Phase-dependent polymerization isomerism in the coordination complexes of a flexible bis(β-diketonato) ligand.

First prepared in the late 70s, the pro-ligand 1,3-bis(3,5-dioxo-1-hexyl)benzene (Hbdhb) contains two acetoacetyl terminations linked to a central 1,3-phenylene unit through dimethylene bridges. Since each termination can be either in diketonic or keto-enolic form, in organic solution it exists as a mixture of three spectroscopically resolvable tautomers. In the presence of pyridine, Co and the bdhb anion form a crystalline dimeric compound with formula [Co(bdhb)(py)] (2) and a Co⋯Co separation of more than 11 Å.

Experimental and theoretical studies of the electronic transport of an extended curcuminoid in graphene nano-junctions.

Exploiting the potential of curcuminoids (CCMoids) as molecular platforms, a new 3.53 nm extended system (pyACCMoid, 2) has been designed in two steps by reacting a CCMoid with amino-terminal groups (NH-CCMoid, 1, of 1.79 nm length) with polycyclic aromatic hydrocarbon (PAH) aldehydes.

Benchmarking Periodic Density Functional Theory Calculations for Spin-State Energies in Spin-Crossover Systems.

Spin energetics is one of the biggest challenges associated with energy calculations for electronic structure methods. The energy differences of the spin states in spin-crossover compounds are very small, making them one of the most difficult systems to calculate. Few methods provide accurate results for calculating these energy differences.

Accurate state energetics in spin-crossover systems using pure density functional theory.

The energy difference between different spin states of systems with transition metals is an outstanding challenge for electronic structure calculation methods. The small energy difference between high- and low-spin states in spin-crossover systems makes most post-Hartree-Fock or density functional theory-based methods provide inaccurate values. A test case of twenty systems showing spin transitions has been used to evaluate the accuracy of a new family of training -GGA (Generalized Gradient Approximation) functionals.

Thermal Jahn-Teller Distortion Changes and Slow Relaxation of Magnetization in Mn(III) Schiff Base Complexes.

The impact that the anion and alkyl group has on the electronic structures and magnetic properties of four mononuclear Mn(III) complexes is explored in [Mn(salEen-Br)]Y (salEen-Br = 2-{[2-(ethylamino)ethylimino]methyl}-4-Br-phenol; Y = ClO and BF·1/3CHCl ) and [Mn(salBzen-Br)]Y (salBzen-Br = 2-{[2-(benzylamino)ethylimino]methyl}-4-Br-phenol; Y = ClO and BF ). X-ray structures of [Mn(salEen-Br)]ClO·0.45CH , [Mn(salEen-Br)]BF·0.

New series of mononuclear β-diketonate cerium(III) field induced single-molecule magnets.

Five new β-diketonate Ce mononuclear complexes, [Ce(Btfa)(HO)] (1), [Ce(Btfa)(phen)] (2), [Ce(Btfa)(bipy)] (3), [Ce(Btfa)(terpy)] (4) and [Ce(Btfa)(bathophen)(DMF)] (5), where Btfa = 4,4,4-trifluoro-1-phenyl-1,3-butanedionate, phen = 1,10-phenanthroline, bipy = 2,2'-bipyridyl, terpy = 2,2':6',2''-terpyridine and bathophen = 4,7-diphenyl-1,10-phenanthroline, have been synthesized and structurally characterized through X-ray diffraction of single crystals. The central Ce atom displays a coordination number of 8 for 1, 2 and 3 and of 9 for 4 and 5. Under a 0 T external magnetic field, none of the given compounds exhibits single molecule magnet (SMM) behaviour.

Improving spin crossover characteristics in heteroleptic [Fe(qsal-5-I)(qsal-5-OMe)]A complexes.

A family of heteroleptic spin crossover (SCO) [Fe(qsal-5-I)(qsal-5-OMe)]A·sol (qsal-5-X = 5-X-2-[(8-quinolylimino)methyl]phenolate; A = NO1 sol = 2MeOH, NCS2 sol = 0.75MeOH·1.3HO, BF3 sol = MeOH, OTf4, sol = MeOH) complexes have been synthesized.

Increasing the Magnetic Blocking Temperature of Single-Molecule Magnets.

The synthesis of single-molecule magnets (SMMs), magnetic complexes capable of retaining magnetization blocking for a long time at elevated temperatures, has been a major concern for magnetochemists over the last three decades. In this review, we describe basic SMMs and the different approaches that allow high magnetization-blocking temperatures to be reached. We focus on the basic factors affecting magnetization blocking, magnetic axiality and the height of the blocking barrier, which can be used to group different families of complexes in terms of their SMM efficiency.

Fe-Gd Ferromagnetic Cyclic Coordination Cluster [FeGd(teaH)(N)(HO)] with Magnetic Anisotropy─Theory and Experiment.

The synthesis, structural, and magnetic characterization of [FeLn(teaH)(N)(HO)] (Ln = Gd and Y) and the previously reported isostructural Dy analogue are discussed. The commonly held belief that both Fe and Gd can be regarded as isotropic ions is shown to be an oversimplification. This conclusion is derived from the magnetic data for the Y analogue in terms of the zero-field splitting seen for Fe and from the fact that the magnetic data for the new Gd analogue can only be fit employing an additional anisotropy term for the Gd ions.

The spin magnetic order of Co ( ≤ 5) clusters.

The magnetism of transition metal clusters has been for decades a complicated puzzle, with experimental results disagreeing with calculations performed within the density functional theory formalism. In this work, we provide a key to this puzzle by investigating the lowest-energy spin states of cobalt cluster, Co ( ≤ 5), using CASSCF/NEVPT2 calculations with very large active spaces. The geometries as well as the spin configurations adopted by the clusters in their ground-state are known from experiments, making Co clusters an ideal model system for theoretical investigation.

Redox-Programmable Spin-Crossover Behaviors in a Cationic Framework.

Metal-organic frameworks (MOFs) provide versatile platforms to construct multi-responsive materials. Herein, by introducing the neutral tetradentate ligand and the linear dicyanoaurate(I) anion, we reported a rare cationic MOF [Fe(TPB){Au(CN)}]I·4HO·4DMF (TPB = 1,2,4,5-tetra(pyridin-4-yl)benzene) with hysteretic spin-crossover (SCO) behavior near room temperature. This hybrid framework with an open metal site (Au) exhibits redox-programmable capability toward dihalogen molecules.

Insights into the Spin Dynamics of Mononuclear Cerium(III) Single-Molecule Magnets.

Four novel Ce mononuclear complexes of formulas [Ce(ntfa)(MeOH)] (), [Ce(ntfa)(5,5'-Mebipy)] (), [Ce(ntfa)(terpy)] (), and [Ce(ntfa)(bipy)] (), where ntfa = 4,4,4-trifluoro-1-(naphthalen-2-yl)butane-1,3-dionato, 5,5'-Mebipy = 5,5'-dimethyl-2,2'-dipyridyl, terpy = 2,2':6',2″-terpyridine, and bipy = 2,2'-bipyridine, have been synthesized and structurally characterized with Ce displaying coordination numbers of 8, 8, 9, and 10, respectively. Magnetic measurements indicate that all the complexes show a field-induced single-ion magnet behavior under a small applied dc field. The magnetic analysis shows the relevance of the different spin relaxation mechanisms in the magnetic relaxation of the Ce compounds, with special emphasis on the local-mode process.

Dinuclear Fluoride Single-Bridged Lanthanoid Complexes as Molecule Magnets: Unprecedented Coupling Constant in a Fluoride-Bridged Gadolinium Compound.

A new synthetic method allows isolating fluoride-bridged complexes BuN{[M(3NO,5Br-HL)](μ-F)} (M = Dy, ; M = Ho, ; M = Gd, ) and BuN{[Dy(3Br,5Cl-HL)](μ-F)}·2HO, ·2HO. The crystal structures of ·5CHCH,··2HO·0.75THF, , and ·2HO·2THF show that all of them are dinuclear compounds with linear single fluoride bridges and octacoordinated metal centers.

Spin-Phonon Coupling and Slow-Magnetic Relaxation in Pristine Ferrocenium.

We report the spin dynamic properties of non-substituted ferrocenium complexes. Ferrocenium shows a field-induced single-molecule magnet behaviour in DMF solution while cobaltocene lacks slow spin relaxation neither in powder nor in solution. Multireference quantum mechanical calculations give a non-Aufbau orbital occupation for ferrocenium with small first excitation energy that agrees with the relatively large measured magnetic anisotropy for a transition metal S=1/2 system.

Magnetic anisotropy in Yb complex candidates for molecular qubits: a theoretical analysis.

The magnetic properties of mononuclear YbIII complexes have been explored by using multiconfigurational CASPT2/RASSI calculations. Such complexes, in particular the case of [Yb(trensal)] complex, have been proposed as molecular qubits due to their spin dynamics properties. We have verified the accuracy of the theoretical approach to study such systems by comparing with experimental magnetic data.

Metal-Organic Nanocapsules with Functionalized s-Heptazine Ligands.

A metalloorganic capsule was synthesized where the ligand is a derivative of heptazine with three carboxylic groups that are coordinated to Cu cations, forming paddle-wheel motifs. Each nanocapsule is neutral, with 12 Cu centers and 8 ligands adopting a rhombicuboctahedron shape. It has almost 3 nm diameter, and the main intermolecular interactions in the solid are π··· π stacking between the CN heptazine moieties.

Single molecule magnets of cobalt and zinc homo- and heterometallic coordination polymers prepared by a one-step synthetic procedure.

The synthesis of 1D cobalt and zinc monometallic and heterometallic coordination polymers (CPs) was carried out applying one-pot synthetic methods by using either supercritical carbon dioxide or ethanol as the solvent. A collection of four 1D CPs were thus obtained by the combination of a metal (or a mixture of metals) with the linker 1,4-bis(4-pyridylmethyl)benzene. The used metallic complexes were zinc and cobalt hexafluoroacetylacetonate, which can easily incorporate pyridine ligands in the coordination sphere of the metal centre.

Dysprosium-based complexes with a flat pentadentate donor: a magnetic and ab initio study.

The reactivity of the well-known pentadentate N3O2 Schiff base H2L (2,6-bis(2-hydroxyphenyliminomethyl)pyridine) towards a lanthanoid metal, in this case DyIII, has been investigated for the first time. This reactivity markedly depends on the pH of the medium and, accordingly, two different complexes, [Dy(HL)(NO3)2]·H2O (1·H2O) and [Dy(L)(NO3)(EtOH)(H2O)]·2H2O (2·2H2O), could be isolated from dysprosium(iii) nitrate and H2L. In addition, reaction of H2L with dysprosium(iii) chloride in methanol yields [Dy(HL')2][Dy(L)(Cl2)] (3), where H2L' ((6-(2-hydroxyphenyliminomethyl)-2-methoxyhydroxymethyl)pyridine) is an N2O2 hemiacetal donor derived from the partial hydrolysis of the H2L ligand, and subsequent addition of the methanol solvent to the carbonyl group.

Modular supramolecular dimerization of optically tunable extended aryl viologens.

Cucurbit[8]uril (CB[8]) mediated assembly of extended aryl viologens (EVs) into optically tunable dimers is reported for the first time. We show that the modular design and synthesis of a new class of π-conjugated viologen derivatives with rigid aromatic or heteroaromatic bridging units as well as electron donating molecular recognition motifs enable their self-assembly into 2 : 2 complexes with CB[8]. The quantitative dimerization process involving these two molecular components in an aqueous solution enables excimer-like interactions between closely packed charged guests giving rise to distinct spectroscopic behavior.

Dinuclear CoYvs. tetranuclear CoY complexes: the effect of increasing molecular size on magnetic anisotropy and relaxation dynamics.

A new CoII2YIII2 complex with the formula [{Co(μ-L)Y(NO3)}2(μ-CO3)2]·2CH3OH·2H2O (where H2L = N,N',N''-trimethyl-N,N''-bis(2-hydroxy-3-methoxy-5-methylbenzyl)diethylenetriamine) has been prepared and its structure solved by single-crystal X-ray diffraction. The tetranuclear structure is formed by the connection of two [Co(μ-L)Y(NO3)] dinuclear units through two carbonate bridging ligands, which exhibit a μ3-κ2-O,O':κ-O:κ-O'' tetradentate coordination mode. The CoII ion exhibits a slightly distorted octahedral CoN3O3 coordination environment.

Hexagonal Bipyramidal Dy(III) Complexes as a Structural Archetype for Single-Molecule Magnets.

Single-molecule magnets (SMMs), are regarded as excellent nanomaterials for high-density information storage and quantum computing. The local symmetry of the crystal field for the metal ion plays an important role in pursuing a high-performance SMM. Herein, two highly stable distorted hexagonal bipyramidal (quasi- D) Dy complexes exhibiting slow relaxation of the magnetization are reported.

Anion-π Interactions in Computer-Aided Drug Design: Modeling the Inhibition of Malate Synthase by Phenyl-Diketo Acids.

Human infection by Mycobacterium tuberculosis (Mtb) continues to be a global epidemic. Computer-aided drug design (CADD) methods are used to accelerate traditional drug discovery efforts. One noncovalent interaction that is being increasingly identified in biological systems but is neglected in CADD is the anion-π interaction.

Dissecting RAF Inhibitor Resistance by Structure-based Modeling Reveals Ways to Overcome Oncogenic RAS Signaling.

Clinically used RAF inhibitors are ineffective in RAS mutant tumors because they enhance homo- and heterodimerization of RAF kinases, leading to paradoxical activation of ERK signaling. Overcoming enhanced RAF dimerization and the resulting resistance is a challenge for drug design. Combining multiple inhibitors could be more effective, but it is unclear how the best combinations can be chosen.

Coming full circle: constructing a [Gd] wheel dimer by dimer and the importance of spin topology.

The syntheses, structures, magnetic and thermodynamic properties of three related triethanolamine-based Gd complexes are described. The smallest, a dimer ([Gd]), can be viewed as the subunit from which the two larger complexes, a linear tetramer ([Gd]) and a cyclic hexamer ([Gd]), are composed by further deprotonation of the triethanolamine ligand. In all cases, nearest neighbour magnetic ions are weakly correlated by antiferromagnetic isotropic exchange, whose strength does not change significantly from one complex to another; J ranging from -0.

Influence of the Disposition of the Anisotropy Axes into the Magnetic Properties of Mn Dinuclear Compounds with Benzoato Derivative Bridges.

The two new Mn dinuclear compounds [{Mn(HO)(phen)}(μ-4-CHCHCOO)(μ-O)](ClO)·3CHCN·HO (1·3CHCN·HO) and [{Mn(HO)(phen)}(μ-O)(μ-2-BrCHCOO){Mn(NO)(phen)}]NO (2) have been synthesized. Their structural data reveal significant differences in the shape of the coordination octahedron around the Mn ions in both compounds. The different distortions from ideal geometry incite a very different magnetic behavior, affecting both the zero-field splitting parameters of the Mn ions (D and E) and the magnetic interaction between them.