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Four alkyl chains and cyclohexane modified FeII complexes [Fe(Ln)(L')](ClO4)2⋅solv (n=1, 2, 3, 4) were synthesized and characterized. X‐ray diffraction study showed that these complexes were constituted by asymmetric mononuclear FeII entities, incorporating alkyl‐chain‐modified bppCOOH (2,6‐bis(1H‐pyrazol‐1‐yl)isonicotinic acid) ligands and 6,6"‐2,6‐dimethoxyphenyl‐substituted terpy ligand (L'). Magnetic susceptibility measurements revealed that complexes 1, 2, and 3 were in the high spin state across the measured temperature range, whereas complex 4 displayed an incomplete spin crossover phenomenon, with a transition temperature (T1/2) at 240 K. Investigations into variable‐temperature structure and magneto‐structural correlations revealed that the integration of alkyl‐chain‐modified bipyridyl units fostered the π⋅⋅⋅π intra‐ and intermolecular interactions, contributing to distinct crystal stacking and spatial configurations in complex 4 when compared to its counterparts. These findings underscore the pivotal influence of intramolecular interactions on the FeII spin states and highlight the significance of designing flexible ligands for modulating spin‐crossover characteristics. [ABSTRACT FROM AUTHOR]

A dinuclear Fe(II) spin crossover (SCO) complex with the formula [Fe2L5(NCS)4]·2DMF·2H2O (1) was synthesised from 1-naphthylimino-1,2,4-triazole (L). Complex 1 exhibits an incomplete thermally induced spin transition with a transition temperature T1/2 of 95 K and a thermally trapped metastable high-spin state at low temperatures. Furthermore, it undergoes a reversible light-induced spin crossover by alternate irradiation with 532 and 808 nm lasers. [ABSTRACT FROM AUTHOR]

The design of magnetic molecular materials exhibiting multiple functions has garnered significant interest owing to their potential applications in molecular switches, sensors, and data storage devices. In this study, we synthesized a two-dimensional (2D) FeII-based Hofmann-type coordination polymer, namely {Fe(DPPE)2[Ag(CN)2]2}·2EtOH (1), using a luminescent ligand 1,1-diphenyl-2,2-di(4-pyridylbiphenyl)ethylene (DPPE). Single-crystal structural analyses and magnetic measurements revealed a thermally induced spin crossover (SCO) with the transition temperature T1/2 = 231 K. Variable-temperature fluorescence emission spectra indicated the coexistence of spin crossover and fluorescence properties. Moreover, a pronounced dielectric change (Δε′ = 1.2 at 0.5 kHz) was observed during the SCO process, confirming the simultaneous magnetic and dielectric switching arising from the rearrangement of 3d electrons and deformation of the FeII-centered coordination sphere. This work provides an approach to explore the interplay between magnetic, dielectric, and fluorescence properties, and holds significance for developing multifunctional molecular materials. [ABSTRACT FROM AUTHOR]

The modular construction method provides a feasible way to construct pre-designed cyano-bridged {LnIIIMIV/V} systems with more attractive structures and adjustable interactions between 4d/5d and 4f ions. In this work, the pentadentate Schiff-base ligands H2Ln (H2L1: 2,6-diacetylpyridine bis(nicotinoylhydrazone); H2L2: 2,6-diacetylpyridine bis(isonicotinoylhydrazone)) with multiple coordination sites were designed to coordinate with DyIII ions firstly, and then combined with K4M(CN)8·2H2O (M = W, Mo) by a liquid–liquid diffusion method to successfully synthesize two trinuclear structures {Dy[MIV(CN)8]0.5(HL1)(H2O)3}2·8H2O (1: M = W; 2: M = Mo), and two dinuclear structures {[Dy[MIV(CN)8](H3L2)(H2O)3]}·sol (3: M = W, sol = 11.5H2O; 4: M = Mo, sol = 2CH3OH·9.5H2O). Interestingly, deprotonation occurs in ligand H2L1 during the formation of complexes 1 and 2, while deprotonation/protonation processes both occur in ligand H2L2 during the synthesis of complexes 3 and 4. Magnetic analyses reveal that complexes 1–4 are all field-induced single-ion magnets (SIMs). The energy barriers (Ueff/kB) of complexes 1 and 2 are 92.83 K and 101.08 K, respectively, which are nearly three-fold higher than those of complexes 3 (30.19 K) and 4 (32.77 K). Ab initio calculations were performed on these series of {LnIIIMIV} heteronuclear complexes to provide more insights into the magnetic relaxation properties. This work provides another example of improving the SMM behaviors of cyano-bridged {LnIIIMIV} systems by deprotonation/protonation at different sites in the ligands. [ABSTRACT FROM AUTHOR]

Cyano‐bridged 4d–4f molecular nanomagnets have re‐called increasing research interests in molecular magnetism since they offer more possibilities in achieving novel nanomagnets with versatile structures and magnetic interactions. In this work, four β‐diketone ligands bearing different substitution N‐sites were designed and synthesized, namely 1‐(2‐pyridyl)‐3‐(3‐pyridyl)‐1,3‐propanedione (HL1), 1,3‐Bis (3‐pyridyl)‐1,3‐propanedione (HL2), 1‐(4‐pyridyl)‐3‐(3‐pyridyl)‐1,3‐propanedione (HL3), and 1,3‐Bis (4‐pyridyl)‐1,3‐propanedione (HL4), to tune the magnetic relaxation behaviors of cyano‐bridged {DyIIIMoV} systems. By reacting with DyCl3 ⋅ 6H2O and K4Mo(CN)8 ⋅ 2H2O, four cyano‐bridged complexes, namely {[Dy[MoV(CN)8](HL1)2(H2O)3]} ⋅ 6H2O (1), {[Dy[MoV(CN)8](HL2)(H2O)3(CH3OH)]}2 ⋅ 2CH3OH ⋅ 3H2O (2), {[Dy[MoV(CN)8](HL3)(H2O)2(CH3OH)] ⋅ H2O}n (3), and {[Dy[MoV(CN)8](HL4)2(H2O)3]} ⋅ 2H2O⋅CH3OH (4) were obtained. Structural analyses revealed that 1 and 4 are binuclear complexes, 2 has a tetragonal structure, and 3 exhibits a stair‐like polymer chain structure. The DyIII ions in all complexes have eight‐coordinated configurations with the coordination spheres DyO7N1 for 1 and 4, DyO6N2 for 2, and DyO5N3 for 3. Magnetic measurements indicate that 1 is a zero‐field single‐molecule magnet (SMM) and complexes 2–4 are field‐induced SMMs, with complex 4 featuring a two‐step relaxation process. The magnetic characterizations and ab initio calculations revealed that changing the N‐sites in the β‐diketone ligands can effectively alter the structures and magnetic properties of cyano‐bridged 4d–4f nanomagnets by adjusting the coordination environments of the DyIII centers. [ABSTRACT FROM AUTHOR]

Colossal and anisotropic thermal expansion is a key function for microscale or nanoscale actuators in material science. Herein, we present a hexanuclear compound of [(Tp*)FeIII(CN)3]4[FeII(Ppmp)]2⋅2 CH3OH (1, Tp*=hydrotris(3,5‐dimethyl‐pyrazol‐1‐yl)borate and Ppmp=2‐[3‐(2′‐pyridyl)pyrazol‐1‐ylmethyl]pyridine), which has a rhombic core structure abbreviated as {FeIII2FeII2}. Magnetic susceptibility measurements and single‐crystal X‐ray diffraction analyses revealed that 1 underwent thermally‐induced spin transition with the thermal hysteresis. The FeII site in 1 behaved as a spin crossover (SCO) unit, and significant deformation of its octahedron was observed during the spin transition process. Moreover, the distortion of the FeII centers actuated anisotropic deformation of the rhombic {FeIII2FeII2} core, which was spread over the whole crystal through the subsequent molecular rearrangements, leading to the colossal anisotropic thermal expansion. Our results provide a rational strategy for realizing the colossal anisotropic thermal expansion and shape memory effects by tuning the magnetic bistability. [ABSTRACT FROM AUTHOR]

Two 3d transition metal mononuclear complexes, [(Fe L 2)(ClO4)2]2·CH3CN (1) and (Co L 2)(ClO4)2·2CH3CN (2), have been prepared from a rigid tetradentate bpybox (L = 6,6′-bis(2,5-dihydrooxazol-4-yl)-2,2′-bipyridine) ligand. Single crystal X-ray diffraction analyses together with the help of calculations show that both compounds are octa-coordinate. Direct current magnetic studies reveal their significant magnetic anisotropy. Impressively, field-induced relaxation of magnetism is observed in the two complexes and the apparent anisotropy barriers are 14.1 K for 1 and 21.6 K for 2, respectively. Theoretical calculations reveal that two Fe(II) centers in 1 have small negative D values of −4.897 and −4.825 cm−1 and relatively small E values of 0.646 and 0.830 cm−1, indicating a uniaxial magnetic anisotropy. In contrast, the D and E values in the Co(II) center of 2 are 46.42 cm−1 and 11.51 cm−1, featuring a rhombic anisotropy. This work demonstrates that field-induced slow magnetic relaxation in 3d transition metal complexes with high coordination numbers can be manipulated through rigid ligand design. [ABSTRACT FROM AUTHOR]