Selected Bond Distances Research Articles

Trinuclear Nickel Catalyst for Water Oxidation: Intramolecular Proton-Coupled Electron Transfer Triggered Trimetallic Cooperative O–O Bond Formation

Trinuclear Nickel Catalyst for Water Oxidation: Intramolecular Proton-Coupled Electron Transfer Triggered Trimetallic Cooperative O–O Bond Formation

Crystallographic structure, activity prediction, and hydrogen bonding analysis of some CSD-based 3,3'-bis-indole derivatives: A review

Herein we report crystallographic comparison of some geometrical and structural features for a series of biologically relevant bis-indole derivatives. Selected bond distances and bond angles of interest in a series of bis-indole derivatives have been discussed in detail. The biological activity of the substances has been correlated with based the structure-activity relationships (SAR) base which provides the different possibility of activity (Pa) and possibility of inactivity (Pi). For a better understanding of the packing interactions existing among these derivatives, an overview of crystal structure analysis with emphasis on the intramolecular hydrogen bonding in some bis-indole derivatives is presented. The role of hydrogen bonding in the crystal structure assembly of bis-indole derivatives has been found to be predominant and this observation reveals significant impact of hydrogen bonding in high value of drug-likeness of these bio-molecules.

Thermally Induced Reversible Metal-to-Metal Charge Transfer in Mixed-Valence {Fe III 4 Fe II 4 } Cubes

Thermally Induced Reversible Metal-to-Metal Charge Transfer in Mixed-Valence {Fe ^III ₄ Fe ^II ₄ } Cubes

Radical Mechanism of Ir III /Ni II -Metallaphotoredox-Catalyzed C(sp 3 )–H Functionalization Triggered by Proton-Coupled Electron Transfer: Theoretical Insight

Photoredox catalysis can be induced to activate organic substrates or to modulate the oxidation state of transition-metal catalysts via unique single-electron transfer processes, so as to achieve c...

Crystal-Chemical Properties of Synthetic Almandine-Pyrope Solid Solution by X-Ray Single-Crystal Diffraction and Raman Spectroscopy

Crystal-chemical properties of synthetic Almandine-Pyrope (Alm-Pyr) solid solutions were investigated by X-ray single-crystal diffraction and Raman spectroscopy. Garnet solid solution with different compositions were synthesized from powder at 4.0 GPa and annealed at 1200 °C for 48 h by a multi-anvil pressure apparatus. Garnet crystals with different sizes (about 60–1000 μm) were obtained from synthesis. The results of X-ray single-crystal diffraction show that the unit cell constants decrease with increasing Pyr contents in the synthetic Alm-Pyr crystals due to the smaller ionic radius of Mg2+ in eightfold coordination than that of Fe2+. The data exhibit obviously positive deviations from ideal mixing volumes across the Alm-Pyr join which may be caused by the distortion of the SiO4 tetrahedron. Moreover, the significant decrease in the average M-O bond length and volume of the [MgO8]/[FeO8] dodecahedron with increasing Pyr contents are the most important factors to the decrease in the Alm-Pyr crystal unit cell constant and volume. On the other hand, selected bond distances (average <M-O>, <Al-O>, and <D-O> distances) have a linear correlation with the unit-cell parameter, but the <Si-O> distance has nonlinear correlation. With increasing the unit-cell parameter, the average <M-O> distance increases significantly, followed by the average <D-O> and <Al-O> distances. While the <Si-O> distance changes negligibly further confirming the conclusion that the significant decrease of the average M-O bond length of the [MgO8]/[FeO8] dodecahedron with increasing Pyr contents are the most important factors to the decrease in the Alm-Pyr crystal unit cell volume. In the Raman spectra collected for the Alm-Pyr solid solutions, Raman vibration mode assignments indicate that the Raman vibrational spectra change along the Alm-Pyr binary solution. The mode frequencies of Si-O stretching, Si-O bending, and the rotation of the SiO4-tetrahedron (R(SiO4)) decrease linearly, while the translational modes of the SiO4-tetrahedron (T(SiO4)) increase with increasing Alm contents.

A DFT/TDDFT investigation on the efficiency of novel dyes with ortho-fluorophenyl units (A1) and incorporating benzotriazole/benzothiadiazole/phthalimide units (A2) as organic photosensitizers with D–A2–π–A1 configuration for solar cell applications

Novel derivatives of OD1 with D–A2–π–A1 configuration have been designed. The calculated geometrical parameters and optoelectronic properties are compared with those of the parent triphenylamine-based dye molecule (OD1) comprising a triphenylamine terminal electron-rich group (D), 3,4-ethylene dioxythiophene π-spacer, fluorophenyl electron-withdrawing group (A1), and cyanoacrylic acid anchor group. The designed derivatives differ from OD1 with D–π–A1 configuration in the incorporation of an electron-acceptor group (A2) between the donor group and π-spacer unit, namely benzotriazole (BTZ), benzothiadiazole (BTDZ), or phthalimide (PHI), denoted as ND2-BTZ, ND3-BTDZ, and ND4-PHI, respectively. The effects of the incorporation of each electron-deficient unit on the geometry, absorption spectra, and electrochemical properties are investigated by using density functional theory (DFT) and time-dependent (TD)DFT methods. Additionally, the preferred dye adsorption process on model Ti(OH)4 is investigated. The results for the binding energy, selected bond distances, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels and their distribution, energy gaps, and total density of states (TDOS) plots are discussed and analyzed. The intermolecular interaction between two monomers of each dye and iodine is also investigated, and the complexation energy [corrected for the basis set superposition error (BSSE)] is calculated and analyzed. The results reveal that the introduction of the BTDZ and PHI functional groups is more promising for formation of organic dyes with D–A2–π–A1 configuration.

Excited-state intramolecular proton transfer in non-fused five- and fused six-membered ring pyrrole-pyridine hydrogen bond systems

Abstract The non-fused five-membered ring structure of 2-(1H-pyrrol-2-yl)pyridine (5-HB) is more flexible than the fused six-membered ring structure of 10,11,12,13-tetrahydro-9H-quinolino[8,7-a]carbazole (6-HB) to form the intramolecular hydrogen bond between pyrrole and pyridine, while the six-membered ring structure possesses more favorable distance and orientation between pyrrole and pyridine. In the present work, we carried out the electronic structure calculations and nonadiabatic dynamics simulations to gain insight into the effect of different structure feature on the excited-state intramolecular proton transfer (ESIPT) processes of 5-HB and 6-HB. The geometric parameters, IR vibrational spectra, bond critical point (BCP) parameters and reduced density gradient (RDG) show that the intramolecular hydrogen bond of 6-HB is much stronger than that of 5-HB. The 6-HB has a lower kinetic stability and a higher chemical activity than 5-HB through the analysis of the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). The pyridine N1 atom of 6-HB shows much stronger ability than that of 5-HB to attract the hydrogen proton based on the natural population analysis (NPA). The analysis of the potential energy curves and time evolution of selected bond distances indicate that the ESIPT process of fused six-membered ring structure is easier and faster than the non-fused five-membered ring structure. Our findings might be useful for the design of relevant ESIPT systems.

Synthesis, characterization, antimicrobial activity, and QSAR studies of some new 6‐substituted phenyl 3‐(4‐chlorophenyl)‐3a,4,8,8a‐tetrahydro‐[1,3,2]dioxaborepino [5,6‐d]isoxazoles

Abstract3‐(4‐Chlorophenyl)‐3a,4,8,8a‐tetrahydro‐[1,3,2]dioxaborepino[5,6‐d] isoxazoles were synthesized from the reaction of (3‐(4‐chlorophenyl)‐4,5‐dihydroisoxazole‐4,5‐diyl)dimethanol with substituted phenylboronic acids. Crystal structure of 1‐(4‐(3‐(4‐chlorophenyl)‐3a,4,8,8a‐tetrahydro‐[1,3,2]dioxaborepino[5,6‐d]isoxazol‐6‐yl)phenyl) ethanone was studied and the values of selected bond distances (Å), bond angles (°), and dihedral angles (°) were found in agreement with the calculated (DFT, B3LYP/6‐311++G(d,p)) values. Antimicrobial activity of these new compounds was also studied against a panel of microorganisms including Staphylococcus aureus, Enterococcus faecalis, Pseudomonas aeruginosa, Escherichia coli, Streptococcus mutans, and Candida albicans. Most of the dioxaborepines exhibited fair activities against these microorganisms. The pMIC values of the compounds were first correlated with Hammett polar substituent constant (σ) together with lipophilic constant (π) and statistically significant 2D correlations were obtained. In addition, the pMIC values of the compounds were correlated with some theoretical descriptors and fair 2D‐QSAR models with clogP, SAA, and μ as independent variables were obtained.

Temperature Dependence of NMR Parameters Calculated from Path Integral Molecular Dynamics Simulations

The influence of temperature on NMR chemical shifts and quadrupolar couplings in model molecular organic solids is explored using path integral molecular dynamics (PIMD) and density functional theory (DFT) calculations of shielding and electric field gradient (EFG) tensors. An approach based on convoluting calculated shielding or EFG tensor components with probability distributions of selected bond distances and valence angles obtained from DFT-PIMD simulations at several temperatures is used to calculate the temperature effects. The probability distributions obtained from the quantum PIMD simulations, which includes nuclear quantum effects, are significantly broader and less temperature dependent than those obtained with conventional DFT molecular dynamics or with 1D scans through the potential energy surface. Predicted NMR observables for the model systems were in excellent agreement with experimental data.

Crystal Structure of 3-Bromo-7-(dimethylamino)-4-methylcoumarin

Coumarin derivatives are a useful component for developing new materials, such as fluorescence materials and laser dyes; non-linear optical materials and reagents; photorefractive materials; photoresistors; intermediates for drug synthesis; luminescence materials; analytical reagents, etc.1,2 Coumarin 311, 7-(dimethylamino)-4-methylcoumarin, is also used as laser dyes. It gives laser emission at around 453 nm in ethanol. The crystal structure of coumarin 311 has already been reported.3 However the fluorence property and crystal structure of 3-bromo-7-(dimethylamino)-4-methylcoumarin (1) has not yet been reported. We now report on the crystal structure of 1 with the aim of the contributing to a deeper understanding of the substituent effect at the 3-position of coumarin 311 on the structure and crystal packing. Compound (1), shown in Fig. 1, was synthesized by the reaction of 7-(dimethylamino)-4-methylcoumarin with bromine in glacial acetic acid, as reported in a previous paper.4 The spectral data of 1 are as follows: mp 168 – 169 C, 1H NMR (CDCl3) d 2.53 (3H, s), 3.06 (6H, s), 6.48 (1H, d, J = 2.6 Hz), 6.62 (1H, dd, J = 9.0 Hz, 2.6 Hz), and 7.43 (1H, d, J = 9.0 Hz). 13C NMR (CDCl3) d 19.15, 40.1(2C), 97.7, 106.2, 109.3, 109.4, 125.8, 151.5, 152.8, 154.1, and 158.0. Compound (1) gave a strong emission band at 442 nm in chloroform solution (1.0 ¥ 10–5 M) when excited at 380 nm. Single crystals of 1 were grown in chloroform at room temperature. Data collection and refinement parameters are listed in Table 1. The H atoms were positioned with the idealized geometry, and were refined to be isotropic (Uiso(H) = 1.2Ueq(C)) using a riding model with C–H = 0.95 A for aromatic H atoms and C–H = 0.98 A for methyl H atoms. The selected bond distances and angles are collected in Table 2. An ORTEP drawing of the molecule of 1 is shown in Fig. 2. The molecule is almost planar with a maximum deviation of –0.154(2)A for N1. The dihedral angle between the pyrone ring Crystal Structure of 3-Bromo-7-(dimethylamino)-4-methylcoumarin

Haloboration of internal alkynes with boronium and borenium cations as a route to tetrasubstituted alkenes.

Hail boration! 2-Dimethylaminopyridine-ligated dihaloborocations [X2B(2-DMAP)](+) with a strained four-membered boracycle were used for the haloboration of terminal and dialkyl internal alkynes (see scheme). Esterification then provided vinyl boronate esters as useful precursors to tetrasubstituted alkenes. Following mechanistic studies, the scope of the haloboration was expanded simply by variation of the amine. Pin = 2,3-dimethyl-2,3-butanedioxy.

Synthesis, spectral identification, electrochemical behavior and theoretical investigation of new zinc complexes of bis((E) 3-(2-nitrophenyl)-2-propenal)propane-1,2-diimine

Synthesis, spectroscopic, electrochemical behavior and theoretical investigation of some zinc complexes of a new Schiff base ligand of bis((E) 3-(2-nitrophenyl)-2-propenal)propane-1,2-diimine (L) with a general formula of ZnLX2(X=Cl−, Br−, I−, SCN− and N3-) are described. The ligand and its complexes were identified by elemental analysis, molar conductivity, UV–Visible spectra, FT-IR spectra, 1H NMR and 13C NMR spectra. The complexes were found to be molecular and non-electrolyte based on conductivity measurement. The spectral data confirm coordination of ligand and anions(X−) to zinc ion center. Electrochemical behavior of ligand and complexes were investigated by cyclic voltammetry technique exhibiting different redox behavior of complexes with respect to free ligand so that the ligand and complexes showed quasi-reversible and irreversible electron transfer processes respectively. Molecular structures of the ligand and complexes have been optimized at the UB3LYP/LANL2MB∗ level of theory. Accordingly some theoretical thermodynamical and/or structural parameters such as HF-energy, Gibbs free energy, enthalpy, selected bond distances, bond angles and torsion angles of optimized structures are presented.

Monophosphine-Cyclopalladated Ferrocenylpyrimidine Complex: Synthesis, Crystal Structure and Reusable Catalytic System for Coupling Reaction of Aryl Chlorides in PEG-400

Since the first report on the use of palladacycles for the Suzuki and Heck reactions by Herrmann, Beller and coworkers in 1995, a wide variety of known and new palladacycles have been successfully used in the coupling reactions. Employing aryl chlorides for this reaction has been focused because aryl chlorides are cheaper and more available than their bromides and iodide counterparts. However, only a few palladacycles have proved to be efficient for the activation of notoriously unreactive aryl chlorides. In most cases the catalysts employed need to be used in relatively high loadings, and poor recovery, which negated the advantages associated with the use of aryl chlorides. PEGs [poly(ethylene glycol)] have clear advantages as a solvent in organic synthesis because they are cheap, steady, readily available, and nontoxic. Recently, liquid PEGs have been adopted as a new approach for catalyst recycling, in a broad range of catalytic organic reactions. We have also found biaryl phosphine adducts of cyclopalladated ferrocenylpyrimidine are very efficient for the amination of aryl chlorides in PEG-400. These adducts combine the stability induced by the presence of a palladacycle framework with the high activity commonly associated with phosphine ligands, and were far more active than the corresponding dimeric palladacycle. As a continuation of our interest in the synthesis and application of cyclopalladated complexes, we have prepared a new phosphine adduct of palladacycle 2 from the reaction of cyclopalladated ferrocenylpyrimidine dimer 1 with commercially available 2-dicyclohexylphosphanyl-2'-(N,N-dimethylamino)biphenyl (DCPAB) (Scheme 1) and examined its activity in the coupling reactions. Complex 2 is airand moisture-stable, both in solid state and in solution. It is very soluble in chloroform, dichloromethane and acetone, but insoluble in petroleum ether and n-hexane. The new complex was fully characterized by elemental analysis, IR, H NMR and ESI-MS. These spectra were well consistent with the title complex. Moreover, the molecular structure of 2 has been ascertained by means of X-ray studies. The molecule of 2 together with selected bond distances and angles is shown in Figure 1. The Pd atom is in a slightly distorted square-planar environment bonded to the phosphorus atom, the chlorine atom, the pyrimidinyl nitrogen atom and the carbon atom of the ferrocenyl moiety. The Pd–P bond length of 2 is similar to those of the related DCPAB-palladacycles, while the above bond length of 2 is longer than those of the related PPh3-palladacycles possibly due to the steric bulk of the DCPAB ligand. 16-18 In the crystal of 2 there exist two types of intermolecular C–H···Cl hydrogen bonds, which link the molecules into a 2D

Air‐Stable, Highly Fluorescent Primary Phosphanes

Air‐Stable, Highly Fluorescent Primary Phosphanes

Biological-Activity Predictions, Crystallographic Comparison and Role of Packing Interactions in Androstane Derivatives of Steroids

A total of 60 molecules of androstane derivatives of steroids (1–60) have been undertaken to predict their pharmacological effects, specific mechanisms of action, known toxicities, drug likeness, etc., by using the statistics of multilevel neighbourhoods of atoms (MNA) descriptors for active and inactive fragments. The biological activity spectra for substances have been correlated on SAR base (Structure–activity relationships data and knowledge base) which provides the different Pa (probability of activity) and Pi (probability of inactivity). The Lipinski’s rule predicts that all the androstane derivatives have stronger preponderance for “cancer-like-drug” molecules and some of their related analogous have been entered in the ANCI (American National Cancer Institute) database. Some selected bond distances and bond angles of interest have been taken into account and deviation of bond distances/bond angles, vis-a-vis the substitutional group and X–H···A intra/intermolecular hydrogen bonds have been discussed in detail. X–H···A intra/intermolecular hydrogen bonds in the identified molecules have been described with the standard distance and angle cut-off criteria. D–θ and d–θ scatter plots for X–H···A intra-and intermolecular interactions are presented for better understanding of packing interactions existing among these derivatives. Comparison of contacts from H(C) to O and H(O) to O, vis-a-vis their crystal structure reveals that contacts from H(O) to O predominate over H(C) to O. Solvent–solute/solute–solvent interactions have also been investigated to understand more complicated processes that occur for biomolecules in aqueous solutions. Most of the molecules show high value of drug-likeness whereas molecule-3 (82.5%), 36 (87.2%), 41 (83.7%), 43 (86.5%) and 50 (85.9%) exhibit low value of drug-likeness, instead of observed range of 90.3–99.2%. Steroidal molecules are held in their defined 3-D structures by hydrogen bonds. The hydrogen bonding/solvent–solvent interactions for a steroidal molecule (androstane derivative) are plotted in Figure. The asymmetric unit cell in androstane derivative contains two crystallographically independent molecules and two acetic acid molecules. The two acetic acid molecules are connected to one another through solvent–solvent [O6(Acetic acid)–H6C(O6)···5′(Acetic acid); O6′(Acetic acid)–H6′C(O6′)···O5(Acetic acid)] interactions. The solvent-solvent interactions as observed in said steroidal derivative are rarely found in steroids and such investigations could be important to understand more complicated processes that occur for biomolecules in aqueous solutions.

Comparative Crystallographic and Hydrogen-bonding Analysis of Pregnane Derivatives

A crystallographic comparison comprised of some geometrical and structural features of a steroids series (pregnane derivatives) is made in the present paper. Some selected bond distances and bond angles of interest are discussed in detail. Conformations of individual ring systems in a series of 46 pregnane derivatives have been calculated and discussed. Correlation of ring conformations especially the rarer ones, vis-a-vis the multiple bonds and ring junctions has been discussed. Graphical presentations of ring conformations are made for all the five- and six-membered rings to show the relative frequency of their occurrence. 17β-side chain conformation is discussed in some pregn-20-one structures. X–H···A intra- and intermolecular interactions in the identified derivatives have been discussed with the standard distance and angle cut-off criteria. Distance-angle scatter plots for both kinds of interactions are presented for a better understanding of the packing interactions which exist in pregnane molecules.

The First Structurally Determined Ruthenium Nitrate Complex of Chelating Diphosphine Ligand

Among the reported functionalized complexes, oxo and nitrido ruthenium or osmium complexes containing multidentate nitrogen-based ligands have proven to be especially valuable in mechanistic and oxidative catalytic studies. During the last decade the chemistry of inorganic and organometallic complexes with phosphine ligands has been well developed to apply them to catalysts. Therefore it is of interest to combine these two characteristics to prepare oxo complexes surrounded by the phosphine ligands. A general way to synthesize Ru-oxo complexes can be started from the related Ru-chloro species via the corresponding Ru-aquo complexes. Oxidation of the Ru-aquo complexes by a powerful one-electron oxidant like (NH4)2Ce(NO3) (CAN) can lead to the formation of the final products. Accordingly we prepared and characterized ruthenium di-chloro complexes, [Ru(dppm)2Cl2] and [Ru(dppe)2Cl2], by using the reaction of [Ru(PPh3)2Cl2] with the dppm or dppe ligand (PPh3: triphenylphosphine, dppm: 1,1-bis(diphenylphosphino)methane, dppe: 1,2-bis(diphenylphosphino)ethane). A ruthenium di-aquo complex, [Ru(dppm)2(H2O)2](PF6)2, can be obtained by adding AgClO4 to the [Ru(dppm)2Cl2] complex followed by precipitating with saturated NH4PF6 solution. CAN in HClO4 was added into the di-aquo complex and the residue was put into the refrigerator. The crystals obtained by diffusion method from acetone/water show the formation of an unexpected complex rather than the desired ruthenium di-oxo species. In organic chemistry CAN has been known to catalyze the ring opening reaction of different epoxides through the formation of nitrate compound in aprotic solvent, which is a key intermediate in the stereoselective syntheses and is useful for a variety of oxidative transformations. The photochemical reaction of CAN with olefins also produced 1,2nitrate adduct via the initial formation of nitrate radical. It is quite interesting to show that CAN can be used to prepare the nitrate complexes in coordination chemistry. Here we found out that the reaction of CAN in perchloric acid with the di-aquo complex gave the unusual nitrate complex rather than the di-oxo complex. In the reaction it is presumed that the more labile aquo group in the di-aquo complex can be quickly substituted by the nitrate anion in a bi-dentate fashion, which is more favorable in entropy. The structure of the nitrate complex, which turned out to be [Ru(dppm)2(O2NO)][ClO4], has been determined from X-ray diffraction. The perspective view with the numbering scheme of the atoms is shown in Figure 1. The complex consists of discrete [Ru(dppm)2(O2NO)] and ClO4, which contains a ruthenium atom surrounded by two chelating diphosphine ligands and the nitrate ligand. The presence of the nitrate ligand coordinated to the ruthenium metal was confirmed by a singlet resonance at 13.8 ppm in the N NMR spectrum and that of the perchlorate anion by a sharp singlet peak at 1.01 ppm in the Cl NMR spectrum. The magnitude of the splitting of peaks at 1435 and 1232 cm−1 observed in the FT IR spectrum re-confirmed that the nitrate ligand coordinated to the metal in a bi-dentate way. The coordination polyhedron around the ruthenium metal is described as a severely distorted octahedron. Selected bond distances and angles listed in Table 1 are comparable with other structurally characterized complexes containing the dppm ligand. The Ru-P bond distances range from 2.277(1) to 2.393(1) A. The phosphorous atoms coordinated to ruthenium metal deviate strongly from a square planar arrangement as noted by the P1-Ru-P2 and P3-Ru-P4 bond angles of less than 90 (70.76(3) and 70.35(3), respectively) for two phosphorous atoms bonded to the ruthenium metal cis to one another and by the P1-Ru-P4 and P2-Ru-P3 angles of less than 180 (103.8(1) and 102.7(1), respectively) for those in the opposite position.

Comparative crystallographic and hydrogen-bonding analysis of cholestane derivatives

A crystallographic comparison of some geometrical and structural features for a series of steroids (cholestane derivatives) is made in the present paper. Selected bond distances and bond angles of interest are discussed in detail. Conformations of individual ring systems in a series of 28 cholestane derivatives are calculated and discussed. Graphical presentations of ring conformations are made for all the five- and six-membered rings to show the frequency of their occurrence. X--H...A intra- and intermolecular interactions in the identified molecules are discussed with the standard distance and angle cut-off criteria. Distance-angle scatter plots for both kinds of interactions are presented for better understanding of packing interactions existing in cholestane molecules.

A neutron diffraction study on ceria-neodia solid solutions

Neutron diffraction studies were carried out to ascertain the structural details of the composition Ce0.5Nd0.5O1.750. The structure was unequivocally found to be that of C-type cubic. The refinement on an F-type cubic lattice was found to be unacceptable because of high R values. Selected bond distances are also being reported. In addition, the neutron diffraction studies on a typical defective F-type composition Ce0.75Nd0.25O1.875 were also carried out.

Liquid crystalline macrocycles containing phenylpyrimidine unitsElectronic supplementary information (ESI) available: the procedures and analytical data for all compounds and a table with selected bond distances and bond angles of the crystal structure of compound C are available as supplementary data. See http://www.rsc.org/suppdata/jm/b2/b210271d/

Several different macrocyclic liquid crystals consisting of two calamitic 2-phenylpyrimidine or 5-phenylpyrimidine units connected at both ends by polyether or alkyl chains have been synthesised by macrocyclisation reactions under high dilution conditions. The nature of the rigid core has a strong impact on the liquid crystalline phases formed. All 2-phenylpyrimidine paracyclophanes show nematic phases, whereas for the series of the 5-phenylpyrimidine derivatives smectic A-phases are exclusively formed. This behaviour is related to conventional calamitic phenylpyrimidine liquid crystals, but the mesophases are strongly stabilised in the macrocycles. An exchange of polyether chains by alkyl chains leads to significant mesophase stabilisation, whereas increasing the spacer length reduces mesophase stability. Pre-organization of the calamitic cores and micro-segregation of chemically distinct molecular parts are discussed as reasons for the observed effects of molecular structure on the mesophase behaviour of these compounds.