Light-Induced, Structural Matrix Guided Stepwise Spin-State Switching in 3d-5d Molecular Assembly.

A new iron(II) molecular complex {[W(CN)][Fe(bik*)]}BF·7HO·1.5CHOH (.7HO·1.

Stereochemically Active Lone Pair Leads to Birefringence in the Vacancy Ordered CsSbCl Perovskite Single Crystals.

Stereochemically active lone pair (SCALP) cations are attractive units for realizing optical anisotropy. Antimony(III) chloride perovskites with the SCALP have remained largely unknown to date. We synthesized a new vacancy ordered CsSbCl perovskite single crystals with SbCl octahedral linkage containing the SCALP.

Stimuli-responsive magnetic materials: impact of spin and electronic modulation.

Addressing molecular bistability as a function of external stimuli, especially in spin-crossover (SCO) and metal-to-metal electron transfer (MMET) systems, has seen a surge of interest in the field of molecule-based magnetic materials due to their enormous potential in various technological applications such as molecular spintronics, memory and electronic devices, switches, sensors, and many more. The fine-tuning of molecular components allow the design and synthesis of materials with tailored properties for these vast applications. In this Feature Article, we discuss a part of our research work into this broad topic, pertaining to the recent discoveries in the field of switchable molecular magnetic materials based on SCO and MMET systems, along with some historical background of the area and related accomplishments made in recent years.

Spin-state switching: chemical modulation and the impact of intermolecular interactions in manganese(III) complexes.

A series of mononuclear manganese(III) complexes [Mn(X-sal-323)](ReO) (X = 5 Cl, 1; X = 5 Br, 2; X = 3,5 Cl, 3; X = 3,5 Br, 4; and X = 5 NO, 5), containing hexadentate ligands prepared using the condensation of ,'-bis(3-aminopropyl)ethylenediamine and 5- or 3,5-substituted salicylaldehyde, has been synthesized. Variable temperature single-crystal X-ray diffraction, magnetic, spectroscopic, electrochemical, and spectroelectrochemical analyses, and theoretical calculations have been used to explore the role of various ligand substituents in the spin-state switching behavior of the prepared manganese(III) complexes. All five complexes consist of an analogous distorted octahedral monocationic MnNO surrounding offered by the flexible hexadentate ligand and ReO as the counter anion.

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

A two-step thermo-induced spin-state switching was observed in a cyanide-bridged [FeFe] molecular square complex, {[Fe(pzTp)(CN)][Fe(L)]}[Fe(pzTp)(CN)]·4CHOH·2HO [1·4MeOH·2HO; pzTp = tetrakis(pyrazol-1-yl)borate and L = bis(1-ethylimidazol-2-yl)ketone (bik*)], which was characterized fully by single-crystal X-ray diffraction, (photo)magnetic measurements, and spectroscopic techniques. 1·4MeOH·2HO exhibited a two-step thermo-induced spin transition with (1) ↑ = 306 K and (2) ↑ = 370 K converting the low-temperature ground state, {[(FeIIILS)(FeIILS)](FeIIILS)} into the high-temperature state, {[(FeIIILS)(FeIIHS)](FeIIILS)} a stable intermediate phase. The desolvated phase, 1 also exhibited a gradual but reversible thermo-induced spin state change with a value of 190 K, significantly shifted to a lower temperature.

Realizing the Lowest Bandgap and Exciton Binding Energy in a Two-Dimensional Lead Halide System.

Finding stable analogues of three-dimensional (3D) lead halide perovskites has motivated the exploration of an ever-expanding repertoire of two-dimensional (2D) counterparts. However, the bandgap and exciton binding energy in these 2D systems are generally considerably higher than those in 3D analogues due to size and dielectric confinement. Such quantum confinements are most prominently manifested in the extreme 2D realization in ()PbI ( = 1 or 2) series of compounds with a single inorganic layer repeat unit.

ON/OFF Photo(switching) along with Reversible Spin-State Change and Single-Crystal-to-Single-Crystal Transformation in a Mixed-Valence Fe(II)Fe(III) Molecular System.

A mixed-valence Fe(II)Fe(III) molecular system, {[Fe(pzTp)(CN)][Fe(bik)]}·[Fe(pzTp)(CN)]·4MeOH (·4MeOH) (bik = bis-(1-methylimidazolyl)-2-methanone, pzTp = tetrakis(pyrazolyl)borate), exhibits single-crystal-to-single-crystal (SC-SC) transformation while increasing the temperature and is converted into {[Fe(pzTp)(CN)][Fe(bik)]}·[Fe(pzTp)(CN)] (). Both complexes exhibit thermo-induced spin-state switching behavior along with reversible SC-SC transformation, where the low-temperature [FeFe] phase transforms into a high-temperature [FeFe] phase. ·4MeOH exhibits an abrupt spin-state switching with at 355 K, whereas undergoes a gradual and reversible spin-state switching with a lower at 338 K.

Impact of Counteranion on Reversible Spin-State Switching in a Series of Cobalt(II) Complexes Containing a Redox-Active Ethylenedioxythiophene-Based Terpyridine Ligand.

The self-assembly of a redox-active ethylenedioxythiophene (EDOT)-terpyridine-based tridentate ligand and cobalt(II) unit with different counteranions has led to a series of new cobalt(II) complexes [Co()](X) (X = BF (), ClO (), and BPh ()) ( = 4'-(3,4-ethylenedioxythiophene)-2,2':6',2″-terpyridine). The impact of various counteranions on stabilization and spin-state switching of the cobalt(II) center was explored through detailed magneto-structural investigation using variable temperature single-crystal X-ray diffraction, magnetic, spectroscopic, electrochemical, and spectroelectrochemical studies. All three complexes - consisted of an isostructural dicationic distorted octahedral CoN coordination environment offered by the two ligands in a bis-meridional fashion and BF, ClO, and BPh as a counteranion, respectively.

Tuning of spin crossover properties in a series of mononuclear cobalt(II) complexes based on a macrocyclic tetradentate ligand and pseudohalide coligands.

The three mononuclear cobalt(II) complexes, [Co(L)(NCX)] (L = ,'-di--butyl-2,11-diaza[3,3](2,6)pyridinophane, and X = S (1), Se (2), and [C(CN)] (3)), have been synthesized and characterized using variable temperature single-crystal X-ray crystallography, and spectroscopic, magnetic, and electrochemical studies. All three complexes have a similar distorted octahedral CoN coordination geometry produced by the macrocyclic tetradentate ligand L and two NCX co-ligands in the position. Complexes 1 and 2 crystallized in the monoclinic 2/ ( = 4) space group, while complex 3 was isolated in the monoclinic 2/ ( = 4) space group.

Effect of Ligand Chain Length for Tuning of Molecular Dimensionality and Magnetic Relaxation in Redox Active Cobalt(II) EDOT Complexes (EDOT=3,4-Ethylenedioxythiophene).

Four cobalt(II) complexes, [Co(L1) (NCX) (MeOH) ] (X=S (1), Se (2)) and {[Co(L2) (NCX) ]}n (X=S (3), Se (4)) (L1=2,5-dipyridyl-3,4,-ethylenedioxylthiophene and L2=2,5-diethynylpyridinyl-3,4-ethylenedioxythiophene), were synthesized by incorporating ethylenedioxythiophene based redox-active luminescence ligands. All these complexes have been well characterized using single-crystal X-ray diffraction analyses, spectroscopic and magnetic investigations. Magneto-structural studies showed that 1 and 2 adopt a mononuclear structure with CoN O octahedral coordination geometry while 3 and 4 have a 2D [4×4] rhombic grid coordination networks (CNs) where each cobalt(II) center is in a CoN octahedral coordination environment.

Impact of counter anions on spin-state switching of manganese(III) complexes containing an azobenzene ligand.

Four mononuclear manganese(III) complexes coordinated with photo-active hexadentate azobenzene ligands, [Mn(5azo-sal-323)](X) (X = Cl, 1; X = BF, 2; X = ClO, 3; X = PF, 4), were prepared. The impact of various counter anions on the stabilization and switching of the spin state of the manganese(III) center was explored through detailed magneto-structural investigation using variable temperature single-crystal X-ray diffraction, magnetic, spectroscopic, and spectroelectrochemical studies, along with theoretical calculations. All four complexes consisted of an isostructural monocationic distorted octahedral MnNO coordination environment offered by the hexadentate ligand and Cl, BF, ClO, and PF as counter anions respectively.

Mycobactin Analogues with Excellent Pharmacokinetic Profile Demonstrate Potent Antitubercular Specific Activity and Exceptional Efflux Pump Inhibition.

In this study, we have designed and synthesized pyrazoline analogues that partially mimic the structure of mycobactin, to address the requirement of novel therapeutics to tackle the emerging global challenge of antimicrobial resistance (AMR). Our investigation resulted in the identification of novel lead compounds and as potential mycobactin biosynthesis inhibitors against mycobacteria. Moreover, candidates efficiently eradicated intracellularly surviving mycobacteria.

Thermo- and photoinduced spin state switching in an iron(II) 2D coordination network associated with large light-induced thermal hysteresis and tuning of dimensionality ligand modulation.

Three iron(ii) complexes, [Fe(L1)2(NCS)2(MeOH)2] (1), [Fe(L1)2(NCSe)2(MeOH)2] (2), and [Fe(L2)2(NCS)2]n (3) (L1 = 2,5-dipyridyl-3,4-ethylenedioxythiophene and L2 = 2,5-diethynylpyridinyl-3,4-ethylenedioxythiophene), have been synthesized using redox-active luminescent ethylenedioxythiophene (EDOT)-based ligands, and characterized by variable temperature single-crystal X-ray diffraction, (photo)magnetic, optical reflectivity, and spectroscopy studies. Magneto-structural investigations revealed that 1 and 2 are mononuclear with a FeN4O2 octahedral coordination geometry and remain in a high-spin (HS) (S = 2) state in a temperature range of 2-280 K. Interestingly, a 2D coordination network structure with FeN6 surrounding each iron center was observed for 3, which exhibits reversible thermo-induced spin-state switching between the paramagnetic high-spin (HS) (S = 2) and diamagnetic low-spin (LS) (S = 0) states at around 105 K (T1/2).

Reversible Photo- and Thermo-Induced Spin-State Switching in a Heterometallic {} WFe Molecular Square Complex.

Following the complex-as-a-ligand strategy, self-assembly of [W(CN)] and iron(II) with bidentate nitrogen donor ligand bik (bik = bis(1-methyl-1-imidazol-2-yl)ketone) ligand affords a cyanide-bridged [WFe] molecular square complex [HNBu]{[W(CN)][Fe(bik)]}·6HO·CHOH (). The complex was characterized by single-crystal X-ray diffraction analyses, (photo)magnetic studies, optical reflectivity, electrochemical studies, and spectroscopic studies. Structural analyses revealed that in the [WFe] square motif tungsten(V) and iron(II) centers reside in an alternate corner of the square and are bridged by the cyanide ligands.

Effect of Ligand Modulation on Metal-to-Metal Electron Transfer in a Series of [FeCo] Molecular Square Complexes.

A series of three new cyanide-bridged [FeCo] molecular square complexes, namely, {[Fe(Tp*)(CN)][Co(L)]}(BF)·2DMF (L = bik (), bik* (), and vbik (); Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate, bik = bis(1-methyl-1-imidazol-2-yl)ketone, bik* = bis(1-ethyl-1-imidazol-2-yl)ketone, and vbik = bis(1-vinyl-1-imidazol-2-yl)ketone; DMF = dimethylformamide) were synthesized and characterized by single-crystal X-ray diffraction analyses and by magnetic, electrochemical, and spectroscopic measurements. Magnetic studies reveal that all three complexes exhibit temperature-induced metal-to-metal electron transfer (MMET) from a high-spin Co(II) center to a low-spin Fe(III) center, transforming a high-temperature paramagnetic {Fe-CN-Co} ground state into a low-temperature diamagnetic {Fe-CN-Co} state with a decrease in the temperature from 300 to 100 K. Complexes and show the interconversion of the paramagnetic {Fe-CN-Co} ground state into a diamagnetic {Fe-CN-Co} state in a single-step transition with values of 180 and 186 K, respectively, while a two-step MMET with value of 214 and 178 K was observed for complex .

Effect of ligand substituents and tuning the spin-state switching in manganese(iii) complexes.

Three mononuclear manganese(iii) complexes based on flexible hexadentate ligands obtained from the condensation of N,N'-bis(3-aminopropyl)ethylenediamine and salicylaldehyde or salicylaldehyde with substitutions at the 5 or 3,5 positions, namely [Mn(X-sal-323)](BPh) (X = 5 H, 1; X = 5 Br, 2, and X = 3,5 Br, 3) have been synthesized. The impact of ligand substituents has been studied by variable temperature single-crystal X-ray diffraction analyses, and magnetic, spectroscopic and electrochemical investigations. The complexes have an analogous monocationic MnNO surrounding offered by the flexible hexadentate ligand in a distorted octahedral geometry.

Reversible Spin-State Switching and Tuning of Nuclearity and Dimensionality via Nonlinear Pseudohalides in Cobalt(II) Complexes.

The self-assembly of a macrocyclic tetradentate ligand, cobalt(II) tetrafluoroborate, and nonlinear pseudohalides (dicyanamide and tricyanomethanide) has led to two cobalt(II) complexes, {[Co()(μ-dca)](BF)·MeOH} () and [Co()(μ-tcm)](BF) () ( = ,'-di--butyl-2,11-diaza[3,3](2,6)pyridinophane; dca = dicyanamido; tcm = tricyanomethanido). Both complexes were characterized by single-crystal X-ray diffraction, spectroscopic, magnetic, and electrochemical studies. Structural analyses revealed that displays a one-dimensional (1D) coordination polymer containing [Co()] repeating units bridged by μ-dicyanamido groups in positions, while represents a discreate dinuclear cobalt(II) molecule bridged by two μ-tricyanomethanido groups in a conformation.

Stepwise spin-state switching in a manganese(III) complex.

A mononuclear manganese(iii) complex containing a flexible hexadentate chelating ligand has been prepared and characterized by performing, at various temperatures, single-crystal X-ray diffraction analyses and magnetic, spectroscopic, and electrochemical studies. The complex was shown to consist of an MnN4O2 octahedral coordination environment, and to exhibit reversible two-step thermally induced spin-state switching, a gradual one at 168 K and an abrupt one at 103 K. Structural analyses revealed the existence of three spin-states, namely high-spin, low-spin, and intermediate states, during the spin-state switching process.

ON/OFF Photoswitching and Thermoinduced Spin Crossover with Cooperative Luminescence in a 2D Iron(II) Coordination Polymer.

A 2D coordination polymer, {[Fe()(NCSe)]·6MeOH·14HO} (; = 2,5-dipyridylethynylene-3,4-ethylenedioxythiophene), has been synthesized based on a redox active luminescence ligand. possesses a 2D [4 × 4] square-grid network where the iron(II) center is in a FeN octahedral coordination environment. displays reversible thermoinduced high-spin (HS; = 2) to diamagnetic low-spin (LS; = 0) ON/OFF spin-state switching with a value of 150 K.