Wasinee Phonsri

Downsized materials of iron( iii ) spin crossover complexes are reported, with small decreases in hysteresis widths, but no significant change in the abruptness of spin crossover.

Designing and integrating Fe(III)-based spin crossover (SCO) complexes onto substrates remains a challenging goal with only a handful of examples reported. In this work, we successfully synthesized and characterized three [Fe(qsal-OR)₂]NO₃ (qsal-OR = 5-alkoxy-2-[(8-quinolylimino)methyl]phenolate) complexes, in which R = C₁₂H₂₅ 1, C₁₆H₃₃ 2, and C₂₂H₄₅ 3 to explore the impact of alkyl chain on the modulation of SCO activity and potential for self-assembly on a glass surface. The SCO is found to be gradual and incomplete in all cases, with the LS state more stabilised as the alkyl group shortens. We also demonstrate that all complexes form stable Langmuir films and achieve good transfer ratios to the glass surface, with 2 being the best in terms of stability. This paves the way for the SCO modulation of complexes in this class and the development of SCO devices.

Mononuclear lanthanoidate complexes [Bu₄N][Ln(QCl₄)] have been used as precursors to obtain new heterobimetallic complexes [Ln₂Mn(QCl)₈]. The change from mononuclear to trinuclear complexes enhances their single molecule magnetic (SMM) behaviour.

A series of Ni(II) trinuclear complexes, [Ni3(sala-X)6] (sala-X = o-[(p-X-phenylimino)methyl]phenol; X = Br 1-Br, Me 1-Me and OMe 1-OMe), have been prepared and fully characterised. X-ray crystallographic studies reveal that the complexes are composed of three face-sharing octahedral Ni(II) metal ions bridged by the phenoxide oxygens of the sala-X ligands. Magnetic studies indicate that the magnetic Ni(II) centres are ferromagnetically coupled with the substituent group having only a minor impact on the magnitude of coupling. DFT calculations also support ferromagnetic coupling with smaller Ni-O-Ni angles leading to slightly larger coupling constants in line with previous studies.

A family of iron(III) spin crossover complexes with different counteranions, [Fe(qsal-F)₂]A (qsal-F = 4-fluoro-2-[(8-quinolylimino)methyl]phenolate; A = PF₆^–1, OTf^–2, NO₃^–3, ClO₄^–4, BF₄^–5, or NCS^–6) have been prepared. All compounds are isostructural and crystallize (triclinic P1̅ space group) with two independent iron(III) centers (Fe1 and Fe2) in the asymmetric unit. No solvent molecules are found in the crystal lattice, allowing us to directly probe the relative influence of anion variation on the spin crossover characteristics. The crystal packing is governed by three types of π–π interactions (type A, type B, and type C), which form undulating 1D chains. Additional interactions (π–F, C–H···O/F, and P4AE) connect the neighboring chains to form a complex supramolecular network. Hirshfeld surface analysis supports these findings. The anions are located between the cationic [Fe(qsal-F)₂]⁺ chains; hence, similar interchain distances (d_chain) are observed irrespective of the anion. However, the interplane distances (d_plane) are influenced by the crystal packing and increase proportionally with the anion size. Magnetic studies reveal that smaller anions tend to stabilize the low-spin state (NO₃^–3, ClO₄^–4, and BF₄^–5), while larger anions (PF₆^–1 and OTf^–2) exhibit lower transition temperatures (T_onset for 1 = 200 K and T for 2 = 190 K) and gradual spin crossovers. The anomaly is 6, where, despite having the smallest anion, it exhibits the lowest transition temperature with magnetic hysteresis in the first step (T_1/2↑ = 170 K and T_1/2↓ = 157 K). This suggests the size, shape, and supramolecular connectivity of the anion all influence the magnetic properties.

A linear diamine-bisisophthalate bridging linker N,N′-bis(1,3-dicarboxyphenyl-5-methylene)-1,3-dimethylpropanediamine, designed to incorporate amine/ammonium functionalities in the core of the ligand, has been isolated as the pentahydrate of its dihydrochloride salt (H₆L)Cl₂·5H₂O. Using this compound, four new coordination polymers have been formed, namely poly-[M(H₂L)]·4.5H₂O (1M, where M = Co, Zn, Cd) and poly-[Cd(H₂L)(OH₂)]·DMF·7H₂O (2). Compounds 1M are isostructural 2D coordination polymers that contain 1D channels occupied by water molecules. In the case of 1Co these form a well ordered hydrogen-bonding network as determined by single crystal X-ray studies. Compound 2, synthesised under similar conditions, is a 1D coordination polymer in which the metal is partially solvated. DC and AC magnetic studies of 1Co, which posseses a mononuclear cobalt(II) node, revealed single molecule magnet behaviour (SMM) with an effective barrier height U_eff of 37.7 K and τ₀ = 1.02 × 10⁻⁹ s, among the highest reported for Co^II coordination polymers.

Three iron(III) complexes, [Fe(qnal)₂]Y {qnal = 1‐[(8‐quinolinylimino)methyl]‐2‐naphthalenolate; Y = NO₃ 1, BPh₄·CH₂Cl₂ 2, NCS 3} have been prepared to explore anion effects in spin crossover systems. Structural studies on 2 reveal supramolecular chains formed by π–π and C–H···π interactions between the [Fe(qnal)₂]⁺ cations. Magnetic susceptibility measurements show the onset of spin crossover in 1 above 200 K, while complete spin crossover is observed in 2 and 3 with T_1/2 = 285 and 340 K, respectively. Unusually, 2 also undergoes light‐induced excited spin state trapping (LIESST) at 980 nm with ca. 65 % efficiency and T(LIESST) = 25 K and reverse‐LIESST at 660 nm with full reversibility over many cycles. The results highlight the important influence that the anion has on thermal and light‐activated spin crossover properties.

The complexes trans -[Fe ^II (LC ₄ ) ₂ (NCS) ₂ ] ( 1C4 ) and trans -[Fe ^II (LC ₁₀ ) ₂ (NCS) ₂ ] ( 1C10 ) undergo thermally hysteretic spin-crossover with T _1/2 = 127.5 K and 119.0 K respectively.

The first example of a “double spin crossover” material, [Fe^II(3,5-Me₂ tris(pyrazolyl)methane)(tris(pyrazolyl)methane)][Fe^III azodiphenolate]ClO₄·2MeCN was synthesised by reacting a spin crossover Fe^II complex cation with a spin crossover Fe^III complex anion.

Two families of neutral tetraoxolene-bridged dinuclear rare earth complexes of general formula [((HBpz₃)₂RE)₂(μ-tetraoxolene)] (RE = Y and Dy; HBpz₃ ⁻ = hydrotris(pyrazolyl)borate; tetraoxolene = fluoranilate (fa²⁻; 1-RE) or bromanilate (ba²⁻; 2-RE)) have been synthesised and characterised. In each case, the bridging tetraoxolene ligand is in the diamagnetic dianionic form and each rare earth metal centre has two HBpz₃ ⁻ ligands completing the coordination. Electrochemical studies on the soluble 2-RE family reveal a tetraoxolene-based reversible one-electron reduction. Bulk chemical reduction with cobaltocene affords the cobaltocenium (CoCp⁺) salt of the 1e-reduced analogue: [CoCp][((HBpz₃)₂RE)₂(μ-ba˙)] (3-RE) that incorporates a radical trianionic form of the bromanilate bridging ligand. Alternating current (ac) magnetic susceptibility studies of 2-Dy reveal slow magnetic relaxation only in the presence of an applied magnetic field, but reduction to radical-bridged 3-Dy affords frequency-dependent peaks in the out-of-phase ac susceptibility in zero applied field. Exchange coupling between the Dy(III) ions and the radical bridging ligand thus reduces zero-field magnetisation quantum tunnelling and confers single-molecule magnet status on the complex. Comprehensive analysis of the magnetic relaxation data indicates that a combination of Orbach, Raman and direct relaxation processes are required to fit the data for both dysprosium bromanilate complexes.