Interconversion between cyclodimer and cyclotrimer: Synthesis and characterization of cyclo-[Pd(II)Cl2(N-N)] complexes

The reaction of (COD)PdCl₂ (COD = 1,5-cyclooctadiene) with (3-Py)₂SiR₁R₂ (3-Py = 3-pyridyl; R₁ = Ph, R₂ = Ph (m-pdps); R₁ = Ph, R₂ = Me (m-pmps)) in acetone affords single crystals consisting of cyclodimers, [PdCl₂((3-Py)₂SiR₁R₂)]₂, whereas the same reaction in a mixture of dichloromethane and ethanol yields amorphous spheres consisting of cyclotrimers, [PdCl₂((3-Py)₂SiR₁R₂)]₃. In a boiling chloroform solution, the cyclodimers are completely converted to cyclotrimers. These cyclotrimers, in the 10−60 °C range, are partly returned to cyclodimers. By contrast, the reaction of (COD)PdCl₂ with (3-Py)₂SiR₁R₂ (R₁ = Bu, R₂ = Me (m-pbms); R₁ = dodecyl, R₂ = Me (m-pddms)) yields amorphous spheres consisting of cyclotrimers irrespective of solvents. Both [PdCl₂(m-pbms)]₃ and [PdCl₂(m-pddms)]₃ are initially cyclotrimers in chloroform, but they exist as a mixture of cyclodimers and cyclotrimers in solution in the 10−60 °C range. The metallacycles tend to form cyclodimers in the order m-pdps > m-pmps > m-pbms > m-pddms. The equilibrium between cyclodimers and the cyclotrimers is sensitive to solvent, temperature, and concentration as well as molecular structure.     

Copper(II) complexes as superoxide dismutase mimics: Synthesis, characterization, crystal structure and bioactivity of copper(II) complexes

Two new copper(II) complexes of the type [Cu(L)X₂), where L = (E)-N-phenyl-2-[phenyl (pyridine-2-yl)methylene]hydrazinecarboxamide X = Cl/Br have been synthesized and characterized by elemental analyses, FAB (fast atomic bombardment) magnetic measurements, electronic absorption, conductivity measurements cyclic voltammetry (CV) and Electron paramagnetic resonance (epr) spectroscopy. The structures of these complexes determined by single crystal X-ray crystallography show a distorted square based pyramidal (DSBP) geometry around copper(II) metal center. The distorted CuN₂OX (X = Cl/Br) basal plane in them is comprised of two nitrogen and one oxygen atoms of the meridionally coordinated ligand and a chloride or bromide ion and axial position is occupied by other halide ion. The epr spectra of these complexes in frozen solutions of DMSO showed a signal at g ca. 2. The trend in g-value (g_|| > g_⊥ > 2.00) suggest that the unpaired electron on copper(II) has d_x²-y² character. Biological activities in terms of superoxide dismutase (SOD) and antimicrobial properties of copper(II) complexes have also been measured. The superoxide dismutase activity reveals that these two complexes catalyze the fast disproportionation of superoxide in DMSO solution.     

Synthesis and structure of monoribbed-functionalized disulfide iron(II) clathrochelates and their coordination as the ligands toward platinum(II) and platinum(IV) ions

Disulfide monoribbed-functionalized clathrochelates (i.e., fuctionalization of one of the three α-dioximate fragments) with ribbed thioalkyl, S₃-thioalkyl and hydroxythioalkyl substituents have been synthesized starting from the FeBd₂(Cl₂Gm)(BF)₂ precursor (where Bd²⁻ and Cl₂Gm²⁻ are α-benzyldioxime and dichloroglyoxime dianions) using the corresponding thiol/triethylamine system in dichloromethane solution. Clathrochelate S₆-dithiol in basic media underwent the intramolecular dealkylation to yield the S₃-thiocrown etheric clathrochelate. Clathrochelates obtained have been studied as the ligands toward Pt²⁺ and Pt⁴⁺ ions. The S-demethylation reaction of the methylsulfide complex with [PtCl₄]²⁻ dianion produced the polynuclear complexes of the dianionic clathrochelate dithiolate ligand. The reaction of n-butylsulfide clathrochelate with the trans-Pt^IVCl₄(C₆H₅CH₂CN)₂ afforded the binuclear compound with the disulfide iron(II) clathrochelate as a monodentate ligand. The obtained macrobicycles, their clathrochelate derivatives, and polynuclear complexes have been characterized using elemental analysis, MALDI-TOF and PD mass, IR, UV-Vis, and NMR spectra, and X-ray crystallography. The encapsulated iron(II) ion coordination polyhedra distortion angle φ values and the main distances in the molecules of polynuclear complexes have been deduced (obtained) using ⁵⁷Fe Mössbauer parameters and EXAFS data, respectively.     

Synthesis and characterization of new ruthenium(II) complexes containing coupled di(2-pyridyl) and 1,3-dithiole units

Two new ruthenium (II) complexes containing coupled di(2-pyridyl) and 1,3-dithiole units, cis-[Ru(Medpydt)₂(NCS)₂] (2, Medpydt = dimethyl 2-(di(2-pyridyl)methylene)-1,3-dithiole-4,5-dicarboxylate) and cis-[Ru(H₂dpydt)₂(NCS)₂] (3, H₂dpydt = 2-(di(2-pyridyl)methylene)-1,3-dithiole-4,5-dicarboxylate), have been synthesized and characterized. The structure of complex 2 has been determined by X-ray crystallography. There exist intermolecular H-bonding interactions between carbomethoxy groups on neighboring pyridine rings giving rise to 2D H-bonded arrays. The metal-to-ligand charge-transfer (MLCT) absorptions were observed around 480 nm. Redox properties of ruthenium complexes have been investigated by cyclic voltammetry. Solar cells involving thin films of anatase TiO₂ impregnated with cis-[Ru(H₂dpydt)₂(NCS)₂] were prepared, and the photovoltaic performance was preliminarily investigated.     

Low-spin, mononuclear, Fe(III) complexes with P,N donor hemilabile ligands: A combined experimental and theoretical study

Two new mononuclear Fe(III) complexes, [FeCl₃{PPh₂(p-C₆H₄NMe₂)-P}₃](1) (PPh₂(p-C₆H₄NMe₂): 4-(dimethylamino)phenyldiphenylphosphine) and [FeCl₃(PPh₂py-P)(PPh₂py-P,N)] (2) (PPh₂py: diphenyl(2-pyridyl)phosphine) were synthesized by reacting anhydrous FeCl₃ with respective ligand in acetonitrile solution under refluxing condition. Both the complexes were characterized by elemental analysis, FAB-Mass, FTIR, UV-Vis, ESR, Cyclic Voltammetry and magnetic measurement. The FAB mass spectra of complexes 1 and 2 show molecular ion peak at m/z 1078 [M]⁺ and m/z 687 [M−1]⁺, respectively, indicating mononuclear nature of the complexes. UV-Vis spectra of the complexes were consistent with low-spin, octahedral geometry. The variable temperature magnetic susceptibility measurement (73-323 K) of these complexes is also consistent with the paramagnetic nature of the complexes with a ground state spin S = ½. The Fe(III) centers of these two complexes remain low-spin, both at room temperature and liquid nitrogen temperature, was also indicated by the ESR analysis. Cyclic Voltammetry of both the complexes show an irreversible oxidation wave attributed to Fe³⁺ → Fe⁴⁺ + e⁻ along with the peak for ligand oxidation. Theoretical calculations (B3LYP) of the complexes show that for complex 1, a trans geometry of the two phosphorous atoms and for complex 2, a mer,cis structures are the most favored geometrical isomer. TDDFT calculations were performed to interpret the observed bands in the UV-Visible spectra.     

Novel dioxomolybdenum(VI) and oxomolybdenum(V) complexes with pyridoxal thiosemicarbazone ligands: Synthesis and structural characterisation

New molybdenum complexes were prepared by the reaction of [Mo^VIO₂(acac)₂] or (NH₄)₂[Mo^VOCl₅] with different N-substituted pyridoxal thiosemicarbazone ligands (H₂L¹ = pyridoxal 4-phenylthiosemicarbazone; H₂L² = pyridoxal 4-methylthiosemicarbazone, H₂L³ = pyridoxal thiosemicarbazone). The investigation of monomeric [MoO₂L¹(CH₃OH)] or polymeric [MoO₂L^1-3] molybdenum(VI) complexes revealed that molybdenum is coordinated with a tridentate doubly-deprotonated ligand. In the oxomolybdenum(V) complexes [MoOCl₂(HL^1-3)] the pyridoxal thiosemicarbazonato ligands are tridentate mono-deprotonated. Crystal and molecular structures of molybdenum(VI) [MoO₂L¹(CH₃OH)]·CH₃OH, and molybdenum(V) complexes [MoOCl₂(HL¹)]·C₂H₅OH, as well as of the pyridoxal thiosemicarbazone ligand methanol solvate H₂L³·MeOH, were determined by the single crystal X-ray diffraction method.     

Solid-state and proton NMR characterization of an iron(II) complex of a tridentate, facially coordinating N,N,O donor ligand

Despite the many enzymes that use 2-His-1-carboxylate facial triads to bind iron(II), there are few crystallographically characterized synthetic iron(II) complexes of tridentate ligands that bind through two imidazoles and one carboxylate. We report ¹H NMR characterization of the equilibrium between one such ligand and aqueous Fe²⁺. The formation of 1:1 and 2:1 complexes is evident, but the 1:1 complex is never the exclusive compound in solution. This behavior has not been reported previously for N,N,O ligand-iron(II) complexes. The 2:1 ligand/iron complex crystallizes from solution, and it has been completely characterized including an X-ray crystal structure.     

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.     

Polynuclear and polymeric metal complexes based upon 1,2,4-triazolyl functionalized adamantanes

A series of coordination compounds [Cd₂(trad)₇Br₂][Cd(trad)Br₃]₂ (1), [Cd₃(trad)₆{N(CN)₂}₄(H₂O)₂](N(CN)₂)₂ (2), [{Cd₂(trad)₅}{Cd(N(CN)₂)₆}]·3CH₃OH (3), [{Cd₃(trad)₆(SeCN)₂}{Cd(SeCN)₄}₂] (4), [Cd₂(trad)₃(NCS)₄] (5), [Cd₃(tr₂ad)₃(μ-NCS)₃](NCS)₃ (6), [Cd₃(tr₂ad)₆](NO₃)₆·22H₂O (7), [Cu₃(tr₂ad)₄(SO₄)(H₂O)₃](SO₄)₂·34H₂O (8) and [Cu₂(OH)(tr₂ad)₂](NO₃)₃·4H₂O (9) (trad = 4-(adamantan-1-yl)-1,2,4-triazole; tr₂ad = 1,3-bis(1,2,4-triazol-4-yl)-adamantane) revealed the potential of 1,2,4-triazolyl functionalized adamantanes for design of metal-organic polymers incorporating polynuclear coordination units as multiconnected nodes. Structures 1-5 are based upon characteristic di- and trinuclear clusters involving triple triazole bridges [M(μ₂-trad)₃M] (M = Cd), while doubling of the ligand functionality (tr₂ad) allows integration of the clusters into 3D polymeric frameworks 6-9 (M = Cd, Cu).     

New phospholyl complexes of groups 4 and 6: Syntheses, characterisation and polymerisation studies

[M(P₃C₂^tBu₂)(CO)₃I] (M = Mo, 1, W, 2) have been synthesised and reacted with PCl₅ for oxidation study purposes. Compounds Ti(P₃C₂^tBu₂)(Ind)Cl₂], 3, and [Zr(P₃C₂^tBu₂)(Cp)Cl₂], 4, were detected spectroscopically, but showed to be too unstable to be isolated. A Ti(IV) complex, [Ti(P₃C₂^tBu₂)Cl₃], 5, has been formed from the reaction of [TiCl₄] with the base-free ligand K(P₃C₂^tBu₂), while the Ti(III) species, [Ti(P₃C₂^tBu₂) Cl₂(THF)], 6, was prepared from [TiCl₃(THF)₃]. Compounds 5 and 6 were studied as ethylene catalyst precursors after activation with MAO. In the studied conditions, complex 5 is the most active one with an activity of 2.2 × 10⁵ g(molTi [E] h)⁻¹, one order of magnitude higher than compound 6. The produced polymer is linear polyethylene.