Two new perovskite-like coordination polymers, A2[KFe­(CN)6], were constructed by employing guanidinium and acetamidinium as A-site cations, respectively. Their cation-controlled two-step phase transitions as well as the relevant dielectric responses were uncovered by the combined techniques of the variable-temperature single-crystal X-ray structural analyses and dielectric measurements. With a similar size and shape, the A-site cations reveal similar two-step thermal-induced transitions on their motional dynamics, i.e., from a frozen order state to an in-plane rotational disorder state, and to a melt-like disorder state. However, the variation of the A-site cations on their symmetries and dipole moments makes noticeable impacts on the symmetry breaking, the critical temperatures, and the dielectric responses for the two-step structural phase transitions, i.e., the D 3h nonpolar guanidinium results in an R3̅c ↔ R3̅m ↔ Fm3̅m transition, whereas the C 2v polar acetamidinium results in a C2/m ↔ R3̅m ↔ Fm3̅m transition. Investigations of these two coordination polymers demonstrate a fine modulation on the phase transition behaviors and dielectric responses by changing the symmetries and dipole moments of A-site cations.

The first thiocyanate-bridged double perovskite-type coordination polymer [NH 4 ] 2 [NiCd(SCN) 6 ] is reported here, which undergoes a reversible structural phase transition at around 120 K. An orderdisorder mechanism for this transition is disclosed by X-ray structural analyses, dielectric measurement, as well as molecular dynamics simulations.

Stimuli‐responsive materials that can be reversibly switched by light are of immense interest. Among them, photo‐responsive spin crossover (SCO) complexes have great promises to combine the photoactive inputs with multifaceted outputs into switchable materials and devices. However, the reversible control the spin‐state change by photochromic guests is still challenging. Herein, we report an unprecedented guest‐driven light‐induced spin change (GD‐LISC) in a Hofmann‐type metal–organic framework (MOF), [Fe(bpn){Ag(CN)2}2]⋅azobenzene. (1, bpn=1,4‐bis(4‐pyridyl)naphthalene). The reversible trans–cis photoisomerization of azobenzene guest upon UV/Vis irradiation in the solid‐state results in the remarkable magnetic changes in a wide temperature range of 10–180 K. This finding not only establishes a new switching mechanism for SCO complexes, but also paves the way toward the development of new generation of photo‐responsive magnetic materials.

Treatment of CoCl 2 •6H 2 O and tris(pyrazolyl-1-yl)borate tricyanoiron(III) anions at 55 °C afforded a series of new Fe-Co polynuclear clusters: {Co 2 Cl 2 (DMF) 4 [(Tp 4-Me )Fe(CN) 3 ] 2 } (1; Tp 4-Me = hydridotris(4methylpyrazol-1-yl)borate), (H 3 O + )@{Co 4 Cl 4 [(Tp 4-Me )Fe(CN) 3 ] 4 } (2), (MePh 3 P) 4 {Co 6 Cl 6 [(Tp 4-Me )Fe(CN) 3 ] 6 }•15CH 3 CN•3CH 3 OH•2H 2 O (3), and (BnEt 3 N) 4 {Co 5 Cl 8 [(Tp*)Fe(CN) 3 ] 4 }•4CH 3 CN•2H 2 O (4; Tp*= hydridotris(3,5dimethylpyrazol-1-yl)borate). They feature an asymmetric [Fe 2 Co 2 (CN) 4 ] square, a pseudocubic [Fe 4 Co 4 (CN) 12 ] cluster, a distorted-hexagonal-prism-shaped [Fe 6 Co 6 (CN) 18 ] cage, and a bis(trigonal-bipyramidal) cluster of [Fe 4 Co 5 (CN) 12 ] fused at one cobalt center, respectively. The Co(II) ions adopt a four-coordinate tetrahedral geometry except for half of 1 in an octahedral geometry. It should be mentioned that 3 and 4 provide two novel molecular skeletons in the cyanometalate family. Interestingly, 1 behaved as a single-molecule magnet with an effective energy barrier for spin reverse of 30.7 K at zero dc field. Our result demonstrated a possible self-assembly route toward high-nuclearity cyanide-bridged clusters by introducing four-coordinate cobalt(II) ions.

The pursuit of spin crossover (SCO) materials with photo-switchable multistability is driven by the fascinating perspectives toward light-response switches and opto-magnetic memory devices. Herein, we report a 3D Hofmann-type metal...