A thermoresponsive Fe-Co based discrete Prussian Blue Analogue (PBA) with general formula [Fe(Tp)(CN)3]2[Co{en(Bn)py}]2(ClO4)2 •4MeOH•4H2O i.e. [1•4MeOH•4H2O] is reported, which discloses a sharp and high temperature ETCST along with the wide...

The new 3D Hofmann-type coordination polymer [Fe(dpyu){Pt(CN) 4 }]•9H 2 O [dpyu = 1,3-di(pyridin-4-yl)urea] exhibits reversible interchange between two-and one-step spin-crossover behavior, associated with desorption/resorption of lattice water molecules. Solvent water removal also induces an increase of the spin-transition temperature, indicating strong lattice cooperativity, observed for the first time in a 3D Hofmann-type coordination polymer.

The interplay of host−guest interactions and controlled modulation of spin-crossover (SCO) behavior is one of the most exploited topics regarding data storage, molecular sensing, and optical technologies. In this work, we demonstrate the experimental approach of tuning the SCO behavior via controlled modulation of the spin-state cooperativity in a 2D Hofmann coordination polymer, [Fe II Pd-Removal of the solvent changes the four-step transition to a complete one-step spin transition with an enhanced hysteresis width (∼20 K). Structural analysis of solvated (1•1.3MeOH) and partially desolvated (1•0.3MeOH) compounds reveals that the crystal system changes from a monoclinic C2/c space group to an orthorhombic Imma space group, where the Fe II sites are present in a more symmetrically equivalent environment. Consequently, the axial ligand-field (LF) strength and face-to-face interactions of the ligands were increased by removing the guest, which is reflected in the highly cooperative SCO in 1 (desolvated compound). Also, the shift of the CN bond stretching frequencies and decrease of their relative intensities from the variable-temperature Raman spectroscopic measurements further corroborate the SCO behavior. Besides, theoretical calculations reveal that the singlet ( 1 Γ) LF terms decrease by removing guest molecules, enhancing the molecular population in the low-spin state at low temperature, as experimentally observed for 1. Notably, fine tuning of the SCO behavior via host−guests interactions provides a great opportunity to design potential chemosensors.

Spin crossover complexes that reversibly interconvert between two stable states imitate a binary state of 0 and 1, delivering a promising possibility to address the data processing concept in smart materials. Thus, a comprehensive understanding of the modulation of magnetic transition between high spin and low spin and the factors responsible for stabilizing the spin states is an essential theme in modern materials design. In this context, the present review attempts to provide a concise outline of the design strategy employed at the molecular level for fine-tuning the spin-state switching in Fe II -based Hofmann-type coordination polymers and their effects on the optical and magnetic response. In addition, development towards the nanoscale architectures of HCPs, i. e., in terms of nanoparticles and thin films, are emphasized to bridge the gap between the laboratory and reality.

Two two-dimensional (2D) Hofmann-type coordination frameworks are synthesized by employing the square planar tetracyanometallate building blocks and an amine-functionalized isoquinoline ligand with the general formula of [Fe(L) 2 {M(CN) 4 }] (L = 5-amino isoquinoline) (M = Pt (1Pt) and Pd (1Pd)) to explore the spin-state switching behavior. The inclusion of the amine functional group in the isoquinoline ligand plays a major role in exhibiting a complete spin crossover (SCO) behavior under ambient atmospheric pressure. The effective host−host supramolecular interaction such as strong π•••π stacking and N−H•••C interactions between interlayer 2D sheets of {Fe II [Pt (CN) 4 ]} n is responsible for the abrupt hysteretic spin transition behavior. Interestingly, the applied external pressure enhances the stabilization of the low spin states revealing a one-step abrupt and hysteretic spin transition near room temperature.