A photoisomerizable diarylethene-derived ligand, phen*, has been successfully introduced into a spin-crossover iron(II) complex, [Fe(H2B(pz)2)2phen*] (1; pz =1-pyrazolyl). A ligand-based photocyclization (photocycloreversion) in 1 modifies the ligand field, which, in turn, results in a highly efficient paramagnetic high-spin → diamagnetic low-spin (low-spin → high-spin) transition at the coordinated Fe(II) ion. The reversible photoswitching of the spin states, and thus the associated magnetic properties, has been performed in solution at room temperature and has been directly monitored by measuring the magnetic susceptibility via the Evans method. The observed spin-state photoconversion in 1 exceeds 40%, which is the highest value for spin-crossover molecular switches in solution at room temperature reported to date. The photoexcited state is extraordinarily thermally stable, showing a half-time of about 18 days in solution at room temperature. Because of the outstanding photophysical properties of diarylethenes, including single-crystalline photochromism, molecular switch 1 may offer a promising platform for controlling the magnetic properties in the solid state and ultimately at the single-molecule level with light at room temperature.

Spin-crossover metal complexes are highly promising magnetic molecular switches for prospective molecule-based devices. The spin-crossover molecular photoswitches developed so far operate either at very low temperatures or in the liquid phase, which hinders practical applications. Herein, we present a molecular spin-crossover iron(II) complex that can be switched between paramagnetic high-spin and diamagnetic low-spin states with light at room temperature in the solid state. The reversible photoswitching is induced by alternating irradiation with ultraviolet and visible light and proceeds at the molecular level.

During the past 10 years iron-catalyzed reactions have become established in the field of organic synthesis. For example, the complex anion [Fe(CO)3 (NO)](-) , which was originally described by Hogsed and Hieber, shows catalytic activity in various organic reactions. This anion is commonly regarded as being isoelectronic with [Fe(CO)4 ](2-) , which, however, shows poor catalytic activity. The spectroscopic and quantum chemical investigations presented herein reveal that the complex ferrate [Fe(CO)3 (NO)](-) cannot be regarded as a Fe(-II) species, but rather is predominantly a Fe(0) species, in which the metal is covalently bonded to NO(-) by two π-bonds. A metal-N σ-bond is not observed.

Thin films of a molecular spin crossover iron(ii) complex featuring a photochromic diarylethene-based ligand have been grown by sublimation in ultra-high vacuum on Au(111) and investigated by photoelectron spectroscopies.

Thin films of Fe(ii) complex with a diarylethene-based ligand featuring spin-crossover have been grown by sublimation in ultra-high vacuum on highly oriented pyrolytic graphite and spectroscopically characterized through a multi technique approach.

Fe‐katalysierte Reaktionen haben sich in den vergangenen 10 Jahren fest in der organischen Synthese etabliert. Das ursprünglich von Hogsed und Hieber beschriebene komplexe Ferrat [Fe(CO)3(NO)]− zeigt katalytische Aktivität in zahlreichen organischen Reaktionen und wird allgemein als isoelektronisch zum [Fe(CO)4]2− betrachtet. Allerdings zeigt der letztgenannte Komplex kaum katalytische Aktivität. Die hier vorgestellten spektroskopischen und quantenchemischen Untersuchungen zeigen, dass das komplexe Ferrat [Fe(CO)3(NO)]− nicht wie angenommen als eine Fe−II‐Spezies, sondern vielmehr als eine Fe0‐Spezies, in der das Metall kovalent über zwei π‐Bindungen an ein NO− gebunden ist, aufgefasst werden sollte. Eine Metall‐N‐σ‐Bindung wird nicht beobachtet.

Spin-crossover metal complexes are highly promising magnetic molecular switches for prospective moleculebased devices.T he spin-crossover molecular photoswitches developed so far operate either at very low temperatures or in the liquid phase,which hinders practical applications.Herein, we present am olecular spin-crossover iron(II) complex that can be switched between paramagnetic high-spin and diamagnetic low-spin states with light at room temperature in the solid state.T he reversible photoswitching is induced by alternating irradiation with ultraviolet and visible light and proceeds at the molecular level.Spin-crossover (SCO) metal complexes are aw ell-known class of molecular switches whose magnetic,c onductive, color,and other physicochemical properties can be reversibly switched by external triggers,s uch as temperature,p ressure, or light.[1] Six-coordinate iron(II) species,which are the most common SCO complexes,o ffer the opportunity to shift reversibly between diamagnetic low-spin (LS, S = 0) and paramagnetic high-spin (HS, S = 2) electronic states.S uch SCO metal complexes are considered as promising candidates for future applications in molecular electronics and spintronics,c ommunication networks,u ltra-high-density memory systems,displays,and sensors. [2] To be integrated into devices,amolecular switch should ideally operate under ambient conditions:a tr oom temperature and atmospheric pressure.M uch effort has therefore been devoted to the design of SCO complexes that are switchable at room temperature.[3] Systems featuring at hermal hysteresis loop near room temperature and thus showing athermally induced memory effect under ambient conditions have been highly desired. [2a,4] However,a ddressing the spin state with light is more attractive because of short response times,l ow power dissipation, and high selectivity.T hus, bistable coordination polymers that are switchable by means of ap hotoinduced phase transition at room temperature were developed.[5] This type of switching requires strong interaction between monomeric units,asachieved by covalent bonding within the crystal lattice of the polymer.Importantly, switching at the single-molecule level is fundamentally impossible in such systems,t hus diminishing the potential advantage of SCO switches over established bistable bulkphase materials and nanomaterials used in modern technology.P hotoswitching genuinely at the single-molecule level has been realized in the light-induced excited spin state trapping (LIESST) effect.

A bisoxamate ligand containing three different types of coordination sites was designed and synthesized. The developed synthetic strategy was adopted to prepare a related 1,2-bis(2-hydroxybenzamido)benzene-derived ligand. Nickel(II) complexes of both the novel ligands were obtained and characterized by X-ray crystallography, NMR, electronic absorption spectroscopy, and theoretical calculations.