Supramolecular Assembly of Mg(II) Complexes Directed by Associative Lone Pair−π/π−π/π−Anion−π/π−Lone Pair Interactions

Abstract

Two Mg(II) malonate complexes with protonated 2-aminopyridine and protonated 2-amino-4-picoline as counterions, namely, (C(5)H(7)N(2))(4)[Mg(C(3)H(2)O(4))(2)(H(2)O)(2)](ClO(4))(2) (1) and (C(6)H(8)N(2)H)(2)[Mg(C(3)H(2)O(4))(2)(H(2)O)(2)] x 4 H(2)O (2) [C(5)H(7)N(2) = protonated 2-aminopyridine, C(3)H(4)O(4) = malonic acid, C(6)H(8)N(2)H = protonated 2-amino-4-picoline], have been synthesized from purely aqueous media, and their crystal structures have been determined by single-crystal X-ray diffraction. The role of lone pair...pi interactions in stabilizing the self-assembly process appears to be of great importance in both complexes. Additional weak forces like anion...pi and noncovalent O...O interactions are also found to be operating in 1. A rare combination of lone pair...pi and anion...pi interactions in 1, of the type lone pair...pi/pi...pi/pi...anion...pi/pi...lone pair, is observed, and this unusual supramolecular network is fully described here. An attempt to prepare an analogous complex with 2-amino-4-picoline resulted in 2, which is isomorphous with our recently reported transition-metal complexes of the type (C(6)H(8)N(2)H)(2)[M(C(3)H(2)O(4))(2)(H(2)O)(2)] x 4 H(2)O (M = Ni/Co/Mn). A high-level DFT-D study (RI-B97-D/TZVP) has been used to characterize the different noncovalent interactions present in the solid state. We have also analyzed some crystal fragments to examine energetically some important assemblies that drive the crystal packing. Finally, we have studied the influence of magnesium on some hydrogen-bonding interactions.

Anion-π Interactions in Supramolecular Chemistry and Catalysis

“…This field of research has recently attracted attention and several works have appeared in the literature [89,91]. For instance, the anion-π + interaction participates in the formation of a robust recognition motif in the transition metal malonate complexes using protonated 2-amino-4-picoline and 2-aminopyridine as the auxiliary ligands [89,90]. As expected, these complexes exhibit very large (>80 kcal/mol) interaction energies [62] showing the pentafluorobenzamide, the bromide and the tetraethylammonium cation.…”

“…The geometric and energetic features of anion-π + complexes of several aromatic cations (tropylium, quinolizinylium) and various anions have been reported along with crystallographic structures [87,88]. This field of research has recently attracted attention and several works have appeared in the literature [89,91]. For instance, the anion-π + interaction participates in the formation of a robust recognition motif in the transition metal malonate complexes using protonated 2-amino-4-picoline and 2-aminopyridine as the auxiliary ligands [89,90].…”

Synthesis, crystal structure, and luminescent properties of metal complexes bearing 2,6-pyridine-diacylhydrazide ligands: supramolecular assemblies via intermolecular interactions

“…The process of the self-assembly of a supramolecular framework is based on the extension of individual molecules by noncovalent or weak covalent interactions, including Van der Waals, electrostatic and hydrophobic interactions, hydrogen bonds, as well as p-p and ion-p stacking [11][12][13][14][15][16][17][18][19][20][21]. Among these, hydrogen bonding and p-p stacking interactions have been considered to play active roles in the formation of ordered supramolecular chains, layers, and three-dimensional frameworks, the research on which is of great interest for the development of supramolecular chemistry [22][23][24][25][26][27][28][29].…”

“…Among these ligands, aromatic carboxylate-containing or amide-containing ligands are often employed due to their facile coordination to metal ions and inclination to form H-bonds of COOHÁÁÁN, COOHÁÁÁO, and N-HÁÁÁO, etc., as well as the potential p-p stacking interaction between the aromatic rings [14,17,19,23,30,31]. N,N 0 -bis(salicyl)-2,6-pyridine-dicarbohydrazide (H 6 L) ligand possesses eleven potential donor groups (one pyridine group, four carbonyl groups, two phenolic groups, and four amide moieties).…”

Multiple anion···π interactions with a soft selenium atom: Accommodation of NCSe− anions inside hydrophobic pockets of adamantane/1,2,4-triazole coordination framework

“…Since coordination of the heterocycle to the metal ions enhances the ability for the anion···π interactions [4], this phenomenon is relevant for the solid-state coordination chemistry as an important factor governing disposition of counter anions, their recognition and selective binding [5]. It was considered as a design tool for the generation of supramolecular structures involving different types of π···anion···π and anion···π···anion sandwiches [6,7], double interactions with polycyclic receptors [8], anion···π and hydrogen bonding [7] and combined anion···π, lone pair···π and π/π interactions [9]. The cooperative effect of these forces is particularly prevalent for the anions located in the predefined cages with π-acidic surface [10] and therefore such systems themselves provide a useful probe for studying the weaker anion···π and lone pair···π bonding.…”