Mix and match - controlling the functionality of spin-crossover materials through solid solutions and molecular alloys.

The influence of dopant molecules on the structure and functionality of spin-crossover (SCO) materials is surveyed. Two aspects of the topic are well established. Firstly, isomorphous inert metal ion dopants in SCO lattices are a useful probe of the energetics of SCO processes.

Activating a high-spin iron(II) complex to thermal spin-crossover with an inert non-isomorphous molecular dopant.

[Fe(bpp)][ClO] (bpp = 2,6-bis{pyrazol-1-yl}pyridine; monoclinic, 2/) is high-spin between 5-300 K, and crystallises with a highly distorted molecular geometry that lies along the octahedral-trigonal prismatic distortion pathway. In contrast, [Ni(bpp)][ClO] (monoclinic, 2) adopts a more regular, near-octahedral coordination geometry. Gas phase DFT minimisations (ω-B97X-D/6-311G**) of [M(bpp)] complexes show the energy penalty associated with that coordination geometry distortion runs as M = Fe (HS) ≈ Mn (HS) < Zn ≈ Co (HS) ≲ Cu ≪ Ni ≪ Ru (LS; HS = high-spin, LS = low-spin).

A Survey of the Angular Distortion Landscape in the Coordination Geometries of High-Spin Iron(II) 2,6-Bis(pyrazolyl)pyridine Complexes.

Reaction of 2,4,6-trifluoropyridine with sodium 3,4-dimethoxybenzenethiolate and 2 equiv of sodium pyrazolate in tetrahydrofuran at room temperature affords 4-(3,4-dimethoxyphenylsulfanyl)-2,6-di(pyrazol-1-yl)pyridine (), in 30% yield. The iron(II) complexes [Fe][BF] () and [Fe][ClO] () are high-spin with a highly distorted six-coordinate geometry. This structural deviation from ideal symmetry is common in high-spin [Fe(bpp)] (bpp = di{pyrazol-1-yl}pyridine) derivatives, which are important in spin-crossover materials research.

Iron(II) complexes of 2,6-bis(imidazo[1,2-]pyridin-2-yl)pyridine and related ligands with annelated distal heterocyclic donors.

Following a published synthesis of 2,6-bis(imidazo[1,2-]pyridin-2-yl)pyridine (L), treatment of α,α'-dibromo-2,6-diacetylpyridine with 2 equiv. 2-aminopyrimidine or 2-aminoquinoline in refluxing acetonitrile respectively gives 2,6-bis(imidazo[1,2-]pyrimidin-2-yl)pyridine (L) and 2,6-bis(imidazo[1,2-]quinolin-2-yl)pyridine (L). Solvated crystals of [Fe(L)][BF] (1[BF4]2) and [Fe(L)][BF] (2[BF4]2) are mostly high-spin, although one solvate of 1[BF4]2 undergoes thermal spin-crossover on cooling.

Ligand-Directed Metalation of a Gold Pyrazolate Cluster.

Solid "[Au]" (H = 3-[pyrid-2-yl]-5-butyl-1-pyrazole) can be crystallized as cyclic [Au(μ-)] and [Au(μ-)] clusters from different solvents. The crystalline tetramer contains a square Au core with an HT:TH:TH:HT arrangement of ligand substituents, which preorganizes the cluster to chelate to additional metal ions via its pendant pyridyl groups. The addition of 0.

Jahn-Teller Switching of a Redox-Active Nickel(III) Center in a Homoleptic Thiolato Metalloligand Environment.

Treatment of nickel(II) nitrate with the iridium(III) metalloligand -[Ir(apt)] (apt = 3-aminopropanethiolate) gave the trinuclear complex [Ni{Ir(apt)}](NO) ([](NO)), in which the nickel center has a formal oxidation state of +III. Chemical or electrochemical oxidation and reduction of [](NO) generated the corresponding trinuclear complexes [Ni{Ir(apt)}](NO) ([](NO)) and [Ni{Ir(apt)}](NO) ([](NO)) with one-electron oxidated and reduced states, respectively. Single-crystal X-ray crystallography revealed that the nickel center in [](NO) is situated in a highly distorted octahedron due to Jahn-Teller effect, while the nickel center in each of [](NO) and [](NO) adopts a normal octahedral geometry.

Di-Iron(II) [2+2] Helicates of Bis-(Dipyrazolylpyridine) Ligands: The Influence of the Ligand Linker Group on Spin State Properties.

Four bis[2-{pyrazol-1-yl}-6-{pyrazol-3-yl}pyridine] ligands have been synthesized, with butane-1,4-diyl (L ), pyrid-2,6-diyl (L ), benzene-1,2-dimethylenyl (L ) and propane-1,3-diyl (L ) linkers between the tridentate metal-binding domains. L and L form [Fe (μ-L) ]X (X =BF or ClO ) helicate complexes when treated with the appropriate iron(II) precursor. Solvate crystals of [Fe (μ-L ) ][BF ] exhibit three different helicate conformations, which differ in the torsions of their butanediyl linker groups.

Iron(II) Complexes of 4-(Alkyldisulfanyl)-2,6-di(pyrazolyl)pyridine Derivatives. Correlation of Spin-Crossover Cooperativity with Molecular Structure Following Single-Crystal-to-Single-Crystal Desolvation.

The complex salts [Fe( )]X ( ; = 4-(isopropyldisulfanyl)-2,6-bis(pyrazolyl)pyridine; X = BF , ClO ) form solvated crystals from common organic solvents. Crystals of ·MeCO show abrupt spin transitions near 160 K, with up to 22 K thermal hysteresis. ·MeCO cocrystallizes with other, less cooperative acetone solvates, which all transform into the same solvent-free materials ·sf upon exposure to air, or mild heating.

Correction: Heteroleptic iron(II) complexes of chiral 2,6-bis(oxazolin-2-yl)-pyridine (PyBox) and 2,6-bis(thiazolin-2-yl)pyridine ligands - the interplay of two different ligands on the metal ion spin state.

Correction for 'Heteroleptic iron(II) complexes of chiral 2,6-bis(oxazolin-2-yl)-pyridine (PyBox) and 2,6-bis(thiazolin-2-yl)pyridine ligands - the interplay of two different ligands on the metal ion spin state' by Namrah Shahid , , 2022, , 4262-4274, DOI: 10.1039/d2dt00393g.

Heteroleptic iron(II) complexes of chiral 2,6-bis(oxazolin-2-yl)-pyridine (PyBox) and 2,6-bis(thiazolin-2-yl)pyridine ligands - the interplay of two different ligands on the metal ion spin sate.

Complexation of Fe[ClO]·6HO by 1 equiv. 2,6-bis((4)-4-phenyl-4,5-dihydrooxazol-2-yl)pyridine (()-LPh) and 2,6-bis((4)-4-phenyl-4,5-dihydrothiazol-2-yl)pyridine (()-LPh) cleanly affords [Fe(()-LPh)(()-LPh)][ClO]; [Fe(()-LiPr)(()-LiPr)][ClO] (LiPr = 2,6-bis(4-isopropyl-4,5-dihydrooxazol-2-yl)pyridine; LiPr = 2,6-bis(4-isopropyl-4,5-dihydrothiazol-2-yl)pyridine) was prepared by a similar route. The compounds exhibit thermal spin-crossover in solution, at temperatures midway between the corresponding [Fe(()-LR)(()-LR)][ClO] and [Fe(()-LR)(()-LR)][ClO] (R = Ph or iPr) species.

Structures and Spin States of Iron(II) Complexes of Isomeric 2,6-Di(1,2,3-triazolyl)pyridine Ligands.

Iron(II) complex salts of 2,6-di(1,2,3-triazol-1-yl)pyridine (L) are unexpectedly unstable in undried solvent. This is explained by the isolation of [Fe(L)(HO)][ClO] and [Fe(NCS)(L)(HO)]·L, containing L bound as a monodentate ligand rather than in the expected tridentate fashion. These complexes associate into 4 grid structures through O-H···N hydrogen bonding; a solvate of a related 4 coordination framework, -[Cu(μ-L)(HO)][BF], is also presented.

Spin-States of Diastereomeric Iron(II) Complexes of 2,6-Bis(thiazolin-2-yl)pyridine (ThioPyBox) Ligands and a Comparison with the Corresponding PyBox Derivatives.

This report investigates homoleptic iron(II) complexes of thiazolinyl analogues of chiral PyBox tridentate ligands: 2,6-(4-phenyl-4,5-dihydrothiazol-2-yl)pyridine (Ph), 2,6-(4-propyl-4,5-dihydrothiazol-2-yl)pyridine (Pr), and 2,6-(4--butyl-4,5-dihydrothiazol-2-yl)pyridine (-Bu). Crystallographic data imply the larger and more flexible thiazolinyl rings reduce steric clashes between the R substituents in homochiral [Fe(()-R)] or [Fe(()-R)] (R = Ph, Pr, or -Bu), compared to their PyBox (R) analogues. Conversely, the larger heterocyclic S atoms are in close contact with the R substituents in heterochiral [Fe(()-Ph)(()-Ph)], giving it a more sterically hindered ligand environment than that in [Fe(()-Ph)(()-Ph)] (Ph = 2,6-(4-phenyl-4,5-dihydrooxazol-2-yl)pyridine).

The number and shape of lattice solvent molecules controls spin-crossover in an isomorphous series of crystalline solvate salts.

Crystals of [FeL2][BF4]2·nMeCN (L = N-(2,6-di{pyrazol-1-yl}pyrid-4-yl)acetamide; n = 1 or 2) and [FeL2][ClO4]2·MeCN are isomorphous. When n = 1 the compounds exhibit an abrupt, hysteretic spin-transition below 200 K, but when n = 2 the material remains high-spin on cooling. [FeL2]X2·EtCN (X- = BF4- or ClO4-) are isomorphous with the MeCN solvates and undergo their spin-transition at almost the same temperature.

The effect of tether groups on the spin states of iron(II)/bis[2,6-di(pyrazol-1-yl)pyridine] complexes.

The synthesis of six 2,6-di(pyrazol-1-yl)pyridine derivatives bearing dithiolane or carboxylic acid tether groups is described: [2,6-di(pyrazol-1-yl)pyrid-4-yl]methyl (R)-lipoate (L1), 2-[(2,6-di(pyrazol-1-yl)pyridine)-4-carboxamido]ethyl (R)-lipoate (L2), 2-[(2,6-di(pyrazol-1-yl)pyridine)-4-carboxy]ethyl (R)-lipoate (L3), N-([2,6-di(pyrazol-1-yl)pyrid-4-ylsulfanyl]-2-aminoethyl (R)-lipoamide (L4), 2-[(2,6-di(pyrazol-1-yl)pyridine)-4-carboxamido]acetic acid (L5) and 2-[(2,6-di(pyrazol-1-yl)pyridine)-4-carboxamido]propionic acid (L6). The iron(ii) perchlorate complexes of all the new ligands exhibit gradual thermal spin-crossover (SCO) in the solid state above room temperature, except L4 whose complex remains predominantly high-spin. Crystalline [Fe(L6)2][ClO4]2·2MeCN contains three unique cation sites which alternate within hydrogen-bonded chains, and undergo gradual SCO at different temperatures upon warming.

The flexibility of long chain substituents influences spin-crossover in isomorphous lipid bilayer crystals.

[Fe(bpp)2][BF4]2 (bpp = 2,6-di{pyrazol-1-yl}pyridine) derivatives with a bent geometry of hexadec-1-ynyl or hexadecyl pyrazole substituents are isomorphous, and high-spin at room temperature. However, only the latter compound undergoes an abrupt, stepwise spin-transition on cooling. This may reflect the different conformational flexibilities of their long chain substituents.

Influence of ligand substituent conformation on the spin state of an iron(II)/di(pyrazol-1-yl)pyridine complex.

The temperature of the solution-phase spin-crossover equilibrium in iron(ii) complexes of 4-alkylsulfanyl-2,6-di{pyrazol-1-yl}pyridine (bppSR) complexes depends strongly on the alkylsulfanyl substituent. DFT calculations imply this reflects the conformation of the alkylsulfanyl groups, which lie perpendicular to the heterocyclic ligand donors in [Fe(bppStBu)2]2+ but are oriented co-planar with the ligand core for smaller SR substituents.

Structural Transformations and Spin-Crossover in [FeL ] Salts (L=4-{tert-Butylsulfanyl}-2,6-di{pyrazol-1-yl}pyridine): The Influence of Bulky Ligand Substituents.

4-(tert-Butylsulfanyl)-2,6-di(pyrazol-1-yl)pyridine (L) was obtained in low yield from a one-pot reaction of 2,4,6-trifluoropyridine with 2-methylpropane-2-thiolate and sodium pyrazolate in a 1:1:2 ratio. The materials [FeL ][BF ] ⋅solv (1[BF ] ⋅solv) and [FeL ][ClO ] ⋅solv (1[ClO ] ⋅solv; solv=MeNO , MeCN or Me CO) exhibit a variety of structures and spin-state behaviors including thermal spin-crossover (SCO). Solvent loss on heating 1[BF ] ⋅x MeNO (x≈2.

Manipulating metal spin states for biomimetic, catalytic and molecular materials chemistry.

This article surveys the relationship between ligand type, coordination geometry and metal spin state in complexes of iron and other metal ions. Compounds and materials containing high-, intermediate- and low-spin metal ions differ in their molecular structures, their physical properties and their chemical reactivity. Implications and applications of these variations are summarised, including the use of base metals in light-harvesting dyes and in different forms of catalysis.

Modulating the Magnetic Properties of Copper(II)/Nitroxyl Heterospin Complexes by Suppression of the Jahn-Teller Distortion.

A series of six-coordinate [Cu(L)L][BF] (L = 2,6-bis{1-oxyl-4,4,5,5-tetramethyl-4,5-dihydro-1-imidazol-2-yl}pyridine) complexes are reported. Ferromagnetic coupling between the Cu and L ligand spins is enhanced by an L coligand with distal methyl substituents, which is attributed to a sterically induced suppression of its Jahn-Teller distortion.

Elucidating the Structural Chemistry of a Hysteretic Iron(II) Spin-Crossover Compound From its Copper(II) and Zinc(II) Congeners.

Annealing [FeL ][BF ] ⋅2 H O (L=2,6-bis-[5-methyl-1H-pyrazol-3-yl]pyridine) affords an anhydrous material, which undergoes a spin transition at T =205 K with a 65 K thermal hysteresis loop. This occurs through a sequence of phase changes, which were monitored by powder diffraction in an earlier study. [CuL ][BF ] ⋅2 H O and [ZnL ][BF ] ⋅2 H O are not perfectly isostructural but, unlike the iron compound, they undergo single-crystal-to-single-crystal dehydration upon annealing.

Molecular squares, coordination polymers and mononuclear complexes supported by 2,4-dipyrazolyl-6H-1,3,5-triazine and 4,6-dipyrazolylpyrimidine ligands.

The Fe[BF4]2 complex of 2,4-di(pyrazol-1-yl)-6H-1,3,5-triazine (L1) is a high-spin molecular square, [{Fe(L1)}4(μ-L1)4][BF4]8, whose crystals also contain the unusual HPzBF3 (HPz = pyrazole) adduct. Three other 2,4-di(pyrazol-1-yl)-6H-1,3,5-triazine derivatives with different pyrazole substituents (L2-L4) are unstable in the presence of first row transition ions, but form mononuclear, polymeric or molecular square complexes with silver(i). Most of these compounds involve bis-bidentate di(pyrazolyl)triazine coordination, which is unusual for that class of ligand, and the molecular squares encapsulate one or two BF4-, ClO4- or SbF6- ions through combinations of anionπ, AgX and/or C-HX (X = O or F) interactions.

Supramolecular Iron Metallocubanes Exhibiting Site-Selective Thermal and Light-Induced Spin-Crossover.

Treatment of Fe[BF]·6HO with 4,6-di(pyrazol-1-yl)-1-pyrimid-2-one (HL) or 4,6-di(4-methylpyrazol-1-yl)-1-pyrimid-2-one (HL) affords solvated crystals of [{Fe(OH)}⊂Fe(μ-L)][BF] (, HL = HL; , HL = HL). The centrosymmetric complexes contain a cubic arrangement of iron(II) centers, with bis-bidentate [L] ligands bridging the edges of the cube. The encapsulated [Fe(OH)] moiety templates the assembly through 12 O-H···O hydrogen bonds to the [L] hydroxylate groups.

Heterometallic Coordination Polymer Gels Supported by 2,4,6-Tris(pyrazol-1-yl)-1,3,5-triazine.

Complexes of type [M(tpt)]X (M = Fe, Co, Ni; tpt = 2,4,6-tri{pyrazol-1-yl}-1,3,5-triazine; X = BF or ClO ) crystallize in a cubic lattice, with the metal ion and ligand conformation showing unusual symmetry-imposed disorder. Addition of 1 equiv AgX to the corresponding preformed [M(tpt)]X salt in concentrated MeNO solution affords thixotropic gels. Gelation was not observed in analogous reactions using [Mn(tpt)][ClO], or from reactions in other, more donating solvents.

Relationship between the Molecular Structure and Switching Temperature in a Library of Spin-Crossover Molecular Materials.

Structure-function relationships relating the spin-crossover (SCO) midpoint temperature () in the solid state are surveyed for 43 members of the iron(II) dipyrazolylpyridine family of SCO compounds. The difference between in the solid state and in solution [Δ(latt)] is proposed as a measure of the lattice contribution to the transition temperature. Negative linear correlations between the SCO temperature and the magnitude of the rearrangement of the coordination sphere during SCO are evident among isostructural or near-isostructural subsets of compounds; that is, a larger change in the molecular structure during SCO stabilizes the high-spin state of a material.