New four- and five-coordinated complexes of cobalt with sterically hindered o-iminobenzoquinone ligands: synthesis and structure

New square planar Co^II(ISQ-iPr)₂ (1), Co^II(ISQ-Me)₂ (2) and five-coordinate Co^III(ISQ-Me)₂Cl cobalt complexes (3) (ISQ-iPr=4,6-di-tert-butyl-N-(2,6-di-iso-propylphenyl)-o-iminobenzosemiquinonate radical-anion, ISQ-Me=4,6-di-tert-butyl-N-(2,6-di-methylphenyl)-o-iminobenzosemiquinonate radical-anion) have been prepared using different methods. Complexes 1-3 have been characterized by IR, UV-Vis, EPR spectroscopy. Molecular structures of 1 and 3 were determined using X-ray crystallography. It has been established from variable-temperature magnetic susceptibility measurements and X-band EPR spectroscopy that 1 and 2 possess an S=1/2 ground state. In the complex molecules the unpaired electrons of o-iminobenzosemiquinonate radical ligands (S_rad=1/2) are strongly coupled antiferromagnetically. The sterical hindrances of N-aryl in o-iminobenzosemiquinonate ligands prevent the formation of a hexacoordinate species.     

Unexpected structural and electronic effects of internal rotation in diruthenium paddlewheel complexes containing bulky carboxylate ligands

A series of complexes containing the bulky carboxylate ligand 2,4,6-triisopropylbenzoate (TiPB) of type trans-[Ru₂(TiPB)₂(O₂CCH₃)₂X] [X = Cl (1), PF₆ (2)] and [Ru₂(TiPB)₄X] [X = Cl (3), PF₆ (4)] have been synthesised. The corresponding complexes trans-[Ru₂(TiPB)₂(O₂CCH₃)₂] (5) and [Ru₂(TiPB)₄] (6) were also isolated. Magnetic susceptibility measurements indicate that the diruthenium cores have the expected three (1-4) or two (5 and 6) unpaired electrons consistent with σ²π⁴δ²(δ^∗π^∗)³ and σ²π⁴δ²δ^∗2π^∗2 electronic configurations. Compounds 1-4 and 6 were structurally characterised by X-ray crystallography, and show the expected paddlewheel arrangement of carboxylate ligands around the diruthenium core. The diruthenium cores of complexes 3, 4 and 6 are all distorted to minimise steric interactions between the bulky carboxylate ligands. The Ru-Ru bond length in the complex 6 [2.2425(6) Å] is the shortest observed for a diruthenium tetracarboxylate and, surprisingly, is 0.014 Å shorter than in the analogous complex 4, despite an increase in the formal Ru-Ru bond order from 2.0 (6) to 2.5 (4). This is rationalised in terms of the extent of internal rotation, or distortion, about the diruthenium core. This was supported by density functional theory calculations on the model complexes [Ru₂(O₂CH)₄] and [Ru₂(O₂CH)₄]⁺, that demonstrate the relationship between Ru-Ru bond length and internal rotation. Electrochemical and electronic absorption data were recorded for all complexes in solution. Comparison of the data for the ‘bis-bis’ (1, 2 and 5) and tetra-substituted (3, 4 and 6) complexes indicates that the shortening of the Ru-Ru bond length results in a small increase in energy of the near-degenerate δ^∗ and π^∗ orbitals.     

Organoosmium complexes of imidazole-containing chelate acceptor ligands

The complexes [(L)Os(η⁶-Cym)Cl](PF₆), Cym = p-cymene and L = bis(1-methylimidazol-2-yl)ketone (bik) or bis(1-methylimidazol-2-yl)glyoxal (big), were obtained and characterized with respect to spectroscopy, crystal structure (big complex) and (spectro)electrochemical behaviour at variable temperatures. DFT calculations confirm the structure of [(big)Os(η⁶-Cym)Cl]⁺ with imidazolyl-N-bonded Os^II in a boat-shaped seven-membered chelate ring with small N-Os-N angles (<84°). Reduction of this compound proceeds reversibly to a neutral complex of the α-semidione radical anion ligand big⁻; EPR and IR spectroelectrochemistry indicate very little participation from the heavy metal in the spin distribution. The analogous [(bik)Os(η⁶-Cym)Cl]⁺ could not be reduced reversibly to the ketyl radical complex but displayed a more reversible oxidation at high potential.     

Synthesis of cobalt(III) complexes with novel open chain oxime ligands and metal-ligand coordination in aqueous solution

Cobalt(III) complexes with new open chain oxime ligands: N,N′-bis(2-hydroxyiminopropionyl)-1,2-aminoethane (H₂pen) and N,N′-bis(2-hydroxyiminopropionyl)-1,3-diaminopropane (H₂pap) have been investigated. Single crystals of Co(papH₋₁)(Im₂)·CH₃OH (1) and Co(papH₋₁)(MEA)₂·1.5H₂O (2) (where Im = imidazole, MEA = monoethanolamine) suitable for X-ray crystallography were grown by slow evaporation of methanol/water solutions at room temperature. The molecular structures have been determined using single-crystal X-ray diffraction methods. The potentiometric and spectrophotometric results in aqueous solution reveal that both of the open chain ligands show a very high efficacy in the coordination of Co(II) ions. As it has been indicated, differences between the two oxime ligands in complexing ability may be attributed to the longer -CH₂- chain in H₂pap and by that a better fit of the relatively large Co(II) ion to the accessible binding site. One of the complex species confirmed under inert atmosphere, namely of type Co(LH₋₁)⁻ (where L = pap or pen), has been shown as the “active” form, capable of dioxygen uptake followed by irreversible oxidation to Co(III).     

Novel cobalt(II) complexes with pyridyl/ether or pyridyl/thioether ligands. The conversion of pyridyl/thioether cobalt(II) complex to pyridyl/sulfinato cobalt(III) compound

Two new cobalt(II) complexes of symmetric hexadentate mixed-ligand N,O [1,12-bis(2-pyridyl)-5,8-dioxa-2,11-diazadodecane (pydado)] and N,S [1,12-bis(2-pyridyl)-5,8-dithia-2,11-diazadodecane (pydadt)] donor atoms have been synthesized as perchlorate salts. The crystal structures show that [Co(pydado)](ClO₄)₂ · H₂O (1) crystallizes in the triclinic space group and [Co(pydadt)](ClO₄)₂ (2) crystallizes in the monoclinic space group P2_1/c. The cation [Co(pydado)]²⁺ is pseudo-octahedral with the two pyridyl groups in trans position. However, in [Co(pydadt)]²⁺ complex, the size of thioether sulfur atoms imposes a distorted octahedral geometry; the pyridyl groups and the sulfur atoms are in trans position. The reaction of the complex 2 and hydrogen peroxide resulted to the oxidation of Co^II into Co^III and the thioether groups of the ligand to sulfinate groups with elimination of the central ethylenic group of pydadt. Thus, complex 2 was converted to bis[3-(2-pyridylmethylamino)ethanesulfinate] cobalt(III) complex (3) {[Co(pynso)₂](ClO₄) · 0.5H₂O}. The X-ray crystal structure reveals that the compound 3 crystallizes in the triclinic space group with the same donor atoms (N_pyridyl, N_amine and S) belonging to the two ligands in cis-position. In aqueous solution, the stability constants of the Co(II) chelates with these two ligands, determined by potentiometry, show the formation of [Co(LH)]³⁺ and [CoL]²⁺ species in all cases. The chelating power of pydadt ligand is slightly greater than that of pydado.     

Synthesis, structures and spectroscopic properties of palladium(II) complexes with tridentate piperidyl-containing pincer ligands

A new series of square planar palladium(II) complexes with pincer ligands, pip₂NCN⁻ (pip₂NCNH = 1,3-bis(piperidylmethyl)benzene) and pip₂NNN (2,6-bis(piperidylmethyl)pyridine), has been prepared: Pd(pip₂NCN)X (X = Cl, Br, I), [Pd(pip₂NCN)(L)](BF₄) (L = pyridine, 4-phenylpyridine), and [Pd(pip₂NNN)Cl]Cl. The X-ray crystal structures of Pd(pip₂NCN)Br, [Pd(pip₂NCN)(L)]BF₄, and [Pd(pip₂NNN)Cl]Cl confirm the tridentate coordination geometries of the pincer ligands. For the pip₂NCN⁻ complexes, each piperidyl ring adopts a chair conformation with the metal center at an equatorial position on the N(piperidyl) atom. However, one of the piperidyl groups of Pd(pip₂NNN)Cl⁺ adopts a previously unobserved coordination geometry, effectively placing the metal center at an axial position on the N(piperidyl) atom. ¹H NMR and UV-Vis absorption measurements provide additional insight into the electronic structures of these complexes. The ¹H NMR spectra of Pd(pip₂NCN)X (X = Cl, Br, I) are consistent with deshielding of the pip₂NCN⁻ ligand resonances along the Cl < Br < I series, in opposition to the relative halogen electronegativities. It is suggested that this trend is consistent with decreasing filled/filled repulsions between the dπ orbitals of the metal center and the lone pair orbitals of the halide ligands along this series. Electronic absorption spectra support the notion that ligand-to-metal charge-transfer states are stabilized in these palladium(II) complexes relative to their platinum(II) analogues.     

Early transition metal complexes of dinucleating Pacman ligands: X-ray crystal structures of mixed-valence V/V complexes

The use of a Schiff-base calixpyrrole (L) as a dinucleating ligand for early transition metals is described. Salt elimination reactions between the crystallographically-characterised [K₄(THF)₃(PhMe)(L)] and titanium(III) and vanadium(III) halides form the new dinuclear complexes [(MCl)₂(L)] (M = Ti, V). Adventitious, and partial, oxidation of [(VCl)₂(L)] resulted in the formation of the unusual mixed-valence vanadyl complexes [(VO)(S)(VCl)(L)] (S = THF or pyridine), which both adopt desired Pacman geometries in the solid state in which the oxo ligand is accommodated within the dinuclear molecular cleft.     

Pd(II) complexes containing N-alkyl-3-pyridine-5-trifluoromethyl pyrazole ligands: Synthesis, NMR studies and X-ray crystal structures

Palladium [PdCl₂(L)] complexes with N-alkylpyridylpyrazole derived ligands [2-(5-trifluoromethyl-1H-pyrazol-3-yl)pyridine (L¹), 2-(1-ethyl-5-trifluoromethyl-1H-pyrazol-3-yl)pyridine (L²), 2-(1-octyl-5-trifluoromethyl-1H-pyrazol-3-yl)pyridine (L³), and 2-(3-pyridin-2-yl-5-trifluoromethyl-pyrazol-1-yl)ethanol (L⁴) were synthesised. The crystal and molecular structures of [PdCl₂(L)] (L = L², L³, L⁴) were resolved by X-ray diffraction, and consist of monomeric cis-[PdCl₂(L)] molecules. The palladium centre has a typical square-planar geometry, with a slight tetrahedral distortion. The tetra-coordinate metal atom is bonded to one pyridinic nitrogen, one pyrazolic nitrogen and two chlorine ligands in cis disposition. Reaction of L (L², L⁴) with [Pd(CH₃CN)₄](BF₄)₂, in the ratio 1M:2L, gave complexes [Pd(L)]₂(BF₄)₂. Treatment of [PdCl₂(L)] (L = L², L⁴) with NaBF₄ and pyridine (py) and treatment of the same complexes with AgBF₄ and triphenylphosphine (PPh₃) yielded [Pd(L)(py)₂](BF₄)₂ and [Pd(L)(PPh₃)₂](BF₄)₂ complexes, respectively. Finally, reaction of [PdCl₂(L⁴)] with 1 equiv of AgBF₄ yields [PdCl(L⁴)](BF₄).     

Iridium and rhodium complexes containing dichalcogenoimidodiphosphinato ligands

Treatment of [MCl(CO)(PPh₃)₂] with K[N(R₂PQ)₂] afforded [M{N(Ph₂PQ)₂}(CO)(PPh₃)] (M = Ir, Rh; Q = S, Se). The IR C=O stretching frequencies for [M(CO)(PPh₃){N(Ph₂PQ)₂}] were found to decrease in the order S > Se. Treatment of [M(COD)Cl]₂ with K[N(Ph₂PQ)₂] afforded [M(COD){N(Ph₂PQ)₂}] (COD = 1,5-cyclooctadiene; M = Ir, Rh; Q = S, Se). Treatment of [Ir(ol)₂Cl] with afforded (ol = cyclooctene COE, C₂H₄; Q = S, Se). Oxidative addition of [Ir(CO)(PPh₃){N(Ph₂PS)₂}] and [Ir(COD){N(Ph₂PS)₂}] with HCl afforded [Ir(H)(Cl)(CO)(PPh₃){N(Ph₂PS)₂}] and trans-[Ir(H)(Cl)(COD){N(Ph₂PS)₂}], respectively. Oxidative addition of [Ir(CO)(PPh₃){N(Ph₂PS)₂}] with MeI afforded [Ir(Me)(I)(CO)(PPh₃){N(Ph₂PS)₂}]. Treatment of [Ir(COE)₂Cl]₂ with K[N(R₂PO)₂] afforded [Ir(COE)₂{N(Ph₂PO)₂}] that reacted with MeOTf (OTf = triflate) to give [Ir{N(Ph₂PO)₂}(COE)₂(Me)(OTf)]. The crystal structures of [Ir(CO)(PPh₃){N(Ph₂PS)₂}], [M(COD){N(Ph₂PS)₂}] (M = Ir, Rh), (ol = COE, C₂H₄), trans-[Ir(H)(Cl)(COD){N(Ph₂PS)₂}], and [Ir(COE)₂{N(Ph₂PO)₂}] have been determined.     

New acylhydridorhodium(III) complexes containing terdentate PNN ligands from the reaction of diolefinic rhodium(I) complexes with o-(diphenylphosphino)benzaldehyde in the presence of chelating amino ligands

[{Rh(cod)Cl}₂] (cod=1,5-cyclooctadiene) reacts with o-(diphenylphosphino)benzaldehyde (PPh₂(o-C₆H₄CHO)) (Rh:P=1:1) in the presence of aromatic diamines or 8-aminoquinoline (NN) to give acylhydride [Rh(Cl)(H){PPh₂(o-C₆H₄CO)}(NN)] species. The oxidative addition of PPh₂(o-C₆H₄CHO) in the presence of (NN) and PPh₃ gives cationic species [Rh(H){PPh₂(o-C₆H₄CO)} (PPh₃)(NN)]⁺ containing mutually trans phosphorus atoms. When (NN)=8-aminoquinoline, a mixture of two isomers is obtained. These isomers differ in the nitrogen cis to the hydride, amino or quinolinic. By using Rh:PPh₂(o-C₆H₄CHO)=1:2 stoichiometric ratios, oxidative addition of one PPh₂(o-C₆H₄CHO) and P-coordination of another PPh₂(o-C₆H₄CHO) occurs. The aldehyde group undergoes then a condensation reaction with the coordinated amine to afford new PNN terdentate ligands, phosphine-amino-imine when (NN)=diamine or phosphine-diimine when (NN)=8-aminoquinoline. These reactions give selectively the corresponding complexes [Rh(H){PPh₂(o-C₆H₄CO)}(PNN)]⁺ containing trans phosphorus atoms and the hydride cis to the new imino group. X-ray diffraction studies of the PNN complexes are reported.     

Direct synthesis and crystal structures of new heteropolynuclear complexes containing aminoalcohol ligands: From heterobi- (Co/Zn) to heterotrimetallic (Cu/Co/Zn) compounds

Three novel heterometallic complexes [Co₂Zn₂(Dea)₂(HDea)₂(NCS)₄] · 4dmso (1), [CuCoZn₂(Dea)₃Cl₃(HOMe)] · MeOH (2) and [CuCoZn(Me₂Ea)₄(NCS)₂(OAc)] (3) have been prepared from zerovalent zinc, cobalt thiocyanate and a dimethylsulfoxide solution of diethanolamine (1), zerovalent copper, cobalt chloride, zinc chloride and a methanol solution of diethanolamine (2), zerovalent copper, cobalt thiocyanate, zinc acetate and an acetonitrile solution of 2-(dimethylamino)ethanol in air (3) [H₂Dea is diethanolamine and HMe₂Ea is 2-(dimethylamino)ethanol]. The structures of all complexes were determined by single crystal X-ray analysis. Compound 1 consists of a centrosymmetric molecule based on a Co₂Zn₂O₆ core. In contrast to 1, the coordination cores of the structures of the heterotrimetallic complexes, CuCoZn₂O₆ (for 2) and CuCoZnO₄ (for 3) have no inversion centre. Both 2 and 3 possess a similar CuCoZnO₄ fragment that can be viewed as an incomplete distorted cube.     

Silver (I) poly(1,2,4-triazolyl)borate complexes containing monodentate phosphane ligands

New silver (I) derivatives containing monodentate tertiary phosphanes and anionic poly(triazol-1-yl)borate ligands have been prepared from the reaction of AgNO₃ and PR₃ (R = Ph, Bn, o-tolyl, m-tolyl, p-tolyl) and potassium dihydrobis(1,2,4-triazolyl)borate, K[H₂B(tz)₂], or potassium hydrotris(1,2,4-triazolyl)borate, K[HB(tz)₃]; their solid state and solution properties have been investigated through analytical and spectroscopic measurements (IR, ¹H-, and ³¹P NMR). The ¹H- and ³¹P NMR solution spectra in some cases can be interpreted on the basis of a dissociation of [{H₂B(tz)₂}Ag(PR₃)₂] into [{H₂B(tz)₂}Ag(PR₃)] and PR₃. All the compounds are soluble in chlorinated solvents and are non-electrolytes in CH₂Cl₂ and acetone solutions. [{H₂B(tz)₂}Ag(PPh₃)₂] and [{H₂B(tz)₂}Ag{P(m-tolyl)₃}₂] are simple mononuclear arrays, the silver atoms lying in four-coordinate N₂AgP₂ environments. Owing to the presence of the methyl substituents on the phosphane ligand, the complex [{HB(tz)₃}Ag{P(o-tolyl)₃}], as expected, is mononuclear. In [{H₂B(tz)₂}Ag{P(p-tolyl)₃}], the silver environment is still four-coordinate but PAgN₃, utilizing the coordinating capability of one of the additional (‘exo’-) ring nitrogens not only to complete the four-coordinate array about the silver but, necessarily, to link successive asymmetric units into a single-stranded polymer.     

Synthesis and structure of rhodium complexes containing extended terpyridyl ligands

The reaction of the extended terpyridyl ligands, 4^′-(4^′′′-pyridyl)-2, 2^′:6^′,2″-terpyridine (qtpy), and 4^′-phenyl-2,2^′:6^′,2^′′-terpyridine (ptpy) with RhCl₃ and [tpyRhCl₃] (where tpy=2,2^′:6^′,2^′′-terpyridine) has been investigated. This has led to the isolation and characterisation of four new complexes. All the new complexes have had their molecular structures confirmed via X-ray crystallography studies. It has been shown that, consistent with related systems, changes in the electronic properties of the coordinated ligand results in modulation of the electrochemical and photophysical properties of the complex to which it is coordinated.     

Structure-dependent spectroscopic and redox properties of copper(I) complexes with bidentate iminopyridine ligands

A series of iminopyridine ligands; cyclopropylpyridin-2-ylmethyleneamine (A), cyclopentylpyridin-2-ylmethyleneamine (B), cyclohexylpyridin-2-ylmethyleneamine (C), and cycloheptylpyridin-2-ylmethyleneamine, (D) and their copper(I) complexes, [Cu(L)₂]⁺ (1a-1d) and [Cu(L)(PPh₃)₂]⁺ (2a-2d) have been synthesized and characterized by CHN analyses, ¹H NMR and IR and UV-Vis spectroscopy. Structures of 1a, 1b, 1c and 2a were determined by X-ray crystallography. The coordination polyhedron about the Cu^I center in the complexes is best described as a distorted tetrahedron. The dihedral angles between the least-squares planes of the chelate ligands show considerable variation from 86.1° in 1a to 68.3° in 1b, indicating the importance of packing forces in the crystalline environment. The UV-Vis spectra of the complexes are characterized by first metal to ligand charge transfer bands increasing in wavelength with increasing size of the ring substituents in the ligands, except for the cyclopropyl compounds (1a and 2a), in good agreement with the variation of the dihedral angles between the ligand planes. Cyclic voltammetry of the complexes indicates a quasireversible redox behavior for the complexes. The bulkier ligands (PPh₃) inhibit the geometric distortion within the oxidized form and the redox potentials of complexes 2a-2d are shifted to more positive values, therefore.     

Pendant arm length control of dimensionality in cobalt dipyridylamine coordination polymers containing meta-benzenedicarboxylate ligands

Hydrothermal synthesis has afforded a pair of divalent cobalt coordination polymers containing meta-substituted benzenedicarboxylate and 4,4′-dipyridylamine (dpa) ligands, in which the length of the pendant arms on the anionic components dictates the overall dimensionality. [Co(1,3-phda)(dpa)(H₂O)]_n (1, 1,3-phda = 1,3-phenylenediacetate) possesses a ruffled (4,4) rhomboid grid 2-D layered structure with an 5-connected sqp supramolecular net. Use of a meta-substituted benzenedicarboxylate with shorter pendant arms generated {[Co(1,3-bdc)(dpa)]·3H₂O}_n (2, 1,3-bdc = 1,3-benzenedicarboxylate), which displays a 3-D network structure with 6⁵8 topology. Antiferromagnetic coupling, in conjunction with zero-field splitting, was evident across the supramolecular Co-O-H?O-Co patterns in 1 and the syn-syn bridged {Co(OCO)}₂ dimeric units in 2.     

Silver(I) methanesulfonate complexes containing diphosphine ligands: Spectroscopic and structural characterization

1:1 and 2:1 adducts of diphosphine ligands R₂P(R′)_nPR₂ (dppm: R = Ph, R′ = CH₂, n = 1; dppe: R = Ph, R′ = CH₂, n = 2; dppp: R = Ph, R′ = CH₂, n = 3; dppb: R = Ph, R′ = CH₂, n = 4; dppf: R = Ph, R′ = ferrocenyl, n = 1) with silver(I) methanesulfonate have been synthesized and characterized both in solution (¹H, ³¹P NMR) and in the solid state (IR, single crystal X-ray structure analysis). The two different stoichiometries have been found to depend on the molar ratio of ligand to metal employed and the nature of the diphosphine ligand. In AgO₃SMe:dppp,dppb (1:1)₂, in the [Ag(P^P)₂Ag] arrays, the silver atoms are also bridged by anion oxygen atoms, in disparate fashion commensurate with the different Ag?Ag distances.     

Synthesis and characterization of cobalt(II)-salicylate complexes derived from N4-donor ligands: Stabilization of a hexameric water cluster in the lattice host of a cobalt(III)-salicylate complex

The syntheses and structural characterization of four cobalt(II)-salicylate complexes, [(TPA)Co^II(HSA)](ClO₄) (1), [(isoBPMEN)Co^II(HSA)](BPh₄) (2), [(TPzA)Co^II(HSA)](ClO₄) (3) and [(6Me₃TPA)Co^II(HSA)](BPh₄) (4) [TPA = tris(2-pyridylmethyl)amine, isoBPMEN = N¹,N¹-dimethyl-N²,N²-bis(2-pyridylmethyl)ethane-1,2-diamine, TPzA = tris((3,5-dimethyl-1H-pyrazole-1-yl)methyl)amine and 6Me₃TPA = tris(6-methyl-2-pyridylmethyl)amine] are described. While 2, 3 and 4 are unreactive towards dioxygen, 1 reacts slowly with molecular oxygen to a cobalt(III)-salicylate complex, [(TPA)Co^III(SA)](ClO₄) (1a). Two different crystalline forms, 1a and 1a·4H₂O were isolated depending upon the condition of oxidation and crystallization. The solid-state structures of cobalt(III)-salicylate unit in both 1a and 1a·4H₂O show a six-coordinate distorted octahedral coordination geometry at the cobalt(III) center ligated by the tetradentate ligand (TPA) where the dianionic salicylate (SA) binds in a bidentate fashion through one carboxylate and one phenolate oxygen. The hydrated form 1a·4H₂O reveals a hexameric water cluster formation in the inorganic lattice host. The complex cation and the perchlorate counterion are involved in stabilizing the (H₂O)₆ cluster in a rare ‘pentamer planar+1’ conformation. A one-dimensional water tape consisting of edge-shared water hexamers is observed. The water tape represents a subunit of ice structure.     

Structural and redox properties in thioether-based (N/S) copper(II/I) complexes: Experimental and theoretical investigations

The complexes [Cu^IN₂(SMe)₂](ClO₄) (1) and [Cu^IIN₂(SMe)₂(CF₃SO₃)₂] (2) in both Cu^I and Cu^II redox states from N₂(SMe)₂ ligand (N,N-(2-pyridylmethyl)bis(2-methyl-thiobenzyl)amine) have been synthesized and structurally characterized by X-ray crystallography. Electrochemical studies show that the two complexes interconvert during the one electron transfer. Comparison with another complex with tBu instead Me groups on the thioether ligand shows detectable changes in X-ray structures and in redox properties. Theoretical calculations on the different steps of the redox process have been performed. Values underline steric constraints induced by the substitutions on thioether alkyl groups.     

Synthesis,structures and urease inhibitory activity of cobalt(III) complexes with Schiff bases

A series of new cobalt(III) complexes were prepared. They are [CoL¹(py)₃]·NO₃ (1), [CoL²(bipy)(N₃)]·CH₃OH (2), [CoL³(HL³)(N₃)]·NO₃ (3), and [CoL⁴(MeOH)(N₃)] (4), where L¹, L², L³ and L⁴ are the deprotonated form of N′-(2-hydroxy-5-methoxybenzylidene)-3-methylbenzohydrazide, N′-(2-hydroxybenzylidene)-3-hydroxylbenzohydrazide, 2-[(2-dimethylaminoethylimino)methyl]-4-methylphenol, and N,N′-bis(5-methylsalicylidene)-o-phenylenediamine, respectively, py is pyridine, and bipy is 2,2′-bipyridine. The complexes were characterized by infrared and UV–Vis spectra, and single crystal X-ray diffraction. The Co atoms in the complexes are in octahedral coordination. Complexes 1 and 4 show effective urease inhibitory activities, with IC₅₀ values of 4.27 and 0.35 μmol L⁻¹, respectively. Complex 2 has medium activity against urease, with IC₅₀ value of 68.7 μmol L⁻¹. While complex 3 has no activity against urease. Molecular docking study of the complexes with Helicobacter pylori urease was performed.     

Examining the impact of steric and electronic variation in N2S scorpionate ligands on the properties of zinc(II) and cadmium(II) complexes

A series of LZn(II)Br (1-4) and LCd(II)Cl complexes (9-11) has been prepared by the reaction of metal halide precursors with the lithium salts of the N₂S⁻ ligands bis(3,5-diisopropylpyrazol-1-yl)dithioacetate (L¹), bis(3,5-di-tert-butylpyrazol-1-yl)dithioacetate (L²), N-phenyl-2,2-bis(3,5-diisopropylpyrazol-1-yl)thioacetamide (L³) and N-phenyl-2,2-bis(3,5-di-tert-butylpyrazol-1-yl)thioacetamide (L⁴). Characterization by X-ray crystallography and DOSY NMR studies indicate that LZnBr complexes 1-4 are mononuclear both in the solid state and in solution. Steric differences between ligands L¹-L⁴ result in distortion from an ideal tetrahedral geometry for each complex, with the degree of distortion depending on the bulk of the ligand substituents. In contrast, the related complex L³CdCl was shown by X-ray crystallography to dimerize in the solid state to form the chloride-bridged five-coordinate complex [L³CdCl]₂ (10). Despite 10 having a dinuclear structure in the solid state, DOSY NMR studies indicate 9-11 exist as mononuclear LCdCl species in solution. In addition, Zn(II) cyanide complexes of the form LZnCN [L = L¹ (5), L³ (7), L⁴ (8)] have been characterized and the X-ray structure of 8 determined. Moreover, density functional theory calculations have been conducted which yield important insight into the bonding in 1-4 and 5-8 and the electronic impact of ligands L¹-L⁴ on the zinc(II) ion and its ability to function as a Lewis acid catalyst.