Cooperative spin crossover leading to bistable and multi-inert system states in an iron(III) complex

Cooperativity among spin centres has long been the royal road in spin crossover (SCO) research to impose magnetic bistability in terms of thermal hysteresis. In this work we access magnetic multi-inert states of the iron(III) compound {FeL2[B(Ph)4]} ≡ FeB at low temperature, in addition to thermal bistability. The packing of the low-spin and high-spin forms of crystalline FeB differs only marginally what ultimately leads to structural conservatism. This indicates that the SCO-immanent breathing of the complex cation is almost fully compensated by the anion matrix. The unique cooling rate dependence of the residual low-temperature magnetisation in FeB unveils continuous switching between the trapped high-spin (ON) and the relaxed low-spin state (OFF). The macroscopic ratio of the spin states (ON:OFF) can be adjusted as a simple function of the cooling rate. That is, cooperative spin crossover can be the source of bistable and multi-inert system states in the very same material.

Mononuclear Fe(III) complexes with 2,4-dichloro-6-((quinoline-8-ylimino)methyl)phenolate: synthesis, structure, and magnetic behavior

Three Fe(III)-based coordination complexes [Fe(dqmp)2](NO3)·H2O (1), [Fe(dqmp)2](BF4)·2CH3COCH3 (2), and [Fe(dqmp)2](ClO4) (3) were synthesized from Fe(NO3)3·9H2O/Fe(ClO4)3·xH2O, NaBF4, and 2,4-dichloro-6-((quinoline-8-ylimino)methyl)phenol (Hdqmp) in methanol/acetone and characterized. The structures of complexes 1-3 were determined via single-crystal X-ray crystallography at 100 K and room temperature, and their magnetic properties in the solid and solution forms were investigated. All complexes showed meridional structures with two tridentate dqmp- ligands coordinated with Fe(III) cations. In the solid state, complex 1 showed an abrupt and complete spin crossover at 225 K, whereas complexes 2 and 3 exhibited an incomplete spin crossover at 135 and 150 K, respectively. In a dimethylformamide solution, the complexes showed counterion-dependent spin transitions. In contrast to the solid state, in solution, complex 1 did not exhibit complete spin crossover. However, complexes 2 and 3 showed more complete spin transitions in solutions than in the solid state. The relaxation times, T1 and T2, for 1 and 2 were determined and both increased with temperature from 220 to 380 K. The T1 of 1 was larger than that of 2 at 380 K, and the T1 values were larger than the T2 values.

Synthesis and crystal structures of three Schiff bases derived from 3-formyl-acetyl-acetone and o-, m- and p-amino-benzoic acid

Treatment of 3-formyl-acetyl-acetone with the isomeric o-, m- and p-amino-benzoic acids led to the formation of the corresponding Schiff bases, namely, 3-[(2-carb-oxy-phenyl-amino)-methyl-idene]pentane-2,4-dione, 1, 3-[(3-carb-oxy-phenyl-amino)-methyl-idene]pentane-2,4-dione, 2, and 3-[(4-carb-oxy-phenyl-amino)-methyl-idene]pentane-2,4-dione, 3, all C13H13NO4, that contain a planar amino-methyl-ene-pentane-2,4-dione core with a strong intra-molecular N-H⋯O hydrogen bridge. The carb-oxy-phenyl groups attached to the nitro-gen atom are almost coplanar to the central mol-ecular fragment. Depending on the position of the carboxyl unit, different supra-molecular structures with hydrogen-bonding networks are formed in the three title structures.

Halogen-Substituted Spin-Crossover Fe(III) Compounds with Photoresponsive Properties

Halogen-substituted Fe(III) compounds, [Fe(Hphsalpm^X)₂]PTFB (Hphsalpm^X = 5-X-(R,S)-((phenyl(2-pyridyl)methylimino)methyl)phenol, PTFB = phenyltrifluoroborate; X = F for 1, Cl for 2, Br for 3) and [Fe(Hphsalpm^X)₂]PTFB·MeOH (X = I for 4·MeOH), were synthesized. Compounds 1, 4·MeOH, and its desolvated form 4 exhibited an invariant high-spin state in the whole temperature range, while 2 and 3 underwent gradual, nonhysteretic, and incomplete spin crossover (SCO) with transition temperatures (T_C) of 153 and 220 K, respectively. Interestingly, the SCO-active compounds 2 and 3 showed light-induced excited spin-state trapping (LIESST) effects at 10 K, and light-induced reversible ON/OFF switching behaviors were realized by alternately using 880 and 1064 nm light, while the thermally inert compound 4·MeOH unexpectedly showed a reverse-LIESST effect. These results may help to design and synthesize new photoresponsive SCO Fe(III) compounds for the development of switchable materials.

Switchable on-off spin-crossover properties of iron(ii) compounds by trimming intermolecular hydrogen bonds

Reversible single crystal-to-single crystal transformations from [FeL₂(NCS)₂]·3MeOH (1·3MeOH, L = 2-(anthracen-10-yl)-1H-imidazo[4,5-f][1,10]phenanthroline) to 1 and 1·2H₂O were reported, which were accompanied by on-off switching of the spin-crossover properties.

Influence of anion induced geometry change in Zn(ii) on the magnetization relaxation dynamics of Dy(iii) in Zn–Dy–Zn complexes

A series of [Zn₂Dy(L₁)₂(OAc)₄](X) where X = (NO₃)_0.92(Br)_0.08 (1), ClO₄ (2), Cl (3) and PF₆ (4) complexes were synthesized and their dc and ac magnetic data investigated. Experimental results are validated through MOLCAS calculations.

Copper(ii) complexes with tridentate Schiff base-like ligands: solid state and solution structures and anticancer activity

We report 15 new Cu(ii) complexes with tridentate NNO β-acylenamino ligands derived from 2-picolylamine and bearing up to three alkyl, alkoxy, alkoxycarbonyl, or (pseudo)halide substituents.