The allosteric positive cooperativity accompanying the formation of compact [CuI(α,α’-diimine)2]+ building blocks

contributed to the historically efficient synthesis of metalcontaining catenates and knotted assemblies. However, its

limited magnitude can easily be overcome by the negative

chelate cooperativity that controls the overall formation of

related polymetallic multistranded helicates and grids. Despite

the more abundant use of analogous dioxygen-resistant

[AgI(α,α’-diimine)2]+ units in modern entangled metallosupramolecular

assemblies, a related thermodynamic justification

was absent. Solid-state structural characterizations show

the successive formation of [AgI(α,α’-diimine)(CH3CN)][X] and

[AgI(α,α’-diimine)2][X] upon the stepwise reactions of α,α’-

diimine=2,2’-bipyridine (bpy) or 1,10-phenanthroline (phen)

derivatives with AgX (X=BF4

􀀀 , ClO4

􀀀 , PF6

􀀀 ). In room-temperature,

5–10 mM acetonitrile solutions, these cationic complexes

exist as mixtures in fast exchange on the NMR

timescale. Spectrophotometric titrations using the unsubstituted

bpy and phen ligands point to the statistical (=noncooperative)

binding of two successive bidentate ligands

around AgI, a mechanism probably driven by the formation of

hydrophobic belts, that overcomes the unfavorable decrease

in the positive charge borne by the metallic cation. Surprisingly,

the addition of methyl groups adjacent to the nitrogen

donors (6,6’ positions in dmbpy; 2,9 positions in dmphen)

induces positive cooperativity for the formation of [Ag-

(dmbpy)2]+ and [Ag(dmphen)2]+, a trend assigned to additional

stabilizing interligand interactions. Adding rigid and

polarizable phenyl side arms in [Ag(Brdmbpy)2]+ further

reinforces the positively cooperative process, while limiting

the overall decrease in metal–ligand affinity.