Synthesis, crystal structure and magnetic properties of a chain coordination polymer {[Cu4L2(H2O)] · H2O}n

A chain coordination polymer with the chemical formula {[Cu₄L₂(H₂O)] · H₂O}_n, has been synthesized by the assembly reaction of K₂CuL · 1.5H₂O and Cu(OAC)₂ · H₂O with a 1:1 mole ratio in methanol, where H₄L = 2-hydroxy-3-[(E)-({2-[(2-hydroxybenzoyl)imino]ethyl}imino)methyl] benzoic acid, OAC⁻ = CH₃COO⁻. The crystal structure was determined by single-crystal X-ray diffraction analysis, the compound has chain molecular structure formed by dissymmetrical tetranuclear units. The magnetic measurements showed that Cu-Cu of the complex exhibit antiferromagnetic interactions, and satisfactory fittings to the observed magnetic susceptibility data were obtained by assuming a binuclear system, and further using molecular field approximation to deal with magnetic exchange interactions between binuclear systems.     

A seven-coordinate Fe compound: [Fe{O(CH2CO2)2}(H2O)2(NO3)]. Preparation, structure and magnetic properties

A seven-coordinate Fe^III complex, [Fe(oda)(H₂O)₂(NO₃)], was obtained after dissolving Fe(NO₃)₃ · 9H₂O in an aqueous solution of oxydiacetic acid (H₂oda) at room temperature. In the solid state, the Fe^III center adopts a pentagonal bipyramid geometry with an {FeO₇} core formed by a tridentate oda²⁻ and a bidentate in the equatorial plane, and two axial water molecules. Magnetic measurements and EPR spectra revealed the presence of S = 5/2 Fe^III centers with rhombic zero field splitting parameters (D = 0.81 cm⁻¹, E/D = 0.33 ). Weak antiferromagnetic interactions with J ≈ −0.06 cm⁻¹ operating between neighboring Fe ions connected through Fe-O-C-O?H-O-Fe paths are estimated using the molecular field approximation.     

Interactions of tertiary phosphines with p-benzoquinones; X-ray structures of [HO(CH2)3]3PC6H2(O)(OH)(MeO) and Ph3PC6H3(O)(OH)

Phosphonium zwitterions of a known type were obtained in high yield via a 1:1 reaction of p-benzoquinone or methoxy-p-benzoquinone with the tertiary phosphines R₃P [R = (CH₂)₃OH, Ph, Et, Me] and Ph₂MeP, in acetone or benzene at room temperature. In all cases, attack of the P-atom occurs at a C-atom rather than at an O-atom. The products were characterized to various degrees by elemental analysis, ³¹P{¹H}, ¹H and ¹³C NMR spectroscopies, and mass spectrometry, and two of the zwitterions, the new [HO(CH₂)₃]₃P⁺C₆H₂(O⁻)(OH)(MeO) and the known Ph₃P⁺C₆H₃(O⁻)(OH), were structurally characterized by X-ray analysis. The PEt₃ reaction also produces small amounts of the ‘dimeric’, μ-oxo co-product Et₃P⁺C₆H₂(O⁻)(OH)-O-C₆H₃(O⁻)P⁺Et₃ that is tentatively characterized by 1D- and 2D-NMR data. 2,5-Di-tert-butyl- and 2,3,5,6-tetramethyl-p-benzoquinone do not react with [HO(CH₂)₃]₃P under the conditions noted above. Heating D₂O solutions of the water-soluble zwitterions R₃P⁺C₆H₃(O⁻)(OH) [R = (CH₂)₃OH, Et] at 90 °C for 72 h leads to complete H/D exchange of the H-atom in the position ortho to the phosphonium center.     

Aqueous acid-base chemistry involving dioxovanadium(V) complexes of 2,6-pyridinedimethanol, and the X-ray structures of Na[VO2{2,6-(OCH2)2NC5H3}] · 4H2O and [1-H-2,6-(HOCH2)2NC5H3]Cl

Reaction of NH₄VO₃ with 2,6-pyridinedimethanol in water at 85 °C followed by the room temperature addition of HCl (aq) yields [HVO₂(pydim)]_x (pydim = 2,6-pyridinedimethanolato dianion), as a sparingly soluble off-white solid. This acid may be deprotonated by titration with NaOH (aq), yielding Na[VO₂(pydim)] · 4H₂O, which has been structurally characterized by single-crystal X-ray diffraction. Treating Na[VO₂(pydim)] · 4H₂O with HCl (aq) regenerates [HVO₂(pydim)]_x, but reaction with additional NaOH (aq) displaces the pyridinedimethanolato ligand from the vanadium center. Similarly, treating [HVO₂(pydim)]_x with excess HCl (aq) strips the pyridinedimethanolato ligand from the vanadium center and yields the adduct [H₃(pydim)]⁺Cl⁻ as one component in a mixture of products. This adduct has been structurally characterized by single-crystal X-ray diffraction. The optimum pH range for stable dioxovanadium(V) complexes stabilized by the 2,6-pyridinedimethanolato ligand is at least 1.5-9.4.     

Reactions of cyanooxo-molybdates and -tungstates with picolinic acid, 2-pyridinecarboxaldehyde and 2,2′-pyridil: X-ray crystal structure of (PPh4)2[Mo(CN)4O(pic)] · 2.5H2O

The syntheses of (PPh₄)₂[M(CN)₃O(pic)] · nH₂O (M = Mo, W; n = 2.5, 4; pic = picolinate anion) as well as (PPh₄)₂[Mo(CN)₄O(apic)] · 3H₂O (apic = 2-pyridinecarboxaldehyde) are presented. The salts have been characterised by elemental analysis, IR and UV-Vis spectroscopy, cyclic voltammetry and X-ray crystal structure determination of (PPh₄)₂[Mo(CN)₃O(pic)] · 2.5H₂O. The anion in the latter salt is approximately octahedral with O and N donor atoms of pic situated in the trans and cis position to the MoO bond, respectively. The picolinate complexes have the characteristic MLCT bands in the visible spectra with the absorption maxima linearly dependent on the Reichardt’s E_T solvent parameter. These complexes are shown to exhibit the strongest solvatochromic effect of all studied tricyanooxo and hexacyano complexes of Mo(IV) and W(IV). The obtained values of E_1/2 in these salts [0.333 V (Mo) and 0.018 V (W) in 1,2-C₂H₄Cl₂] were found to be the highest of all [M(CN)₃O(LL)]²⁻ type complexes making these salts show reversibility in a remarkable variety of solvents. The oxidation of coordinated apic to pic has been demonstrated by means of electronic spectroscopy. The isolated salts were used to monitor the reaction of [M(CN)₄O(H₂O)]²⁻ with 2,2′-pyridil in water-ethanol solution. It was found that 2,2′-pyridil disproportionate to Hpic and apic in the first step and the other decomposition products of 2,2′-pyridil postulated in the literature were not observed.     

2D network coordination polymers of lanthanide with N-(2-pyridylmethyl)iminodiacetic acid: Hydrothermal syntheses, crystal structures and luminescent properties

Six lanthanide two-dimensional network coordination polymers with the general formula of [Ln(pmida)(NO₃)(H₂O)]_n, where Ln = La (1), Nd (2), Sm (3), Gd (4), Dy (5), Er (6) and pmida²⁻ = N-(2-pyridylmethyl)iminodiacetate, have been synthesized by hydrothermal process and characterized by elemental analysis, Infrared spectroscopy, thermogravimetric analysis and single-crystal X-ray diffraction. All crystals are isostructural and crystallize in the monoclinic space group P2₁/a. The lanthanide(III) ion is nine-coordinated in a geometry of distorted tricapped trigonal prism by two N atoms and two O atoms from one pmida²⁻ ligand, two bridging carboxylate O atoms from other two pmida²⁻ ligands, two O atoms of a bidentate chelating nitrate and a O atom of a coordinated water molecule. The luminescent properties of [Sm(pmida)(NO₃)(H₂O)]_n (3) and [Dy(pmida)(NO₃)(H₂O)]_n (5) were investigated.     

New molybdenum(V) complexes based on the {Mo2O4} structural core with esters or anions of malonic and succinic acid

A series of malonato complexes of molybdenum(V) was prepared by reacting (PyH)₅[MoOCl₄(H₂O)]₃Cl₂ or (PyH)_n[MoOBr₄]_n with malonic acid (H₂mal) or a half-neutralized acid, hydrogen malonate (Hmal⁻), at ambient conditions: (PyH)₃[Mo₂O₄Cl₄(μ₂-Hmal)] · CH₃CN (1), (PyH)₃[Mo₂O₄Br₄(μ₂-Hmal)] · CH₃CN (2), (PyH)₂[Mo₂O₄Cl(η²-mal)(μ₂-Hmal)Py] (3), (3,5-LutH)₂(H₃O) [Mo₂O₄(η²-mal)₂(μ₂-Hmal)] (4), (PyH)[Mo₂O₄Cl₂(μ₂-Memal)Py₂] (5), (3,5-LutH)[Mo₂O₄Cl₂(μ₂-Memal)(3,5-Lut)₂] (6), (PyH)[Mo₂O₄Cl₂(μ₂-Etmal)Py₂] (7), (3,5-LutH)[Mo₂O₄Cl₂(μ₂-Prmal)(3,5-Lut)₂] (8) and [{Mo₂O₄(μ₂-Memal)Py₂}₂(μ₂-OCH₃)₂] (9) (where Py = pyridine, C₅H₅N; PyH⁺ = pyridinium cation, C₅H₅NH⁺; 3,5-Lut = 3,5-lutidine, C₇H₉N; 3,5-LutH⁺ = 3,5-lutidinium cation, C₇H₉NH⁺; mal²⁻ = malonate, ⁻OOCCH₂COO⁻; Memal⁻ = monomethyl malonate, ⁻OOCCH₂COOCH₃; Etmal⁻ = monoethyl malonate, ⁻OOCCH₂COOC₂H₅ and Prmal⁻ = monopropyl malonate, ⁻OOCCH₂COOC₃H₇). The complex anions of compounds 1-8 have a common structural feature: a dinuclear, singly metal-metal bonded {Mo₂O₄}²⁺ core with the carboxylate moiety of the malonato ligand coordinated in a syn-syn bidentate bridging manner to the pair of metal atoms. The remaining four coordination sites of the {Mo₂O₄}²⁺ core are occupied with halides in 1 and 2, with halides/pyridine ligands in 5-8, with a pair of bidentate malonate ions in 4 and with the combination of all in 3. The neutral molecules of 9 consist of two {Mo₂O₄}²⁺ cores linked with a pair of methoxide ions into a chain-like, tetranuclear cluster. An esterification of malonic acid was observed to take place in the reaction mixtures containing alcohols. Solvothermal reactions with malonic acid carried out at 115 °C produced anionic acetato complexes as found in (PyH)[Mo₂O₄Cl₂(μ₂-OOCCH₃)Py₂] · Py (10), (PyH)[Mo₂O₄Cl₂(μ₂-OOCCH₃)Py₂] (11), (3,5-LutH)[Mo₂O₄Cl₂(μ₂-OOCCH₃)(3,5-Lut)₂] (12) and (4-MePyH)₃[Mo₂O₄Cl₂(μ₂-OOCCH₃)(4-MePy)₂]₂Cl (13) (4-MePy = 4-methylpyridine, C₆H₇N). The acetate coordinated in the syn-syn bidentate bridging mode in all. Reactions of (PyH)₅[MoOCl₄(H₂O)]₃Cl₂ with succinic acid (H₂suc) at ambient conditions resulted in a complex with a half-neutralized acid, (PyH)[Mo₂O₄Cl₂(μ₂-Hsuc)Py₂] · Py (14) (Hsuc⁻ = hydrogen succinate, ⁻OOC(CH₂)₂COOH), while those carried out at 115 °C in a tetranuclear succinato complex, (4-MePyH)₂[{Mo₂O₄Cl₂(4-MePy)₂}₂(μ₄-suc)] (15) (suc²⁻ = succinate, ⁻OOC(CH₂)₂COO⁻). The tetranuclear anion of 15 consists of two {Mo₂O₄}²⁺ cores covalently linked with a tetradentate succinato ligand. The compounds were fully characterized by infrared vibrational spectroscopy, elemental analyses and X-ray diffraction studies.     

Kinetic studies on the first dihydrogen aquacomplex, [Ru(H2)(H2O)5]: Formation under H2 pressure and catalytic H/D isotope exchange in water

The ruthenium(II) hexaaqua complex [Ru(H₂O)₆]²⁺ reacts with dihydrogen under pressure to give the η²-dihydrogen ruthenium(II) pentaaqua complex [Ru(H₂)(H₂O)₅]²⁺.The complex was characterized by ¹H, ²H and ¹⁷O NMR: δ_H = −7.65 ppm, J_HD = 31.2 Hz, δ_O = −80.4 ppm (trans to H₂) and δ_O = −177.4 ppm (cis to H₂).The H-H distance in coordinated dihydrogen was estimated to 0.889 Å from J_HD, which is close to the value obtained from DFT calculations (0.940 Å).Kinetic studies were performed by ¹H and ²H NMR as well as by UV-Vis spectroscopy, yielding the complex formation rate and equilibrium constants: k_f = (1.7 ± 0.2) × 10⁻³ kg mol⁻¹ s⁻¹ and K_eq = 4.0 ± 0.5 mol kg⁻¹.The complex formation rate with dihydrogen is close to values reported for other ligands and thus it is assumed that the reaction with dihydrogen follows the same mechanisn (I_d).In deuterated water, one can observe that [Ru(H₂)(H₂O)₅]²⁺ catalyses the hydrogen exchange between the solvent and the dissolved dihydrogen.A hydride is proposed as the intermediate for this exchange.Using isotope labeling, the rate constant for the hydrogen exchange on the η²-dihydrogen ligand was determined as k₁ = (0.24 ± 0.04) × 10⁻³ s⁻¹.The upper and lower limits of the pK_a of the coordinated dihydrogen ligand have been estimated:3 < pK_a < 14.     

New rhodium complexes of the tetradentate ligand bis(diacetylmonoxime-imino)propane 1,3 (H2dopn): synthesis and crystal structure of trans-[Rh(Hdopn)Cl]2 and trans-[Rh(Hdopn)(I)2]

The reaction between [Rh(H₂O)₆](ClO₄)₃ and the monoanion Hdopn⁻ (H₂dopn=bis(diacetylmonoxime-imino)propane 1,3=3,9-dimethyl-4,8-diazaundeca-3,8-diene-2,10-dione dioxime) afforded a new dimeric rhodium(II) compound of formula [Rh(Hdopn)(H₂O)]₂(ClO₄)₂ · H₂O (1). Treatment of methanolic solution of 1 with NaX (X=Cl⁻, Br⁻, I⁻) results in the replacement of water with halides in 1, leading to the formation of [Rh(Hdopn)X]₂ rhodium(II) dimers. The X-ray crystal structure of [Rh(Hdopn)Cl]₂ · 0.5H₂O (2) was determined showing a [Rh(II)-Rh(II)] core. Upon the reaction of 1 with NaI carried out in air, [Rh(Hdopn)(I)₂] (3) was isolated and characterized by a single-crystal X-ray diffraction analysis.     

Formation and structural chemistry of the unusual cyanide-bridged dinuclear species [Ru2(NN)2(CN)7] (NN = 2,2′-bipyridine or 1,10-phenanthroline)

Crystallisation of simple cyanoruthenate complex anions [Ru(NN)(CN)₄]²⁻ (NN = 2,2′-bipyridine or 1,10-phenanthroline) in the presence of Lewis-acidic cations such as Ln(III) or guanidinium cations results, in addition to the expected [Ru(NN)(CN)₄]²⁻ salts, in the formation of small amounts of salts of the dinuclear species [Ru₂(NN)₂(CN)₇]³⁻. These cyanide-bridged anions have arisen from the combination of two monomer units [Ru(NN)(CN)₄]²⁻ following the loss of one cyanide, presumably as HCN. The crystal structures of [Nd(H₂O)_5.5][Ru₂(bipy)₂(CN)₇] · 11H₂O and [Pr(H₂O)₆][Ru₂(phen)₂(CN)₇] · 9H₂O show that the cyanoruthenate anions form Ru-CN-Ln bridges to the Ln(III) cations, resulting in infinite coordination polymers consisting of fused Ru₂Ln₂(μ-CN)₄ squares and Ru₄Ln₂(μ-CN)₆ hexagons, which alternate to form a one-dimensional chain. In [CH₆N₃]₃[Ru₂(bipy)₂(CN)₇] · 2H₂O in contrast the discrete complex anions are involved in an extensive network of hydrogen-bonding involving terminal cyanide ligands, water molecules, and guanidinium cations. In the [Ru₂(NN)₂(CN)₇]³⁻ anions themselves the two NN ligands are approximately eclipsed, lying on the same side of the central Ru-CN-Ru axis, such that their peripheries are in close contact. Consequently, when NN = 4,4′-^tBu₂-2,2′-bipyridine the steric bulk of the t-butyl groups prevents the formation of the dinuclear anions, and the only product is the simple salt of the monomer, [CH₆N₃]₂[Ru(^tBu₂bipy)(CN)₄] · 2H₂O. We demonstrated by electrospray mass spectrometry that the dinuclear by-product [Ru₂(phen)₂(CN)₇]³⁻ could be formed in significant amounts during the synthesis of monomeric [Ru(phen)(CN)₄]²⁻ if the reaction time was too long or the medium too acidic. In the solid state the luminescence properties of [Ru₂(bipy)₂(CN)₇]³⁻ (as its guanidinium salt) are comparable to those of monomeric [Ru(bipy)(CN)₄]²⁻, with a ³MLCT emission at 581 nm.     

Structural and equilibrium studies on mixed ligand complexes of Co(II), Ni(II), Cu(II) and Zn(II) with N-(2-benzimidazolyl)methyliminodiacetic acid and typical N, N donor ligands

Mixed ligand complexes: [Co(L)(bipy)] · 3H₂O (1), [Ni(L)(phen)] · H₂O (2), [Cu(L)(phen)] · 3H₂O (3) and [Zn(L)(bipy)] · 3H₂O (4), where L²⁻ = two -COOH deprotonated dianion of N-(2-benzimidazolyl)methyliminodiacetic acid (H₂bzimida, hereafter, H₂L), bipy = 2,2′ bipyridine and phen = 1,10-phenanthroline have been isolated and characterized by elemental analysis, spectral and magnetic measurements and thermal studies. Single crystal X-ray diffraction studies show octahedral geometry for 1, 2 and 4 and square pyramidal geometry for 3. Equilibrium studies in aqueous solution (ionic strength I = 10⁻¹ mol dm⁻³ (NaNO₃), at 25 ± 1 °C) using different molar proportions of M(II):H₂L:B, where M = Co, Ni, Cu and Zn and B = phen, bipy and en (ethylene diamine), however, provides evidence of formation of mononuclear and binuclear binary and mixed ligand complexes: M(L), M(H₋₁L)⁻, M(B)²⁺, M(L)(B), M(H₋₁L)(B)⁻, M₂(H₋₁L)(OH), (B)M(H₋₁L)M(B)⁺, where H₋₁L³⁻ represents two -COOH and the benzimidazole N₁-H deprotonated quadridentate (O⁻, N, O⁻, N), or, quinquedentate (O⁻, N, O⁻, N, N⁻) function of the coordinated ligand H₂L. Binuclear mixed ligand complex formation equilibria: M(L)(B) + M(B)²⁺ ? (B)M(H₋₁L)M(B)⁺ + H⁺ is favoured with higher π-acidity of the B ligands. For Co(II), Ni(II) and Cu(II), these equilibria are accompanied by blue shift of the electronic absorption maxima of M(II) ions, as a negatively charged bridging benzimidazolate moiety provides stronger ligand field than a neutral one. Solution stability of the mixed ligand complexes are in the expected order: Co(II) < Ni(II) < Cu(II) > Zn(II). The Δ log K_M values are less negetive than their statistical values, indicating favoured formation of the mixed ligand complexes over the binary ones.     

Syntheses, crystal structures, and magnetic properties of two cyclic dimer M2L2 complexes constructed from a new nitronyl nitroxide ligand and M(hfac)2 (M = Cu, Mn)

Two new binuclear radical complexes derived from a new long nitronyl nitroxide ligand, 2-[4-(5-pyrimidyl)phenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (4-NITPhPyrim), and M(hfac)₂ (M²⁺ = Cu²⁺, Mn²⁺; hfac⁻ = hexafluoroacetylacetonato), [Cu(hfac)₂(4-NITPhPyrim)]₂ · 4H₂O (1) and [Mn(hfac)₂(4-NITPhPyrim)]₂ · 4H₂O (2), were synthesized as well as characterized structurally and magnetically. X-ray analysis indicates that 1 and 2 are rectangle-like centrosymmetric dimer M₂L₂ complexes. Magnetic measurements indicate that there are two types of magnetic exchanges in 1: the ferromagnetic (FM) exchange between the Cu(II) ion and the directly bonded nitroxide unit (J₁ = 24.20 cm⁻¹) and the weak FM exchange of Cu-NIT through the pyrimidine and phenyl rings (J₂ = 0.62 cm⁻¹). Besides the strong antiferromagnetic (AFM) coupling between the Mn(II) ion and the directly bonded nitroxide unit (J = −87.61 cm⁻¹), there is a weak FM interaction between the two Mn-NIT pairs (θ = 0.39 K) in 2.     

Square-planar copper(II) complexes with tetradentate amido-carboxylate ligands. Crystal structure of Na2[Cu(obap)]2 · 2H2O. Strain analysis and spectral assignments of complexes

Novel N-N-N-O-type of tetradentate ligands H₃obap (H₃obap = oxamido-N-aminopropyl-N′-benzoic acid) and H₃maeb (H₃maeb = malamido-N-aminoethyl-N′-benzoic acid) and the corresponding square-planar copper(II) complexes have been prepared and characterized. The obap³⁻ and maeb³⁻ ligands coordinate to the copper(II) ion via four ligating atoms (three deprotonated atoms: one carboxylate oxygen and two deprotonated amide nitrogens; one amine nitrogen) with in-plane square chelation. A four coordinate, square-planar geometry has been established crystallographically for the binuclear Na₂[Cu(obap)]₂ · 2H₂O complex. Structural data correlating the square-planar geometry of the [Cu(obap)]⁻ unit and an extensive strain analysis are discussed in relation to the information obtained for similar complexes. The infrared and electronic absorption spectra of the complexes are discussed in comparison to the related complexes of known geometries. Antibacterial activity of ligands and copper(II) complexes towards common Gram-negative and Gram-positive bacteria are reported as well.     

Synthesis, structure, magnetic and electrochemical properties of an oxydiacetate iron(II) complex

Compound [{Fe(oda)(H₂O)₂} · H₂O]_n (1) [oda=O(CH₂COO)₂ ²⁻] has been obtained by reaction of FeCl₂ · 4H₂O with a 1:1 mixture of O(CH₂COOH)₂ and Na₂CO₃ in water. The structure is polymeric with concatenated {Fe(oda)(H₂O)₂} units extended in one direction. Each iron centre is six-coordinated by the tridentate planar oda ligand, two mutually trans water molecules and one oda oxygen atom from an adjacent {Fe(oda)(H₂O)₂} unit. Complex 1 is isomorphous with cobalt and zinc analogues. Magnetic susceptibility measurements down to 2 K showed high-spin non-correlated Fe(II) ions with a typical Curie-Weiss behaviour. Differential-pulse voltammetry establishes a value of 0.488 V versus NHE for the Fe(III)/Fe(II) redox potential of this iron complex in 0.25 mol dm⁻³ NaNO₃.     

Multinuclear magnetic resonance study of Pt(II) compounds with sulfoxide ligands and crystal structures of complexes of the types [Pt(R2SO)X3] and Pt(R2SO)2Cl2

Pt(II) complexes of the types K[Pt(R₂SO)X₃], NR₄[Pt(R₂SO)X₃] and Pt(R₂SO)₂Cl₂ (where X = Cl or Br) were characterized by multinuclear magnetic resonance spectroscopy (¹⁹⁵Pt, ¹H and ¹³C). In ¹⁹⁵Pt NMR, the chloro ionic compounds have shown signals between −2979 and −3106 ppm, while the cis disubstituted complexes were observed at higher fields, between −3450 and −3546 ppm. The signal of the compound trans-Pt(DPrSO)₂Cl₂ was found at higher field (−3666 ppm) than its cis analogue (−3517 ppm), since π-back-donation is considerably less effective in the trans geometry. In ¹H NMR, a single signal was observed for the sulfoxide in [Pt(DMSO)Cl₃]⁻, but for the other more sterically hindered ligands, two series of resonances were observed for the protons in α and β positions. The coupling constant ³J(¹⁹⁵Pt-¹H) are between 15 and 33 Hz. The ¹³C NMR results were interpreted in relation to the concept of inversed polarization of the π sulfoxide bond. The ²J(¹⁹⁵Pt-¹³C) values vary between 35 and 66 Hz, while a few ³J(¹⁹⁵Pt-¹³C) couplings were observed (13-26 Hz). The crystal structures of five monosubstituted ionic compounds N(n-Bu)₄[Pt(TMSO)Cl₃], N(Me)₄[Pt(DPrSO)Cl₃], K[Pt(EMSO)Cl₃], K[Pt(TMSO)Br₃] · H₂O and N(Et)₄[Pt(DPrSO)Br₃] and one disubstituted complex cis-Pt(DBuSO)₂Cl₂ were determined. The trans influence of the different ligands is discussed.     

Aminocarboxylate complexes of vanadium(III): Electronic structure investigation by high-frequency and -field electron paramagnetic resonance spectroscopy

Aminocarboxylate complexes of vanadium(III) are of interest as models for biologically and medicinally relevant forms of this interesting and somewhat neglected ion. The V(III) ion is paramagnetic, but not readily suited to conventional EPR, due to its integer-spin ground state (S = 1) and associated large zero-field splitting (zfs). High-frequency and -field EPR (HFEPR), however, has the ability to study such systems effectively. Three complexes, all previously structurally characterized: Na[V(trdta)] · 3H₂O, Na[V(edta)(H₂O)] · 3H₂O, and [V(nta)(H₂O)₃] · 4H₂O (where trdta stands for trimethylenediamine-N,N,N′,N′-tetraacetate and nta stands for nitrilotriacetate) were studied by HFEPR. All the investigated complexes produced HFEPR responses both in the solid state, and in aqueous solution, but those of [V(nta)(H₂O)₃] · 4H₂O were poorly interpretable. Analysis of multi-frequency HFEPR spectra yielded a set of spin Hamiltonian parameters (including axial and rhombic zfs parameters: D and E, respectively) for these first two complexes as solids: Na[V(trdta)] · 3H₂O: D = 5.60 cm⁻¹, E = 0.85 cm⁻¹, g = 1.95; Na[V(edta)(H₂O)] · 3H₂O: D = 1.4 cm⁻¹, E = 0.14 cm⁻¹, g = 1.97. Spectra in frozen solution yielded similar parameters and showed multiple species in the case of the trdta complex, which are the consequence of the flexibility of this ligand. The EPR spectra obtained in frozen aqueous solution are the first, to our knowledge, of V(III) in solution in general and show the applicability of HFEPR to these systems. In combination with very insightful previous studies of the electronic absorption of these complexes which provided ligand-field parameters, it has been possible to describe the electronic structure of V(III) in [V(trdta)]⁻ and [V(edta)(H₂O)]⁻; the quality of data for [V(nta)(H₂O)₃] does not permit analysis. Qualitatively, six-coordinate V(III) complexes with O,N donor atoms show no electronic absorption band in the NIR region, and exhibit relatively large magnitude zfs (D ? 5 cm⁻¹), while analogous seven-coordinate complexes do have a NIR absorption band and show relatively small magnitude zfs (D < 2 cm⁻¹).     

Single molecule magnet: Heterodinuclear cyano-bridged cubic cluster [(Tp)8Fe4Ni4(CN)12] (Tp = hydrotris(1-pyrazolyl)borate)

The octanuclear cyano-bridged cluster [(Tp)₈Fe₄Ni₄(CN)₁₂] · H₂O · 24CH₃CN (1) (Tp = hydrotris(1-pyrazolyl)borate) showing magnetic properties of single-molecule magnet has been synthesized by reaction of [fac-Fe(Tp)(CN)₃]⁻ with {(Tp)Ni(NO₃)} species formed from an equimolar reaction mixture of Ni(NO₃)₂ · 6H₂O and KTp in MeCN. The X-ray analysis of 1 shows molecular cube structure in which Fe^III and Ni^II ions reside in alternate corners. The average intramolecular Fe?Ni distance is 5.124 Å. Out-of-phase ac susceptibility and reduce magnetization measurements show that 1 is a single molecule magnet with ground spin state S = 6 and spin reversal energy barrier U = 14 K. Magnetic hysteresis loops were also observed by applying fast sweeping field.     

Metal complexes with the ligand derived from 6-acetyl-1,3,7-trimethyllumazine and benzohydrazide. Molecular structures of two new Co(II) and Rh(III) complexes and analysis of in vitro antitumor activity

The structures and spectroscopic properties of new Mn(II), Co(II), Cd(II), Hg(II), Ag(I), Rh(III), and Ir(I) complexes with the ligand BZLMH derived from 6-acetyl-1,3,7-trimethyllumazine (lumazine = pteridine-2,4(1H,3H)-dione) and benzohydrazide are reported. Complexes have been characterized by elemental analyses, spectroscopic studies (IR, UV-vis, ¹H, ¹³C and ¹⁵N NMR) and magnetic measurements. In all the complexes, the lumazine-derived ligand appears to be coordinated in either tridentate (N5, N61 and O63) or tetradentate forms (O4, N5, N61 and O63). The molecular structures of the [Co(BZLMH)(H₂O)(CH₃CN)₂](ClO₄)₂ · CH₃CN and [RhCl₂(BZLM)(CH₃CN)] · CH₃CN complexes, determined by single crystal X-ray diffraction, have allowed to corroborate both coordination behaviours.The cytotoxic activity of the free ligand and complexes against human neuroblastoma NB69 cell line is also described. The differential analysis of the initial cytotoxic screening data has shown good activity only for the [RhCl₂(BZLM)(CH₃CN)] · CH₃CN compound at concentrations at around 2 μM; for the other complexes, a modulation of the cell growth was not found upon complexation, this non-specific effect strongly suggesting an apoptotic behaviour.     

The preparation and structural elucidation of uranium (VI) complexes and salts of the phosphorus ylides Ph3PCHCOPh, Ph3PC(COMe)(COPh) and Ph3PCHCOOCH2CH3

The reaction in methanol of the phosphorus ylides Ph₃PCHCOPh, benzoylmethylenetriphenylphosphorane (BPPY), and Ph₃PC(COMe)(COPh), α-acetyl-α-benzoylmethylenetriphenylphosphorane (ABPPY) with UO₂(NO₃)₂ · 6H₂O at 273 K leads to the formation of O-coordinated bis(ylide)-uranium (VI) complexes of the type [UO₂(ylide)₂(NO₃)₂], whereas the reaction of BPPY and UO₂(NO₃)₂ · 6H₂O under reflux in benzene yields the salt . The reaction of Ph₃PCHCOOCH₂CH₃, carbethoxymethylenetriphenylphosphorane (EPPY) with UO₂(CH₃COO)₂ · 2H₂O produces the salt [H-EPPY]⁺[UO₂(CH₃COO)₃]⁻. The structures of the free ylides ABPPY and EPPY are also discussed.     

Synthesis and characterization of chromium(III) octaphenylporphyrin complexes with various axial ligands: An insight into porphyrin distortion

Influence of axial ligands, MeCN, H₂O, py, and piperidine (pip), on distortion of (2,3,5,10,12,13,15,20-octaphenylporphinato)chromium(III), [Cr(OPP)]⁺, was investigated by X-ray crystallography and UV-vis and ESR spectroscopies. In crystal structures of [Cr(OPP)(MeCN)(H₂O)]ClO₄ · MeCN and [Cr(OPP)(H₂O)₂]ClO₄ · 3THF, the OPP²⁻ ligand had a planar structure. On the other hand, crystal structures of [Cr(OPP)(pip)₂]ClO₄ · 2CH₂Cl₂ and [Cr(OPP)(py)₂]ClO₄ exhibited a waved structure and a saddle-shaped structure with ruffling, respectively. In the UV-vis spectrum of [Cr(OPP)(py)₂]ClO₄ in CH₂Cl₂, the large red shift of the Soret band was observed. Furthermore, the small D value of 0.10 cm⁻¹ was obtained for [Cr(OPP)(py)₂]ClO₄ from the ESR spectrum in frozen 1,2-dichloroethane solution at 5 K. These results suggest that the OPP²⁻ ligand is distorted both in solid and in solution, and that the axial ligand would exert some effects on the porphyrin distortion.