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

Abstract

The cyanido-bridged square-like molecules with d/f metal ions occupying the corners of the square are considered molecular models of the Prussian Blue Analogues (PBAs) because they reproduce one face of their 3D face-centered cubic structure, being called low-dimensional PBAs. Such highly regular complexes provide unique insights into the short-range magnetic exchange interaction between the metal ions of PBAs and exhibit magnetic properties which are not found for PBAs. This review focuses on the preparative routes and magneto-structural characterization of d-d(d′)/d-f tetranuclears with a square-like topology generating rich families of molecular switches and nanomagnets. Relevant examples that provided a better comprehension of the magnetic behavior of PBAs, including subtle chemical factors that interfere in the photo- and thermally induced electron transfer are reviewed herein. A special attention is paid to the design of d-f cyanido-bridged squares, less numerous compared to the d-d/d′ ones, that proved to be suitable model compounds for the theoretical treatment of the magnetic exchange interaction between d and f spin carriers across the cyanide ligand. The square-shaped PBAs represent a very active area of research that is enriched yearly with new examples with potential for the development of molecular-scaled electronic devices.

Alkoxy-Bridged Dicopper(II) Cores Meet Tetracyanonickelate Linkers: Structural, Magnetic, and Theoretical Investigation of Cu/Ni Coordination Polymers

“…Heterometallic coordination polymers (CPs) incorporating magnetically active building blocks have gained increased attention in recent years because of possible cooperative phenomena of the magnetic spins. − The strongest magnetic coupling between the spins of the nearest-neighbor paramagnetic centers is typically mediated by short bridging ligands, including oxo, cyano, azido, or carboxylate moieties, which have extensively been studied due to their ability to transmit magnetic exchange of different nature and magnitude. − Considering the dependence of the magnetic interactions on the type of metal ion and the superexchange path, the selection of transition metals and bridging groups emerges as a key feature in the construction of heterometallic coordination systems. , …”

Near room temperature stepwise spin state switching and photomagnetic effect in a mixed-valence molecular square

“…Such photomagnetic effect is associated with the metal-to-metal electron transfer (MMET) from Fe II LS to Co III LS center, which is coupled with spin-state switching at the cobalt center. 9,11–13 In the last few decades, several groups across the world have been investigating strategies to reduce the dimensionality of PB or PBAs and to build their molecular model complexes, which will possess similar physical properties as that of the parent compounds. Following the complex as ligand strategy, numerous examples of molecular analogues of PBAs, such as molecular cube, 14–17 square, 11,18–52 dinuclear unit, 53–56 and chain, 57–62 have been synthesized and reported based on the use of [Fe III (L)(CN) x ] − metalloligand towards partially blocked cobalt precursors (L = poly(pyrazolyl) scorpionate ligand), some of which exhibit MMET, spin crossover (SCO), single-molecule magnet (SMM), and single-chain magnet (SCM) behavior.…”

“…9,11–13 In the last few decades, several groups across the world have been investigating strategies to reduce the dimensionality of PB or PBAs and to build their molecular model complexes, which will possess similar physical properties as that of the parent compounds. Following the complex as ligand strategy, numerous examples of molecular analogues of PBAs, such as molecular cube, 14–17 square, 11,18–52 dinuclear unit, 53–56 and chain, 57–62 have been synthesized and reported based on the use of [Fe III (L)(CN) x ] − metalloligand towards partially blocked cobalt precursors (L = poly(pyrazolyl) scorpionate ligand), some of which exhibit MMET, spin crossover (SCO), single-molecule magnet (SMM), and single-chain magnet (SCM) behavior. Based on the temperature-dependence of magnetization, generally, five different types of SCO systems have been observed, namely abrupt, gradual, hysteretic, stepwise, and incomplete type.…”

Manipulating Metal-to-Metal Electron Transfer in Cyano-Bridged [Fe2Co]-Assembled Coordination Polymers

“…In 2004, Dunbar and co-workers reported a discrete pentanuclear [Fe 2 Co 3 ] complex realizing thermally induced ETCST at the molecular level . Until now, numerous cyano-bridged FeCo polynuclear complexes − and coordination polymers − ,− exhibiting the ETCST phenomenon have been reported. The systematic study of the structure–property relationships in the ETCST complexes is invaluable for exploring and strategically fabricating the electron transfer materials with switchable characteristics and functions.…”