Syntheses, structures and antimicrobial activities of various metal complexes of hinokitiol

Metal-oxygen bonding complexes (M = Mg^II, Mn^II, Ni^II, Mo^VI, W^VI, Pd^II, Sb^III, Bi^III, Fe^III, Ti^IV, K^I, Ba^II, Zr^IV and Hf^IV) with a hinokitiol (Hhino; 2-hydroxy-4-isopropylcyclohepta-2,4,6-trienone or β-thujaplicin) ligand, which has two unequivalent oxygen donor atoms, were synthesized and characterized by elemental analysis, TG/DTA, FT-IR and solution (¹H and ¹³C) NMR spectroscopy. Single-crystal X-ray structure analysis revealed various molecular structures for the complexes, which were classified into several families of family, i.e. type A [M^II(hino)₂(L)]₂ (M = Mg^II, Mn^II, Ni^II; L = EtOH or MeOH), with a dimeric structure consisting of one bridging hino⁻ anion, one chelating hino⁻ anion and one alcohol or water molecule, type B, with the octahedral, cis-dioxo, bis-chelate complexes cis-[M^VIO₂(hino)₂] (M = Mo^VI, W^VI), type C, with square planar complex [M^II(hino)₂] (M = Pd^II), type D, with tris-chelate, 7-coordinate complexes with one inert electron pair [M^III(hino)₃] (M = Sb^III, Bi^III), type D′, with the bis-chelate, pseudo-6-coordinate complexes with one inert electron pair [M^III(hino)₂X] (M = Sb^III, X = Br), type E, with tris-chelate, 6-coordinate complexes with Δ and Λ isomers [M^III(hino)₃] (M = Fe^III), type E′ of bis-chelate, 6-coordinate complex [M^IV(hino)₂X₂] (M = Ti^IV, X = Cl), type F, with water-soluble alkali metal salts [M^I(hino)] (M = K^I), and type H, with tetrakis-chelate, 8-coordinate complexes [M^IV(hino)₄](M = Zr^IV, Hf^IV). These structural features were compared with those of metal complexes with a related ligand, tropolone (Htrop). The antimicrobial activities of these complexes, evaluated in terms of minimum inhibitory concentration (MIC; μg mL⁻¹) in two systems, were compared to elucidate the relationship between structure and antimicrobial activity.     

Synthesis and characterization of [Fe(III)(qsal)2][M(III)(pds)2] (M = Cu, Au)

Salts of the Fe(III) spin crossover cation [Fe^III(qsal)₂]⁺ (qsalH = N-(8-quinolyl)salicylaldimine) and monoanions [M^III(pds)₂]⁻ (M = Cu, Au; pds = pirazine-2,3-diselenolate) with formula [Fe^III(qsal)₂][M^III(pds)₂] were prepared and characterized by single crystal X-ray diffraction and magnetic measurements. These two salts present magnetic properties essentially due to the Fe^III centres in the high-spin state (S = 5/2), and do not have any spin transition.     

Ligand-to-ligand electron transfer and temperature induced valence tautomerism in o-dioxolene chelated manganese complexes

Three polymeric o-dioxolene chelated manganese(III) complexes, {[Mn^III(H₂L¹)(Cl₄Cat)₂][Mn^III(Cl₄Cat)₂(H₂O)₂]}_∞ (1) (L¹ = N,N′-bis(2-pyridylmethyl)-1,4-butanediamine, Cl₄Cat = tetrachlorocatecholate dianion], {[Mn^III(H₂L¹)(Br₄Cat)₂][Mn^III(Br₄Cat)₂(H₂O)₂]·4DMF}_∞, (2) and {[Mn^III(H₂L²)(Br₄Cat)₂][Mn^III(Br₄Cat)₂(DMF)₂]}_∞ (3) (L² = N,N′-bis(2-pyridylmethyl)-1,6-hexanediamine, Br₄Cat = tetrabromocatecholate dianion) have been synthesized and structures were determined by X-ray crystallography. All the complexes were fully characterized by various spectroscopic techniques and their electronic properties are described. It was found that the simple protonation or deprotonation of the bridging ligand (L¹ or L²) coordinated to metal-dioxolene chromophore induce a change in the oxidation state of the coordinated dioxolene ligand without affecting the metal oxidation state. As a result, drastic change in the optical absorption properties of the complexes is observed in the visible and near-IR region as the transformation involves semiquinone-catecholate ligands. Moreover, all three complexes undergo thermally induced valence tautomerism in solution. For all the complexes, on increasing the temperature, the intensity of the lower energy Inter Valence Charge Transfer (IVCT) band at about 1930 nm increases with corresponding decrease of 600 nm band with an isosbestic point at 1820 nm due to the formation of mixed valence species Mn^II(X₄SQ)(X₄Cat)⁻ from (X = Cl or Br) by the transfer of one electron from Cat²⁻ to Mn^III center.     

Optical properties of Ag(tripod)X with tripod = 1,1,1-tris(diphenyl-phosphinomethyl)ethane and X = Cl and I: Intraligand and ligand-to-ligand charge transfer

The complexes Ag^I(tripod)X with tripod = 1,1,1-tris(diphenylphosphinomethyl)ethane and X⁻ = Cl⁻ and I⁻ are luminescent in solution at r.t. It is suggested that the emission is a phosphorescence which originates from a tripod intraligand state for X = Cl (λ_max = 464 nm) and a X⁻ → tripod ligand-to-ligand charge transfer state for X = I (λ_max = 482 nm).     

Synthesis and crystal structures of trans-dichlorobis{tri(2-methylphenyl)stibine}palladium(II) and trans-dibromobis{tri(2-methylphenyl)stibine}palladium(II)

Tri(2-methylphenyl)stibine reacts with [PdX₂(cod)] or PdX₂ (X = Cl or Br) to give the trans-[PdX₂{Sb(2-Me- C₆H₄)₃}₂]. The single crystal X-ray structures of trans-[PdX₂{Sb(2-Me-C₆H₄)₃}₂] (X = Cl or Br) revealed that the palladium atom is a square planar environment with mutually trans-Sb(2-methylphenyl)₃ ligands. Iodine analogous of complex can also be prepared from trans metallation reaction with sodium iodine.     

Facile pyramidal inversion at phosphorus in [R3EP7W(CO)3] type complexes: An EXSY NMR study

A series of [R₃EP₇W(CO)₃]²⁻ complexes where (E = Si, Ge, Sn, Pb; R = alkyl, phenyl) were prepared from [P₇W(CO)₃]³⁻ and R₃EX reagents (X = Cl, Br) in dmf or CH₃CN solutions. The Pb derivatives were prepared at −50 °C and are not thermally stable. The compounds were characterized by ³¹P NMR spectroscopy and selected ESI-MS studies. All compounds undergo rapid inversion at the ER₃-bound phosphorus atom. The barriers to inversion were measured by way of 2D ³¹P EXSY experiments at various temperatures. The analysis showed very low barriers to pyramidal inversion (ΔG^‡ 10.3-13.5 kcal/mol) that were essentially enthalpic in origin. The activation barriers generally increased with increasing electronegativity of the E atom and the steric bulk of the ER₃ substituents. The latter was interpreted by way of a non-linear transition state.     

Synthesis, spectroscopy and structural characterization of silver(I) complexes containing unidentate N-donor azole-type ligands

From the interaction between azole-type ligands L and AgX (X = NO₃ or ClO₄) or [AgX(PPh₃)_n] (X = Cl, n = 3; X = MeSO₃, n = 2), new ionic mononuclear [Ag(L)₂]X and [Ag(PPh₃)₃L][X] or neutral mono-([Ag(PPh₃)_nL(X)]) or di-nuclear ([{Ag(PPh₃)(L)(μ-X)}₂]) complexes have been obtained which have been characterized through elemental analysis, conductivity measurements, IR, ¹H NMR and, in some cases, also by ³¹P{¹H} NMR spectroscopy, and single-crystal X-ray studies. Stoichiometries and molecular structures are dependent on the nature of the azole (steric hindrance and basicity), of the counter ion, and on the number of the P-donor ligands in the starting reactants. Solution data are consistent with partial dissociation of the complexes, occurring through breaking of both Ag-N and Ag-P bonds.     

A sterically hindered tetrakis(pyrazolyl)borate: Synthesis, characterization and coordinative behaviour

The sterically hindered tetrakis-(3-(p-tolylpyrazolyl)borate [pz⁰Tp^p-Tol] has been prepared and its reaction with CuX₂.nH₂O (X = Cl or acetate (OAc), M(NO₃)₂.6H₂O (M = Ni, or Co) and MCl₂ (M = Zn or Cd) has been investigated. [M(pz⁰Tp^p-Tol)X(Hpz^p-Tol)] (M = Cu, X = Cl or OAc; M = Ni or Co, X = NO₃) and [M(pz⁰Tp^p-Tol)Cl(Hpz^p-Tol)_2-n(H₂O)_n] have been synthesised and their spectroscopic properties described, the five-coordinated Cu species being also structurally characterized. The methyl groups in the para-tolyl fragments of the ligand strongly influences the stoichiometry and structure of the metal complexes.     

Nature of the Ln-Co magnetic interactions in compounds [Ln2Co3(C5H4NPO3)6] · 4H2O with open-framework structures

The reactions of Ln(NO₃)₃ · xH₂O, CoSO₄ · 7H₂O or ZnSO₄ · 6H₂O and 2-pyridylphosphonic acid under hydrothermal conditions result in heterometallic phosphonate compounds with formula [Ln₂M₃(C₅H₄NPO₃)₆] · 4H₂O (Ln₂M₃; M = Co^II or Zn^II; Ln = La^III, Ce^III, Pr^III, Nd^III, Sm^III, Eu^III, Gd^III, Tb^III, Dy^III). These compounds are isostructural and crystallize in a chiral cubic space group I2₁3. Each structure contains the {LnO₉} polyhedra and {MN₂O₄} octahedra which are connected by edge-sharing to form an inorganic open-framework structure with a 3-connected 10-gon (10, 3) topology. The nature of Ln^III-Co^II magnetic interactions in Ln₂Co₃ is investigated by a comparison with their Ln^III-Zn^II analogues. It is found that the Ln^III-Co^II interaction is weak antiferromagnetic for Ln = Ce and ferromagnetic for Ln = Sm, Gd, Tb and Dy. In the cases of Ln = Pr, Nd and Eu, no significant magnetic interaction is observed.     

Exploring the properties of mixed valence cyanide bridged dinuclear complexes: Solvent stabilization of electronic isomers

We report here the synthesis and properties of a family of mixed-valence cyanide-bridged dinuclear complex ions trans-[(L′L₄Ru^II(μ-NC)Fe^III(CN)₅]⁻ (with L = pyridine or 4-dimethylaminopyridine (dmap) and L′ = pyridine, 4-methoxypyridine (meopy) or 4-dimethylaminopyridine)) whose properties could be adjusted smoothly by changing the acceptor properties of the solvent and the σ donor properties of the L′ pyridine ligand. In solution these complexes exhibit an intense solvent-dependent MM′CT (Ru^II → Fe^III) absorption in the near infrared region. Analysis of this band in different complexes and solvents suggests an enhanced interaction as the energies of the metal centers come closer. From this trend the anion trans-[(dmap)₅Ru(μ-NC)Fe(CN)₅]⁻ (dmap = 4-dimethylaminopyridine) in water is expected to belong to the class II-III, but its spectral properties indicates a ground state with Ru(III)-Fe(II) character. The stabilization of this electronic isomer is probably related to the better donor properties of the hexacyanoferrate(II) moiety and its stronger interaction with water.     

Preparation, crystal structures and spectroscopic properties of novel [MCl3 − n(P)3 + n] (M = Co, Rh; n = 0, 1, 2 or 3) series of complexes containing tripodal tridentate phosphine, 1,1,1-tris(dimethylphosphinomethyl)ethane

Cobalt(III) and rhodium(III) complexes of the series of [M^IIICl_3 − n(P)_3 + n]ⁿ⁺ (M = Co or Rh; n = 0, 1, 2 or 3) have been prepared with the use of 1,1,1-tris(dimethylphosphinomethyl)ethane (tdmme) and mono- or didentate phosphines. The single-crystal X-ray analyses of both series of complexes revealed that the M-P and M-Cl bond lengths were dependent primarily on the strong trans influence of the phosphines, and secondarily on the steric congestion around the metal center resulting from the coordination of several phosphine groups. In fact, the M-P(tdmme) bonds became longer in the order of [MCl₃(tdmme)] < [MCl₂(tdmme)(PMe₃)]⁺ < [MCl(tdmme)(dmpe)]²⁺ (dmpe = 1,2-bis(dimethylphosphino)ethane) < [M(tdmme)₂]³⁺ for both Co^III and Rh^III series of complexes, while the M-Cl bond lengths were shortened in this order (except for [M(tdmme)₂]³⁺). Such a steric congestion around the metal center can also account for the structural and spectroscopic characteristics of the series of complexes, [MCl(tdmme)(dmpm, dmpe or dmpp)]²⁺ (dmpm = bis(dimethylphosphino)methane, dmpp = 1,3-bis(dimethylphosphino)propane). The X-ray analysis for [CoCl(tdmme)(dmpm or dmpe)](BF₄)₂ showed that all Co-P bonds in the dmpm complex were shorter by 0.03-0.04 Å than those in the dmpe complex. Furthermore, the first d-d transition energy of the Co^III complexes and the ¹J_Rh-P(tdmme) coupling constants observed for the Rh^III complexes indicated an unusual order in the coordination bond strengths of the didentate diphosphines, i.e., dmpm > dmpe > dmpp.     

The structural definition of adducts of stoichiometry AgX:dppf (1:1)(n), X = simple anion, dppf = bis(diphenylphosphino)ferrocene

Single crystal X-ray structural characterizations are recorded for an array of adducts of the form AgX:dppf (1:1)_(n), X = simple (pseudo-)halide or oxy-anion, ‘dppf’ = bis(diphenyl phosphino)ferrocene, for adducts X = Cl (new phase), Br, I, SCN, OCN, CN, NO₃ (new phase), O₂CCH₃, n = 2, the form being dimeric [(dppf-P,P′)Ag(μ-X)₂Ag(P,P′-dppf)], for X = I, SCN, [Ag(μ-X)₂(P-dppf-P′)₂Ag′]; for X = O₂CCF₃, n = ∞, the form is an extended polymer: ?Ag(O · CO · CF₃)(P-dppf-P′)Ag′(O?. A dichloromethane solvate phase of CuI:dppf (1:1)₂ (also centrosymmetric) is also recorded. Synthetic procedures for all adducts have been reported. All compounds have been characterized both in solution (¹H, ¹³C, ³¹P NMR, ESI MS) and in the solid state (IR). The topology of the structures in the solid state was found to depend on the nature of the counterion.     

Synthesis and X-ray structural characterization of tris(l-glycinato)vanadium(III) and trans-tetraquadichlorovanadium(III) chloride

Despite the importance of V^III in biology, only three V^III complexes of naturally occurring amino acids have been structurally characterized. We report the structure of the first vanadium complex incorporating a glycine ligand, [V(Gly)₃] · 2DMSO, which crystallizes in a monoclinic system with space group Cc, a = 8.9186(5) Å, b = 21.5347(9) Å, c = 9.9064(5) Å and β = 110.536(3)°. The X-ray structural data show the central V^III metal octahedrally coordinated by three bidentate glycinato ligands arranged a mer configuration, with both Δ and Λ enantiomers present in the unit cell. The bulk sample was isolated as [V(Gly)₃] · DMSO · NaCl. Structural comparisons are made with the corresponding homoleptic glycinato complexes of Co^III, Cr^III and Ni^II. The structure of trans-[V(OH₂)₄Cl₂]Cl · 2H₂O has also been re-determined. This latter complex crystallizes in a monoclinic system in the P2(1)/c space group, a = 6.4381(9) Å, b = 6.3843(9) Å, c = 11.7980(17) Å and β = 98.057(2)°. The vanadium atom lies at a crystallographic inversion centre within the distorted octahedron formed by the four water and two chloride ligands.     

Magnesium (II) poly(pyrazolyl)borate derivatives - Synthesis, spectral and structural studies

A series of magnesium complexes of general formula [Mg(Tp^x)₂] (Tp^x = Tp, Tp^∗, Tp^∗Cl, pzTp) and [Mg(Tp^x)X] (X = Cl, Tp^x = Tp^tBu or pz⁰Tp^p-Tol; X = acetate, Tp^x = Tp^tBu) were synthesised from magnesium chloride or acetate and M(Tp^x) (M = K, Na or Tl) in dichloromethane or alcoholic solution. These compounds are air-stable solids, sparingly soluble in most organic solvents; they have been characterized by elemental analysis, IR, ¹H and ¹³C NMR spectra and, in selected cases, also by conductivity and molecular weight measurements. Single crystal X-ray diffraction studies of [Mg(Tp)₂], [Mg(Tp*)₂] and [Mg(Tp*^Cl)₂] show unsolvated neutral bis(tripod ligand)magnesium(II) molecules with six-coordinate magnesium atoms (〈Mg-N〉 2.167(6), 2.19(2), 2.205(4) Å).     

Mo(II) complexes: A new family of cytotoxic agents?

Several molybdenum complexes, [Mo(η³-C₃H₅)X(CO)₂(N-N)] (N-N = 1,10-phenanthroline, phen: X = CF₃SO₃T1, X = Br B1, X = Cl C1; N-N = 2,2′-bipyridyl, X = CF₃SO₃T2, X = Br B2) and [W(η³-C₃H₅)Br(CO)₂(phen)] (W1) have been synthesized and characterized. Their antitumor properties have been tested in vitro against human cancer cell lines cervical carcinoma (HeLa) and breast carcinoma (MCF-7) using a metabolic activity test (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, MTT), leading to IC₅₀ values ranging from 3 to 45 μM, approximately. Most complexes exhibited significant antitumoral activity. Complexes B1 and T2 were chosen for subsequent studies aiming to understand their mechanism of action. Cellular uptake of molybdenum and octanol/water partition assays revealed that both B1 and T2 exhibit a selective uptake by cells and intermediate partition coefficients. The binding constants of B1 and T2 with ct DNA, as determined by absorption titration, are 2.08 (± 0.98) × 10⁵ and 3.68 (± 2.01) × 10⁵ M^− 1, respectively. These results suggest that they interact with DNA changing its conformation and possibly inducing cell death, and may therefore provide a valuable tool in cancer chemotherapy.     

Synthesis and solvatochromism studies of new mixed-chelate dinuclear copper(II) complexes with different counter ions

Four new symmetric mixed-chelate dinuclear complexes type [Cu₂(L)₂(TAE)]X₂, where TAE = tetraacetylethane; L = N,N-dimethyl-N′-benzylethylenediamine (L¹) or N,N′-dibenylethylenediamine (L²); X = ClO₄ or BPh₄ have been synthesized and characterized on the bases of elemental analysis, spectroscopic and conductance measurements. The X-ray crystal analysis of [Cu₂(L¹)₂(TAE)](ClO₄)₂ demonstrated that the two copper(II) ions are not equivalent. The axial position of the first copper is occupied by a ClO₄⁻ ion with a square pyramidal geometry whereas; the second copper ion resides in an octahedral environment determined by two perchlorate anions. However, in solution, the perchlorate ions are driven out by solvent molecules leading to their solvatochromism. The solvatochromism of the complexes were investigated in various organic solvents and also were compared with those of the corresponding mononuclear complexes [Cu(L)(acac)]ClO₄. Their solvatochromism were also investigated with different solvent parameters models using stepwise multiple linear regression (SMLR) method. The results suggested that the DN parameter of the solvent has the dominate contribution to the shift of the d-d absorption band of the complexes. The results demonstrated that the complexes with counter ions of BPh₄ are more solvatochromic in very weak donor solvents owing to their disinclination in ion-pair formation.     

Manganese(III) complexes of N2O2 donor 5-bromosalicylideneimine ligands: Combined effects of electron withdrawing substituents and chelate ring size variations on electrochemical properties

A series of mononuclear manganese(III) complexes of formulae [Mn(L)(X)(H₂O)] (1-13) and [Mn(L)(X)] (14-17) (X = ClO₄, F, Cl, Br, I, NCS, N₃), derived from the Schiff bases of 5-bromosalicylaldehyde and different types of diamine (1,2-diaminoethane, 1,2-diaminopropane, 1,3-diaminopropane and 1,4-diaminobutane), have been synthesized and characterized by the combination of IR, UV-Vis spectroscopies, cyclic voltammetry and by X-ray crystallography. The redox properties of all the manganese(III) complexes show grossly identical features consisting of a reversible or quasireversible Mn^III/Mn^II reduction. Besides Mn^III/Mn^II reduction, the complexes 4, 5, 10, 13 and 16 also show reversible or quasireversible Mn^III/Mn^IV oxidation. A linear correlation has been found for the complexes 5, 7, 11 and 13 [Mn(L²)(X)(H₂O)] (X = F, Cl, Br, I) when E_1/2 [Mn^III/Mn^II] is plotted against Mulliken electronegativities (χ_M). The effect of the flexibility of the ligand on redox potential has been studied. It has been observed that the manganese(II) state is stabilized with increasing flexibility of the ligand environment. The crystal structure of 6 shows an octahedral geometry.     

Assembly and upconversion luminescence of lanthanide-organic frameworks with mixed acid ligands

Three new lanthanide coordination polymers based on mixed acid ligands [Ln(oba)(ox)_0.5(H₂O)₂]_n (Ln = Y (1); Er (2); Yb (3). H₂oba = 4,4′-oxybis (benzoic acid); H₂ox = oxalic acid) were prepared by hydrothermal reactions and characterized by single-crystal X-ray diffraction. In these complexes, lanthanide ions are bridged by oba ligands to form 1D double-stranded chains, which are further connected by ox ligands, resulting in the formation of 2D (4,4) grids. The upconversion emission of the Y:Er-Yb co-doped coordination polymer was studied and the unusual blue emission for the Er(III) complexes was observed, which arises from the ²H_9/2 → ⁴I_15/2 transition and can be explained by three-photon excitation mechanism which is mostly phonon-dependent. The introduction of the oxalate anion without high-energy vibrational groups is beneficial to the increasing intensity of upconversion fluorescence. The magnetic properties of complexes 2 and 3 were investigated. The decrease of χ_MT over the temperature range of 300-2 K and the negative value of θ are due primarily to the splitting of the ligand field of the Er^III and Yb^III ions together with the possible weak antiferromagnetic coupling between the rare earth ions.     

Binuclear manganese(III) complexes of an unsymmetric pyrazolate-based compartmental ligand with hard donor set

The synthesis, crystal structure and magnetic properties of manganese(III) binuclear complexes [Mn^III₂(L-3Н)₂(CH₃ОH)₄]·2CH₃ОH (1) and [Mn^III₂(L-3Н)₂(Py)₄]·2Py (2) (L = 3-[(1E)-N-hydroxyethanimidoyl]-4-methyl-1H-pyrazole-5-carboxylic acid) are reported. The ligand contains two distinct donor compartments formed by the pyrazolate-N and the oxime or the carboxylic groups. The complexes were characterized by X-ray single crystal diffraction, revealing that both 1 and 2 consist of dinuclear units in which the two metal ions are linked by double pyrazolate bridges with a planar {Mn₂N₄} core. Cryomagnetic measurements show antiferromagnetic interaction with g = 1.99, J = −3.6 cm⁻¹, Θ = −2.02 K for 1 and g = 2.00, J = −3.7 cm⁻¹, Θ = 1.43 K for 2.     

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.