Synthesis, mixed-spin-state structure and Langmuir-Blodgett deposition of amphiphilic Fe(iii) quinolylsalicylaldiminate complexes.

Designing and integrating Fe(iii)-based spin crossover (SCO) complexes onto substrates remains a challenging goal with only a handful of examples reported. In this work, we successfully synthesized and characterized three [Fe(qsal-OR)2]NO3 (qsal-OR = 5-alkoxy-2-[(8-quinolylimino)methyl]phenolate) complexes, in which R = C12H251, C16H332, and C22H453 to explore the impact of alkyl chain on the modulation of SCO activity and potential for self-assembly on a glass surface. The SCO is found to be gradual and incomplete in all cases, with the LS state more stabilised as the alkyl group shortens. We also demonstrate that all complexes form stable Langmuir films and achieve good transfer ratios to the glass surface, with 2 being the best in terms of stability. This paves the way for the SCO modulation of complexes in this class and the development of SCO devices.

Thermal Jahn-Teller Distortion Changes and Slow Relaxation of Magnetization in Mn(III) Schiff Base Complexes.

The impact that the anion and alkyl group has on the electronic structures and magnetic properties of four mononuclear Mn(III) complexes is explored in [Mn(salEen-Br)2]Y (salEen-Br = 2-{[2-(ethylamino)ethylimino]methyl}-4-Br-phenol; Y = ClO4- 1 and BF4-·1/3CH2Cl2 2) and [Mn(salBzen-Br)2]Y (salBzen-Br = 2-{[2-(benzylamino)ethylimino]methyl}-4-Br-phenol; Y = ClO4- 3 and BF4- 4). X-ray structures of [Mn(salEen-Br)2]ClO4·0.45C6H14 1-hexane, [Mn(salEen-Br)2]BF4·0.33CH2Cl2·0.15C6H14 2-dcm-hexane, and 3-4 reveal that they crystallize in ambient conditions in the monoclinic P21/c space group. Lowering the temperature, 2-dcm-hexane uniquely exhibits a structural phase transition toward a monoclinic P21/n crystal structure determined at 100 K with the unit cell trebling in size. Remarkably, at room temperature, the axially elongated Jahn-Teller axis in 2-dcm-hexane is poorly defined but becomes clearer at low temperature after the phase transition. Magnetic susceptibility measurements of 1-4 reveal that only 3 and 4 show slow relaxation of magnetization with Δeff/kB = 27.9 and 20.7 K, implying that the benzyl group is important for observing single-molecule magnet (SMM) properties. Theoretical calculations demonstrate that the alkyl group subtly influences the orbital levels and therefore very likely the observed SMM properties.

Antibacterial and antibiofilm efficacy of Solanum lasiocarpum root extract synthesized silver/silver chloride nanoparticles against Staphylococcus haemolyticus associated with bovine mastitis.

Staphylococcus haemolyticus is a cause of bovine mastitis, leading to inflammation in the mammary gland. This bacterial infection adversely affects animal health, reducing milk quality and yield. Its emergence has been widely reported, representing a significant economic loss for dairy farms. Interestingly, S. haemolyticus exhibits higher levels of antimicrobial resistance than other coagulase-negative Staphylococci. In this study, we synthesized silver/silver chloride nanoparticles (Ag/AgCl-NPs) using Solanum lasiocarpum root extract and evaluated their antibacterial and antibiofilm activities against S. haemolyticus. The formation of the Ag/AgCl-NPs was confirmed using UV-visible spectroscopy, which revealed maximum absorption at 419 nm. X-ray diffraction (XRD) analysis demonstrated the crystalline nature of the Ag/AgCl-NPs, exhibiting a face-centered cubic lattice. Fourier transform infrared (FT-IR) spectroscopy elucidated the functional groups potentially involved in the Ag/AgCl-NPs synthesis. Transmission electron microscopy (TEM) analysis revealed that the average particle size of the Ag/AgCl-NPs was 10 nm. Antimicrobial activity results indicated that the minimum inhibitory concentration (MIC) and maximum bactericidal concentration (MBC) of the Ag/AgCl-NPs treatment were 7.82-15.63 µg/mL towards S. haemolyticus. Morphological changes in bacterial cells treated with the Ag/AgCl-NPs were observed under scanning electron microscopy (SEM). The Ag/AgCl-NPs reduced both the biomass of biofilm formation and preformed biofilm by approximately 20.24-94.66 % and 13.67-88.48 %. Bacterial viability within biofilm formation and preformed biofilm was reduced by approximately 21.56-77.54 % and 18.9-71.48 %, respectively. This study provides evidence of the potential of the synthesized Ag/AgCl-NPs as an antibacterial and antibiofilm agent against S. haemolyticus.

Improving spin crossover characteristics in heteroleptic [FeIII(qsal-5-I)(qsal-5-OMe)]A complexes.

A family of heteroleptic spin crossover (SCO) [FeIII(qsal-5-I)(qsal-5-OMe)]A·sol (qsal-5-X = 5-X-2-[(8-quinolylimino)methyl]phenolate; A = NO3-1 sol = 2MeOH, NCS-2 sol = 0.75MeOH·1.3H2O, BF4-3 sol = MeOH, OTf-4, sol = MeOH) complexes have been synthesized. Most of the complexes exhibit gradual SCO, with the exception of NCS, which is principally high spin. In contrast, the OTf complex shows an abrupt hysteretic SCO (35 K) after solvent loss. The magnetic properties of this complex are significantly improved in comparison to the related homoleptics, [Fe(qsal-I)2]OTf 5 (hysteresis, 8 K) and [Fe(qsal-5-OMe)2]OTf·CH2Cl26 (gradual SCO). Structural studies reveal that slight changes in the crystal packing cause stronger interactions improving the cooperativity. These findings are supported by DFT calculations using the r2SCAN functional in which the calculated structures show that SCO from the LS to the HS state causes pronounced scissoring of the 1D π-π chains and substantial changes in their relative orientation following loss of MeOH.

Bidirectional photoswitchability in an iron(iii) spin crossover complex: symmetry-breaking and solvent effects.

The impact of solvent on spin crossover (SCO) behaviour is reported in two solvates [Fe(qsal-I)2]NO3·2ROH (qsal-I = 4-iodo-2-[(8-quinolylimino)methyl]phenolate; R = Me 1 or Et 2) which undergo abrupt and gradual SCO, respectively. A symmetry-breaking phase transition due to spin-state ordering from a [HS] to [HS-LS] state occurs at 210 K in 1, while T1/2 = 250 K for the EtOH solvate, where complete SCO occurs. The MeOH solvate exhibits LIESST and reverse-LIESST from the [HS-LS] state, revealing a hidden [LS] state. Moreover, photocrystallographic studies on 1 at 10 K reveal re-entrant photoinduced phase transitions to a high symmetry [HS] phase when irradiated at 980 nm or a high symmetry [LS] phase after irradiation at 660 nm. This study represents the first example of bidirectional photoswitchability and subsequent symmetry-breaking from a [HS-LS] state in an iron(iii) SCO material.

Preparation and physicochemical characterization of sildenafil cocrystals.

Sildenafil is a specific inhibitor of the phosphodiesterase type 5 (PDE-5) enzyme that protects cyclic guanosine monophosphate from breakdown by PDE-5. It is a biopharmaceutical categorization system Class II medication with low bioavailability because it is almost insoluble in water. The objectives of this study were to prepare sildenafil cocrystals with co-former molecules including aspirin (acetylsalicylic acid [ASA]), fumaric acid (FMA), and benzoic acid (BZA) to improve the water solubility of sildenafil. The cocrystals were prepared by antisolvent addition (AA) and slow solvent evaporation (SE) methods. The stoichiometric ratios of sildenafil and co-former molecules were varied. The obtained crystals were characterized by stereomicroscope, Fourier transformed infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR), and powder X-ray diffraction (PXRD). The water solubility of sildenafil cocrystals was compared with sildenafil base. In the AA method, the crystals only form in sildenafil-ASA reaction. These crystals were not cocrystals between sildenafil and ASA because they were formed to new substances that were confirmed by single-crystal X-ray diffraction. In the SE method, the cocrystals were successfully prepared in the reaction of sildenafil with ASA, FMA, and BZA which use acetone or ethyl acetate as a solvent. The obtained crystals are irregular shapes and their FT-IR, NMR, and PXRD results exhibited the characteristics of sildenafil and its co-former. The stoichiometric ratios of sildenafil and co-formers after cocrystallization were different from an initial of crystallization. The sildenafil cocrystals with ASA, FMA, and BZA by SE method had higher water solubility than sildenafil base. The sildenafil-FMA cocrystals had the highest water solubility and increased up to five times when compared with sildenafil base.

Synthesis, characterization and anticancer activity of Fe(II) and Fe(III) complexes containing N-(8-quinolyl)salicylaldimine Schiff base ligands.

A series of Fe(II) complexes (1-4) and Fe(III) complexes (5-8) from Fe(II)/(III) chloride and N-(8-quinolyl)-X-salicylaldimine Schiff base ligands (Hqsal-X2/X: X = Br, Cl) were successfully synthesized and characterized by spectroscopic (FT-IR, 1H-NMR), mass spectrometry, thermogravimetric analysis (TGA), and single crystal X-ray crystallographic techniques. The interaction of complexes 1-8 with calf thymus DNA (CT-DNA) was determined by UV-Vis and fluorescence spectroscopy. The complexes exhibited good DNA-binding activity via intercalation. The molecular docking between a selected complex and DNA was also investigated. The in vitro anticancer activity of the Schiff base ligands and their complexes were screened against the A549 human lung adenocarcinoma cell line. The complexes showed anticancer activity toward A549 cancer cells while the free ligands and iron chloride salts showed no inhibitory effects at 100 µM. In this series, complex [Fe(qsal-Cl2)2]Cl 6 showed the highest anticancer activity aginst A549 cells (IC50 = 10 µM). This is better than two well-known anticancer agents (Etoposide and Cisplatin). Furthermore, the possible mechanism for complexes 1-8 penetrating A549 cells through intracellular ROS generation was investigated. The complexes containing dihalogen substituents 1, 2, 5, and 6 can increase ROS in A549 cells, leading to DNA or macromolecular damage and cell-death induction.

OctaDist: a tool for calculating distortion parameters in spin crossover and coordination complexes.

OctaDist is an interactive and visual program for determination of structural distortion in octahedral coordination complexes such as spin crossover complexes, single-ion magnets, perovskites or metal-organic frameworks. OctaDist computes the octahedral distortion parameters initially designed in the context of the spin-crossover phenomenon and denoted ζ, Σ, and Θ from standard structural files. The program also provides additional tools for molecular analyses and visualization. It emphasizes performance, flexibility, ease of use, application programming interface (API) consistency, and clear documentation. The modules and classes in OctaDist can be easily customized to include new algorithms or analytical tools. OctaDist is cross-platform supported for modern operating systems and is available as open-source distributed under the GNU General Public License version 3.

Conformational polymorphism in a cobalt(II) dithiocarbamate complex.

Two conformational polymorphs of (N,N-dibutyldithiocarbamato-κ2S,S')[tris(3,5-diphenylpyrazol-1-yl-κN2)hydroborato]cobalt(II), [Co(C45H34BN6)(C9H18NS2)] or [TpPh2Co(S2CNBu2)], 1, are accessible by recrystallization from dichloromethane-methanol to give orthorhombic polymorph 1a, while slow evaporation from acetonitrile produces triclinic polymorph 1b. The two polymorphs have been characterized by IR spectroscopy and single-crystal X-ray crystallography at 150 K. Polymorphs 1a and 1b crystallize in the orthorhombic space group Pbca and the triclinic space group P-1, respectively. The polymorphs have a trans (1a) and cis (1b) orientation of the butyl groups with respect to the S2CN plane of the dithiocarbamate ligand, which results in an intermediate five-coordinate geometry for 1a and a square-pyramidal geometry for 1b. Hirshfeld surface analysis reveals minor differences between the two polymorphs, with 1a exhibiting stronger C-H...S interactions and 1b favouring C-H...π interactions.

Spin Crossover in Iron(III) Quinolylsalicylaldiminates: The Curious Case of [Fe(qsal-F)2](Anion).

A family of iron(III) spin crossover complexes with different counteranions, [Fe(qsal-F)2]A (qsal-F = 4-fluoro-2-[(8-quinolylimino)methyl]phenolate; A = PF6- 1, OTf- 2, NO3- 3, ClO4- 4, BF4- 5, or NCS- 6) have been prepared. All compounds are isostructural and crystallize (triclinic P1̅ space group) with two independent iron(III) centers (Fe1 and Fe2) in the asymmetric unit. No solvent molecules are found in the crystal lattice, allowing us to directly probe the relative influence of anion variation on the spin crossover characteristics. The crystal packing is governed by three types of π-π interactions (type A, type B, and type C), which form undulating 1D chains. Additional interactions (π-F, C-H···O/F, and P4AE) connect the neighboring chains to form a complex supramolecular network. Hirshfeld surface analysis supports these findings. The anions are located between the cationic [Fe(qsal-F)2]+ chains; hence, similar interchain distances (dchain) are observed irrespective of the anion. However, the interplane distances (dplane) are influenced by the crystal packing and increase proportionally with the anion size. Magnetic studies reveal that smaller anions tend to stabilize the low-spin state (NO3- 3, ClO4- 4, and BF4- 5), while larger anions (PF6- 1 and OTf- 2) exhibit lower transition temperatures (Tonset for 1 = 200 K and T for 2 = 190 K) and gradual spin crossovers. The anomaly is 6, where, despite having the smallest anion, it exhibits the lowest transition temperature with magnetic hysteresis in the first step (T1/2↑ = 170 K and T1/2↓ = 157 K). This suggests the size, shape, and supramolecular connectivity of the anion all influence the magnetic properties.

Room temperature conductance switching in a molecular iron(iii) spin crossover junction.

Herein, we report the first room temperature switchable Fe(iii) molecular spin crossover (SCO) tunnel junction. The junction is constructed from [FeIII(qsal-I)2]NTf2 (qsal-I = 4-iodo-2-[(8-quinolylimino)methyl]phenolate) molecules self-assembled on graphene surfaces with conductance switching of one order of magnitude associated with the high and low spin states of the SCO complex. Normalized conductance analysis of the current-voltage characteristics as a function of temperature reveals that charge transport across the SCO molecule is dominated by coherent tunnelling. Temperature-dependent X-ray absorption spectroscopy and density functional theory confirm the SCO complex retains its SCO functionality on the surface implying that van der Waals molecule-electrode interfaces provide a good trade-off between junction stability while retaining SCO switching capability. These results provide new insights and may aid in the design of other types of molecular devices based on SCO compounds.

Abrupt spin crossover in iron(iii) complexes with aromatic anions.

Two iron(iii) spin crossover complexes, [Fe(qsal-X)2]OTs·nH2O, (Br 1·H2O; I, 2·2H2O or non-solvated 1, 2) have been prepared and fully characterized. Structural studies of 1·H2O and 2·2H2O reveal the presence of 1D π-π chains linking the Fe(iii) centres and a strong XO halogen bond. In both complexes the 1D π-π chains are angled relative to each other, enforced by C-HX interactions. Magnetic studies reveal abrupt spin crossover in 1 (T1/2↓ = 258 K and T1/2↑ = 260 K) and 2 (T1/2 = 298 K) with T1/2 increasing on going from Br to I. The presence of abrupt spin crossover in both complexes shows that aromatic anions can be effective in the design of cooperative spin crossover systems.

The First Observation of Hidden Hysteresis in an Iron(III) Spin-Crossover Complex.

Molecular magnetic switches are expected to form the functional components of future nanodevices. Herein we combine detailed (photo-) crystallography and magnetic studies to reveal the unusual switching properties of an iron(III) complex, between low (LS) and high (HS) spin states. On cooling, it exhibits a partial thermal conversion associated with a reconstructive phase transition from a [HS-HS] to a [LS-HS] phase with a hysteresis of 25 K. Photoexcitation at low temperature allows access to a [LS-LS] phase, never observed at thermal equilibrium. As well as reporting the first iron(III) spin crossover complex to exhibit reverse-LIESST (light-induced excited spin state trapping), we also reveal a hidden hysteresis of 30 K between the hidden [LS-LS] and [HS-LS] phases. Moreover, we demonstrate that FeIII spin-crossover (SCO) complexes can be just as effective as FeII systems, and with the advantage of being air-stable, they are ideally suited for use in molecular electronics.

Solvatomorphism and anion effects in predominantly low spin iron(iii) Schiff base complexes.

A series of iron(iii) complexes [Fe(naphEen)2]X·sol (naphEen = 1-{[2-(ethylamino)-ethylimino]methyl}-2-naphtholate; X = F, sol = 0.5CH2Cl2·H2O 1; sol = H2O, X = Cl, 2 and X = Br 3) and [Fe(naphEen)2]I 4 has been prepared. The UV-Vis spectra reveal clear differences for 1 which DFT/TDDFT calculations suggest are due to an equilibrium between [Fe(naphEen)2]F and [Fe(naphEen)2F], the latter having a coordinated F ligand. The X-ray crystal structures of 2-4 show LS Fe(iii) centres in all cases and extensive aryl interactions that link the Fe centres into supramolecular squares. In 3 at room temperature the compound loses half an equivalent of water resulting in a change in space group from Monoclinic P21/n to C2/c. Magnetic studies indicate that 1 is trapped in a mixed spin state being ca. 40% HS while 2-4 are effectively low spin up to 350 K. In contrast, Mössbauer spectroscopic studies of 1 indicate a gradual but incomplete spin crossover. The magnetic properties of 2-4 contrast with the related [Fe(salEen-X)2]anion derivatives which are often spin crossover active.

Self-assembly of a mixed-valence FeII-FeIII tetranuclear star.

A unique self-assembled mixed-valence FeII-FeIII tetranuclear star has been comprehensively characterised showing a large magnetic anisotropy at the peripheral FeII centres, ferromagnetic coupling between the iron centres and field-induced SMM behaviour.

Slow relaxation of magnetization in a bis-mer-tridentate octahedral Co(ii) complex.

Reaction of a rigid tridentate ligand o-[(1H-imidazol-2-yl)methylideneamino]phenol (2-H2imap) with Co(ClO4)2 in the presence of NaN3, or Co(NO3)2 without a base yields [CoII(2-Himap)2] 1 and [CoIII(2-Himap)2]NO3·MeOH 2, respectively. Both complexes exhibit a mer-octahedral geometry with the cobalt centre being distorted along an octahedral-trigonal prismatic pathway. The packing in 1 and 2 is dominated by H-bonding forming 2D sheets and 1D chains, respectively. Detailed dc and ac magnetic studies indicate that 1 is a field-induced single-ion magnet (SIM) with D = 36.7 cm-1 and E = 2.0 cm-1. Extensive ab initio calculations support these conclusions and suggest that relaxation of the magnetization occurs principally through direct quantum tunnelling in the ground state, with the Raman process dominant in an applied field. This contrasts with the recently reported series of mer-[Co(L)2] (L = monoanionic NNO donor ligand; Inorg. Chem., 2017, 56, 6056-6066) complexes where D is negative, as these compounds have a more ambiguous geometry, and highlights the importance of supramolecular interactions in subtly altering the coordination sphere thereby impacting the magnetic behaviour.

Hysteretic spin crossover driven by anion conformational change.

A new air stable FeIII spin crossover (SCO) complex has been synthesized. The compound undergoes abrupt SCO near room temperature with T1/2 (↓) = 244 K and T1/2 (↑) = 278 K. Structural studies of the complex in the high spin and low spin state show that the strong cooperativity and thus the wide hysteresis is driven by an unprecedented anionic conformational change.

Solvent modified spin crossover in an iron(iii) complex: phase changes and an exceptionally wide hysteresis.

Solvent effects in a series of Fe(iii) spin crossover (SCO) complexes [Fe(qsal-I)2]OTf·sol (sol = MeOH 1, EtOH 2, n-PrOH 3, i-PrOH 4, acetone 5 and MeCN 6) are explored. SCO is abrupt in 1 (following MeOH loss) and 2, gradual for 3 (T1/2 = 199 K) and 4 (T1/2 = 251 K) and incomplete, even up to 350 K, for 5 and 6. In [Fe(qsal-I)2]OTf SCO occurs at T1/2↓ = 225 K and T1/2↑ = 234 K (ΔT = 9 K), while aged samples of 2 exhibit an exceptionally wide hysteresis of 80 K (T1/2↓ = 139 K and T1/2↑ = 219 K). In contrast, fresh samples of 2 exhibit stepped SCO with hysteresis varying from 2 to 42 K. VT-PXRD (variable temperature powder X-ray diffraction) studies indicate a new phase, 2b, is formed upon cooling below 180 K along with a minor LS phase 2c. Phase 2c and the HS phase 2a undergo a spin transition at T1/2↓ = 180 K and T1/2↑ = 215 K with phase 2b exhibiting two-step SCO. Structural studies in both spin states, except 6, show the cations are linked through extensive π-π interactions to form 1D chains. A combination of P4AE (parallel fourfold aryl embrace) and I···X (X = I, O, π) interactions create tightly packed 3D supramolecular networks. This study emphasizes that while solvent may result in only small structural changes SCO characteristics can be impacted dramatically.

Abrupt two-step and symmetry breaking spin crossover in an iron(III) complex: an exceptionally wide [LS-HS] plateau.

[Fe(qsal-Br)2]NO3·2MeOH is reported which undergoes abrupt two step symmetry breaking spin crossover, T½(1st step) = 136 K and T½(2nd step) = 232 K with a hysteresis of 16 K and 5 K, respectively, and an unprecedented [HS-LS] plateau of 96 K.

Stepped spin crossover in Fe(III) halogen substituted quinolylsalicylaldimine complexes.

The reaction of Fe(NCS)3 prepared in situ in MeOH with Hqsal-X (Hqsal-X = 5-X-N-quinolylsalicylaldimine) in CH2Cl2 yields the FeIII complexes, [Fe(qsal-X)2]NCS·solvent (X = F 1; X = Cl, 2, Br, 3 solvent = MeOH; X = I, solvent = 0.25CH2Cl2·0.5MeOH 4) in moderate to good yields. IR spectroscopy confirms that NCS− acts as a counteranion only and that the qsal-X ligand is bound to the FeIII centre. SQUID magnetometric studies reveal stepped hysteretic spin crossover in 1 and 2, which is abrupt in both steps in latter compound. Mössbauer spectroscopic studies of 1 and 2 support these conclusions. The bromo derivative, 3, undergoes half spin crossover up to 340 K while 4 is low spin at all temperatures measured. The spin transition temperature, T1/2 is found to increase on moving from F to Br. UV-Vis and NMR spectroscopic studies indicate that 1­4 have spin states intermediate between HS and LS in solution. Structural studies show that 1, 2 and 3 crystallize in triclinic P while 4 is in monoclinic P21/c. Crystallographic studies of 1 at 100, 200 and 270 K show that spin crossover proceeds from a [LS­LS] state through a [LS­HS] intermediate to a [HS­HS] state (LS = low spin, S = 1/2, HS = high spin, S = 5/2). Similar results are found for 3 although this time a [LS­IS] state exists at 123 K while a [LS­HS] state is found at 295 K (IS = intermediate spin state where partial spin crossover has occurred). Both 2 and 4 are found to have LS FeIII centres although the latter contains two crystallographically independent FeIII centres in the asymmetric unit. The crystal packing in 1­4 consists of extensive π­π interactions through the planar qsal-X ligands and CH∙∙∙X (X = O, halogen) and/or X∙∙∙π (X = halogen) interactions which result in pseudo 3D supramolecular networks. This results in high cooperativity in 1 and 2 and is probably responsible for the hysteretic stepped spin crossover in these compounds.