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Roger D. Willett

Bio: Roger D. Willett is an academic researcher. The author has contributed to research in topics: Crystal structure & Molecular geometry. The author has an hindex of 5, co-authored 5 publications receiving 322 citations.

Papers
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Journal ArticleDOI
TL;DR: The crystal structures of the isomorphous garnet-red copper salts, KCuCl3 and NH4CuCl3, have been determined as discussed by the authors, and each compound contains discrete, planar, Cu2Cl6= dimers.
Abstract: The crystal structures of the isomorphous garnet‐red copper salts, KCuCl3 and NH4CuCl3, have been determined. Each compound contains discrete, planar, Cu2Cl6= dimers. These dimers are stacked above each other along the crystallographic a axis. The cation exhibits a ninefold coordination.KCuCl3 is antiferromagnetic below 30°K. Both KCuCl3 and NH4CuCl3 are pleochroic with maximum visible absorption when the electric vector is parallel with the Cu–Cu vector of the dimer.

125 citations

Journal ArticleDOI
TL;DR: The crystal structure of the yellow compound (NH4)2CuCl4 has been determined by x-ray diffraction studies as discussed by the authors, and the compound crystallizes in the orthorhombic space group Cmca with a=15.46 A, b=7.20 A, and c =7.33 A. The structure contains discrete, planar CuCl4= ions with Cu-Cl distances of 2.30 and 2.79 A.
Abstract: The crystal structure of the yellow compound (NH4)2CuCl4 has been determined by x‐ray diffraction studies. The compound crystallizes in the orthorhombic space group Cmca with a=15.46 A, b=7.20 A, and c=7.20 A. The structure contains discrete, planar CuCl4= ions with Cu–Cl distances of 2.30 and 2.33 A. These ions are then bonded together by longer Cu–Cl bonds of 2.79 A to form infinite two‐dimensional sheets. The yellow compounds (CH3NH3)2CuCl4 and (C2H5NH3)2CuCl4 probably have closely related structures.

94 citations

Journal ArticleDOI
TL;DR: The crystal structure of (CH3)2NH2CuCl3 has been determined by x-ray diffraction techniques as discussed by the authors, which contains approximately planar Cu2Cl6= dimers which contain two bridging chlorine atoms.
Abstract: The crystal structure of (CH3)2NH2CuCl3 has been determined by x‐ray diffraction techniques. The compound contains approximately planar Cu2Cl6= dimers which contain two bridging chlorine atoms. All Cu–Cl bond distances in the dimer are approximately 2.3 A and all bond angles approximately 90°. The crystals are pleochroic with maximum visible absorption when the electric vector is parallel to the [301] direction.

59 citations

Journal ArticleDOI
TL;DR: The crystal structures of three red complexes of copper (II) chloride with the molecular formulas Cu2Cl4(CH3CN)2, Cu3Cl6(CH 3CN), and Cu5Cl10 (C3H7OH)2 have been determined as mentioned in this paper.
Abstract: The crystal structures of three red complexes of copper (II) chloride with the molecular formulas Cu2Cl4(CH3CN)2, Cu3Cl6(CH3CN)2, and Cu5Cl10 (C3H7OH)2 have been determined. Each compound contains discrete molecules in which the copper atoms and their ligands lie essentially in a plane. Within each molecule, adjacent copper atoms are bridged by two chlorine atoms equidistant from the copper atoms. Each copper atom forms four bonds, with Cu–Cl≃2.3 A while Cu–O or Cu–N bonds are just less than 2.0 A. Bond angles are approximately 90°. In all cases the organic molecules are bonded to copper atoms in positions which are trans for the entire molecule. Molecules are bridged together by longer Cu–Cl bonds which vary from 2.6 to 3.2 A.

46 citations

Journal ArticleDOI
TL;DR: The crystal structure of the new complex, CH3NH3NiCl3, has been determined in this article, where the electronic absorption spectrum has been measured over the range 6000-45 000 cm−1 for the nickel chloride complex.
Abstract: The crystal structure of the new complex, CH3NH3NiCl3, has been determined. The compound crystallizes in the space group Cmcm with a=6.94, b=14.94, and c=5.95 A. Each nickel ion has a distorted octahedral coordination with two chloride ions at 2.405 A and four chloride ions at 2.351 A. Adjacent octahedra along the c axis share faces to form infinite (NiCl3)nn— chains parallel to this axis. The electronic absorption spectrum has been measured over the range 6000–45 000 cm−1. The spectrum is characteristic of octahedral d8 complexes and yields a value of Dq=700 cm−1 for the nickel chloride complex.

10 citations


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TL;DR: A complete Intermediate Neglect of Differential Overlap model suitable for the examination of transition metal complexes is described in this paper, which is characterized by the inclusion of all the one-center exchange terms necessary for rotational invariance and accurate spectroscopic predictions, as well as an accurate description of integrals involving 3D atomic orbitals.
Abstract: A complete Intermediate Neglect of Differential Overlap model suitable for the examination of transition metal complexes is described. The model is characterized by the inclusion of all the one-center exchange terms necessary for rotational invariance and accurate spectroscopic predictions, as well as an accurate description of integrals involving 3d atomic orbitals. The model is within the unrestricted Hartree-Fock formalism, and a method for spin purification is described. Problems with convergence of the self-consistent field are discussed, and a method that has been found successful in aiding the convergence is outlined. The model has been applied to many transition metal systems. In this article the results of calculations on the chlorides of Fe, Co and Cu are described. The results of these calculations are compared with experiment, and with the results of calculations by other methods.

681 citations

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TL;DR: This review highlights the different types of photoluminescence that may be attained from layered halide perovskites, with an emphasis on how the emission may be systematically tuned through changes to the bulk crystalline lattice: changes in composition, structure, and dimensionality.
Abstract: Layered halide perovskites offer a versatile platform for manipulating light through synthetic design. Although most layered perovskites absorb strongly in the ultraviolet (UV) or near-UV region, their emission can range from the UV to the infrared region of the electromagnetic spectrum. This emission can be very narrow, displaying high color purity, or it can be extremely broad, spanning the entire visible spectrum and providing high color rendition (or accurately reproducing illuminated colors). The origin of the photoluminescence can vary enormously. Strongly correlated electron–hole pairs, permanent lattice defects, transient light-induced defects, and ligand-field transitions in the inorganic layers and molecular chromophores in the organic layers can be involved in the emission mechanism. In this review, we highlight the different types of photoluminescence that may be attained from layered halide perovskites, with an emphasis on how the emission may be systematically tuned through changes to the bu...

460 citations

Journal ArticleDOI
TL;DR: M06-L local functional of the M06 family largely improves over the local spin density approximation and the generalized gradient approximation, and is about equally as accurate as B3LYP or PBE0.
Abstract: The performance of the M06 family of exchange-correlation potentials for describing the electronic structure and the Heisenberg magnetic coupling constant (J) is investigated using a set of representative open-shell systems involving two unpaired electrons. The set of molecular systems studied has well defined structures, and their magnetic coupling values are known experimentally. As a general trend, the M06 functional is about equally as accurate as B3LYP or PBE0. The performance of local functionals is important because of their economy and convenience for large-scale calculations; we find that M06-L local functional of the M06 family largely improves over the local spin density approximation and the generalized gradient approximation.

203 citations