A series of heteroleptic iron(III) spin crossover (SCO) complexes, [Fe(qsal-I)(qsal-X)]NTf₂ (X = F 1, Cl 2, Br 3, 5-OMe 4), have been synthesized. The complexes exhibit diverse SCO behaviors influenced by the conformational flexibility of the NTf₂− (bis(trifluoromethanesulfonyl)imide) anion. Magnetic studies reveal that 1 and 4 undergo complete SCO, with 4 showing a two-step transition indicative of mixed-spin states. In contrast, 2 and 3 are stabilized in the low-spin (LS) state. Single-crystal X-ray diffraction studies indicate that 1 and 4 crystallize in triclinic P1¯ with parallel 1D π–π chains connected by C−H···π interactions, facilitating SCO transitions. Conversely, 2 and 3 adopt a packing with angled chains (ca. 15°), locking the compounds in the LS state enforced by C−H···I interactions. The NTf₂− anion plays a key role in modulating these transitions, exhibiting temperature-dependent conformational changes (syn and intermediate) in 1 and 4, while remaining fixed in the syn conformation in 2 and 3. Notably, some magnetic transitions occur independently of structural changes, and vice-versa. These findings highlight the interplay between anion conformation, crystal packing, and magnetic behavior, offering new insights for the design of SCO materials with tunable properties.

We report the reverse micelle synthesis, structural characterisation and magnetic properties of iron(iii) spin crossover (SCO) nanomaterials based on [Fe(qsal)2]NO3, [Fe(qsal-I)2]OTf and [Fe(qsal-I)2]NTf2 using sodium dioctylsulfosuccinate (NaAOT) and hexane. The synthesis and characterization of a new complex, [Fe(qsal)2]NO3·EtOH is also reported. Systematic variation of micellar conditions including surfactant content in the polar and organic phases, reaction time, and solvent choice enabled the controlled formation of parallelogram, plate-like and rod-like shapes for [Fe(qsal)2]NO3, [Fe(qsal-I)2]OTf and [Fe(qsal-I)2]NTf2, respectively, as confirmed by FESEM. Magnetic studies reveal abrupt spin crossover with a narrower hysteresis width compared to the bulk materials. Nanomaterials of [Fe(qsal-I)2]OTf exhibit a 4 K hysteresis (T 1/2↑ = 231 K and T 1/2↓ = 227 K) while those of [Fe(qsal-I)2]NTf2 display a 27 K hysteresis (T 1/2↑ = 275 K and T 1/2↓ = 248 K) comparable to the bulk. The results demonstrate that reverse micelle methods can reliably produce iron(iii) SCO nanomaterials, advancing their potential for integration into functional devices.

This tutorial review introduces the basic concepts of spin crossover with a focus on crystallographic studies.

We developed a sensitive voltammetric sensor for detecting aromatic phenylenediamine (PD) isomers: para -phenylenediamine ( p -PD), ortho -phenylenediamine ( o -PD), and meta -phenylenediamine ( m -PD).

Three iron(III) spin crossover compounds, [Fe(salBzen-5-OMe)2]A, where HsalBzen-5-OMe = 2-[(2-benzylaminoethylimino)methyl]-4-methoxyphenol and A = Cl- 1, Br- 2, I- 3, have been synthesized and fully characterized. UV-vis spectroscopy reveals two LMCT bands corresponding to the LS and HS states in solution. X-ray crystallography indicates that the compounds crystallize in monoclinic P21/n or P21/c (1), (2) or tetragonal P43212 (3) phases. At room temperature, complexes 1 and 2 display HS FeIII centers, while complex 3 adopts an LS state. Notably, complexes 1 and 2 exhibit symmetry breaking, decoupling the phenomenon from spin crossover. A variety of intermolecular interactions, including C-Hpi, C-HO, N-HO, C-Hanion, and N-Hanion, are responsible for linking the cations and forming a 3D supramolecular network. SQUID magnetometry studies show that compounds 1 and 2 remain high spin down to 10 K, while complex 3 undergoes a gradual spin crossover above 350 K. Crystallization of 2 at lower temperatures and humidity gives a tetragonal phase P43212 (2') that exhibits a spin crossover profile very similar to 3. Moreover, the crystal structure of 2' reveals temperature-dependent modulation. These results highlight the significant role of counterions in modulating the magnetic properties of these compounds and demonstrate the independent control of symmetry breaking and spin crossover. This work offers valuable insights for designing advanced functional materials for molecular spintronics and materials science.

Redox-active coordination complexes provide a versatile platform for molecular recognition at electrochemical interfaces, particularly for non-electroactive analytes. Herein, we report a novel copper(II) complex based on a methylthio-imidazole Schiff base ligand (Cu(II)-ImaSMe), designed for the non-enzymatic electrochemical detection of creatinine, a key biomarker for kidney function. The complex adopts a five-coordinate geometry with vacant coordination sites and an extended hydrogen-bonding network that facilitates analyte interaction and self-assembly on gold surfaces. Integrated spectroscopic, electrochemical, and density functional theory (DFT)/time-dependent DFT (TDDFT) analyses reveal the mechanism of coordination-induced electronic reorganization at the metal center. The sensor exhibits a linear response over the range of 0.14-20.0 mM, with a detection limit of 40 mu M (3 sb/m). Excellent selectivity is achieved against common urinary interferences including ascorbic acid, uric acid, dopamine, urea, lactate, arginine, and creatine. The sensor demonstrated good agreement with a standard clinical assay, with recoveries of 97.3-100.5 % in human urine samples.

A Zn-metal organic framework has been synthesized, [Zn4(ad)3(BPTC)(H2O)4]center dot 0.75ad center dot 0.25NO3 center dot 2.5DMF center dot 2.5H2O (ZnAB MOF) (ad = adenine, BPTC = biphenyl-3,3 ',5,5 '-tetracarboxylic acid) and characterized by X-ray single crystallography. The crystal structure reveals a 3D framework with two differently sized channels with the structure confirmed by IR, TGA and elemental analysis. This MOF has also been prepared in the form of a MOF film on a Zn metal sheet in situ with one continuous layer 60 mu m thick. The materials fluoresce at 352, 433 and 355, 423 nm (lambda ex = 310 nm), for MOF powder and MOF film, respectively. The fluorescence is quenched by nitrofuran antibiotics allowing the MOF to be used in their detection. Specifically, the nitrofuran antibiotics nitrofurazone (NFZ) and nitrofurantoin (NFT) exhibit significant quenching. ZnAB MOF powder shows higher sensitivity than the ZnAB MOF film with higher fluorescence quenching, Stern-Volmer constant (KSV) and limit of detection (LOD). However, the ZnAB MOF film exhibits superior repeatability for nitrofuran detection. Fluo-rescence quenching of NFZ and NFT may occur via fluorescence resonance energy transfer (FRET) and/or photoinduced electron transfer (PET).

The impact that the anion and alkyl group has on the electronic structures and magnetic properties of four mononuclear Mn(III) complexes is explored in [Mn(salEen-Br)2]Y (salEen-Br = 2-{[2-(ethylamino)ethylimino]methyl}-4-Br-phenol; Y = ClO4- 1 and BF4-·1/3CH2Cl2 2) and [Mn(salBzen-Br)2]Y (salBzen-Br = 2-{[2-(benzylamino)ethylimino]methyl}-4-Br-phenol; Y = ClO4- 3 and BF4- 4). X-ray structures of [Mn(salEen-Br)2]ClO4·0.45C6H14 1-hexane, [Mn(salEen-Br)2]BF4·0.33CH2Cl2·0.15C6H14 2-dcm-hexane, and 3-4 reveal that they crystallize in ambient conditions in the monoclinic P21/c space group. Lowering the temperature, 2-dcm-hexane uniquely exhibits a structural phase transition toward a monoclinic P21/n crystal structure determined at 100 K with the unit cell trebling in size. Remarkably, at room temperature, the axially elongated Jahn-Teller axis in 2-dcm-hexane is poorly defined but becomes clearer at low temperature after the phase transition. Magnetic susceptibility measurements of 1-4 reveal that only 3 and 4 show slow relaxation of magnetization with Δeff/kB = 27.9 and 20.7 K, implying that the benzyl group is important for observing single-molecule magnet (SMM) properties. Theoretical calculations demonstrate that the alkyl group subtly influences the orbital levels and therefore very likely the observed SMM properties.

Supramolecular interactions are central to self-assembly. Recently, Liu and coworkers revealed that π–π interactions drive the self-assembly of a diamondoid superstructure with superior photophysical properties. This report highlights that careful molecular design of building blocks can aid in the construction of complex superstructures.

A series of three compounds [Fe(salEen-5-I)(2)]Cl 1, [Fe(salEen-5-I)(2)]Br 2, and [Fe(salEen-5-I)(2)]I 3 in which salEen-5-I = 2-{[(2-(ethylamino)ethyl]imino)methyl}-4-iodophenolate is reported. Magnetic studies reveal that 2 exhibits an abrupt 2-step spin crossover close to room temperature around 288 K, while 1 and 3 exhibit gradual incomplete spin crossover spanning over 200 K. The use of structural parameters A-C to describe the nearest and next nearest neighbor contacts allows us to rationalize not only the abruptness of the spin crossover but also the stepped nature of the spin crossover in 2. Comparisons with previously reported [Fe(salEen-5-Br)(2)]ClO4 and [Fe(salEen-5-I)(2)]ClO4 reveal that this magnetostructural relationship is applicable to a wider range of members of this family of complexes.

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 = C12H251, C16H332, and C22H453 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.

A series of three solvates [Fe(naphPren) 2 ]I·CH 2 Cl 2 1, [Fe(naphPren) 2 ]I·CHCl 3 2 and [Fe(naphPren) 2 ]I·acetone 3 showing thermal and light-induced spin crossover is reported.

This work investigates the impact of the Cu:N ratio in the nitrogen layer of a Cu(001) substrate coated with [Fe(SalEen-I)2 ]Br, an Fe(III) spin crossover (SCO) molecule. Specifically, we probe Cu/Cu(001), Cu3N/Cu(001), Cu2N/Cu(001), and CuN/Cu(001) substrates. To explore the molecule-substrate interaction, density functional theory calculations with Hubbard-U correction (DFT+U) and van der Waals interactions were conducted. From the analysis of the electronic structure, we propose that Cu2N/Cu(001) is the best candidate due to its weak chemical bonding to the adsorbed molecule and preservation of SCO bistability. Based on the total-energy calculations of various adsorption geometries and binding sites, the iodine atoms of the molecule adsorbed diagonally on copper atoms of the Cu2N(001) surface in the low-spin state is the most stable configuration. The energy difference between the high- and low-spin states of this configuration is 8.48 kJ/mol, which is significantly decreased compared to that of the free molecule of 29.14 kJ/mol.

The impact of solvent on spin crossover (SCO) behaviour is reported in two solvates [Fe(qsal-I)2]NO3·2ROH (qsal-I = 4-iodo-2-[(8-quinolylimino)methyl]phenolate; R = Me 1 or Et 2) which undergo abrupt and gradual SCO, respectively. A symmetry-breaking phase transition due to spin-state ordering from a [HS] to [HS-LS] state occurs at 210 K in 1, while T1/2 = 250 K for the EtOH solvate, where complete SCO occurs. The MeOH solvate exhibits LIESST and reverse-LIESST from the [HS-LS] state, revealing a hidden [LS] state. Moreover, photocrystallographic studies on 1 at 10 K reveal re-entrant photoinduced phase transitions to a high symmetry [HS] phase when irradiated at 980 nm or a high symmetry [LS] phase after irradiation at 660 nm. This study represents the first example of bidirectional photoswitchability and subsequent symmetry-breaking from a [HS-LS] state in an iron(iii) SCO material.

A family of heteroleptic spin crossover (SCO) [FeIII(qsal-5-I)(qsal-5-OMe)]A·sol (qsal-5-X = 5-X-2-[(8-quinolylimino)methyl]phenolate; A = NO3-1 sol = 2MeOH, NCS-2 sol = 0.75MeOH·1.3H2O, BF4-3 sol = MeOH, OTf-4, sol = MeOH) complexes have been synthesized. Most of the complexes exhibit gradual SCO, with the exception of NCS, which is principally high spin. In contrast, the OTf complex shows an abrupt hysteretic SCO (35 K) after solvent loss. The magnetic properties of this complex are significantly improved in comparison to the related homoleptics, [Fe(qsal-I)2]OTf 5 (hysteresis, 8 K) and [Fe(qsal-5-OMe)2]OTf·CH2Cl26 (gradual SCO). Structural studies reveal that slight changes in the crystal packing cause stronger interactions improving the cooperativity. These findings are supported by DFT calculations using the r2SCAN functional in which the calculated structures show that SCO from the LS to the HS state causes pronounced scissoring of the 1D π-π chains and substantial changes in their relative orientation following loss of MeOH.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.