Polar Self‐Assembly: Steric Effects Leading to Polar Mixed‐Ligand Coordination Cages

Abstract

We present a highly unusual example of self-assembly, specifically a polar, mixed-ligand cage which forms in preference to symmetrical homo-ligand products, and which suggests that steric effects can be exploited to obtain novel non-uniform polyhedral cages. In particular, reaction between the bulky tripodal triphosphine 2,4,6-tris(diphenylphosphino)triazine, L1, the non-bulky tripodal trinitrile 2,4,6-tris(cyanomethyl)trimethylbenzene, L2 and silver hexafluoroantimonate, AgSbF6, in a 3:1:4 ratio gives the mixed-ligand aggregate [Ag4(L1)3(L2)(SbF6)]3+, 1-SbF6, instantly as the only product in quantitative yield. The X-ray crystal structure of complex 1-SbF6 is consistent with the suspected solution-state structure. The cage derives from trigonal-pyramidal geometry, the basal vertices of which are defined by three bulky triphosphines, L1, and the apical vertex by the non-bulky trinitrile, L2. There is apical elongation amounting to 19% in comparison to the ideal uniform tetrahedron. The cage also encapsulates an SbF6 anion. 19F NMR spectra in solution for the analogous PF6 complex [Ag4(L1)3(L2)(PF6)]3+, 1-PF6, confirm that one anion is also encapsulated in solution. The synthesis of the analogous CF3SO3(-) complex, [Ag4(L1)3(L2)(OTf)]3+, 1-OTf, in solution is also described, although 1-PF6 and 1-OTf could not be isolated due to slow decomposition in solution. The selective formation of these mixed-ligand cages is discussed in terms of ligand-ligand and ligand-included anion steric repulsions, which we propose prevent the formation of the competing hypothetical homo-ligand tetrahedral structure [Ag4(L1)4(SbF6)]3+, and thus favour the mixed ligand cage. "Cage cone angles" for L1 and L2 are estimated at 115 degrees and 101 degrees, respectively. Variable-temperature 31P NMR spectroscopy shows that complex 1-SbF6 and the related previously reported partial tetrahedral complex [Ag4(L1)3(anion)]3+ undergo dynamic twisting processes in solution between enantiomeric C3-symmetry conformations.

Diversity and Complexity through Reversible Multiple Orthogonal Interactions in Multicomponent Assemblies

“…3) as well as on two different weak interactions and reversible bonds. Provisionally, it should suffice to categorize these by the operating interactions: two different metal-ligand interactions, [9][10][11][12][13] metal-ligand coordination + reversible covalent bond, [14,15] metal-ligand coordination + ion-dipole interaction, [7,16] metal-ligand coordination + hydrogen bonding, [17,18] metal-ligand coordination + p-p stacking, [19] reversible covalent bond + ion-dipole interaction, [20] and two different reversible covalent bonds. [21] Supramolecular multicomponent (n !…”

Control of metal-directed self-assembly by metal–amine interactions

“…19- 22 Steric effects of bridging 20- 23 and supporting ligands 24-26 also may have a crucial role in determining the nuclearity of self-assembled products. We are currently interested in the application of the above mentioned effects in sensing purposes of functional groups present in biological compounds, in particular amino-groups.…”

“…The results of the titrations in the presence of nPrNH 2 and PDA are shown in Table 1 (other diamines except 1,2-ethylenediamines behave similarly). Interestingly, one equivalent of the monoamine and 0.5 equivalents of the diamine (relative to L), the amount which is sufficient to replace one amide oxygen atom on each metal, induced stabilization of the assembly by almost two orders of magnitude in b 22 . If the guest concentration was high enough to substitute two intramolecular metal-oxygen bonds on each metal, 3 : 2 stoichiometry was observed.…”

Two 1D [CuxIx]-based coordination polymers of tetraphosphine ligands

“…Both compounds were characterized by elemental analysis, IR spectroscopy, 1 H and 31 P{ 1 H} NMR, ESI-MS and thermogravimetric analysis, and their structures were determined by single crystal X-ray diffraction. In 1, [Cu 2 I 2 ] cores are interconnected by dppeda ligands in a l-g 2 :g 2 end-toend mode to form a 1D chain, while in 2 stair-like [Cu 4 I 4 ] cores are linked by dpppda ligands in a unique Z-shaped l-g 2 :g 2 side-by-side mode to produce the other kind of 1D chain.Ó 2009 Elsevier B.V. All rights reserved.In the past decades, the design and synthesis of multi-phosphine ligands have attracted much attention [1-8] due to their versatile ligating capability as well as rich structural chemistry and unique physical and chemical properties of their metal complexes [9][10][11][12][13][14][15][16]. Among the multiphosphine ligands, several tetraphosphine ligands and their metal complexes that showed interesting luminescent properties, catalytic and anticancer performances, have been extensively investigated [17][18][19][20].…”