Self-assembly of organometallic Pd(II) complexes via CH3π interactions: The first example of a cyclopalladated compound with herringbone stacking pattern

Two binuclear cyclometallated compounds [Pd(C²,N-dmba)(μ-N₃)]₂ (1) and [Pd₂(C²,N-dmba)₂(μ-N₃)(μ-Cl)] (2) (dmba = N,N-dimethylbenzylamine) have been synthesized and characterized by elemental analysis, IR and NMR spectroscopies and single crystal X-ray diffraction crystallography. The ability of CH₃ groups to form C(sp³)Hπ hydrogen bonds with phenyl rings is responsible for the molecular self-assembly within the crystals of 1 and 2. Compound 1 crystallizes as one-dimensional supramolecular chains whereas the crystal packing of 2 consists of a herringbone of sandwiches composed by two inversely related [Pd₂(C²,N-dmba)₂(μ-N₃)(μ-Cl)] molecules.     

Hypergolic Behavior of Pyridinium Salts Containing Cyanoborohydride and Dicyanamide Anions with Oxidizer RFNA

A series of low‐cost, pyridinium cation‐based hypergolic ionic liquids (HIL) containing amine, butyl, or allyl substituents with cyanoborohydride [BH₃CN]⁻ and dicyanamide [DCA]⁻ anions were developed and characterized. The investigated physicochemical properties include melting and decomposition temperature, viscosity, density, heat of formation (ΔH_f) and specific impulse (I_sp). The ignition delay (ID) of all HILs was tested with the oxidizer RFNA. The HIL, 1‐allyl 4‐amino pyridinium dicyanamide, exhibited highest density (1.139 g cm⁻³) amongst the known pyridinium HILs. The heats of formation predicted on the basis of Gaussian 09 suit programs were within the range of − 30 to 356 kJ mol⁻¹. The structure of HIL, 1‐butyl 4‐aminopyridinium cyanoborohydride, was examined by single‐crystal X‐ray diffraction, which revealed hydrogen bonding between anion and cation as N1−H1N ⋅⋅⋅ N3=2.07 Å, N1−H2N ⋅⋅⋅ H1B1=2.18 Å, and N1−H2N ⋅⋅⋅ H2B1=2.21 Å, respectively. HIL (1‐allyl 4‐aminopyridiniun cyanoborohydride) exhibited highest I_sp of 228 s amongst the designed series.     

New (κ-C,N)-palladacyclic complexes with benzimidazol-2-ylidene ligand: Synthesis, crystal structures and characterization

Reaction of unsymmetrical benzimidazolium bromides (1) with Ag₂O and subsequent transmetallation with chloro-bridged dinuclear palladacycle, [Pd(dmba)(μ-Cl)]₂ (dmba: N,N-dimethylbenzylamine) afforded benzannulated monocarbene complexes [Pd(dmba)(NHC)Cl], 2. The palladacycles (2a–c) were characterized by elemental analysis; NMR spectroscopy and the molecular structure of 2a and 2c were determined by X-ray crystallography.     

Two rod-based 3-D lead(II) tetrafluoroterephthalate coordination frameworks with sra topology: Syntheses, structures, and properties

Two three-dimensional (3-D) Pb^II coordination frameworks [Pb(BDC-F₄)(CH₃OH)]_n (1) and [Pb(BDC-F₄)(DMF)(CH₃OH)]_n (2) have been prepared by the reactions of Pb(NO₃)₂ with a rigid dicarboxyl compound tetrafluoroterephthalic acid (H₂BDC-F₄) in different solvents. Single crystal X-ray diffraction reveals that both complexes show the unusual rod-based coordination networks with sra topology, although they crystallize in different space groups (C2/c and ). Their spectroscopic, thermal, and fluorescence properties have also been studied.     

NBu4[{Au(C6F5)3}2(μ-PPh2)]: a gold(III) phosphide with a single atom bridging the metallic centers

Reaction of [Au(C₆F₅)₃(PPh₂H)] with [Au(C₆F₅)₃(tht)] and NBu₄(acac) (acac=acetylacetonate) leads to the synthesis of NBu₄[{Au(C₆F₅)₃}₂(μ-PPh₂)] (1), an unprecedented complex with two gold(III) centers bonded to a unique bridging atom without any other stabilizing effect. The novel di-bridged gold(III) phosphide [Au₂(C₆F₅)₄(μ-PPh₂)₂] (2) is obtained by treatment of diphenylphosphine with [Au₂(C₆F₅)₄(μ-Cl)₂]. The crystal structures of both derivatives have been determined by X-ray diffraction.     

A mononuclear copper(II) complex of a protonated unsymmetrical dinucleating Schiff base ligand

Reaction of the unsymmetrical and potentially dinucleating Schiff base ligand HL¹ with copper(II) salts has given mono- and dinuclear metal complexes. The structure of a mononuclear complex of diprotonated HL¹, [Cu(H₂L¹)(OH₂)](ClO₄)₃·H₂O·CH₃OH_, has been determined.     

Preparation and structural characterisation of a Cd(II) complex with unusual geometry

Reaction of Cd(NO₃)₂ · 4H₂O with ethyl-2-pyridinecarboxylate yields [Cd(NO₃)₂(C₅H₄NCOOEt)₂]. Elemental analyses, conductivity measurements, infrared, ¹H and ¹³C{¹H} NMR spectroscopies and single-crystal X-ray diffraction enabled us to characterise this complex. The crystal structure consists of monomeric units in which the cadmium atom is eight-coordinated.     

TDDFT study of electronic spectra of photochromic dinuclear molybdenum complex

The time-dependent density functional theory (TDDFT) was applied to the calculation of the electronic spectrum of a dinuclear molybdenum complex, [Mo₂(μ-S₂)(μ-S₂C₂R₂)₂ (S₂C₂R₂)₂] (R=H), which was a model for the photochromic complex (R=Ph). The calculated results showed that TDDFT based on B3LYP theory would be useful for the calculation of electronic spectra of molybdenum compounds.     

Differential reactivity of SH bonds towards platinum(0). Direct synthesis of a low symmetry platinum (II) complex with hydrido, phosphine and N,S-cysteinato ethyl ester ligands

The chelate assisted oxidative addition of the H---S bond of L-cysteine esters HSCH₂C^*H(COOR)NH₂ (R = Me, Et), to Pt(PPh₃)₄ yields the low symmetry cysteine complexes [Pt(H)(SCH₂C^*H(COOR)NH₂)(PPh₃)] in one step, with displacement of three moles of triphenylphosphine, only when an excess of the cysteine ester is used. With HSCH₂CH₂NH₂ the excess is not necessary: the 1:1 reaction yields [Pt(H)(SCH₂CH₂NH₂)(PPh₃)]. Bulkier HSCH₂CH₂NMe₂ and HSCMe₂CH(COOMe)NH₂ (penicillamine methyl ester) do not react, even when an excess of ligand is used. 2-Aminothiophenol gives trans-[Pt(H)(SC₆H₄-2-NH₂)(PPh₃)₂] and does not form a chelate complex.     

Synthesis of a novel μ-acetate bridged dinuclear Cu(II) complex as model compound for the active site of tyrosinase: crystal structure, magnetic properties and catecholase activity

Reaction of the ligand N,N,N^′,N^′-bis[(2-hydroxybenzyl)(N-methylimidazolyl)]-2-ol-1,3-propendiamine (Hbhbmipo) with copper(II) perchlorate and sodium acetate in acetonitrile/ethanol leads to the assembly of a novel dinuclear copper(II) complex. The crystal structure, magnetic properties and its catecholase activity are reported. Both copper(II) ions are set in a distorted square pyramidal coordination sphere with a N₂O₃ donor set resulting in a CuCu distance of 3.382(5) Å. To our knowledge this is the first example of a dinuclear Cu(II) complex with square pyramidal coordination geometry in which the N₂O₃ donor set contains N-imidazol and O-phenol. The complex represents a structural model for a tyrosine intermediate in the proposed mechanism during hydroxylation of monophenols.     

Synthesis of a novel tetranuclear Cu(II) complex with the dinucleating ligand α,α′-bis(N-1,4,7-triazacyclononane)-m-xylene (XYL-tacn): first crystal structure of [(CuCl)4(XYL-tacn)2(μ-Cl)2][PF6]2

Reaction of the ligand α,α^′-bis(N-1,4,7-triazacyclononane)-m-xylene (XYL-tacn) with copper(II) chloride and sodium hexafluorophosphate in acetonitrile/methanol leads to the assembly of a remarkable tetranuclear copper(II) complex. The crystal structure and magnetic properties of the novel tetranuclear Cu(II) complex are reported. The complex exhibits an unusual [(CuCl)₄(μ-Cl)₂] binding mode with a Cu··· Cu distance of 6.856(3) Å.     

Synthesis and characterization of a rare hemiacetalate bridged incomplete Cu4II dicubane cluster

Reaction of 2-pyridinecarboxaldehyde [(Py)CHO] with Cu(NO₃)₂·2.5H₂O in the presence of 4-aminopyridine and NaN₃ in MeOH lead to an incomplete double-cubane [Cu₄{PyCH(O)(OMe)}₄(N₃)₄] (1) in 87% isolated yield, representing a rare type of metal cluster containing bridging hemiacetalate ligand [pyCH(O)(OMe)]^?1 which was characterized by single crystal structure analysis and variable temperature magnetic behavior.     

Copper(II) azide complexes of [Cu(acac)(N3)(dpyam)] and [Cu(μ-N3-κN1)(C2N3-κN1)(dpyam)]2: Synthesis,crystal structure and magnetism

Two new compounds, [Cu(acac)(N₃)(dpyam)] (1), (acac = acetylacetonate; dpyam = di-2-pyridylamine) and [Cu(μ-N₃-κ^N1)(C₂N₃- κ^N1) (dpyam)]₂ (2), have been synthesized and characterized by single-crystal X-ray diffraction and magnetic analyses. Compound 1 is a mononuclear compound in which each of two independent Cu(II) ions is penta-coordinated with a distorted square pyramidal geometry with distortion parameters τ = 0.21 and 0.16. In contrast, compound 2 is an azido-bridged dinuclear compound with monodentate dicyanamide anions and the Cu(II) ions display a distorted trigonal bipyramidal geometry with τ = 0.73 and end-on azido bridges providing an equatorial–axial position between the metal ions. The EPR spectra of powdered samples for 1 and 2 have also been investigated. Magnetic susceptibility measurements of compound 2 reveal a very weak ferromagnetic interaction between the Cu(II) ions with a J value of +5.8 cm⁻¹.     

Tautomerism of a compartmental Schiff base ligand and characterization of a new heterometallic CuII–DyIII complex — Synthesis,structure and magnetic properties

A crystal structure of a compartmental ligand N,N′-bis(2,3-dihydroxybenzylidene)-1,3-diaminopropane (H₄L = C₁₇H₁₈N₂O₄) (1) containing N₂O₂-inner and O₄-outer coordination sites and a characterization of its novel diphenoxo-bridged discrete dinuclear complex [CuDy(H₂L)(MeOH)(NO₃)₃]·2MeOH (2) are reported. The Schiff base ligand 1 crystallizes in the orthorhombic P2₁2₁2₁ space group with a molecule in a bent conformation. The compound at 100 and 293 K displays the keto-enol tautomerism with the equilibrium in both temperatures shifted with a different degree towards the zwitterionic keto-amino form. The quantum chemical calculations showed preferences for enol-imino form in a gas phase and for keto-amine in solutions. The keto-amino tautomer is stabilized by intermolecular interactions. The complex 2 crystallizes in the triclinic P-1 space group as a dinuclear compound with Cu^IIDy^III core. The Dy(III) ion is nine-coordinated whereas the coordination number of Cu(II) is five. The temperature dependence of the magnetic susceptibility and the field-dependent magnetization indicated that the interaction between Cu(II) and Dy(III) metal centers in 2 is ferromagnetic.     

Syntheses,crystal structures and magnetic property of two azido-bridged coordination polymers with 1,2-diaminocyclohexane as co-ligand

Two azido-bridged coordination polymers, [Ni(L)(μ_1,1-N₃)₂] (1) and [Cu(L)(μ_1,1,3-N₃)(N₃)] (2) (L = 1,2-diaminocyclohexane), have been synthesized and characterized by elemental analyses, IR spectra and X-ray structural analyses. Complex 1 is a one-dimensional helical chain coordination polymer with both azides as μ_1,1-bridge, which exhibits interesting wheel motif. Complex 2 shows two-dimensional layer network in which an azide acts as μ_1,1,3-bridge and the other azide as monodentate ligand. Cyclic voltammogram gives quasi-reversible redox wave of Cu(II)/Cu(I) pair. Variable-temperature magnetic property of 1 was investigated, which shown strong ferromagnetic interaction arising from the μ_1,1-azido bridging nickel(II) chains.     

Approaches to the Chemical,Electrochemical, and Photochemical Activation of Carbon Dioxide by Transition Metal Complexes

The activation of CO₂ by chemical, electrochemical, and photochemical means is discussed. Binuclear transition metal complexes mediate oxygen atom transfers from CO₂ by three distinct chemical pathways: (i) deoxygenation of CO₂, (ii) multiple bond metathesis, and (iii) disproportionation. The complex Ir₂ (μ-CNR)₂(CNR)₂(dmpm),(dmpm = bis(dimethylphosphino)methane) undergoes double cycloaddition of CO₂ to its μ-CNR ligands. A subsequent reaction produces the bis(carbamoyl) complex [Ir₂(μ-CO)(μ-H)(CONHR)₂(CNR)₂(dmpm)₂]Cl. Isotope labelling studies show that the μ-CO ligand results from net deoxygenation of CO₂. In contrast, the binuclear nickel complex Ni₂(μ-CNMe)(CNMe)₂(dppm)₂ (dppm = bis-(diphenylphosphino)methane) reacts with liquid CO₂ to give the tricarbonyl complex Ni₂(μ-CO)(CO)₂(dppm)₂. Isotope labelling indicates that the carbonyl ligands are not derived from CO₂ deoxygenation, but from C/CO triple bond metathesis. The reaction of CO₂ with the Ir(0) complex Ir₂(CO)₃(dmpm)₂ leads to CO₂ disproportionation by formation of the carbonate, Ir₂(CO₃)(CO)₂(dmpm)₂, and tetracarbonyl, Ir₂(CO)₄(dmpm)₂, complexes. The complex Ir₂(CO₃)(CO)₂ (dmpm)₂ undergoes reversible O-atom transfers from its carbonate ligand. The electrochemical activation of CO₂ by the binuclear Ni₂(μ-CNMe)(CNMe)₂(dppm)₂ and trinuclear [Ni₃(μ-CNMe)(μ-I)(dppm)₃][PF₆] species is described. The triangular nickel complex [Ni₃(μ₃-CNMe)(μ₃-I)(dppm)₃][PF₆] is an electrocatalyst for the reduction of CO₂. The cluster exhibits a reversible single electron reduction at E⁰(^+/0) = −1.09 V vs. Ag/AgCl. In the presence of CO₂, the cluster reduces CO₂ by an EC' electrochemical mechanism. The reduction products correspond to the disproportionation and H-atom abstraction products of CO₂^*−, with a partitioning ratio of 10:1. Isotope labelling studies with ¹³CO₂ indicate that ¹³CO₂^*− disproportionation produces ¹³CO and ¹³CO₃²⁻. Studies of the photochemical activation of CO₂ by Ni₂(μ-CNMe)(CNMe)₂(dppm)₂ are described. The bimolecular photochemical addition of CO₂ to the complex was examined by laser transient absorbance spectroscopy. Photolysis at 355nm in the presence of CO₂ (1 atm) leads to cycloaddition of CO₂ to the μ-CNMe ligand and the complex Ni₂(μ-CN(Me)C(O)O)(CNMe)₂(dppm)₂ with Φ₃₅₅=0.05. The triplet excited state of Ni,(μ-CNMe)(CNMe)₂(dppm)₂ was determined to react with CO₂ with the bimolecular reaction rate constant k = 1 × 10⁴ M⁻¹ s⁻¹. Bridging ligand substituent effects and solvent dependence of the lowest energy electronic absorption spectral bands of the series of complexes, Ni₂(μ-L)(CNMe)₂(dppm)₂, L = CNMe, CNC₆H₅, CN-p-C₆H₄Cl. and CN-p-C₆H₄Me, confirm the assignment of di-metal to bridging ligand charge transfer (M₂→μ-LCT). This assignment is supported by results of extended Hückel calculations which indicate a LUMO of predominantly μ-isocyanide π* character. A systematic study of the nature of the lowest excited states of related d¹⁰–d¹⁰ binuclear complexes of the type Ni₂(μ-L)(CNMe)₂(dppm)₂, where L = CNMe(Ph)⁺, CNMe₂⁺, CNMe(C₅H₁₁)⁺, CNMe(H)⁺, CNMe(CH₂C₆H₅)⁺, and NO⁺ reveals dramatic differences in the lowest excited states of the three classes of complexes: μ-isocyanide, μ-aminocarbyne, and μ-nitrosyl. Spectroscopic and extended Hückel MO studies confirm that the μ-isocyanide complexes are characterized by di-metal to bridging ligand charge transfer (M₂ → μ-LCT) excited states. However, the μ-aminocarbyne and μ-nitrosyl complexes exhibit bridging ligand to metal charge transfer (μ-L→M₂) and intraligand (IL) lowest excited states, respectively.     

Photoluminescence Properties of a New Homochiral srs-Type Coordination Polymer Employing Dinuclear [Zn2(COO)3] Units as Building Blocks

Qe report a new compound, namely [Zn₂(BTC)(NO₃)(DMA)₃]_n, with 1,3,5-benzenetricarboxylic acid (H₃BTC) and N,N′-dimethylacetamide (DMA) by the solvothermal method. The compound is characterized by elemental analysis, thermal analysis and X-ray diffraction (XRD). Single crystal XRD analysis reveals that the compound is an extended three-dimensional framework containing dinuclear [Zn₂(COO)₃] units as building blocks and can be simplified into a 3-connected srs topological network. There are two kinds of graceful helical chains with opposite chirality. The compound exhibits strong photoluminescent properties at room temperature.     

{[Cu(phen)]3Cl4}2[GeMo12O40]: Synthesis,crystal structure and magnetic property of a new trinuclear copper complex based on germanomolybdate

A new trinuclear copper complex based on germanomolybdate, {[Cu(phen)]₃(μ₂-Cl)₄}₂[GeMo₁₂O₄₀] (1) (phen = 1,10-phenanthroline), has been hydrothermally synthesized and structurally characterized by elemental analysis, IR spectroscopy, TG analysis, X-ray powder diffraction (XRPD) and single-crystal X-ray diffraction. Single crystal X-ray analysis reveals that the structural unit of 1 consists of two coordination cations {[Cu(phen)]₃(μ₂-Cl)₄}²⁺ (1a) and a saturated Keggin-type germanomolybdate polyoxoanion [GeMo₁₂O₄₀]^4?. In 1, the most intriguing feature is that each trinuclear copper cation {[Cu(phen)]₃(μ₂-Cl)₄}²⁺ is constructed from three [Cu(phen)]²⁺ cations bridged by four μ₂-Cl atoms. Magnetic measurements indicate 1 shows the ferromagnetic exchange interactions within Cu^II centers.     

Synthesis,structure and characterization of 1D threefold-bridging copper(II) chain with strong ferromagnetic coupling

A 1D chain Cu(II) complex: [Cu(2-Clnic)(μ_1,1-N₃)(CH₃OH)]_n(1) (2-Clnic=2-chloronicotinate) has been synthesized and characterized by IR, elemental analysis, X-ray crystal diffraction and magnetic properties. Single-crystal structural analysis shows that complex 1 consists of 1D Cu(II) chains containing threefold bridging ligands, one μ_1,1-azido, one (syn–syn) 2-chloronicotinate and one methanol molecule. The magnetic susceptibilities of 1 has been investigated, indicating strong ferromagnetic interactions with J = 81.22 cm^?1.     

Synthesis,structure and magnetic properties of a trinuclear cyano-bridged complex [Cu(bappz)(μ-NC)Ni(CN)2(μ-CN)Cu(bappz)](ClO4)2 {bappz=1,4-bis(3-aminopropyl)piperazine}

The bimetallic trinuclear complex [Cu(bappz)(μ-NC)Ni(CN)₂(μ-CN)Cu(bappz)](ClO₄)₂ (bappz=1,4-bis(3-aminopropyl)piperazine) has been prepared from the reaction of [Cu(bappz)](ClO₄)₂ and K₂[Ni(CN)₄] in water and its crystal and molecular structure has been determined. The structure consists of a trinuclear [Cu(bappz)(μ-NC)Ni(CN)₂(μ-CN)Cu(bappz)]²⁺ cation and two perchlorate anions. The bridging [Ni(CN)₄]²⁻ anion is coordinated by two [Cu(bappz)]²⁺ cations through two cyano groups, providing a novel trinuclear structure with the Cu–(NC)–Ni–(CN)–Cu linkage. The nickel(II) ion is four-coordinated by carbon atoms from four cyano groups (two of them, in trans position, form a bridge) in a square planar arrangement, whereas both the copper(II) ions are five-coordinated by four bappz nitrogens and one cyanide nitrogen in a distorted square–pyramidal geometry. The temperature dependence of magnetic susceptibility was measured for this compound over the range of 2–300 K. The magnetic investigation showed the presence of a very weak antiferromagnetic interaction (superexchange interaction parameter J=−0.54 cm⁻¹) between the copper atoms through the diamagnetic [Ni(CN)₄]²⁻ ion.