (1) and [M(mal)₂(H₂O)₂](H₂DACO) (M = Ni for 2, and Co for 3) are ion-pair products and managed by charge-assistant noncovalent interactions (DACO = 1,5-diazacyclooctane, and DACH = 1,4-diazacycloheptane). In these structures, the similar mononuclear [M(mal)₂(H₂O)₂]²⁻ building blocks are connected by hydrogen bonds to form 2D networks (with the aid of one lattice water in the case of 1), which are further extended by the cationic diamine components to yield 3D pillar-layered solids. While [Cd(mal)(H₂O)₂]_n (4) is a neutral polymeric complex, in which the similar [Cd(mal)₂(H₂O)₂]²⁻ subunits are propagated by additional Cd-O coordinative forces to result in the final 2D layer.     

Molecular sensing behavior of the first Mn(I)-compound of di-2-pyridylketone-p-nitrophenylhydrazone (dpknph), fac-[Mn(CO)3(dpknph)Br]

The reaction between [Mn(CO)₅Br] and di-2-pyridylketone-p-nitrophenylhydrazone (dpknph) in diethyl ether under ultrasonic conditions gave fac-[Mn(CO)₃(dpknph)Br] in good yield. Optical and thermodynamic measurements on fac-[Mn(CO)₃(dpknph)Br] in non-aqueous polar solvents revealed reversible interconversion between two intense charge transfer absorption bands due to π-π* (dpk), followed by dpk → nitro intraligand charge transfer transition (ILCT), mixed with metal ligand charge transfer transition (MLCT) due to . In non-polar solvents, a single absorption band appeared. Extinction coefficients of 46 200 ± 2000 and 28 400 ± 2000 M⁻¹ cm⁻¹ were calculated in DMSO for the low- and high-energy electronic states of fac-[Mn(CO)₃(dpknph)Br] using excess NaBF₄. Changes in enthalpy (ΔH^ø) of +14.0 and −12.1 kJ mol⁻¹, entropy (ΔS^ø) of +28.65 and −64.30 J mol⁻¹ K⁻¹, and free energy (ΔG^ø) of +5.48 and +7.08 kJ mol⁻¹ at 298 K were calculated for the interconversion between the high and low energy electronic states of fac-[Mn(CO)₃(dpknph)Br]. These results allow for the use of these systems (fac-[Mn(CO)₃(dpknph)Br] and surrounding solvent or solute molecules) as optical sensors for a variety of physical and chemical stimuli that include metal ions. Group 12 metal ions in concentrations as low as 1.00 × 10⁻⁹ M can be detected and determined using fac-[Mn(CO)₃(dpknph)Br] in dmso in the presence and absence of NaBH₄.     

A new mixed-valence hexanuclear cobalt complex, [Co4Co2(dea)2(Hdea)4)(piv)4](ClO4)2·H2O: Synthesis, crystal structure and magnetic properties

A new Co^II/Co^III hexanuclear complex, [Co₄^IICo₂^III(dea)₂(Hdea)₄)(piv)₄](ClO₄)₂·H₂O 1, has been obtained by reacting cobalt(II) perchlorate, diethanolamine, and pivalic acid (H₂dea = diethanolamine and piv = pivalato anion). The cobalt ions are held together by four μ₃ and four μ₂ alkoxo bridges as well as by four syn-syn carboxylato groups. The hexanuclear motif contains four Co(II) and two Co(III) ions. The {Co^II₄Co^III₂(μ₂-O)₄(μ₃-O)₄} core can be described as a four face-sharing monovacant and bivacant distorted heterocubane units. The cobalt(III) ions are hexacoordinated. Two of the cobalt(II) are hexacoordinated, while the two others are pentacoordinated with a bipyramidal stereochemistry. The magnetic properties of 1 have been investigated in the temperature range 1.9-300 K. Compound 1 exhibits an overall antiferromagnetic behaviour with a ground singlet spin state.     

Comparative reactivity of triorganosilanes, HSi(OEt)3 and HSiEt3, with IrCl(CO)(PPh3)2. Formation of IrCl(H)2(CO)(PPh3)2 or Ir(H)2(SiEt3)(CO)(PPh3)2 depending on the substituents at Si

Reaction of HSi(OEt)₃ with IrCl(CO)(PPh₃)₂ (5:1 molar ratio) at room temperature for 1 h gives IrCl(H){Si(OEt)₃}(CO)(PPh₃)₂ (1), which is observed by the ¹H and ³¹P{¹H} NMR spectra of the reaction mixture. The same reaction, but in 20:1 molar ratio at 50 °C for 24 h produces IrCl(H)₂(CO)(PPh₃)₂ (2) rather than the expected product Ir(H)₂{Si(OEt)₃}(CO)(PPh₃)₂ (3) that was previously reported to be formed by this reaction. Accompanying formation of Si(OEt)₄, (EtO)₃SiOSi(OEt)₃, and (EtO)₂HSiOSi(OEt)₃ is observed. On the other hand, trialkylhydrosilane HSiEt₃ reacts with IrCl(CO)(PPh₃)₂ (10:1 molar ratio) at 80 °C for 84 h to give Ir(H)₂(SiEt₃)(CO)(PPh₃)₂ (4) in a high yield, accompanying with a release of ClSiEt₃.     

Dioxouranium complexes as ligand. Synthesis and characterization of sandwich-type polyoxometalates [X2W18(UO2)2{(H2O)3M}2O68] (X = As and P) (M = Co, Cu, Mn, Ni and Zn)

The title complexes are synthesized by the reaction of an unusual ligand of [K₂P₂W₁₈(UO₂)₂O₆₈]¹²⁻ (1) and [KAs₂W₁₈(UO₂)₂O₆₈]¹³⁻ (2) with divalent metal ions of Co^II, Cu^II, Mn^II, Ni^II and Zn^II in 1:2 mole ratio and are characterized by elemental analysis, IR, ³¹P NMR, UV-Vis spectroscopy, TGA, and single crystal structure analysis. Crystals of [P₂W₁₈(UO₂)₂{(H₂O)₃Co}₂O₆₈]¹⁰⁻ (1a) and [As₂W₁₈(UO₂)₂{(H₂O)₃Cu}₂O₆₈]¹⁰⁻ (2b) are orthorhombic space group Cmca. Both 1a and 2b have structures in which two [M(H₂O)₃] (M = Co^II, Cu^II) and two UO₂ groups are sandwiched between two symmetry equivalent (XW₉) (X = P, As) units in a virtual C_i symmetry. In solution, 1a and [P₂W₁₈(UO₂)₂{(H₂O)₃Zn}₂O₆₈]¹⁰⁻ (1d) give two-line P NMR spectra that are consistent with a C_s symmetry structures so, are not consistent with the solid-state structures. The sodium salts of them give one-line P NMR spectra and are consistent with the C_i symmetry of solid-state structures. The uranium atoms have pentagonal-bipyramidal coordination, achieved by three equatorial bonds to the one XW₉ and two bonds to the other. The M atoms have octahedral or square pyramidal coordination, but only one bond to the one XW₉ and one bond to the other.     

Synthesis and multinuclear magnetic resonance spectroscopy of the novel ionic Pt(II) mixed-ligands complexes cis- and trans-[Pt(amine)2(pyrimidine)2](NO3)2

Novel ionic mixed-ligands complexes of the types cis- and trans-[Pt(amine)₂(pm)₂](NO₃)₂ (where pm = pyrimidine) were synthesized and studied in the solid state by IR spectroscopy and in aqueous solution by multinuclear (¹⁹⁵Pt, ¹H and ¹³C) magnetic resonance spectroscopy. The results of the solution NMR characterization have shown that the isolated compounds are pure. In ¹⁹⁵Pt NMR, the cis RNH₂ complexes were observed at slightly lower fields (ave. −2441 ppm) than the equivalent trans analogues (ave. −2448 ppm). For Me₂NH, the difference between the two isomers is larger (29 ppm). The complexes are observed at lower fields (difference of 100 ppm) than the corresponding [Pt(amine)₄]²⁺ complexes, which might indicate the presence of π-backdonation in the Pt-pm bond. In ¹H NMR, the coupling constants ³J(¹⁹⁵Pt-¹H_amine) are larger in the cis compounds (38-48 Hz) than in the trans analogues (30-36 Hz). The ³J(¹⁹⁵Pt-¹H_pm) values are also larger for the cis isomers. In ¹³C NMR spectroscopy, the coupling constants ³J(¹⁹⁵Pt-¹³C_amine) are 36 Hz (ave.) for the cis complexes and 26 Hz (ave.) for the trans isomers, while the ²J(¹⁹⁵Pt-¹³C_amine) are 18 Hz (cis) and 14 Hz (trans), respectively. The ³J(¹⁹⁵Pt-¹³C_5(pm)) values are 36 Hz (cis) and 28 Hz (trans). A few ²J(¹⁹⁵Pt-¹³C_pm) couplings were observed (7-10 Hz).     

Synthesis and study of Pt(II)-aromatic amines complexes of the types cis- and trans-Pt(amine)2(NO3)2 and cis-Pt(amine)2(R(COO)2)

Complexes of the types cis- and trans-Pt(amine)₂(NO₃)₂ with amines containing a phenyl group were synthesized and studied mainly by IR and multinuclear magnetic resonance spectroscopies. The cis complexes could be synthesized pure only with the amines of the type Ph-R-NH₂ (R = alkyl), while pure trans compounds were synthesized with all the studied amines. In ¹⁹⁵Pt NMR spectroscopy, the dinitrato complexes of the amines Ph-R-NH₂ were observed around −1700 ppm for the cis isomers and at about −1580 for the trans complexes. For the other amines, where a phenyl ring is directly attached to the amino group, the signals were observed at lower fields, −1528 ppm for cis-Pt(PhNH₂)(NO₃)₂ and around −1450 ppm for all the trans isomers. There is a linear relationship between the δ(Pt) of the Pt(amine)₂(NO₃)₂ complexes and the pK_a of the protonated amines. The coupling constants ²J(¹⁹⁵Pt-¹HN) are larger in the cis compounds (ave. 76 Hz) than in the trans isomers (ave. 63 Hz). The complexes cis-Pt(amine)₂(R(COO)₂) with bidentate dicarboxylato ligands were also synthesized and characterized mainly by IR spectroscopy. The compounds apparently decompose in DMF and are too insoluble in other solvents for solution studies.     

Vibrational and structural mapping of [Os(bpy)3] and [Os(phen)3]

Structural changes between [Os^IIL₃]²⁺ and [Os^IIIL₃]³⁺ (L: 2,2′-bipyridine; 1,10-phenanthroline) and molecular and electronic structures of the Os^III complexes [Os^III(bpy)₃]³⁺ and [Os^III(phen)₃]³⁺ are discussed in this paper. Mid-infrared spectra in the ν(bpy) and ν(phen) ring stretching region for [Os^II(bpy)₃](PF₆)₂, [Os^III(bpy)₃](PF₆)₃, [Os^II(phen)₃](PF₆)₂, and [Os^III(phen)₃](PF₆)₃ are compared, as are X-ray crystal structures. Absorption spectra in the UV region for [Os^III(bpy)₃](PF₆)₃ and [Os^III(phen)₃](PF₆)₃ are dominated by very intense absorptions (ε = 40 000-50 000 M⁻¹ cm⁻¹) due to bpy and phen intra-ligand π → π^∗ transitions. In the visible region, relatively narrow bands with vibronic progressions of ∼1500 cm⁻¹ appear, and have been assigned to bpy or phen-based, spin-orbit coupling enhanced, ¹π → ³π^∗ electronic transitions. Also present in the visible region are ligand-to-metal charge transfer bands (LMCT) arising from π(bpy) → t_2g(Os^III) or π(phen) → t_2g(Os^III) transitions. In the near infrared, two broad absorption features appear for oxidized forms [Os^III(bpy)₃](PF₆)₃ and [Os^III(phen)₃](PF₆)₃ arising from dπ-dπ interconfigurational bands characteristic of dπ⁵Os^III. They are observed at 4580 and 5090 cm⁻¹ for [Os^III(bpy)₃](PF₆)₃ and at 4400 and 4990 cm⁻¹ for [Os^III(phen)₃](PF₆)₃. The bpy and phen infrared vibrational bands shift to higher energy upon oxidation of Os(II) to Os(III). In the cation structure in [Os^III(bpy)₃](PF₆)₃, the Os^III atom resides at a distorted octahedral site, as judged by ∠N-Os-N, which varies from 78.78(22)° to 96.61(22)°. Os-N bond lengths are also in general longer for [Os^III(bpy)₃](PF₆)₃ compared to [Os^II(bpy)₃](PF₆)₂ (0.010 Å), and for [Os^III(phen)₃](PF₆)₃ compared to [Os^II(phen)₃](PF₆)₂ (0.014 Å). Structural changes in the ligands between oxidation states are discussed as originating from a combination of dπ(Os^II) → π^∗ (bpy or phen) backbonding and charge redistribution on the ligands as calculated by natural population analysis.     

A trinuclear copper(II) complex with 2,5-pyridine-dicarboxylato bridges - [Cu3(2,5-pydc)2(Me5dien)2(H2O)2(BF4)2] · H2O: Synthesis, crystal structure and magnetic properties

A trinuclear copper(II) complex, [Cu₃(2,5-pydc)₂(Me₅dien)₂(BF₄)₂(H₂O)₂] · H₂O 1, has been constructed from 2,5-pyridine-dicarboxylato bridges (2,5-pydc²⁻) and N,N,N′,N″,N″-pentamethyl-diethylenetriamine (Me₅dien) acting as a blocking ligand. The copper ions, within the centrosymmetric trinuclear cations, are connected by two 2,5-pydc²⁻ bridges, with an intramolecular Cu···Cu separation of 8.432 Å. The central copper ion exhibits an elongated octahedral geometry, with semicoordinated ions, while the terminal ones are pentacoordinated (distorted square-pyramidal geometry). The cryomagnetic investigation of 1 reveals an antiferromagnetic coupling of the copper(II) ions (J = −5.9 cm⁻¹, H = −JS_Cu1S_Cu2 − JS_Cu2S_Cu1a).