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Synthesis and Characterization of Metal–Organic Frameworks
Published in T. Grant Glover, Bin Mu, Gas Adsorption in Metal-Organic Frameworks, 2018
Prior to the refinement of crystal structure, initial modeled structures must be prepared. If similar MOF structures are available, they can provide good starting points to build a modeled structure that can be used for Rietveld refinement. If not, there are two main strategies; one is the direct use of the diffraction data, which is referred to as the direct method. In this case, several initial structures can be obtained, from which a plausible structure is selected for further refinement. The second strategy is to utilize Fourier transform intensity information to locate the atoms. For example, a three-dimensional Patterson map is calculated to assign the heavy atom positions/coordinates. More recently, a way to reconstruct an electron density map has been developed and is known as the charge flipping method.153–155 With the resulting modeled structures in hand, Rietveld refinement is performed to adjust the position of atoms in the unit cell.
Physical Methods for Characterizing Solids
Published in Elaine A. Moore, Lesley E. Smart, Solid State Chemistry, 2020
Crystal structures are solved by creating a set of trial phases for the structure factors. Until around 10 years ago, basically two main methods existed for doing this. The first is known as the Patterson method and since it relies on the presence of at least one (but not many) heavy atoms in the unit cell it is useful for solving many inorganic molecular structures. The second is via direct methods and these are best used for structures in which the atoms have similar scattering properties. Direct methods calculate mathematical probabilities for phase values and hence enable the construction of an electron density map of the unit cell; theoreticians have produced packages of accessible computer programs for solving and refining structures.
Finite Element Concepts In One-Dimensional Space
Published in Steven M. Lepi, Practical Guide to Finite Elements, 2020
While direct methods attempt to remove as many zeros as possible from the solution process, some (often many) zeros still remain. Using an iterative method, no zeros need be processed. This can lead to a significant decrease in the amount of time needed to solve certain finite element equilibrium equations. The most dramatic reduction in computation time is realized when solving problems with volume elements. When solving large problems using surface elements, direct methods may be faster and use substantially less RAM. The only advantage of an iterative method in such a case is some reduction in hard disk storage requirements; see Ramsay [30] for details.
Zero-dimensional antimony(III) halides templated by ruthenium complexes: photoluminescence, thermochromism and photo/electrical performances
Published in Inorganic and Nano-Metal Chemistry, 2023
Naixin Wu, Chun Chen, Shitong Lin, Haohong Li, Peipei He, Huidong Zheng
The intensity data collection were executed on a Rigaku Weissenbery IP diffractometer diffractometer using graphite-monochromated MoKαradiation (λ= 0.71073 Å) at 293(2) K. The correction of Lp factors and multi-scan absorption correction were applied. Crystal structures were solved by the direct method with program SHELXS and refined with the least-squares program SHELXL.[27]The structures were verified using the ADDSYM algorithm from the program PLATON,[28]and no higher symmetries were found. Non-hydrogen atoms were refined anisotropically, and hydrogen atoms of C–H were generated geometrically. The relatively higher residuals for 2 are around the I atoms (residual peaks of 4.53 e/Å3, 1.02 Å from I(2) atom; holes of −3.28e/Å3, 0.78 Å from I(2) atom), which are due to the absorption correction problems with heavy I atoms. Crystallographic data and refinement details are listed in Table 1. Selected bond lengths and angles are given in Table 2,and hydrogen bonds are shown in Tables 3. Crystallographic data for the structures reported in this article have been deposited with the Cambridge Crystallographic Data Center as supplementary publication nos. CCDC-1003858, 1003861. Copy of the data can be obtained free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html.
Synthesis and crystal structures of a polymeric trimethyltin(IV) and a tetranuclear dibutyltin(IV) complex with azo-carboxylates derived from 4- or 3-amino benzoic acid and naphthalen-1 or 2-ol
Published in Journal of Coordination Chemistry, 2021
Paresh Debnath, Pratima Debnath, Keisham Surjit Singh, Lesław Sieroń, Waldemar Maniukiewicz
Single crystal X-ray diffraction data of 1 and 2 were collected by the ω-scan technique using MoKα (λ = 0.71073 Å) radiation. The crystals were studied at 100K using a RIGAKU XtaLAB Synergy, Dualflex, Pilatus 300K diffractometer [43] equipped with Photon Jet micro-focus X-ray Source. Data collection, cell refinement, data reduction and absorption correction were carried out using CrysAlis PRO software [43]. The crystal structures were solved by direct methods with the SHELXT 2018/2 program [44]. Positional parameters of non-H-atoms were refined by a full-matrix least-squares method on F2 with anisotropic thermal parameters using the SHELXL 2018/3 program [44]. All hydrogens were placed in calculated positions (C–H = 0.93–0.98 Å) and included as riding contributions with isotropic displacement parameters set to 1.2–1.5 times the Ueq of the parent atom. The molecular structures and packing diagrams were drawn with MERCURY [45]. Crystal data and structure refinement parameters are summarized in Table 1.
Temperature-dependent crystal structure and fluorescence properties of a tetranuclear copper(I) cluster from in situ [2 + 3] cycloaddition synthesis
Published in Journal of Coordination Chemistry, 2018
Yi Liu, Yu Hui Tan, Chang Shan Yang, Bin Wang, Chang Feng Wang, Shao Peng Chen, Yun Zhi Tang, He Rui Wen
A yellow, block crystal of 1 with dimensions of 0.029 mm × 0.027 mm × 0.019 mm was mounted on a Bruker P4 diffractometer with graphite-monochromated Mo Kα radiation (λ = 0.71073 Å) at 100, 150, 200, and 299 K, respectively, using the θ-2θ scan technique. The data were corrected for Lp and absorption effects. The crystal structures were solved by direct methods with the SHELXS-97 program [20]. For convenience, we label the structure at 100, 150, 200, and 299 K as 1100 K, 1150 K, 1200 K, and 1299 K. Detailed information about their crystal data and structure determination are summarized in Table 1. Selected interatomic distances and bond angles are given in Table S1 (Supporting Information). In addition, we surprisingly found that there are four thiophene rings in one asymmetric unit of 1, in which two thiophene rings are obviously disordered [21], mainly in the S and C atoms (S2, S3, S5, S6, C22, C23, C25, C26), which are similar to the other analogous compounds [22]. Detailed data on anisotropic displacement parameters and atomic occupancies at 299 and 100 K are shown in Table S2 (Supporting Information). Copies of this information may be obtained free of charge from the Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK, Fax (int. code)-44(1223)336-033 or E-mail: [email protected] or http://www.ccdc.cam.ac.ck. CCDC No. for 1100K 1510782 and for 1299K 1510785.