Nitrogen Atoms Of Ligand Research Articles

Iridium Half-Sandwich Complexes with Di- and Tridentate Bis(pyridylimino)isoindolato Ligands: Stoichiometric and Catalytic Reactivity

A series of κ2-(N,N)-coordinated bis(2-pyridylimino)isoindolato (BPI) complexes [Cp*Ir(BPI)Cl], which possess “three-legged piano-stool” structures, with the iridium atom being coordinated by the Cp* ligand 2 × N and Cl, were prepared via deprotonation of the BPIH ligands with either potassium hydride or LDA and subsequent reaction with [Cp*IrCl2]2 in THF. Cationic complexes [Cp*Ir(BPI)]+ containing κ3-(N,N,N)-coordinated BPI ligands were prepared as well as complexes with bidentate-coordinated BPI ligands, where the chloride ligand was substituted by either neutral or anionic ligands. Substitution in the ortho-position of the PBI ligands led to the formation of cycloiridated κ3-(N,N,C) species. Upon substitution of the anionic ligand by triphenylphosphine, a product was obtained with a hitherto unobserved κ2-(N,N) coordination of oMe-BPI to the metal center via the deprotonated nitrogen atom of the isoindole unit and one of the imine nitrogen atoms of the BPI ligand. A series of (para-cymene) osmium half...

Cyclic (alkyl)(amino)carbenes (CAACs): stable carbenes on the rise.

CONSPECTUS: Carbenes are compounds that feature a divalent carbon atom with only six electrons in its valence shell. In the singlet state, they possess a lone pair of electrons and a vacant orbital and therefore exhibit Lewis acidic and Lewis basic properties, which explains their very high reactivity. Following the preparation by our group in 1988 of the first representative, a variety of stable carbenes are now available, the most popular being the cyclic diaminocarbenes. In this Account, we discuss another class of stable cyclic carbenes, namely, cyclic (alkyl)(amino)carbenes (CAACs), in which one of the electronegative and π-donor amino substituents of diaminocarbenes is replaced by a σ-donating but not π-donating alkyl group. As a consequence, CAACs are more nucleophilic (σ-donating) but also more electrophilic (π-accepting) than diaminocarbenes. Additionally, the presence of a quaternary carbon in the position α to the carbene center provides steric environments that differentiate CAACs dramatically from all other ligands. We show that the peculiar electronic and steric properties of CAACs allow for the stabilization of unusual diamagnetic and paramagnetic main group element species. As examples, we describe the preparation of room temperature stable phosphorus derivatives in which the heteroatom is in the zero oxidation state, nucleophilic boron compounds, and phosphorus-, antimony-, boron-, silicon-, and even carbon-centered neutral and cationic radicals. CAACs are also excellent ligands for transition metal complexes. The most recent application is their use for the stabilization of paramagnetic complexes, in which the metal is often in a formal zero oxidation state. Indeed, bis(CAAC)M complexes in which the metal is gold, copper, cobalt, iron, nickel, manganese, and zinc have been isolated. Depending on the metal, the majority of spin density can reside either on the metal or on the carbene carbons and the nitrogen atoms of the CAAC ligand. In contrast to diaminocarbenes, the higher basicity of CAACs makes them poor leaving groups, and thus they cannot be used for classical organocatalysis. However, because of their superior electrophilicity and smaller singlet-triplet gap, CAACs can activate small molecules at room temperature, such as CO, H2, and P4, as well as enthalpically strong bonds, such as B-H, Si-H, N-H, and P-H. Lastly, excellent results have been obtained in palladium, ruthenium, and gold catalysis. CAAC-metal complexes are extremely thermally robust, which allows for their utilization in harsh conditions. This property has been used to perform a variety of gold-catalyzed reactions in the presence of basic amines, including ammonia and hydrazine, which usually deactivate catalysts.

Tuning the Dimensionality of Polyoxometalate-Based Materials by Using a Mixture of Ligands

Five molecular one-, two-, or three-dimensional (1D, 2D, or 3D) organic–inorganic hybrid polyoxometalates (POMs) based on the {ε-PMoV8MoVI4O40Zn4} (εZn) Keggin unit have been synthesized under hydrothermal conditions using a mixture of O- and N-donor ligands. (TBA)6[PMoV8MoVI4O37(OH)3Zn4]2(C14H8O4)3·6H2O (ε2(biphen)3) is a 3D material with two interpenetrated networks built from dimeric (εZn)2 POMs linked by 4,4′-biphenyldicarboxylate (biphen) ligands. (TBA)2[PMoV8MoVI4O38(OH)2Zn4](C7H6N2)3(C14H8O4)1/2·H2O (ε(bim)3(biphen)1/2), (TBA)3[PMoV8MoVI4O38(OH)2Zn4](C7H6N2)2(C8H4O4)·6H2O (ε(bim)2(isop)), (TBA)7/3[PMoV8MoVI4O38(OH)2Zn4](C7H6N2)8/3(C8H4O4)2/3 (ε(bim)8/3(bdc)2/3), and (TBA)3[PMoV8MoVI4O38(OH)2Zn4](C7H6N2)2(C9H3O6)2/3·6H2O (ε(bim)2(trim)2/3) all consist of monomeric εZn units bound to two types of organic ligands: benzimidazole (bim) and one of the following carboxylate ligands: biphen, 1,3-benzenedicarboxylate (isop), 1,4-benzenedicarboxylate (bdc), or 1,3,5-benzenetricarboxylate (trim) ligands. While ε(bim)3(biphen)1/2 is a molecular complex, ε(bim)2(isop) and ε(bim)8/3(bdc)2/3 adopt a chain arrangement, and ε(bim)2(trim)2/3 is a 2D compound. In these materials, the limitation of the dimensionality is a direct consequence of the protonation of the nitrogen atom of the bim ligands. The electrocatalytic activity for the hydrogen evolution reaction (HER) of these five new POM-based coordination polymers has been studied, showing that their performance depends mainly on the presence of the εZn Keggin units but also on their structure. Modified electrodes fabricated with ε(bim)2(trim)2/3 entrapped in a carbon paste revealed that this hybrid is the most efficient electrocatalyst of the series, being stable and catalyzing the HER in the pH 1–5 range.

Synthesis, crystal structure, and properties of an azido-bridged 1D nickel hexaazamacrocyclic complex

A new complex of [Ni(C15H32N6)(N3)]ClO4 · H2O was obtained by the reaction of macrocyclic precursor complex [Ni(C15H32N6)]ClO4 with sodium azide in water solution, and characterized by EA, IR, PXRD and single-crystal X-ray diffraction (CIF file CCDC no. 930570). Single X-ray diffraction analysis reveals that the central nickel(II) ion displays six-coordinate octahedral coordination geometry by coordination with four nitrogen atoms of N3− macrocyclic ligand and two nitrogen atoms of ligand. In this complex, each μ1,3-N3− binds two nickel(II) ions, resulting a 1D chain. Magnetic measurements have been performed on the complex, showing strong antiferromagnetic coupling interaction within the metal center.

Co(II), Cu(II), Mn(II) and Ni(II) complexes of maleic hydrazide

The binding of 3d transition metals to maleic hydrazide (3,6-dihydroxypyridazine) has been investigated. Cobalt(II), copper(II), manganese(II) and nickel(II) complexes of maleic hydrazide have been prepared, crystallized and studied by various spectroscopic techniques. X-ray crystallographic structures of ML2·nH2O complexes with all four metal ions have been obtained. In all of the complexes two maleic hydrazides bind as unidentate ligands. Water molecules occupy the remaining coordination sites. In the cobalt(II) and nickel(II) complexes, which are isomorphous, the ligand binds through a single ligand nitrogen atom whereas in the manganese(II) and copper(II) complexes the ligand binds through a ligand oxygen atom. The metal ions all have six coordinate octahedral geometries except the copper(II) complex which has a five-coordinate square pyramidal geometry.

Synthesis, characterization and thermal properties of phthaloylbis(paramethoxyphenylcarbamide) chelate polymers of divalent transition metals

Seven novel divalent transition metal chelate polymer complexes commonly known as coordination polymers or chelate polymers or coordination complexes such as [Mn (pbpmpc) (H2O)2]n (1), {[Co(pbpmpc) (H2O)2] 4H2O}n (2), {[Ni (pbpmpc) (H2O)2] 2H2O}n (3), {[Cu (pbpmpc) (H2O)2] 1H2O}n (4), {[Zn (pbpmpc)]}n (5), {[Cd (pbpmpc)]}n (6) and {[Hg (pbpmpc)] 1H2O}n (7) were synthesized under an aprotic solvent with phthaloyl bis (paramethoxyphenylcarbamide) (pbpmpc) as a polydentate ligand. The authenticities of these chelate polymers were characterized by elemental analyses: diffuse reflectance spectroscopy, magnetic susceptibility measurements, Fourier transform infrared (FT-IR), X-ray diffraction (XRD), thermal analyses and scanning electron microscope (SEM) techniques. SEM and XRD investigations significantly revealed a distinct morphology behavior of ligand and chelate polymers. The infrared spectroscopy supports the interaction of nitrogen and oxygen atoms of a polydentate ligand with a metal ion, while diffuse reflectance study is a powerful technique that suggests an octahedral geometry for all the chelate polymers except zinc, cadmium and mercury ions, which were further supported by other instrumental techniques. The decomposition steps and thermal stabilities of these chelate polymers were studied by thermal analysis techniques. The thermal stabilities of chelate polymers were identified on the basis of release of coordinated water and decomposition of backbone structure (ligand).

Yttrium and samarium complexes with a linked 1,4,7-triazacyclononane-aryloxide ancillary ligand

The reaction of yttrium trichloride with the stoichiometric amount of the potassium salt of the 1-(3,5-di-tert-butyl-2-hydroxybenzyl)-4,7-diisopropyl-1,4,7-triazacyclononane ligand (iPr2-TACN-CH2C6H2tBu2OH) (TACN = 1,4,7-triazacyclononane) in DME affords in good yield complex [iPr2-TACN-CH2C6H2tBu2O]YCl2 (1). This complex is characterized by elemental analysis and 1H nuclear magnetic resonance; the solid state structure is determined by the single crystal X-ray diffraction analysis. In complex 1, the metal centre is six-coordinated by the aryloxide oxygen atom, the three nitrogen atoms of the TACN ligand, and two chlorine atoms. The X-ray structure of isomorphic samarium complex [iPr2-TACN-CH2C6H2tBu2O]SmCl2 (2) is also determined.

Cd(II) and Zn(II) complexes of two new hexadentate Schiff base ligands derived from different aldehydes and ethanol amine; X-ray crystal structure, IR and NMR spectroscopy studies

Four new [Cd(H2L1)(NO3)]ClO4 (1), [Zn(H2L1)](ClO4)2 (2), [Cd(H2L2)(NO3)]ClO4 (3), and [Zn(H2L2)](ClO4)2 (4), complexes were prepared by the reaction of two new Schiff base ligands and Cd(II) and Zn(II) metal ions in equimolar ratios. The ligands H2L1 and H2L2 were synthesized by reaction of 2-[2-(2-formyl phenoxy)ethoxy]benzaldehyde and/or 2-[2-(3-formyl phenoxy)propoxy]benzaldehyde and ethanol amine and characterized by IR, 1H and 13C NMR spectroscopy. All complexes were characterized by IR, 1H and 13C NMR, COSY, and elemental analysis. Also, the complex 1 was characterized by X-ray in addition to the above methods. The X-ray crystal structure of compound 1 showed that all nitrogen and oxygen atoms of ligand (N2O4) and a molecule of nitrate with two donor oxygen atom have been coordinated to the metal ion and the Cd(II) ion is in an eight-coordinate environment that is best described as a distorted dodecahedron geometry.

Crystallographic Study of a coordination polymer based on Zn2+ion

Several studies have aimed to better understand coordination polymers, which are structures based on a connection between a metal ion and an organic ligand that extends infinitely, forming a macro-structure1. The interest in this type of structure is mainly due to its properties, such as its pore-forming ability, presenting many potential applications2 like selective separations, catalysis and gas storage. It is interesting to study the structure of coordination polymers to focus in some particular future application. In these way, a coordination polymer was synthetized by simple mixture with isonicotinylhydrazine (INH) and 1,2,4,5-benzenetetracarboxylic acid (BTC) ligands and zinc metallic ion. Yellow single crystals were formed in solution and one was separated, measured and solved by single crystal X-ray diffraction. The crystal-data for the structure were collected using an Oxford GEMINI A-Ultra diffractometer with MoKα radiation (λ = 0.71073 Å) at room temperature and solved using SHELXL-97 program3. The compound crystallized in monoclinic crystalline system in space group P21/c, cell parameters: a=9.2502(6) Å, b= 15.0004(6) Å, c=9.2947(4) Å, β= 108.4590(6), V=1223,35 Å3and Z=4. The final statistical parameters of the structure refinement were R=0.0326, wR=0.0835 and S=1,053. In this compound the BTC and INH ligands are coordinated like a bridge to two zinc ions. The BTC forms chelates by two carboxylate groups and INH coordinates by pyridine ring and by chelate at hydrazide group. This polymer extends in only one direction along a axis forming a 1D network. There is only one metallic zinc ion crystallographically independent on structure, it is in a distorted octahedral geometry with oxygen and nitrogen atoms of ligands and one coordinated water molecule in its coordination sphere. The 1D network formed by coordination polymers stabilizes the crystalline arrangement by hydrogen bonds between carboxylate and hydrazide groups and coordinated water molecules.

Nickel(II) complexes of pentadentate N5 ligands as catalysts for alkane hydroxylation by using m-CPBA as oxidant: a combined experimental and computational study.

A new family of nickel(II) complexes of the type [Ni(L)(CH(3)CN)](BPh(4))(2), where L=N-methyl-N,N',N'-tris(pyrid-2-ylmethyl)-ethylenediamine (L1, 1), N-benzyl-N,N',N'-tris(pyrid-2-yl-methyl)-ethylenediamine (L2, 2), N-methyl-N,N'-bis(pyrid-2-ylmethyl)-N'-(6-methyl-pyrid-2-yl-methyl)-ethylenediamine (L3, 3), N-methyl-N,N'-bis(pyrid-2-ylmethyl)-N'-(quinolin-2-ylmethyl)-ethylenediamine (L4, 4), and N-methyl-N,N'-bis(pyrid-2-ylmethyl)-N'-imidazole-2-ylmethyl)-ethylenediamine (L5, 5), has been isolated and characterized by means of elemental analysis, mass spectrometry, UV/Vis spectroscopy, and electrochemistry. The single-crystal X-ray structure of [Ni(L(3))(CH(3)CN)](BPh(4))(2) reveals that the nickel(II) center is located in a distorted octahedral coordination geometry constituted by all the five nitrogen atoms of the pentadentate ligand and an acetonitrile molecule. In a dichloromethane/acetonitrile solvent mixture, all the complexes show ligand field bands in the visible region characteristic of an octahedral coordination geometry. They exhibit a one-electron oxidation corresponding to the Ni(II) /Ni(III) redox couple the potential of which depends upon the ligand donor functionalities. The new complexes catalyze the oxidation of cyclohexane in the presence of m-CPBA as oxidant up to a turnover number of 530 with good alcohol selectivity (A/K, 7.1-10.6, A=alcohol, K=ketone). Upon replacing the pyridylmethyl arm in [Ni(L1)(CH(3)CN)](BPh(4))(2) by the strongly σ-bonding but weakly π-bonding imidazolylmethyl arm as in [Ni(L5)(CH(3)CN)](BPh(4))(2) or the sterically demanding 6-methylpyridylmethyl ([Ni(L3)(CH(3)CN)](BPh(4))(2) and the quinolylmethyl arms ([Ni(L4)(CH(3)CN)](BPh(4))(2), both the catalytic activity and the selectivity decrease. DFT studies performed on cyclohexane oxidation by complexes 1 and 5 demonstrate the two spin-state reactivity for the high-spin [(N5)Ni(II)-O(.)] intermediate (ts1(hs), ts2(doublet)), which has a low-spin state located closely in energy to the high-spin state. The lower catalytic activity of complex 5 is mainly due to the formation of thermodynamically less accessible m-CPBA-coordinated precursor of [Ni(II) (L5)(OOCOC(6)H(4)Cl)](+) (5 a). Adamantane is oxidized to 1-adamantanol, 2-adamantanol, and 2-adamantanone (3°/2°, 10.6-11.5), and cumene is selectively oxidized to 2-phenyl-2-propanol. The incorporation of sterically hindering pyridylmethyl and quinolylmethyl donor ligands around the Ni(II) leads to a high 3°/2° bond selectivity for adamantane oxidation, which is in contrast to the lower cyclohexane oxidation activities of the complexes.

Cadmium(II) iodide molecular coordination compounds with 4-methylpyridine and 4-methylquinoline

The coordination compounds [CdI2(4-MePy)2] (I) and [CdI2(4-MeQuin)2] (II) where Quin is quinoline have been synthesized, and their structure has been solved. Crystals of complex I are monoclinic, space group C2/c, a = 13.353(1) A, b = 16.653(1) A, c = 14.380 (1) A, β = 103.17(1)°, V = 3113.5(4) A3, ρcalcd = 2.425 g/cm3, Z = 8. Crystals of complex II are monoclinic, space group P21/c, a = 10.647(1) A, b = 25.264(1) A, c = 8.610(1) A, β = 113.73(1)°, V = 2120.1(3) A3, ρcalcd = 2.044 g/cm3, Z = 4. Polymer [CdI2(4-MePy)2]∞ chains running in the direction [001] are formed in the structure of complex I. Each of the two crystallographically nonequivalent Cd(1) and Cd(2) atoms are octahedrally surrounded by the four iodine and two nitrogen atoms of the 4-MePy ligand. The Cd(1)⋯Cd(2) distance in a chain is 4.33 A. The structure of complex II is built of [CdI2(4-MeQuin)2] discrete neutral clusters. The two iodine and two nitrogen atoms of the 4-MeQuin ligand participate in the coordination of the Cd2+ ion. The cadmium coordination polyhedron is a distorted tetrahedron (Cd-Iavg, 2.72 A; Cd-Navg, 2.30 A; angles N(I)CdN(I), 98.3–121.8°). The minimum and maximum values correspond to the ICdI angle and NCdN angle, respectively. Complex I is photoluminescent in the solid state at room temperature.

Spectroscopic and quantum-chemical investigations of chloro-bis-bipyridyl complexes of ruthenium(II) with 4-substituted pyridine ligands

The luminescence spectra of cis-[Ru(bpy)2(L)Cl]+ (bpy is 2,2′-bipyridyl; L is pyrazine, pyridine, 4-amino-pyridine, 4-picolin, isonicotinamide, 4-cyanopyridine, or 4,4′bipyridyl) complexes are studied in alcoholic (4: 1 EtOH-MeOH) solutions at 77 K. A linear correlation is found between the energy of the lowest electronically excited metal-to-ligand charge transfer (3MLCT) state dπ(Ru) → π* (bpy) and the parameter pKa of the free 4-substituted pyridines and pyrazine used as ligands L. The [B3LYP/6-31G + LanL2DZ(Ru)] hybrid method of the density functional theory is used to optimize the geometry of complexes and calculate their electronic structure and the charge distribution on the atoms of the nearest environment of the ruthenium ion. It is shown that there exists a linear unambiguous correlation between the negative charge on the nitrogen atom (qNL) of ligands L coordinated in the complex and the parameters pKa of free ligands. The calculated energies of 3MLCT excited states almost linearly (correlation coefficient 0.958) depend on the charge qNL, which completely agrees with experimental data.

Mixed Alkyl Hydrido Complexes of Zinc: Synthesis, Structure, and Reactivity

The (NNNN)-type macrocycle 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane (Me3TACD, 1,4,7-Me3[12]aneN4) reacted with 1 equiv of ZnEt2 under ethane elimination to give the mononuclear ethyl complex [(Me3TACD)ZnEt] (1). Upon treatment of (Me3TACD)H with 2 equiv of ZnEt2, the dinuclear complex [(Me3TACD)(ZnEt)(ZnEt2)] (2) was formed, which was converted with an additional 1 equiv of (Me3TACD)H to 1. Reaction of 1 with PhSiH3 led to the formation of a tetranuclear ethyl hydrido complex [{(Me3TACD)ZnEt}2(ZnEtH)2] (3). Single-crystal X-ray diffraction study revealed 3 to be a centrosymmetric dimer featuring two [(Me3TACD)ZnEt] units coordinated to a [Zn(μ-H)2Zn] core via amido nitrogen atoms of the Me3TACD ligands. Substitution of the two [(Me3TACD)ZnEt] units in 3 by N-heterocyclic carbene IMes [1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene] gave [(IMes)ZnEtH]2 (4b). The mixed alkyl hydrido complexes [(IMes)ZnRH]2 (R = Me, 4a; Et, 4b) were alternatively synthesized in quantitative yield by reacting [(IMes)ZnR2] (R = Me, Et) with [(IMes)ZnH2]2 in 2:1 ratio. Methyl complex 4a reacted with CO2 (p(CO2) = 0.5 bar) under facile insertion of CO2 into Zn–H bonds to give dinuclear formate complex [(IMes)ZnMe(O2CH)]2 (5a). Treatment of 4b with CO2 (p(CO2) = 0.5 bar) afforded a mixture of di- and trinuclear formate complexes [(IMes)ZnEt(O2CH)]2 (5b) and [(IMes)2Zn3Et3(O2CH)3] (6) under elimination of one IMes as CO2 adduct IMes·CO2.

Computational design of mixed-ligand adducts of Co aminovinyl ketonates with redox-active o-quinones and their derivatives

The adducts of cobalt aminovinyl ketonates with o-benzoquinones, o-benzoquinone imines, and o-benzoquinone diimines were studied by the density functional theory method (B3LYP*/6-311++G(d,p)). For all of the compounds, the ground states are low-spin structures containing a trivalent cobalt atom and a redox-active ligand in the semiquinonate form. The bulky substituents at the bis-chelate and ligand nitrogen atoms favor a decrease in the energy difference between the low-spin and high-spin isomers of the adducts containing LSCoIII and HSCoII atoms, respectively. These compounds can exhibit valence tautomerism in the crystalline state, but the relatively low stabilization energies of the high-spin isomers in solutions may induce a competing process: dissociation into the original bis-chelate and redox-active ligand.

Hydrogen bond induced chiral symmetry breaking in the crystallization of nickel(II) complexes

A pair of enantiomers formulated as {Δ-cis-[Ni(en)2OAc][ClO4]} n (Δ-1) and {Λ-cis-[Ni(en)2OAc][ClO4]} n (Λ-1) (en = diaminoethane, OAc− = acetate anion) were obtained when nickel acetate was reacted with diaminoethane and sodium perchlorate in the absence of any chiral source, whereas the reactions of nickel acetate with 1,3-propanediamine and sodium perchlorate only gave a centrosymmetric complex [Ni(1,3-pn)2OAc][ClO4] (2) (1,3-pn = 1,3-propanediamine). Single-crystal X-ray diffraction analyses of all three complexes indicated that the central Ni(II) atoms all have a distorted octahedral coordination geometry, being coordinated by four nitrogen atoms of the diamine ligands, plus two oxygen atoms of OAc−. In complexes Δ-1 and Λ-1, the monomers of {Δ-cis-[Ni(en)2OAc]}+ and {Λ-cis-[Ni(en)2OAc]}+ are connected through intermolecular hydrogen bonds to generate one-dimensional right- and left-handed homochiral helical chains, respectively, while the monomers of [Ni(1,3-pn)2OAc]+ are linked by similar intermolecular hydrogen bonds to form one-dimensional zigzag chains instead of helical chains. The chiral natures of complexes Δ-1 and Λ-1 have been confirmed by circular dichroism spectroscopy.

Synthesis, structure, and electrochemical properties of [M(N-MeIm)6]2+ (M = Ni, Co, Cu) associated with [HgCl4]2−

Reaction of Hg(NO3)2 with 4 equivalent KI in water afford K2[HgI4]. By using K2[HgI4] as the precursor, three new heterobimetallic compounds [Ni(N-MeIm)6][HgI4] (I), [Co(N-MeIm)6][HgI4] (II), and [Cu(N-MeIm)6][HgI4] (III) have been characterized by elemental analysis, IR spectra, and the singlecrystal X-ray crystallorgraphy analysis. Three complexes are isomorphous and crystallized in monoclinic symmetry space group P21/c. The coordination around each center metal(II) atom is octahedral with six nitrogen atoms of N-MeIm ligand. Each structure contains one tetrahedral [HgI4]2− as an anion to balance the charge of the molecular. Thermogravimetry analysis indicates these complexes have the similar departure process and cyclic voltammogram exhibits a significant pair of redox peaks.

Synthesis, crystal structure and electrocatalytic behavior of a copper (II) complex derived from acylpyrazolone double Schiff bases

A new double Schiff base complex, Cu(PMαFP)2en (HPMαFP = 1‐phenyl‐3‐methyl‐4‐(2‐furoyl)‐5‐pyrazolone, en = ethylenediamine), has been synthesized and characterized by elemental analysis, IR, UV, fluorescence spectra, thermal analysis, X‐ray single crystal diffraction and cyclic voltammetry (CV). Its crystal structure is monoclinic with space group Pbca and cell parameters: a = 22.263(3)Å, b = 13.671(2)Å, c = 10.0920(16)Å, Z = 4, S = 1.028, R1 = 0.0500 and wR2 = 0.1285. It was found that the Cu2+ ion is located in the coordination center. The Cu(II) has a slightly distorted plane quadrilateral coordination environment with two oxygen atoms and two nitrogen atoms of double Schiff base ligand in the equatorial plane. The complex has a one‐dimensional chain supramolecular structure, which is connected by CH…N bonding interactions. In the electrochemical experiments, the CV curve displays an oxidation peak in the presence of uric acid with Ep = 0.216V in pH = 7.0, showing that the Cu(PMαFP)2en/glassy carbon modified electrode has an electrocatalytic activity toward uric acid.

Synthesis and characterization of a new nano lead(II) three-dimensional coordination polymer with 8-hydroxyquinolin ligand by sonochemical method: A precursor for preparation of PbO nano-structure

Nano-structure of a new 3D Pb(II) coordination polymer, [Pb3(8-HQuin)2(μ-Br)4]n (1), 8-HQuin=8-hydroxyquinolin ligand was synthesized by a sonochemical method. The new nano-structure was characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), IR spectroscopy and elemental analyses. The structure of compound 1 was determined by single-crystal X-ray diffraction and shown to consist of 3D polymeric units. The lead atoms have two different coordination numbers 4 and 6 in compound 1. The Lead centers are four-coordinated by two oxygen atoms and one nitrogen atom of 8-hydroxyquinolin ligands, and one bridged Br− atom. The six-coordinated lead centers are coordinated by nitrogen and oxygen atoms of 8-hydroxyquinolin ligands and 4 or 5 bridged Br− anions. The thermal stability of the bulk materials of compound 1 was studied by thermal gravimetric and differential thermal analysis (TGA/DTA). Calcination of the nano compound 1 at 500°C under air atmosphere yielded nano-sized particles of PbO characterized by scanning electron microscopy (SEM) and X-ray powder diffraction (XRD).

Dinuclear ruthenium complexes containing a new ditopic phthalazin-bis(triazole) ligand that promotes metal–metal interactions

Much attention has been paid to heterocyclic N-containing ligands due to their applicability as bridging ligands in the synthesis of redox active dinuclear metal complexes. With this aim, we report the synthesis and full characterization of a novel phthalazine-triazole ligand (1,4-bis(1-methyl-1H-1,2,3-triazol-4-yl)phthalazine). Moreover, we show that the phthalazine nitrogen atoms of this N-heterocyclic ligand are more reactive towards alkylating agents than the triazole groups. New ruthenium(II) complexes containing this ligand have been obtained and characterized both structurally and electrochemically. The geometry imposed by the ligand allows the placement of two ruthenium centers in very close proximity so that efficient through-space interactions take place, a concept of crucial importance for electron transfer processes.

X-ray structure and spectroscopy of novel trans-[Ni(L)(NO3)2] and [Ni(L)](ClO4)2·2H2O complexes

Ni(L)(NO3)2 (complex 1) and [Ni(L)](ClO4)2⋅2H2O (complex 2) [L=3,14-diethyl-2,6,13,17-tetraazatricyclo(16.4.0.07,12)docosane] have been prepared and structurally characterized by single-crystal X-ray diffraction at 200K. For these constrained macrocycle complexes, nickel(II) exists in a distorted octahedral environment with the four nitrogen atoms of the macrocyclic ligands and two oxygen atoms from nitrate in axial positions in complex 1. The macrocyclic ligand in complex 1 adopts the most stable trans-III conformation. The Ni–N distances in both the complex 1 (2.094(4)–2.051(4)Å) and complex 2 (2.042(8)–1.996(7)Å), are typical but the axial ligands are coordinating, with NiO bond length, 2.198(3)Å for complex 1. The complex 2 adopts square planner geometry around the Ni(II) with four nitrogen atoms from macrocyclic ligand. The crystals are stabilized in a 3-D network by intra and intermolecular hydrogen bonds that are formed among the secondary nitrogen hydrogen atoms and nitrate in 1, and intermolecular hydrogen bonds are formed by perchlorate and NH groups in 2. The electronic absorption, IR and PL spectral properties are also discussed.