New [2 × 2] Copper(I) Grids as Anion Receptors. Effect of Ligand Functionalization on the Ability to Host Counteranions by Hydrogen Bonds

Abstract

Several complexes with a [2 × 2] grid structure have been obtained by the self-assembly of different copper(I) salts and ligands of the type 4,6-bis(pyrazol-1-yl)pyrimidine containing different substituents on the heterocycles. The main goal has been to evaluate the influence over the solid state and solution behavior of the functionalization of the pyrimidine ring with a primary amino substituent. The molecular and crystalline structures of some derivatives have been determined by X-ray diffraction. The grids contain two open voids formed by pairs of ligands facing one another on opposite sides of the grid in a somewhat divergent manner. One counteranion is hosted in each void interacting through hydrogen bonds and anion-π interactions. The presence of the amino group that points toward the inside of the cavity dominates the interactions in the void and apparently determines the orientation of the hosted counteranion and that of the ligands. With the exception of the derivative with chloride as the anion, the grid structure is preserved in solution (NMR and UV-vis) and some cation-anion interaction, increased by the presence of the amino group, exists also in solution (DOSY experiments). The experiments of anion interchange performed in solution indicate that a higher stability is found for the host-guest aggregates with OTs(-) (p-Me-C(6)H(4)SO(3)) and NO(3)(-). While for these anions a 1:2 stoichiometry is reached, for the rest of the anions tested (ReO(4)(-), OTf(-), and PF(6)(-)), only weaker 1:1 complexes are formed. Computational studies support the presence of anion-π interactions.

Anion receptor chemistry: highlights from 2010

“…The anion forms Z 1 interaction to a carbon atom of one triazine ring with a CÁ Á ÁCl distance of 3.342 A ˚and is further bound by a C-HÁ Á ÁCl (CÁ Á ÁCl distance The anion-p interactions towards the anion encapsulated in the 2 Â 2 grid like metallo-macrocycles formed by four Cu(I) centres linked by the four aminopyrimidine based ligands 186 and 187 were reported by Manzano and co-workers. 112 The crystal structures of the ClO 4 À complex of 186 and 187 as well as the BF 4 À and OTf À (trifluoromethanesulfonate anion) complex of 187 reveal close contacts between the encapsulated anion and the centroid of the aminopyrimidine moiety of the ligand. The shortest OÁ Á Ácentroid distance in the ClO…”

Novel self-assembled supramolecular architectures of Mn(ii) ions with a hybrid pyrazine–bipyridine ligand

“…Grid-type complexes have potential applications such as molecular-scale sensors, switches and information storage devices in nanotechnology. [25][26][27] Grids play also an important role in the host-guest chemistry because they can accommodate anions 28 or small molecules 29 in their cavities.…”

Supramolecular Iron Metallocubanes Exhibiting Site-Selective Thermal and Light-Induced Spin-Crossover

“…Complexation of Fe­[BF 4 ] 2 ·​6H 2 O by L 3 or L 4 yielded pale yellow powders, one of which afforded the 1D coordination polymer [Fe­(μ-L 3 )­(OH 2 )­(OCMe 2 )]­[BF 4 ] 2 ·​H 2 O ( 5 ·​H 2 O) after recrystallization from acetone/diethyl ether (Figures S29 and S30). All these results highlight the importance of O–H·​·​·​O hydrogen bonding in templating the cubane cluster.…”

“…2-Methyl-4,6-bis(pyrazol-1-yl)-1,3-pyrimidine (L 3 ), 39 2-amino-4,6bis(pyrazol-1-yl)-1,3-pyrimidine (L 4 ), 39 and the reagent sodium 4,6dichloro-pyrimidin-2-onate 40 were prepared by the literature procedures.…”

“…These are the largest molecules yet known to exhibit site-selective SCO. Experimental Section 2-Methyl-4,6-bis(pyrazol-1-yl)-1,3-pyrimidine (L 3 ), 39 2-amino-4,6bis(pyrazol-1-yl)-1,3-pyrimidine (L 4 ) 39 and the reagent sodium 4,6-dichloro-pyrimidin-2-onate 40 were prepared by the literature procedures. Synthesis of 4,6-di(pyrazol-1-yl)-1H-pyrimid-2-one (HL 1 ).…”