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Two polymorphs of [Rh(μ-I)(COD)]₂.

ABSTRACT: The solid-state structure of di-μ-iodido-bis-{[(1,2,5,6-η)-cyclo-octa-1,4-diene]rhodium(I)}, [Rh₂I₂(C₈H₁₂)₂] or [Rh(μ-I)(COD)]₂, was determined from two crystals with different morphologies, which were found to correspond to two polymorphs containing Rh dimers with significantly different mol-ecular structures. Both polymorphs are monoclinic and the [Rh(μ-I)(COD)]₂ mol-ecules in each case possess C₂ v symmetry. However, the core geometry of the butterfly-shaped Rh₂I₂ core differs substanti-ally. In the C2/c polymorph, the core geometry of [Rh(μ-I)(COD)]₂ ^B is bent, with a hinge angle of 96.13 (8)° and a Rh⋯Rh distance of 2.9612 (11) Å. The P2₁/c polymorph features a more planar [Rh(μ-I)(COD)]₂ ^P core geometry, with a hinge angle of 145.69 (9)° and a Rh⋯Rh distance of 3.7646 (5) Å.

SUBMITTER: Ullery DR

PROVIDER: S-EPMC8423016 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Here we present a detailed ab initio study of two experimentally synthesized bismuth niobate BiNbO4 (BNO) polymorphs within the framework of density functional theory (DFT). We synthesized orthorhombic α-BNO and triclinic β-BNO using a solid-state reaction technique. The underlying Pnna and P1̄ crystal symmetries along with their respective phase purity have been confirmed from Rietveld refinement of the powdered X-ray diffraction measurements in combination with generalized gradient approximation of Perdew-Burke-Ernzerhof (GGA-PBE) based DFT simulations. The scanning electron micrographs revealed average grain sizes to be 500 nm and 1 μm for α-BNO and β-BNO respectively. The energy-dispersive X-ray spectroscopy identified the Bi, Nb, and O with proper stoichiometry. The phase purity of the as-synthesized samples was further confirmed by comparing the local density approximation (LDA) norm-conserving pseudo-potential based DFT-simulated Raman peaks with that of experimentally measured ones. The relevant bond vibrations detected in Fourier transform infrared spectroscopy were matched with GGA-PBE derived phonon density of states simulation for both polymorphs. The structural stability and the charge dynamics of the polymorphs were verified from elastic stress and born charge tensor simulations respectively. The dynamical stability of the α-BNO was confirmed from phonon band structure simulation using density functional perturbation theory with Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional. The electronic band gaps of 3.08 and 3.36 eV for α-BNO and β-BNO measured from UV-Vis diffuse reflectance measurements were matched with the sophisticated HSE06 band structure simulation by adjusting the Hartree-Fock exchange parameter. Both GGA-PBE and HSE06 functional were used to simulate complex dielectric function and its derivatives with the help of Fermi's golden rule to define the optical properties in the linear regime. All these may have provided a rigorous theoretical analysis for the experimentally synthesized α-BNO and β-BNO polymorphs.

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Two polymorphs of [Rh(μ-I)(COD)]₂.

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Two polymorphs of [Rh(μ-I)(COD)]2.

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Two polymorphs of [Rh(μ-I)(COD)]₂.