Experimental and Theoretical Investigations of Magnetic Exchange Pathways in Structurally Diverse Iron(III) Schiff-Base Complexes

Magneto-structural studies on a number of doubly end-on cyanate and azide bridged dinuclear nickel(ii) complexes with {N3O} donor Schiff base ligands

Two new doubly μ _1,1-N₃ bridged (1 and 3) and six new doubly μ _1,1-NCO bridged Ni^II complexes (2, 4-8) with six different N₃O donor Schiff base ligands have been synthesized and magneto-structurally characterized. All these neutral complex molecules are isostructural and constitute edge sharing bioctahedral structures. Magnetic studies revealed that all these complexes exhibit ferromagnetic interaction through bridging pseudohalides with ferromagnetic coupling constant J being significantly higher for azide-bridged complexes than that of the cyanate analogues. This is consistent with the literature reported data and also the presence of polarizable π systems and two different N and O donor atoms in cyanate ion, rendering it a poor magnetic coupler in comparison to azide analogues. Although, the magneto-structurally characterized doubly μ _1,1-N₃ bridged Ni^II complexes are abundant, only few such complexes with μ _1,1-bridging NCO^- ions are reported in the literature. Remarkably, addition of these six new examples in this ever-growing series of doubly μ _1,1-NCO bridged systems gives us an opportunity to analyse the precise magneto-structural correlation in this system, showing a general trend in which the J value increases with an increase in bridging angles. Therefore, the high degree of structural and magnetic resemblances by inclusion of six new examples in this series is the major achievement of the present work. An elaborate DFT study was performed resulting in magneto-structural correlation showing that nature and value of the J-parameter is defined not only by Ni-N_b-Ni bond angles, but an important role is also played by the Ni1-Ni2-N_b-X_t dihedral angle (N_b and X_t are bridging N and terminal N or O atom of bridging ligands, respectively).

Synthesis and structural, magnetic and spectroscopic characterization of iron(III) complexes with in situ formed ligands from methyl-2-pyridyl ketone transformations

Reactions of methyl-2-pyridyl ketone, pyCOMe, with FeCl₃·6H₂O in various solvents gave complexes [Fe₄Cl₆(OMe)₂(L1)₂]·0.7MeCN·0.4MeOH (1·0.7MeCN·0.4MeOH) and [Fe₃Cl₄(bicine)(L2)]·Me₂CO·0.2H₂O (2·Me₂CO·0.2H₂O). The ligands (L1)^2- = pyCO(Me)CHCOpy (in 1) and (L2)^2- = pyCO(Me)CH₂CO(OMe)py (in 2) are formed in situ, through an aldol reaction-type mechanism between the carbanion pyC(O)CH₂^- (formed by the nucleophilic attack of the MeO^- in pyCOMe) and pyCOMe which results in the formation of a new C-C bond. The intermediate compound undergoes attack in the -CH₂- or -CO- group by a MeO^- group, and the new ligands (L1)^2- and (L2)^2-, respectively, are formed. The molecular structure of 1 consists of three corner-sharing [Fe₂O₂] rhombic units in cis-arrangement. The two terminal Fe^III ions display distorted square pyramidal geometry and the two central Fe^III ions are distorted octahedral. The molecular structure of 2 consists of two corner-sharing [Fe₂O₂] rhombic units, with the two terminal Fe^III ions in distorted square pyramidal geometry and the central Fe^III in distorted octahedral. The differentiation in the coordination environment of the Fe^III ions in 1-2 is reflected in the values of the Mössbauer hyperfine parameters. In agreement with theoretical calculations, the square pyramidal sites exhibit a smaller isomer shift value in comparison to the octahedral sites. Magnetic studies indicate antiferromagnetic interactions leading to an S = 0 ground state in 1 and to an S = 5/2 ground state in 2, consistent with Electron Paramagnetic Resonance spectroscopy. Mössbauer spectra of 2 indicate the onset of relaxation effects below 80 K. At 1.5 K the spectrum of 2 consists of magnetic sextets. The determined hyperfine magnetic fields are consistent with the exchange coupling scheme imposed by the crystal structure of 2. Theoretical calculations shed light on the differences in the electronic structure between the square pyramidal and the octahedral sites.

Hydroxido supported and differently networked octanuclear Ni6Ln2 [Ln = GdIII and DyIII] complexes: structural variation, magnetic properties and theoretical insights

Solvent derived hydroxido bridge driven Ni₆Ln₂ [Ln = Gd^III (1) and Dy^III (2)] coordination aggregates of two different types has been synthesized. Magnetic susceptibility study confirms field induced slow relaxation of magnetization for Ni₆Dy₂.

Switching of easy-axis to easy-plane anisotropy in cobalt(ii) complexes

In situ microcalorimetry monitored assembly and coligand induced switching of the magnetic anisotropy sign have been observed in a β-diketonate-Co(ii) system.

Solvent vapor-induced polarity and ferroelectricity switching

Vapor-induced crystal to crystal transformation between non-polar [Fe(sap)(acac)(sol)] (H₂sap = 2-salicylideneaminophenol, acac = acethylacetate, sol = MeOH, pyridine) and polar [Fe(sap)(acac)(DMSO)] was demonstrated. It provides an example of switchable ferroelectric behaviour attributted to the structural phase transition triggered by solvent vapour.

Electronic Structure Modeling of Metal-Organic Frameworks

Owing to their molecular building blocks, yet highly crystalline nature, metal-organic frameworks (MOFs) sit at the interface between molecule and material. Their diverse structures and compositions enable them to be useful materials as catalysts in heterogeneous reactions, electrical conductors in energy storage and transfer applications, chromophores in photoenabled chemical transformations, and beyond. In all cases, density functional theory (DFT) and higher-level methods for electronic structure determination provide valuable quantitative information about the electronic properties that underpin the functions of these frameworks. However, there are only two general modeling approaches in conventional electronic structure software packages: those that treat materials as extended, periodic solids, and those that treat materials as discrete molecules. Each approach has features and benefits; both have been widely employed to understand the emergent chemistry that arises from the formation of the metal-organic interface. This Review canvases these approaches to date, with emphasis placed on the application of electronic structure theory to explore reactivity and electron transfer using periodic, molecular, and embedded models. This includes (i) computational chemistry considerations such as how functional, k-grid, and other model variables are selected to enable insights into MOF properties, (ii) extended solid models that treat MOFs as materials rather than molecules, (iii) the mechanics of cluster extraction and subsequent chemistry enabled by these molecular models, (iv) catalytic studies using both solids and clusters thereof, and (v) embedded, mixed-method approaches, which simulate a fraction of the material using one level of theory and the remainder of the material using another dissimilar theoretical implementation.

Halogen Bonding in New Dichloride-Cobalt(II) Complex with Iodo Substituted Chalcone Ligands

The synthesis and properties of new chalcone ligand 4I-L ((2E)-1-[4-(1H-imidazol-1-yl)phenyl]-3-(4-iodophenyl)prop-2-en-1-one) and tetracoordinate Co(II) complex [Co(4I-L)2Cl2], (1a), are reported in this article. Upon recrystallization of 1a, the single crystals of [Co(4I-L)4Cl2]·2DMF·3Et2O (1b) were obtained and crystal structure was determined using X-ray diffraction. The non-covalent interactions in 1b were thoroughly analyzed and special attention was dedicated to interactions formed by the peripheral iodine substituents. The density functional theory (DFT), atoms in molecule (AIM) and noncovalent interaction (NCI) methods and electronic localization function (ELF) calculations were used to investigate halogen bond formed between the iodine functional groups and co-crystallized molecules of diethyl ether.

Impact of the Schiff base ligand substituents on the solid state and solution properties of eleven iron(iii) complexes

A series of novel iron(iii)-Schiff base complexes have been prepared and structurally characterised. Their stereochemical, magnetic and redox properties were correlated with the molecular design of the corresponding N₃O₂-pentadentate Schiff base ligand.

Ion-pair complexes of Schiff base Fe(iii) cations and complex anions

We report on the crystal structure and magnetic properties of four new ion-pair complexes.

Iron(iii) bis(pyrazol-1-yl)acetate based decanuclear metallacycles: synthesis, structure, magnetic properties and DFT calculations

The synthesis, structural aspects, magnetic interpretation and theoretical rationalizations for a new member of the ferric wheel family, a decanuclear iron(iii) complex with the formula [Fe₁₀(bdtbpza)₁₀(μ₂-OCH₃)₂₀] (1), featuring the N,N,O tridentate bis(3,5-di-tert-butylpyrazol-1-yl)acetate ligand, are reported. The influence of the steric effect on both the core geometry and coordination mode is observed. Temperature dependent (2.0-300 K range) magnetic susceptibility studies carried out on complexes 1 established unequivocally antiferromagnetic (AF) interactions between high-spin iron(iii) centers (S = 5/2), leading to a ground state S = 0. The mechanism of AF intramolecular coupling was proved using a broken-symmetry approach within the density functional method at the B3LYP/def2-TZVP(-f)/def2-SVP level of theory.

Synthesis and magneto-structural studies on a new family of carbonato bridged 3d–4f complexes featuring a [CoII3LnIII3(CO3)] (Ln = La, Gd, Tb, Dy and Ho) core: slow magnetic relaxation displayed by the cobalt(ii)–dysprosium(iii) analogue

A new series of carbonato-bridged complexes containing a CoII3LnIII3 core have been synthesized.

Anion coordination directed synthesis patterns for [Ni4] aggregates: structural changes for thiocyanate coordination and ligand arm hydrolysis

Competitive bridging modes of HO⁻ and NCS⁻ were explored for four Ni^II-based coordination aggregates in cubane and dicubane topology.

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.

Tetranuclear Ni(ii) and Co(ii) Schiff-base complexes with an M4O6 defective dicubane-like core: zero-field SMM behavior in the cobalt analogue

Two tetranuclear Ni₄ and Co₄ complexes were prepared and characterized. Their magnetic properties were thoroughly studied and it was revealed that the Co₄ compound behaves as a zero-field single-molecule magnet.

An octanuclear Schiff-base complex with a Na2Ni6 core: structure, magnetism and DFT calculations

An octanuclear complex with a Na₂Ni₆ core was prepared and characterized. Its magnetic properties were thoroughly studied by experimental and theoretical methods.

Solvent-induced structural diversity in tetranuclear Ni(ii) Schiff-base complexes: the first Ni4single-molecule magnet with a defective dicubane-like topology

The tetranuclear Ni^IIcomplexes with the Ni₄O₄cubane-like core (1) and the Ni₄O₆defective dicubane core (2) were studied, and the latter identified as a first single-molecule magnet with such topology.

Structural and magnetic properties of heptacoordinated MnII complexes containing a 15-membered pyridine-based macrocycle and halido/pseudohalido axial coligands

Heptacoordinated Mn^II compounds with a pentadentate 15-membered pyridine-based macrocycle and two axially coordinated halido/pseudohalido coligands, having a monomeric or polymeric composition, were investigated.