4-membered Ring Research Articles

Synthesis, molecular, and crystal structure of 3,4-bis[(2,6-di-tert-butyl-4H-pyran-4-ylidene)methyl]cyclobut-3-ene-1,2-dione and -1,2-dithione

Two new dyes have been prepared, 3,4-bis[(2,6-di-tert-butyl-4H-pyran-4-ylidene)methyl]-cyclobut-3-ene-1,2-dione and -1,2-dithione. Their molecular and crystal structures have been studied by X-ray diffraction, and their spectral properties have been characterized. The heterocyclic fragments in the dyes molecules are in the trans-position with respect to the bonds connecting chromophore CH group with the 4-membered ring. Substitution of the carbonyl oxygen to sulfur leads to change in the crystal packing.

A novel cobalt (I) coordination polymer with mixed thiocyanate and quinoline ligands: Crystal structure, magnetism and luminescent properties

A new Co(I) one-dimensional coordination polymer [Co(SCN)(ql)]n (ql=quinoline) (1) has been synthesized and characterized by IR, elemental analysis, TG technique and X-ray crystallography. Co(I) atom has a distorted trigonal pyramidal N2S2 (1) environment with two S atoms and one N atom from three μ-1,1,3-thiocyanate bridge ligands and one N atom from ql ligand. Two S atoms from two μ-1,1,3-SCN− bridging ligands bridge two centers to obtain bimetallic 4-membered ring. Adjacent 4-membered rings are linked by a pair of μ-1,1,3-SCN− bridging ligands to form a 1D stair-case like chain. The luminescent properties and magnetic properties of the polymer 1 were investigated in the solid state.

Investigation on phase transformation mechanism of zeolite NaY under alkaline hydrothermal conditions

The phase transformation mechanism of zeolite NaY under alkaline hydrothermal conditions was investigated by UV Raman spectroscopy, X-ray diffraction, X-ray fluorescence and scanning electron microscopy techniques. The results revealed that the products and transformation rate are dependent on the alkalinities. All of the starting and resulting zeolites are constructed with the 4-ring and 6-ring secondary building units. The products have lower Si/Al ratio, higher framework density and smaller pore size, which are more stable under alkaline hydrothermal condition. During the phase transformation the fragments of faujasite are formed, then the fragments combine to form different zeolites depending on basicity. Zeolite NaY crystals are consumed as the reservoir for the transformation products during the recrystallization process. For the first time, a 4-membered ring intermediate was found at the early stage of the recrystallization process. A cooperative interaction of liquid and solid phases is required for inducing the phase transformation.

Conversion of biomass to γ-valerolactone by catalytic transfer hydrogenation of ethyl levulinate over metal hydroxides

A series of low-cost readily-assembled eco-friendly metal hydroxides were examined as catalysts in the synthesis of a novel platform molecule, γ-valerolactone (GVL), from biomass-derived ethyl levulinate (EL) via hydrogen transfer reaction. Among these catalysts, ZrO(OH)2·xH2O was found to be most active. EL conversion of 93.6% and GVL selectivity of 94.5% were achieved when 2-propanol was used as a hydrogen donor at 473K with a reaction time of only 1h. The complete reaction pathway and the probable main by-products for the conversion of EL to GVL were clearly deduced for the first time. The ZrO(OH)2·xH2O catalyst could be reused at least ten times without any significant loss of catalytic activity. Furthermore, characterizations were carried out on the fresh and spent ZrO(OH)2·xH2O catalysts with XRD, FT-IR, BET, TGA-DTA. Combined with the results of poisoning experiments, a plausible mechanism for catalytic transfer hydrogenation (CTH) of EL to GVL was proposed to be consisted of a catalytic cycle involving a six member ring transition state.

Theoretical investigation of layered zeolite frameworks: Surface properties of 2D zeolites

Surface properties of layered zeolite frameworks, or 2D zeolites, derived from zeolites UTL and ITH are probed by interaction with several small molecules (CH4, CO2, H2O, H2, N2). The dominant feature of the 2D zeolites is the dense grid of the surface silanol groups formed after dissolution of the double 4-member ring building units of the parent 3D zeolites. Compared to the original 3D zeolite frameworks, several distinctive effects contribute to the changes in binding energies: (i) hydrogen-bond and electrostatic interactions with surface silanols, (ii) the confined space effect enhancing dispersion interactions in 3D zeolites and (iii) structural flexibility of 2D zeolites.

Methanol-to-Olefin Conversion over Zeolite Catalysts: Active Intermediates and Deactivation

Methanol-to-olefin (MTO) conversion over various zeolites with different topologies, Si/Al molar ratios, and crystallite sizes were investigated to verify the effects of pore shape and size, acidity, and external surface area on the catalytic activity, product selectivity, and deactivation. The IR and electron spin resonance (ESR) study of zeolite catalysts used in MTO also proceeded to deduce the active intermediates formed in their cages or pores. The zeolites with 8 membered-ring (MR) pore entrances such as CHA, ERI, LTA, and UFI commonly exhibited high selectivity to lower olefins due to their small entrances, but the CHA catalyst with the smallest cage maintained its activity longer than other 8MR zeolites. The slow condensation of polymethylbenzene (PolyMB) to polyaromatic hydrocarbons (PAH) on MOR zeolite with a high Si/Al molar ratio due to its low concentration of strong acid sites resulted in a slow deactivation. The extremely small crystallites of H-SAPO-34 and H-ZSM-5 less than 100 nm showed an adverse effect in MTO; while the large crystallites above 1,000 nm also exhibited poor catalytic performance because of their small external surface. The study of IR regarding the adsorbed and occluded materials on zeolites demonstrated the effect of pore shape and size on the active intermediates: the zeolites with larger pores and cages allowed the formation of alkylbenzenes with long alkyl groups which preferred to be condensated to PAH. The well-resolved hyperfine splitting of ESR spectra observed on H-SAPO-34 used in MTO clearly illustrated the presence of hexamethylbenzenium radical cations. The small intersections of phosphorous-modified H-ZSM-5 allowed the formation of tetramethylbenzenium radical cations in MTO. The formation of PolyMB radical cations, their role as active intermediates and the effect of topology, acidity, and crystallite size of zeolites on their deactivation were discussed.

The glassy and supercooled state of elemental sulfur: Vibrational modes, structure metastability, and polymer content

We report a detailed investigation of vibrational modes, structure, and dynamics of elemental sulfur in the glassy and the supercooled state, using Raman scattering and ab initio calculations. Polarized Raman spectra are recorded--for sulfur quenched from 473 K--over a broad temperature range from 93 K to 273 K where the supercooled liquid crystallized. The temperature induced shifts of the majority of the vibrational modes are determined and compared with the corresponding ones of crystalline sulfur. Analysis of the reduced isotropic spectra showed that the structure of the quenched product is composed of eight member rings (S8) and polymeric chains (Sμ) with a relative fraction comparable to that of the parent liquid at 473 K. Low temperature spectra, where spectral line broadening due to thermal effects is limited, revealed that two different polymeric species are present in the glass with distinct vibrational frequencies. Their interpretation was assisted by ab initio calculations used to simulate the vibrational frequencies of polymeric chains S(8k) (k = 1, ..., 7). Theoretical results exhibit an increasing breathing mode frequency for sulfur chains up to k = 2, although it remains constant beyond the above value. The polymeric content is metastable; heating the glass above its glass transition temperature, T(g), destabilizes the chains and drives them back to the more thermodynamically stable rings. This bond interchange mechanism provides the structural origin of a secondary relaxation process in supercooled sulfur reported long ago, which has been also considered as a complication in the correct fragility estimation of this material. Finally, the Boson peak of the glass was found to exhibit strong temperature dependence even at temperatures below T(g).

Kinetics and mechanism of intramolecular aldol condensation of 2,5-hexadione, a DFT and MP2 study

A theoretical study of kinetics and mechanism of intramolecular aldol condensation of 2,5-hexadione was performed using DFT methods at B3LYP and MP2 levels of theory using 6-311g, 6-311g*, 6-311G**, 6-311++G and 6-311++G** basis sets. Equilibrium molecular geometries and harmonic vibrational frequencies of the reactant, transition states, and products were calculated. Two reaction paths were studied. The considered rate constants and activation thermodynamic parameters were calculated. The results indicated a fairly good agreement with experimental data. It was demonstrated that the five member ring is the most stable one for all calculations. These calculations showed that the reaction proceeds through an asynchronous concerted mechanism.

Synthesis and Characterization of Five, Sevene Heterocyclic Membered Rings

New compounds containing heterocyclic units have been synthesized. These compounds include 2-amino 5- phenyl-1,3,4-thiadiazole (1) as starting material to prepare the Schiff bases 2N[3-nitrobenzylidene -2 hydroxy benzylidene and 4-N,N-dimethyl aminobenzylidene] -5-phenyl-1,3,4-thiadiazole (2abc) , 2N[3-nitrophenyl, 2-hydroxyphenyl or 4-N,N-dimethylaminophenyl] 3-]2-amino-5-phenyl-1,3,4-thiadiazole]-2,3-dihydro-[1,3]oxazepine-benzo-4,7-dione] (3abc), 2N[3-nitrophenyl,2-hydroxyphenyl,4-N,N-dimethylaminophenyl]-3-[2-amino-5-phenyl-1,3,4-thiadiazole-2-yl]-2,3-dihydro-[1,3]oxazepine-4,7-dione[(4abc), 2-N-[3-nitrophenyl, 2-hydroxyphenyl or 4-N,N-dimethylaminophenyl]-3-[2-amino-5-phenyl-1,3,4-thiadiazole-2yl]-1,2,3-trihydro-benzo-[1,2-e][1,3] diazepine-4,7-dione (5abc) ,2N[2-(3-nitrophenyl,2-hydroxyphenyl or 4-N,N-dimethylaminophenyl)]-4-oxo-1,3-thiazolidine-3-yl]-2-amino-5-phenyl-1,3,4-thiadiazole (6abc), 2-N-[5-(3-nitrophenyl,2-hydroxyphenyl or 4-N,N-dimethylaminophenyl)-tetrazolo-1-yl]-2-amino-5-phenyl-1,3,4-thiadiazole (7abc) , 2-N-[5-(3-nitrophenyl,2-hydroxyphenyl or 4-N,N-dimethylaminophenyl)-3-[2-amino-5-phenyl-1,3,4-thiadiazole-2-yl]-2,3-dihydro-[1,3]oxazepine-benzo-4,7-dithione (8abc) , 2-N-[5-(3-nitrophenyl,2-hydroxyphenyl or 4-N,N-dimethylaminophenyl)-3-[2-amino-5-phenyl-1,3,4-thiadiazole-2-yl]-2,3-dihydro-[1,3]oxazepine -4,7-dithione -5-ene (9abc) and 2-N-[5-(3-nitrophenyl,2-hydroxyphenyl or 4-N,N-dimethylaminophenyl)-3-[2-amino-5-phenyl-1,3,4-thiadiazole-2-yl] -1,2,3-trihydro-benzo-[1,2-e][1,3] diazepine -4,7-dithione - (10abc) . the structures of these compounds were characterized by FT-IR, 1H,13C-NMR,Uv/vis spectroscopy and the melting points were determined besides the evaluation of its biological activity.

Synthesis and Characterization of Five, Sevene Heterocyclic Membered Rings

New compounds containing heterocyclic units have been synthesized. These compounds include 2-amino 5- phenyl-1,3,4-thiadiazole (1) as starting material to prepare the Schiff bases 2N[3-nitrobenzylidene -2 hydroxy benzylidene and 4-N,N-dimethyl aminobenzylidene] -5-phenyl-1,3,4-thiadiazole (2abc) , 2N[3-nitrophenyl, 2-hydroxyphenyl or 4-N,N-dimethylaminophenyl] 3-]2-amino-5-phenyl-1,3,4-thiadiazole]-2,3-dihydro-[1,3]oxazepine-benzo-4,7-dione] (3abc), 2N[3-nitrophenyl,2-hydroxyphenyl,4-N,N-dimethylaminophenyl]-3-[2-amino-5-phenyl-1,3,4-thiadiazole-2-yl]-2,3-dihydro-[1,3]oxazepine-4,7-dione[(4abc), 2-N-[3-nitrophenyl, 2-hydroxyphenyl or 4-N,N-dimethylaminophenyl]-3-[2-amino-5-phenyl-1,3,4-thiadiazole-2yl]-1,2,3-trihydro-benzo-[1,2-e][1,3] diazepine-4,7-dione (5abc) ,2N[2-(3-nitrophenyl,2-hydroxyphenyl or 4-N,N-dimethylaminophenyl)]-4-oxo-1,3-thiazolidine-3-yl]-2-amino-5-phenyl-1,3,4-thiadiazole (6abc), 2-N-[5-(3-nitrophenyl,2-hydroxyphenyl or 4-N,N-dimethylaminophenyl)-tetrazolo-1-yl]-2-amino-5-phenyl-1,3,4-thiadiazole (7abc) , 2-N-[5-(3-nitrophenyl,2-hydroxyphenyl or 4-N,N-dimethylaminophenyl)-3-[2-amino-5-phenyl-1,3,4-thiadiazole-2-yl]-2,3-dihydro-[1,3]oxazepine-benzo-4,7-dithione (8abc) , 2-N-[5-(3-nitrophenyl,2-hydroxyphenyl or 4-N,N-dimethylaminophenyl)-3-[2-amino-5-phenyl-1,3,4-thiadiazole-2-yl]-2,3-dihydro-[1,3]oxazepine -4,7-dithione -5-ene (9abc) and 2-N-[5-(3-nitrophenyl,2-hydroxyphenyl or 4-N,N-dimethylaminophenyl)-3-[2-amino-5-phenyl-1,3,4-thiadiazole-2-yl] -1,2,3-trihydro-benzo-[1,2-e][1,3] diazepine -4,7-dithione - (10abc) . the structures of these compounds were characterized by FT-IR, 1H,13C-NMR,Uv/vis spectroscopy and the melting points were determined besides the evaluation of its biological activity.

Synthesis and characterization studies of new five member ring metal chelates derived from benzion phenoxyacetyl hydrazone(H2BPAH)

The reaction of benzion phenoxyacetyl hydrazone (H2BPAH) with some bivalent metal ions yields simple metal chelates having the general formula [Cd(H2BPAH)Cl2], [Cu(HBPAH)OAc(H2O)], [Pd(HBPAH)2], [Ni(BPAH)(H2O)3] and [UO2(BPAH)(H2O)3]. Elemental analyses, molar conductivity measurements, magnetic moment and spectral (IR, 1H NMR, UV–Vis) studies have been used to elucidate their structures. The IR spectral data show that H2BPAH behaves in a different manner. Spectral and magnetic studies suggest different structures for Co(II), Cu(II) and Ni(II) ions, in good agreement with their structures, indicating high purity of all the compounds. The antibacterial studies of the present complexes show that they have a moderate antibacterial activity; however the ligand retards the corrosion.

Pb2B3O5.5(OH)2 and [Pb3(B3O7)](NO3): Facile Syntheses of New Lead(II) Borates by Simply Changing the pH Values of the Reaction Systems

Using lead metaborate as starting material, by only adjusting pH values of the reaction systems, a series of lead(II) borates were obtained in high yields. The new polar material, namely, Pb2B3O5.5(OH)2 (1), crystallizes in the noncentrosymmetric space group Pnn2 of the orthorhombic system. Its structure features a novel three-dimensional (3D) anionic network with large 14 member rings (MRs) tunnels composed of unique one-dimensional (1D) chains and dimeric B2O7 fragments, both of which are built up from solely BO4 tetrahedra, and the Pb(2+) cations are located at the above 14-MRs tunnels. The synergistic effect of the stereoactive lone-pairs on Pb(2+) cations in 1 produces a strong SHG response of ∼3× KDP (KH2PO4) which is type I phase-matchable. The first example of lead(II) borate nitrate, namely, [Pb3(B3O7)](NO3) (2), crystallizes in space group Pnma, and its structures features a 3D lead(II) borate cationic network structure in which (B3O7)(5-) anions are bridged by lead(II) cations, the nitrate anions are isolated, and located at the small voids of the cationic network. Thermal stability and optical properties as well as theoretical calculations based on density functional theory (DFT) methods were also performed.

Efficient and Accurate Methods for Characterizing Effects of Framework Flexibility on Molecular Diffusion in Zeolites: CH4 Diffusion in Eight Member Ring Zeolites

Molecular dynamics (MD) and transition state theory (TST) methods are becoming efficient tools for predicting diffusion of molecules in nanoporous materials. The accuracy of predictions, however, often depends upon a major assumption that the framework of the material is rigid. This saves a considerable amount of computational time and is often the only method applicable to materials for which accurate force fields to model framework flexibility are not available. In this study, we systematically characterize the effect of framework flexibility on diffusion in four model zeolites (LTA, CHA, ERI, and BIK) that exhibit different patterns of window flexibility. We show that for molecules with kinetic diameters comparable to (or larger than) the size of the window the rigid framework approximation can produce order(s) of magnitude difference in diffusivities as compared to the simulations performed with a fully flexible framework. We also show that simple recipes to include the effect of framework flexibility are not generally accurate. To account for framework flexibility effects efficiently and reliably, we introduce two new methods in which the flexible structure is approximated as a set of discrete rigid snapshots obtained from simulations of dynamics of an empty framework, using either classical or, in principle, ab initio methods. In the first method, we perform MD simulations of diffusion in a usual manner but replace the rigid structure with a new random snapshot at a certain characteristic frequency corresponding to the breathing motion of the window, while keeping positions of adsorbate molecules constant. In the second method, we directly compute cage to cage hopping rates in each rigid snapshot using TST and average over a distribution of snapshots. Excellent agreement is obtained between diffusivities predicted with these two new methods and direct MD simulations using fully flexible structures. Both methods are orders of magnitude more efficient than the simulations with the fully flexible structure. The new methods are broadly applicable for fast and accurate predictions of both infinite dilution and finite loading diffusivities of simple molecules in zeolites and other nanoporous materials, generally without the need for an accurate flexible force field.

Organometallic Tin Compounds Derived from 2‐Benzimidazole Propionic Acid

AbstractReactions of 2‐benzimidazole propionic acid (1) with [Sn(nBu)3]2O and SnPh3OH gave mononuclear organometallic tin esters 2 and 3, respectively, where 1 is coordinated to the tin atom through the carboxylate group. Further reactions of 2 with DMSO and 3 with methanol, ethanol, pyridine, DMSO, THF and water afforded the corresponding tin compounds coordinated by the base 4–10, respectively. X‐ray diffraction analyses of 5, 6 and 10 were obtained. The solid‐state structures showed that the ligand 1 is bound through both oxygen atoms of the carboxylic group with the Lewis base anti to it. Reaction of 1 with di‐n‐butyltin oxide produced a tetranuclear distannoxane (11) by the association of four Sn(nBu)2 groups, two oxygen atoms and four ligands. Four of the oxygen atoms are tricoordinate. The tin atoms are hexacoordinate with distorted octahedral geometries. The macromolecule has in total seven fused rings. Five of them are four membered rings arranged in a ladder‐type arrangement and the other two are six membered rings. The aliphatic chains and the benzimidazole groups are perpendicularly oriented to the polycyclic arrangement giving a sandwich with polar bonds in the middle and covered by the aliphatic and aromatic groups. In all compounds the ligands showed a chiral helicoidal preferred conformation.

Theoretical Investigation of PAHs: Implications to Diffuse Interstellar Bands

AbstractAbout a thousand optical absorption features on the interstellar extinction curve popularly known as the Diffuse Interstellar Bands (DIBs) have been observed. The numbers are increasing every year, thanks to the improvement in telescope and spectroscopic technology. Ultra-high resolution spectroscopic observations and emission features corresponding to some of the DIBs suggest that, some if not all, of these features are due to large molecules. The strength of DIBs depend on the amount of reddening which is directly proportional to the amount of material present between the background star and the observer. Since, the strengths of the DIBs are not strongly correlated with each other, there must be several carriers. Time Dependent Density Functional Theory (TDDFT) calculations are useful in narrowing down molecular systems that may be further investigated in the laboratory.The observations of the unidentified infrared (UIR) bands point towards the widespread presence of Polycyclic Aromatic Hydrocarbon (PAH) molecules. Though, not a single PAH has been discovered in interstellar space, these are the largest molecules suspected to be present. PAHs are stable towards energetic environment prevailing under interstellar conditions rendering these molecules to be good candidates as DIB carriers. We report TDDFT calculations to predict electronic transitions of neutral, protonated-deuteronated and PAHs with five member rings with various sites of protonation and deuteronation. Compared to their neutral forms, these charged isoelectronic forms of PAHs are predicted to have active transitions in the visible region, which means they are suitable candidates as carriers for some of the DIBs and laboratory studies are warranted for these systems.

Synthesis of [m.n]Cyclophanes: Regiochemistry Transfer from Vinyl Halides to Cyclophanes via Fischer Carbene Complexes

The double benzannulation of bis-carbene complexes of chromium with α,ω-diynes generates [m.n]cyclophanes in which all three rings are generated in a single reaction. This triple annulation process is very flexible allowing for the construction of symmetrical [n.n]cyclophanes and unsymmetrical [m.n]cyclophanes as well as isomers in which the two benzene rings are both meta bridged or both para bridged, and isomers that contain both meta and para bridges. The connectivity patterns of the bridges in the cyclophanes can be controlled by regioselectivity transfer from the bis-vinyl carbene complexes in which the substitution pattern of the vinyl groups in the carbene complexes dictate the connectivity pattern in the [m.n]cyclophanes. This synthesis of [n.n]cyclophanes is quite flexible with regard to ring size and can be used with tether lengths ranging from n=2 to n=16 and thus to ring sizes with up to 40 member rings. The only limitation to regioselectivity transfer from the carbene complexes to the [m.n]cyclophanes was found in the synthesis of para,para-cyclophanes with four carbon tethers for which the loss of fidelity occurred with the unexpected formation of meta,para-cyclophanes.

Thermal behavior of Sterculia striata oil

The thermal behavior of Sterculia striata oil, which is rich in fatty acids containing a cyclopropenyl ring in their chain, mainly malvalic acid (7-(2-octylcycloprop-1-en-1-yl) heptanoic acid) and sterculic acid (8-(2-octylcycloprop-1-en-1-yl) octanoic acid), is evaluated. Thermogravimetric analysis (TGA) has shown that weight loss occurs from 280°C. Differential scanning calorimetric (DSC) analysis indicates two exothermic events: one related to the ring opening in cyclopropenoids fatty acids chains and another to the pyrolitic decomposition of the oil, mainly the cracking of the ester groups. 1H NMR analysis revealed that the opening process of the cyclopropenyl ring starts at 150°C, probably via either a di-radical or a vinylcarbene intermediates. This process leads to the formation of a six members ring with a double bond in a terminal chain. After 280°C, the pyrolysis starts to decompose the ester groups into carboxylic acids. FT-IR analysis corroborated the results found by the other techniques.

Structural properties of core and surface of silica nanoparticles investigated by Raman spectroscopy

We studied the experimental Raman spectra of various commercial silica nanoparticles of average diameter from 7 to 40 nm and specific surface from 50 to 380 m2/g. We found that the peculiarities of the particles Raman spectra systematically depend on their specific surface. In detail, the peak position of the R band at about 440 cm−1 shifts towards high wavenumbers following an almost linear dependence on the specific surface. Similarly, the amplitudes of the D1 and D2 bands, at about 495 and 605 cm−1, respectively, increase linearly with the same quantity. Our results are interpreted in the frame of the shell model for the nanoparticles clarifying that the network of the core of the nanoparticles is comparable to the bulk silica materials, whereas the surface shell has a ring statistic shifted to the low member rings and features an higher density. Copyright © 2013 John Wiley & Sons, Ltd.

Raman study of Kr ion irradiated sodium aluminoborosilicate glass

Raman spectroscopy was used to investigate the microstructure evolution of sodium aluminoborosilicate glass after 4MeV Kr17+ ions irradiation at various fluences from 3.1×1011 to 1.8×1015ions/cm2. The Si–O–Si vibration band around 450cm−1 was slightly shifted to higher Raman shift after irradiation, and stabilized after the nuclear deposited energy reached about 1024eV/cm3. An increase in the population of 3-membered rings and decrease in the species of 4-membered rings were evidenced in the irradiated samples. These have been correlated to the densification process of glass. Depolymerization of glass network caused by Kr ion irradiation was also observed. These results indicate that the microstructural modifications caused by Kr ion irradiation are the consequence of ballistic effects.

HRMC_2.0: Hybrid Reverse Monte Carlo method with silicon, carbon and germanium potentials

The Hybrid Reverse Monte Carlo (HRMC) code models the atomic structure of materials via the use of a combination of constraints including experimental diffraction data and an empirical energy potential. In this version update, germanium potential parameters are introduced and constraints based on the coordination, average coordination and the total bond angle distribution are implemented. Other additional changes include a constraint on three member ring formation, a constraint on porosity and an extension to handle systems with up to three different elements. Program SummaryProgram title: HRMC version 2.0Catalogue identifier: AEAO_v2_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEAO_v2_0.htmlProgram obtainable from: CPC Program Library, Queen’s University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 94759No. of bytes in distributed program, including test data, etc.: 751023Distribution format: tar.gzProgramming language: Fortran 90.Computer: Any computer capable of running executables produced by the Fortran 90 compiler. For example, the code runs in Windows 7, once compiled with the GNU Fortan 95 compiler.Operating system: Unix, Windows.RAM: Depends on the type of empirical potential used, number of atoms and which constraints are employed. Typically below 2 GB for a system with a few thousand atoms.Classification: 7.7.Does the new version supersede the previous version?: YesCatalogue identifier of previous version: AEAO_v1_1Journal reference of previous version: Comput. Phys. Comm. 182 (2011) 542Nature of problem:Atomic modeling using a combination of empirical potentials, fits to experimental data and other chemically or physically motivated constraints.Solution method:Single move Metropolis Monte Carlo method used to minimize total energy and discrepancy between simulation and experimental data.Reasons for new version:Extension of capabilities from old version.Summary of revisions:Inclusion of Stillinger–Weber parameters for germanium, inclusion of a bond angle distribution constraint, inclusion of more general coordination, average coordination and porosity/volume constraints. Variable step sizes are now supported. Extension to systems containing up to three elements. New quench schemes to control constraint weighting throughout the simulation have been included. Constraints to forbid three member ring formation have been developed. There are changes to the input/output structure.Running time:1000 s for a test run on a Intel Xeon 2.93 GHz—Nehalem series processor.