Crystallographic Evidence of Nitrate−π Interactions Involving the Electron-Deficient 1,3,5-Triazine Ring

Abstract

The reaction of Zn(NO3)2.6H2O or Cu(NO3)2.3H2O with the star-shaped ligand 2,4,6-tris(di-2-picolylamino)[1,3,5]triazine (dipicatriz) in acetonitrile results in the formation of the mono- or trinuclear coordination compounds [Zn(dipicatriz)(NO3)2] (1), [Zn3(dipicatriz)(NO3)6](CH3CN)3 (2), and [Cu3(dipicatriz)(NO3)2(H2O)6](NO3)4 (3), depending on the metal-to-ligand ratios used during the crystallization process. Their crystal structures exhibit unique supramolecular interactions. Compounds 1 and 2 show anion-pi interactions between coordinated nitrate ions and the s-triazine ring. Compound 3 exhibits remarkable interactions between two noncoordinated nitrate anions and the two faces of the electron-deficient heteroaromatic ring, corroborating earlier theoretical investigations in this area. New theoretical investigations have been carried out on nitrate-pi interactions, taking into account the particular position of the anion toward the aromatic ring observed in the crystal structures.

Metal–organic frameworks exhibiting strong anion–π interactions

“…Comparable parameters (F … p 2.80-3.04 Å ) were registered only for the extreme electron deficient tetrazine and the AsF 6 2 anion. 8,10 The only known precedent for such interaction of non-coordinated NO 3 2 anions (with 1,3,5-triazine cycle) revealed appreciably longer O … p distances (3.20 Å ), while the results of an ab initio study (2.75 Å ; Q = 86.2u) 11 exactly agree with the geometry of structures 1 and 2.…”

Interaction of an extended series of N-substituted di(2-picolyl)amine derivatives with copper(II). Synthetic, structural, magnetic and solution studies

“…The final ligand in the series, 2,4,6-tris[di(2-picolyl)amino]triazine 9, represents a new example of the relatively less common ligand category incorporating a trisubstituted triazine core. 16,52 Reaction of 9 in dichloromethane with Cu(ClO 4 ) 2 •6H 2 O in methanol in a 1:3 molar ratio followed by slow diffusion of diethyl ether vapour into the solution yielded green-blue crystals. Despite the results of a visible spectrophotometric titration of 9 into an acetonitrile Cu(II) nitrate solution (concentration: 4.6 mM) clearly showing the stepwise formation of 1:1, 2:1 and 3:1 (M:L) complex species and presence in the literature of an X-ray structure of a Cu(II) nitrate complex of 9 showing a 3:1 (M:L) stoichiometry, 16 a peak at m/z = 1034 in the ESI mass spectrum for a dinuclear [2Cu + L + 2ClO 4 + Cl] + ion (with the isotopic distribution for this ion in excellent agreement with the calculated pattern for a di-copper species) suggested the possibility that the present complex was a dinuclear species.…”

Hydrogen-bonded frameworks of bis(2-carboxypyridinium) hexafluorosilicate and bis(2-carboxyquinolinium) hexafluorosilicate dihydrate

“…Atoms O1 v and O2 vi [symmetry codes: (v) 1 2 À x, y À 1 2 , 1 2 À z; (vi) À 1 2 À x, y À 1 2 , 1 2 À z] are situated almost exactly above the ring centroid with relatively short OÁ Á Ácentroid distances (3.22 and 3.30 A Ê ) ( Table 5). Such stacking may be compared with recently documented examples of %Á Á Áanion (heteroatom) interactions, which are characteristic for the most electron-de®cient systems of 1,2,4,5-tetrazine (Schottel et al, 2006) and 1,3,5-triazine (Maheswari et al, 2006)…”