Themed collection Spin State Switches in Molecular Materials Chemistry

Guest editors Shinya Hayami, Stephen M. Holmes and Malcolm A. Halcrow introduce this Journal of Materials Chemistry C themed issue on spin-state switches in molecular materials chemistry.

The spin transition temperature of the Cu(II)-nitroxide complex was found to shift by approximately 100 K toward higher temperatures when the hydrostatic pressure increased to ∼0.04 GPa.

Femtosecond optical spectroscopy reveals coherent structural trapping accompanying spin-state photoswitching in a Fe^III spin-crossover material.

Me₄N[Fe(py₃COH)(NCS)₃](H₂O) showed an abrupt spin-crossover with thermal hysteresis, and temperature-scan rate dependence was recorded upon heating.

The composites composed of the cobalt terpyridine complex [Co^II(MeO-terpy)₂]₂₊ and the diblock copolypeptide amphiphiles (including glutamic acid and leucine) with rectangular morphology and reverse spin transition were prepared.

We report the structural and variable temperature magnetic properties of divalent cobalt complex containing the ligand 1-(2-pyridylazo)-2-phenanthrol (papl). This complex provides a rare example of spin-crossover in cobalt complexes with redox-active NNO donor ligands.

A luminescent charge neutral Fe(II) complex [Fe(L¹)₂] with above room temperature hysteretic spin crossover (SCO) is reported; a phase transition is associated with SCO as inferred from thermal and SAXS studies.

Supramolecular interactions between the terminal pyridyl groups and TCNQ radicals induce structural distortions in [Co(pyterpy)₂](TCNQ)₂ spin-crossover materials.

A novel 1-D photomagnetic L-Cu^II–[Mo^IV(CN)₈]⁴⁻ complex was obtained, in which the photomagnetic effect is fully reversible by heating above 253 K, and partially reversible by irradiation with red and infrared light.

Bis(1,2,3,5-dithiadiazolyl)-4,4′-biphenylene exhibits spatially inhomogeneous, stepwise phase transitions, which are caused by a “bond frustration”, as seen in frustrated gear trains.

A covalently-linked electron donor–acceptor–acceptor molecule was utilized to study the effect of electron-nuclear hyperfine coupling on the dephasing of the zero quantum coherence in spin correlated radical pairs.

Calculations using the hybrid meta-GGA TPSSh exchange–correlation functional have been employed to model the spin-transition in dinuclear iron(II) systems.

Nanoparticles of the compound [Fe(Htrz)₂trz]BF₄ are shown to have a rod shape. Their size is found to control the width of the thermal hysteresis displayed in the spin crossover of this material, while the removal of surfactant results systematically in a reduction of the hysteresis width, by up to 16 K, both effects being original and important for potential applications.

We present a systematic study of the key synthetic parameters that control the growth of Fe–triazole spin-crossover nanoparticles and the effect of this size modulation on the spin transition.

Complexes bearing a polyheteroaromatic fluorophore show a modulation of the fluorescence depending on the spin state of the metal centre.

A 1-bpp-functionalized Anderson POM was reacted with Fe²⁺.

Drop-casting [Fe(bpp)₂][BF₄]₂ (bpp = 2,6-di[pyrazol-1-yl]pyridine) onto HOPG affords chain-of-beads nanostructures. SAMs of bpp derivatives with sulfur-containing tethers are also described.

An amphidynamic crystal shows a two-step structural transformation; the steps are coupled to both hysteretic magnetic phase transitions and dielectric anomalies.

A new series of amphiphilic alkylurea functionalised iron(III) sal₂trien complexes were prepared by substitution of phenolic ligand site with OC_nH_2n–NHC(O)NHC_mH_2m+1 tails (n = 5, 9, m = 4, 12, 14, 16).

A large iron(II) tetrahedral cage displays temperature induced spin-crossover and liesst effects.

We report on a thermochromic paper with reverse printing performance.

A novel Fe(II) complex with a π-radical anion exhibited a complete spin crossover transition with a stable paramagnetic state due to a strong chalcogen-bond and π-stacking interactions.

Vacuum-evaporable Fe(II) complexes exhibit greatly different spin-crossover behaviour in thin films deposited from the gas phase and the crystalline bulk.

Halogen ions in the Co(II) SCO–CPs [CoX₂(pyterpy)] (X = Cl and Br) impacted on their SCO behaviour and porosity.

Fundamental structural, magnetic and photomagnetic properties of Fe(II) and Co(II) complexes of alkyl-chain substituted ligands are described.

We demonstrate multi-modal sensing capabilities of short chain alcohols of spin crossover compounds by integrating them into a micrometric TAG sensitive to the colour and birefringence.

The spin-crossover cooperativity of a Hoffman-like metal–organic framework is dramatically modulated by introducing different aromatic guest molecules (benzene, naphthalene, anthracene, and ferrocene) with the thermal hysteresis width ranging from 0 K to 73 K.

A ground-triplet molecule 25FBPBN showed spin-transition-like behaviour with a small hysteresis, while 3FBPBN maintained a single phase.

SiO₂-coated Fe-triazole spin-crossover nanoparticles were functionalized with dansyl luminophores.

Water is crucial in exerting a confinement pressure or matrix effect on the spin transition of the SCO material in MCM-41.