Phenoxazinone Synthase-Like Catalytic Activity of Bi- and Trinuclear Copper(II) Complexes with 2-Benzylethanolamine: Experimental and Theoretical Investigations

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.

Synthesis Strategies and Structures of Molecular Heterometallic Oxo Clusters

Multinuclear heterometallic oxo clusters, composed of two or more different metal cations bridged by oxo ligands, represent an important class of molecular complexes known for their unique magnetic, catalytic, and electrochemical properties resulting from cooperative interactions between the metal cations. If three or more types of metal cations can be arranged as designed, their chemical and physical properties can be precisely and flexibly controlled, potentially creating innovative materials. However, research on hetero-trimetallic and hetero-tetrametallic oxo clusters remains limited. This review presents an interdisciplinary search of multinuclear heterometallic oxo clusters, regardless of the type of ligand, to explain and classify their synthesis strategies and structures. By cataloging crystallographically characterized heterometallic oxo clusters using ligand-per-metal values and synthesis method notations, valuable insights have been gained into effective synthesis methods for the precise arrangement of metal cations. The advantages and disadvantages of one-pot synthesis methods and synthesis strategies for achieving precise structural control of heterometallic oxo clusters are discussed with an emphasis on the prediction of their final structures. The insights from this review are expected to drive the development of synthetic and analytical techniques for the precise synthesis of heterometallic complexes in a predictable way.

Halogen-Dependent Diversity and Weak Interactions in the Heterometallic Ni/Cd Complex Solids: Structural and Theoretical Investigation

Three novel heterometallic Ni/Cd coordination compounds [Ni(en)3][CdCl4]∙3dmso (1), [Ni(en)2(dmf)2][CdBr4] (2), and [Ni(en)3]2[CdI4](I)2 (3) have been synthesized through the self-assembly process in a one-pot reaction of cadmium oxide, nickel salt (or nickel powder), NH4X (X = Cl, Br, I), and ethylenediamine in non-aqueous solvents dmso (for 1) or dmf (for 2 and 3). Formation of the one- (1) or three-dimensional (2 and 3) hydrogen-bonded frameworks has been observed depending on the nature of the [CdX4]2- counter-anion, as well as on the nature of the solvent. The electronic structures of [Ni(en)3]2+ and [Ni(en)2(dmf)2]2+ cations were studied at the DFT and CASSCF levels, including the ab initio ligand field theory (AILFT) calculations. The non-covalent intermolecular contacts between the cationic nickel and anionic cadmium blocks in the solid state were investigated by the QTAIM analysis. The mechanism of ligand substitution at the nickel center in [Ni(en)2(dmf)2]2+ was theoretically investigated at the ωB97X-D4/ma-def2-TZVP//DLPNO-CCSD(T)/ma-def2-TZVPP level. The results demonstrate that thermodynamic factors are structure-determining ones due to low energy barriers of the rotation of dmf ligands in [Ni(en)2(dmf)2]2+ (below 3 kcal mol-1) and the reversible transformation of [Ni(en)2(dmf)2]2+ into [Ni(en)3]2+ (below 20 kcal mol-1).

Supramolecular Diversity, Theoretical Investigation and Antibacterial Activity of Cu, Co and Cd Complexes Based on the Tridentate N,N,O-Schiff Base Ligand Formed In Situ

The four new complexes, [Cu(HL¹)(L²)Cl] (1), [Cu(HL¹)(L¹)]∙Cl∙2H₂O (2), [Co(L¹)₂]∙Cl (3) and [Cd(HL¹)I₂]∙dmso (4), have been prepared by one-pot reactions of the respective chloride or iodide metal salt with a non-aqueous solution of the polydentate Schiff base, HL¹, resulted from in situ condensation of benzhydrazide and 2-pyridinecarboxaldehyde, while a ligand HL², in case of 1, has been formed due to the oxidation of 2-pyridinecarboxaldehyde under reaction conditions. The crystallographic analysis revealed that the molecular building units in 1-4 are linked together into complex structures by hydrogen bonding, resulting in 1D, 2D and 3D supramolecular architectures for 1, 2 and 4, respectively, and the supramolecular trimer for 3. The electronic structures of 1-4 were investigated by the DFT theoretical calculations. The non-covalent interactions in the crystal structures of 1-4 were studied by means of the Hirshfeld surface analysis and the QTAIM theory with a special focus on the C-H⋯Cl bonding. From the DFT/DLPNO-CCSD(T) calculations, using a series of charged model {R₃C-H}⁰⋯Cl^- assemblies, we propose linear regressions for assessment of the interaction enthalpy (ΔH, kcal mol^-1) and the binding energy (BE, kcal mol^-1) between {R₃C-H}⁰ and Cl^- sites starting from the electron density at the bond critical point (ρ(r_BCP), a.u.): ΔH = -678 × ρ(r) + 3 and BE = -726 × ρ(r) + 4. It was also has been found that compounds 1, 3 and 4 during in vitro screening showed an antibacterial activity toward the nine bacteria species, comprising both Gram-positive and Gram-negative, with MIC values ranging from 156.2 to 625 mg/L. The best results have been obtained against Acinetobacter baumannii MβL.

Investigating the effect of lanthanide radius and diamagnetic linkers on the framework of metallacrown complexes

By changing the stoichiometric ratios, the one-pot reaction of the glycinehydroxamic acid (H2glyha) ligand with copper(ii) and lanthanide(iii) salts in the presence of diamagnetic [Na2{Fe(CN)5(NO)}] led to two series of isostructural complexes, which can be designated as heterotrimetallic dimeric clusters [{LnCu5(glyha)5}{Fe(CN)5(NO)}(H2O)4]2·xNO3·yH2O (x = 2, y = 11 for La (1), x = 2, y = 11 for Pr (2), and x = 2, y = 11 for Nd (3)) and heterotetrametallic coordination polymers [Na{LnCu5(glyha)5}{Fe(CN)5(NO)}2(H2O)x·yH2O]n (x = 6, y = 4 for Sm (4), x = 6, y = 0 for Gd (5), x = 6, y = 4 for Tb (6), x = 5, y = 5 Dy (7), and x = 6, y = 4 for Ho (8)). Each molecular structure contains LnIII[15-metallacrown-5] nodes and diamagnetic [Fe(CN)5(NO)]2- linkers. The resulting products demonstrate diversified structural frameworks due to the radius effect of LnIII ions and different bridging fashions of diamagnetic [Fe(CN)5(NO)]2- linkers. An analysis of magnetic susceptibilities reveals that 7 exhibits ferromagnetic coupling between CuII and DyIII ions and field-induced SMM behavior.

Co-existence of ferro- and antiferromagnetic interactions in a hexanuclear mixed-valence CoMnMn cluster sustained by a multidentate Schiff base ligand

The successful utilization of the "direct synthesis" approach yielded the unprecedented hexanuclear complex of formula [Co₂MnMn(L¹)₄Cl₂(μ₃-O)₂(dmf)₄]·2dmf (1) (H₃L is the Schiff base derived from the condensation of salicylaldehyde and 3-aminopropane-1,2-diol). Single crystal X-ray analysis revealed that 1 crystallizes in the monoclinic system P2₁/c and it contains a rare mixed-valence {CoMnMn(μ₂-O)₈(μ₃-O)₂} core where all metal ions are linked through the phenolato and alkoxo groups of the L^3- ligand. Besides the charge balance resulting from the X-ray structure, the oxidation state of the metal ions has been confirmed by XPS spectroscopy. Cryomagnetic studies indicate the coexistence of ferro- (Mn^IV-Mn^II, J₂ = +1.10(3) cm^-1, J₃ = +2.19(3) cm^-1; Mn^II-Mn^II, j = +0.283(3) cm^-1) and antiferromagnetic interactions (Mn^IV-Mn^IV, J₁ = -17.31(4) cm^-1), with the six-coordinate Co^III ions being diamagnetic. DFT type calculations were carried out to substantiate these values. The energy diagram for the different spin states using the best-fit parameters shows the occurrence of six low-lying spin states (S = 0-5) which are close in energy but clearly separated from the remaining ones, with the ground spin state being S = 5. Complex 1 is found to be the first example where weak ferromagnetic exchange between Mn^II ions through the long -O-Mn^IV-O- pathway takes place.

A Million Crystal Structures: The Whole Is Greater than the Sum of Its Parts

The founding in 1965 of what is now called the Cambridge Structural Database (CSD) has reaped dividends in numerous and diverse areas of chemical research. Each of the million or so crystal structures in the database was solved for its own particular reason, but collected together, the structures can be reused to address a multitude of new problems. In this Review, which is focused mainly on the last 10 years, we chronicle the contribution of the CSD to research into molecular geometries, molecular interactions, and molecular assemblies and demonstrate its value in the design of biologically active molecules and the solid forms in which they are delivered. Its potential in other commercially relevant areas is described, including gas storage and delivery, thin films, and (opto)electronics. The CSD also aids the solution of new crystal structures. Because no scientific instrument is without shortcomings, the limitations of CSD research are assessed. We emphasize the importance of maintaining database quality: notwithstanding the arrival of big data and machine learning, it remains perilous to ignore the principle of garbage in, garbage out. Finally, we explain why the CSD must evolve with the world around it to ensure it remains fit for purpose in the years ahead.

Heterotrimetallic complexes in molecular magnetism

The most representative examples of coordination compounds containing three different paramagnetic metal ions are reviewed, with a special emphasis on their magnetic properties.

Facile Fabrication of Ordered Component-Tunable Heterobimetallic Self-Assembly Nanosheet for Catalyzing "Click" Reaction

How to maximize the number of desirable active sites on the surface of the catalyst and minimize the number of sites promoting undesirable side reactions is currently an important research topic. In this study, a new way based on the synergism to achieve the successful fabrication of an ordered heterobimetallic self-assembled monolayer (denoted as BMSAM) with a controlled composition and an excellent orientation of metals in the monolayer was developed. BMSAM consisting of phenanthroline and Schiff-base groups was prepared, and its novel heterobimetallic (Cu and Pd) self-assembled monolayer anchored in silicon (denoted as Si-Fmp-Cu-Pd BMSAM) with a controlled composition and a fixed position was fabricated and characterized by UV, cyclic voltammetry, Raman, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), X-ray diffraction (XRD), inductively coupled plasma atomic emission spectroscopy (ICP-AES), and water-drop contact angle (WDCA) analyses. The effects of Si-Fmp-Cu-Pd BMSAM on its catalytic properties were also systematically investigated using "click" reaction as a template by WDCA, XPS, SEM, XRD, ICP-AES and in situ Fourier transform infrared analyses in a heterogeneous system. The results showed that the excellent catalytic characteristic could be attributed to the partial (ordered or proper distance) isolation of active sites displaying high densities of specific atomic ensembles. The catalytic reaction mechanism of the click reaction interpreted that the catalytic process mainly occurred on the surface of the monolayer, internal active site (Pd) and rationalized that the Cu(I) species and Pd(0) reduced from the Cu(II) and Pd(II) catalyst were active species, which had a proper distance between two different metals. The cuprate-triazole intermediate and the palladium intermediate, whose production is the key step, should lie in a proper position between the copper and active palladium sites, with which the reaction rate of transmetalation would be improved to increase the amount of the undesired Sonogashira coupling product.

A platinum(ii)–palladium(ii)–nickel(ii) heterotrimetallic coordination polymer showing a cooperative effect on catalytic hydrogen evolution

Stepwise construction of a 1D heterotrimetallic coordination polymer containing all three group 10 metal ions and its heterogeneous catalytic activity for electrochemical hydrogen evolution are reported.

Direct synthesis of a {Co₆(III)Fe₆(III)} dodecanuclear complex, revealing an unprecedented molecular structure type

A novel heterometallic Co6Fe6 Schiff base complex, possessing an unprecedented {M12(μ-X)22} branched structure (according to the search via the Cambridge Structural Database), has been prepared using the "direct synthesis" approach and characterized by single crystal X-ray diffraction and magnetometry.

Magneto-structural variety of new 3d–4f–4(5)d heterotrimetallic complexes

Three families of heterotrimetallic chains with different topologies, have been obtained by reacting Schiff-base bicompartmental [Cu^II(L¹)] complexes and lanthanide(iii) salts, with (NHBu₃)₃[M(CN)₈] (M = Mo^V, W^V).