A new dinuclear unsymmetric copper(II) complex as model for the active site of catechol oxidase

The crystal structure, magnetic, redox and spectroscopic properties of a novel unsymmetrical dinuclear copper(II) complex, prepared by the reaction between copper(II) perchlorate, sodium acetate and the unsymmetrical, binucleating ligand HTPPNOL, where HTPPNOL is N,N,N′-tris-(2-pyridylmethyl)-1,3-diaminopropan-2-ol, is reported. HTPPNOL (1 equiv.) reacted with 1 equiv. of copper(II) ion, in methanol, and produced the mononuclear copper complex [Cu(TPPNOL)](ClO₄)(BPh₄) (1). On the other hand, the reaction of 1 equiv. of HTPPNOL with 2 equiv. each of copper (II) ion and acetate, in methanol, produced the dinuclear complex [Cu₂(TPPNOL)(OOCCH₃)](ClO₄)₂ (2), whose structure has been determined by X-ray diffraction. In complex 2, as a result of the inherent asymmetry of the ligand HTPPNOL, one copper ion is five-coordinated (distorted trigonal-bipyramidal) while the other copper is four-coordinated (distorted square-planar). Then, as a result of the presence of distinct geometries for the metal centres, complex 2 exhibits a ferromagnetic coupling (J=+25.41 cm⁻¹). Titration experiments carried out on the dinuclear complex suggest a pK_a=8.0, which was related to the aquo/hydroxo equilibrium. Complex 2 is able to oxidise 3,5-di-tert-butylcatechol to the respective o-quinone. The oxidation reaction was studied by following the appearance of the quinone spectrophotometrically, at pH 8.0 and 25 °C.     

Copper(II) promoted imidazolidine ring formation and complexation: A unique reaction course

The reaction of Cu(II) ions with a sodium salt of new Schiff base ligand NaL¹, sodium N-2-methyl pyridine-2-imine benzoate, in alkaline medium produced an imine bond coupled ligand and a novel complex, Na₂[Cu(L³)₂], L³ = 2,5-di(2-benzoic acid)-4-(2-pyridine)-1-(2-methyl-2-pyridine)-imidazolidine. When the reduced form of the sodium salt of the Schiff base ligand, NaL², is employed, a simple hexacoordinated copper(II) complex, [Cu(L²)₂], [L²]⁻ = bis(N-(2-methylpyridine)-2-aminomethylbenzoate), was isolated. The compounds were characterized by spectroscopic methods and the molecular structures of [Cu(L²)₂] and Na₂[Cu(L³)₂] were determined by single-crystal X-ray diffraction methods. Reaction mechanism for the synthesis of, Na₂[Cu(L³)₂], copper(II) promoted imine bond coupling is proposed and discussed. The redox behavior of [Cu(L²)₂] and Na₂[Cu(L³)₂], studied using cyclic voltammetry and electron paramagnetic resonance spectroscopic methods, are also discussed.     

Manganese(II) complexes of an acyclic phenol-based dinucleating ligand with four methoxyethyl chelating arms: synthesis, structure, magnetism and electrochemistry

Dinuclear manganese(II) complexes [Mn₂(bomp)(PhCO₂)₂]BPh₄ (1), [Mn₂(bomp)(MeCO₂)₂]BPh₄ (2), and [Mn₂(bomp)(PhCO₂)₂]PF₆ (3) were synthesized with a dinucleating ligand 2,6-bis[bis(2-methoxyethyl)aminomethyl]-4-methylphenol [H(bomp)]. Dinuclear zinc complex [Zn₂(bomp)(PhCO₂)₂]PF₆ (4) was also synthesized for the purpose of comparison. X-ray analysis revealed that the complex 1·CHCl₃ contains two manganese ions bridged by the phenolic oxygen and two benzoate groups, forming a μ-phenoxo-bis(μ-benzoato)dimanganese(II) core. Magnetic susceptibility measurements of 1–3 over the temperature range 1.8–300 K indicated antiferromagnetic interaction (J=−4 to −6 cm⁻¹). Cyclic voltammograms of 3 showed a quasi-reversible oxidation process at +0.9 V versus a saturated sodium chloride calomel reference electrode, assigned to Mn^IIMn^II/Mn^IIMn^III.     

Complexes of copper(II) dihalide with 2,2′-dipyridylamine. X-ray diffraction structures of the [dibromo-bis(dipyam)copper(II)]–water (1:2) and di[chloro-bis(dipyam)copper(II)]diiodide–acetonitrile (1:2) complexes

The formation of complexes between copper(II) halides and 2,2′-dipyridylamine (dipyam) has been studied systematically. Only complexes with a 1:1 and 1:2 metal-to-ligand ratio are formed. Some mixed chloro–iodide and halide–PF₆ compounds have also been isolated. The X-ray diffraction structures of the [Cu(dipyam)₂Br₂] · 2H₂O (I) and the [Cu(dipyam)₂Cl]₂I₂ · 2CH₃CN (II) complexes are reported. I is a rare example of an octahedral coordination among the copper(II) halide complexes of dipyam. The two bromo atoms, which occupy the apical positions, are H-bonded to the water molecules of crystallization. II is a dimer, where each copper forms a cationic chloro-complex of approximately trigonal bipyramidal geometry, the dimerization being due to hydrogen bonds formed by the NH group of one of the two dipyams coordinated to each metal atom with the chlorine atom of the centrosymmetric cationic complex. The iodide anions are hydrogen-bonded to the NH groups of the dipyams not involved in the dimerization.     

Synthesis, crystal structures and magnetic studies of dicyanamide bridged two new 1D copper(II) complexes

Two new dicyanamide bridged 1D polynuclear copper(II) complexes [Cu(L¹){μ_1,5-N(CN)₂}]_n (1) [L¹H = C₆H₅C(O)NHNC(CH₃)C₅H₄N] and [Cu(L²){μ_1,5-N(CN)₂}]_n (2) [L²H=C₆H₅C(O)CHC(CH₃)NCH₂CH₂N(CH₃)₂] have been synthesised and structures of both the complexes and their crystal packing arrangements have been established by X-ray crystallography. For complex 1, a tridentate hydrazone ligand (L¹H) obtained by the condensation of benzhydrazide and 2-acetylpyridine is used, whereas a tridentate Schiff base (L²H) derived from benzoylacetone and 2-dimethylaminoethylamine is employed for the preparation of complex 2. Variable temperature magnetic susceptibility measurement studies indicate there are weak antiferromagnetic interactions with J values −0.10 and −1.41 cm⁻¹ for 1 and 2, respectively.     

Synthesis, spectroscopic properties and X-ray crystal structures of two dinuclear alkoxo-bridged copper(II) compounds with the ligand bis(1-methyl-2-benzimidazolyl) propane. A unique alkoxo-bridged Cu(II) dinuclear compound with an additional bidentate bridging triflate anion

Based on the new ligand bis(1-methyl-2-benzimidazolyl) propane (abbreviated as mtbz) several new copper(II) coordination compounds have been prepared and characterized structurally and spectroscopically. Two representative compounds, i.e. [Cu₂(mtbz)₂(CH₃)₂- (CF₃SO₃)](CF₃SO₃) (1) and [Cu₂(mtbz)₂(CH₃O)₂](ClO₄)₂ (4) were characterized structurally by X-ray diffraction. Crystal data for 1: monoclinic, space group P2₁/c, a=13.6585(5), B=39.981(3), C=20.919(1) Å, β=125.98(1)°, Z=8. Crystal data for 4: monoclinic, space group P2₁/c, a=13.115(2), B=9.523(2), C=17.908(4) Å, β=111.71(1)°, Z=2. Structures 1 and 4 each consist of a dinuclear unit with bridging methoxo groups and one ligand linked to each copper via an N atom. Structure 1 (which consists of two dinuclear, crystallographically independent, but chemically identical units) has the two copper atoms bridged by a triflate anion, providing each copper atom a square-pyramidal coordination, while the copper atoms in structure 4 have an almost a square-planar geometry. The Cu---Cu distances (Å) within the dinuclear units are: 1, 2.9775(13), 2.9751(13); 4, 2.9872(16); the Cu---O---Cu bridging angles (°) are: 1, 101.7(3), 101.7(3), 100.9(3), 102.1(3); 4, 103.2(2). The mid-IR section focused on the vibrations of the triflate anion reveals interesting results concerning the assignments of that anion related to the v_as(S---O) band. Characteristic Cu---O vibrations in the far-IR section were found at 386 and 230 cm⁻¹ for the methoxo-bridged and 454 and 332 cm⁻¹ for the ethoxo-bridged compounds. These dinuclear species are EPR silent, and only a weak signal of monomeric impurities is observed. They also show a diamagnetic behavior below room temperature.     

Convenient preparation of [CuX(PCy3)2](X = Br, I, SCN, N3) complexes. X-ray crystal structure of [Cu(N3)(PCy3)2] (Cy = cyclo-C6H11)

The labile cations [Cu(F-BF₃)(PCy₃)₂] and [Cu(OTf)(PCy₃)₂] are versatile precursors for the formation of [Cu(X)(PCy₃)₂] (X = Br, I, SCN, N₃) complexes by metathesis with NaX. The azide [Cu(N₃)(PCy₃)₂] is triclinic, space group , a = 9.755(4), B = 22.78(1), C = 9.284(6) Å, = 96.76(3), β = 115.36(3), γ = 94.20(5)°, Z = 2.     

Nitrogen, sulfur and oxygen donor adducts with copper(II) complexes of antitumor 2-formylpyridinethiosemicarbazone analogs: Physicochemical and cytotoxic studies

The preparation of N-, S- and O-donor ligand adducts with CuX⁺(HX=6-methyl-2-formylpyridinethiosemicarbazone (6HL); 2-formylpyridine-2^′-methylthiosemicarbazone (2′L); 2-formylpyridine-4′-methylthiosemicarbazone (4′HL)) is described. The N-donors, 2,2′-bipyridyl (bipy), 4-dimethylaminopyridine (dmap) give the complexes [Cu(6L)(bipy)]PF₆, [Cu(6L)(bipy)]Cl·5H₂O, [Cu(4′L)(bipy)]PF₆, [Cu(6L)(dmap)₂]PF₆·2.5 H₂O and [Cu(4′L)(dmap)₂]PF₆·H₂O which have been characterized by physical and spectroscopic techniques. Pentafluorothiophenolate (pftp) gives S-donor complexes [CuX(pftp)] (X=6L and 4′L) and thiolato co-ordination is proposed on the basis of spectroscopic evidence. Paratritylphenolate (ptp) and HPO²⁻₄ give O-donor complexes [Cu(6L)(ptp)], [Cu(4′L)(ptp)], [{Cu(6L)}₂HPO₄]·4H₂O, and [{Cu(4^′L)}₂HPO₄]·5H₂O which have been characterized by physical and spectroscopic techniques, as have the precursor complexes [Cu(6L)(CH₃COO)]·H₂O, [Cu(4′L)(CH₃COO)], Cu(6HL)(CF₃COO)](CF₃COO)·0.5H₂O, [Cu(4′HL)(CF₃COO)](CF₃COO), [Cu(2′L)Cl₂] and [Cu(2′L)(NO₃)₂]. Protonation constants for the ligands and some of their complexes have been determined. 2-Formylpyridinethiosemicarbazone (HL) complexes of silver, gold, zinc, mercury, cadmium and lead are also discussed. Cytotoxicity against the human tumor cell line HCT-8 and antiviral data for selected compounds are presented.     

Syntheses and characterization of mono- and di-N-hydroxyethylated tetraaza macrocycles containing eight C-methyl groups and their nickel(II) and copper(II) complexes

New partially N-hydroxyethylated 14-membered tetraaza macrocycles 1,8-bis(2-hydroxyethyl)-3,5,7,7,10,12,14,14-octamethyl-1,4,8,11-tetraazacyclotetradecane (L²) and 1-(2-hydroxyethyl))-3,5,7,7,10,12,14,14-octamethyl-1,4,8,11-tetraazacyclotetradecane (L³) have been synthesized selectively by the one-step reaction of 2,5,5,7,9,12,12,14-octamethyl-1,4,8,11-tetraazacyclotetradecane (L¹) with 2-hydroxyethyl bromide. The complexes [NiL³]²⁺, [CuL²]²⁺, and [CuL³]²⁺ have been prepared and characterized. The complex [CuL²](ClO₄)₂ has a square-pyramidal coordination geometry with one apical oxygen atom; only one of the two hydroxyethyl groups is coordinated to the metal ion. Electronic absorption spectra of [CuL³](ClO₄)₂ containing one hydroxyethyl pendant arm indicate that the geometry is similar to that of [CuL²](ClO₄)₂. Unexpectedly, the nickel(II) complex [NiL³](ClO₄)₂ has a severely distorted trigonal bipyramidal coordination geometry with the oxygen atom of the pendant arm at the equatorial position. The Ni---O bond distance of the nickel(II) complex is shorter, or not longer, than the Ni---N bond distances. The ligand in [CuL²]²⁺ is in the RRSS (trans-III) configuration, as usual, whereas that in [NiL³]²⁺ has the RRRR (trans-V) conformation. The coordination geometry and properties of [NiL³]²⁺ are quite different from those reported for other related nickel(II) complexes containing one functional pendant arm.     

Monomeric and dimeric mixed-ligand copper(II) complexes of 2,2′-bipyridine/1,10-phenanthroline and 1-methylimidazole with imidazoles as catalysts for superoxide dismutation

Monomeric complexes [Cu(LL)(L′)(NO₃)₂] (where LL is 2,2′-bipyridine or 1,10-phenanthroline and L′ is 1-methylimidazole) and dimeric complexes [Cu₂(LL)₂(L″)]NO₃ (where L″ is an anion of imidazole or 2-methylimidazole) have been synthesized. These complexes show a d-d transition in the range of 600 to 710 nm. The infrared spectra of monomeric complexes show that the NO₃⁻ is coordinated to copper as a monodentate ligand through an oxygen atom. The ESR spectra of monomeric complexes indicate that the ligands are bonded in axial environment around copper (square pyramidal geometry) with three nitrogen donors occupying an equatorial plane. The ESR spectra of dimeric complexes show a broad signal at about G = 2 with an additional weak signal at about G = 4. This suggests that two copper atoms are in close proximity of < 7 Å. The ESR studies reveal that the formation of imidazolate-bridged binuclear copper(II) complexes from [Cu(LL)(L′)(NO₃)₂] and imidazole is pH dependent with apparent pK_a values of 8.25 to 8.30. The superoxide dismutase activity of ICu(phen)(L′)(NO₃)₂], [Cu(bipy)(L′)(NO₃)₂], and [Cu₂(bipy)₂(L′)₂(L″)]NO₃ has been measured and the latter two complexes show better activity than the former complex.     

Platinum(II) complexes of chelating and monodentate thiourea monoanions incorporating chiral, fluorescent or chromophoric groups

The reaction of cis-[PtCl₂(PPh₃)₂] with trisubstituted thioureas [R¹R²NC(=S)NHR³] in refluxing methanol with triethylamine base, followed by addition of NaBPh₄ gives the salts [Pt{SC(=NR¹R²)NR³}(PPh₃)₂]BPh₄ in high yield; a range of thiourea substituents, including chiral, fluorescent and chromophoric groups can be incorporated. The azo dye-derived complex [Pt{SC(=N(CH₂CH₂)₂O)NC₆H₄N=NC₆H₄NMe₂}(PPh₃)₂]BPh₄ has been characterised by a single-crystal X-ray diffraction study. The formation of a fluorescein-derivatised platinum–thiourea complex is also described. Reaction of cis-[PtCl₂(PPh₃)₂] with PhNHC(S)NHPh or EtNHC(S)NHEt, triethylamine and NaBPh₄ gives, respectively, [Pt{SC(=NHPh)NPh}(PPh₃)₂]⁺ and the known cation [Pt{SC(=NHEt)NEt}(PPh₃)₂]⁺, isolated as tetraphenylborate salts. Reaction of cis-[PtCl₂(PPh₃)₂] with an excess of Na[MeNHC(S)NCN] in methanol gives the bis(thiourea monoanion) complex trans-[Pt{SC(=N---CN)NHMe}₂(PPh₃)₂], characterised by NMR spectroscopy and an X-ray crystal structure determination. When cis-[PtCl₂(PPh₃)₂] is reacted with 1 equiv. of Na[MeNHC(S)N---CN] in methanol, with added NaBPh₄, a mixture of isomers of the [Pt{SC(=NHCN)NMe}(PPh₃)₂]⁺ cation is obtained.     

1D copper(II) and zinc(II) coordination polymers containing an unusual twisted oxalate bridge

Two new copper(II) complexes, Cu(L1)(ClO₄)₂ (1), {[(μ-oxalate)Cu(L1)] · 5H₂O}_n (2), and a zinc(II) complex, {[(μ-oxalate)Zn(L2)] · 3H₂O · 0.5DMF}_n (3) (L = 3,14-dimethyl-2,6,13,17-tetraazatricyclo[14,4,0^1.18,0^7.12]docosane), have been synthesized and characterized by X-ray crystallography. In 1, the ligand conformation is planar, and the octahedral coordination about the copper(II) ion is completed by weakly interacting ions. In 2 and 3, bridging oxalate ligands coordinate to copper(II) or zinc(II) ions in an unusually twisted bis-monodentate (trans-1,1′-bicoordination) mode.

The rigidity and steric hindrance of macrocycles L1 and L2 by the introduction of two cyclohexane rings and methyl groups on a cyclam (1,4,8,11-tetraazacyclotetradecane) skeleton cause the bridging oxalate ligands to adopt such unusual geometries in 2 and 3.     

Tetrakis-[1-methylimidazoline-2(3H)-thione]-μ2-[1-methylimidazoline- 2(3H)-thione]-Di-Copper(I) sulphate trihydrate: Preparation, thermal analysis and crystal structure

1-emthylimidazoline-2(3H)-thione (mimtH) reacts with copper(II) sulphate pentahydrate in aqueous acetone to produce the dinuclear complex, Cu₂(mimtH)₅SO₄ · 3H₂O; the formula has been established by a combination of chemical and thermal analysis. The monoclinic crystals, (space group P_c, Z = 2), contain dinuclear cations, sulphate ions and water molecules. The dinuclear cation, Cu₂(mimtH)₅²⁺, consists of two trigonal copper(I) atoms, four terminal, monodentate, S-donating mimtH molecules and one S-bridging (μ₂) mimtH molecule. Some average dimensions are:Cu---S, 2.258 Å and S---Cu---S, 120.0°; the Cu---S---Cu bridging angle is 94.8° and the Cu---Cu separation distance is 3.308 Å.     

Polynuclear copper(II) complexes with μ2-1,1-azide bridges. Structural and magnetic properties

Two novel, weakly antiferromagnetically coupled, tetranuclear copper(II) complexes [Cu₄(PAP)₂(μ₂-1,1-N₃)₂(μ₂-1,3-N₃)₂(μ₂-CH₃OH)₂(N₃)₄ (1) (PAP = 1,4-bis-(2′-pyridylamino)phthalazine) and [Cu₄(PAP3Me)₂ (μ₂-1,1-N₃)₂(μ₂-1,3-N₃)₂(H₂O)₂(NO₂)₂]- (NO₃)₂ (2) (PAP3Me = 1,4-bis-(3′-methyl-2′-pyridyl)aminophthalazine) contain a unique structural with two μ₂-1,1-azide intramolecular bridges, and two μ₂-1,3-azide intermolecular bridges linking pairs of copper(II) centers. Four terminal azide groups complete the five-coordinate structures in 1, while two terminal waters and two nitrates complete the coordination spheres in 2. The dinuclear complexes [Cu₂(PPD)(μ₂-1,1-N₃)(N₃)₂(CF₃SO₃)]CH₃OH) (3) and [Cu₂(PPD)(μ₂-1,1-N₃)(N₃)₂(H₂O)(ClO₄)] (4) (PPD = 3,6-bis-(1′-pyrazolyl)pyridazine) contain pairs of copper centers with intramolecular μ₂-1,1-azid and pyridazine bridges, and exhibit strong antiferromagnetic coupling. A one-dimensional chain structure in 3 occurs through intermolecular μ₂-1,1-azide bridging interactions. Intramolecular Cu-N₃-Cu bridge angles in 1 and 2 are small (107.9 and 109.4°, respectively), but very large in 3 and 4 (122.5 and 123.2°, respectively), in keeping with the magnetic properties. 2 crystallizes in the monoclinic system, space group C2/c with a = 26.71(1), b = 13.51(3), c = 16.84(1) Å, β = 117.35(3)° and R = 0.070, R_w = 0.050. 3 crystallizes in the monoclinic system, space group P2₁/c with a = 8.42(1), b = 20.808(9), c = 12.615(4) Å, β = 102.95(5)° and R = 0.045, R_w = 0.039. 4crystallizes in the triclinic system, space group P1, with a = 10.253(3), b = 12.338(5), c = 8.072(4) Å, = 100.65(4), β = 101.93(3), γ = 87.82(3)° and R = 0.038, R_w = 0.036 . The magnetic properties of 1 and 2 indicate the presence of weak net antiferromagnetic exchange, as indicated by the presence of a low temperature maximum in χ_m (80 K (1), 65 K (2)), but the data do not fit the Bleaney-Bowers equation unless the exchange integral is treated as a temperature dependent term. A similar situation has been observed for other related compounds, and various approaches to the problem will be discussed. Magnetically 3 and 4 are well described by the Bleaney-Bowers equation, exhibiting very strong antiferromagnetic exchange (− 2J = 768(24) cm⁻¹ (3); − 2J = 829(11) cm⁻¹ (4)).     

Synthesis, crystal structure and magnetic properties of the first structurally characterized 1,2-dithiocroconato-containing Cu(II) complex, [Cu(bpca)(H2O)]2[Cu(1,2-dtcr)2]·2H2O

The first crystal and molecular structure of a transition metal complex containing 1,2-dithiocroconate (1,2-dtcr, dianion of 1,2-dimercaptocylopent-1-ene-3,4,5-trione), [Cu(bpca)(H₂O)]₂[Cu(1,2-dtcr)₂]·2H₂O (where bpca is the bis(2-pyrdidylcarbonyl)amide anion), has been determined by single crystal X-ray diffraction methods. The compound crystallizesin the monoclinic syste, space group P2₁/c, with a = 11.661(3), b = 20.255(6), c = 8.265(3) Å, ß = 107.26(2)° and Z = 2. The structure is formally built of [Cu(1,2-dtcr)₂]²⁻ and [Cu(bpca)(H₂O)]⁺ ions and water of hydration. The copper atom of the anion is situated at a crystallographic inversion centre, bonded to four sulfur atoms in a planar, approximately square arrangement. In the cation the copper equatorial plane is formed by the three nitrogen atoms of the bpca ligand and a water oxygen atom. In addition there is a very weak axial bond to one of the sulfur atoms of a 1,2-dtcr ligand in the anion. Through these latter weak bonds each anion is connected to, and sandwiched between, two cations, resulting in neutral, trinuclear, centrosymmetric formula units. The triple-decker molecules are arranged in stacks along the crystallographic a-axis creating close contacts between the terminal copper atoms and bpca groups of the neighbouring molecules. This intermolecular interaction is, however, too weak to define the structure as a chain compound. The distance between adjacent copper atoms within the trinuclear unit is 4.189(1) Å, while the shortest intra-stack metal-metal separation between terminal copper atoms is 5.281(1) Å. Variable-temperature magnetic susceptibility measurements in the temperature r.2–140 K reveal that a Curie law is followed; with three non-interacting copper(II) ions in the formula unit.     

Copper(II) complexes with (2-hydroxybenzyl-2-pyridylmethyl)amine–Hbpa: syntheses, characterization and crystal structures of the ligand and [Cu(II)(Hbpa)2](ClO4)2·2H2O

Copper(II) complexes were synthesized and characterized by means of elemental analysis, IR and visible spectroscopies, EPR and electrochemistry, as well as X-ray structure crystallography. The group consists of discrete mononuclear units with the general formula [Cu(II)(Hbpa)₂](A)₂·nH₂O, where Hbpa=(2-hydroxybenzyl-2-pyridylmethyl)amine and A=ClO₄ ⁻, n=2 (1), CH₃COO⁻, n=3 (2), NO₃ ⁻, n=2 (3) and SO₄ ²⁻, n=3 (4). The structures of the ligand Hbpa and complex 1 have been determined by X-ray crystallography. Complexes 1–4 have had their UV–Vis spectra measured in both MeCN and DMF. It was observed that the compounds interact with basic solvents, such that molecules coordinate to the metal in axial positions in which phenol oxygen atoms are coordinated in the protonated forms. The values were all less than 1000 M⁻¹ cm⁻¹. EPR measurements on powdered samples of 1–3 gave g/A values between 105 and 135 cm⁻¹, typical for square planar coordination environments. Complex 4·3H₂O exhibits a behaviour typical for tetrahedral coordination. The electrochemical behaviour for complexes 1 and 2 was studied showing irreversible redox waves for both compounds.     

Studies on copper(II) complexes of o-quinone monooximes. 7. Cyanato adducts of bis(4-chloro-1,2-benzoquinone 2-oximato)copper(II), Cu(Clqo)2

Two novel adducts of Cu(Clqo)₂ (Clqo = 4-chloro-1,2-benzoquinone 2-oximato),i.e. K[Cu(Clqo)₂(NCO)] (1) and (Bu₄N)₂[Cu(Clqo)₂(NCO)]OCN (2) have been isolated and characterized by vibrational and electronic spectra. In both compounds the copper(II) atom is pentacoordinated; in fact the X-ray crystal structure determination of complex2 showed that only one of the two cyanato groups is N-bonded of the Cu^II center, while the other one is non-coordinated.     

The versatile coordination chemistry of tricyanoethenolate, [(NC)2C=C(CN)O]

The reaction of meso-tetrakis (4-dimethoxyphenyl) porphinatomanganese(II), MnTP_OMeP, with TCNE (TCNE = tetracyanoethylene) leads to the formation of [MnTP_OMeP]⁺ [TCNE]⁻ and [MnTP_OMeP]⁺[OC(CN)C(CN)₂]⁻. The single-crystal X-ray structures of the latter as well as [Cu(bipy)₂Cl]⁺ [OC(CN)C(CN)₂]⁻ were determined. The former has a disordered [OC(CN)C(CN)₂]⁻ bridging via C and O between a pair of Mn^III sites, whereas the latter has an isolated [OC(CN)C(CN)₂]⁻ unbound to Cu^II. The IR characterization for μ₂-C,O bound [OC(CN)C(CN)₂]⁻ is at 2219m and 2196s (νCN) cm⁻¹ and at 1558s (νCO) cm⁻¹ while for unbound [OC(CN)C(CN)₂]⁻ it is at 2210m, 2203m, 2181m (νCN) cm⁻¹ and at 1583s (νCO) cm⁻¹.     

Isolation of a thermodynamically unfavorable [Ni(DACO)2] complex and its isomer: syntheses, characterization, crystal structures and theoretical study (DACO=1,5-diazacyclooctane)

Two Ni^II complexes of 1,5-diazacyclooctane (DACO), [Ni(DACO)₂]Br₂ (I) and [Ni(DACO)₂]Br·ClO₄ (II) have been newly synthesized and characterized. Single crystal X-ray diffraction analysis of DACO and both Ni^II complexes reveals that DACO takes boat/chair conformation in the solid state and its Ni^II complexes. In complex I, Ni^II ion is at the center of symmetry, which is four-coordinated by nitrogen donors of DACO. However, in complex II, an unexpected coordination mode of [M(DACO)₂]²⁺ (M=Cu^II and Ni^II) was found, in which two DACO ligands are related to each other by a mirror plane and the coordination sphere of Ni^II is a distorted planar geometry. Furthermore, complexes I and II form quite different packing patterns (macrocycle or chain) through hydrogen bonds, which may be a key role to stabilize the crystals. The results of theoretical calculation indicate that complex I has thermodynamic stability, while II has chemical stability. Therefore, both of them have the probability to be obtained from different reaction processes or conditions.     

Ferrocenyl-derived face-capping ligands: syntheses and molecular structures of [(FcTt)Cu]4 and [FcTt]2M (M = Fe, Co, Ni; FcTt = ferrocenyltris((methylthio)methyl)borate)

The synthesis and characterization of a ferrocenyl-derived tridentate ligand, ferrocenyltris((methylthio)methyl)borate (FcTtP⁻), and its representative metal complexes, [(FcTt)Cu]₄ and [FcTt]₂M (M = Fe, Co and Ni), are reported. The M = Fe complex exhibits spin-crossover behavior with a μ_eff = 1.19 μ_B at 25°C. The low-spin Co(II) derivative (1.88 μ_B) exhibits a characteristic axial electron paramagnetic resonance (EPR) spectrum, g_av = 2.13, A = 53 G and A_¦ = 43 G. The [FcTt]₂M complexes display reversible two-electron redox processes assigned to ligand-centered events about 200 mV negative of the ferrocene-ferrocenium couple. [(FcTt)Cu]₄ and [FcTt]₂Ni have been characterized by X-ray diffraction. X-ray data for [(FcTt)Cu]₄: monoclinic space group C2/c, with a = 24.3747(3) Å, b = 20.0857(2) Å, c = 17.2747(4) Å, β = 95.843(1)°, V = 8413.5(3) ų, and Z = 4; [FcTt]₂Ni: monoclinic space group C2/c, with a = 12.6220(3) Å, b = 11.6002(3) Å, c = 25.0125(7) Å, β = 94.067(1)°, V = 3653.1(2) ų, and Z = 4.