Manipulating Electron-Transfer Events in [Fe4Co4] Cubes via a Mixed-Ligand Approach: The Impact of Elastic Frustration

Assembling Smallest Prussian Blue Analogs Using Chiral Hydrogen Bond-Donating Unit toward Complete Phase Transition

Exploring methods for assembling functional materials at the molecular level may yield functional expressions derived from the assembly method. This study developed novel switchable molecular assemblies characterized by abrupt, complete phase transitions promoted via hydrogen bonding with a chiral carboxylic acid. These assemblies were prepared by aggregating discrete molecules that are unresponsive to external stimuli. Furthermore, enantiopure hydrogen-bond donor (HBD) molecules provide switchable compounds with cooperative and abrupt phase transitions, whereas the racemic mixture of the HBD provides a hydrogen-bonded one-dimensional compound with a broad and incomplete phase transition when structural disordering is observed. This study presents a novel strategy for observing metal-to-metal electron-transfer-coupled spin transitions via hydrogen-bond formation.

Hierarchically Assembled Gigantic Fe/Co Cyanometallate Clusters Exhibiting Electron Transfer Behavior Above Room Temperature

The construction of large and complex supramolecular architectures through self-assembly is at the forefront of contemporary coordination chemistry. Notwithstanding great success in various systems using anionic bridges (e.g., O2- or S2-) or organic ligands (e.g., pyridine or carboxylate ligands), the assembly of large cyanide-bridged clusters with increasing nuclearity remains a formidable synthetic challenge. In this study, it is achieved in preparing two heterometallic cyanometallate clusters with unprecedented complexity, [Fe20Co20] (1) and [Fe12Co15] (2), by creating the "flexibility" through a versatile ligand of bis((1H-imidazol-4-yl)methylene)hydrazine (H2L) and low-coordinate cobalt. Complex 1 features a super-square array of four cyanide-bridged [Fe4Co4] cube subunits as the corners that are interconnected by four additional [FeCo] units, resulting in a torus-shaped architecture. Complex 2 contains a lantern-like core-shell cluster with a triple-helix kernel of [Co3L3] enveloped by a [Fe12Co12] shell. The combined structure analysis and mass spectrometry study reveal a hierarchical assembly mechanism, which sheds new light on constructing cyanometallate nanoclusters with atomic precision. Moreover, complex 1 undergoes a thermally induced electron-transfer-coupled spin transition (ETCST) between the diamagnetic {FeII LS(µ-CN)CoIII LS} and paramagnetic {FeIII LS(µ-CN)CoII HS} configurations (LS = low spin, HS = high spin) above room temperature, representing the largest molecule displaying electron transfer and spin transition characteristic.

3 nm-wide Cyanometallate Fe-Co Tape Exhibiting Single-Chain Magnet Behavior

Treatment of Co(OTf)2·6H2O, Li[(pzTp)FeIII(CN)3], and H3PMo12O40·nH2O in protic solvents afforded two structurally related Fe-Co cyanometallate complexes: [{(pzTp)Fe(CN)3}3Co3(MeOH)10][PMo12O40]·H2O·11MeOH (1, pzTp- = tetra(pyrazolyl)borate) and {[(pzTp)Fe(CN)3]4Co3(MeOH)5(H2O)3}n[HPMo12O40]n·3 nMeOH·6.5nH2O (2). Complex 1 consists of a cyanide-bridged hexanuclear [Fe3Co3] cage, characterized by the fused conjunction of two mutually perpendicular trigonal bipyramids (TBPs, [Fe2Co3] and [Co2Fe3]), while complex 2 showcases an intricate cyanide-bridged Fe-Co tape comprising a central chain backbone of vertex-sharing [Fe2Co3] TBPs alongside peripheral [Fe2Co2] squares. Complex 2 is among the widest one-dimensional coordination assemblies characterized by the single-crystal X-ray diffraction technique. Magnetic studies revealed that complex 2 behaved as a single chain magnet with an effective energy barrier (Ueff/kB) of 46.8 K. Our findings highlight the possibilities in the development of cyanometallate-POM hybrid materials with captivating magnetic properties.

Modulation of single-chain magnet behaviour in a heterometallic Fe2Co cyanide-bridged 2D sheet

A cyanide-bridged Fe2Co 2D sheet exhibiting electron transfer coupled spin transition (ETCST) with co-existence of magnetic ordering below 50 K is reported. The complex exhibits single-chain magnet behaviour where the uncoordinated water molecules act as an exchange-breaking impurity by allowing only a fraction of the molecule to undergo a spin state change. The paramagnetic centres prevail throughout the chain on desolvation, thereby increasing the number of correlated units in the chain.

Anthryl-functionalized cyanide-bridged Fe/Co cubes

Two anthryl-functionalized cyanide-bridged [Fe4Co4] cube complexes, [(pzTp)Fe(CN)3Co(TpEtOAn)]4[OTf]4·8MeCN·7Et2O (1) and [NEt4]3[(pzTp)Fe(CN)3Co(TpEtOAn)]4[OTf]7·5MeCN·2Et2O (2) (pzTp- = tetrapyrazolylborate, TpEtOAn = 2,2,2-tris-(pyrazol-1-yl)ethoxy(9-methyl-anthracene)), were synthesized and characterized. The crystallographic study revealed that the [Fe4Co4] cubes are arranged into a linear supramolecular chain through significant anthryl-anthryl π-π stacking interactions in complex 1, whereas a zigzag supramolecular 1D assembly is observed in 2. The magnetic measurements showed that both compounds exhibited incomplete transitions from the paramagnetic {FeIIILS(μ-CN)CoIIHS} state to the diamagnetic {FeIILS(μ-CN)CoIIILS} state at about 200 K. The luminescence measurement of 1 in solution revealed an enhancement of the emission upon dilution or addition of perfluoronaphthalene (PFN) molecules, which could be attributed to the suppression of the aggregation-caused quenching (ACQ) effect, suggesting possible aggregation of the cube units in the solution.