Multipolar refinements of structural models fitting extensive sets of X‐ray diffraction (XRD) data from single crystals of 1,3‐bis(dimethylamino)squaraine [SQ, C8H12N2O2] and its dihydrate [SQDH, C8H12N2O2∙2H2O], collected at very low T (18 ± 1 K for SQ, 20 ± 1 K for SQDH), led to an accurate description of their crystal electron density distributions. Atomic volumes and charges have been estimated from the experimental charge densities using the Quantum Theory of Atoms in Molecules (QTAIM) formalism. Our analysis confirms the common representation (in the literature and textbooks) of the squaraine central, four‐membered squarylium ring as carrying two positive charges, a representation that has been recently questioned by some theoretical calculations: the integrated total charge on the C4 fragment is estimated as ca. +2.4e in SQ and +2.2e in SQDH. The topology of the experimental electron density for the SQ squaraine molecule is modified in the dihydrated crystal by interactions between the methyl groups and the H2O molecules in the crystal. Maps of the molecular electrostatic potential in the main molecular planes in both crystals clearly reveal the quadrupolar charge distribution of the squaraine molecules. Molecular quadrupole tensors, as calculated with the PAMoC package using both Stewart and QTAIM distributed multipole analysis (DMA), are the same within experimental error.

Experimental charge density analysis and electrostatic properties of crystalline 1,3‐ bis(Dimethylamino)squaraine and its dihydrate from low temperature (t = 18 and 20 k) xrd data / R. Destro, P. Roversi, R. Soave, A. Hovestad, L. Lo Presti. - In: CRYSTALS. - ISSN 2073-4352. - 10:10(2020 Oct 02), pp. 894.1-894.20. [10.3390/cryst10100894]

Experimental charge density analysis and electrostatic properties of crystalline 1,3‐ bis(Dimethylamino)squaraine and its dihydrate from low temperature (t = 18 and 20 k) xrd data

R. Destro
Primo
Supervision
;
R. Soave
Formal Analysis
;
L. Lo Presti
Ultimo
Membro del Collaboration Group
2020

Abstract

Multipolar refinements of structural models fitting extensive sets of X‐ray diffraction (XRD) data from single crystals of 1,3‐bis(dimethylamino)squaraine [SQ, C8H12N2O2] and its dihydrate [SQDH, C8H12N2O2∙2H2O], collected at very low T (18 ± 1 K for SQ, 20 ± 1 K for SQDH), led to an accurate description of their crystal electron density distributions. Atomic volumes and charges have been estimated from the experimental charge densities using the Quantum Theory of Atoms in Molecules (QTAIM) formalism. Our analysis confirms the common representation (in the literature and textbooks) of the squaraine central, four‐membered squarylium ring as carrying two positive charges, a representation that has been recently questioned by some theoretical calculations: the integrated total charge on the C4 fragment is estimated as ca. +2.4e in SQ and +2.2e in SQDH. The topology of the experimental electron density for the SQ squaraine molecule is modified in the dihydrated crystal by interactions between the methyl groups and the H2O molecules in the crystal. Maps of the molecular electrostatic potential in the main molecular planes in both crystals clearly reveal the quadrupolar charge distribution of the squaraine molecules. Molecular quadrupole tensors, as calculated with the PAMoC package using both Stewart and QTAIM distributed multipole analysis (DMA), are the same within experimental error.
Charge density; Electrostatics; Low temperature; Non–covalent interactions; Quantum Theory of Atoms in Molecules; Single crystal; Squaraine; X‐ray diffraction
Settore CHIM/02 - Chimica Fisica
Settore CHIM/06 - Chimica Organica
2-ott-2020
Article (author)
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2434/790986
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