The structures of 8 alternate-stack adducts of TCNQ with neutral N-bases were determined by X-ray diffraction. Their packings contain 96 contacts <(sum vdW radii) dividable in CT or EDA classes as: (i) 56 sigma*<--n [12 inter and 5 intra X-H...:Y (X,Y=N,O,Cl); 31 inter and 8 intra C-H...:Y (Y=N,O) H-bonds]; (ii) 2 pi*<--n C<--:N; (iii) 11 sigma*<--pi C-H<--(C,N); (iv) 21 pi*<--pi C<--(C,O); and (v) 6 sigma*<--sigma C-H<--H-C interactions. The sigma*<--n contacts link molecules in planar ribbons by saturating lone-pair n-donors (:Y) by a maximum of X-H or C-H acceptors. These ribbons are interlinked in alternate vertical stacks by pi*<--pi contacts or in herring-bone packings by pi*<--n or sigma*<--pi ones. In spite of their alternate geometry, 4/8 crystalline adducts are black with metallic luster imputable to delocalized electronic bands, a fact successfully interpreted in terms of specific packing substructures held together by proper EDA interactions. Finally, a simple three-component model of the forces acting in neutral molecular crystals (dispersion, exchange, and CT or EDA attractions) is discussed, showing that it is theoretically well-grounded in the classical perturbation theory and suggesting that it could be profitably used in synergy with other well-established methods of crystal-packing analysis based on electron densities and electrostatic potentials.
Adducts of TCNQ with Neutral Nitrogen Bases. Their Rationalization in Terms of Intermolecular Charge-Transfer (CT) or Electron Donor-Acceptor (EDA) Interactions
BERTOLASI, Valerio;GILLI, Paola;GILLI, Gastone
2012
Abstract
The structures of 8 alternate-stack adducts of TCNQ with neutral N-bases were determined by X-ray diffraction. Their packings contain 96 contacts <(sum vdW radii) dividable in CT or EDA classes as: (i) 56 sigma*<--n [12 inter and 5 intra X-H...:Y (X,Y=N,O,Cl); 31 inter and 8 intra C-H...:Y (Y=N,O) H-bonds]; (ii) 2 pi*<--n C<--:N; (iii) 11 sigma*<--pi C-H<--(C,N); (iv) 21 pi*<--pi C<--(C,O); and (v) 6 sigma*<--sigma C-H<--H-C interactions. The sigma*<--n contacts link molecules in planar ribbons by saturating lone-pair n-donors (:Y) by a maximum of X-H or C-H acceptors. These ribbons are interlinked in alternate vertical stacks by pi*<--pi contacts or in herring-bone packings by pi*<--n or sigma*<--pi ones. In spite of their alternate geometry, 4/8 crystalline adducts are black with metallic luster imputable to delocalized electronic bands, a fact successfully interpreted in terms of specific packing substructures held together by proper EDA interactions. Finally, a simple three-component model of the forces acting in neutral molecular crystals (dispersion, exchange, and CT or EDA attractions) is discussed, showing that it is theoretically well-grounded in the classical perturbation theory and suggesting that it could be profitably used in synergy with other well-established methods of crystal-packing analysis based on electron densities and electrostatic potentials.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
