Abstract:The reaction of the dilithio compound 1,3-[{Li(tmeda)}2{C6H4(CHSiMe3)2}]
(2) with Hg(OAc)2 followed by treatment with aqueous HCl is highly stereoselective and yields quantitatively
meso-1,3-[C6H4(CHSiMe3HgCl)2] (3). In
the solid state, molecules of 3
are connected through the formation of intermolecular
head-to-tail Hg2Cl2 bridges. The
resulting polymer has
a ladder-type structure.
Synthesis and crystal structures of three porphyrin-based polyfunctional Lewis acids 1-3 are reported. Intermolecular HgCl⋅⋅⋅HgCl (linear and μ-type) interactions in the solid state of the peripherally ArHgCl-decorated compound 3 lead to a fascinating 3D supramolecular architecture. Compound 3 shows a selective fluorescence quenching response to picric acid and discriminates other nitroaromatic-based explosives. For the first time, an electron-deficient polyfunctional Lewis acid is shown to be useful for the selective detection and discrimination of nitroaromatic explosives. The Stern-Volmer quenching constant and detection limits of compound 3 for picric acid are the best among the reported small-molecular receptors for nitroaromatic explosives. The electronic structure, Lewis acidity, and selective sensing characteristics of 3 are well corroborated by DFT calculations.
Synthesis and crystal structures of three porphyrin-based polyfunctional Lewis acids 1-3 are reported. Intermolecular HgCl⋅⋅⋅HgCl (linear and μ-type) interactions in the solid state of the peripherally ArHgCl-decorated compound 3 lead to a fascinating 3D supramolecular architecture. Compound 3 shows a selective fluorescence quenching response to picric acid and discriminates other nitroaromatic-based explosives. For the first time, an electron-deficient polyfunctional Lewis acid is shown to be useful for the selective detection and discrimination of nitroaromatic explosives. The Stern-Volmer quenching constant and detection limits of compound 3 for picric acid are the best among the reported small-molecular receptors for nitroaromatic explosives. The electronic structure, Lewis acidity, and selective sensing characteristics of 3 are well corroborated by DFT calculations.
“…In the crystal, intermolecular sub-van der Waals Hg···Cl contacts ranging from 3.159 to 3.244 Å ( r vdw (Cl) = 1.58−1.78 Å, r vdw (Hg) = 1.73−2.00 Å) 25 are responsible for the association of molecules of 4 into dimeric units (Figure , Table ). These dimeric units are formed by reciprocal chelation of a Hg−Cl moiety of one molecule by its bidentate counterpart, a phenomenon also observed in the structures of {[2,4,6-(CH 3 ) 3 C 6 H 2 ]N[(CH 2 ) 2 HgCl] 2 } and meso -1,3-[C 6 H 4 (CHSiMe 3 HgCl) 2 ] . Each dimer interacts with two neighbors by formation of head-to-tail Hg 2 Cl 2 bridges and two other neighbors by formation of Hg 2 O 2 bridges (Figure , Table ) to from a highly cross-linked three-dimensional network 2b…”
Section: Resultsmentioning
confidence: 79%
“…In each layer, the formation of dimeric units can first be recognized (Figure ). As in 4 , these dimers are formed by reciprocal chelation of a Hg−Cl moiety of one molecule by its bidentate counterpart. , Additional van der Waals Hg···Cl and Hg···F contacts ( r vdw (F) = 1.30−1.38 Å, r vdw (Cl) = 1.58−1.78 Å, r vdw (Hg) = 1.73−2.00 Å) 25 (Table ) connect the dimers leading to the highly networked structure depicted in Figure . 6 View showing the layered structure of 6 . 7 View of layer of type A in the crystal of 6 .…”
Incremental addition of DMF or DMSO to a solution of 1,2-bis(chloromercurio)tetrafluorobenzene (3) in acetone results in a change of the 199Hg NMR chemical shift of 3. The
titration curves thus obtained can be fitted and indicate the formation of the 1:1 host−guest complexes 3·μ
2
-DMF (4) and 3·μ
2
-DMSO (5). The stability constants of 4 and 5 have
been determined and are respectively equal to 1.8 (±0.2) M-1 and 8.0 (±0.8) M-1. The X-ray
crystal structures of 4 and 3·μ
2
-acetone (6) have been determined. In the structure of 4, the
carbonyl oxygen atom is coordinated to three mercury atoms and has a distorted-tetrahedral
geometry. In 6 however, the acetone oxygen is coordinated to only two mercury atoms and
exhibits a trigonal-planar geometry. While it is difficult to detect any metrical changes
undergone by the organic substrates upon chelation, the IR carbonyl stretching frequency
of 4 (νCO 1635 cm-1) and 6 (νCO 1639 cm-1) indicates that the carbon oxygen bond is weakened.
Accordingly, the 13C CP/MAS NMR carbonyl carbon chemical shifts of 4 (167 ppm) and 6
(215 ppm) provide evidence for a substantial polarization of the carbonyl. By comparison of
the 13C CP/MAS NMR carbonyl carbon chemical shift, the Lewis acidity of 3 toward acetone
can be evaluated to be just inferior to that of MgCl2. Finally, both 4 and 6 have complex and
highly networked supramolecular structures which result from intermolecular Hg···Cl and
Hg···F or Hg···O contacts.
“…These Hg ؒ ؒ ؒ Cl contacts are in the range of 3.32-3.33 Å which is comparable to the sum of the van der Waals radii of the respective elements (r vdw (Cl) = 1.58-1.78 Å, 33 r vdw (Hg) = 1.73-2.00 Å) 34 and is within the range found for other organomercury halides (Table 2). [37][38][39] The overall structure of 2 is that of a framework wherein layers of 1ؒTHF are linked by pillars of sandwiched benzene molecules (Fig. 2).…”
The crystallization of 1,2-bis(chloromercurio)tetrafluorobenzene (1) from a mixture of THF and benzene yields 1ؒTHFؒ0.5C 6 H 6 (2), which contains the Lewis base-Lewis acid adduct 1ؒµ-THF associated to benzene. When 1 is crystallized from a mixture of propylene oxide and benzene, a compound of composition 1ؒ1.5C 6 H 6 (3) is obtained. Both 2 and 3 have been analyzed by solid-state 13 C CP/MAS NMR spectroscopy and their structures have been investigated by X-ray crystallography. The solid state structure of 2 is that of a framework wherein layers of 1ؒµ-THF are linked by pillars of sandwiched benzene molecules. The cohesion of this framework results from the presence of intermolecular Hg ؒ ؒ ؒ Cl interactions as well as arene-1,2-bis(chloromercurio)tetrafluorobenzene π-π stacking interactions. The crystal structure of 3 reveals the existence of parallel polymeric chains of 1 embedded in a benzene matrix in which the benzene molecules adopt an edge-to-face arrangement. The polymeric chains of 1 are formed by Hg ؒ ؒ ؒ Cl and Hg ؒ ؒ ؒ F interactions that link the monomers. Finally, part of the benzene molecules in 3 interacts with molecules of 1 by Hg ؒ ؒ ؒ π rather than π-π stacking interactions.
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