Manipulating Fe(II) spin states to achieve higher anti-tumor cell activities in multinuclear complexes.

Exploring the different spin states of central metals in the complex to regulate the anti-tumor activity of cancer cells is of great significance in drug design and clinical use. However, it is a challenge to build a strong coupling between spin states and anti-tumor activities in one system. Herein, we present two complexes {FeL[Pd(CN)]}·2HO (L = Bztpen (1), Bztppn (2); Bztpen = -benzyl-,','-tris(2-pyridylmethyl)ethylenediamine, Bztppn = -benzyl-,','-tris(2-pyridylmethyl)propylenediamine) showing different cytotoxic activities actuated by fine-tuning the structure with different spin states of Fe(II).

Effects of mono- or di-fluoro-substitution on spin crossover behavior in a pair of Schiff base-like Fe-coordination polymers.

Spin crossover (SCO) has long been a hot topic in the field of molecular magnetism owing to its unique bistability character. Rational control of thermal hysteresis and transition temperature () is crucial for their practical applications, which rely on precise manipulation of the substituents of SCO coordinating ligands and molecular packing interactions. In this study, we designed two different bridging ligands (2-FDPB: 4,4'-(2-fluoro-1,4-phenylene)dipyridine; 2,3-FDPB: 4,4'-(2,3-difluoro-1,4-phenylene)dipyridine) featuring one and two fluoro substitution on the central benzene ring and applied a Schiff base-like equatorial tetradentate ligand {diethyl(,)-2,2'-[4,5-difluoro-1,2-phenyl-bis(iminomethylidyne)]bis(3-oxobutanoate)-(2-)-,',O3,O3'} (HL) to coordinate with the Fe ion.

Reversible light-induced spin state switching in a dinuclear Fe(II) spin crossover complex.

A dinuclear Fe(II) spin crossover (SCO) complex with the formula [FeL(NCS)]·2DMF·2HO (1) was synthesised from 1-naphthylimino-1,2,4-triazole (L). Complex 1 exhibits an incomplete thermally induced spin transition with a transition temperature of 95 K and a thermally trapped metastable high-spin state at low temperatures. Furthermore, it undergoes a reversible light-induced spin crossover by alternate irradiation with 532 and 808 nm lasers.

Simultaneous magneto-dielectric transitions in a fluorescent Hofmann-type coordination polymer.

The design of magnetic molecular materials exhibiting multiple functions has garnered significant interest owing to their potential applications in molecular switches, sensors, and data storage devices. In this study, we synthesized a two-dimensional (2D) Fe-based Hofmann-type coordination polymer, namely {Fe(DPPE)[Ag(CN)]}·2EtOH (1), using a luminescent ligand 1,1-diphenyl-2,2-di(4-pyridylbiphenyl)ethylene (DPPE). Single-crystal structural analyses and magnetic measurements revealed a thermally induced spin crossover (SCO) with the transition temperature = 231 K.

Manipulating fluorescence by photo-switched spin-state conversions in an iron(ii)-based SCO-MOF.

Manipulating fluorescence by photo-switched spin-state conversions is an attractive prospect for applications in smart magneto-optical materials and devices. The challenge is how to modulate the energy transfer paths of the singlet excited state by light-induced spin-state conversions. In this work, a spin crossover (SCO) Fe-based fluorophore was embedded into a metal-organic framework (MOF) to tune the energy transfer paths.

Regulating Magnetic Relaxations of Cyano-Bridged {Dy Mo } Systems by Tuning the N-Sites in β-Diketone Ligands.

Cyano-bridged 4d-4f molecular nanomagnets have re-called increasing research interests in molecular magnetism since they offer more possibilities in achieving novel nanomagnets with versatile structures and magnetic interactions. In this work, four β-diketone ligands bearing different substitution N-sites were designed and synthesized, namely 1-(2-pyridyl)-3-(3-pyridyl)-1,3-propanedione (HL ), 1,3-Bis (3-pyridyl)-1,3-propanedione (HL ), 1-(4-pyridyl)-3-(3-pyridyl)-1,3-propanedione (HL ), and 1,3-Bis (4-pyridyl)-1,3-propanedione (HL ), to tune the magnetic relaxation behaviors of cyano-bridged {Dy Mo } systems. By reacting with DyCl  ⋅ 6H O and K Mo(CN)  ⋅ 2H O, four cyano-bridged complexes, namely {[Dy[Mo (CN) ](HL ) (H O) ]} ⋅ 6H O (1), {[Dy[Mo (CN) ](HL )(H O) (CH OH)]}  ⋅ 2CH OH ⋅ 3H O (2), {[Dy[Mo (CN) ](HL )(H O) (CH OH)] ⋅ H O} (3), and {[Dy[Mo (CN) ](HL ) (H O) ]} ⋅ 2H O⋅CH OH (4) were obtained.

Colossal Anisotropic Thermal Expansion through Coupling Spin Crossover and Rhombus Deformation in a Hexanuclear {Fe Fe } Compound.

Colossal and anisotropic thermal expansion is a key function for microscale or nanoscale actuators in material science. Herein, we present a hexanuclear compound of [(Tp*)Fe (CN) ] [Fe (Ppmp)] ⋅2 CH OH (1, Tp*=hydrotris(3,5-dimethyl-pyrazol-1-yl)borate and Ppmp=2-[3-(2'-pyridyl)pyrazol-1-ylmethyl]pyridine), which has a rhombic core structure abbreviated as {Fe Fe }. Magnetic susceptibility measurements and single-crystal X-ray diffraction analyses revealed that 1 underwent thermally-induced spin transition with the thermal hysteresis.

Bistable Optoelectronic Properties Originated from the Scissoring Motion of the TEMPO Skeleton in Supramolecular Radical Ferroelectrics.

Bistable materials with multiphysical channels, such as optical, electrical, and magnetic properties, have been paid dramatic attention due to their alternativity of the signal status in electronic devices. Herein, three stable supramolecular radicals ([(NH-TEMPO)(18-crown-6)][XF] (, X = P; , X = As; , X = Sb)) were synthesized and characterized. The former two molecules present ferroelectric phase transitions around 381.

Constructing spin crossover-fluorescence bifunctional iron(II) complexes based on tetraphenyl ethylene-decorated AIEgens.

Investigating spin crossover (SCO)-fluorescence bifunctional materials and establishing their structure-function relationships are attractive topics in chemistry and materials science. However, it remains challenging to preserve the fluorescence and SCO properties simultaneously in aggregated solid states. Herein, we design an ()-2,6-bis(1-pyrazol-1-yl)-4-(4-(1,2,2-triphenylvinyl)styryl)pyridine (tpe-bpp) ligand, which contains coordinated SCO and fluorescence units of an aggregation-induced emission luminogen (AIEgen).

Simultaneous Photo-Induced Magnetic and Dielectric Switching in an Iron(II)-Based Spin-Crossover Hofmann-Type Metal-Organic Framework.

Molecular materials possessing photo-tunable polarization switching is promising for optical switches, smart sensors, and data storage devices. However, it is challenging to devise a molecular material featuring simultaneous switchable magnetic and dielectric properties with regard to non-invasive and convenient light stimulus. Herein, we report a new Hofmann-type metal-organic framework (MOF) {Fe(bpt)[Pt(CN) ]} ⋅ 0.

Spin-Crossover Tuned Rotation of Pyrazolyl Rings in a 2D Iron(II) Complex towards Synergetic Magnetic and Dielectric Transitions.

Materials showing synergy of magnetic and dielectric transitions are promising candidates for future molecular devices. The challenge is how to realize synergy between spin and dielectric transitions with responses to external stimuli. Herein, we design a 2D spin crossover (SCO) complex, [Fe (dpa)][(pzTp)Fe (CN) ] (1) (dpa=1,2-bis(4-pyridyl)ethyne and pzTp=tetrakis(pyrazolyl)borate).

Construction of spin-crossover dinuclear cobalt(II) compounds based on complementary terpyridine ligand pairing.

The self-assembly of multinuclear SCO complexes is appealing in which unique properties may be discovered due to enhanced intramolecular and intermolecular interactions. In this work, three dinuclear cobalt(II) complexes, named Co-1, Co-2, and Co-3, were prepared based on a complementary terpyridine ligand pair strategy. The complexes were accurately synthesized by the solvothermal method in which dinuclear complexes were directional assemblies from cobalt(II) ions, terpy bearing 2,6-dimethoxyphenyl substituents at the terpyridyl 6,6''-positions, and ditopic terpy built with different linkers (alkynyl for 1, diynyl for 2, and phenyl for 3).

Slow magnetic relaxation in mononuclear octa-coordinate Fe(II) and Co(II) complexes from a Bpybox ligand.

Two 3d transition metal mononuclear complexes, [(FeL)(ClO)]·CHCN (1) and (CoL)(ClO)·2CHCN (2), have been prepared from a rigid tetradentate bpybox (L = 6,6'-bis(2,5-dihydrooxazol-4-yl)-2,2'-bipyridine) ligand. Single crystal X-ray diffraction analyses together with the help of calculations show that both compounds are octa-coordinate. Direct current magnetic studies reveal their significant magnetic anisotropy.

[Au(CN)]-Armed [FeFe] Square Complex Showing Unusual Spin-Crossover Behavior Due to a Symmetry-Breaking Phase Transition.

The incorporation of two different cyanide building blocks of [(Tp)Fe(CN)] and [Au(CN)] into one molecule afforded a novel hexanuclear [FeFeAu] complex (), in which the cyanide-bridged [FeFe] square was further grafted by two [Au(CN)] fragments as long arms in orientations. Complex undergoes a gradual spin crossover (SCO) ffrom low-spin (LS) to high-spin (HS) state for the Fe(II) centers upon desolvation. Remarkably, its desolvated phase () exhibits a reversible but atypical two-step (sharp-gradual) SCO behavior with considerable hysteresis (21 K).

Manipulating Selective Metal-to-Metal Electron Transfer to Achieve Multi-Phase Transitions in an Asymmetric [Fe Co]-Assembled Mixed-Valence Chain.

Manipulation of multi-functions in molecular materials is promising for future switching and memory devices, although it is currently difficult. Herein, we assembled the asymmetric {Fe Co} unit into a cyanide-bridged mixed-valence chain {[(Tp)Fe(CN) ] Co(BIT)} ⋅ 2CH OH (1) (Tp=hydrotris(pyrazolyl)borate and BIT=3,4-bis-(1H-imidazol-1-yl)thiophene), which showed reversible multi-phase transitions accompanied by photo-switchable single-chain magnet properties and a dielectric anomaly. Variable-temperature X-ray structural studies revealed thermo- and photo-induced selective electron transfer (ET) between the Co and one of the Fe ions.

Four mononuclear dysprosium complexes with neutral Schiff-base ligands: syntheses, crystal structures and slow magnetic relaxation behavior.

Four mononuclear 9-coordinate Dy-based complexes, [Dy(HL)(NO)(CHOH)] (1Dy), [Dy(HL)(NO)(HO)] (2Dy), [Dy(HL)(NO)]·CHCN (3Dy), and [Dy(HL)(NO)] (4Dy), have been constructed by neutral Schiff-base ligands (1-[-(4-R)aminomethylidene-2()-naphthalenone, R = -Cl (HL), -NO (HL), -OCH (HL), -I (HL)). By tuning the terminal substituent group of HL ligands, the number of HL ligands coordinated to the central Dy ion unexpectedly varies from 2 to 3, and the local symmetry around the Dy ion reduces from to . Magnetic measurements reveal that 2Dy can display single-ion magnet (SIM) behavior in zero dc field, while 1Dy, 3Dy and 4Dy show field-induced slow magnetic relaxation.

Thermal and photoinduced spin-crossover of mononuclear Fe complexes based on bppCHO ligand.

Two new iron(II) complexes [Fe(bppCHO)](ClO) (1·ClO4) and [Fe(bppCHO)](BF)·HO (1·BF4) were synthesized by using 2,6-di(1-pyrazol-1-yl)isonicotinaldehyde (bppCHO) as the ligand. The structures and spin states of the complexes were characterized by single-crystal X-ray diffraction and magnetic susceptibility measurements. Complex 1·ClO4 exhibits light-induced excited spin state trapping (LIESST) up to 53 K and two-step spin-crossover (SCO) over room temperature, in which the first step shows a thermal hysteresis of 26 K, whereas 1·BF4 exhibits a gradual SCO behavior.

An azido-bridged [FeII4] grid-like molecule showing spin crossover behaviour.

The supramolecular self-assembly synthetic strategy provides a valid tool to obtain polynuclear Fe(II) complexes having effective communication between the metal centres and distinct spin crossover behaviour. Despite the great success in constructing various magnetic molecules, progress has not been made in SCO complexes based on azido bridges. In this article, the coordination-driven supramolecular assembly based on 3,6-substituted pyridazine and azide is presented to afford two Fe(II) grid-like complexes: [(L)FeII4(N)][BPh]·sol (1, L = 3,6-bis(3,5-dimethyl-1-pyrazol-1-yl)pyridazine and 2, L = 3,6-di(pyridin-2-yl)pyridazine).

Probe metal binding mode of imine covalent organic frameworks: cycloiridation for (photo)catalytic hydrogen evolution from formate.

Metalation of covalent organic frameworks (COFs) is a critical strategy to functionalize COFs for advanced applications yet largely relies on the pre-installed specific metal docking sites in the network, such as porphyrin, salen, 2,2'-bipyridine, We show in this study that the imine linkage of simple imine-based COFs, one of the most popular COFs, readily chelate transition metal (Ir in this work) cyclometalation, which has not been explored before. The iridacycle decorated COF exhibited more than 10-fold efficiency enhancement in (photo)catalytic hydrogen evolution from aqueous formate solution than its molecular counterpart under mild conditions. This work will inspire more functional cyclometallated COFs to be explored beyond catalysis considering the large imine COF library and the rich metallacycle chemistry.

Switching the magnetic hysteresis of an [Fe-NC-W]-based coordination polymer by photoinduced reversible spin crossover.

Magnetic bistable materials that feature magnetic hysteresis are comparable to elementary binary units and promising for application in switches and memory devices. In this work, we report a material that consists of parallel cyanide-bridged [Fe-W] coordination chains linked together through rigid bis(imidazolyl)-benzene ligands and displays multiple magnetic states. The paramagnetic high-spin and diamagnetic low-spin states of the spin-crossover Fe ions can be interconverted by reversible light-induced excited spin state trapping (LIESST) by alternating between light irradiation of 808 and 473 nm.

Ligand symmetry significantly affects spin crossover behaviour in isomeric [Fe(pybox)] complexes.

The understanding of the correlation between the spin-state behaviour and the structural features in transition-metal complexes is of pronounced importance to the design of spin crossover compounds with high performance. However, the study of the influence of ligand symmetry on the spin crossover properties is still limited due to the shortage of suitable structural systems. Herein we report the magneto-structural correlations of three mononuclear Fe(ii) isomers with respect to their ligand symmetry.

Asymmetric Coordination Toward a Photoinduced Single-Chain Magnet Showing High Coercivity Values.

The production of photo-switchable molecular nanomagnets with substantial coercivity, which is indispensable for information storage and process applications, is challenging. Introducing photo-responsive spin-crossover units provides a feasible means of controlling the magnetic anisotropy, interactions, and overall nanomagnet properties. Herein, we report a cyanide-bridged chain 1⋅12H O ({[( Tp)Fe (CN) ] Fe (Pmat) } ⋅12 H O) generated by linking the Fe -based spin-crossover unit with the [( Tp)Fe(CN) ] ( Tp: tetrakis(pyrazolyl)borate) building block in the presence of asymmetric ditopic ligand Pmat ((4-pyridine-4-yl)methyleneamino-1,2,4-triazole).

A Mixed-Valence {Fe } Cluster Exhibiting Metal-to-Metal Charge-Transfer-Switched Spin Crossover.

It is promising and challenging to manipulate the electronic structures and functions of materials utilizing both metal-to-metal charge transfer (MMCT) and spin-crossover (SCO) to tune the valence and spin states of metal ions. Herein, a metallocyanate building block is used to link with a Fe -triazole moiety and generates a mixed-valence complex {[(Tp )Fe (CN) ] [Fe (trz-ph) ]}⋅[Ph PMe] ⋅[(Tp )Fe (CN) ] (1; trz-ph=4-phenyl-4H-1,2,4-triazole). Moreover, MMCT occurs between Fe and one of the Fe sites after heat treatment, resulting in the generation of a new phase, {[(Tp )Fe (CN) ][(Tp )Fe (CN) ] [Fe Fe (trz-ph) ]}⋅ [Ph PMe] ⋅[(Tp )Fe (CN) ] (1 a).

Construction of SCO-Active Fe(II) Mononuclear Complexes from the Thio-pybox Ligand.

The development of new spin-crossover complexes provides novel promising switching materials with significant potential at the molecular level. Ter-imine-type molecules represent one of the important classes of ligands in creating SCO-active complexes. Herein we report a family of mononuclear Fe(II) SCO-active compounds constructed from a new type of ter-imine ligand named the thio-pybox ligand (2,6-bis(4,4-dimethyl-4,5-dihydrothiazol-2-yl)pyridine, ).