Anion Modified Spin Crossover in [Fe(qsal-4-F)]+ Complexes with a 4-Position Substituted Qsal Ligand

Four iron(III) complexes, [Fe(qsal-4-F)₂]Y·sol (Hqsal-4-F = 4-fluoro-N-(8-quinolyl)salicylaldimine; Y = NO₃^-, sol = 0.91MeOH·0.57H₂O (1_NO3); Y = PF₆^- (2_PF6); Y = BF₄^- (3_BF4); Y = OTf^-, sol =1.5MeOH (4_OTf)), with a new 4-position substituted qsal type ligand Hqsal-4-F have been synthesized and structurally and magnetically characterized. Complexes 1_NO3-3_BF4 consist of 1D chains formed by the [Fe(qsal-4-F)₂]⁺ cations connected by π-π and C-H···O interactions, which are further linked by more weak interactions to form 2D layers and 3D networks. On the other hand, complex 4_OTf has a structure of nearly isolated 1D column where the [Fe(qsal-4-F)₂]⁺ cations are connected by π-π, C-H···π, and C-F···π interactions. Magnetic studies revealed the occurrence of two-step symmetry-breaking SCO in 1_NO3 and two-step gradual SCO in 2_PF6. Complex 3_BF4 undergoes a gradual SCO, whereas 4_OTf remains almost high-spin. The smaller anions tend to stabilize the low-spin state, while larger anions tend to stabilize the high-spin state. In addition, the intermediate spin state of 1_NO3 could be thermally trapped by quenching from the high temperature, thereby kinetically suppressing the spin transition to the full low-spin state. This work represents a good example that the position of the substituent and the anions plays critical roles in the preparation of SCO materials with tunable properties.

Tuning of spin-crossover behavior in two cyano-bridged mixed-valence FeIII2FeII trinuclear complexes based on a TpR ligand

With the use of TpR derivatives, we have demonstrated the modulation in the SCO behavior in two analogous trinuclear complexes. Moreover, a change in the spin transition temperature via solvent loss is observed.

Syntheses, structural modulation, and slow magnetic relaxation of three dysprosium(III) complexes with mononuclear, dinuclear, and one-dimensional structures

Three mononuclear, dinuclear and one-dimensional dysprosium(III) complexes based on 3-azotriazolyl-2,6-dihydroxybenzoic acid (H₄ATB) of [Dy(H₃ATB)₃]·3H₂O (1), [Dy₂(H₂ATB)₂(H₂DHB)₂(H₂O)₄]·2CH₃CN·5H₂O (2), and [Dy₂(H₂ATB)₂(DCB)(DMF)₂(H₂O)₂]·4DMF (3) were synthesized and structurally characterized by X-ray single crystal diffraction (H₃DHB = 2,6-dihydroxybenzoic acid, H₂DCB = 1,4-dicarboxybenzene). Complex 1 was used as a precursor to synthesize complexes 2 and 3, and 2 was further used to synthesize 3. Complex 1 is a mononuclear complex, in which the Dy(III) ion is in a nine-coordinated structure surrounded by three tridentate chelate H₃ATB^- ligands. Complex 2 displays a dinuclear structure bridged by two μ₂ carboxyl groups of two H₂DHB^- ligands and two μ_1,1-O atoms from the phenolic hydroxyl groups of two H₂ATB^2- ligands. Complex 3 shows a one-dimensional structure formed by two bridging DCB^2- ligands. The magnetic measurements were performed on three complexes 1-3, and they showed different magnetic behavior. Complex 1 shows a field-induced slow magnetic relaxation. Complexes 2 and 3 display distinct slow magnetic relaxation under zero dc field with energy barriers (U_eff) of 26(2) cm^-1 and 11(1) cm^-1, respectively. The magnetic behavior of three complexes 1-3 was investigated by ab initio calculations.

High temperature anionic Fe(III) spin crossover behavior in a mixed-valence Fe(II)/Fe(III) complex

Two ion-pair Fe(iii) complexes (PPh4)[FeIII(HATD)2]·2H2O (1, H3ATD = azotetrazolyl-2,7-dihydroxynaphthalene) and [FeII(phen)3][FeIII(HATD)2]2·3DMA·3.5H2O (2, phen = 1,10-phenanthroline, DMA = N,N-dimethylformamide) were synthesized by employing the tridentate ligand H3ATD. Crystal structure analyses reveal that complexes 1 and 2 consist of FeIII ions in an octahedral environment where a FeIII ion is coordinated by two HATD2- ligands forming the [FeIII(HATD)2]- core. The shortest cationanion distance between the phosphorus ion of the (PPh4)+ cation and the ferric ion of the [FeIII(HATD)2]- anion is 13.190 Å in complex 1, whereas that between the ferrous ion of the [FeII(Phen)3]2+ cation and the ferric ion of the [FeIII(HATD)2]- anion is 7.821 Å in complex 2. C-HC and C-HO hydrogen interactions between the [FeII(phen)3]2+ cation and the [FeIII(HATD)2]- anion are observed in 2. Face-to-face π-π stacking interactions between naphthalene rings with the separated interplanar center to center distances of 3.421-3.680 Å were observed, which result in a one-dimensional supramolecular chain in complexes 1 and 2. Magnetic measurements show that complex 1 is in the low-spin (LS) state below 500 K, whereas 2 undergoes a high temperature spin crossover (SCO) between 360 and 500 K. Magneto-structural relationship studies reveal that π-stacking, hydrogen interactions and Coulomb interactions between the [FeIII(HATD)2]- anion and the [FeII(phen)3]2+ cation play a crucial role in the high temperature Fe(iii) SCO behaviour of complex 2.