Restricting the versatile metal-binding behaviour of adenine by using deaza-purine ligands in mixed-ligand copper(II) complexes

In order to deepen our understanding of the versatile behaviour of adenine (Hade) as ligand, we have synthesized four novel ternary copper(II) complexes having two deazaadenine ligands, namely 4-azabenzimidazole (H4abim) or 7-azaindole (H7azain) as N1,N6-dideazaadenine or N1,N6,N7-trideazaadenine, respectively. The related compounds were studied by thermal, spectral and single crystal X-ray diffraction methods. In [Cu(NBzIDA)(H4abim)]_n (1) the recognition between H4abim and the (N-benzyliminodiacetate)-copper(II) chelate only displays the formation of the Cu–N7(purine-like) bond, in contrast to Hade behaviour in [Cu(NBzIDA-like)(Hade)(H₂O)]·H₂O (Cu–N3(Hade) bond reinforced by N9–H···O(IDA-like) interaction). In [Cu(EIDA)(H7azain)(H₂O)] (2, EIDA = N-ethyliminodiacetate ligand), [Cu(NBzIDA)(H7azain)(H₂O)] (3) and [Cu(μ₂-SO₄)(H7azain)₂(H₂O)₂]_n (4), H7azain binds Cu(II) centre by the Cu–N3(purine-like) bond, reinforced by a N9–H···O(IDA-like or sulfate) intra-molecular interligand interaction.     

The reaction of copper(II) and 2-hydrazino-2-imidazoline leading to the in situ formation of bisimidazoline (biz). Crystal structure and vibrational spectroscopy of mixed-valence [Cu(biz)2][Cu2Br4] complex

The reaction of Cu(OH)₂ and 2-hydrazino-2-imidazoline hydrobromide surprisingly resulted in complex compound where Cu(II) ions are chelated by a new ligand, namely bisimidazoline (biz). As has been found in the X-ray analysis, the [Cu(biz)₂]²⁺ cations are accompanied by [Cu₂Br₄]²⁻ anions, which makes the whole compound of metal-mixed-valency type. Both ions are centrosymmetric and quasi-planar. The Cu(II) coordination environment is a rectangle with almost equal Cu–N bond lengths (1.984(3), 1.987(3) Å). The electrostatic interaction of both complex ions is strengthened by two strong N–H···Br and four weaker (C–H···Br, C–H···N) hydrogen bonds. The relatively simple IR and Raman spectra were interpreted with help of quantum calculations carried out at the B3LYP/LanL2DZ level. The characterization of computed normal vibrations and correlating observed bands is given in terms of approximate D_2h symmetry. The most intense band resulting from the Cu–N stretching vibration (B_3u) was located at 342 cm⁻¹, by ⁶³Cu and ⁶⁵Cu isotope substitution. The chemical reactions leading to the formation of presented compound are also proposed.     

Iron/copper promoted oxidative homo-coupling reaction of terminal alkynes using air as the oxidant

An inexpensive catalytic system, which used a readily available Fe(acac)₃ and trace quantity of Cu(acac)₂ as the co-catalyst and air as the oxidant for the homo-coupling of terminal alkynes, has been developed. The catalytic system could also apply to the cross-coupling reaction of two different terminal alkynes.     

Synthesis,crystal structure and hydrolysis of a dinuclear copper(II) complex constructed by N2O donor Schiff base and 4,4′-bipyridine: Discrete supra-molecular ensembles vs. oligomers

The tridentate Schiff base ligand, 7-amino-4-methyl-5-aza-3-hepten-2-one (HAMAH), prepared by the mono-condensation of 1,2-diaminoethane and acetylacetone, reacts with Cu(BF₄)₂ · 6H₂O to produce initially a dinuclear Cu(II) complex, [{Cu(AMAH)}₂(μ-4,4′-bipy)](BF₄)₂ (1) which undergoes hydrolysis in the reaction mixture and finally produces a linear polymeric chain compound, [Cu(acac)₂(μ-4,4′-bipy)]_n (2). The geometry around the copper atom in compound 1 is distorted square planar while that in compound 2 is essentially an elongated octahedron. On the other hand, the ligand HAMAH reacts with Cu(ClO₄)₂ · 6H₂O to yield a polymeric zigzag chain, [{Cu(acac)(CH₃OH)(μ-4,4′-bipy)}(ClO₄)]_n (3). The geometry of the copper atom in 3 is square pyramidal with the two bipyridine molecules in the cis equatorial positions. All three complexes have been characterized by elemental analysis, IR and UV–Vis spectroscopy and single crystal X-ray diffraction studies. A probable explanation for the different size and shape of the reported polynuclear complexes formed by copper(II) and 4,4′-bipyridine has been put forward by taking into account the denticity and crystal field strength of the blocking ligand as well as the Jahn–Teller effect in copper(II).     

Cobalt(II), nickel(II) and copper(II) compounds derived from template reactions of enantiomerically pure 2-amino-thiazoles

Herein we report the syntheses and structural analyses of three coordination compounds Co(L)₂ (3), Ni(L)₂, (4) and Cu(L)₂ (5) (L = bis[(4R,5R)-4-methyl-5-phenyl-4,5-dihydro-thiazol-2-yl]-amine) prepared by template reactions from the optically active ligand (4R,5R)-4-methyl-5-phenyl-4,5-dihydro-thiazol-2-yl-amine (1) and CoCl₂·6H₂O, NiBr₂·3H₂O or Cu(OAc)₂·H₂O The template reactions involve the condensation of two molecules of thiazol-2-yl-amine and elimination of one NH₃. The resulting bidentate ligand coordinates to the metal ion through the imine nitrogen atoms forming a six-membered ring, presenting an electronic delocalization which averages the four M–N bond lengths. The distorted tetrahedral geometry of the metal atoms gives place to complex electronic spectra for compounds 3–5. A mixed ionic compound (6) formed by three cations (4S,5S)-3,4-dimethyl-5-phenyl-thiazolidin-2-ylidene ammonium, one dianion tris-(thiocyano)bromide cobaltate and one bromide, obtained from reaction of (4S,5S)-3,4-dimethyl-5-phenyl-thiazolidin-2-ylidene ammonium thiocyanate (2) and CoBr₂ is also described. Compounds 3–6 were characterized in the solid state by UV–Vis–NIR and IR spectroscopy, mass spectrometry and X-ray diffraction analyses. Metal···H–C, S···H–C interactions were observed in 3–6, whereas in 6, also Br···H–N, Br···H–C and Br···S, S···S short contacts were found.     

Synthesis of a new N,N-ethane-1,2-bis(4-methoxyphenyl)carbothioamide ligand and its Cu(I) and Ag(I) complexes

[Cu(H₂L)(PPh₃)₂]NO₃ · 0.5H₂O (2) and [Ag(H₂L)(PPh₃)₂]NO₃ · 0.5H₂O (3) complexes of a new flexible thioamide ligand; N,N′-ethane-1,2-bis(4-methoxyphenyl)carbothioamide H₂L (1) have been synthesized using PPh₃ as a coligand. The synthesized compounds have been characterized with the help of elemental analyses, IR, ¹H, ¹³C and ³¹P NMR spectroscopy. The ligand and its Cu(I) complex have been studied by single crystal X-ray crystallography. The ligand acts as a neutral S-donor and forms a nine-membered chelate ring in [Cu(H₂L)(PPh₃)₂]NO₃ · 0.5H₂O. The molecular packing is stabilized by an anionic cavity formed by intermolecular hydrogen bonding between the basal plane of the complex molecule and the nitrate ions. The square shaped columnar channel has dimensions of 5.489(25) [N(11)–H(11A)?O(13)?H(21A)N(21)] × 3.693(7) [N(11)–C(11)–C(21)–N(21)] Å.     

Copper(II)-saccharinato complexes with piperazine and N-(2-aminoethyl)piperazine ligands

Two copper(II) complexes of the saccharinate anion (sac) with piperazine (ppz) and N-(2-aminoethyl)piperazine (aeppz), namely [Cu(sac)₂(ppz)(H₂O)]_n (1) and trans-[Cu(sac)₂(aeppz)₂] (2), have been synthesized and characterized by elemental analyses, UV–Vis, FT-IR, TGA/DTA, X-ray diffraction and magnetic measurements. The ppz ligands in 1 bridge the copper(II) centers through both nitrogen atoms to form a 1D helical chain structure and the distorted trigonal-bipyramidal coordination geometry at each copper center is completed by an aqua and a pair of N-bonded sac ligands. The helical chains are linked by Ow–H?O hydrogen bonds to build a 2-D network. In complex 2, copper(II) ions are octahedrally coordinated by two sac anions and two neutral aeppz ligands, displaying a distorted octahedral coordination. Sac is O-bonded via the carbonyl group, while ppzea acts as a N,N′-bidentate chelating ligand. The molecules are connected by N–H?N and N–H?O hydrogen bonds, forming a linear chain. In the thermal decomposition of both complexes, the removal of the aqua and ppz or aeppz ligand takes place endothermically in the first stages and the sac moiety undergoes highly exothermic decomposition at higher temperatures to give CuO.     

Complexes of N-thiophosphorylthiourea (EtO)2P(O)CH2C6H4-4-[NHC(S)NHP(S)(OiPr)2] with Zn(II), Cd(II), Co(II) and Cu(PPh3)(I)

Reaction of O,O’-diisopropylthiophosphoric acid isothiocyanate (iPrO)₂P(S)NCS with diethyl 4-aminobenzylphosphonate (EtO)₂P(O)CH₂C₆H₄-4-NH₂ leads to the new N-thiophosphorylated thiourea (EtO)₂P(O)CH₂C₆H₄-4-[NHC(S)NHP(S)(OiPr)₂] (HL). Reaction of the potassium salt of HL with Zn(II), Cd(II) and Co(II) in aqueous EtOH leads to complexes of formula M(L-S,S’)₂ (ML₂). Heteroligand copper(I) complex of HL and triphenylphosphine was prepared by the reaction of the potassium salt KL and Cu(PPh₃)₃I. Copper in complex Cu(PPh₃)L is bound by one PPh₃ and one SCNPS fragment of the chelating ligand. Compounds obtained were investigated by IR, UV–Vis, ¹H and ³¹P{¹H} NMR spectroscopy, and microanalysis. The structures of HL and Cu(PPh₃)L were investigated by single crystal X-ray diffraction analysis.     

Dinuclear oxomolybdenum(VI) acetylacetonates: Crystal and molecular structure of Mo2O5(acac)2L2 (L = D2O,DMF)

The behavior of MoO₂(acac)₂ (acac = acetylacetonate) towards representative amines, amides, sulfoxides and phosphine oxides in common solvents has been examined. Compounds of the composition Mo₂O₅(acac)₂L₂ [L = H₂O, D₂O, dimethylformamide (DMF), dimethylacetamide (DMA), dimethylbenzamide (DMBA), tetramethylurea (TMU), dimethylsulfoxide (DMSO), dibutylsulfoxide (Bu₂SO), p-tolylsulfoxide (p-Tol₂SO), tributylphosphine oxide (OPBu₃), triphenylphosphine oxide (OPPh₃), hexamethylphosphoramide (HMPA)], derived from partial hydrolysis of MoO₂(acac)₂ followed by condensation and coordination of L, can readily be isolated. The crystal and molecular structures of Mo₂O₅(acac)₂L₂ (L = D₂O, DMF) have been established by X-ray diffraction analysis.     

The first bis(orotato–N,O) complex: Synthesis,crystal structure,spectroscopic and thermal characterization of (chaH)2[Cu(HOr–N,O)2(cha)] · 2H2O (cha = cyclohexylamine and HOr = orotate(2−))

The novel bis(cyclohexylaminium) cyclohexylaminebis(orotate–N,O)cuprate(II) dihydrate, (C₆H₁₅N)₂[Cu(C₅H₂N₂O₄)₂(C₆H₁₄N)] · 2H₂O, has been prepared and characterized by elemental analysis, magnetic measurements, FT-IR and UV–Vis spectroscopy, thermal analysis and X-ray diffraction. The Cu(II) complex crystallizes in the monoclinic space group P2₁/c. The copper atom in the five-coordinated (chaH)₂[Cu(HOr–N,O)₂(cha)] · 2H₂O is chelated by a deprotonated pyrimidine nitrogen atom and carboxylate oxygen atom as a bis(bidentate) ligand and the cyclohexylamine ligand completes the square-pyramidal coordination. The thermal decomposition of the complex has been predicted by the help of thermal analysis (TG, DTG and DTA).     

Mechanistic studies of the sensitized photoreduction of bis(acetylacetonato)copper(II) by phenylalkyl ketones

Bis(acetylacetonato)copper(II) (Cu(acac)₂) interacts with both the triplet excited state and the triplet biradical of phenylalkyl ketones which undergo the Norrish type II reaction. Mechanistic studies by static quenching methods show that the triplet biradicals interact with the paramagnetic copper species, leading to the preferential formation of cyclobutanols without the formation of new products; in the presence of Ph₃P the former interaction causes the known reduction of Cu(acac)₂) to Cu(acac)(Ph₃P)₂, with a rate constant of about 6 × 10⁹ M⁻¹ s⁻¹. It is shown that Ph₃P interacts with one reactive intermediate, the triplet excited state ketone. The results of extensive kinetic analysis strongly support the proposed reaction mechanism.     

Stabilities and coordination modes of histidine in copper(II) mixed-ligand complexes with ethylenediamine,diethylenetriamine or N,N,N′,N″,N″-pentamethyldiethylenetriamine in aqueous solution

Solution equilibrium studies on the Cu(II)–polyamine–histidine ternary systems (polyamine: ethylenediamine (en), diethylenetriamine (dien), N,N,N′,N″,N″-pentamethyldiethylenetriamine (Me₅dien)) have been performed by pH-potentiometry, UV–Vis spectrophotometry and EPR methods. The obtained results suggest the formation of the mixed-ligand complexes with [Cu(A)(His)]⁺ stoichiometry in all studied systems. Additionally, in the systems with dien and Me₅dien protonated [Cu(A)(H–His)]²⁺ species also exists in acid solution. Our spectroscopic results indicate the tetragonal geometry for the [Cu(en)(His)]⁺, the geometry slightly deviated from square pyramidal for the [Cu(dien)(His)]⁺ and strongly deviated from square pyramidal towards trigonal bipyramidal for the [Cu(Me₅dien)(His)]⁺ species. The coordination modes in these mixed-ligand complexes are discussed.     

Crystal structure,spectroscopy and magnetism of a dinuclear strongly antiferromagnetically coupled N-oxido-bridged Cu(II) compound with 2,2′-bipyridine-1,1′-dioxide (bpdo) as a ligand; [Cu2(bpdo)2Br4]

A new dinuclear compound, [Cu₂(bpdo)₂Br₄], (in which bpdo = 2,2′-Bipyridine-1,1′-dioxide), has been synthesized and fully characterized, including the X-ray and the magnetic susceptibility. Each copper(II) ion in the dinuclear compound has a distorted square pyramidal geometry with the basal plane formed by two oxygen atoms of two ligand molecules which are bridging between the Cu ions with Cu–O distances of 2.021(2) and 2.039(2) Å and two bromide atoms with Cu–Br distances of 2.3577(6) and 2.3665(7) Å. The fifth position is occupied by a non bridging oxygen atom of a ligand with a Cu–O distance of 2.197(2) Å. The distance between the Cu ions is 3.334 Å, while the Cu–O–Cu angle is 110.37(9)°. The magnetic susceptibility measurements (from 5 to 350 K) agree with a very strong antiferromagnetic interaction with a large singlet–triplet splitting (J) of −905 cm⁻¹. At high T (above 250 K) a triplet powder EPR is observed.     

Anion-induced assembly of two distinct copper(II) coordination polymers with a versatile multidentate N-donor ligand

Reaction of a ligand N-(3,5-di-2-pyrazinyl-4H-1,2,4-triazol-4-yl)-2-pyrazinecarboxamide (Hpztp) with CuSO₄ and Cu(acac)₂ (acac = acetylacetonate), respectively, yields two distinct Cu^II coordination polymers {[Cu₃(pztp)₂(SO₄)₂(H₂O)₂]·3H₂O} _n and {[Cu(pztp)(acac)]·0.5H₂O} _n . Both complexes have been structurally determined and also characterized by physicochemical and spectroscopic methods. The results reveal that by using different anions (SO₄ ^2? versus acac^?), the dimensionality (from 2D to 1D) of the resulting coordination architectures as well as conformations and binding fashions of the pztp ligand are significantly changed. That is to say, the selection of anions will play a key role in inducing the formation of the crystalline materials. The thermal stabilities of both complexes have also been explored and discussed.     

Synthesis and characterization of metal substituted AlxCr1−x(acetylacetonate)3 single-source precursors for their application to MOCVD of thin films

A detailed study, involving the synthesis of a single-source precursor containing two metal ions sharing the same crystallographic site, has been undertaken to elucidate the use of such a single-source precursor in a CVD process for growing thin films of oxides comprising these two metals, ensuring a uniform composition and distribution of metal ions. The substituted complexes Cr_1−xAl_x(acac)₃, where acac = acetylacetonate, have been prepared by a co-synthesis method, and characterized using UV–Vis spectroscopy, TGA/DTA measurements, and single crystal X-ray diffraction at low temperature. All the studied compositions crystallize in the monoclinic space group P2₁/c with Z = 4 in the unit cell. It was observed that the ratio (Al:Cr) of the site occupancy for the metal ions, obtained from single crystal refinement, is in agreement with the results obtained from complexometric titrations. All the solid state structures have the metal in an octahedral environment forming six-membered chelate rings. M–O acac bond lengths and disorder in the terminal carbon have been studied in detail for these substituted metal–organic complexes. One composition among these was chosen to evaluate their suitability as a single-source precursor in a LPMOCVD process (low-pressure metal–organic chemical vapour deposition) for the deposition of a substituted binary metal oxide thin film. The resulting thin films were characterized by X-ray diffraction, scanning electron microscopy, and infrared spectroscopy.     

Decavanadates with [Et3NH] and [Me2HN(CH2)2NHMe2]: Variation in protonation state and self-assembly

Synthesis, thermal behaviour and crystal structures of [Et₃NH]₄[V₁₀O₂₆(OH)₂] (1) and [Me₂HN(CH₂)₂NHMe₂]₃[V₁₀O₂₈] · 4H₂O (2) are reported. In the crystal lattice of 1, the anions form discrete dimers via O–H···O hydrogen bonds and the cations are connected to the respective anions through N–H···O hydrogen bonds. On the other hand, 2 forms a complex three-dimensional network due to involvement of the cations, the anions and the lattice water in O–H···O and N–H···O hydrogen bonds.     

Synthesis,structure and spectral studies on mixed ligand copper(II) complexes of diimines and acetylacetonate

Two new mixed ligand complexes of copper(II) with acetylacetonate (acac), 2,2′-bipyridine (bpy) and 1,10-phenanthroline (phen) belonging to the class of cytotoxic and antineoplastic compounds known as CASIOPEINAS^® were synthesized and structurally characterized. Crystals of both complexes [Cu(acac)(bpy)(H₂O)]NO₃ · H₂O (1), [Cu(acac)(phen)Br] (2) contain square pyramidal Cu(II) complex species. In frozen solution both compounds give well resolved EPR spectra with very similar parameters.     

Asymmetric Michael addition promoted by (R,R)-trans-1,2-diaminocyclohexane in ionic liquids

In tetrafluoroborate based ionic liquids fair yields and enantiomeric excesses up to 91% were obtained in the Michael addition of ethyl cyclohexanone-2-carboxylate to methyl vinyl ketone, using (R,R)-trans-1,2-diaminocyclohexane as chiral auxiliary (37% mol/mol with respect to the donor). The presence of catalytic amounts of metal sources [Ni(OAc)₂ · 4H₂O, Co(acac)₂, FeCl₃ · 6H₂O, LaCl₃, Cu(OAc)₂ · H₂O] did not improve the activity, and, in some instances, caused a drop of enantioselectivity. Reactions carried out in the absence of any metal and with a Michael donor/diamine molar ratio of 20 allowed us to ascertain that the reaction can be performed catalytically.     

Piperazinediium,Zr(IV) and Ce(IV) pyridine-2,6-dicarboxylates: Syntheses,characterizations, crystal structures, ab initio HF,DFT calculations and solution studies

The novel title compounds, (pipzH₂)_1.5(pydcH)₃·3.7H₂O, 1, (pipzH₂)[Zr(pydc)₃]·8H₂O, 2 and (pipzH₂)[Ce(pydc)₃]·8H₂O, 3 in which pydcH₂ is pyridine-2,6-dicarboxylic acid and pipz is piperazine were obtained in aqueous solution. The compounds were characterized by IR, ¹H NMR and ¹³C NMR spectroscopy, elemental analyses, and X-ray crystallography. Compound 1 is resulted from proton transfer between pydcH₂ and pipz. However, compounds 2 and 3 are resulted from complexation of 1 and corresponding metallic salts. Both compounds 2 and 3 contain three pyridine-2,6-dicarboxylate species as tridentate ligands, one piperazinediium as counter ion, and eight-uncoordinated water molecules in the asymmetric unit. In both structures each M(IV) is coordinated in a distorted tricapped trigonal prism geometry by three nitrogen and six oxygen atoms of carboxylate groups of three (pydc)²⁻ fragments. In the crystal structures of 1, 2 and 3, extensive O–H···O, N–H···O and C–H···O hydrogen bonds as well as electrostatic forces, C–H···π, C–O···π and π–π stacking play important roles in stabilizing structures. The geometrical parameters of the [M(pydc)₃]²⁻ anionic complexes, where M = Ce(IV), Zr(IV) have been optimized with the B3LYP method of density functional theory (DFT) and ab initio Hartree–Fock (HF) methods for comparison. In addition, we have studied the structures of (pydc)²⁻ anion and its mono and doubly protonated forms, (pydcH)⁻ and pydcH₂. The electronic properties of the anionic complexes and ligands have been investigated based on the natural bond orbital (NBO) analysis at the B3LYP method which verifies that the synergistic effect has been occurred in the title complexes. In solution study of 2, the stoichiometry and stability constant of complexation of pipz, pydc, pydc–pipz proton transfer system and Zr(IV) ion in aqueous solution were investigated by potentiometric method.