Tetrameric Copper Research Articles

Structural and Magnetic Properties of Dimeric and Tetrameric Copper (II) Complexes with Simple Bidentate Ligands and Phosphate Bridges

AbstractMonomeric [Cu(DACH)(L)]2+ (DACH=1,2‐diaminocyclohexane) heteroleptic copper(II) complexes (1–4) on reaction with diphenyl phosphate yielded dinuclear phosphate bridged copper(II) complexes [Cu2L2(dpp)3]+ (5–7), [dpp=diphenyl phosphate; L=bpy (5), Phen (6), 5, 6 dimethyl phenanthroline, (7)] and a tetra‐nuclear [Cu4(2,9‐dmp)2(dpp)4(OH)2]2+ complex (8) (2, 9 dmp=2, 9 dimethyl phenanthroline). Interestingly, isomeric ligands 5,6‐dmp and 2,9‐dmp yielded dinuclear complex 7 and tetra‐nuclear complex 8 triggered by steric effects. Even though the initial combination contains mixed bidentate ligands, the resulting complexes have only one type of bidentate ligand around the copper(II) ions. These reactions involve ligand expulsion to form the phosphate bridged complexes. All the phosphate bridged complexes 5–8 were characterized by elemental analysis, absorption spectrum, FT‐IR, ESI‐MS, and single‐crystal XRD. The molecular structures show Cu(II) in square pyramidal/trigonal bipyramidal geometry with phosphate in μ‐1,3‐bridging mode. All complexes exhibit intra‐antiferromagnetic interactions with negative J values from variable temperature magnetic susceptibility study by SQUID measurements.

A Novel Mineral-like Copper Phosphate Chloride with a Disordered Guest Structure: Crystal Chemistry and Magnetic Properties.

Novel copper phosphate chloride has been obtained under middle-temperature hydrothermal conditions. Its crystal structure was established based on the low-temperature X-ray diffraction data: Na2Li0.75(Cs,K)0.5[Cu5(PO4)4Cl]·3.5(H2O,OH), sp. gr. C2/m, a = 19.3951(8) Å, b = 9.7627(3) Å, c = 9.7383(4) Å, β = 99.329(4)°, T = 150 K, MoKα (λ = 0.71073 Å), R = 0.049. The crystal structure includes tetrameric copper clusters as the main building blocks, which are built of four CuO4Cl pyramids sharing apical Cl vertices. The clusters are combined through phosphate groups and additional copper-centered polyhedra to form two mostly ordered periodic layers. Between the layers and inside the framework channels, alkali ions, H2O molecules, or OH groups are statistically distributed. Na2Li0.75(Cs,K)0.5[Cu5(PO4)4Cl]·3.5(H2O,OH) is a synthetic modification of a sampleite-polymorph of the lavendulan mineral group and represents a new member in a mero-plesiotype series of copper phosphates and arsenates, for which the crystal structures contain two-periodic [Cu4X(TO4)4]∞ modules (T = As, P; X = Cl, O). Magnetically, this phase exhibits the phase transition at TC = 6.5 K, below which it possesses a weak ferromagnetic moment.

The crystal structure of tetrameric copper(II) complexes, Hirshfeld surface analysis, and vector analyses of Cu4OCl6L4 complexes with N-donor ligands

It is known, that in the Cu4OX6L4 (X = Cl, Br) complexes can be present many different ligands L, including bioligands. The synthesis and characterization of Cu4OBCl6(ron)4 (1) and Cu4OCl6(3-Mepy)4 (2) (where ron is ronicol or 3-methanolpyridine and 3-Mepy is 3-methylpyridine) are reported. The complexes under study were X-ray structure analysis and Hirshfeld surface analysis. Tetranuclear Cu4OX6L4 complexes with molecular structure (Fig. 1) can help to better understand the role of donor–acceptor and electron-transfer properties in copper proteins. The coordination sphere about each copper(II) atom is trigonal bipyramidal with three chlorine atoms in the equatorial plane. The apical positions are occupied by the central oxygen atom and the nitrogen atom of the respective ligand (CuCl3ON). Here are studied chloridocomplexes of some N-donor ligands, L = chloro-promazine, ronicol (3-pyridylmethanol), 2-ethylpyrazine, seven derivatives of pyrazol and for comparisons 3-methylpyridine. The Cu4OCl6L4 molecule is regarded as a supramolecular model of interactions between bioligand L and hypothetical “round-shaped” coordination tetra-receptor Cu4OCl6. Vector calculations applied usualy to mechanical and electrical macroconstructions are here applied to microconstructions represented by structures of Cu4OX6L4 molecules. For vector calculations each Cu4OX6L4 structure is placed (Fig. 1) into the three-dimensional Cartesian coordinate system with the central oxygen atom O1 placed in its origin 0. Studied bioligands are compared and described by molecular structural dynamics and corresponding shifts of electron densities by means of bond lenghts (O1–Cu, Cu–L, Cu–X) and structural distances (O1···X, O1···L).

Tetrameric copper(II) metallocyclic complex bearing an amino acid derived Schiff base ligand: Structure, catalytic and antioxidant activities

The synthesis, characterization of a new anhydro copper(II) complex derived from N-(2′-hydroxy acetophenone)glycinate ligand (LGly) is reported. The structure of the copper(II) complex was determined by single crystal X-ray diffraction (SCXRD), showing a tetranuclear metallocycle. The structure and spectroscopic characterization, as well as catalytic and antioxidant applications, are reported.

A novel tetramer copper(I) complex containing diallylphosphine ligands: Synthesis, characterization and catalytic application in A3-coupling (Aldehyde-Amine-Alkyne) reactions

A novel tetrameric copper(I) complex containing tert-butyldiallylphosphine ligands, [CuCl{tBu-P(CH2CH=CH2)2}]4 (2), has been synthesized and characterized by structural and spectroscopic methods. X-ray diffraction analysis showed that 2has a cubane-like solid structure of formula [CuCl{κ1(P)-tBu-P(CH2CH=CH2)2}]4. In solution, a dynamic behavior generated by the cubane⇄chair isomerization was detected by variable temperature NMR analysis. DFT calculations have been performed to explain the observed dynamic equilibrium in solution. The use of copper(I) complex 2 as catalyst for the synthesis of propargylamines via A3-coupling reactions has been tested. Complex 2 is capable of promoting A3-coupling reactions of both aromatic and aliphatic aldehydes with cyclic secondary amines and phenylacetylene. The reaction proceeds under mild condition and absence of solvent.

Solvent-mediated single-crystal-to-single-crystal transformation from a dimeric to tetrameric copper(i) complex based on a substituted pyridine derived from a Diels–Alder adduct

A solution of [Cu2I2L2(MeCN)2] (1) in dichloromethane (DCM) assisted the removal of MeCN and N-(4-pyridinyl)-9,10-dihydroethanoanthracene-11,12-dicarboximide (L) from the crystal of 1, leading to an unprecedented SCSC transformation.

Synthesis, characterization and catalytic properties of multinuclear copper(II) complexes

Four tetranuclear [Cu4(O)(Ln)2(CH3COO)4] (1, 2, 4 and 5) and one pentanuclear [Cu5(OH)2(L3)2(CH3COO)6] (3) with N2O-donor Schiff-base ligands have been synthesized, where HL1=4-methyl-2,6-bis(2-hydroxyethyliminomethyl)phenol for complex 1, HL2=4-methyl-2,6-bis(3-hydroxypropyliminomethyl)phenol for complex 2, HL3=4-methyl-2,6-bis(4-hydroxybutyliminomethyl)phenol for complex 3, HL4=4-methyl-2,6-bis(5-hydroxypentyliminomethyl)phenol for complex 4 and HL5=4-methyl-2,6-bis(6-hydroxyhexyliminomethyl)phenol for complex 5. These complexes have been characterized by elemental analysis, FT-IR, UV–Vis spectroscopy. The structures of 1, 3, 4 and 5 have been determined by single crystal X-ray diffraction studies. X-ray analysis reveals that complexes 1, 4 and 5 are μ4-oxido-bridged tetrameric copper(II) complexes, where four copper atoms arrange themselves around an oxidooxygen atom at the vertices of a distorted tetrahedron. The pentanuclear complex, 3, has been found to have two μ3-hydroxido bridging ligands each connecting three copper atoms. These complexes have been employed as catalyst for the epoxidation of olefins in the presence of tert-butyl hydroperoxide (TBHP) as the oxidant under mild conditions.

The templating effect of halides in the tetrameric copper(II) [Cu2(LH)2(μ4-X)Cu2(LH)2]3+ complexes (LH2 = N-(2-pyridylmethyl)-N,N-bis-[2′-hydroxy-5′-methyl-benzyl]-amine; X = Br, Cl). Synthesis and magneto-structural characterization

The synthesis, magnetic and structural characterization of two tetrameric copper(II) complexes {N(C4H9)4}-[Cu2(LH)2(μ4-Br)Cu2(LH)2](PF6)4 (1) and [Cu2(LH)2(μ4-Cl)Cu2(LH)2](Cl)2(PF6) (2) is described. LH stands for the hemi-deprotonated anion of the tripodal aminophenol ligand N-(2-pyridylmethyl)-N,N-bis-[2′-hydroxy-5′-methyl-benzyl]-amine. The complexes are tetrametallic species formed around the central halide ion which behaves as an anion template for the formation of the tetranuclear species, by bridging two dimeric phenoxo bridged [Cu2(LH)2]2+ units. The magnetic behaviour is dominated by the strong antiferromagnetic exchange within the dimeric unit, mediated by the phenoxo bridges: J=−439(4)cm−1, g=2.10(2) for (1) and J=−429(2)cm−1, g=2.090(9) for (2).

Copper Diamidocarbene Complexes: Characterization of Monomeric to Tetrameric Species

Treatment of CuCl with 1 equiv of the in situ prepared N-mesityl-substituted diamidocarbene 6-MesDAC produced a mixture of the dimeric and trimeric copper complexes [(6-MesDAC)CuCl]2 (1) and [(6-MesDAC)2(CuCl)3] (2). Combining CuCl with isolated, free 6-MesDAC in 1:1 and 3:2 ratios gave just 1 and 2, respectively, while increasing the ratio to >5:1 allowed the isolation of small amounts of the tetrameric copper complex [(6-MesDAC)2(CuCl)4] (3). Efforts to bring about metathesis reactions of 1 with MOtBu (M = Li, Na, K) proved successful only for M = Li to afford the spectroscopically characterized ate product [(6-MesDAC)CuCl·LiOtBu·2THF] (5). Attempts to crystallize this species instead gave a 1:1 mixture of 1 and the monomer [(6-MesDAC)CuCl] (6). The X-ray structures of 1–3 and 1 + 6, along with the cation [Cu(6-MesDAC)2]+ (4), have been determined.

Hexanuclear copper–nickel and copper–cobalt complexes for thin film deposition of ceramic oxide composites

Heterobimetallic molecular Cu–Ni and Cu–Co complexes [Cu2Ni4(acac)2(dmae)2(dmaeH)2(OH)(TFA)6] (1) and [Cu2Co4(acac)2(dmae)2(dmaeH)2(OH)(TFA)6] (2) [dmae = N,N-dimethylaminoethanol, TFA = trifluoroacetic acid and acac = 2,4-pentanedionate] were prepared and tested as precursors for the deposition of mixed metal oxide composite thin films. The complexes were synthesized by reaction of the tetrameric copper(II) complex [Cu(dmae)(TFA)]4 with M(acac)2·xH2O [M = Ni, x = 2; Co, x = 1] in THF and were characterized by melting point, elemental analysis, FT-IR spectroscopy, TG/DTG and single-crystal X-ray diffraction. The complexes are isomorphous and crystallize in the triclinic centrosymmetric space group P. Aerosol assisted chemical vapour deposition (AACVD) studies carried out on (1) and (2) showed that they are promising precursors for the deposition of thin films of crystalline CuO–NiO and Cu2O–CoO composites, respectively. The size, shape, surface morphology, microstructure, chemical composition and crystallinity of the resulting mixed-metal oxide composite thin films were analysed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The analysis proved that the thin films are crystalline, uniform, smooth and tightly adherent to the substrates.

Theoretical study of the structure, bonding and electronic spectrum of the tetrameric copper (I) amide complex [CuN(SiMe3)2

The tetrameric copper amide cluster, [CuN(SiMe3)2]4, has been previously shown to exhibit interesting spectral properties including a large Stokes shift in the emission spectrum. The photoluminescence has been suggested to arise from phosphorescence from an excited state involving enhanced Cu–Cu bonding. In this study the molecular structure and bonding of [CuN(SiMe3)2]4 are studied in the ground state and excited states using density functional theory. Density functional theory calculations are shown to accurately reproduce the geometry of the complex using both the full structure and using a model complex. Time dependent density functional theory calculations are used to simulate the electronic spectrum of the model complex and assign the observed absorption bands to specific electronic transitions. It is found that the two observed near-UV absorption bands arise from transitions between the HOMO and LUMO/LUMO+1 of the complex. Both excited states involve population of orbitals with Cu–Cu bonding character. ΔSCF optimization of the lowest lying 3Eu state indicates significant Cu–Cu bonding enhancement and short Cu–Cu distances in a Jahn–Teller distorted structure. QTAIM analysis also support enhanced Cu–Cu bonding in the excited state.

Ratiometric Pulse–Chase Amidination Mass Spectrometry as a Probe of Biomolecular Complex Formation

Selective chemical modification of protein side chains coupled with mass spectrometry is often most informative when used to compare residue-specific reactivities in a number of functional states or macromolecular complexes. Herein, we develop ratiometric pulse-chase amidination mass spectrometry (rPAm-MS) as a site-specific probe of lysine reactivities at equilibrium using the Cu(I)-sensing repressor CsoR from Bacillus subtilis as a model system. CsoR in various allosteric states was reacted with S-methyl thioacetimidate (SMTA) for pulse time, t, and chased with excess of S-methyl thiopropionimidate (SMTP) (Δ = 14 amu), quenched and digested with chymotrypsin or Glu-C protease, and peptides were quantified by high-resolution matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry and/or liquid chromatography electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). We show that the reactivities of individual lysines from peptides containing up to three Lys residues are readily quantified using this method. New insights into operator DNA binding and the Cu(I)-mediated structural transition in the tetrameric copper sensor CsoR are also obtained.

Four μ4-oxo-bridged copper(ii) complexes: magnetic properties and catalytic applications in liquid phase partial oxidation reactions

Four copper(II) complexes, [Cu(4)(O)(L(n))(2)(CH(3)COO)(4)] with N(2)O-donor Schiff-base ligands, where HL(1) = 4-methyl-2,6-bis(cyclohexylmethyliminomethyl)phenol for complex 1, HL(2) = 4-methyl-2,6-bis(phenylmethyliminomethyl)phenol for complex 2 x CH(3)CN, HL(3) = 4-methyl-2,6-bis(((3-tri-fluoromethyl)phenyl)methyliminomethyl)phenol for complex 3, HL(4) = 4-methyl-2,6-bis(((4-tri-fluoromethyl)phenyl)methyliminomethyl)phenol for complex 4, were synthesized and characterized by elemental analysis, FT-IR, UV-vis spectroscopy and finally by single crystal X-ray diffraction study. X-Ray analysis reveals that all of these are mu(4)-oxo-bridged tetrameric copper(II) complexes. Four copper atoms arrange themselves around an oxygen atom tetrahedrally. Magnetic susceptibility measurements show the existence of very strong antiferromagnetic coupling among these ions (J = -210.1 to -271.3 cm(-1)), mediated by the oxygen atoms. Catalysis of the epoxidation of cyclohexene, styrene, alpha-methylstyrene and trans-stilbene by these complexes has been carried out homogeneously as well as heterogeneously by immobilizing the metal complexes over 2D-hexagonal mesoporous silica. The results obtained in both the catalytic conditions show that the olefins are converted to the respective epoxides in good yield together with high selectivity.

Synthesis and structural characterization of two new polynuclear metal thiosaccharinates: Hexakis(thiosaccharinato)hexasilver(I) and tetrakis(thiosaccharinato)tetracopper(I)

The title compounds, for short Ag 6(tsac) 6 ( 1) and [Cu 4(tsac) 4(MeCN) 2] · 2MeCN ( 2), were prepared by the reaction of thiosaccharin with Ag(I) or Cu(II) salts in different solvents. The new complexes were characterized by FT-IR, Raman, UV–Vis and NMR spectroscopy. Their crystal and molecular structures were determined by X-ray diffraction methods. The structures were solved from 1621 ( 1) and 7080 ( 2) reflections with I > 2 σ( I) and refined to agreement R1-factors of 0.0261 ( 1) and 0.0456 ( 2). Ag 6(tsac) 6 molecule derives from the clustering of six Ag(tsac) moieties related to each other through the crystallographic 3-bar ( S 6) symmetry operations of the R 3 ¯ space group. This results in a highly regular molecular structure where the silver atoms are at the corners of an octahedral core slightly compressed along one of its three-fold axis [inter-metallic Ag⋯Ag contacts of 3.1723(4) and 3.1556(4) Å]. The six thiosaccharinate ligands bridge neighboring Ag atoms along the C 3-axis through Ag–N bonds [ d(Ag–N) = 2.285(2) Å] at one end and bifurcated Ag–S(thione)–Ag bonds [Ag–S distances of 2.4861(7) and 2.5014(8) Å] at the other end. In contrast, the 2 compound is arranged in the lattice as an irregular tetrameric copper complex [Cu 4(tsac) 4(MeCN) 2] where the metals show different environments. Two copper ions are four-fold coordinated to three tsac ions through the N-atom of one tsac [Cu–N distances of 2.112(3) and 2.064(3) Å] and the thione sulfur atom of the other two [Cu–S distances in the range from 2.284(1) to 2.358(1) Å] and to a MeCN solvent molecule [Cu–N distances of 1.983(4) and 2.052(3) Å]. The other two copper ions are in three-fold environment, one trans-coordinated to two tsac ions [Cu–N distances of 1.912(3) and 1.920(3) Å] and to the thione S-atom of a third ligand [ d(Cu–S) = 2.531(1) Å], the other one to the thione sulfur atom of three tsac ligands [Cu–S distances in the range from 2.229(1) to 2.334(1) Å]. The clustering renders the metals to short distances from each other, the shorter Cu⋯Cu distance being 2.6033(7) Å, as to presume the existence of weak inter-metallic interaction within the cluster.

Wells–Dawson anion, a useful building block to construct one-dimensional chain as a chelate ligand coordinating with transition metal cations

Two composite compounds, [{Cu(PPD) 2}(As 2W 18O 60)]·2H 2PPD·14H 2O 1 (PPD = p-phenylenediamine) and [Cu 4(Hen) 2As 2W 18O 68]·4H 2en·18H 2O 2 (en = ethylenediamine) have been prepared under mild hydrothermal conditions with difference in pH values of the initial reaction solutions and structurally characterized by single-crystal X-ray diffraction. Compound 1 exhibits a one-dimensional chain constructed from Wells–Dawson anions and Cu(II) coordination complex. It is the first example of a one-dimensional chain based on Wells–Dawson anions that act as chelate ligands to coordinate with transition metal. Compound 2 is constructed from trivacant Keggin polyanions linked through tetrameric copper unit, which coordinates with organonitrogen ligands.

The α-Iminophospholide Ligands

The reaction of phospholide ions with imidoyl chlorides in the presence of tBuOK gives the alpha-iminophospholides that are isolated as their trimethylstannyl derivatives. These derivatives in turn react with metal chlorides to give complexes of the title ligands. A DFT study shows that substantial electronic delocalization takes place between the imino group and the phospholyl ring in these anions. The X-ray crystal structure of one stannylphosphole shows a highly pyramidal phosphorus atom (sum of angles = ca. 280 degrees ). A tetrameric copper complex has also been structurally characterized.

Nanosized Polymetallic Resorcinarene-Based Host Assemblies that Strongly Bind Fullerenes

Polymetallic nanodimensional assemblies have been prepared via metal directed assembly of dithiocarbamate functionalized cavitand structural frameworks with late transition metals (Ni, Pd, Cu, Au, Zn, and Cd). The coordination geometry about the metal centers is shown to dictate the architecture adopted. X-ray crystallographic studies confirm that square planar coordination geometries result in "cagelike" octanuclear complexes, whereas square-based pyramidal metal geometries favor hexanuclear "molecular loop" structures. Both classes of complex are sterically and electronically complementary to the fullerenes (C(60) and C(70)). The strong binding of these guests occurred via favorable interactions with the sulfur atoms of multiple dithiocarbamate moieties of the hosts. In the case of the tetrameric copper(II) complexes, the lability of the copper(II)-dithiocarbamate bond enabled the fullerene guests to be encapsulated in the electron-rich cavity of the host, over time. The examination of the binding of fullerenes has been undertaken using spectroscopic and electrochemical methods, electrospray mass spectrometry, and molecular modeling.

How Bulky Is a Bulky Ligand: Energetic Consequences of Steric Constraint in Ligand-Directed Cluster Assembly and Disassembly

Steric tuning of N-aryl groups of homologous amidinate ligands affords discrete dimeric and tetrameric copper(I) clusters in solid state, but they undergo dynamic dimer-dimer and tetramer-dimer interconversion in solution. A delicate interplay between steric constraint and mechanical stability shapes the reaction coordinate of this process. Thermodynamic and kinetic parameters dictating such cluster assembly and disassembly immediately suggest a means to experimentally quantify energies that are associated with ligand steric bulk.

Iron and copper complexes of tetraphenyl-m-benziporphyrin: reactivity of the internal C-H bond.

Iron and copper complexes of tetraphenyl-m-benziporphyrin (TPmBPH)H have been prepared and structurally characterized. The iron system, (TPmBPH)Fe(II)Br, contains a high-spin Fe(II) center. In the solid state the complex forms dimeric units linked by weak CH.Br hydrogen bonds. The Cu complex contains a tetrameric copper cluster with a Cu(2)Cl(4)(2)(-) unit bridging two [(TPmBPCl)Cu(II)](+) fragments. The formation of (TPmBPCl)H represents an example of copper-catalyzed chlorination on the internal carbon atom of (TPmBPH)H.

Iminodiacetyl-hydroxamate derivatives as metalloproteinase inhibitors: equilibrium complexation studies with Cu(II), Zn(II) and Ni(II)

Two new iminodiacetyl-hydroxamate derivatives, the N-benzyl- N-carboxymethyl-iminoacetohydroxamic acid (H 2L 1) and the N-benzyl- N′-hydroxypiperazine-2,6-dione (HL 2), have been recently reported as very effective inhibitors against a set of zinc-containing matrix metalloproteinases (MMPs). Herein, aimed at understanding that inhibitory function, these compounds are studied in their complex formation equilibria with three biologically relevant first-row transition M 2+ metal ions (M=Cu, Zn, Ni) by using potentiometric and spectroscopic techniques. At physiological conditions, complexation of these metal ions by H 2L 1 mostly occurs with formation of 1:1 species by tridentate co-ordination (O,N,N) (carboxylate-amino-hydroxamate), whereas complexation with HL 2 mainly involves the formation of 1:2 (M:L) species with normal (O,O) hydroxamate coordination. Moreover, at higher pH, H 2L 1 is able to form a pentanuclear tetrameric copper complex with an interesting 12-metallacrown-4 structure.