Proton sponge lead halides containing 1D polyoctahedral chains
- 23 December 2020
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in CrystEngComm
- Vol. 23 (5), 1126-1139
- https://doi.org/10.1039/d0ce01695k
Abstract
Hybrid one-dimensional lead halides, containing the protonated 1,8-bis(dimethylamino)naphthalene moiety (C14H19N2, monoprotonated “proton sponge”), were prepared by simple one-pot methods and investigated in terms of crystal structure, morphology, thermal stability and electronic properties. The as-precipitated (C14H19N2)PbBr3 and (C14H19N2)PbI3 species are isostructural and crystallize in the orthorhombic Pbca space group, resulting in 1D crystal phases with ([PbX3]−)∞ chains (built by face-sharing [PbX6] octahedra; X = Br, I), among which the (C14H19N2)+ cations are inserted. The two compounds display complete miscibility in the solid state: both (C14H19N2)PbI2Br and (C14H19N2)PbIBr2 crystal phases were successfully synthetized and do not show segregation effects. TGA and DSC measurements showed that, while all these materials are stable up to 250 °C, the iodine-rich (C14H19N2)PbI3 and (C14H19N2)PbI2Br species undergo an irreversible phase transition around 220 °C to a high-temperature phase, with a smaller molar volume and an apparent symmetry lowering (to orthorhombic Pca21). In these two cases, variable-temperature X-ray diffraction measurements showed a substantial crystal-to-crystal transformation, without intermediate melting or amorphization. The thermal expansion coefficients of (C14H19N2)PbI3 and (C14H19N2)PbBr3 are highly anisotropic and on the order of 10−4 K−1 along the b crystallographic axis. Microscopic and spectroscopic measurements were performed to complement the structural analysis of the samples: band gaps in the near UV range (3.3 and 3.8 eV for (C14H19N2)PbI3 and (C14H19N2)PbBr3, respectively) were obtained.Funding Information
- Ministero dell’Istruzione, dell’Università e della Ricerca (PRIN-2017L8WW48)
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