A Spin-Frustrated Trinuclear Copper Complex Based on Triaminoguanidine with an Energetically Well-Separated Degenerate Ground State

Controlled Modification of Triaminoguanidine-Based μ3 Ligands in Multinuclear [VIVO]/[VVO2] Complexes and Their Catalytic Potential in the Synthesis of 2-Amino-3-cyano-4H-pyrans/4H-chromenes

Reaction of tris(2-hydroxybenzylidene)-triaminoguanidinium chloride (I·HCl) and tris(5-bromo-2-hydroxybenzylidene)-triaminoguanidinium chloride (II·HCl) with [VIVO(acac)2] (1:1 molar ratio) in refluxing methanol resulted in mononuclear [VIVO] complexes, [VIVO(H2L1')(MeOH)] (1) and [VIVO(H2L2')(MeOH)] (2), respectively, where I and II undergo intramolecular triazole ring formation. Aerial oxidation of 1 and 2 in MeOH in the presence of Cs2CO3 gave corresponding cis-[VVO2] complexes Cs[(VO2)(H2L1')] (3) and Cs[(VO2)(H2L2')] (4). However, reaction of an aerially oxidized methanolic solution of [VIVO(acac)2] with I·HCl and II·HCl in the presence of Cs2CO3 (in 1:1:1 molar ratio) gave mononuclear complexes Cs[(VO2)(H3L1)] (5) and Cs[(VO2)(H3L2)] (6) without intramolecular triazole ring formation. Similar anionic trinuclear complexes Cs2[(VO2)3(L1)] (7) and Cs2[(VO2)3(L2)] (8) were isolable upon increasing the amounts of the vanadium precursor and Cs2CO3 to 3 equiv to the reaction applied for 5 and 6. Keeping the reaction mixture of 1 in MeOH under air gave [VVO(H2L1')(OMe)] (9). Structures of 3, 7, 8, and 9 were confirmed by X-ray crystal structure study. A permanent porosity in the crystalline metal-organic framework of 7 confirmed by single-crystal X-ray investigation was further verified by the BET study. Along with a suitable reaction mechanism, these synthesized compounds were explored as effective catalysts for the synthesis of biomolecules 4H-pyran/4H-chromenes.

Acute Bite Angle POP- and PSP-Type Ligands and Their Trinuclear Copper(I) Complexes: Synthesis and Photo-Luminescence Properties

In the current work, the rational synthesis of trinuclear copper complexes, incorporating acute bite angle POP- and PSP-type ligands, is reported. The in situ formation of POP (Ph2P-O-PPh2) or PSP (Ph2P-S-PPh2) ligands in the presence of a copper(I) precursor gave access to various trinuclear copper complexes of the form [Cu3(μ3-Hal)2(μ-PXP)3]PF6 [X = O; Hal = Cl (1), Br (2), I (3) and X = S; Hal = Cl (5), Br (6), I (7)]. Related iodide-containing complexes and clusters, such as [Cu4(μ3-I)4(Ph2PI)4] (4) and [Cu3(μ3-I)2(μ-I)(μ-PSP)2] (8), could also be obtained via the variation of the reaction stoichiometry. The investigation of the photo-optical properties by photo-luminescence spectroscopy has demonstrated that the phosphorescence in the visible region can be switched off through the mere change of the heteroatom in the ligand backbone (POP vs PSP ligand scaffold). Theoretical studies have been conducted to complement the experimental photo-optical data with detailed insights into the occurring electronic transitions. Consequently, this systematic study paves the way for tuning the photo-optical properties of transition metal complexes in a more rational way.

A Trinuclear High-Spin Iron(III) Complex with a Geometrically Frustrated Spin Ground State Featuring Negligible Magnetic Anisotropy and Antisymmetric Exchange

The trinuclear high-spin iron(III) complex [Fe₃Cl₃(saltag^Br)(py)₆]ClO₄ {H₅saltag^Br = 1,2,3-tris[(5-bromo-salicylidene)amino]guanidine} was synthesized and characterized by several experimental and theoretical methods. The iron(III) complex exhibits molecular 3-fold symmetry imposed by the rigid ligand backbone and crystallizes in trigonal space group P3̅ with the complex cation lying on a crystallographic C₃ axis. The high-spin states (S = ⁵/₂) of the individual iron(III) ions were determined by Mößbauer spectroscopy and confirmed by CASSCF/CASPT2 ab initio calculations. Magnetic measurements show an antiferromagnetic exchange between the iron(III) ions leading to a geometrically spin-frustrated ground state. This was complemented by high-field magnetization experiments up to 60 T, which confirm the isotropic nature of the magnetic exchange and negligible single-ion anisotropy for the iron(III) ions. Muon-spin relaxation experiments were performed and further prove the isotropic nature of the coupled spin ground state and the presence of isolated paramagnetic molecular systems with negligible intermolecular interactions down to 20 mK. Broken-symmetry density functional theory calculations are consistent with the antiferromagnetic exchange between the iron(III) ions within the presented trinuclear high-spin iron(III) complex. Ab initio calculations further support the absence of appreciable magnetic anisotropy (D = 0.086, and E = 0.010 cm^-1) and the absence of significant contributions from antisymmetric exchange, as the two Kramers doublets are virtually degenerate (ΔE = 0.005 cm^-1). Therefore, this trinuclear high-spin iron(III) complex should be an ideal candidate for further investigations of spin-electric effects arising exclusively from the spin chirality of a geometrically frustrated S = ¹/₂ spin ground state of the molecular system.

Antisymmetric Exchange in a Real Copper Triangular Complex

The antisymmetric exchange, also known as the Dzyaloshinskii-Moriya interaction (DMI), is an effective interaction that may be at play in isolated complexes (with transition metals or lanthanides, for instance), nanoparticles, and highly correlated materials with adequate symmetry properties. While many theoretical works have been devoted to the analysis of single-ion zero-field splitting and to a lesser extent to symmetric exchange, only a few ab initio studies deal with the DMI. Actually, it originates from a subtle interplay between weak electronic interactions and spin-orbit couplings. This article aims to highlight the origin of this interaction from theoretical grounds in a real tri-copper(II) complex, capitalizing on previous methodological studies on bi-copper(II) model complexes. By tackling this three-magnetic-center system, we will first show that the multispin model Hamiltonian is appropriate for trinuclear (and likely for higher nuclearity) complexes, then that the correct application of the permutation relationship is necessary to explain the outcomes of the ab initio calculations, and finally, that the model parameters extracted from a binuclear model transfer well to the trinuclear complex. For a more theory-oriented purpose, we will show that the use of a simplified structural model allows one to perform more demanding electronic structure calculations. On this simpler system, we will first check that the previous transferability is still valid, prior to performing more advanced calculations on the derived two-magnetic-center model system. To this end, we will explain in detail the physics of the DMI in the copper triangle of interest, before advocating further theory/experiment efforts.

Capped Nanojars: Synthesis, Solution and Solid-State Characterization, and Atmospheric CO2 Sequestration by Selective Binding of Carbonate

Nanojars are a class of supramolecular anion-incarcerating coordination complexes that self-assemble from Cu²⁺ ions, pyrazole, and a strong base in the presence of highly hydrophilic anions. In this work, we show that if the strong base (e.g., NaOH or Bu₄NOH) is replaced by a weak base such as a trialkylamine, capped nanojars of the formula [{Cu₃(μ₃-OH)(μ-pz)₃L₃}CO₃⊂{Cu(μ-OH)(μ-pz)}_n] (pz = pyrazolate anion; L = neutral donor molecule; n = 27-31) are obtained instead of the conventional nanojars. Yet, to obtain capped nanojars, the conjugate acid side product originating from the weak base must be separated by transferring it to water either by precipitation of the water-insoluble capped nanojars or by liquid-liquid extraction. Full characterization using electrospray ionization mass spectrometry, UV-vis and variable-temperature ¹H NMR spectroscopy in solution, and single-crystal X-ray diffraction, elemental analysis, and solubility studies in the solid state reveals similarities as well as drastic differences between capped nanojars and nanojars lacking the [Cu₃(μ₃-OH)(μ-pz)₃L₃]²⁺ cap. Acid-base reactivity studies demonstrate that capped nanojars are intermediates in the pH-controlled assembly-disassembly of nanojars. During the self-assembly of capped nanojars, CO₂ is selectively sequestered from air in the presence of other atmospheric gases and converted to carbonate, the binding of which is selective in the presence of NO₃^-, ClO₄^-, BF₄^-, Cl^-, and Br^- ions.

A new class of DyIII-SIMs associated with a guanidine-based ligand

A family of four mononuclear DyIII complexes of the guanidine-based ligand L [L = tris(2-hydroxybenzylidene)triaminoguanidine] with formulas [DyLCl2(DMF)2]·DMF·CH3OH (1), [DyL2(CH3OH)2]Br·H2O·3CH3OH (2), [DyL2(H2O)2]SCN·3H2O·CH3OH (3) and [DyL2(CH3OH)2]SCN·CH3CN·CH3OH (4) were successfully prepared by varying reaction conditions. Complex 1 is seven-coordinate, with three N2O from ligand L along with two equatorially trapped DMF molecules and two axial Cl- anions, adopting pentagonal bipyramidal D5h symmetry. Complexes 2-4 have somewhat similar structures with six donor N4O2 sites from two ligands and two O from corresponding solvent molecules, featuring a N4O4 octa-coordinate environment with triangular dodecahedron D2d symmetry. Magnetic investigations indicated that complex 1 did not demonstrate single-molecule magnetic behavior, while complexes 2-4 were single-ion magnets (SIMs) under zero applied DC field with the effective energy barriers (Ueff) of 207.3 (2), 222.5 (3) and 311.7 K (4), respectively. The different types of coordinated solvent molecules and counter anions caused changes in intermolecular interactions and coordination geometries that severely affected their magnetic dynamics. The magnetic behaviors of these complexes were investigated through complete-active space self-consistent field (CASSCF) calculations with the inclusion of spin-orbit effects. Calculations revealed that the measured differences in magnetic behaviors originated mainly from intermolecular and crystal-packing effects as isolated complexes 1-4 have almost identical electronic and magnetic properties.

Spin-Electric Coupling in a Cobalt(II)-Based Spin Triangle Revealed by Electric-Field-Modulated Electron Spin Resonance Spectroscopy

A cobalt(II)-based spin triangle shows a significant spin-electric coupling. [Co3 (pytag)(py)6 Cl3 ]ClO4 ⋅3 py crystallizes in the acentric monoclinic space group P21 . The intra-triangle antiferromagnetic interaction, of the order of ca. -15 cm-1 (H=-JSa Sb ), leads to spin frustration. The two expected energy-degenerate ground doublets are, however, separated by a few wavenumbers, as a consequence of magnetic anisotropy and deviations from threefold symmetry. The Co3  planes of symmetry-related molecules are almost parallel, allowing for the determination of the spin-electric properties of single crystals by EFM-ESR spectroscopy. The spin-electric effect detected when the electric field is applied in the Co3  plane was revealed by a shift in the resonance field. It was quantified as ΔgE /E=0.11×10-9  m V-1 , which in terms of frequency corresponds to approximately 0.3 Hz m V-1 . This value is comparable to what was determined for a Cu3  triangle despite the antiferromagnetic interaction being 20 times larger for the latter.

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.

Spin-frustration with two quasi-degenerated spin states of a copper(II) heptanuclear complex obtained from an amino acid ligand

The Cu(ii) heptanuclear complex (Cu7atac) was synthesised using the hydrated amino acid ligand 2-(5-amino-1H-1,2,4-triazol-3-yl)acetic acid (Hatac·H2O). Single crystal X-ray diffraction analysis revealed a μ3-hydroxo bridged Cu(ii) heptanuclear complex, consisting of two triangular subunits and one Cu(ii) ion as a bridge with the formula [Cu7(atac)6(μ3-OH)2(NO3)2(H2O)10](NO3)4. The magnetic behaviour of this discrete 0D complex shows strong antiferromagnetic couplings between Cu(ii) mediated by N,N bonding and an anti-anti modes of the carboxylate anion of the ligand atac-. The magnetic data were fitted considering a 3J model. To support the model used to fit the magnetic data of the Cu7atac complex, theoretical calculation methods (complete active space self-consistent field, CASSCF, density functional theory (DFT) using the UKS TPSS/Def2-TZVP//Def2-SVP level and periodic boundary conditions (PBC) using PBE/DZVP-MOLOPT-GTH) were performed to obtain the spin states, spin density map and J couplings. The theoretical results suggest that Cu7atac is a spin-frustrated complex in the ground state, in which the doublet spin state co-exists with the quartet spin state.

Variation of the Chain Geometry in Isomeric 1D Co(NCS)2 Coordination Polymers and Their Influence on the Magnetic Properties

Two different isomers of [Co(NCS)₂(4-chloropyridine)₂]_n (3C and 3L) were synthesized from solution and by thermal decomposition of Co(NCS)₂(4-chloropyridine)₂(H₂O)₂ (2), which show a different metal coordination leading to corrugated chains in 3C and to linear chains in 3L. Solvent mediated conversion experiments prove that 3C is thermodynamically stable at room temperature where 3L is metastable. Magnetic measurements reveal that the magnetic exchange in 3L is comparable to that observed for previously reported related chain compounds, whereas in 3C with corrugated chains, the ferromagnetic interaction within the chains is strongly suppressed. The magnetic ordering takes place at 2.85 and 0.89 K, for 3L and 3C, respectively, based on specific heat measurements. For 3L the field dependence of magnetic relaxations in antiferromagnetically ordered ferromagnetic chains is presented. In addition, 3L is investigated by FD-FT THz-EPR spectroscopy, revealing a ground to first excited state energy gap of 14.0 cm^-1. Broken-symmetry DFT calculations for 3C and 3L indicate a ferromagnetic intrachain interaction. Ab initio CASSCF/CASPT2/RASSI-SO computational studies reveal significantly different single-ion anisotropies for the crystallographically independent cobalt(II) centers in 3C and 3L. Together with the geometry of the chains this explains the magnetic properties of 3C and 3L. The ab initio results also explain the weaker exchange interaction in 3C and 3L as compared to previously reported [Co(NCS)₂(L)₂]_n compounds with linear chains.

Magnetocaloric Effect in Cu5-NIPA Molecular Magnet: A Theoretical Study

We calculated the magnetocaloric properties of the molecular nanomagnet Cu5-NIPA, consisting of five spins S = 1 / 2 arranged in two corner-sharing triangles (hourglass-like structure without magnetic frustration). The thermodynamics of the system in question was described using the quantum Heisenberg model solved within the field ensemble (canonical ensemble) using exact numerical diagonalization. The dependence of the magnetic entropy and magnetic specific heat on the temperature and the external magnetic field was investigated. The isothermal entropy change for a wide range of initial and final magnetic fields was discussed. Due to plateau-like behavior of the isothermal entropy change as a function of the temperature, a high degree of tunability of magnetocaloric effect with the initial and final magnetic field was demonstrated.

Octanuclear nickel phosphonate core forming extended and molecular structures

Three new nickel(ii) phosphonate complexes {[Na₂Ni₈(L)₆]·nSolv}_m (L = SAA³⁻ (1), BSAA³⁻ (2), NAA³⁻ (3); Solv = H₂O, MeOH; m = ∞ (1, 2), 1 (3)) possessing a new octanuclear {Ni₈} phosphonate core were obtained and studied in detail.

Molecular enneanuclear CuII phosphates containing planar hexanuclear and trinuclear sub-units: syntheses, structures, and magnetism

Highly symmetric enneanuclear copper(ii) phosphates [Cu9(Pz)6(μ-OH)3(μ3-OH)(ArOPO3)4(DMF)3] (PzH = pyrazole, Ar = 2,6-(CHPh2)2-4-R-C6H2; R = Me, 2MeAr; Et, 2EtAr; iPr, 2iPrAr; and Ar = 2,6-iPr2C6H3, 2Dip) comprising nine copper(ii) centers and pyrazole, hydroxide and DMF as ancillary ligands were synthesized by a reaction involving the arylphosphate monoester, 1, copper(i)chloride, pyrazole, and triethylamine in a 4 : 9 : 6 : 14 ratio. All four complexes were characterized by single crystal structural analysis. The complexes contain two distinct structural motifs within the multinuclear copper scaffold: a hexanuclear unit and a trinuclear unit. In the latter, the three Cu(ii) centres are bridged by a μ3-OH. Each pair of Cu(ii) centers in the trinuclear unit are bridged by a pyrazole ligand. The hexanuclear unit is made up of three dinuclear Cu(ii) motifs where the two Cu(ii) centres are bridged by an -OH and a pyrazole ligand. The three dinuclear units are connected to each other by phosphate ligands. The latter also aid the fusion of the trinuclear and the hexanuclear motifs. Magnetic studies reveal a strong antiferromagnetic exchange between the Cu(ii) centres of the dinuclear units in the hexanuclear part and a strong spin frustration in the trinuclear part leading to a degenerate ground state.

Metal-Bonded Redox-Active Triarylamines and Their Interactions: Synthesis, Structure, and Redox Properties of Paddle-Wheel Copper Complexes

Four new triphenylamine ligands with different substituents in the para position and their corresponding copper(II) complexes are reported. This study includes their structural, spectroscopic, magnetic, and electrochemical properties. The complexes possess a dinuclear copper(II) paddle‐wheel core, a building unit that is also common in metal‐organic frameworks. Electrochemical measurements demonstrate that the triphenylamine ligands and the corresponding complexes are susceptible to oxidation, resulting in the formation of stable radical cations. The square‐wave voltammograms observed for the complexes are similar to those of the ligands, except for a slight shift in potential. Square‐wave voltammetry data show that, in the complexes, these oxidations can be described as individual one‐electron processes centered on the coordinated ligands. Spectroelectrochemistry reveals that, during the oxidation of the complexes, no difference can be detected for the spectra of successively oxidized species. For the absorption bands of the oxidized species of the ligands and complexes, only a slight shift is observed. ESR spectra for the chemically oxidized complexes indicate ligand‐centered radicals. The copper ions of the paddle‐wheel core are strongly antiferromagnetic coupled. DFT calculations for the fully oxidized complexes indicate a very weak ferromagnetic coupling between the copper ions and the ligand radicals, whereas a very weak antiferromagnetic coupling is found among the ligand radicals.

Electric Field Control of Spins in Molecular Magnets

Coherent control of individual molecular spins in nanodevices is a pivotal prerequisite for fulfilling the potential promised by molecular spintronics. By applying electric field pulses during time-resolved electron spin resonance measurements, we measure the sensitivity of the spin in several antiferromagnetic molecular nanomagnets to external electric fields. We find a linear electric field dependence of the spin states in Cr_{7}Mn, an antiferromagnetic ring with a ground-state spin of S=1, and in a frustrated Cu_{3} triangle, both with coefficients of about 2  rad s^{-1}/V m^{-1}. Conversely, the antiferromagnetic ring Cr_{7}Ni, isomorphic with Cr_{7}Mn but with S=1/2, does not exhibit a detectable effect. We propose that the spin-electric field coupling may be used for selectively controlling individual molecules embedded in nanodevices.

Molecular electronic spin qubits from a spin-frustrated trinuclear copper complex

The trinuclear copper(ii) complex [Cu3(saltag)(py)6]ClO4 (H5saltag = tris(2-hydroxybenzylidene)triaminoguanidine) was synthesized and characterized by experimental as well as theoretical methods. This complex exhibits a strong antiferromagnetic coupling (J = -298 cm-1) between the copper(ii) ions, mediated by the N-N diazine bridges of the tritopic ligand, leading to a spin-frustrated system. This compound shows a T2 coherence time of 340 ns in frozen pyridine solution, which extends to 591 ns by changing the solvent to pyridine-d5. Hence, the presented compound is a promising candidate as a building block for molecular spintronics.

A dinuclear molybdenum(VI) complex with a triaminoguanidine ligand: synthesis and structure of [Mo2O4(OH2)(DMF)(H t Bu6L)]·3DMF ([H6 t Bu6L]Cl=tris(3,5-di-tert-butyl-2-hydroxybenzylidene)-triaminoguanidinium chloride)

Interaction of (NH4)6Mo7O24·4H2O with tris-(3,5-di-tert-butyl-2-hydroxy-benzylidene)triaminoguanidinium chloride [H6 t Bu6L]Cl in DMF-H2O resulted in isolation of a neutral dinuclear Mo(VI) complex [Mo2O4(OH2)(DMF)(H t Bu6L)]·3DMF. The C 3-symmetric-type ligand H t Bu6L is coordinated to two cis-{MoO2}2+ moieties via phenolic-oxygen, guanidine nitrogen and azomethine nitrogen atoms, and the remaining sixth coordination sites of the molybdenum centers are occupied by the oxygen atoms from the solvent molecules.

Magnetic relaxation in cobalt(ii)-based single-ion magnets influenced by distortion of the pseudotetrahedral [N2O2] coordination environment

Cobalt(ii) complexes with different dihedral angles between the bidentate ligands show a significant variation in their magnetic relaxation behavior.

Metal-ion induced ferromagnetic polarization in a mixed-spin system

Three new 3d-3d heterometallic complexes, [CuM^II(hmb)₆(OH)]ClO₄·H₂O (M = Zn (1), Ni (2) and Co (3)) (Hhmb = 2-hydroxy-3-methoxy-benzaldehyde), have been synthesized. Structural analysis reveals that the three complexes are isostructural. Three Cu^II ions are in a perfect trigonal geometrical frustration and form a tetrahedral frustrated system with the introduced fourth ion Zn^II/Ni^II/Co^II. Magnetic studies indicate the antiferromagnetic coupling between metal ions in all 1, 2 and 3. Due to the geometrical frustration, spin-frustrated magnetism is also a typical feature of 1-3 and the magnetostructural correlation is far more complicated than their structures. The detailed magnetic investigation found that the ground state spin of 2 cannot be simply determined by the antiferromagnetically linear arrangement of spins, because the strong antiferromagnetic coupling between Cu^II and Ni^II ions quenches the spin frustration and ferromagnetically polarizes the spins of the [Cu] unit. Contrarily, the antiferromagnetic coupling between Cu^II and Co^II ions is not strong enough in 3, so there is no similar behaviour compared to 2.

Formation of Highly Thermostable Copper-Containing Energetic Coordination Polymers Based on Oxidized Triaminoguanidine

A series of novel highly thermostable energetic coordination polymers (ECPs), with promising mechanical sensitivity properties, were prepared by an in situ oxidation-coordination reaction of triaminoguanidine hydrochloride with copper nitrate in aqueous solution. The molecular structures and properties of these ECPs could be tuned, by varying the ratios and concentrations of the starting materials. Our ECPs exhibit remarkable thermostability (>390 °C) and very low sensitivity to impact (Im > 98 J). The best-performing material (ECP-5) has a calculated detonation velocity of 8969 m·s(-1) and a decomposition peak temperature of 396.9 °C, demonstrating an outstanding balance between two inherently contradicting properties: high detonation performance and very low sensitivity.

Sulfate-bridged dimeric trinuclear copper(II)-pyrazolate complex with three different terminal ligands

The reaction of CuSO4·5H2O, 4-chloro-pyrazole (4-Cl-pzH) and tri-ethyl-amine (Et3N) in di-methyl-formamide (DMF) produced crystals of di-aqua-hexa-kis-(μ-4-chloro-pyrazolato-κ(2) N:N')bis-(N,N-di-methyl-formamide)di-μ3-hydroxido-bis-(μ4-sulfato-κ(4) O:O':O'':O'')hexa-copper(II) N,N-di-methyl-formamide tetra-solvate dihydrate, [Cu3(OH)(SO4)(C3H2ClN2)3(C3H7NO)(H2O)]2·4C3H7NO·2H2O. The centrosymmetric dimeric molecule consists of two trinuclear copper-pyrazolate units bridged by two sulfate ions. The title compound provides the first example of a trinuclear copper-pyrazolate complex with three different terminal ligands on the Cu atoms, and also the first example of such complex with a strongly binding basal sulfate ion. Within each trinuclear unit, the Cu(II) atoms are bridged by μ-pyrazolate groups and a central μ3-OH group, and are coordinated by terminal sulfate, H2O and DMF ligands, respectively. Moreover, the sulfate O atoms coordinate at the apical position to the Cu atoms of the symmetry-related unit, providing square-pyramidal coordination geometry around each copper cation. The metal complex and solvent mol-ecules are involved in O-H⋯O hydrogen bonds, leading to a two-dimensional network parallel to (10-1).

[CrF(O2 C(t) Bu)2 ]9 : Synthesis and Characterization of a Regular Homometallic Ring with an Odd Number of Metal Centers and Electrons

The first regular homometallic ring containing an odd number of metal centers is reported. The ring was synthesized by means of amine-templated self-assembly. Extensive physical characterization studies, including magnetic measurements, powder inelastic neutron scattering (INS), and DFT calculations, show that the molecule has a near perfect match to the expected behavior for a frustrated system with the lowest energy pair of S=1/2 spin states separated by only 0.1 meV (0.8 cm(-1) ).

A unusual two-dimensional azido-Cu(ii) network with benzoate derivative as a co-ligand exhibiting ferromagnetic order and slow magnetic relaxation

A 2D layer-like Cu(ii) compound with multiple-bridges of azido, carboxylate and hydroxyl ligands, featuring strong ferromagnetic coupling and slow magnetic relaxation.