Manipulating the spin crossover behaviour in a series of cyanide-bridged {FeIII2FeII2} molecular squares through NCE⁻ co-ligands

Abstract

Manipulating the transition temperature (T1/2) of spin-crossover (SCO) complexes capable of fulfilling practical criteria through different synthetic strategies is one of the main focuses in the field of molecular magnetism....

Cyanido-Bridged Heterobimetallic Molecular Squares: Low-Dimensional Models of Prussian Blue Analogues and Beyond

“…Consequently, the d - d / d ′ squares became a very fruitful research area devoted to the magnetic behavior of the tetranuclear PBAs. Among the cyanido building-blocks, the dicyano-[Fe II/III (AA) 2 (CN) 2 ] n+ (AA = didentate ligand; n = 0 and 1) − and tricyano- fac -[M­(CN) 3 {RB­(R′(pz) 3 }] (R = H, methyl, 2-methyl propyl, pyrazol; R′ = H, methyl) derivatives − proved to be suitable to synthesize molecular squares in their reactions with 3 d metal ions whose coordination sphere is partially blocked with didentate AA ligands, such as bipy, 4,4′-dimethyl 2,2′-bipyridine (4,4′-Me 2 bipy), and 1,10-phenantroline (phen) or a tridentate one coordinated to the M III cation in a fac stereochemistry.…”

“…The cyanido-based fac -[Fe III (CN) 3 {RB­(R 1–3 (pz) 3 }] − complexes, bearing three coordination sites blocked by the pyrazolylborate type ligand and three terminal cyanide groups in a fac arrangement, were extensively used to assemble molecular squares (R = H, 2-methylpropyl, pyrazol; R 1,2,3 = H, methyl; Scheme ). Therefore, the resulting d - d / d ′ square-like tetranuclear compounds became a rich area of investigation of reversible thermal-/light-/X-ray induced magnetism, ,− spin crossover, − as well as slow relaxation of the magnetization and SMM properties. − …”

“…More recently, Zhang et al reported a series of mixed-valence {Fe III Fe II } 2 square-like molecules of general formula {[{HBR 3,5 (pz) 3 }­Fe III (CN) 3 ] 2 [Fe II (TPPO)­(NCX)] 2 }·Sol resulted from the assembling of the [Fe­{HBR 3,5 (pz) 3 }­(CN) 3 ] − metalloligand and the in situ preformed [Fe II (TPPO)­(NCX)] + complex cation [X = S, Se, and BH 3 with Sol = 2CH 3 OH·6H 2 O, 2MeCN·2CH 2 Cl 2 ·2H 2 O, and 4CH 3 OH·2MeCN, respectively; TPPO = tris­(2-pyridyl)­phosphine oxide]. These three compounds undergo complete spin crossover processes from {Fe LS III Fe HS II } to {Fe LS III Fe LS II }, characterized by an increase of T 1/2 from 214 to 250 and 288 K, as far as the ligand field becomes stronger along the series E = S, Se, and BH 3 (Figure a).…”

“…Views of the cyanido-bridged mixed-valence (a) square-shaped tetranuclear unit {[{HBR 3,5 (pz) 3 }­Fe III (CN) 3 ] 2 [Fe II (TPPO)­(NCX)] 2 } and (b) hexanuclear entity {[{HBR 4 (pz) 3 }­Fe II (CN) 3 ] 2 [Fe III (tpa)] 2 [Fe III (OR′)­(tpa)] 2 } 6+ with an inner square motif …”

Mixed-valence {FeII2FeIII4} hexanuclear complexes with thermally induced Fe(iii) spin-crossover behavior

“…30–39 In various studies, scholars have prepared a series of low-dimensional polycyanide metal salt complexes whose structural backbone contains the Fe III –CN–M II sequence (M II = Fe II , Co II , and Mn II ), including bis, tri, tetra, octa, and pentadecanuclear complexes. 40–44 These molecules exhibit remarkable thermally induced SCO magnetic bistable properties. The primary synthetic strategies mentioned in the literature to bring out synergistic effects are: (1) covalent junctions (bridging ligands) to form coordination polymers, 45–48 (2) π–π stacking among the SCO sites, 49–51 and (3) hydrogen bonding.…”