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The extreme sensitivity of trivalent lanthanide ions to crystal field variations led to the emergence of single-molecule magnetic switching under various stimuli. The use of pressure as an external stimulus instead of classic light irradiation, oxidation or any chemical reactions allows a fine tuning of the magnetic modulation. Here the well-known pure isotopically enriched [ 162 Dy(tta) 3 (L)]⋅C 6 H 14 ( 162 Dy) Single-Molecule Magnet (SMM) (tta - =2-2-thenoyltrifluoroacetonate and L=4,5-bis(propylthio)-tetrathiafulvalene-2-(2-pyridyl)benzimidazole-methyl-2-pyridine) was experimentally investigated by single-crystal diffraction and squid magnetometry under high applied pressures. Both reversible piezochromic properties and pressure modulation of the slow magnetic relaxation behavior were demonstrated and supported by ab initio calculations. The magnetic study of the diluted sample [ 162 Dy 0.05 Y 0.95 (tta) 3 (L)]⋅C 6 H 14 ( 162 Dy@Y) indicated that variations in the electronic structure have mainly intermolecular origin with weak intramolecular contribution. Quantitative magnetic interpretation concludes to a deterioration of the Orbach process for the benefit of both Raman and QTM mechanisms under applied pressure., (© 2023 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Paddlewheel-type binuclear complexes featuring metal-metal bonding have been the subject of widespread interest due to fundamental concern in their electronic structures and potential applications. Here, we explore the molecular and electronic structures of diiron(II,II) complexes with N,N'-diarylformamidinate ligands. While a paddlewheel-type diiron(II,II) complex with N,N'-diphenylformamidinate ligands (DPhF) exhibits the centrosymmetric [Fe 2 (μ-DPhF) 4 ] structure, a minor alteration in the ligand system, i. e., switching from phenyl to p-tolyl N-substituted formamidinate ligand (DTolF), resulted in the isolation of an unprecedented non-centrosymmetric [Fe(μ-DTolF) 3 Fe(κ 2 -DTolF)] complex. Both complexes were characterized using single-crystal X-ray diffraction, magnetic measurements, 57 Fe Mössbauer spectroscopy, and cyclic voltammetry along with high-level ab-initio calculations. The results provide a new view on a range of factors controlling the ground-state electronic configuration and structural diversity of homoleptic diiron(II,II) complexes. Model calculations determined that the Mayer bond orders for Fe-Fe interactions are significantly lower than 1 and equal to 0.15 and 0.28 for [Fe 2 (μ-DPhF) 4 ] and [Fe(μ-DTolF) 3 Fe(κ 2 -DTolF)], respectively., (© 2022 Wiley-VCH GmbH.)

Solution-based syntheses are omnipresent in chemistry but are often associated with obvious disadvantages, and the search for new mild and green synthetic methods continues to be a hot topic. Here, comparative studies in four different reaction media were conducted, that is, the solid-state mechano- and slow-chemistry synthesis, melted phase, and solution protocols, and the impact of the employed solvent-free solid-state versus liquid-phase synthetic approaches was highlighted on a pool of products. A moderately exothermic model reaction system was chosen based on bis(pentafluorophenyl)zinc, (C 6 F 5 ) 2 Zn, and 2,2,6,6-tetramethylpiperidinyl oxide (TEMPO) as a stable nitroxyl radical, anticipating that these reagents may offer a unique landscape for addressing kinetic and thermodynamic aspects of wet and solvent-free solid-state processes. In a toluene solution two distinct paramagnetic Lewis acid-base adducts (C 6 F 5 ) 2 Zn(η 1 -TEMPO) (1) and (C 6 F 5 ) 2 Zn(η 1 -TEMPO) 2 (2) equilibrated, but only 2 was affordable by crystallization. In turn, crystallization from the melt was the only method yielding single crystals of 1. Moreover, the solid-state approaches were stoichiometry sensitive and allowed for the selective synthesis of both adducts by simple stoichiometric control over the substrates. Density functional theory (DFT) calculations were carried out to examine selected structural and thermodynamic features of the adducts 1 and 2. Compound 2 is a unique non-redox active metal complex supported by two nitroxide radicals, and the magnetic studies revealed weak-to-moderate intramolecular antiferromagnetic interactions between the two coordinated TEMPO molecules., (© 2021 Wiley-VCH GmbH.)

Bistable and stimuli-responsive molecule-based materials are promising candidates for the development of molecular switches and sensors for future technologies. The CN-bridged {NH 4 [Ni(cyclam)][Fe(CN) 6 ]⋅5 H 2 O} n chain exists in two valence states: Ni II -Fe III (1 HT ) and Ni III -Fe II (1 LT ) and shows unique multiresponsivity under ambient conditions to various stimuli, including temperature, pressure, light, and humidity, which generate measurable response in the form of significant changes in magnetic susceptibility and color. The electron-transfer phase transition 1 LT ↔1 HT shows room-temperature thermal hysteresis, can be induced by irradiation, and shows high sensitivity to small applied pressure, which shifts it to higher temperatures. Additionally, it can be reversibly turned off by dehydration to the {NH 4 [Ni II (cyclam)][Fe III (CN) 6 ]} n (1 d) phase, which features the Ni II -Fe III valence state over the whole temperature range, but responds to pressure by yielding Ni III -Fe II above 1.06 GPa., (© 2020 Wiley-VCH GmbH.)

A two-step hysteretic Fe II spin crossover (SCO) effect was achieved in programmed layered Cs{[Fe(3-CNpy) 2 ][Re(CN) 8 ]}⋅H 2 O (1) (3-CNpy=3-cyanopyridine) assembly consisting of cyanido-bridged Fe II -Re V square grid sheets bonded by Cs + ions. The presence of two non-equivalent Fe II sites and the conjunction of 2D bimetallic coordination network with non-covalent interlayer interactions involving Cs + , [Re V (CN) 8 ] 3- ions, and 3-CNpy ligands, leads to the occurrence of two steps of thermal SCO with strong cooperativity giving a double thermal hysteresis loop. The resulting spin-transition phenomenon could be tuned by an external pressure giving the room-temperature range of SCO, as well as by visible-light irradiation, inducing an efficient recovery of the high-spin Fe II state at low temperatures. We prove that octacyanidorhenate(V) ion is an outstanding metalloligand for induction of a cooperative multistep, multiswitchable Fe II SCO effect., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Discrete molecular species that can perform certain functions in response to multiple external stimuli constitute a special class of multifunctional molecular materials called smart molecules. Herein, cyanido-bridged coordination clusters {[Fe II (2-pyrpy) 2 ] 4 [M IV (CN) 8 ] 2 }⋅4 MeOH⋅6 H 2 O (M=Mo (1 solv), M=W (2 solv) and 2-pyrpy=2-(1-pyrazolyl)pyridine are presented, which show persistent solvent driven single-crystal-to-single-crystal transformations upon sorption/desorption of water and methanol molecules. Three full desolvation-resolvation cycles with the concomitant change of the host molecules do not damage the single crystals. More importantly, the Fe 4 M 2 molecules constitute a unique example where the presence of the guests directly affects the pressure-induced thermal spin crossover (SCO) phenomenon occurring at the Fe II centres. The hydrated phases show a partial SCO with approximately two out-of-four Fe II centres undergoing a gradual thermal SCO at 1 GPa, while in the anhydrous form the pressure-induced SCO effect is almost quenched with only 15 % of the Fe II centres undergoing high-spin to low-spin transition at 1 GPa., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The photoinduced properties of the octacoordinated complex K 4 Mo IV (CN) 8 ⋅2 H 2 O were studied by theoretical calculations, crystallography, and optical and magnetic measurements. The crystal structure recorded at 10 K after blue light irradiation reveals an heptacoordinated Mo(CN) 7 species originating from the light-induced cleavage of one Mo-CN bond, concomitant with the photoinduced formation of a paramagnetic signal. When this complex is heated to 70 K, it returns to its original diamagnetic ground state, demonstrating full reversibility. The photomagnetic properties show a partial conversion into a triplet state possessing significant magnetic anisotropy, which is in agreement with theoretical studies. Inspired by these results, we isolated the new compound [K(crypt-222)] 3 [Mo IV (CN) 7 ]⋅3 CH 3 CN using a photochemical pathway, confirming that photodissociation leads to a stable heptacyanomolybdate(IV) species in solution., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The synthesis, crystal structures, spectroscopic characterization, and comprehensive quantum-chemical calculations for a novel series of anion-π hybrid salts (XPh 4 ) 2 [M(CN) 4 ][HAT(CN) 6 ]⋅3 MeCN (X=P, M=Ni II (1), Pd II (3), Pt II (5); X=As, M=Ni II (2), Pd II (4), Pt II (6); HAT(CN) 6 =1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile) are presented. The systems comprise 1D {[M(CN) 4 ] 2- ;[HAT(CN) 6 ]} ∞ stacks, in which the electron-rich metal complexes adjust their orientation to match the electron-deficient areas of HAT(CN) 6 . Electronic charge-transfer interactions along the stacks result in polarization of electron density within HAT(CN) 6 and in perturbations along the {[M(CN) 4 ] 2- ;[HAT(CN) 6 ]} ∞ contacts. Electronic structure analysis suggests, for example, a relocation of 0.1-0.2 e per molecule from [M(CN) 4 ] 2- to HAT(CN) 6 and anion-π interaction energies of around -65 kcal mol -1 . A reversible structural single-crystal-to-single-crystal transformation, through desolvation/resolvation processes in the solid state, is also reported and a scheme for the formation of anion-π [M(CN) 4 ] 2- /HAT(CN) 6 adducts in MeCN is proposed., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The homoleptic mononuclear compound [Co(bpp-COOMe) 2 ](ClO 4 ) 2  (1) (bpp-COOMe=methyl 2,6-di(pyrazol-1-yl)pyridine-4-carboxylate) crystallizes in the monoclinic C2/c space group, and the cobalt(II) ion possesses a pseudo-octahedral environment given by the two mer-coordinated tridentate ligands. Direct-current magnetic data, single-crystal torque magnetometry, and EPR measurements disclosed the easy-axis nature of this cobalt(II) complex, which shows single-molecule magnet behavior when a static field is applied in alternating-current susceptibility measurements. Diamagnetic dilution in the zinc(II) analogue [Zn(bpp-COOMe) 2 ](ClO 4 ) 2  (2) afforded the derivative [Zn 0.95 Co 0.05 (bpp-COOMe) 2 ](ClO 4 ) 2  (3), which exhibits slow relaxation of magnetization even in zero field thanks to the reduction of dipolar interactions. Theoretical calculations confirmed the overall electronic structure and the magnetic scenario of the compound as drawn by experimental data, thus confirming the spin-phonon Raman relaxation mechanism, and a direct quantum tunneling in the ground state as the most plausible relaxation pathway in zero field., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A huge increase in the magnetization of two coordination chains based on tetravalent octacyanidometalates (W IV and Mo IV ) is observed on irradiation with 436 nm light, while no such behavior is observed for the Nb IV analogue. A photomagnetic response based solely on [W IV (CN) 8 ] 4- is demonstrated for the first time. The observed behavior is attributed to the light-induced excited spin state trapping (LIESST) effect at the octacyanidometalate, and to the resulting magnetic exchange ON/OFF photoswitching between the Mn II center and the photoinduced high-spin (S=1) W IV or Mo IV centers., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A family of distorted trigonal pyramidal transition-metal complexes [M II (N 3 N)Li(THF)] (M=Mn, Fe, Co, Ni) have been studied as candidates for mononuclear single-molecule magnets. Magnetic anisotropy of the family depends on the electronic configuration of the central ion, with the Co analogue exhibiting pronounced SMM behavior., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The heptacyanotungstate(IV) anion was isolated in the salt (n-Bu4 N)3 [W(IV) (CN)7 ] (1) from the reduction of (n-Bu4 N)3 [W(V) (CN)8 ] with concomitant loss of one cyanide ligand. The anion in 1 adopts a slightly distorted pentagonal bipyramidal geometry with an average W-C distance of 2.169 Å. The spectroscopic and magnetic properties are described., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Given the recent advent of mononuclear single-molecule magnets (SMMs), a rational approach based on lanthanides with axially elongated f-electron charge cloud (prolate) has only recently received attention. We report herein a new SMM, [Li(THF)4[Er{N(SiMe3)2}3Cl]⋅2 THF, which exhibits slow relaxation of the magnetization under zero dc field with an effective barrier to the reversal of magnetization (ΔEeff/kB =63.3 K) and magnetic hysteresis up to 3 K at a magnetic field sweep rate of 34.6 Oe s(-1). This work questions the theory that oblate or prolate lanthanides must be stabilized with the appropriate ligand framework in order for SMM behavior to be favored., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Lanthanide-based extended coordination frameworks showing photocontrolled single-molecule magnet (SMM) behavior were prepared by combining highly anisotropic Dy(III) and Ho(III) ions with the carboxylato-functionalized photochromic molecule 1,2-bis(5-carboxyl-2-methyl-3-thienyl)perfluorocyclopentene (H2 dae), which acts as a bridging ligand. As a result, two new compounds of the general formula [{Ln(III) 2 (dae)3 (DMSO)3 (MeOH)}⋅10 MeOH]n (M=Dy for 1 a and Ho for 2) and two additional pseudo-polymorphs [{Dy(III) 2 (dae)3 (DMSO)3 (H2 O)}⋅x MeOH]n (1 b) and [{Dy(III) 2 (dae)3 (DMSO)3 (DMSO)}⋅x MeOH]n (1 c) were obtained. All four compounds have 2D coordination-layer topologies, in which carboxylate-bridged Ln2 units are linked together by dae(2-) anions into grid-like frameworks. All four compounds exhibited a strong reversible photochromic response to UV/Vis light. Moreover, both 1 a and 2 show field-induced SMM behavior. The slow magnetic relaxation of 1 a is influenced by the photoisomerization reaction leading to the observation of the cross-effect: photocontrolled SMM behavior., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)