Cystallographic studies of addition compounds of hexafluorobenzene. Crystal structure of the 1:1 adduct with N,N-dimethylaniline

Abstract

The 1:1 addition compound between N,N-dimethylaniline and hexafluorobenzene crystallizes at room temperature in a monoclinic cell. A lattice with space group I2/m and a = 6.927 (1), b = 14.833 (2), c = 7.071 (1) A, fl = 103.67 (1) ° was chosen rather than a Bravais lattice with space group C2/m. The structure was refined to R = 0.060 for 280 counter data. The structure is disordered with the N,N-dimethylaniline molecule in two different orientations. The partner molecules are stacked alternately in infinite columns, and the mean separation between the molecular planes is 3.52 A. The benzene rings of the partner molecules overlap in a way which is often found in charge-transfer complexes.

Charge density studies on 2,3,5,6-tetrafluoro- and pentafluoropyridine

“…All these values are in the same range as those for hexafluorobenzene in the solid phase (1.330(9) Å). 23 The bond angles at nitrogen are 117.37(5)u for TFP and 118.06(6)u for both nitrogen atoms for PFP, which is slightly larger than in pyridine at 116.6u. A substitution of all carbon atoms as in PFP is not expected to alter the angles substantially, but in the case of TFP the para-position still bears a hydrogen atom.…”

“…The situation for PFP is much more complex. The bond critical point on the AIL between F(4) and F(9)9 shows the maximal intermolecular r-value at 0.05 eÅ 23 . This corresponds to the minimal intermolecular atomic distance.…”

“…Such shrinkage has already been proposed for the gaseous state of PFP and finds its parallels in the shrinkage observed when comparing benzene with penta- 22 or hexafluorobenzene. 23 C(3) bond in TFP (1.3828(4) Å) is slightly shorter than the corresponding ones in PFP (C(2)-C(3) 1.3907 (8), C(3)-C(4) 1.3901(8) Å, (C(7)-C(8) 1.3914 (10), C(8)-C(9) 1.3912(9) Å), but both are longer than the corresponding bonds in solid pyridine at 1.378 Å. The gas phase value is, however, comparable at 1.397(1) Å.…”

Structure of the 1:1 complex between N,N-dimethyl-p-toluidine and hexafluorobenzene

“…In the HFB complex with N,N-dimethylaniline (DMA) (Dahl, 1977) the benzene rings of adjacent molecules within the stack overlap approximately as in the complex with hexamethylbenzene (Dahl, 1973), and this overlap seems to be typical for HFB complexes with n donors. In the complex with N,N,N',N'-tetramethyl-p-phenylenediamine (Dahl, 1979) the overlap is somewhat different, but here the partially tetrahedral geometry of the N atoms indicates that the amine is an n-donor.…”

“…Crystal structures of molecular complexes of hexafluorobenzene (HFB) with partners which are closely related to each other seem to form a more coherent pattern than the majority of the known crystal structures of electron-donor-acceptor complexes between aromatic molecules (Dahl, 1977;Herbstein, 1971;Prout & Kamenar, 1973). This may in part be due to the small size of the F atoms and the disc shape of the HFB molecule, which reduce the importance of steric hindrance for the molecular packing.…”