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Against the Norm: Non Irving–Williams Transmetalation in Transition Metal Dimers
Sydney S. Woodhouse, Tyson N. Dais, Alvaro Etcheverry-Berrios, Euan K. Brechin, Joseph R. Lane, and Paul G. Plieger.
Abstract
We report the synthesis and characterization of three dinuclear 3d3d′ complexes, CuCu ([CuII2L(NO3)2]), MnMn ([MnII2L(MeOH)2(NO3)2], and CuMn ([CuIIMnIIL(NO3)2]), that utilize the ligand, H2L (6,6′-dimethoxy-2,2’-[(1,3-propylene)dioxybis(nitrilomethylidyne)]diphenol). The relative stabilities of these complexes were investigated using experimental and computational techniques, revealing a non-Irving-Williams transmetalation, whereby a MnII ion can displace a CuII ion from its binding pocket in CuCu to yield the more stable CuMn complex. Magnetic characterization of the reported complexes revealed an unexpected ferromagnetic coupling between the two CuII ions of CuCu with J = +63.0 cm–1.
Inorg. Chem., 2022, 61, 17819. DOI: 10.1021/acs.inorgchem.2c03113
Guest-induced magnetic exchange in paramagnetic [M2L4]4+ coordination cages
Mukesh K. Singh, Alvaro Etcheverry-Berrios, Julia Vallejo, Sergio Sanz, José Martínez-Lillo, Gary S. Nichol, Paul J. Lusby and Euan K. Brechin.
Abstract
Paramagnetic complexes that possess magnetically switchable properties show promise in a number of applications. A significantly underdeveloped approach is the use of metallocages, whose magnetic properties can be modulated through host–guest chemistry. Here we show such an example that utilises a simple [CuII2L4]4+ lantern complex. Magnetic susceptibility and magnetisation data shows an absence of exchange in the presence of the diamagnetic guest triflate. However, replacement of the bound triflate by ReBr62− switches on antiferomagnetic exchange between the Cu and Re ions, leading to an S = 1/2 ground state for the non-covalent complex [ReBr62−⊂CuII2L4]2+. Comparison of this complex to a “control” palladium-cage host–guest complex, [ReBr62−⊂PdII2L4]2+, shows that the encapsulated ReBr62− anions retain the same magnetic anisotropy as in the free salt. Theoretically calculated spin-Hamiltonian parameters are in close agreement with experiment. Spin density analysis shows the mode of interaction between the CuII and ReIV centres is through the Re-Br⋯Cu pathway, primarily mediated through the Cu(dx2−y2)|Brsp|Re(dyz) interaction. This is further supported by overlap integral calculations between singly occupied molecular orbitals (SOMOs) of the paramagnetic ions and natural bonding orbitals analysis where considerable donor-to-acceptor interactions are observed between hybrid 4s4p orbitals of the Br ions and the empty 4s and 4p orbitals of the Cu ions.
Dalton Trans., 2022, 51, 8377. DOI: 10.1039/D2DT01385A
Broadening the scope of high structural dimensionality nanomaterials using pyridine-based curcuminoids
Laura Rodríguez-Cid, Wenjie Qian, Joseline Iribarra-Araya, Alvaro Etcheverry-Berrios, Eulalia Martínez-Olmos, Duane Choquesillo-Lazarte, Eva Carolina Sañudo, Olivier Roubeau, Ana María López-Periago, Arántzazu González-Campo, José G. Planas, Mònica Soler, Concepción Domingo and Núria Aliaga-Alcalde.
Abstract
We present a new heteroditopic ligand (3pyCCMoid) that contains the typical skeleton of a curcuminoid (CCMoid) decorated with two 3-pyridyl groups. The coordination of 3pyCCMoid with ZnII centres results in a set of novel coordination polymers (CPs) that display different architectures and dimensionalities (from 1D to 3D). Our work analyses how synthetic methods and slight changes in the reaction conditions affect the formation of the final materials. Great efforts have been devoted toward understanding the coordination entities that provide high dimensional systems, with emphasis on the characterization of 2D materials, including analyses of different types of substrates, stability and exfoliation in water. Here, we foresee the great use of CCMoids in the field of CPs and emphasize 3pyCCMoid as a new-born linker.
Dalton Trans., 2021, 50, 7056. DOI: 10.1039/D1DT00708D
Kinetic selection of Pd4L2 metallocyclic and Pd6L3 trigonal prismatic assemblies
Helen O’Connor, Marco Coletta, Alvaro Etcheverry-Berrios, Gary S. Nichol, Euan K. Brechin and Paul Lusby.
Abstract
The self-assembly of Pd4L2 metallocylcic and Pd6L3 trigonal prismatic assemblies are described. The selection of one species over the other has been achieved by careful choice of ancilliary ligands, which switch the dynamics of the Pd-pyridine bonds such that a highly unusual and distorted smaller assembly can be kinetically trapped en route to the more energetically favourable larger species. Both assemblies provide promise as easy to access multicavity reaction vessels.
Chem. Commun., 2020, 56, 11799. DOI: 10.1039/D0CC05311B
Putting the Squeeze on Molecule-Based Magnets: Exploiting Pressure to Develop Magneto-Structural Correlations in Paramagnetic Coordination Compounds
Alvaro Etcheverry-Berrios, Simon Parsons, Konstantin V. Kamenev, Michael R. Probert, Stephen A. Moggach, Mark Murrie, and Euan K. Brechin.
Abstract
The cornerstone of molecular magnetism is a detailed understanding of the relationship between structure and magnetic behaviour, i.e., the development of magneto-structural correlations. Traditionally, the synthetic chemist approaches this challenge by making multiple compounds that share a similar magnetic core but differ in peripheral ligation. Changes in the ligand framework induce changes in the bond angles and distances around the metal ions, which are manifested in changes to magnetic susceptibility and magnetisation data. This approach requires the synthesis of a series of different ligands and assumes that the chemical/electronic nature of the ligands and their coordination to the metal, the nature and number of counter ions and how they are positioned in the crystal lattice, and the molecular and crystallographic symmetry have no effect on the measured magnetic properties. In short, the assumption is that everything outwith the magnetic core is inconsequential, which is a huge oversimplification. The ideal scenario would be to have the same complex available in multiple structural conformations, and this is something that can be achieved through the application of external hydrostatic pressure, correlating structural changes observed through high-pressure single crystal X-ray crystallography with changes observed in high-pressure magnetometry, in tandem with high-pressure inelastic neutron scattering (INS), high-pressure electron paramagnetic resonance (EPR) spectroscopy, and high-pressure absorption/emission/Raman spectroscopy. In this review, which summarises our work in this area over the last 15 years, we show that the application of pressure to molecule-based magnets can (reversibly) (1) lead to changes in bond angles, distances, and Jahn–Teller orientations; (2) break and form bonds; (3) induce polymerisation/depolymerisation; (4) enforce multiple phase transitions; (5) instigate piezochromism; (6) change the magnitude and sign of pairwise exchange interactions and magnetic anisotropy, and (7) lead to significant increases in magnetic ordering temperatures.
Magnetochemistry, 2020, 6, 32. DOI: 10.3390/magnetochemistry6030032
Single-Molecule Transport of Fullerene-Based Curcuminoids
Diana Dulić, Alfredo Rates, Edison Castro, Jacqueline Labra-Muñoz, Daniel Aravena, Alvaro Etcheverry-Berrios, Daniel Riba-López, Eliseo Ruiz, Núria Aliaga-Alcalde, Monica Soler, Luis Echegoyen and Herre S. J. van der Zant.
Abstract
We present experimental and theoretical studies of single-molecule conductance through nonplanar fullerocurcuminoid molecular dyads in ambient conditions using the mechanically controllable break junction technique. We show that molecular dyads with bare fullerenes form configurations with conductance features related to different transport channels within the molecules, as identified with filtering and clustering methods. The primary channel corresponds to charge transport through the methylthio-terminated backbone. Additional low-conductance channels involve one backbone side and the fullerene. In fullerenes with four additional equatorial diethyl malonate groups attached to them, the latter transport pathway is blocked. Density functional theory calculations corroborate the experimental observations. In combination with nonequilibrium green functions, the conductance values of the fullerocurcuminoid backbones are found to be similar to those of a planar curcuminoid molecule without a fullerene attached. In the nonplanar fullerocurcuminoid systems, the highest-conductance peak occurs partly through space, compensating for the charge delocalization loss present in the curcuminoid system.
J. Phys. Chem. C, 2020, 124, 2698. DOI: 10.1021/acs.jpcc.9b10166
A new family of fullerene derivatives: fullerene-curcumin conjugates for biological and photovoltaic applications
Edison Castro, Maira R. Cerón, Andrea Hernandez Garcia, Quentin Kim, Alvaro Etcheverry-Berrios, Mauricio J. Morel, Raúl Díaz-Torres, Wenjie Qian, Zachary Martinez, Lois Mendez, Frank Perez, Christy A. Santoyo, Raquel Gimeno-Muñoz, Ronda Esper, Denisse A. Gutierrez, Armando Varela-Ramirez, Renato J. Aguilera, Manuel Llano, Monica Soler, Núria Aliaga-Alcalde and Luis Echegoyen.
Abstract
The synthesis and characterization of a family of [60]fullerocurcuminoids obtained via Bingel reactions is reported. The new C60 derivatives include curcumin and curcuminoids with a variety of end groups. Preliminary biological experiments show the potential activity of the compound containing a curcumin addend, which exhibits moderate anti-HIV-1 and radical scavenger properties, but no anti-cancer activity. In addition, the new fullerocurcuminoids exhibit HOMO/LUMO energy levels that are reasonably matched with those of perovskites and when they were tested in perovskite solar cells (PSCs) as the electron transporting material (ETM), photoconversion efficiencies ranging from 14.04–14.95% were obtained, whereas a value of 16.23% was obtained for [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) based devices.
RSC Adv., 2018, 8, 41692. DOI: 10.1039/C8RA08334G
Electric-field induced bistability in single-molecule conductance measurements for boron coordinated curcuminoid compounds
Ignacio José Olavarría-Contreras, Alvaro Etcheverry-Berrios, Wenjie Qian, Cristian Gutiérrez-Cerón, Aldo Campos-Olguín, E. Carolina Sañudo, Diana Dulić, Eliseo Ruiz, Núria Aliaga-Alcalde, Monica Soler and Herre S. J. van der Zant.
Abstract
We have studied the single-molecule conductance of a family of curcuminoid molecules (CCMs) using the mechanically controlled break junction (MCBJ) technique. The CCMs under study contain methylthio (MeS–) as anchoring groups: MeS-CCM (1), the free-ligand organic molecule, and two coordination compounds, MeS-CCM-BF2 (2) and MeS-CCM-Cu (3), where ligand 1 coordinates to a boron center (BF2 group) and to a CuII moiety, respectively. We found that the three molecules present stable molecular junctions allowing detailed statistical analysis of their electronic properties. Compound 3 shows a slight increase in the conductance with respect to free ligand 1, whereas incorporation of BF2 (compound 2) promotes the presence of two conductance states in the measurements. Additional experiments with control molecules point out that this bistability is related to the combination of MeS– anchoring groups and the BF2 moiety within the structure of the molecules. Theoretical calculations show that this can be explained by the presence of two conformers once compound 2 is anchored between the gold electrodes. An energy minimum is found for a flat structure but there is a dramatic change in the magnitude and orientation of dipole moment (favouring a non-flat conformer in the presence of an external electric field) due to a conformational change of one of the terminal MeS– groups. The results thus point to an intricate interplay between the applied bias voltage and the molecule dipole moment which could be the basis for designing new molecules aiming at controlling their conformation in devices.
Chem. Sci., 2018, 9, 6988. DOI: 10.1039/C8SC02337A
Formation of self-assembled monolayer of curcuminoid molecules on gold surfaces
Isadora Berlanga, Alvaro Etcheverry-Berrios, Andy Mella, Domingo Jullian, Victoria Alejandra Gómez, Núria Aliaga-Alcalde, Victor Fuenzalida, Marcos Flores and Monica Soler.
Abstract
We investigated the formation of self-assembled monolayers of two thiophene curcuminoid molecules, 2-thphCCM (1) and 3-thphCCM (2), on polycrystalline gold substrates prepared by immersion of the surfaces in a solution of the molecules during 24 h. The functionalized surfaces were studied by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). Despite the fact that both molecules have the same composition and almost the same structure, these molecules exhibit different behavior on the gold surface, which can be explained by the different positions of the sulfur atoms in the terminal aromatic rings. In the case of molecule 1, the complete formation of a SAM can be observed after 24 h of immersion. In the case of molecule 2, the transition from flat-lying to upright configuration on the surface is still in process after 24 h of immersion. This is attributed to the fact that molecule 2 have the sulfur atoms more exposed than molecule 1.
Appl. Surf. Sci., 2017, 392, 834. DOI: 10.1016/j.apsusc.2016.09.077
Multiscale Approach to the Study of the Electronic Properties of Two Thiophene Curcuminoid Molecules
Alvaro Etcheverry-Berrios, Ignacio Olavarría, Mickael L. Perrin, Raúl Díaz‐Torres, Domingo Jullian, Ingrid Ponce, José H. Zagal, Jorge Pavez, Sergio O. Vásquez, Herre S. J. van der Zant, Diana Dulić, Núria Aliaga‐Alcalde and Monica Soler.
Abstract
We studied the electronic and conductance properties of two thiophene–curcuminoid molecules, 2-thphCCM (1) and 3-thphCCM (2), in which the only structural difference is the position of the sulfur atoms in the thiophene terminal groups. We used electrochemical techniques as well as UV/Vis absorption studies to obtain the values of the HOMO–LUMO band gap energies, showing that molecule 1 has lower values than 2. Theoretical calculations show the same trend. Self-assembled monolayers (SAMs) of these molecules were studied by using electrochemistry, showing that the interaction with gold reduces drastically the HOMO–LUMO gap in both molecules to almost the same value. Single-molecule conductance measurements show that molecule 2 has two different conductance values, whereas molecule 1 exhibits only one. Based on theoretical calculations, we conclude that the lowest conductance value, similar in both molecules, corresponds to a van der Waals interaction between the thiophene ring and the electrodes. The one order of magnitude higher conductance value for molecule 2 corresponds to a coordinate (dative covalent) interaction between the sulfur atoms and the gold electrodes.
Chem. Eur. J., 2016, 22, 12808. DOI: 10.1002/chem.201601187
Neonicotinic analogues: Selective antagonists for α4β2 nicotinic acetylcholine receptors
Manuel Faundez-Parraguez, Nicolas Farias-Rabelo, Juan Pablo Gonzalez-Gutierrez, Alvaro Etcheverry-Berrios, Jans Alzate-Morales, Francisco Adasme-Carreño, Rodrigo Varas, Isabel Bermudez and Patricio Iturriaga-Vasquez.
Abstract
Nicotine is an agonist of nicotinic acetylcholine receptors (nAChRs) that has been extensively used as a template for the synthesis of α4β2-preferring nAChRs. Here, we used the N-methyl-pyrrolidine moiety of nicotine to design and synthesise novel α4β2-preferring neonicotinic ligands. We increased the distance between the basic nitrogen and aromatic group of nicotine by introducing an ester functionality that also mimics acetylcholine (Fig. 2). Additionally, we introduced a benzyloxy group linked to the benzoyl moiety. Although the neonicotinic compounds fully inhibited binding of both [α-125I]bungarotoxin to human α7 nAChRs and [3H]cytisine to human α4β2 nAChRs, they were markedly more potent at displacing radioligand binding to human α4β2 nAChRs than to α7 nAChRs. Functional assays showed that the neonicotinic compounds behave as antagonists at α4β2 and α4β2α5 nAChRs. Substitutions on the aromatic ring of the compounds produced compounds that displayed marked selectivity for α4β2 or α4β2α5 nAChRs. Docking of the compounds on homology models of the agonist binding site at the α4/β2 subunit interfaces of α4β2 nAChRs suggested the compounds inhibit function of this nAChR type by binding the agonist binding site.
Bioorg. Med. Chem., 2013, 21, 2687. DOI: 10.1016/j.bmc.2013.03.024
Dr Alvaro Etcheverry-Berrios, MRSC FHEA 