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Modulating the spin-crossover behaviour in porous coordination polymers is not only an excellent way to address the challenges associated with high-order data storage and processing, but the colour change involved in the process reveals their importance as thermal and optical sensors. Herein, we report the guest-induced regulation of the magnetic bi-stability in a Hofmann-type framework, {Fe(pina)[Pd(CN)4]} (1, pina = N-(pyridin-4-yl)isonicotinamide) from ∼26 K (for 1·3.6MeCN, complex 1), to ∼40 K (for 1·stb.4H2O, stb = stilbene, complex 2) by a subsequent change of the guest molecules from CH3CN to stilbene. While the electronic interactions stabilize the LS states through effective π⋯π stacking between the guest stilbene and the host layers, chemical pressure, i.e., the steric effect of the stilbene molecule, stabilizes the HS states, and the overall competition between them leads to the high thermal hysteresis. To explicate the spin crossover properties to be used as a potential thermal sensor, the guest-free nanoparticles of framework (1) were prepared using the reverse micelle method. Magnetic measurements reveal that the effective downsizing at the nanoscale results in a progressive downward shift with an incomplete gradual SCO behaviour, diminishing the hysteresis loop compared to the abrupt hysteretic transition found at the bulk phase. In addition, these nanoparticles are assimilated as free-standing thermochromic polymeric films as a proof of concept for thermal sensing device. The rationalization of the tunable SCO properties, along with the thermochromic behaviour, opens up a new strategy for the development of new π electron-responsive magnetic materials. [ABSTRACT FROM AUTHOR]

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 FeII‐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. [ABSTRACT FROM AUTHOR]

A thermoresponsive Fe–Co based discrete Prussian blue analogue (PBA) with the 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 a wide hysteresis of 10 K observed for its desolvated complex 1. [ABSTRACT FROM AUTHOR]

Research on the magnetoelectric (ME) effect (or spin-electric coupling) in molecule-based magnetic materials is a relatively nascent but promising topic. Molecule-based magnetic materials have diverse magnetic functionalities that can be coupled to electrical properties. Here we investigate a realization of ME coupling that is fundamental but not heavily studied─the coupling of magnetic spin level crossings to changes in electric polarization. A mixed-valence Mn 4 Na complex with a total ground-state spin S = 5/2 under zero magnetic field and S = 17/2 under high magnetic field undergoes a cascade of ground-state level crossings of the S z states with increasing magnetic field. Magnetization and electrical polarization measurements under pulsed magnetic fields up to 73 T show that each spin level crossing is accompanied by a significant change in electric polarization that is an even function of the applied magnetic field. A molecular Hamiltonian describing antiferromagnetic exchange in a distorted tetrahedron of three Mn III and one Mn II ions matches the data well. We conclude that the ME coupling is caused by magnetostriction within the polar molecule as it distorts to lower its magnetic exchange energy.

The increased anthropogenic emission level of CO 2 urges the development of CO 2 -responsive materials, but is it possible to regulate the inherent electronic properties through weak physisorption of a ubiquitous gas such as CO 2 ? Herein, we intended to answer this imperative question by the first case of CO 2 -actuated variable spin-state stabilisation in an interdigitated Hofmann-type coordination polymer [Fe II Pd(CN) 4 L 2 ] (1, L = methyl isonicotinate), showing a wide shift in transition temperature ( T eq ) from 178 K at P CO 2 = 0 kPa to 229 K at P CO 2 = 100 kPa. Interestingly, the emergence of a stepped behaviour in the heating process below P CO 2 = 10 kPa and overlapping magnetic susceptibility values above P CO 2 = 10 kPa elucidate the selective LS state stabilisation solely correlated with the extent of CO 2 accommodation. Based on the magnetic response and phase transition diagrams obtained under respective P CO 2 , a plausible scenario of the spin-state switching can be interpreted as (1 ls + ) → (1 hs + ) → 1 hs at P CO 2 ≤ 10 kPa, → 1 hs at 100 kPa < P CO 2 ≥ 32 kPa and → → 1 hs at 100 kPa, where 1 and 1' represent CO 2 -free and CO 2 -encapsulated states, respectively. The cooperative CO 2 sorption with SCO based on the varied CO 2 pressure corroborates a novel case for developing CO 2 -responsive magnetic materials henceforth., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Photoresponsive spin-crossover (SCO) molecules are an important class of bistable magnetic molecules with intriguing potential in device applications. The light-induced excited spin state trapping (LIESST) and the combined application of light and temperature can provide access to the metastable region of the SCO profile. The primary obstacle in utilizing light stimuli is the manifestation of light-induced trappings at extremely low temperatures. Herein, we report two novel multiresponsive 2D Hofmann-type coordination polymers exhibiting light-induced excited spin state trapping above liquid nitrogen temperature ( T LIESST = 82 and 81 K). Stimulating the samples in conjugation with light and temperature successfully unveils hysteresis, which is otherwise concealed. Apart from light and temperature, we found that the SCO phenomenon is also responsive to external hydrostatic pressure and exhibits modulation of the hysteresis width and transition temperature shifts with changes in pressure.

A missing member of well-known ternary chalcometallates, a sodium selenogallate, NaGaSe 2 , has been synthesized by employing a polyselenide flux and stoichiometric reaction. Crystal structure analysis using X-ray diffraction techniques reveals that it contains supertetrahedral adamantane-type Ga 4 Se 10 secondary building units. These Ga 4 Se 10 secondary building units are further connected via corners to form two-dimensional (2D) [GaSe 2 ] ∞ - layers stacked along the c -axis of the unit cell, and the Na ions reside in the interlayer space. The compound has an unusual ability to absorb water molecules from the atmosphere or a nonanhydrous solvent to form distinct hydrated phases, NaGaSe 2 · x H 2 O (where x can be 1 and 2), with an expanded interlayer space, as verified by X-ray diffraction (XRD), thermogravimetric-differential scanning calorimetry (TG-DSC), desorption, and Fourier transform infrared spectroscopy (FT-IR) studies. The in situ thermodiffractogram indicates the emergence of an anhydrous phase before 300 °C with the decrease of interlayer spacings and reverting to the hydrated phase within a minute of re-exposure to the environment, supporting the reversibility of such a process. Structural transformation induced through water absorption results in an increase of Na ionic conductivity by 2 orders of magnitude compared to that of the pristine anhydrous phase, as verified by impedance spectroscopy. Na ions from NaGaSe 2 can be exchanged in the solid-state route with other alkali and alkaline earth metals in a topotactic or nontopotactic way, leading to 2D isostructural and three-dimensional networks, respectively. Optical band gap measurements show a band gap of ∼3 eV for the hydrated phase, NaGaSe 2 · x H 2 O, which is in good agreement with the calculated band gap using a density functional theory (DFT)-based method. Sorption studies further confirm the selective absorption of water over MeOH, EtOH, and CH 3 CN with a maximum water uptake of 6 molecules/formula unit at a relative pressure, P / P 0 , of 0.9.

A thermoresponsive Fe-Co based discrete Prussian blue analogue (PBA) with the 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 a wide hysteresis of 10 K observed for its desolvated complex 1.