A new (μ3-carbonato)tricopper(II) complex with symmetry related equilateral triangular array of metal centers; structure and magnetism

Chemical fixation of atmospheric CO2 in tricopper(II)-carbonato complexes with tetradentate N-donor ligands: reactive intermediates, probable mechanisms, and catalytic and magneto-structural studies

In the present era, the fixation of atmospheric CO2 is of significant importance and plays a crucial role in maintaining the balance of carbon and energy flow within ecosystems. Generally, CO2 fixation is carried out by autotrophic organisms; however, the scientific community has paid substantial attention to execute this process in laboratory. In this report, we synthesized two carbonato-bridged trinuclear copper(II) complexes, [Cu3(L1)3(μ3-CO3)](ClO4)3 (1) and [Cu3(L2)3(μ3-CO3)](ClO4)3 (2) via atmospheric fixation of CO2 starting with Cu(ClO4)2·6H2O and easily accessible pyridine/pyrazine-based N4 donor Schiff base ligands L1 and L2, respectively. Under very similar reaction conditions, the ligand framework embedded with the phenolate moiety (HL3) fails to do so because of the reduction of the Lewis acidity of the metal center, inhibiting the formation of a reactive hydroxide bound copper(II) species, which is required for the fixation of atmospheric CO2. X-ray crystal structures display that carbonate-oxygen atoms bridge three copper(II) centers in μ3syn-anti disposition in 1 and 2, whereas [Cu(HL3)(ClO4)] (3) is a mononuclear complex. Interestingly, we also isolated an important intermediate of atmospheric CO2 fixation and structurally characterized it as an anti-anti μ2 carbonato-bridged dinuclear copper(II) complex, [Cu2(L2)2(μ2-CO3)](ClO4)2·MeOH (2-I), providing an in-depth understanding of CO2 fixation in these systems. Variable temperature magnetic susceptibility measurement suggests ferromagnetic interactions between the metal centers in both 1 and 2, and the results have been further supported by DFT calculations. The catalytic efficiency of our synthesized complexes 1-3 was checked by means of catechol oxidase and phenoxazinone synthase-like activities. While complexes 1 and 2 showed oxidase-like activity for aerobic oxidation of o-aminophenol and 3,5-di-tert-butylcatechol, complex 3 was found to be feebly active. ESI mass spectrometry revealed that the oxidation reaction proceeds through the formation of complex-substrate intermediations and was further substantiated by DFT calculations. Moreover, active catalysts 1 and 2 were effectively utilized for the base-free oxidation of benzylic alcohols in the presence of air as a green and sustainable oxidant and catalytic amount of TEMPO in acetonitrile. Various substituted benzylic alcohols smoothly converted to their corresponding aldehydes under very mild conditions and ambient temperature. The present catalytic protocol showcases its environmental sustainability by producing minimal waste.

Magneto-structural properties of carbonato-bridged copper(ii) complexes: fixation of atmospheric CO2

Weak ferromagnetic [Cu₃(dmMePEA)₃(μ₃-CO₃)(ClO₄)₃]ClO₄ (1) and strong antiferromagnetic [Cu₂(iptren)₂(μ₂-CO₃)](ClO₄)₂·H₂O (2) carbonato-bridged Cu(ii) complexes were synthesized via atmospheric fixation of CO₂ in slightly basic solutions.

Trapping atmospheric CO2 with gold

The ability of gold-hydroxides to fix CO2 is reported. [Au(IPr)(OH)] and [{Au(IPr)}2(μ-OH)][BF4] react with atmospheric CO2 to form the trigold carbonate complex [{Au(IPr)}3(μ(3)-CO3)][BF4]. Reactivity studies revealed that this complex behaves as two basic and one cationic Au centres, and that it is catalytically active. DFT calculations and kinetic experiments have been carried out.

A trinuclear copper(II) cryptate and its μ3-CO3 cascade complex: thermodynamics, structural and magnetic properties

The 2,4,6-triethylbenzene-capped hexaamine macrobicycle with pyridyl spacers (pyr) was able to coordinate three copper(II) ions within its cavity. Potentiometric studies performed at 298.2 K in MeOH/H(2)O (50:50 v/v) and at ionic strength 0.10 mol dm(-3) in KNO(3) revealed that trinuclear species predominate in solution from pH 5.0, the hydroxo complexes being the main species, which start forming at unusual very low pH values. The single-crystal X-ray determination of the trinuclear complex showed that the three copper centres have square-planar geometry, arranged in an almost equilateral triangle, and have carbonate bridging the three metal centres. The presence of carbonate resulted from fixation of atmospheric CO(2). The present study represents the first μ(3)-CO(3)-bridged trinuclear copper(II) complex located in the interior of a macrobicyclic cavity. The magnetic data of [Cu(3)(pyr)(μ(3)-CO(3))]·(ClO(4))(4) showed ferromagnetic intramolecular interactions [J=3.80 cm(-1), based on the Hamiltonian H=-J(S(1)S(2)+S(2)S(3)+S(1)S(3))] yielding a spin quartet, S=3/2, ground state. Density functional calculations on the experimental geometry of the trinuclear complex showed that the ferromagnetic nature of the magnetic coupling can be attributed to the syn-anti conformation of the carbonato bridge, and a magneto-structural correlation, based on the different conformations (syn-anti, syn-syn and anti-anti), is presented. The interesting properties observed, namely the lowering of the pK(a) of coordinated water molecules to unusual values and the good fit of the carbonate anion between the copper centres, derive from the special architecture of pyr.

Cadmium(II) and Copper(II) Complexes with Imidazole-Containing Tripodal Polyamine Ligands: pH and Anion Effects on Carbon Dioxide Fixation and Assembling

A new Cd(II) complex [Cd3(L)3(mu3-CO3)](ClO4)4.2CH3CN (1) with two-dimensional (2D) network structure was obtained by reaction of an imidazole-containing tripodal polyamine ligand N1-(2-aminoethyl)-N1-(2-imidazolethyl)-ethane-1,2-diamine (L) with Cd(ClO4)2.6H2O at pH 9.0 in air. The carbonate anions (CO3(2-)) are from the hydration of the atmospheric carbon dioxide, which is the same as in the previously reported Cu(II) complex [Cu3(L)3(mu3-CO3)](ClO4)4.3CH3CN (2). However, the coordination mode of CO3(2-) in 1 is mu3-eta2:eta2:eta2 while the one in 2 is mu3-eta1:eta1:eta1. One-dimensional (1D) chain Cd(II) and Cu(II) complexes [Cd(L)Cl]ClO4.H2O (3) and [Cu(L)(H2O)](ClO4)2 (4) without CO3(2-) were prepared by a similar method as that for 1 and 2 except for the different reaction pH, namely, 3 and 4 were obtained at pH 7 while 1 and 2 were obtained at pH 9. In addition, when Cu(NO3)2 was used to react with L at pH 9, a unique 1D double-stranded helical chain complex [Cu(L)Cl]NO3.1.25H2O (5) was obtained. The results revealed that the reaction pH and the counteranion have great impact on the carbon dioxide absorption and hydration as well as on the assembling and structure of the complexes. The magnetic property of complex 2 was investigated in the temperature range of 1.8-300 K, and weak ferromagnetic coupling among the mu3-eta1:eta1:eta1-CO3(2-) bridged Cu(II) atoms was observed.

Reaction with dioxygen of a Cu(I) complex of 1-benzyl-[3-(2'-pyridyl)]pyrazole triggers ethyl acetate hydrolysis: acetato-/pyrazolato-, dihydroxo- and diacetato-bridged Cu(II) complexes

A copper(I) compound [(L2)Cu(MeCN)2][ClO4] (1) containing a new bidentate N-donor ligand L2, 1-benzyl-[3-(2'-pyridyl)]pyrazole, derived from the condensation of HL1 [HL1 = 3-(2-pyridyl)pyrazole] and benzyl chloride, has been synthesized. Structural analysis reveals that in the copper(I) centre is coordinated by a pyridine and a pyrazole nitrogen from L2 and two MeCN molecules, providing a distorted tetrahedral geometry. Reaction of with dioxygen in N,N'-dimethylformamide (dmf) at 25 degrees C and subsequent workup with MeCO2Et afforded an acetato-/pyrazolato-bridged polymeric copper(II) compound [(mu-L1)Cu(mu-O2CMe)]n (2). Notably, the deprotonated form of HL(1) and MeCO2- have originated from debenzylation of L2 and hydrolysis of MeCO2Et, respectively. The structural analysis of reveals a near-planar {Cu2(mu-L1)2}2+ core unit in which two adjacent Cu(II) ions are bridged by the deprotonated N,N-bidentate pyridylpyrazole units of two L1 and each such {Cu2(mu-L1)2}2+ unit is bridged by MeCO2- in a monodentate bridging mode [Cu...Cu separations (A): 3.9232(4) pyrazolate bridge; 3.3418(4) acetate bridge], providing a polymeric network. Careful oxygenation of in MeCN led to the isolation of a dihydroxo-bridged dicopper(II) compound [{(L2)Cu(mu-OH)(OClO3)}2] (3). Interestingly, complex brings about hydrolysis of MeCO2Et under mild conditions (dmf, ca. 60 degrees C), generating a bis-mu-1,3-acetato-bridged dicopper(II) complex, [{(L2)Cu(dmf)(mu-O2CMe)}2][ClO4]2.dmf.0.5MeCO2H (4). Compounds and have {Cu2(mu-OH)2}2+ [Cu...Cu separation of 2.8474(9) A] and {Cu2(mu-O2CMe)2}2+ cores [Cu...Cu separation: 3.0988(26) and 3.0792(29) A (two independent molecules in the asymmetric unit)] in which each Cu(II) centre is terminally coordinated by L2. A rationale has been provided for the observed debenzylation of L2 and hydrolysis of MeCO(2)Et. The intramolecular magnetic coupling between the Cu(II) (S = 1/2) ions was found to be ferromagnetic (2J = 82 cm(-1)) in the case of , but antiferromagnetic for (2J = -158 cm(-1)) and (2J = -96 cm(-1)). Absorption and EPR spectroscopic properties of the copper(II) compounds have also been investigated.