Solution and Solid State Studies of a Triangle−Square Equilibrium:  Anion-Induced Selective Crystallization in Supramolecular Self-Assembly

Abstract

We report that an equilibrium mixture of triangular and square supramolecular species results when the flexible, ditopic donor unit, trans-bis(4-pyridyl)ethylene, is reacted with the ditopic acceptor unit, cis-(Me(3)P)(2)Pt(OTf)(2), in a one-to-one ratio. Both products are characterized in solution, by way of multinuclear NMR, and in the solid state, via X-ray crystallography. The effects of water and anions, cobalticarborane versus triflate, on the equilibrium are probed. The selective crystallization of either of the two species can be accomplished via the appropriate choice of solvents and ratio of anions present in the system. The dominant species in solution is not always consistent with the most prevalent species in the solid state.

Anion‐Templated Synthesis

“…Another example of anion-induced crystallization was recently reported by Stang et al [38] While studying the triangle-square equilibrium shown in Scheme 19, it was found that the selective crystallization of each one of the two metallapolygons can be selectively achieved by the appropriate choice of solvents and ratio of anions. In acetonitrile a mixture of the square 30 (11 %) and the triangle [38] Figure 12.…”

“…These two systems described by Stoddart et al [37] and by Stang et al [38] demonstrate the importance of anions in inducing selective crystallization of a specific supramolecular assembly. They also point out that the solid-state structure of a thermodynamically controlled system does not necessarily have to be the same than that one present in solution.…”

Drug Delivery by Water-Soluble Organometallic Cages

“…For example, the combination of Pt(PMe 3 ) 2 corner units with 1,2-bis(4-pyridyl)ethylene (bpe) has generated a triangular structure, [{Pt(PMe 3 ) 2 } 3 (bpe) 3 ] 6+ (Fig. 2a) [7], while Pd(en) units (en ¼ ethylenediamine) and 4,4 0 -bipyridine (bipy) gave a cationic square [{Pd(en)} 4 (bipy) 4 ]…”

“…4a). These chiral hosts possess a small hydrophobic cavity 6+ (a) [7] and [{Pd(en)} 4 (bipy) 4 ] 8+ (b) [8] Drug Delivery by Water-Soluble Organometallic Cagescapable of accommodating cationic or neutral guest molecules [12]. Using metal-metal paddlewheel units, Cotton and Murillo have prepared several twoand three-dimensional inorganic assemblies [14].…”

Coordination-Driven Supramolecular Macromolecules via the Directional Bonding Approach

“…4) [33]. The existence of square/triangle equilibria for certain combinations of linear and 90 precursors has also provided evidence for [3+3] triangles, wherein distortions in the building blocks relax the encoded angularities [31,[34][35][36]. In some cases, despite the use of cis-capped square planar metal environments, triangles may still be obtained provided that the ligand can accommodate the necessary distortions [37], as when mixing (en)PtCl 2 with 2,2 0 -bipyrazine in the presence of AgNO 3 [38], or by linking the luminescent Pt(thpy)(Hthpy)Cl or [nBu 4 N][Pt(bzqn)Cl 2 precursors with sodium benzimidazolate, thereby cyclizing a 90 acceptor with a 150 donor [39].…”