Three 2,2′-biimidazole transition metal complex-supported octamolybdates derived from hexamolybdochromate

Three octamolybdate compounds, namely [Cu(H₂biim)₂]₂[β-Mo₈O₂₆{Cu(H₂biim)₂}₂][β-Mo₈O₂₆] (1), [{Fe(H₂biim)₂(Hbiim)}₂(γ-Mo₈O₂₆)]·5H₂O (2), and [{Co(H₂biim)₂(Hbiim)}₂(γ-H₂Mo₈O₂₆)]·5 H₂O (3) (H₂biim = 2,2′-biimidazole) have been hydrothermally synthesized from the reaction of mixtures of hexamolybdochromate ({CrMo₆}), transition metal, and H₂biim in acetate buffer solution, and characterized by physico-chemical and spectroscopic methods. They represent the first examples of the conversion of hexamolybdochromate to octamolybdate. Single-crystal X-ray diffraction analysis reveals that compound 1 is composed of a β-[Mo₈O₂₆]⁴⁻ polyoxoanion bi-supported by two [Cu(H₂biim)₂]²⁺ complex cations, an isolated β-[Mo₈O₂₆]⁴⁻ anion, and two [Cu(H₂biim)₂]²⁺ complex cations. The copper complex cations are situated at two different sites and associate with β-[Mo₈O₂₆]⁴⁻ anions to give 2D layers, which are further packed into a 3D framework via strong hydrogen bonding interactions. Compounds 2 and 3 are isostructural, and contain a γ-[Mo₈O₂₆N₂] unit and two symmetrical {M(H₂biim)₂(Hbiim)} (M=Fe or Co) fragments grafted onto the polyoxoanion through Mo–N bonds. The two compounds also exhibit 3D supramolecular frameworks involving hydrogen bonding interactions.     

Interconversion of copper(II) to copper(I): synthesis,characterization of copper(II) and copper(I) 2,2′-biquinoline complexes and their microbiological activity

The complexes [Cu(biq)₂]Cl₂ and [Cu(biq)₂]BF₄·biq (biq?=?2,2′-biquinoline) have been prepared and characterized. The interconversion to copper(I) complex [Cu(biq)₂]BF₄·biq, from [Cu(biq)₂]Cl₂ has been established. The new complexes have been characterized by elemental analysis, conductivity and magnetic measurements, IR, UV-vis and ¹H- and ¹³C-NMR spectroscopy. The X-ray analysis of the complex [Cu(biq)₂]BF₄·biq supports the assumption of the interconversion of copper(II) to copper(I) in this case. The crystal structure shows that geometry around the metal is severely distorted from T_d, and displays many supramolecular motifs incorporating both hydrophobic (aryl···aryl) and hydrophilic (C–H···F) intermolecular interactions. The microbiological activity of the complexes against bacteria and fungi was found to be high against Candida albicans, and slight to moderate against bacteria. The antimicrobial activity of [Cu(biq)₂]BF₄·biq was slightly better than that observed for [Cu(biq)₂]Cl₂ against both bacteria and fungi.     

Steric effects on complex formation between nickel(II) and (2-imidazoleazo) benzene, 2,2′-biimidazole and 2,2′-bibenzimidazole

Summary The kinetics and mechanism of reversible complexation of Ni^II with (2-imidazoleazo)benzene (IAB), 2,2-biimidazole (Biim) and 2,2-bibenzimidazole (Bibzm) have been investigated at 15–35 °C, I = 0.30 mol dm^–3. The stability constants, K _M, of the [NiL]²⁺ species vary in the sequence: [Ni(IAB)]²⁺ < [Ni(Bibzm)]²⁺ < [Ni(Biim)]²⁺. The values of the spontaneous dissociation rate constant (k _r) at 25 °C decrease in the sequence: [Ni(IAB)]⁺ > [Ni(Biim)]²⁺ > [Ni(Bibzm)]²⁺. The aquation of [Ni(IAB)]²⁺ is insensitive to acid catalysis, whilst [Ni(Biim)]²⁺ is relatively more susceptible towards acid-catalysed aquation than [Ni(Bibzm)]²⁺. The chelate ring in [NiL]²⁺ (L = IAB, Biim or Bibzm) is sterically strained. The formation of [Ni(IAB)]²⁺ and [Ni(Bibzm)]²⁺ may be chelation controlled while the normal I _d mechanism is supported by our data for [Ni(Biim)]²⁺.     

Coordination interactions of alkyl-substituted 2,2′-dipyrrolylmethene derivatives with copper(II) aminoacid complexes

Using the method of electron spectroscopy we showed that reaction of alkyl-substituted 2,2′-dipyrrolylmethene derivatives with copper(II) aminoacid complexes led to the formation of heteroligand complexes with two chelated metallocycles forming their coordination sphere. Formation constants of the heteroligand complexes were established and their interrelations with the structure of the aminoacid residue side group were elucidated. It was found that alongside the ability to the primary solvolytic dissociation of aminoacid complex, the main effect on the formation of combined coordination sphere of the chelate is defined by the steric factor depending on the structure of substituent in the aminoacid.     

Kinetics and mechanism of the oxidation of DL-methionine bybis(2,2′-bipyridyl)copper(II) permanganate

Summary The oxidation ofDL-methionine (MT) bybis(2,2-bipyridyl)copper(II) permanganate (BBCP) to the corresponding sulphoxide is first order in BBCP. Michaelis-Menten-type kinetics were observed with respect to MT. The formation constant of the intermediate complex and the rate constant for its decomposition were evaluated. The thermodynamic and activation parameters were also evaluated. The reaction is catalysed by H⁺ but 2,2-bipyridine does not affect the reaction rate. A mechanism is proposed.     

Crystallographic and computational study of the structure of copper(II) 2,2′-bis(2-oxidobenzylideneamino)-4,4′-dimethyl-1,1′-biphenyl

The reaction of M(OAc)₂ with 2,2′-bis(2-hydroxybenzylideneamino)-4,4′-dimethyl-1,1′-biphenyl (H₂L1) allows the synthesis of 2,2′-bis(2-oxidobenzylideneamino)-4,4′-dimethyl-1,1′-biphenyl complexes of Cu(II) (CuL1), Co(II) (CoL1) and Ni(II) (NiL1) that were characterized by elemental analysis, FTIR spectroscopy and for CuL1 also by X-ray crystallography verifying a tetradentate binding mode of L1 via an (ONNO) motif of the two phenolic oxygen atoms and two azomethine nitrogen atoms. Recrystallization from a solvent mixture of dichloromethane and methanol promotes the formation of methanol adducts. Different binding modes of the methanol–complex were investigated using density functional theory calculations and binding energies, and thermodynamic data of the interaction are reported. The results show that the favored interaction occurs when the methanol molecule acts as a Lewis acid weakly binding via an O–H···O hydrogen bridge to a phenoxide moiety leading to an elongation of the respective M–O bond.

     

Photochemical Behavior of Platinum(II) and Palladium(II) Complexes of 4,4′-Dimethyl-2,2′-Bipyridine

Several mixed-ligand complexes of formula [MX 2 (MBPY)] {where M is Pd(II) or Pt(II); X is Cl m , I m , N 3 m or NO 2 m and MBPY is 4,4'-dimethyl-2,2'-bipyridine} have been prepared. The UV-Vis spectra of these complexes were found to show a low-lying MLCT band and on irradiation at the MLCT band these complexes sensitize the oxidation of 2,2,6,6-tetramethyl-4-piperidinol (XH) in N , N -dimethylformamide (DMF) to 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinoloxy free radical (XO). This photo-oxidation reaction involves singlet molecular oxygen ( 1 O 2 ) as an intermediate and its presence was confirmed by quenching studies using bis(diethyldithiocarbamato)nickel(II) [Ni(DDTC) 2 ], a well-known 1 O 2 quencher. The ability of the complexes to photosensitize the above photo-oxidation reaction follows the order: [Pt ( N 3 ) 2 ( MBPY ) ] ( 2 ) ～ [Pt ( NO 2 ) 2 ( MBPY ) ] ( 3 ) > [PtCl 2 ( MBPY ) ] ( 4 ) > [PtI 2 ( MBPY ) ] ( 1 ) > [Pd ( NO 2 ) 2 ( MBPY ) ] ( 7 ) ～ [Pd ( N 3 ) 2 ( MBPY ) ] ( 6 ) > [PdCl 2 ( MBPY ) ] ( 8 ) > [PdI 2 ( MBPY ) ] ( 5 ), which reflects the nature of the metal ion and the nature of the ligands present in the complexes.     

Soft template synthesis in copper(II)–dithiooxamide–methanal,copper(II)–dithiooxamide–ethanal and copper(II)–dithiooxamide–propanone triple systems in a copper(II)hexacyanoferrate(II) gelatin-immobilized matrix

Novel complexing processes in the Cu^II–dithiooxamide–methanal, Cu^II–dithiooxamide–ethanal and Cu^II–dithiooxamide–propanone triple systems proceeding under specific conditions, to copper(II)hexacyanoferrate(II) gelatin-immobilized matrix systems in contact with aqueous-alkaline (pH 12) solutions containing dithiooxamide and methanal, ethanal or propanone, have been studied. It has been shown that template synthesis leading to the formation of macrocyclic coordination compounds (2,8-dithio-3,7-diaza-5-oxanonandithioamide-1,9)copper(II), (2,8-dithio-3,7-diaza-4,6-dimethyl-5-oxanonandithio-amide-1,9)copper(II) and (4,4,6-trimethyl-2,8-dithio-3,7-diazanonen-6-dithioamide-1,9)copper(II), respectively, takes place under such conditions. Dithiooxamide, methanal, ethanal and propanone act as ligand synthons in these processes.     

Synthesis, Characterization and Crystal Structure of (2,2′-Bipyridine)(μ-maleato)copper(II) Dihydrate

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Structural characterization of copper (II) tetradecanoate with 2,2′-bipyridine and 4,4′-bipyridine to study magnetic properties

This paper presents synthesis, structural characterization and spintronic applications of copper (II) tetradecanoate derived magnetic complexes. The complexes were prepared by a chemical reaction between [Cu₂(CH₃(CH₂)₁₂COO)₄](EtOH)₂ and 2,2′-bipyridine-4,4′-bipyridine ligands respectively. The complexes were further reacted between the product of the first reaction and 4,4′-bipyridine-2,2′-bipyridine respectively. The structural characterization techniques included elemental analysis, Fourier transformed infrared spectroscopy (FTIR), Ultra-violet–Visible (UV–Vis) spectroscopy, polarized optical microscopy, magnetic moment and thermogravimetric analysis. The structural and characterization results suggested that the synthesized complexes were binuclear and mononuclear covalent complexes of copper(II) with structural formulas [Cu₂(η²-(OOCR)₄](4,4′-bpy)2H₂O] and [Cu(η¹-(OOCR)₂(2,2′-bpy) (4,4′-bpy)] respectively.     

Spectroscopic and structural studies of 6,6′-bis(N-methylhydrazine)-2,2′-bipyridine and its mononuclear copper(II) complex

The tetradentate ligand, 6,6′-bis(N-methylhydrazine)-2,2′-bipyridine (L) and its mononuclear copper(II) complex [Cu(L)](ClO₄)₂] (1) have been synthesized and characterized. The crystal structures of L and 1 have been determined by single-crystal X-ray diffraction. Both crystallize in the centrosymmetric monoclinic space group with crystallographic inversion symmetry. The ligand adopts a planar transoid configuration in the solid state. In 1, the Cu(II) is six-coordinate octahedral, defined by N₄O₂ donors from ligand and two perchlorates. The molecular units are connected by intermolecular H-bonds between the hydrazino group of the one unit and coordinated perchlorate of the neighboring two units via N–H ··· O to furnish a 2-D network. Coordinated perchlorates also form an intramolecular H-bond with hydrazine influencing the crystal packing.     

Investigation of complexes of zinc(II) and cadmium(II)DI-n-butyldithiocarbamates with 2,2′-bipyridyl

A new mixed-ligand complex, Cd(S₂CN(C₄H₉)_{2 2})₂(2,2′-Bipy), was synthesized. A polycrystal X-ray diffraction analysis was performed (DRON-3M and DRON-UM1 diffractometers, CuK_α radiation, Ni filter) and the crystal structure was determined [Enraf-Nonius CAD-4 automatic diffractometer, MoK_α radiation, 2440 nonzero independent reflections, 153 refined structural parameters, R is 0.11 for I>2σ(I)]. Crystal data for C₂₈H₄₄CdN₄S₄ : a = 28.716(4), b = 6.848(6), c = 17.188(2) Å, space group Pcca, V-3380.2(7) ų, Z = 4, M = 679.42, dcaU.= 1.335 g/cm3. The structure consists of monomeric molecules in which the cadmium atom has a distorted octahedral environment. The polycrystal diffraction analysis revealed that the complex is isostructural with the defined complex Zn(S₂CN(C₄Hg)₂)₂(2,2′-Bipy). A crystal-chemical search on metal dialkyldithiocarbamates in the Cambridge Structural Database was accomplished and isostructural pairs of Zn and Cd metal complexes were found.     

Electrochemistry of microparticles of tris (2,2′-bipyridine) ruthenium(II) hexafluorophosphate

The electrochemical behaviour of tris(2,2′-bipyridine)ruthenium(II) hexafluorophosphate (Ru(II)) microparticles, immobilised on a graphite electrode and adjacent to an aqueous electrolyte solution, has been studied by cyclic voltammetry and an in situ spectroelectrochemical technique. The solid Ru(II) complex exhibits one reversible redox couple with a formal potential (E_f) of 1.1 V versus Ag¦AgCl. The continuous cyclic voltammetric experiments showed that the Ru(II) microparticles are stable during the electrochemical conversions. The in situ spectroelectrochemical study showed that the absorbance at 463 nm decreased due to the oxidation of Ru(II) to Ru(III). Upon reduction, the growth of absorbance at 463 nm was observed due to the formation of Ru(II) complex and this process was reversible.     

Synthesis and crystal structure of polymeric aqua (2,2′-bipyridine)(μ-isonicotinato)copper(II) nitrate dihydrate

The title complex has been prepared and its crystal structure determined by X-ray diffraction methods. The complex crystallizes in the monoclinic space group P2₁/c. Cu(II) assumes a square pyramidal coordination geometry, formed by two isonicotinate anions, a bipyridine ligand and a coordinated water molecule. Each isonicotinate bridges two Cu atoms through pyridine-N and carboxyl-O atoms, respectively, to form zigzag polymeric chains. Between the polymeric chains, aromatic stacking and hydrogen bonding are observed.     

A cyclometallated analogue of tris(2,2′-bipyridine)ruthenium(II)

A cyclometallated analogue of the well-known tris(2,2′-bipyridine)ruthenium(II) cation has been prepared from 2-phenylpyridine. The bis(2,2′-bipyridine)(2-phenylpyridine-C,N)ruthenium(II) cation is readily prepared from [Ru(bipy)₂Cl₂] and 2-phenylpyridine in the presence of silver(I); the spectroscopic and electrochemical properties of this species are compared with those of [Ru(bipy)₃]²⁺.     

Synthesis and characterization of complexes of the first transition series cations with 2,2′-biimidazole and 2,2′-biimidazolate

Mononuclear [M(hfacac)₂(H₂biim)] complexes, where M = Mn^II, Fe^II, Co^II, Ni^II, Cu^II or Zn^II, hfacac = hexafluoroacetylacetonate, H₂biim = 2,2-biimidazole; dinuclear K₂[M₂(acac)₄(-biim)] (M = Cu^II or Zn^II) and tetranuclear K₂[M₄(acac)₈( ₄-biim)] (M = Co^II or Ni^II) complexes have been prepared and characterized by chemical analysis, conductance measurements, i.r., electronic and e.p.r. spectroscopies and by magnetic susceptibility measurements (in the 2–300 K range). Mn^II, Fe^II and Co^II are in a high spin state. The e.p.r. spectra of Cu^II and Mn^II compounds have been recorded.     

Copper(II)–8-mercaptoquinoline,copper(II)–5,8-dimercaptoquinoline and copper(II)–5-thiomethyl-8-mercaptoquinoline complexing in a copper(II)hexacyanoferrate(II) gelatin-immobilized matrix

Novel complexing processes in the Cu^II–8-mercaptoquinoline, Cu^II–5,8-dimercaptoquinoline and Cu^II–5-thiomethyl-8-mercaptoquinoline systems proceeding in the copper(II)hexacyanoferrate(II) gelatin-immobilized matrix in contact with aqueous solutions of the ligands indicated, have been studied. Under the conditions specified for complexing in the Cu^II–8-mercaptoquinoline system, only a monomeric water-insoluble coordination compound was formed. In the Cu^II–5,8-dimercaptoquinoline system, three coordination compounds were formed and, in the Cu^II–5-thiomethyl-8-mercaptoquinoline system, two such compounds were formed. Conversely, complexing in solution or solid phase results in the formation only coordination compounds in each of the system studied.     

Complexation of copper(II) with 2′,2′-dialkyl-para-tert-butylbenzohydrazides

The complexation of copper(II) with 2′,2′-dimethyl-, 2′,2′-dibutyl-, and 2′,2′-diisobutyl-para-tert-butylbenzohydrazide in water-ethanol media was studied. The reagents (HL) formed [Cu(HL)]²⁺ and [Cu(HL)₂]²⁺ cationic complexes in a weakly acidic medium and uncharged CuL₂ complexes in an alkaline medium. logK _st was calculated for these complexes. The effect of 2′,2′-alkyl radicals on the stability of the complexes was considered. The obtained results were compared with data on the complexation of copper(II) ions with 2′,2′-dialkylbenzohydrazides.     

Bis(2,2′bipyridine) ruthenium(II) complexes

A reinvestigation of the photolysis of [Ru(bipy)₃](NCSe)₂ in ethanol under dinitrogen has failed to give the previously reported [Ru(N₃)₂bipy₂] but, under appropriate conditions, may yield the complex [Ru(NCO)₂bipy₂].