Crystal structure, magnetic properties and Mössbauer studies of [Fe(qsal)2][Ni(dmit)2]

Magnetism, Conductivity and Spin-Spin Interactions in Layered Hybrid Structure of Anionic Radicals [Ni(dmit)2] Alternated by Iron(III) Spin-Crossover Complex [Fe(III)(3-OMe-Sal2trien)] and Ferric Moiety Precursors

In this study, crystals of the hybrid layered structure, combined with Fe(III) Spin-Crossover (SCO) complexes with metal-dithiolate anionic radicals, and the precursors with nitrate and iodine counterions, are obtained and characterized. [Fe(III)(3-OMe-Sal₂trien)][Ni(dmit)₂] (1), [Fe(III)(3-OMe-Sal₂trien)]NO₃·H₂O (2), [Fe(III)(3-OMe-Sal₂trien)]I (3) (3-OMe-Sal₂trien = hexadentate N₄O₂ Schiff base is the product of the condensation of triethylenetetramine with 3-methoxysalicylaldehyde; H₂dmit = 2-thioxo-1,3-dithiole-4,5-dithiol). Bulk SCO transition was not achieved in the range 2.0–350 K for all three compounds. Alternatively, the hybrid system (1) exhibited irreversible segregation into the spatial fractions of Low-Spin (LS) and High-Spin (HS) phases of the ferric moiety, induced by thermal cycling. Fractioning was studied using both SQUID and EPR methods. Magnetic properties of the LS and HS phases were analyzed in the framework of cooperative interactions with anionic sublattice: Anion radical layers Ni(dmit)₂ (1), and H-bonded chains with NO₃ and I (2,3). LS phase of (1) exhibited unusual quasi-two-dimensional conductivity related to the Arrhenius mechanism in the anion radical layers, ρ_||c = 2 × 10⁵ Ohm·cm and ρ_⊥c = 7 × 10² Ohm·cm at 293 K. Ground spin state of the insulating HS phase was distinctive by ferromagnetically coupled spin pairs of HS Fe³⁺, S = 5/2, and metal-dithiolate radicals, S = 1/2.

Iron(III) Azadiphenolate Compounds in a New Family of Spin Crossover Iron(II)–Iron(III) Mixed-Valent Complexes

A new family of mixed valent, double salt spin crossover compounds containing anionic FeIII and cationic FeII compounds i.e., [FeII{(pz)3CH}2][FeIII(azp)2]2·2H2O (4), [FeII(TPPZ)2][FeIII(azp)2]2]·H2O (5) and [FeII(TPPZ)2][FeIII(azp)2]2]·H2O·3MeCN (6) (where (pz)3CH = tris-pyrazolylmethane, TPPZ = 2,3,5,6, tetrapyridylpyrazine and azp2− = azadiphenolato) has been synthesized and characterised. This is the first time that the rare anionic spin crossover species, [FeIII(azp)2]−, has been used as an anionic component in double salts complexes. Single crystal structures and magnetic studies showed that compound 6 exhibits a spin transition relating to one of the FeIII centres of the constituent FeII and FeIII sites. Crystal structures of the anionic and cationic precursor complexes were also analysed and compared to the double salt products thus providing a clearer picture for future crystal design in double spin crossover materials. We discuss the effects that the solvent and counterion had on the crystal packing and spin crossover properties.

High-Temperature Cooperative Spin Crossover Transitions and Single-Crystal Reflection Spectra of [FeIII(qsal)2](CH3OSO3) and Related Compounds

New Fe(III) compounds from qsal ligand, [Fe(qsal)2](CH3OSO3) (1) and [Fe(qsal)2](CH3SO3)·CH3OH (3), along with known compound, [Fe(qsal)2](CF3SO3) (2), were obtained as large well-shaped crystals (Hqsal = N-(8-quinolyl)salicylaldimine). The compounds 1 and 2 were in the low-spin (LS) state at 300 K and exhibited a cooperative spin crossover (SCO) transition with a thermal hysteresis loop at higher temperatures, whereas 3 was in the high-spin (HS) state below 300 K. The optical conductivity spectra for 1 and 3 were calculated from the single-crystal reflection spectra, which were, to the best of our knowledge, the first optical conductivity spectra of SCO compounds. The absorption bands for the LS and HS [Fe(qsal)2] cations were assigned by time-dependent density functional theory calculations. The crystal structures of 1 and 2 consisted of a common one-dimensional (1D) array of the [Fe(qsal)2] cation, whereas that of 3 had an unusual 1D arrangement by π-stacking interactions which has never been reported. The crystal structures in the high-temperature phases for 1 and 2 indicate that large structural changes were triggered by the motion of counter anions. The comparison of the crystal structures of the known [Fe(qsal)2] compounds suggests the significant role of a large non-spherical counter-anion or solvate molecule for the total lattice energy gain in the crystal of a charged complex.

Cooperative spin-crossover transition from three-dimensional purely π-stacking interactions in a neutral heteroleptic azobisphenolate FeIII complex with a N3O3 coordination sphere

The first neutral spin-crossover Fe^III complex with a N₃O₃ coordination sphere formed a purely π-stacking interaction network and exhibited the cooperative transition.

Spin-crossover phenomena of the mononuclear Mn(III) complex tuned by metal dithiolene counteranions

Three ion-pair complexes based on spin-crossover [Mn(5-Br-sal-N-1,5,8,12)]ClO4 with TBA2[Ni(mnt)2], TBA2[Pt(mnt)2] (mnt = maleonitriledithiolate) and TBA[Ni(dmit)2] respectively (dmit = 2-thioxo-1,3-dithiole-4,5-dithiolato) have been synthesized and structurally characterized. Complexes [Mn(5-Br-sal-N-1,5,8,12)]2[Ni(mnt)2] and [Mn(5-Br-sal-N-1,5,8,12)]2[Pt(mnt)2] are isomorphic and show the axial compression of the octahedral coordination environment of Mn(III) ions. With the temperature increasing the equatorial metal-ligand bond lengths show significant elongation, but the axial bond lengths remain unchanged. Complex [Mn(5-Br-sal-N-1,5,8,12)][Ni(dmit)2]·CH3CN contains π-π, p-π and H-bonds weak interactions. Magnetic investigation shows the spin-crossover phenomena for and , and T1/2 has been increased by 230 K comparing with the reactant complex. However, no spin-crossover was observed in complex , and theoretical calculations show that there are weak antiferromagnetic couplings mediated through π-π interactions.

Stepped spin crossover in Fe(iii) halogen substituted quinolylsalicylaldimine complexes

Four iron(iii) spin crossover complexes with halogen substituted ligands are reported. The halogen is correlated with T_1/2 and controls the degree of spin crossover while extensive C–H⋯X and X⋯π interactions increase cooperativity.