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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. In addition, studies have usually focused on calculating energetics of single molecules, while spin-crossover properties are usually experimentally studied in the solid phase. In this paper, we have used periodic boundary conditions employing methods based on density functional theory to calculate the high- and low-spin energy differences for a test case of 20 extended systems. Compounds with different metals and ligands have been selected, and the results indicate that a semiquantitative description of the energy differences can be obtained with the combination of geometry optimization using the PBE functional including many-body dispersion approach and the use of meta-GGA functionals, such as r 2 SCAN but especially KTBM24, for the energy calculation. Other hybrid functionals, such as TPSSh, give generally good results, but the calculation of the exact exchange with periodic boundary conditions involves a huge increase in computer time and computational resources. It makes the proposed nonhybrid functional approach (KTBM24//PBE+MB) a great advantage for the study of periodic systems.

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) 2 ]Y (salEen-Br = 2-{[2-(ethylamino)ethylimino]methyl}-4-Br-phenol; Y = ClO 4 - 1 and BF 4 - ·1/3CH 2 Cl 2 2 ) and [Mn(salBzen-Br) 2 ]Y (salBzen-Br = 2-{[2-(benzylamino)ethylimino]methyl}-4-Br-phenol; Y = ClO 4 - 3 and BF 4 - 4 ). X-ray structures of [Mn(salEen-Br) 2 ]ClO 4 ·0.45C 6 H 14 1-hexane , [Mn(salEen-Br) 2 ]BF 4 ·0.33CH 2 Cl 2 ·0.15C 6 H 14 2-dcm-hexane , and 3 - 4 reveal that they crystallize in ambient conditions in the monoclinic P 2 1 / c space group. Lowering the temperature, 2-dcm-hexane uniquely exhibits a structural phase transition toward a monoclinic P 2 1 / n crystal structure determined at 100 K with the unit cell trebling in size. Remarkably, at room temperature, the axially elongated Jahn-Teller axis in 2-dcm-hexane is poorly defined but becomes clearer at low temperature after the phase transition. Magnetic susceptibility measurements of 1 - 4 reveal that only 3 and 4 show slow relaxation of magnetization with Δ eff / k B = 27.9 and 20.7 K, implying that the benzyl group is important for observing single-molecule magnet (SMM) properties. Theoretical calculations demonstrate that the alkyl group subtly influences the orbital levels and therefore very likely the observed SMM properties.

The synthesis, structural, and magnetic characterization of [Fe III 4 Ln III 4 (teaH) 8 (N 3 ) 8 (H 2 O)] (Ln = Gd and Y) and the previously reported isostructural Dy analogue are discussed. The commonly held belief that both Fe III and Gd III can be regarded as isotropic ions is shown to be an oversimplification. This conclusion is derived from the magnetic data for the Y III analogue in terms of the zero-field splitting seen for Fe III and from the fact that the magnetic data for the new Gd III analogue can only be fit employing an additional anisotropy term for the Gd III ions. Furthermore, the Fe 4 Gd 4 ring shows slow relaxation of magnetization. Our analysis of the experimental magnetic data employs both density functional theory as well as the finite-temperature Lanczos method which finally enables us to provide an almost perfect fit of magnetocaloric properties.

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 II (TPB){Au I (CN) 2 }]I·4H 2 O·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 I ) exhibits redox-programmable capability toward dihalogen molecules. By means of post-synthetic modification, all the linear [Au I (CN) 2 ] - linkers can be oxidized to square planar [Au III (CN) 2 X 2 ] - units, which results in the hysteretic SCO behaviors switching from one-step to two-step for Br 2 and three-step for I 2 . More importantly, the stepwise SCO behaviors can go back to one-step via the reduction by l-ascorbic acid (AA). Periodic DFT calculations using various SCAN-type exchange-correlation functionals have been employed to rationalize the experimental data. Hence, these results demonstrate for the first time that switchable one-/two-/three-stepped SCO dynamics can be manipulated by chemical redox reactions, which opens a new perspective for multi-responsive molecular switches.

Four novel Ce III mononuclear complexes of formulas [Ce(ntfa) 3 (MeOH) 2 ] ( 1 ), [Ce(ntfa) 3 (5,5'-Me 2 bipy)] ( 2 ), [Ce(ntfa) 3 (terpy)] ( 3 ), and [Ce(ntfa) 3 (bipy) 2 ] ( 4 ), where ntfa = 4,4,4-trifluoro-1-(naphthalen-2-yl)butane-1,3-dionato, 5,5'-Me 2 bipy = 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 III 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 III compounds, with special emphasis on the local-mode process. Multiconfigurational calculations were also performed to get more information on the axiality of the compounds.

A new synthetic method allows isolating fluoride-bridged complexes Bu 4 N{[M(3NO 2 ,5Br-H 3 L 1,1,4 )] 2 (μ-F)} (M = Dy, 1 ; M = Ho, 2 ; M = Gd, 3 ) and Bu 4 N{[Dy(3Br,5Cl-H 3 L 1,2,4 )] 2 (μ-F)}·2H 2 O, 4 ·2H 2 O. The crystal structures of 1 ·5CH 3 C 6 H 5 ,· 2 ·2H 2 O·0.75THF, 3 , and 4 ·2H 2 O·2THF show that all of them are dinuclear compounds with linear single fluoride bridges and octacoordinated metal centers. Magnetic susceptibility measurements in the temperature range of 2-300 K reveal that the Gd III ions in 3 are weakly antiferromagnetically coupled, and this constitutes the first crystallographically and magnetically analyzed gadolinium complex with a fluoride bridge. Variable-temperature magnetization demonstrates a poor magnetocaloric effect for 3 . Alternating current magnetic measurements for 1 , 2 , and 4 ·2H 2 O bring to light that 4 ·2H 2 O is an SMM, 1 shows an SMM-like behavior under a magnetic field of 600 Oe, while 2 does not show relaxation of the magnetization even under an applied magnetic field. In spite of this, 2 is the first fluoride-bridged holmium complex magnetically analyzed. DFT and ab initio calculations support the experimental magnetic results and show that apparently small structural differences between 1 and 4 ·2H 2 O introduce important changes in the dipolar interactions, from antiferromagnetic in 1 to ferromagnetic in 4 ·2H 2 O.

A metalloorganic capsule was synthesized where the ligand is a derivative of heptazine with three carboxylic groups that are coordinated to Cu II cations, forming paddle-wheel motifs. Each nanocapsule is neutral, with 12 Cu II 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 C 6 N 7 heptazine moieties. The nanocapsules can form monolayers deposited on graphite as observed by atomic force microscopy, which confirms their stability in solution.

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 6 h ) Dy complexes exhibiting slow relaxation of the magnetization are reported. A hexagonal bipyramidal Dy model complex with 18-crown-6 was also designed to study the relationship between magnetic anisotropy and symmetry. The combined experimental and theoretical results indicate that quantum tunneling is highly dependent on the local symmetries of the crystal field. The magnetic anisotropy becomes much stronger when the symmetry is closer to a standard D 6 h geometry. These results support the conclusion that the hexagonal bipyramidal geometry is a viable one for the design of new classes of SMMs.

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. The study reported herein supports the conclusion that anion-π interactions play a central role in directing the binding of phenyl-diketo acid (PDKA) inhibitors to malate synthase (GlcB), an enzyme required for Mycobacterium tuberculosis virulence. Using density functional theory methods (M06-2X/6-31+G(d)), a GlcB active site template was developed for a predictive model through a comparative analysis of PDKA-bound GlcB crystal structures. The active site model includes the PDKA molecule and the protein determinants of the electrostatic, hydrogen-bonding, and anion-π interactions involved in binding. The predictive model accurately determines the Asp 633-PDKA structural position upon binding and precisely predicts the relative binding enthalpies of a series of 2-ortho halide-PDKAs to GlcB. A screening model was also developed to efficiently assess the propensity of each PDKA analog to participate in an anion-π interaction; this method is in good agreement with both the predictive model and the experimental binding enthalpies for the 2-ortho halide-PDKAs. With the screening and predictive models in hand, we have developed an efficient method for computationally screening and evaluating the binding enthalpy of variously substituted PDKA molecules. This study serves to illustrate the contribution of this overlooked interaction to binding affinity and demonstrates the importance of integrating anion-π interactions into structure-based CADD.

The two new Mn III dinuclear compounds [{Mn(H 2 O)(phen)} 2 (μ-4-CH 3 C 6 H 4 COO) 2 (μ-O)](ClO 4 ) 2 ·3CH 3 CN·H 2 O (1·3CH 3 CN·H 2 O) and [{Mn(H 2 O)(phen)}(μ-O)(μ-2-BrC 6 H 4 COO) 2 {Mn(NO 3 )(phen)}]NO 3 (2) have been synthesized. Their structural data reveal significant differences in the shape of the coordination octahedron around the Mn III 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 III ions (D Mn and E Mn ) and the magnetic interaction between them. Compound 1, with elongation in the monodentate ligand direction, shows antiferromagnetic coupling (ground state S = 0) and local D Mn < 0, while compound 2, with compression in the oxo bridge direction, displays a ferromagnetic interaction (ground state S = 4) and local D Mn > 0. Theoretical CASSCF and DFT calculations corroborate the different magnetic anisotropy and exchange coupling found in both compounds. Moreover, with the help of theoretical calculations, some interesting magneto-structural correlations have been found between the degree of distortion of the coordination octahedra and the magnetic coupling; it becomes more antiferromagnetic when the elongation parameter, Δ, in absolute value is increased.

A family of isostructural, mononuclear Co II complexes with distorted trigonal bipyramidal coordination environments is reported. The degree of distortion as well as the overall symmetry of the molecules varies among the members of the series. Different experimental procedures resulted in the isolation of solvomorphs (pseudopolymorphs with different solvent content) for some of the family members. Importantly, their disparate packing arrangements lead to very different dynamic magnetic behavior. The results of magnetostructural correlations and ab initio calculations reveal that the deciding factor for SMM behavior is not the degree of distortion which, a priori, would be expected to be the case, but rather the interactions between neighboring molecules in the solid state.

The work presented herein shows the experimental and theoretical studies of a mononuclear nickel(II) complex with the largest magnetic anisotropy ever reported. The zero-field-splitting D parameter, extracted from the fits of the magnetization and susceptibility measurements, shows a large value of -200 cm(-1), in agreement with the theoretical value of -244 cm(-1) obtained with the CASPT2-RASSI method.

We previously reported how the synthesis of [Mn(III)12Mn(II)7(μ4-O)8(μ3-η(1)-N3)8(HL(1))12(MeCN)6]Cl2·10MeOH·MeCN (1), which has a Mn19 core corresponding to two supertetrahedral {Mn(II)4Mn(III)6} units sharing a common Mn(II) vertex, can be modified such that the central octacoordinate Mn(II) ion can be replaced by metal ions more likely to favor this coordination geometry such as Dy(III) as exemplified in the compound [Mn(III)12Mn(II)6Dy(III)(μ4-O)8(μ3-Cl)6.5(μ3-N3)1.5(HL)12(MeOH)6]Cl3·25MeOH (2). Here, we report a systematic survey of the effects of incorporating various diamagnetic metal ions M(n+) into this central position. We chose diamagnetic ions with electron configurations with fully occupied or completely empty frontier orbitals in order to gauge the effect on the overall magnetic behavior. The syntheses, structures, and magnetic properties of the heterometallic aggregates [Mn(III)12Mn(II)6Sr(II)(μ4-O)8(μ3-η(1)-N3)7.5(μ3-η(1)-Cl)0.5(HL(1))12(MeCN)6]Cl2·15MeOH (3), [Mn(III)12Mn(II)6Y(III)(μ4-O)8(μ3-η(1)-N3)8(HL(1))12(MeCN)6](NO3)3·11MeOH (4), [Mn(III)12Mn(II)6Cd(II)(μ4-O)8(μ3-η(1)-N3)6.8(μ3-η(1)-Cl)1.2(HL(1))12(MeCN)6](CdCl4)0.25Cl1.5·14.5MeOH (5), and [Mn(III)12Mn(II)6Lu(III)(μ4-O)8(μ3-η(1)-N3)6.5(μ3-η(1)-Cl)1.5(HL(2))12(MeCN)6]Cl3·3H2O·7MeOH·MeCN (6) (H3L(1) = 2,6-bis(hydroxymethyl)-4-methylphenol, H3L(2) = 2,6-bis(hydroxymethyl)-4-fluorophenol) are reported. The aggregates were prepared in one-pot self-assembly reactions of H3L(1) (or H3L(2)), MnCl2·4H2O or Mn(NO3)2·4H2O, NaOAc·3H2O or Et3N, and NaN3 in the presence of the appropriate diamagnetic metal salt in MeCN/MeOH mixtures. Compounds 3-6 crystallize isotypically to 1 in the trigonal space group R3 with Z = 3. The effects on the magnetic properties were investigated, paying attention to the presence of any weak coupling mediated by the diamagnetic cations between the two {Mn(II)3Mn(III)6} S = 39/2 subunits. In the Cd(2+) compound 5, the two {Mn(II)3Mn(III)6} units are magnetically isolated. In 3, 4, and 6, the diamagnetic Sr(2+), Y(3+), and Lu(3+) cations mediate weak antiferromagnetic interactions between the two {Mn(II)3Mn(III)6} subunits. DFT calculations show that the inter-{Mn(II)3Mn(III)6} interactions in the Mn18M systems are attributable to the electronic structure of the central diamagnetic cation, with systems containing trivalent central cations showing stronger antiferromagnetic interactions than those with isoelectronic divalent cations.

Magnetic anisotropy is the property that confers to the spin a preferred direction that could be not aligned with an external magnetic field. Molecules that exhibit a high degree of magnetic anisotropy can behave as individual nanomagnets in the absence of a magnetic field, due to their predisposition to maintain their inherent spin direction. Until now, it has proved very hard to predict magnetic anisotropy, and as a consequence, most synthetic work has been based on serendipitous processes in the search for large magnetic anisotropy systems. The present work shows how the property can be predicted based on the coordination numbers and electronic structures of paramagnetic centers. Using these indicators, two Co(II) complexes known from literature have been magnetically characterized and confirm the predicted single-molecule magnet behavior.

The first cluster mesocate (H(3)O)[{Fe(2)(μ-L)(3)}{Fe(3)(μ(3)-O)(μ-Cl)(3)}]·3EtOH (1) and a new series of cluster helicates, [{Mn(μ-L)(3)}(2){Mn(3)(μ(3)-Cl)}(2)](ClO(4))(2)·2MeOH·6H(2)O (2), [{Cd(μ-L)(3)}(2){Cd(3)(μ(3)-Br)}(2)]Br(2)·2DMF·14H(2)O (3), and [{Cd(μ-L)(3)}(2){Cd(3)(μ(3)-I)}(2)](CdI(4))·3H(2)O (4), have been synthesized by the self-assembly of a C(2)-symmetric tritopic ligand, 2,6-bis[5-(2-pyridinyl)-1H-triazol-3-yl]pyridine (H(2)L) with different metal halogen salts. Single-crystal X-ray diffraction and electrospray ionization mass spectrometry measurements were carried out on these complexes. 1 was crystallized as a triple-stranded pentanuclear mesocate in which a [Fe(II)(3)(μ(3)-O)](4+) triangle core was wrapped by a [Fe(II)(2)(μ-L)(3)](2-) shell. 2-4 have similar octanuclear helicate structures in which two propeller-shaped [M(II)(μ-L)(3)](4-) units embrace two [M(II)(3)(μ(3)-X)](5+) triangles inside. The [M(II)(3)(μ(3)-O/X)](n+) triangle core were found to play an important role in the selective synthesis of the two architectures: the smaller [Fe(II)(3)(μ(3)-O)](4+) triangle core prefers a mesocate structure because it matches the small cavity imposed by the [Fe(II)(2)(μ-L)(3)](2-) shell, while the bigger [M(II)(3)(μ(3)-X)](5+) induces a screwed arrangement of the ligands, thus stabilizing the helicate structure. Variable-temperature magnetic susceptibility measurements indicate that both 1 and 2 display an overall antiferromagnetic coupling. Density functional theory calculations for 1 confirm the strong antiferromagnetic interaction in the central [Fe(II)(3)(μ(3)-O)](4+), while interaction through the triazole bridging ligands is slightly ferromagnetic. For 2, three interaction pathways were considered and all sets of J values reveal the presence of weak antiferromagnetic interaction.

Polynuclear 3d transition metal-Gd complexes are good candidates to present large magnetocaloric effect. This effect is favored by the presence of weak ferromagnetic exchange interactions that have been investigated using methods based on Density Functional Theory. The first part of the study is devoted to dinuclear complexes, focusing on the nature and mechanism of such exchange interactions. The presence of two bridging ligands is found more favorable for ferromagnetic coupling than a triple-bridged assembly, especially for complexes with small M-O···O-Gd hinge angles. Our results show the crucial role of the Gd 5d orbitals in the exchange interaction while the 6s orbital seems to have a negligible participation. The analysis of the atomic and orbital spin populations reveals that the presence of spin density in the Gd 5d orbital is mainly due to a spin polarization effect, while a delocalization mechanism from the 3d orbitals of the transition metal can be ruled out. We propose a numerical DFT approach using pseudopotentials to calculate the exchange coupling constants in four polynuclear first-row transition metal-Gd complexes. Despite the complexity of the studied systems, the numerical approach gives coupling constants in excellent agreement with the available experimental data and, in conjunction with exact diagonalization methods (or Monte Carlo simulations), it makes it possible to obtain theoretical estimates of the entropy change due to the magnetization/demagnetization process of the molecule.

Assembly of paramagnetic Cu(2) complexes with a Schiff base scaffold possessing extended electron delocalization together with a quasi-planar structure onto carbon nanotubes induces a diameter-selective charge transfer from the complex to the nanotubes leading to an interestingly large and tunable ambipolar effect. We used complementary techniques such as electron paramagnetic resonance, absorption spectroscopy, and photoluminescence to ensure the success of the assembly process and the integrity of the complex in the nanohybrid. We carried out density functional theory type calculations to rationalize the experimental results, evidencing the selective enhanced interaction of the metal complexes with one type of nanotube.

The title compound crystallizes in the monoclinic P2(1)/c space group with a = 11.2470(3) Å, b = 5.9034(2) Å, c = 12.0886(3) Å, β = 115.143(1)°, and V = 726.58(4) Å(3) and consists of discrete monomeric NiCl(2)(o-phenylendiamine)(2) molecules. Each o-phen ligand coordinates in a bidentate mode with the chloride ions occupying trans positions in the resulting tetragonally distorted octahedral coordination sphere. Two discrete sets of N-H···Cl hydrogen bonds link the octahedral molecules into a two-dimensional network, with type 1 interactions linking adjacent monomers along the c axis and type 2 interactions linking monomers along the diagonals in the bc plane. Analysis of the magnetic data reveals the existence of weak antiferromagnetic coupling within the layers via these hydrogen bonds, in addition to the presence of zero field splitting, with the best fit obtained for a 1d antiferromagnetic model with g = 2.0917(7), J/k = -2.11(4) K [J = -1.47(3) cm(-1)], and D = 1.05(3) cm(-1) [β = D/|J| = 0.72(6)] for the model with D > 0 and g = 2.0911(6), J/k = -2.26(1) K [J = -1.57(1) cm(-1)], and D = -0.86(1) cm(-1) [β = D/|J| = 0.55(6)] for the model with D < 0. Theoretical calculations of the exchange coupling confirm the experimental results, yielding values of J(1) = -1.39 cm(-1) for the type 1 hydrogen bonds and J(2)/k = -0.56 cm(-1) for the type 2 hydrogen bonds.