Crystal structure of a new transition metal-organic Zn(II) complex

A novel Zn(II) coordination polymer [Zn₂(phen)₂]L₄·3H₂O(1) is synthesized by the reaction of Zn(NO₃)₂, Phen(1,10-phenanthroline), and L(2-mercaptonicotinic acid) at room temperature and structurally characterized by X-ray single crystal diffraction along with IR spectra and elemental analysis. Title complex 1 belongs to the triclinic system with the space group (P-1), a = 10.9373(11) Å, b = 11.6201(12) Å, c = 13.1371(14) Å; α = 116.100(1)°, β = 97.717(2)°, γ = 108.652(2)°, V = 1344.4(2) ų; Z = 2, ρ_calc = 1.596 g·cm^?3, F(000) = 664, R ₁ = 0.0708 and wR ₂ = 0.1823 independent reflections for 18523 observed ones (I > 2σ(I)), and the zinc atom is rendered five-coordinated in a distorted tetragonal pyramid coordination geometry by two nitrogen atoms from the phen molecule, two oxygen atoms from two L molecules, and an oxygen atom from the H₂O molecule. Complex 1 forms a 1D chain by O-H…O hydrogen bonds from free-water, while the 2D layer structure is formed by C-H…O hydrogen bonds through the L ligand of adjacent chains. These compounds further result in a 3D network structure by the intermolecular π…π stacking interaction of the neighbouring layers.     

A binuclear copper(II) complex with unusual magnetism

A binuclear copper(II) complex [Cu₂ (μ-pyo)₂Br₄] _n (where pyo = pyridine N-oxide) has been synthesized and its structure determined by X-ray crystallography. This complex crystallizes in monoclinic, space group P2₁/c, with unit cell dimensions a = 11.020(3) Å, b = 10.049(3) Å, c = 7.905(2) Å, β = 110.609(3)°, and Z = 2. The structure was refined to final R = 0.0311 and wR = 0.0721 for 1302 observed reflections (I > 2σ(I)). In the complex, two Cu(II) ions are bridged by two pyo ligands and four bromides coordinate the Cu(II); the distance between the bridged Cu(II) ions is 3.261 Å. The variable-temperature (4–300 K) magnetic susceptibility data show that the magnetic moment is zero. Thus, there exists very strong anti-ferromagnetic coupling between the bridged binuclear Cu(II) ions. Density functional calculations yield a singlet-triplet splitting 2J = ?1355 cm^?1.     

A weak,short metal-metal bond in a chromium(II) amidinate complex

Treatment of chromium(II) chloride with 2 equiv of Li[tBuNC(CH3)NtBu], Li[iPrNC(CH3)NiPr], or Li[tBuNC(CH3)NEt] (prepared from the corresponding carbodiimides and methyllithium) afforded Cr[tBuNC(CH3)NtBu]2 (1, 50%), Cr[iPrNC(CH3)NiPr]2 (2, 54%), and [Cr(tBuNC(CH3)NEt)2]2 (3, 58%) as deep blue, purple, and amber or metallic green crystals, respectively. Cr[tBuNC(CH3)NtBu]2 and Cr[iPrNC(CH3)NiPr]2 possess monomeric structures in the solid state with tetrahedral and square planar geometries about the chromium centers, respectively. [Cr(tBuNC(CH3)NEt)2]2 exists as a dimer in the solid state, with two mu2-amidinate ligands, two eta2-amidinate ligands, and a chromium-chromium bond length of 1.9601(12) A. [Cr(tBuNC(CH3)NEt)2]2 is diamagnetic in the solid state, as determined by magnetic susceptibility measurement and CP/MAS 13C NMR spectroscopy. However, [Cr(tBuNC(CH3)NEt)2]2 dissociates into paramagnetic monomers in solution, as determined by observation of extremely broad peaks in the 1H NMR spectra in cyclohexane-d12 and benzene-d6, a solution magnetic moment measurement, and by solution molecular weight measurements in benzene. The combined results suggest that the chromium-chromium bond strength in [Cr(tBuNC(CH3)NEt)2]2 is weak and cannot exceed the difference in solvation energies between the dimer and two monomers, plus any increase in metal-nitrogen bond strengths in the monomers.     

Magnetic interactions in a new heterospin complex involving nitroxide radical and oxamido-bridged copper(II)

A new binuclear copper(II) complex [Cu₂(oxpn)(IM2py)₂](ClO₄)₂, containing four spin carriers with pyridyl-substituted nitroxide radicals has been synthesized and characterized structurally and magnetically (oxpn?=?N,N′-bis(3-aminopropyl)oxamido, IM2py?=?2-(2′-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl). The structure of the complex consists of centrosymmetric trans oxamido-bridged copper(II) binuclear units and nitroxide radicals. The coordination geometry around each copper atom is distorted square pyramidal and the apical position is occupied by a nitrogen atom of the imidazoline ring of a radical ligand. Magnetic analysis indicates that the complex exhibits strong antiferromagnetic coupling between copper(II) ions through the oxamido bridge and a ferromagnetic interaction between copper(II) ions and radical ligands. The magnetic behaviour is discussed with reference to the crystal structure.     

Crystal structure of a new copper(II) complex with borodicitric acid

The crystal structure of the double copper(II) complex with borodicitric acid [Cu(H₂O)₅(C₆H₆O₇)₂B]⁺ · [(C₆H₆O₇)₂B]^? · 5H₂O of composition Cu[(C₆H₆O₇)₂B]₂ · 10H₂O has been studied by X-ray crystallography. The crystals are monoclinic, space group P2₁): a = 10.7852(2) ?, b = 9.9980(2) ?, c = 17.9500(5) ?; ?? = 101.126(1)°, FW = 1025.75, V = 1899.18(7) ?³, Z = 2. The dicitratoborate anions with a spirane structure have a normal geometry. The coordination polyhedron of the copper atoms is a distorted octahedron (CN 6 = 4 + 2) with an average equatorial Cu-O distance of 1.965 ± 0.023 ?. The axial positions in the CuO₆ octahedron are occupied by a water molecule and an oxygen atom of one of the citrate ligands: Cu-O(5w), 2.430(3) ?; Cu-O(8), 2.382(3) ?. The crystals have an extended intricate system of hydrogen bonds consisting of 27 unique three-center O-H??O, O(w)??O, and O(w)??O(w??) bonds and four-center O(w)??O, O(w??) bonds with different structural functions.     

Oxamato-bridged trinuclear Ni(II)Cu(II)Ni(II) complexes with irregular spin state structures and a binuclear Ni(II)Cu(II) complex with an unusual supramolecular structure: crystal structure and magnetic properties

Four oxamato-bridged heterotrinuclear Ni(II)Cu(II)Ni(II) complexes of formula ([Ni(bispictn)](2)Cu(pba))(ClO(4))(2).2.5H(2)O (1), ([Ni(bispictn)](2)Cu(pbaOH))(ClO(4))(2).H(2)O (2), ([Ni(cth)](2)Cu(pba))(ClO(4))(2) (3), and ([Ni(cth)](2)Cu(opba))(ClO(4))(2).H(2)O (4) and a binuclear Ni(II)Cu(II) complex of formula [Cu(opba)Ni(cth)].CH(3)OH (5) have been synthesized and characterized by means of elemental analysis, IR, ESR, and electronic spectra, where pba = 1,3-propylenebis(oxamato), pbaOH = 2-hydroxyl-1,3-propylenebis(oxamato), opba = o-phenylenebis(oxamato), bispictn = N,N'-bis(2-pyridylmethyl)-1,3-propanediamine, and cth = rac-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane. The crystal structures of 1, 3, and 5 have been determined. The structures of complexes 1 and 3 consist of trinuclear cations and perchlorate anions, and that of 5 consists of neutral binuclear molecules which are connected by hydrogen bonds and pi-pi interactions to produce a unique supramolecular "double" sheet. In the three complexes, the copper atom in a square-planar or axially elongated octahedral environment and the nickel atom in a distorted octahedral environment are bridged by the oxamato groups, with Cu.Ni separations between 5.29 and 5.33 A. The magnetic properties of all five complexes have been investigated. The chi(M)T versus T plots for 1-4 exhibit the minimum characteristic of antiferromagnetically coupled NiCuNi species with an irregular spin state structure and a spin-quartet ground state. The chi(M)T versus T plot for 5 is typical of an antiferromagnetically coupled NiCu pair with a spin-doublet ground state. The Ni(II)-Cu(II) isotropic interaction parameters for the five complexes were evaluated and are between 102 and 108 cm(-)(1) (H = -JS(Cu).S(Ni)).     

Synthesis, crystal structure and imine bond activation of a copper(II) Schiff base complex

A new copper(II) complex [Cu(HL)(ClO₄)](ClO₄) (1), where HL is a multidentate Schiff base N,N′-(2-hydroxypropane-1,3-diyl)bis(pyridine-2-aldimine), is prepared, structurally characterized by X-ray crystallography and its spectral and electrochemical properties studied. The complex forms a one-dimensional chain in the solid state structure in which the monomeric Cu(HL) units are linked by the perchlorate ligand. The complex has an axially elongated six coordinate geometry (4+2) with a CuN₄O₂ core in which the Schiff base ligand displays a tetradentate mode of bonding in the basal plane. The axial ligand is perchlorate with a significantly long Cu–O bond of ca. 2.6 Å. The one-electron paramagnetic complex displays a cyclic voltammetric response for the Cu(II)/Cu(I) couple at 0.01 V versus SCE in MeCN–0.1 M TBAP. The azomethine bond of the Schiff base in 1 on treatment with H₂O₂ undergoes oxidative conversion to form a bis(picolinato)copper(II) · dihydrate species through the formation of an amido intermediate as evidenced from the solution infrared spectral studies.     

The structure of nitratotriphenylstannyltin(II): A compound with a tin(IV)tin(II) bond

A compound of formula [Sn^II(NO₃) [(C₆H₅)₃ Sn^IV], containing a tin(IV)tin(II) bond, has been prepared, and its crystal structure is determined.     

Disulfide bond cleavage induced by a platinum(II) methionine complex

The cleavage of a disulfide bond and the redox equilibrium of thiol/disulfide are strongly related to the levels of glutathione (GSH)/oxidized glutathione (GSSG) or mixed disulfides in vivo. In this work, the cleavage of a disulfide bond in GSSG induced by a platinum(II) complex [Pt(Met)Cl2] (where Met = methionine) was studied and the cleavage fragments or their platinated adducts were identified by means of electrospray mass spectrometry, high-performance liquid chromatography, and ultraviolet techniques. The second-order rate constant for the reaction between [Pt(Met)Cl2] and GSSG was determined to be 0.4 M(-1) s(-1) at 310 K and pH 7.4, which is 100- and 12-fold faster than those of cisplatin and its monoaqua species, respectively. Different complexes were formed in the reaction of [Pt(Met)Cl2] with GSSG, mainly mono- and dinuclear platinum complexes with the cleavage fragments of GSSG. This study demonstrated that [Pt(Met)Cl2] can promote the cleavage of disulfide bonds. The mechanistic insight obtained from this study may provide a deeper understanding on the potential involvement of platinum complexes in the intracellular GSH/GSSG systems.     

A luminescent Pt(II) complex with a terpyridine-like ligand involving a six-membered chelate ring

The ligand 2-(8'-quinolinyl)-1,10-phenanthroline (1) was prepared in 79% yield by the Friedlander condensation of 8-amino-7-quinolinecarbaldehyde and 8-acetylquinoline. The complex [Pt(1)Cl]+ was prepared and compared with the isomeric 2-(2'-quinolinyl)-1,10-phenanthroline (2) complex. An X-ray analysis indicated that the six-membered chelate ring in the tridentate complex resulted in a relief of angle strain as well as some non-planarity in the bound ligand 1. The control system for photophysical studies is [Pt3Cl]+ where denotes 2-(2'-pyridyl)-1,10-phenanthroline. Relative to the complex of 3, in dichloromethane solution [Pt(1)Cl]+ exhibits noticeably higher energy charge-transfer absorption but slightly lower energy emission. The gap between the onset of absorption and emission is larger because the emission from [Pt(1)Cl]+ originates from a triplet excited state with substantial intra-ligand character. At room temperature in deoxygenated dichloromethane, [Pt(1)Cl]+ has an excited-state lifetime of 310 ns vs. 230 ns for [Pt(1)Cl]+. Within the series, [Pt(1)Cl]+ also exhibits the largest activation barrier for thermally induced quenching at 2730 cm(-1) in fluid dichloromethane solution. However, the barrier is only about 50% larger than that found for [Pt(1)Cl]+. There is reduced ring strain in [Pt(1)Cl]+, but inter-ligand steric interactions weaken the ligand field.     

Luminescence properties of a di-ruthenium(II) complex with an intramolecular hydrogen bond modulated by DNA and copper(II) ion

Modulation of the luminescence properties of a di-ruthenium(II) complex [(bpy)₂Ru(BL)Ru(bpy)₂]⁴⁺ (bpy = 2,2′-bipyridine, BL = 2-hydroxyl-5-methyl-1,3-bis([1,10]phenanthroline-[5,6-d]imidazol-2-yl)benzene) by DNA and/or Cu²⁺ ion has been investigated. It is found that the ruthenium(II) complex can coordinate to the Cu²⁺ ion in both the absence and presence of DNA. Binding to DNA is through electrostatic interactions and the intramolecular hydrogen bond in the complex is located outside of the DNA. The binding constant is 1.6 × 10⁴ M⁻¹. Moreover, it is demonstrated that DNA has the ability to enhance the luminescence intensities of both the di-ruthenium(II) complex and the tri-metallic system generated by chelating with Cu²⁺. Conversely, Cu²⁺ ion can quench the luminescence of both the free ruthenium(II) complex and the DNA-bound ruthenium(II) complex.     

N-O bond homolysis of an iron(II) TEMPO complex yields an iron(III) oxo intermediate

The reaction of TEMPO with the iron(I) synthon PhB(MesIm)(3)Fe(COE) leads to formation of the κ(1)-TEMPO complex PhB(MesIm)(3)Fe(TEMPO). Structural and spectroscopic data establish the complex contains divalent iron bound to a nitroxido anion and is isoelectronic to an iron(II) peroxo complex. Thermolysis of the complex results in N-O bond homolysis, leading to the formation of an iron(III) oxo intermediate. The oxo intermediate is active in oxygen atom transfer reactions and can be trapped by the triphenylmethyl radical to give the iron(II) alkoxo complex PhB(MesIm)(3)Fe(OCPh(3)).     

Bidentate-bridging butyleneglycol in a framework structure with A Co(II) mixed-ligand complex of an imidazoline nitroxyl

Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated from Zhurnal Strukturnoi Khimii, Vol. 33, No. 2, pp. 118–125, March–April, 1992.     

Crystal and molecular structure of a new palladium(II) complex with a coumarin-valine derivate

The new coumarine derivate with methyl ester of 2-((Z)-1(2,4-dioxochroman-3-ylidene)ethylamino)-3-methylbutanoic acid and the corresponding palladium(II) complex are synthesized and characterized by microanalysis, infrared, ¹H and ¹³C NMR spectroscopy. The proposed structure of the ligand was confirmed based on the X-ray structural study.     

A new iron(II) thiocyanato thiocyanogen complex

The reaction between Fe³⁺ and SCN^?, in glacial acetic acid medium, gave a dark red solution which differs from the classical FeSCN²⁺, prepared in aqueous medium, with regard to stability and composition. In contrast to [FeSCN]²⁺ which undergoes photochemical decomposition and is bleached by light and reduced by hydroxylammonium chloride, the new complex is stable towards these agents, but it reacts with water. In addition to the charge transfer band at 480 nm exhibited by both solutions, the new complex exhibits a sharp strong band at 253 nm characteristic of the trithiocyanate ion, [SCN^? + NCSSCN]; thiocyanogen being produced by oxidation of SCN^? by Fe³⁺. The reaction with water is attributed to the hydrolysis of thiocyanogen mainly into sulphate. The presence of thiocyanogen in the new complex enhanced polymerixation and subsequent deposition of solid complex. On the basis of chemical, spectral, and thermal analyses the formula K₂[Fe(SCN)₄(NCSSCN)], is assigned to the new compound.     

The structure of a new copper(II) complex with 3-methyl-5-carboxylatopyrazole

Molecular and crystal structures of a new complex compound of copper(II) with 3-methyl-5-carboxylatopyrazole (CH₃PzCOO^?) with the composition Cu(CH₃PzCOO)₂·H₂O have been determined by single crystal XRD. It has been demonstrated that the carboxylate ion performs the bridging tridentate function. In the equatorial plane coordination occurs through the pyridine N atom of the pyrazole and one of O atoms of the carboxylate group yielding a five-membered metallocycle CuNOC₂. The second O atom of one of the ligands is bound to the neighboring copper(II) ion affording an infinite linear chain. The coordination polyhedron of the copper atom is a square pyramid, coordination core CuN₂O₃.     

A new copper(II) complex as an efficient catalyst of luminol chemiluminescence

A new copper complex (2) has exhibited highly efficient catalytic activity of luminol chemiluminescence in water in the presence of ascorbic acid and dissolved O2 under conditions that conventional catalysts such as Cu(OAc)2, hemin or cyclen-Cu(II) did not show significant activity.     

Rearrangement of the tris(2-pyridylthio)methanido ligand in an iron(II) complex containing an Fe-C bond

Iron(II) tris(2-pyridylthio)methanido (1) containing an Fe-C bond, obtained from the reaction of tris(2-pyridylthio)methane (HL(1)) and iron(II) triflate, reacts with protic acid to generate iron(II) bis(2-pyridylthio)carbene (1a). The carbene complex is converted to an iron(II) complex (2) of the 1-[bis(2-pyridylthio)methyl]pyridine-2-thione ligand (L(3)) upon treatment with a base. Complex 2 reversibly transforms to 1a in the presence of an acid. During the transformation of 1 to 2, a novel rearrangement of L(1) to L(3) takes place. The iron(II) complexes are reactive toward dioxygen to form the corresponding iron(III) complexes.