Dimeric Copper Complexes Research Articles

A (2-(Pyrrolidin-1-yl)ethan-1-olate)(1-oxo-3-phenyl-1,4-dihydronaphthalen-2-olate) μ-Oxo-Bridged Dicopper(II) Dimeric Complex

The reaction of 2-(1H-pyrrol-1-yl)ethanol with 3-hydroxyflavone in the presence of copper(II) bromide yielded a dimeric copper(II) complex, [μ-O-(κ2-O,O-flav)(κ2-N,O-2PEO)Cu]2 (1) (flav = 3-hydroxyflavonolate; 2PEO = 2-(1H-pyrrol-1-yl)ethanolate) with both the flav and 2PEO ligands bound to the copper(II) atom in a κ2-bonding mode. The dimer is held electrostatically by bridging oxygen atoms between two copper atoms. Complex 1 was characterized by single-crystal X-ray diffraction, infrared, and UV-Vis spectroscopy, elemental analysis, and melting point determination. The complex crystallizes in the monoclinic space group P21/n (14) with cell values of a = 11.85340(10) Å, b = 8.51480(10) Å, c = 23.8453(2) Å; β = 99.3920(10)°.

Morphological studies, photocatalytic degradation of organic dyes and anticancer potential of copper sulfide nanoparticles prepared from bis(diallyl dithiocarbamato)copper(II) complex

Bis(diallyl dithiocarbamato)copper(II) complex was synthesized and characterized by single crystal X-ray crystallography. The molecular structure revealed dimeric copper(II) complex consisting of two copper(II) ions that coordinate two molecules of diallydithiocarbamato anions in bidentate chelating modes and the centrosymmetrically related diallydithiocarbamato anions bridges the S-atom of the adjacent chelating ligand to formed square pyramidal geometry around the copper(II) ions. Copper sulfide nanoparticles were prepared at 160 °C by thermolysis of the copper(II) complex in dodecylamine (DDA), hexadecylamine (HDA), and octadecylamine (ODA) to study the effect of capping agents on the structural morphologies, photocatalytic properties, and anticancer potential of the as-prepared copper sulfides nanoparticles. Powder X-ray diffraction patterns confirmed Cu9S5 digenite crystalline phases for CuS-DDA and CuS-HDA while CuS-ODA is covellite crystalline phase. HRTEM images showed spherical particles with particle sizes in the range 2–25 nm. The copper sulfide nanophotocatalysts are efficient for the degradation of bromophenol blue with the highest photocatalytic efficiency of 95.14 % for CuS-DDA followed by CuS-HDA with 94.52 % and 93.95 % for CuS-ODA. The anticancer potentials of the compounds showed that CuS-HDA is the most potent with IC50 values of 1.22 µg/mL against HEK293 and 28.78 µg/mL against HeLa.

Exploiting Coordination Behavior of 7-Azaindole for Mechanistic Investigation of Chan-Lam Coupling and Application to 7-Azaindole Based Pharmacophores.

Multiple spectroscopic techniques, along with single-crystal X-ray analysis, have been used to reveal the detailed structural and electronic information on reaction intermediates of a new copper(II)-DBU catalytic system for the N-arylation of 7-Azaindole. The reaction mixture of Chan-Lam cross-coupling yields two dimeric copper(II)-7-azaindole complexes, including one attached with DBU, prior to adding arylboronic acid and are confirmed structurally and spectroscopically. A suitable mechanism has been proposed using the dimeric copper(II) complex as a catalyst for the coupling reactions. The role of DBU as a base and also as an auxiliary ligand in the course of the reaction has been established. The transmetalated monomeric aryl-copper(II) species generated from the dimeric unit is oxidized by another equivalent of copper(II) to yield an aryl-copper(III) intermediate for facile N-arylation, which has been authenticated with UV-vis spectroscopy. The regeneration of the copper(II)-catalyst by aerial oxidation of colorless copper(I) species (generated via reductive elimination and disproportionation step) is confirmed by mass and absorption spectroscopy. Detailed DFT and TD-DFT calculations help to rationalize the proposed reaction intermediates and their corresponding electronic transitions. Moreover, the confirmation of copper(I)-7-azaindole intermediate via HRMS reaffirmed the involvement of Cu(II)/Cu(III)/Cu(I) species in the Chan-Lam type of coupling. A medicinally-important 7-azaindole-based SHP2 inhibitor has been synthesized via sequential arylation.

Physico-chemical Characterization of Some Metal Complexes Formed by Substituted Thiourea

In view of unique physico-chemical observations affecting the geometry and various properties of the substituted thiourea complexes in literature along with several biological activities, N-(hydroxy)-N,N-diphenyl thiourea was taken up for study. Complexes with geometries of high spin octahedral for iron(II), cobalt(II); tetrahedral & square planar for nickel(II); and dimeric square planar for copper chloride, copper perchlorate, copper acetate and distorted octahedral for copper nitrate were synthesized and characterized based on magnetic moments, visible spectra, diffuse reflectance spectra, electron spin resonance, infrared spectral studies, and thermal analysis.
 Interestingly, the nature of anion influenced the geometry, the complex from copper nitrate salt resulted in a distorted octahedral structure and complexes formed from copper chloride, copper perchlorate, copper acetate exhibited sub-normal magnetic moments, highly insoluble in the most common organic solvents and water. Based on these and spectral data, polymeric or square-planar dimeric geometry with sulfur bridging between copper atoms is proposed. It was confirmed by the application of Bleaney-Bower’s equation for magnetic susceptibility, applicable to dimeric copper complexes.
 The overall thermal behavior of the ligand and complexes were observed and the detailed calculations interestingly lead to confirmation of the above proposed geometrical structures.

The new dimeric copper(II) complex from anticancer drug cytosine arabinoside

In this study, the new copper(II) based cytosine arabinoside (ara-C) analog was synthesized and characterized by analytical and spectroscopic methods. Especially the data obtained from FT-IR spectroscopy showed that ara-C coordinated with copper(II) ions through –C=O and -Nring groups and formed a complex compound in a tetrahedral structure. The proposed structure of this dimeric copper(II) complex was defined as [Cu2(ara-C)2Cl4]. Also, the ability of both compounds to bind to double helix fish sperm DNA (dsDNA) and the damage to the HeLa cell line was investigated. All theoretical chemical activity analyses (hardness and softness parameters, Fukui functions, net charges) of the ara-C and [Cu2(ara-C)2Cl4] molecules were performed with DFT with mixed basis set including LANL2DZ for Cu atom and 6-311G(d,p) for carbon, oxygen, nitrogen, chlorine and hydrogen atoms with B3LYP functional was applied. The stability of the molecule arising from hyperconjugative interactions, charge delocalization was analyzed by using natural bond orbital analysis (NBO) for optimized structure of [Cu2(ara-C)2Cl4]. Also, the interactions between the studied molecules (ara-C and [Cu2(ara-C)2Cl4] with DNA bases such as adenine, cytosine, guanine, and thymine were investigated by using the ECT (electrophilicity-based charge transfer) method. Furthermore, the best binding sites of the DNA (PDB:1BNA) protein to the ligands (ara-C and [Cu2(ara-C)2Cl4] were examined and the binding energies and interaction states were determined by molecular docking study.

A New Dimeric Copper(II) Complex of Hexyl Bis(pyrazolyl)acetate Ligand as an Efficient Catalyst for Allylic Oxidations.

A new dimeric copper(II) bromide complex, [Cu(LOHex)Br(μ-Br)]2 (1), was prepared by a reaction of CuBr2 with the hexyl bis(pyrazol-1-yl)acetate ligand (LOHex) in acetonitrile solution and fully characterized in the solid state and in solution. The crystal structure of 1 was also determined: the complex is interlinked by two bridging bromide ligands and possesses terminal bromide ligands on each copper atom. The two pyrazolyl ligands in 1 coordinate with the nitrogen atoms to complete the Cu coordination sphere, resulting in a five-coordinated geometry—away from idealized trigonal bipyramidal and square pyramidal geometries—which can better be described as distorted square pyramidal, as measured by the τ and χ structural parameters. The pendant hexyloxy chain is disordered over two arrangements, with final site occupancies refined to 0.705 and 0.295. The newly synthesized complex was evaluated as a catalyst in copper-catalyzed C–H oxidation for allylic functionalization through a Kharasch–Sosnovsky reaction without any external reducing agent. Using 0.5 mol% of this catalyst, and tert-butyl peroxybenzoate (Luperox) as an oxidant, allylic benzoates were obtained with up to 90% yield. The general reaction time was only slightly decreased to 24 h but a very significant decrease in the alkene:Luperox ratio to 3:1 was achieved. These factors show relevant improvements with respect to classical Kharasch–Sosnovsky reactions in terms of rate and amount of reagents. The present study highlights the potential of copper(II) complexes containing functionalized bis(pyrazol-1-yl)acetate ligands as efficient catalysts for allylic oxidations.

Unprecedented formation of a μ‐oxobridged dimeric copper (II) complex: Evaluation of structural, spectroscopic, and electronic properties by using theoretical studies and investigations biological activity studies of new Schiff bases derived from pyrazolone

Novel Schiff base Cu (II) complex was synthesized in the present work through condensation of salicylaldehyde with 4‐aminoantipyrine derivative and characterized by spectral and analytical techniques. Crystal structure of the Cu (II) complex was determined by single‐crystal X‐ray diffraction technique. The structure of the complex is quite unexpected and unprecedented. The observation can be due to the in situ oxidation of the methyl groups of the 4‐aminoantipyrine of the Schiff base ligand to CH2OH. Cu2L2 is a two‐centered Ci‐symmetry complex that is bridged by two oxygen atoms from two ligand molecules, with four‐coordinated Cu (II) ion's in a very regular square‐planar fashion. The electrochemical properties of complex in DMSO displayed the electronic effects on the groups on redox potential. Various computational studies such as DFT (density functional theory), MEPs (molecular electrostatic potential), and HS (Hirshfeld surface analysis) were performed to understand the properties of different interactions of the compounds. The DFT computations, geometry optimization of the ligand, and Cu (II) complex (1) were optimized using the B3LYP method with (6‐311G) basis set. Also, HS analysis is used for decoding intermolecular interactions in the crystal system and contribution of component units for the construction of the 3D architecture. Anticancer effects of the ligand and complex in MTT assay against cancer cell lines SW480 were studied. The antioxidant activity results show that the ligand and complex have antioxidant and anticancer activity. Molecular docking study was also carried out for the complex to find its binding affinity to protein B‐cell lymphorna (BCL‐2, PDB ID: 4LXD).

A theoretical insight into the formation of chalcogen bonding (ChB) interactions involving coordinated DMSO molecules as σ-hole donors and benzoate groups as σ-hole acceptors in a dinuclear copper(ii) complex

The formation of two chalcogen bonding (ChB) interactions involving coordinated DMSO molecules as σ-hole donors and the O atoms of carboxylate groups as acceptors in a dimeric copper(ii) complex has been described.

Synthesis, Structure, Magnetic and Catalytic Competency of a Tetradentate (NNOO) Schiff Base Mediated Dimeric Copper(II) Complex

One dinuclear copper(II) complex {μ-[2,2′-{ethane-1,2-diylbis[(azanylylidene)methanylylidene]}- bis(phenolato)]}-{μ-[2,2′-{ethane-1,2-diylbis[(azanylylidene)methanylylidene]}bis(phenolato)]}- dicopper(II), [Cu2(salen)2] (1) [salen2− = [2,2′-{ethane-1,2-diylbis[(azanylylidene)methanylylidene]}- bis(phenolato)] has been isolated and characterized by X-ray diffraction analysis and spectroscopic studies. X-ray single crystal structure examination revealed that each Cu(II) center in the asymmetric unit of 1 adopts a distorted square planar geometry with a CuN2O2 chromophore, where two asymmetric units are attached through congregation of Salen involving Cu-O bond to form dinuclear molecular unit [Cu2(salen)2]. In crystalline state, these dinuclear entities in 1 are extended through C-H···π interactions and π···π interactions displaying a 3D network structure. The variable-temperature magnetic susceptibility measurement asserted a dominant antiferromagnetic interaction between the copper(II) centers through Cu-O-Cu linkage in 1 with J = -1.46 cm-1. The catalytic efficacy of complex 1 was studied in a series of solvents for the oxidation of styrene and cyclooctene using tert-butyl-hydroperoxide (TBHP) as an active oxidant under mild conditions. The catalytic reaction mixture has been analyzed by gas chromatography and it displayed that the yield of the epoxidation and its selectivity is optimum in acetonitrile medium.

Green, homogeneous oxidation of alcohols by dimeric copper(II) complexes

Three pyrazole derivatives, 3,5-dimethyl-1H-pyrazole (DMPz) (I), 3-methyl-5-phenyl-1H-pyrazole (MPPz) (II), and 3,5-diphenyl-1H-pyrazole (DPPz) (III), were prepared via reacting semicarbazide hydrochloride with the acetylacetone, 1-phenylbutane-1,3-dione, and 1,3-diphenylpropane-1,3-dione, respectively. Complexes 1–3 were isolated by reacting CuCl2·2H2O with I–III, respectively, and characterized by CHNS elemental analyses, FT-IR, UV-Vis, 1H and 13C NMR, EPR spectra, and TGA/DTA. Molecular structures of the pyrazole derivatives I–III and copper(II) complexes 2 and 3 were studied through single-crystal XRD analysis to confirm their molecular structures. Overlapping of hyperfine splitting in the EPR spectra of the dimeric copper(II) complexes 1–3 indicates that both copper centers do not possess the same electronic environment in solution. The copper(II) complexes are dimeric in solid state as well as in solution and catalyze the oxidation of various primary and secondary alcohols selectively. Catalysts 1–3 show more than 92% product selectivity toward ketones during the oxidation of secondary alcohols. Surprisingly primary alcohols, which are relatively difficult to oxidize, produce carboxylic acid as a major product (48%–90% selectivity) irrespective of catalytic systems. The selectivity for carboxylic acid rises with decreasing the carbon chain length of the alcohols. An eco-friendly and affordable catalytic system for oxidation of alcohols is developed by the utilization of H2O2, a green oxidant, and water, a clean and greener solvent, which is a notable aspect of the study.

Double end-on azido derivative of a tridentate (NNO) Schiff base dimeric copper(II) complex: synthesis, X-ray structure, magnetic property and catalytic effectiveness

A dimeric copper(II) complex, bis{(2-[1-(aminoethylimino)ethyl]-phenoxo}-di-μ1,1-azido-dicopper(II), [Cu2(L)2(μ2-1,1-N3)2] (1) [L = 2-[1-(aminoethylimino)ethyl]-phenoxo ion], has been isolated using a self-assembly reaction using a 1:1:1 molar ratio of Cu(NO3)2·3H2O, HL and NaN3 in methanol at room temperature and characterized through X-ray diffraction analysis and spectroscopic studies. X-ray structural analysis reveals that 1 consists of two distinct dinuclear molecular units, where each copper(II) center in the individual dinuclear unit adopts a distorted square pyramidal geometry with a CuN4O chromophore ligated through a tridentate (NNO) Schiff base and two N atoms of two different bridging azides in µ1,1-mode. Two Cu(II) centers are linked through double µ2-1,1-N3 bridges to form the dinuclear unit [Cu2(L)2(μ2-1,1-N3)2]. In the crystalline state, the dinuclear units in 1 are associated through weak intermolecular N-H⋯O hydrogen bonds to afford a 2-D sheet structure viewed along the crystallographic a-axis. The small magnitude of the antiferromagnetic interaction (J = –0.45 cm−1) is a result of the long Cu···Cu separation (3.205(2) Å). The catalytic efficacy of 1 was studied in a series of solvents for the epoxidation of alkenes using tert-butyl-hydroperoxide (TBHP) as an efficient oxidant under mild conditions.

Cyanide contaminated water treatment by di-nuclear Cu(II)-cryptate: A supramolecular approach

A popular Cu(II) based metallo-cage cryptate, Complex 1 [LCu2(ClO4)4], is synthesized by using a bicyclic cryptand, L (synthesized in large scale of ≈ 28 gm/batch) and Cu(ClO4)2 for its application towards the removal of toxic CN¯ from cyanide contaminated water and cyanide containing industrial blast furnace (BF) wastewater. Complex 1, having very low solubility in aqueous medium, showed efficient removal of CN¯ (initial CN¯ conc. of 80 ppm to final conc. of 4.21 ppm; ≈ 95 % removal of CN¯) from standard aqueous solution of CN¯ (NaCN in water) within 10 min, through heterogeneous phase mixing as observed from Ion Selective Electrode (ISE) based measurements. Mechanistic investigation towards the binding of cyanide with complex 1 through spectroscopic studies indicated the initial formation of CN¯ bridged green dimeric copper (II) complex upon addition of one equivalent of CN¯ which subsequently decomposed upon addition of further equivalents of CN¯ to produce a colourless solution. Finally, as a real-time application, complex 1 was treated with cyanide contaminated industrial wastewater in the presence of other interfering anions (e.g. Cl¯, SO42−, NO3¯, NO2¯, SCN¯, F¯etc.) which showed fast and efficient removal of cyanide (initial CN¯ conc. of 6.7 ppm to final conc. of 1.3 ppm; ≈ 77 % removal of CN¯ in 30 min) of BF wastewater from lab scale to pilot plant scale. Interestingly, the complex 1 showed recyclability up to six cycles in terms of removal of cyanide with high efficiency (≈ 72–74 % removal of CN¯).

Dimeric complexes of copper (II) arylcarboxylate with 4-cyanopyridine: synthesis, structural characterization and linear absorption properties

Two new dimeric copper (II) complexes containing 2-chlorobenzoato/4-formylbenzoato and 4-cyanopyridine ligands, [Cu2(μ2-O2CC6H4-Cl)4(C5H4N-CN)2] (1) and [Cu2(μ2-O2CC6H4-CHO)4(C5H4N-CN)4] (2), were synthesized and characterized by elemental analysis, FT-IR and ESR spectroscopy and single-crystal X-ray diffraction methods. In the structure of 1, each copperII cation was surrounded by four oxygen atoms from four different carboxylate of four 2-chlorobenzoate molecules and one nitrogen atom of one 4-cyanopyridine ligand. In the crystal structure of 2, each copperII cation was coordinated by four oxygen atoms from one chelating and two bridging 4-formylbenzoate anions and two nitrogen atoms of two 4-cyanopyridine ligands. C–H···O and C–H···Cl hydrogen bonds (for 1) and C–H···O hydrogen bonds and weak C–H···π interactions (for 2) further stabilize the crystal structures. The linear optical absorption characterizations of the complexes were performed by using UV-Vis spectrophotometer. The results obtained from the linear absorption spectra of the complexes observed that these complexes can be used for optical filtration among nearly 600 and 950 nm wavelengths for concentrations which are higher than 4 g/L. Two new dimeric copper (II) complexes were synthesized. The complexes were characterized by elemental analysis, FT-IR and ESR spectroscopy and single-crystal X-ray diffraction methods. [Cu2(μ2-O2CC6H4-Cl)4(C5H4N-CN)2] (1) has a paddle-wheel structure unit. [Cu2(μ2-O2CC6H4-CHO)4(C5H4N-CN)4] (2) has an unusual and unique conformation. The linear optical absorption characterizations of the complexes were investigated. According to the results obtained from the linear absorption spectra of the complexes, these complexes can be used for optical filtration among nearly 600 and 950 nm wavelengths for concentrations which are higher than 4 g/L.

Synthesis and characterization of a double oximato bridged dimeric copper(II) complex and its use in oxidative dimerisation of o-aminophenol

A dinuclear copper(II) complex, [(CH3CN)Cu(L)2Cu](ClO4)2, has been synthesized by reacting an oxime-based tridentate Schiff base ligand, 3-[2-(dimethylamino)-ethylimino] butan-2-one oxime (HL), with copper(II) perchlorate hexahydrate. The complex has been characterized by elemental and spectral analyses. Structure of the complex has been confirmed by single crystal X-ray diffraction technique. The complex may be used as moderate catalyst for the oxidation of o-aminophenol to 2-aminophenoxazine-3-one.

Synthesis, crystal structures and antimicrobial activity of dimeric copper(II) complexes with 2-hydroxyphenyl-ethylidene-dithiocarbazates

The current work reports the synthesis and crystals structure of two copper(II) complexes [(CuL1)2] (1) and [(CuL2)2] (2), with S-allyl-2-(2-hydroxyphenyl-ethylidene)dithiocarbazato and S-benzyl-2-(2-hydroxyphenyl-ethylidene) dithiocarbazato (H2L1 and H2L2, respectively). The single-crystal X-ray analyses reveal dimeric structures of the complexes with a distorted square planar coordination geometry. The phenoxo bridging mode observed in these complexes is located between the two copper atoms with ONS-donor ligands. The crystal packings are stabilized by hydrogen bonds involving the adjacent molecules. The compounds were also characterized by physicochemical and spectroscopic methods. The antibacterial and antifungal properties of the free dithiocarbazates and its Cu(II) complexes have been evaluated against several multiresistant bacteria and fungi. In all experiments, a superior antimicrobial activity of the complexes was observed compared to the free ligands.

Versatile Coordination Modes of Triphospha-1,4-pentadiene-2,4-diamine.

1,3,5-Triphospha-1,4-pentadiene-2,4-diamine reacts with [M(CO)4L] (M = Mo, L = nbd (norbornadiene); M = W, L = 2 CH3CN) to give the chelate complexes [M(CO)4(PMes{C(NHCy)PMes}2-κ P1 ,P3)]. In contrast, an unusual intramolecular rearrangement occurred with [Cu(CH3CN)4]PF6 leading to the dimeric copper(I) complex [Cu(CNCy){PHMesPMesC(NHCy)PMes-κ P1 ,P3}]2(PF6)2. The mechanism of the rearrangement was supported by quantum-mechanical calculations. The transition-metal complexes were characterized by multinuclear NMR spectroscopy, mass spectrometry, infrared spectroscopy, and X-ray crystallography.

Transition metal salts of 2-amino-3,5-dihalopyridine - dimers: syntheses, structures and magnetic properties of (3,5-diCAPH)2Cu2Br6 and (3,5-diBAPH)2Cu2X6

Three dimeric copper(II) complexes have been prepared with the general formula bis(2-amino-3,5-dihalopyridinium)hexahalodicuprate cuprate(II): (3,5-diCAPH)2Cu2Br6 (1), (3,5-diBAPH)2Cu2Cl6 (2) and (3,5-diBAPH)2Cu2Br6 (3) [3,5-diCAPH = 2-amino-3,5-dichloropyridinium; 3,5-diBAPH = 2-amino-3,5-dibromopyridinium]. The compounds have been characterized via single crystal X-ray diffraction and temperature dependent magnetic susceptibility measurements. All three compounds crystallize in monoclinic space groups (1, C2/c; 2 and 3, P21/c) and exhibit alternating layers of hexahalodicuprate ions and organic cations. The hexahalodicuprate ions exhibit short X⋯Cu and X⋯X contacts which link the dimers into a square array. Variable temperature magnetic susceptibility data reveal strong intradimer antiferromagnetic exchange (J = −153, −65, −122 K for 1–3, respectively), but negligible inter-dimer magnetic exchange.

Coordination of the ambiphilic phosphinoborane tBu2PCH2BPh2 to Cu(I)Cl

Abstract A chloro-bridged dimeric copper(I) complex with the ambiphilic phosphinoborane ligand tBu2PCH2BPh2 is reported. The molecular structure was determined by single-crystal X-ray diffraction analysis, revealing a secondary η 1-C interaction of the ligand with the metal center. The complex exhibits green fluorescence when exposed to UV light at 366 nm.

Luminescent Three- and Four-Coordinate Dinuclear Copper(I) Complexes Triply Bridged by Bis(diphenylphosphino)methane and Functionalized 3-(2'-Pyridyl)-1,2,4-triazole Ligands.

A new series of bimetallic Cu(I) complexes 1-5 triply bridged by a monoanionic or charge-neutral functionalized 3-(2'-pyridyl)-1,2,4-triazole in a μ-η1(N),η2(N,N) tridentate binding mode and two bis(diphenylphosphino)methane (dppm) ligands have been synthesized. Complexes 1-5 are singly or doubly charged dinuclear Cu(I) species with an eight-membered Cu2C2P4 ring of {Cu(μ-dppm)2Cu} unit, in which 3 and 4 adopt the boat-boat conformation, while 1, 2, and 5 display the chair-boat form. In these dimeric copper(I) complex cations, one of the two Cu(I) ions is four-coordinated, in a highly distorted N2P2 tetrahedral environment and the other is three-coordinated, in a distorted NP2 trigonal planar arrangement. All these Cu(I) complexes exhibit a comparatively weak low-energy absorption in CH2Cl2 solution, ascribed to the charge-transfer transitions with appreciable 1MLCT contribution, as suggested by time-dependent density functional theory (TDDFT) analyses. Complexes 1-5 display good emission properties in both solution and solid states at ambient temperature, which are well-modulated via structural modification of 3-(2'-pyridyl)-1,2,4-triazole, including the alteration of the substituent type (-CF3, -H, -CH3, and -C(CH3)3) and position (ortho-, meta-, and para-position). Furthermore, the variation of the substituent (-CF3 and -C(CH3)3) on the 5-site of the 1,2,4-triazolyl ring markedly influences the proton activity of the 1,2,4-triazolyl-NH, thus leading to the formation of both singly and doubly charged bimetallic Cu(I) species regulated by the NH ↔ N- conversion, resulting from NH deprotonation of the 1,2,4-triazolyl ring.

Chromotropism in halo-bridged dimers. Structural characterization of bis(μ-halo)bis(halo N-(pyridin-2-ylmethyl)cyclohexanamine copper(II))

Two dinuclear copper(II) complexes, [LCu(μ-Cl)Cl]2 (DMF) (1) and [LCu(μ-Br)Br]2 (2), with the bidentate ligand N-(pyridin-2-ylmethyl)cyclohexanamine, L, were synthesized and characterized by physicochemical and spectroscopic (IR, UV–vis) data. The crystal structural analysis of 1 shows that both copper(II) ions are in a distorted square pyramidal N2Cl3 environment with the apical position of the copper(II) being occupied by the bridging chloride anion which is equatorial to the other copper ion, forming a dimeric copper(II) complex. The chromotropic properties of both complexes, including solvato-, thermo-, and halochromism, were investigated. The complexes show reversible thermochromism in solution which is irreversible in the solid state. It was found that the solvatochromism is due to structural change followed by solvation of the vacant sites of the complexes. Their halochromic properties were studied in pH range of 1–11 by visible absorption spectroscopy. The color changes from blue to green and to colorless are due to deprotonation and protonation of the ligands.