The thermosalient effect is still a rare and poorly understood phenomenon, where crystals suddenly jump, bend, twist or explode upon undergoing a thermally activated phase transition. The synthesis and characterisation of the new spin transition Fe(III) compound [Fe(5-Br-salEen)₂][ClO₄] (salEen = N-ethyl-N-(2-aminoethyl)salicylaldiminate) is described and its thermosalient behaviour reported. It is the first example of a thermosalient effect with a spin transition and magnetic, calorimetric, diffraction, microscopy and computational studies are used to characterise these effects. Both thermosalient effect and spin transition occur around 320 K upon heating and are accompanied by an anisotropic unit cell change with conservation of crystal symmetry that causes a large enough stress of the crystal lattice to induce crystal explosion. This stress can ultimately be traced back to a diffusionless and distortive structural perturbation resulting in a coupled spin transition-thermosalient effect.

New amphiphilic and spin-labile Mn^III complexes based on dianionic N₄O₂-hexadentate sal₂trien or sal₂bapen ligands, which contain OC₆H₁₃, OC₁₂H₂₅, or OC₁₈H₃₇ alkoxy substituents at different positions of the salicylidene unit were prepared (H₂sal₂trien = N,N′′′-bis(salicylidene)-1,4,7,10-tetraazadecane, H₂sal₂bapen = N,N′′′-bis(salicylidene)-1,5,8,12-tetraazadodecane). According to electrochemical measurements, these complexes undergo two (quasi)reversible redox processes. Temperature-dependent magnetic measurements revealed a high-spin configuration for all sal₂trien complexes (S = 2) and gradual spin crossover for sal₂bapen complexes from high to low spin (S = 1). The chain length strongly influences the spin crossover, as C₁₈-functionalization stabilizes the low spin state at much higher temperatures than shorter alkyl chains. Moreover, long alkyl chains allow for spontaneous self-assembly of the molecules, which was investigated in single crystals and in Langmuir-films at the air–water interface. Long alkyl chains (C₁₂ or C₁₈) as well as a mutual syn-orientation of these molecular recognition sites were required for the Langmuir monolayers to be stable.

The mono-dentate, pyridyl containing, nitro naphthalimide ligands N-(4-pyridyl)-4-nitro-1,8-naphthalimide (L₁) and N-(3-pyridyl)-4-nitro-1,8-naphthalimide (L₂) were prepared and complexed with a selection of copper salts [Cu(OAc)₂, Cu(CF₃SO₃)₂ and Cu(ClO₄)₂]. Crystallographic studies were undertaken and revealed that dinuclear acetate bridged complexes resulted from reactions with Cu(OAc)₂, while mononuclear systems resulted from reactions with Cu(CF₃SO₃)₂ and Cu(ClO₄)₂. Despite the differing coordination environments the naphthalimide based ligands provided a range of interesting π-based interactions in the form of π⋯π, anion⋯π, nitro⋯π, solvent⋯π and CO⋯π associations. Solid state EPR spectra were in agreement with the coordination environments observed from crystallography.

A hysteretic spin transition is induced in a solution assembly of a mononuclear Fe^III amphiphilic complex which exhibits only gradual spin crossover in the solid state. The hysteretic behavior is dependent on dynamic solution assembly and removal of solvent causes reversion to the original bulk solid magnetic response.