RCIPL
Repositório Institucional do Politécnico de Lisboa
Entradas recentes
Adenine tagged Mn-based coordination polymer for conversion of carbon dioxide to cyclic carbonates under atmospheric pressure
Publication . Eskemech, Alehegn; Bhakhar, Rubi; Biswas, Pritam; Karmakar, Anirban; Krishnan, Venkata; Koner, Rik Rani
Abstract
Natural processes collectively balance the global carbon cycle, effectively controlling atmospheric carbon dioxide (CO2) levels. However, excessive CO2 emissions due to industrialization and population growth have disrupted natural processes by increasing the atmospheric CO2 concentration. To address this issue, CO2 capture and conversion have been implemented. Metal–organic frameworks (MOFs)/coordination polymers (CPs) with bioligands, such as amino acids and nucleobases, are receiving much interest. However, bio-MOFs are not much reported due to the lack of control over their coordination with metal ions. In this work, we have developed an adenine-tagged Mn-CP with dominant basic sites, [Mn(IPT2–)(Ade)(DMF)]n (IPT2– = isophthalate; Ade = adenine; DMF = N,N′-dimethylformamide). The analysis of isosteric heat (Qst) of CO2 adsorption supported the presence of strong interactions between CO2 and Mn-CP. Mn-CP demonstrated moderate to outstanding performance in coupling CO2 with smaller and larger epoxides at ambient pressure under neat conditions. The thermodynamic activation parameters indicate that Mn-CP operates through an associative mechanism (ΔS⧧ = −283.4 J mol−1 K−1), with a reduced kinetic barrier characterized by ΔH⧧ of 17.28 kJ mol–1 and Ea of 20.5 kJ mol–1. The catalytic efficiency of Mn-CP was particularly notable in the coupling reaction of epichlorohydrin and CO2, yielding 92% of the corresponding cyclic carbonate under atmospheric pressure.
Heterometallic CuCd and Cu2Zn complexes with o-vanillin and its Schiff-base derivative: slow magnetic relaxation and catalytic activity associated with Cu(II) centres
Publication . Vassilyeva, Olga Yu; Nesterova, Oksana V.; Bienko, Alina; Komarnicka, Urszula K.; Buvaylo, Elena A.; Vasylieva, Svitlana M.; Skelton, Brian W.; Nesterov, Dmytro S.
Abstract
In this work, two novel heterometallic mixed-ligand mixed-anion complexes [CuIICdIIClL(o-Van) (OAc)]·3H2O (1) and [CuII2ZnIICl2L2(o-Van)(OAc)] (2) were prepared by reacting fine copper powder and Cd(II) or Zn(II) acetate with an ethanol solution of the Schiff-base ligand HL formed in situ in the condensation reaction of 2-hydroxy-3-methoxy-benzaldehyde (o-VanH) and CH3NH2·HCl. The compounds were thoroughly characterized by elemental analysis, FT-IR, UV/Vis and EPR spectroscopy, cyclic voltammetry, and single-crystal X-ray diffraction, revealing the neutral molecular nature of both the compounds. Catalytic properties of 1 and 2 were studied in the oxidation of hydrocarbons with H2O2 under mild conditions, showing the maximum reaction rate of 4 × 10−5 M s−1 and TOF up to 640 h−1. Both compounds undergo complex transformations in solution as evidenced by kinetic analysis and time-dependent UV/Vis spectroscopy, indicating that the reduced Cu(I) form of 1 is unexpectedly unfavorable. Complex 1 demonstrates slow magnetic relaxation dominated by the direct relaxation process between T = 1.8 and 7 K under an external DC field of 0.2 and 0.4 T, a very rarely observable effect in the coordination compounds of Cu(II).
Complex 2 possesses weak ferromagnetism (J = 4.50 cm−1, zJ’ = −0.201 cm−1 for H = −JS1S2 formalism) occurring through the Cu–O–Cu pathways. Theoretical CASSCF, DFT and TDDFT calculations were applied to investigate the electronic structures of 1 and 2 and rationalize their behavior in solution.
A 3D MOF with Cu20/Cu6 clusters: self-assembly, CO2 encapsulation, structural features, and magnetic properties
Publication . Sliwa, Ewelina I.; Nesterov, Dmytro S.; Klak, Julia; Kirillov, Alexander M.; Smolenski, Piotr
Abstract
Molecular design of multicopper clusters has been of increasing importance in inorganic chemistry, biomedical science, and functional materials. Herein, two new copper compounds were self-assembled from copper(II) monofluoroacetate or trifluoroacetate, elemental copper, and 1,3,5-triaza-7-phosphaadamantane (PTA). The reaction starting from copper(II) monofluoroacetate yielded a tetranuclear cluster, [Cu4II(μ3-OH)2(μ-L)6(PTA=O)2] (1), where L is monofluoroacetate(1−) and PTA=O is the oxide of PTA. Formation of 1 involves the oxidation of PTA and the incorporation of μ3-OH– ligands. In contrast, a similar reaction with copper(II) trifluoroacetate produced a unique three-dimensional metal–organic framework (3D MOF), formulated as [{Cu20II(CO3)(μ3-O)2(μ3-OH)22(μ-L′)12}{Cu6I(μ3-PTA)6(CH3CN)12}]n·6n(L′)·3n(H2O)·2n(CH3CN) (2), where L′ is trifluoroacetate. It comprises Cu20 clusters, with an encapsulated carbonate anion fixed from atmospheric CO2, which are bridged by {Cu6I(PTA)6} units into a 3D MOF. Control experiments confirmed that carbonate originates from ambient CO2 rather than from added carbonate salts. Both 1 and 2 were fully characterized, and their magnetic properties were investigated, revealing dominant antiferromagnetic interactions within the Cu4 and Cu20 clusters, respectively. Density functional theory (DFT) calculations confirmed the antiferromagnetic ground spin state of 1 and disclosed the stability of the Cu20 core in 2. This work highlights the influence of fluorinated carboxylates and atmospheric conditions on the assembly and architecture of multicopper clusters, and extends their family to new examples.
Copper(II) complex with a redox-noninnocent Schiff base bearing a tetraphenyldisiloxane unit: synthesis, structure and catalytic oxidation of cyclohexane
Publication . Wittmann, Christopher; Palamarciuc, Oleg; Dascalu, Mihaela; Cazacu, Maria; Nesterov, Dmytro S.; Pombeiro, Armando; Rapta, Peter; Arion, Vladimir B.
Abstract
An organic–inorganic diamine, 1,3-bis(aminopropyl)tetraphenyldisiloxane, was prepared and introduced as a flexible spacer into the structure of a salen-type Schiff base (H2L7) extending the available small library of similar compounds derived from 1,3-bis(aminopropyl)tetramethyldisiloxane and substituted 2-hydroxybenzaldehydes (H2L1–H2L6). Like the previously reported mononuclear copper(II) complexes [CuL1]–[CuL6], the new copper(II) complex [CuL7], obtained by reaction of Cu(OAc)2·H2O with H2L7 in a mixture of organic solvents, has a tetrahedrally distorted square-planar (N2O2) coordination geometry. X-ray crystallography has shown that compared to [CuL1]–[CuL6] the Si–O–Si angle in [CuL7] is even closer to linear due to stronger intramolecular interactions between Ph groups than between Me groups in the central–R2Si–O–SiR2– fragment (R = Ph and Me, respectively). [CuL7] can be electrochemically reversibly oxidised by two successive one-electron processes, generating stable phenoxyl mono- and diradicals. Both oxidations are ligand-centred, leading to the formation of coordinated phenoxyl radicals. The UV spectrum of [CuL7] consists of π → π* and LMCT σ → d transitions. The low-energy d–d absorption is well described by AILFT CAS(9,5)/NEVPT2 calculations. The one-electron oxidised compound [CuL7]+ should exist in the triplet ground state as 3[CuL7]+ with one unpaired electron located on the dx2−y2 orbital of copper(II) (d9, SCu = ½) and another electron on the molecular orbital (MO) comprising pz oxygen and carbon atoms of the phenoxyl radical (Srad = ½). The broad absorption in the vis-NIR region of the optical spectrum of the one-electron oxidised complex is due to intervalence charge transfer in the triplet species 3[CuL7]+, but not in the [CuL7]2+ one. The doubly oxidised [CuL7] species shows very close doublet and quartet states, where the doublet state has an unpaired electron located on the Cu(II) d-orbital, while the quartet state has one unpaired electron on the Cu(II) d-orbital and two unpaired electrons on π-bonding orbitals. In all state-averaged CASSCF cases, the occupation of the Cu(II) d-orbital is nearly 1.0, indicating its limited involvement in the excited states. Catalytic studies showed that [CuL7] acts as a catalyst for the oxidation of alkanes with peroxides under very unusual solvent-free conditions, converting cyclohexane into cyclohexanol and cyclohexanone (with hydrogen peroxide or tert-butyl hydroperoxide as the oxidant) or into cyclohexanol and ε-caprolactone (with m-chloroperoxybenzoic acid as the oxidant). Theoretical investigations of the catalytic reaction mechanisms disclosed the principal intermediates.
Phenoxazinone synthase-like catalytic activity of bi- and trinuclear copper(II) complexes with 2- benzylethanolamine: experimental and theoretical investigations
Publication . Nesterova, Oksana V.; Bondarenko, Olena E.; Pombeiro, Armando; Nesterov, Dmytro S.
Abstract
The self-assembly reaction of 2-benzylaminoethanol (Hbae) with CuCl2 or Cu(NO3)2 leads to the formation of binuclear [Cu2(bae)2(Cl)2] (1) and [Cu2(Hbae)2(bae)2](NO3)2 (2) complexes, while the trinuclear [Cu3(Hbae)2(bae)2(dmba)2](NO3)2 (3) compound was obtained using the auxiliar bulky substituted 2,2-dimethylbutyric acid (Hdmba). Crystallographic studies reveal the molecular structures of 1 and 2 based on the similar {Cu2(μ-O)2} core, while the structure of 3 features the {Cu3(μ-O)2} core with consecutive arranement of the metal centres, supported by the additional carboxylate bridges. The strong intermolecular hydrogen bonds join the molecular structures into 1D (for 1 and 3) or 2D (for 2) architectures. All three compounds act as catalysts for the aerobic oxidation of 2-aminophenol to the phenoxazinone chromophore (phenoxazinone synthase-like activity) with the maximum reaction rates up to 2.3×10-8 M s-1. The substrate scope involves methyl-, nitro- and chloro-substituted 2-aminophenols, disclosing the negligible activity of nitro-derivatives, while the 6-amino-m-cresol substrate shows the highest activity with the initial reaction rate of 5.8×10-8 M s-1. The mechanism of the rate-limiting reaction step (copper-catalysed formation of 2-aminophenoxyl radicals) was investigated at the DFT level. The combined DFT and CASSCF studies of the copper superoxo CuII-OO⋅ radical species as possible unconventional reaction intermediates resulted in a rational mechanism of H-atom abstraction, where the activation energies follow the experimental reactivity of substituted 2-aminophenols. The TDDFT and STEOM-DLPNO-CCSD theoretical calculations of the absorption spectra of substrates, phenoxazinone chromophores and putative polynuclear species containing 2-aminophenoxo ligand are reported.