Trinuclear, Antiferromagnetically Coupled CuII Complex with an EPR Spectrum of Mononuclear CuII: Effect of Alcoholic Solvents

Utilization of a trinuclear Cu-pyrazolate inorganic motif to build multifunctional MOFs

The current work aims to generate multifunctional MOFs by incorporating a well-known inorganic motif, a trinuclear Cu-pyrazolate [Cu3(μ3-OH)(μ-Pyz)3] (T-CuP) unit, as a node of the network. Accordingly, we report herein the synthesis and properties of five new compounds using five V-shaped dicarboxylic acids as auxiliary ligands. The structural features are consistent with the theme of grafting T-CuP units as nodal points of architectures whose chassis are primarily made of bent acids. V-shaped acids also induce a helical nature inside resulting frameworks. Beside their structural and physical features, T-CuP unit-based MOFs also vindicate our thematic approach of the trinuclear Cu-pyrazolate unit imparting specific physicochemical properties, such as magnetic, electrical, and catalytic properties, to resultant MOFs. The MOFs show excellent catalytic properties in reducing 4-nitrophenol, which could be attributed to the porous nature of the network along with the presence of metal centres with unsaturated coordination within the T-CuP unit. Furthermore, efficient photocatalytic degradation of harmful organic dyes confirms their importance for environmental remediation. The presence of a T-CuP unit and various functional groups also make some of the MOFs suitable candidates for electrical applications, which is indeed manifested in encouraging proton conductivity. Finally, the potential of current MOFs, fitted with a magnetically important trinuclear Cu-pyrazolate motif, as magnetic materials has also been thoroughly investigated.

Observation and deconvolution of a unique EPR signal from two cocrystallized spin triangles

A 16-line pattern has been theoretically predicted, but hitherto not reported, for the Electron Paramagnetic Resonance (EPR) spectrum of antiferromagnetically coupled CuII triangles experiencing isotropic exchange of isosceles magnetic symmetry. Now, the crystallization of such a triangular species and its X-ray structure determination in a polar space group, R3 (No. 146), has enabled its single crystal EPR study. Its detailed magnetic susceptibility, and X- and Q-band, powder and single crystal EPR spectroscopic study reveals the effect of molecular structure and of Dzyaloshinskii-Moriya interactions (DMI) on the g‖, g⊥ and A‖ parameters of the spectrum; DMI is considered for the first time in such a context. Moreover, careful analysis of the spectrum allows the deconvolution of two slightly different cocrystallized magnetic species.

Half-Integer Spin Triangles: Old Dogs, New Tricks

Spin triangles, that is, triangular complexes of half-integer spins, are the oldest molecular nanomagnets (MNMs). Their magnetic properties have been studied long before molecular magnetism was delineated as a research field. This Review presents the history of their study, with references to the parallel development of new experimental investigations and new theoretical ideas used for their interpretation. It then presents an indicative list of spin-triangle families to illustrate their chemical diversity. Finally, it makes reference to recent developments in terms of theoretical ideas and new phenomena, as well as to the relevance of spin triangles to spintronic devices and new physics.

Interaction between Trinuclear Regium Complexes of Pyrazolate and Anions, a Computational Study

The geometry, energy and electron density properties of the 1:1, 1:2 and 1:3 complexes between cyclic (Py-M)3 (M = Au, Ag and Cu) and halide ions (F-, Cl- and Br-) were studied using Møller Plesset (MP2) computational methods. Three different configurations were explored. In two of them, the anions interact with the metal atoms in planar and apical dispositions, while in the last configuration, the anions interact with the CH(4) group of the pyrazole. The energetic results for the 1:2 and 1:3 complexes are a combination of the specific strength of the interaction plus a repulsive component due to the charge:charge coulombic term. However, stable minima structures with dissociation barriers for the anions indicate that those complexes are stable and (Py-M)3 can hold up to three anions simultaneously. A search in the CSD confirmed the presence of (Pyrazole-Cu)3 systems with two anions interacting in apical disposition.

Interactions between H-bonded [CuII3(μ3-OH)] triangles; a combined magnetic susceptibility and EPR study

X-band EPR spectroscopy and magnetic susceptibility studies elucidate the magnetic exchange scheme within a triangular CuII3(μ₃-OH) complex and the intermolecular dipolar interactions between two H-bonded CuII3(μ₃-OH) units.

Halogen-bonded network of trinuclear copper(II) 4-iodo-pyrazolate complexes formed by mutual breakdown of chloro-form and nanojars

Crystals of bis-(tetra-butyl-ammonium) di-μ3-chlorido--tris-(μ2-4-iodo-pyrazolato-κ2N:N')tris-[chlorido-cuprate(II)] 1,4-dioxane hemisolvate, (C16H36N)2[Cu3(C3H2IN2)3Cl5]·0.5C4H8O or (Bu4N)2[CuII3(μ3-Cl)2(μ-4-I-pz)3Cl3]·0.5C4H8O, were obtained by evaporating a solution of (Bu4N)2[{CuII(μ-OH)(μ-4-I-pz)} n CO3] (n = 27-31) nanojars in chloro-form/1,4-dioxane. The decomposition of chloro-form in the presence of oxygen and moisture provides HCl, which leads to the breakdown of nanojars to the title trinuclear copper(II) pyrazolate complex, and possibly CuII ions and free 4-iodo-pyrazole. CuII ions, in turn, act as catalyst for the accelerated decomposition of chloro-form, ultimately leading to the complete breakdown of nanojars. The crystal structure presented here provides the first structural description of a trinuclear copper(II) pyrazolate complex with iodine-substituted pyrazoles. In contrast to related trinuclear complexes based on differently substituted 4-R-pyrazoles (R = H, Cl, Br, Me), the [Cu3(μ-4-I-pz)3Cl3] core in the title complex is nearly planar. This difference is likely a result of the presence of the iodine substituent, which provides a unique, novel feature in copper pyrazolate chemistry. Thus, the iodine atoms form halogen bonds with the terminal chlorido ligands of the surrounding complexes [mean length of I⋯Cl contacts = 3.48 (1) Å], leading to an extended two-dimensional, halogen-bonded network along (-110). The cavities within this framework are filled by centrosymmetric 1,4-dioxane solvent mol-ecules, which create further bridges via C-H⋯Cl hydrogen bonds with terminal chlorido ligands of the trinuclear complex not involved in halogen bonding.

Incarceration of one or two phosphate or arsenate species within nanojars, capped nanojars and nanohelicages: helical chirality from two closely-spaced, head-to-head PO4(3-) or AsO4(3-) ions

Unprecedentedly strong binding of HXO4(2-) and XO4(3-) ions (X = P or As) within self-assembled nanohosts with protein-like anion binding cavities is reported. One of the nanohosts binds two XO4(3-) ions at an unusually short distance, resulting in helical chirality.

New binuclear copper(ii) coordination polymer based on mixed pyrazolic and oxalate ligands: structural characterization and mechanical properties

A new inorganic–organic coordination polymer based on a copper(ii) binuclear complex coordinated with pyrazole (L1), 1-(hydroxymethyl)pyrazole) (L2) and oxalate (Ox) ligands has been unexpectedly obtained.

Synthesis, structure and magnetic properties of hydroxychlorides A3Cu3(OH)Cl8 (A = Cs, Rb) with isolated tricopper

A₃Cu₃(OH)Cl₈ (A = Cs, Rb) features an isolated triangular building unit of [Cu₃(OH)Cl₈]³⁻, displaying ferromagnetic coupling via the Cu(2)–Cl(5)–Cu(3) route.

Multireference ab initio calculations of g tensors for trinuclear copper clusters in multicopper oxidases

EPR spectroscopy has proven to be an indispensable tool in elucidating the structure of metal sites in proteins. In recent years, experimental EPR data have been complemented by theoretical calculations, which have become a standard tool of many quantum chemical packages. However, there have only been a few attempts to calculate EPR g tensors for exchange-coupled systems with more than two spins. In this work, we present a quantum chemical study of structural, electronic, and magnetic properties of intermediates in the reaction cycle of multicopper oxidases and of their inorganic models. All these systems contain three copper(II) ions bridged by hydroxide or O(2-) anions and their ground states are antiferromagnetically coupled doublets. We demonstrate that only multireference methods, such as CASSCF/CASPT2 or MRCI can yield qualitatively correct results (compared to the experimental values) and consider the accuracy of the calculated EPR g tensors as the current benchmark of quantum chemical methods. By decomposing the calculated g tensors into terms arising from interactions of the ground state with the various excited states, the origin of the zero-field splitting is explained. The results of the study demonstrate that a truly quantitative prediction of the g tensors of exchange-coupled systems is a great challenge to contemporary theory. The predictions strongly depend on small energy differences that are difficult to predict with sufficient accuracy by any quantum chemical method that is applicable to systems of the size of our target systems.

"Systematic Synthesis of a Metal Organic Framework Based on Triangular Cu(3)(μ(3)-OH) Secondary Building Units: From a 0-D Complex, to an 1-D Chain and a 3-D Lattice"

Reactions of Cu(CF(3)SO(3))(2) and pyrazole in methanolic solutions in the presence of stoichiometric amounts of py, py/4,4'-bpy, or 4,4'-bpy have yielded two new complexes [Cu(3)(μ(3)-OH)(μ-pz)(3)(py)(3)](CF(3)SO(3))(2)·0.5H(2)O (1) and [{Cu(3)(μ(3)-OH)(μ-pz)(3)(py)(2)}(2)(μ-4,4'-bpy)](CF(3)SO(3))(4) (2), a one-dimensional coordination polymer, {[Cu(3)(μ(3)-OH)(μ-pz)(3)(py)(μ-4,4'-bpy)](CF(3)SO(3))(2)·0.5H(2)O}(n) (3), and a three-dimensional, eight-fold interpenetrated extended lattice, {[Cu(3)(μ(3)-OH)(μ-pz)(3)(μ-4,4'-bpy)(1.5)](CF(3)SO(3))(2)·1.5H(2)O}(n) (4).

Pyrazoles and pyrazolides-flexible synthons in self-assembly

This Perspective summarises the chemistry of the pyrazole ring, and reviews the metal coordination modes adopted by 1H-pyrazoles and their anions. Pyrazolide anions are probably the most versatile ligands in coordination chemistry, with 20 different terminal or bridging coordination modes having been identified so far. Metal cluster compounds supported by pyrazolido ligation are surveyed, concentrating on those reported during the past ten years. Highlights include the wide structural diversity in apparently simple main group pyrazolides; luminescence and charge-transfer complexes in coinage metal pyrazolide clusters; the use of robust metal pyrazolide clusters to construct liquid crystals, supramolecular materials and metal-organic frameworks; and supramolecular complexes formed by pyrazolide-supported metallacrowns.

Rational design of macrometallocyclic trinuclear complexes with superior pi-acidity and pi-basicity

Density functional theory (DFT) has been used to assess the pi-acidity and pi-basicity of metal-organic trimetallic macromolecular complexes of the type [M(mu-L)]3, where M = Cu, Ag, or Au and L = carbeniate, imidazolate, pyridiniate, pyrazolate, or triazolate. The organic compounds benzene, triazole, imidazole, pyrazole, and pyridine were also modeled, and their substituent effects were compared to those of the coinage metal trimers. Our results, based on molecular electrostatic potential surfaces and positive charge attraction energy curves, indicate that the metal-organic macromolecules show superior pi-acidity and -basicity compared to their organic counterparts. Moreover, the metal-organic cyclic trimers are found to exhibit pi-acidity and -basicity that can be systematically tuned both coarsely and finely by judicious variation of the bridging ligand (relative pi-basicity imidazolate > pyridiniate > carbeniate > pyrazolate > triazolate), metal (relative pi-basicity Au > Cu > Ag), and ligand substituents. These computational findings are thus guiding experimental efforts to rationally design novel [M(mu-L)]3 materials for applications in molecular electronic devices that include metal-organic field-effect transistors and light-emitting diodes.