Conformation Of Alkyl Chains Research Articles

Molecular simulations of amine-based organic additives at a steel surface: Effect of the internal molecular structure on adsorption

Lubricating oils mitigate wear in gears and rolling bearings lengthening the lifespan of drivetrain units for electric vehicles. Amine-based organic additives from the lubricating oil contribute to alleviating wear by adsorbing on rubbing steel surfaces of mechanical contacts and forming anti-wear films. Cross-pin wear experiments suggest that additives with branches in polar heads improve wear protection, while remaining environmentally friendly. Experiments show a reasonable correlation with the energy of adsorption calculated from molecular dynamics simulations at large surface coverages. Whereas adsorption strengths and surface coverages are barely affected by the conformation of alkyl chains (cis/trans), they are affected by the length of branches in polar heads of additives. Results suggest better performances for branch lengths containing 3–4 C atoms.

Long-Chain Molecular Crystals Antimony(III) Alkanethiolates Sb(SCnH2n+1)3 (n ≥ 12): Synthesis, Crystal and Electronic Structures, and Supramolecular Self-Assembly via Secondary Interactions.

Currently, there is not much success in solving the molecular and crystal structures of long-chain metal alkanethiolate complexes [M(SCnH2n+1)m] at the atomic level. Taking Sb(SC16H33)3 (1) as an example, we herein disclose the structural characteristics of long-chain trivalent antimony(III) alkanethiolates Sb(SCnH2n+1)3 (n ≥ 12) by single-crystal X-ray crystallography. Specifically, the Sb atom is three-coordinated by alkanethiolate ligands and a slightly distorted triangular pyramid SbS3 core is formed owing to the unique intramolecular stereochemistry of three alkyl chains, namely, two of them almost parallel aligning and the third chain extending alone around the SbS3 core. We further determine the conformation, spatial orientation and packing density of alkyl chains in 1 along with a comparison to those in other long-chain crystalline systems, and reveal the roles of intermolecular van der Waals and Sb···S secondary interactions in molecular self-assembly, which enables 1 to be a layer-structured molecular crystal with a monoclinic P21/c unit cell. The band structures and the atomic orbital contributions to the valence band maximum and conduction band minimum for 1 have also been evaluated by DFT calculations and rationally correlated with its optical absorption property. This study will help understand and discover new structures and structure-property relations of long-chain chemical systems.

Elucidating effect of dicarboxylate anions on nanostructural organization of dicationic imidazolium-based ionic liquids

This work reports the influence of the dicarboxylate anion (oxalate, malonate succinate, glutarate, adipate, pimelate) on the aggregation process of ionic liquids derived from 1,8-bis(3-methylimidazolium-1-yl)-octane [C8(MIM)2] and 1,10-bis(3-methylimidazolium-1-yl)-decano [C10(MIM)2] in water solution. The aggregation behavior was investigated using electrical conductivity, nuclear magnetic resonance, transmission electron microscopy, atomic force microscopy, and zeta potential. Results showed that the aggregates have a wormlike morphology. The CAC values for [C10(MIM)2]2+ increase in the following order: [Oxa] < [Suc] < [Mal] < [Glu] < [Adi] < [Pim], which indicates a direct relationship with the increase in the number of methylene groups of the dianion spacer. In the case of [C8(MIM)2]2+, there was no relationship between the CAC value and the anion’s alkyl spacer chain length, which was attributed to the flexibility and complexity of the dynamic behavior of the aggregates. Anions on the nanorganized structures of micelles are oriented in the way that carboxylate groups are at the aggregate surface (forming hydrogen bonds with cationic heads and water), and apolar alkyl chains are in the hydrophobic (downshift) region of the micelles making an arrangement where they also adopt the bend conformation of alkyl chains. The aggregation of dicationic ILs with dicarboxylate anions is a very innovative topic of investigation in the literature, and more research on different structures, system conditions, and techniques could be done to gain a better understanding of these systems.

Depth-profiling alkyl chain order in unsaturated lipid monolayers on water.

Unsaturated lipids with C=C groups in their alkyl chains are widely present in the cell membrane and food. The C=C groups alter the lipid packing density, membrane stability, and persistence against lipid oxidation. Yet, molecular-level insights into the structure of the unsaturated lipids remain scarce. Here, we probe the molecular structure and organization of monolayers of unsaturated lipids on the water surface using heterodyne-detected sum-frequency generation (HD-SFG) spectroscopy. We vary the location of the C=C in the alkyl chain and find that at high lipid density, the location of the C=C group affects neither the interfacial water organization nor the tail of the alkyl chain. Based on this observation, we use the C=C stretch HD-SFG response to depth-profile the alkyl chain conformation of the unsaturated lipid. We find that the first 1/3 of carbon atoms from the headgroup are relatively rigid, oriented perpendicular to the surface. In contrast, the remaining carbon atoms can be approximated as free rotators, introducing the disordering of the alkyl chains.

Controlling Polymorphic Transitions in n-Type Organic Semiconductor Single Crystals by Alkyl Chain Engineering

Control of polymorphic behavior is crucial for designing functional organic semiconductor devices as even a slight structural difference may translate to dramatically different electronic properties. One route to controlling structure is through stimulus-induced polymorph transitions, which allows for switching those electronic properties. However, despite advances in predicting crystal structures, the molecular design characteristics governing the polymorphic transition mechanism remains unknown. Here, we systematically investigate a series of n-type organic semiconductor molecules based on 2-dimensional quinoidal terthiophene with varying alkyl side chain lengths to modulate two distinct polymorph transitions, one cooperative martensitic transition and the other non-cooperative nucleation and growth transition. In the three molecular systems, we observe that shortening the alkyl chain past a critical length suppresses the cooperative polymorph transition by limiting the alkyl chain conformation change. On the other hand, the nucleation and growth transition temperature increases as the side chain length decreases, possibly driven by the increase in the melting point of the alkyl chains. We also found that tuning the alkyl chain length modulates the associated quinoidal to aromatic biradical switching that drives the nucleation and growth transition, suggesting a synergy between the crystal structure and electronic structure. Ultimately depending on the exact mechanism of the polymorph transition, adjusting the alkyl chain length may lead to tuning of the polymorph transition temperature or suppression of the transition altogether. This offers a potential molecular design rule to target a particular transition mechanism based on the desired behavior for the system.

Structural dynamics of chlorpromazine (CPZ) drug with dipalmitoylphosphatidylcholine (DPPC) lipid: a potential drug for SARS-CoV-2

There is an urgent requirement for drug discovery and more importantly drug repositioning due to infectious new Severe Acute Respiratory Syndrome coronavirus 2. As per the recent report published in the journal L'Encéphale in May 2020, there is a planned ReCoVery Study examining the repurposing the chlorpromazine for the treatment of COVID-19. Here, we apply a combined Raman microspectroscopy and DFT-MD approach to investigate the structural dynamics of the Chlorpromazine (CPZ) drug with dipalmitoylphosphatidylcholine (DPPC) lipid bilayer, identifying the specific position of the drug in the DPPC lipid bilayer. The intensity ratios of the Raman peaks I 2935/I 2880, I 1097/I 1064 and I 1097/I 1129 are representative of the interaction of drugs with lipid alkyl chains and furnish conformation of lipid alkyl chains. Raman imaging microscopy for the study of the distribution of CPZ inside the lipid vesicles is reported. We also investigated the influence of order and disorder ratio in the CPZ on the DPPC liposomes prepared on phase transition temperature. HIGHLIGHTS Drug–membrane interactions using micromolar concentrations of both lipid and drugs. Neuroleptic drug and DPPC vesicles composed of DPPC/drug mixtures reveal qualitative differences between the Raman spectra The temperature-controlled Raman microspectroscopic study has demonstrated that below phase-transition temperature, the fatty acid chains of the phospholipids are stiff and packed in a highly ordered array. DFT and MD simulations to understand molecular interactions, structural dynamics, and Raman spectra. Above phase-transition temperature, the chains are disordered and possess more motional freedom. Communicated by Ramaswamy H. Sarma

Interaction of triblock copolymers (Pluronic®) with DMPC vesicles: a photophysical and computational study

Pluronic/lipid mix promises stealth liposomes with long circulation time and long-term stability for pharmaceutical applications. However, the influence of Pluronics on several aspects of lipid membranes has not been fully elucidated. Herein it was described the effect of Pluronics on the structured water, alkyl chain conformation, and kinetic stability of dimyristoylphosphatidylcholine (DMPC) liposomes using interfacial and deeper fluorescent probes along with computational molecular modeling data. Interfacial water changed as a function of Pluronics’ hydrophobicity with polypropylene oxide (PPO) anchoring the copolymers in the lipid bilayer. Pluronics with more than 30–40 PO units had facilitated penetration at the bilayer while shorter PPO favored a more interfacial interaction. Low Pluronic concentrations provided long-term stability of vesicles by steric effects of polyethylene oxide (PEO), but high amounts destabilized the vesicles as a sum of water-bridge cleavage at the polar head group and the reduced alkyl-alkyl interactions among the lipids. The high kinetic stability of Pluronic/DMPC vesicles is a proof-of-concept of its advantages and applicability in nanotechnology over conventional liposome-based pharmaceutical products for future biomedical applications.

Evaluation of the Molecular Conformation of Surface Alkyl Chains of Alkylsilane-Derived Hybrid Films Using Sum-Frequency Generation Spectroscopy

Alkylsilane-derived hybrid films exhibiting excellent dynamic dewetting behaviors toward various liquids are promising, since they are smooth, highly transparent, and a low environmental burden. However, the detailed mechanism of their unique dynamic dewetting behaviors and its relation to the surface segregation of alkylsilanes during the film formation have not yet been clearly identified. In this study, we prepared various hybrid films by varying the mixing ratios of tetraethoxysilane (TEOS) and n-dodecyltriethoxysilane (C12TES) and investigated the changes in the s-CH2/s-CH3 peak strength ratios of the resulting hybrid films under dry and wet conditions by sum-frequency generation (SFG) spectroscopy. When the static/dynamic water contact angles significantly changed, it was clearly observed that the s-CH2/s-CH3 ratio of each hybrid film under dry and wet condition also changed markedly. With increasing TEOS concentration, the static contact angles became smaller, while the contact angle hysteresis tended to increase because of the increase in gauche defects at the air interface and hydrogen bonds. This finding suggests that the concentration and conformation of the alkyl chains derived from surface-segregated C12TES molecules play an important role in determining the final dewetting behaviors of the hybrid films to water.

Reclined trend of alkyl chain of sodium dodecylbenzenesulfonate molecules induced by friction

Surfactants tend to adsorb on the surface/interface mostly in a directional manner. The alkyl chain orientation and conformation order for molecular monolayers of sodium dodecylbenzenesulfonate (SDBS) at low concentrations are studied by using the sum frequency generation vibrational spectroscopy (SFG-VS). The molecular arrangement of the surfactants adsorbed at the solid/liquid interface is further investigated. It is found that the arrangement of the SDBS at the interface becomes relatively ordered with increasing bulk concentration. Meanwhile, the orientation angle reduces gradually, and the molecules tend to be upright state. In addition, the effect of friction on the conformation order and orientation angle are also analyzed. The intensity of the SDBS vibrational contraction peak becomes lower after friction, which indicates that the anion has a reorientation process at the interface. The arrangement of molecules becomes more disordered due to friction. The orientation angle increases slightly, which indicates the monolayer has an inclined trend relative to the lateral direction on the interface. A modified adsorption model considering friction effect is proposed. This work may provide a reference for the further study of adsorption mechanism and application of surfactants.

Iron/2,6‐Di(pyrazol‐1‐yl)pyridine Complexes with a Discotic Pattern of Alkyl or Alkynyl Substituents

Abstract2,6‐Di(4‐iodopyrazol‐1‐yl)pyridine is converted to 2,6‐di(4‐{alkyn‐1‐yl}pyrazol‐1‐yl)pyridine (L1R; R’=CnH2n−3, n=12, 14, 16) derivatives by Sonogashira reactions. Hydrogenation of these intermediates yields the corresponding 2,6‐di(4‐alkylpyrazol‐1‐yl)pyridine (L2R; R=CnH2n+1) derivatives. Homoleptic Fe[BF4]2 complexes of all these ligands were prepared, bearing four long chain substituents in a discotic‐type array. Crystallographic data from two L1R ligands imply the alkynyl substituents do not undergo intermolecular interdigitation in the solid state, which could explain the lower crystallinity and ill‐defined spin‐crossover in their iron complexes. Solid [Fe(L2R)2][BF4]2 (n=12 and 14) exhibit an irreversible, abrupt low→high‐spin event near 350 K, which is not associated with solvent loss and may involve disordering of their alkyl chain conformations. No mesophase behavior was observed from any of these compounds.

Folding and Unfolding of Acetoxy Group-Terminated Alkyl Chains Inside a Size-Regulable Hemicarcerand.

A resorcinarene-based hemicarcerand, which consists of two cavitands covalently linked to each other by four alkyl chains, allows structural expansion and contraction by demetalation and metalation of Cu(I) cations with a size change of approximately 12 Å. This metal-mediated switching of the two states regulates the conformations of acetoxy group-terminated alkyl chains. A guest binding study reveals the encapsulation of heptyl to undecyl chains in metal-free and Cu(I)-coordinated capsules. The chemical shifts of the acetoxy groups of the bound guests are the same in the metal-free capsule, while those in the Cu(I)-coordinated one differ from each other. This indicates that the metal-free capsule regulates its size to the bound guests, while the bound guests adopt their conformations to the cavity of the Cu(I)-coordinated capsules. 1H NMR measurements and molecular mechanics calculations suggest that the bound guests have extended conformations in the metal-free capsule, while the Cu(I)-coordinated capsule forces the bound guests to adopt folded conformations. The presence of folded conformations is supported by the conformational study with structurally similar capsules and a nonsymmetric guest, allowing us to observe nuclear Overhauser effects stemming from the folded conformations of the guest in the cavity.

Effects of Phytosterol Butyrate Ester on the Characteristics of Soybean Phosphatidylcholine Liposomes.

The nutritional and structural properties of phytosterols (PS)/phytosterol esters (PEs) facilitate their use as substitutes for cholesterol in liposome encapsulation systems designed for oral drugs and health products. The purpose of this study was to determine the effect of phytosterol butyrate ester (PBE) on the properties of liposomes. PBE was encapsulated within liposomes (approximately 60 nm) prepared using soybean phosphatidylcholine using the thin-film hydration method. There was no significant change in the average particle diameter and zeta potential of these liposomal vesicles corresponding to the increasing amounts of encapsulated PBE. The incorporation of PBE increased the polydispersity index (PDI) independent of concentration. Additionally, we observed that the storage stability of PBE liposomes with uniform particle size and approximately spherical shape vesicle was better at low concentration. The results of Fourier-transform infrared (FTIR) spectroscopy and Raman spectroscopy showed that PBE was positioned at the water interface, which increased the order of hydrophobic alkyl chains in the lipid membranes. The incorporation of PBE led to an increase in the trans conformation of hydrophobic alkyl chain and consequently, the thermal stability of liposomes, which was confirmed by differential scanning calorimetry (DSC). The results of powder X-ray diffraction (XRD) analysis confirmed that PBE was present in an amorphous form in the liposomes. Additionally, the incorporation of PBE reduced the micropolarity of the lipid membrane. Thus, when preparing liposomes using thin-film hydration, the presence of PBE affected the characteristics of liposomes.

Effect of Different Ionic Surfactants on the Structural, Photophysical, and Morphological Properties of Water‐Based P3HT:PCBM Nanoparticle Dispersions and Films

AbstractAqueous suspensions of composite nanoparticles of poly(3‐hexylthiophene) (P3HT) and [6,6]‐phenyl C61 butyric acid methyl ester (PCBM) are fabricated by miniemulsion method using three different ionic surfactants. The aim is to study how the length and conformation of the surfactants alkyl chains affect the properties of the nanoparticles. While the morphology and dimensions of the nanoparticles are similar, UV–vis spectroscopy evidences that the internal aggregation and ordering of the P3HT chains varies within the three nanoparticle formulations. The surfactant with branched alkyl chains promote the highest degree of ordering of P3HT chains in the nanoparticles (leading to increased conjugation length). In contrast, the lowest ordering is found for the nanoparticles with the surfactant having the shortest linear alkyl chain. The optical/structural properties of nanoparticles are partially retained in the films. Besides, the surfactant with branched alkyl chains favors the strongest coalescence of nanoparticles in the thin film, promoting a further ordering of the polymeric chains in the most external shell of the nanoparticles as evidenced by steady‐state and time‐resolved UV–vis spectroscopy and confocal fluorescence microscopy. These findings might guide the engineering of new surfactants for composite nanoparticles for optoelectronic applications.

Interaction of the (2√3 × 3)rect. Adsorption-Site Basis and Alkyl-Chain Close Packing in Alkanethiol Self-Assembled Monolayers on Au(111): A Molecular Dynamics Study of Alkyl-Chain Conformation.

We show that the adsorption site basis of the (2√3 × 3)rect. phase of n-alkanethiol self-assembled monolayers plays a key role in determining the molecular conformation of the close-packed alkyl chains. Ten proposed reconstructed Au–S interfaces are used to explore the minimized energy alkyl-chain packing of n-decanethiol molecules using molecular dynamics with the all-atom description. In this comparative study, all models have the same alkyl-chain surface density of four molecules per unit cell; thus, differences are due to the headgroup spacing within the 4-molecule basis as opposed to the average surface density. We demonstrate for the first time the 4-molecule-basis twist structure driven by the packing of alkanethiol molecules in a large simulation box (100 molecules, 25 unit cells) using molecular dynamics. Our results validate the prediction put forward by Mar and Klein that to achieve the 4-molecule-basis twist symmetry observed by the experiment, the headgroups must deviate from the high-symmetry (√3 × √3)R30° sites. The key structural parameters: tilt, twist, and end-group height, as well as their spatial order, are compared with experimental results, which we show is a highly sensitive approach that can be used to vet proposed Au–S interfacial models.

Role of the cationic headgroup to conformational changes undergone by shorter alkyl chain surfactant and water molecules at the air-liquid interface

HypothesisSurfactants are commonly used as corrosion inhibitors for oil-and-gas pipelines. The alkyl chain of surfactants and their overall conformation contributes to the adsorption, flotation, and foam separation in the inhibition process. We hypothesize that the conformation of shorter alkyl chains and chemical nature of surfactants has an effect on the ordering of water molecules at the air-water interface which is not yet well understood. ExperimentsAlkyl (C4, C6, C8, C10, and C12) dimethylbenzylammonium bromides (Quats) were synthesized. Aqueous solutions at 0% and with different salt concentrations were studied at the air-liquid interface using sum frequency generation spectroscopy. Surface tension and pH measurement were also conducted for comparison. FindingsSurfactant solutions at 0%, 1%, and 10% salt showed a zigzag trend for the number of gauche defects. At 0% salt, an increasing trend of OH band intensity at 3182 cm−1 was observed from C6 to C12 SFG spectra. Yet, C4 showed a more prominent SFG signal from strongly hydrogen-bonded water molecules compared to C6. The headgroup’s chemical nature was found to play a role in the ordering of water molecules for a C4 alkyl chain length. The OH band intensity decreases with increasing ionic strength.

Adsorption of gaseous aromatic compounds by linear quaternary ammonium-modified γ-zirconium phosphate

In this work, the intercalation of alkyl trimethylammonium ion (CnN+) and dialkyl dimethylammonium ion (2CnN+) were attempted for α‑zirconium phosphate (α-ZrP) and γ-ZrP. And then a pure intercalation compounds were obtained only for γ-ZrP. It was expected that the intercalation of linear quaternary ammonium ion would produce not only a hydrophobic environment in the interlayer space but also form an appropriate void for the adsorption of hydrophobic air pollutants. The basal spacing of 2CnN+-intercalated γ-ZrP was greater than that of CnN+-intercalated γ-ZrP because CnN+ was arranged in a mono-molecular structure in the interlayer space contrary to the bi-molecular structure of 2CnN+. Furthermore, the alkyl chain in the interlayer space of γ-ZrP was in a gauche form for CnN+, for a smaller carbon number (n), and changed to a trans structure for a larger n. γ-ZrP with a modified interlayer space could adsorb gaseous aromatic hydrocarbons contrary to the nonmodified γ-ZrP. Maximum adsorption was attained for C18N+-intercalated γ-ZrP with a mono-molecular structure and trans structure alkyl chain, although the basal spacing and uptake of alkyl ammonium reached a maximum for 2C18N+-intercalated γ-ZrP. Hence, not only the basal spacing and carbon number but also the void space in the interlayer region affected adsorption. It was interesting to note that the conformation of the long alkyl chain was reversibly changed through adsorption and desorption.

Impact of water on the hydrogen bonding between halide‐based ion‐pairs investigated by Raman scattering and density functional theory calculations

AbstractWe present a study of the impact of water on the size‐ and electronegativity‐dependent hydrogen bonds between cation and anion of imidazolium‐based ionic liquids (ILs) with halide anions. We have combined Raman spectroscopy with density functional theory (DFT) computations to characterize the intermolecular associations of cation–anion–water moieties. The Raman band at ~1,422 cm−1, which is assigned to the ν(N─CH2─CH3) vibration of the ethyl chain in the neat ion pairs (pure ion pairs), is blue shifted by +7, +4, and +3 cm−1 for 1‐ethyl‐3‐methylimidazolim (C2mim) cation‐based C2mim X ion pairs with X = Cl, Br, and I, respectively, in a water‐rich environment. Simultaneously, upon dilution, a new peak at ~1,438 cm−1 starts to appear at the high‐wavenumber side with continuously increasing intensity. These significant perturbations of the ν(N─CH2─CH3) vibrational mode in water environment are a clear indication of the change in the alkyl chain conformation. Further, the relative intensities of the Raman bands at ~2,946 and ~2,950 cm−1 corresponding to νs (CH2) and νas (CH3) of the ethyl chain, respectively, were significantly changed upon dilution, which also confirms the conformational change of the alkyl chain. The Raman band belonging to the C4/5─H stretch mode was significantly blue shifted by +33, +41, and +42 cm−1 going from the studied neat ion pairs having Cl, Br, and I anions to the corresponding water mixtures, respectively. Significant changes were also observed for the ν(C2─H) vibrational mode of the ion pairs in water environment; here, we observed blue shifts of +60, +51, and +50 cm−1 for ion pairs having Cl, Br, and I anions, respectively. These results confirm the weakening of the ion‐pair interaction due to the interaction with water molecules. In contrast to the ILs with halide anions, C2mim BF4 does not show any variation in the Raman peak positions upon dilution. Experimental results are nicely supported by the results of DFT calculations, and a sensible connection was established.

13C NMR Investigations of Hairy-Rod-Like π-Conjugated Mesogens

Two hairy-rod π-conjugated mesogens comprising dihexylfluorene and didecyloxyterphenyl are synthesized, and their mesophase properties are examined by hot-stage optical polarizing microscope and differential scanning calorimetry techniques. Both mesogens exhibit enantiotropic nematic mesophase with broad mesophase range. A detailed 13C NMR study is carried out in solution as well as in nematic mesophase to understand changes in the orientation of the aliphatic chains. Accordingly, the unusual NMR chemical shift value of one of the methylene carbons of the hexyl chain of fluorene moiety in solution is ascribed to ring current effect changes in nematic mesophase owing to variation in the orientation of the hexyl chain. The change in conformation of lateral and alkyl chains in the nematic phase is clearly noticed compared to isotropic solution as the molecular orientation in mesophase is governed by the orientation of the long molecular axis. Furthermore, the 13C-1H dipolar couplings obtained from 2D separated local field experiments in nematic phase aided the assignments of all of the carbons of the molecules besides offering the local order. To comprehend the orientation of the fluorene unit, three order parameters are necessary whereas for the phenyl rings, two order parameters are found to be sufficient. The molecular biaxiality ( S xx - S yy) for fluorene-based mesogen is found to be higher due to the fused nature of the moiety and the presence of dihexyl chains. The orientational ordering of π-conjugated mesogens is crucial as the optoelectronic properties of them critically depend on the orientation of the constituent chromophores. The complete mapping of order parameters of fluorene, the phenyl rings and the alkyl chains showed that despite both molecules exhibiting nematic mesophase, the orientational constraints are governed by the molecular structure as well as the rigidity of the core unit, i.e., fused versus linearly connected rings.

2,6-Bis(pyrazol-1-yl)pyridine-4-carboxylate Esters with Alkyl Chain Substituents and Their Iron(II) Complexes

Two series of 4-(alkoxyphenyl) 2,6-bis{pyrazol-1-yl}pyridine-4-carboxyate (L3R) or alkyl 2,6-bis{pyrazol-1-yl}pyridine-4-carboxyate (L4R) esters have been synthesized and complexed to iron(II), where R = C nH2 n+1 ( n = 6, 12, 14, 16, 18); two other derivatives related to L3R are also reported. While the solid [Fe(L4R)2][BF4]2 compounds are isostructural by powder diffraction and show similar spin state behaviors, the [Fe(L3R)2][BF4]2 series shows more varied structures and magnetic properties. This was confirmed by solvated crystal structures of [Fe(L3R)2][BF4]2 with n = 6, 14, 16, which all adopt the P1̅ space group but show significantly different side-chain conformations and/or crystal packing. The solid complexes are mostly low spin at room temperature, with many exhibiting the onset of thermal spin crossover (SCO) upon warming. Heating the complexes with n ≥ 14 significantly above their SCO temperature transforms them irreversibly into a predominantly high spin state, which is accompanied by structure changes and loss of crystallinity by powder diffraction. These transformations do not coincide with lattice solvent loss and may reflect melting and refreezing of their alkyl chain conformations during the thermal cycle. Four of the complexes exhibit SCO in CD3CN solution with T1/2 = 273-277 K, which is apparently unaffected by their alkyl chain substituents.

Effects of Temperature and Chain Length on the Nanoscale Islands of Alkanethiol Monolayers

The thermal effect on the stability of nanoscale islands of alkanethiols on a gold (111) surface was examined using molecular dynamics simulation. To examine the chain length and temperature dependence, islands made of alkanethiols containing 16, 20, and 24 carbon atoms were simulated at 313–343 K. By analyzing the tilt angle, conformation, orientational order, and backbone plane orientation of alkyl chains, the minimum diameters for stable islands made of 1‐hexadecanethiol, 1‐ecosanethiol, and 1‐tetracosanethiol were determined for different temperatures (313–343 K). These results provide a useful guideline for patterning nanopatterns of thiol by soft nanolithography.