Steric and Electronic Factors Affecting the Conformation of Bimetallic Cu^I Complexes: Effect of the Aliphatic Spacer of Tetracoordinating Schiff‐Base Ligands

Abstract

A family of six homoleptic [Cu (L )] (ClO ) and six heteroleptic [Cu (L )(PPh ) ] (ClO ) bimetallic complexes, in which L are bis-Schiff base ligands with alkyl spacers of variable length (n=2-7 -CH -), were prepared to evaluate the role of the spacer on the formation of helicates or mesocates. In the homoleptic series, spectroscopic and theoretical studies indicate that preferences for a conformation are based on energetic parameters, mainly, the establishment of noncovalent interactions. The odd-even nature of the spacers preconditions the superposition of the aromatic rings to allow the juxtaposition necessary for noncovalent interactions, whereas the increase of the length reduces the strength of such interactions. Consequently, complexes with even-spacers of short length were identified as helicates in solution, [Cu (L )] (n=2, 4). Complexes [Cu (L )] (n=3-7) dissociate in solution to produce the monometallic complexes in equilibrium, [Cu (L )] . The stability of the bimetallic species is discussed in terms of their conformations. The set of heteroleptic complexes was prepared to evaluate the reach of the "odd-even rule" in the solid, which is based on the "zig-zag" arrangements of the spacers. Based on crystallographic information, "S-" and "C"-type conformations of L are related to even and odd spacers, respectively. This trend is considered in addition to other factors to explain preferences for either a mesocate or helicate conformation in the homoleptic series.

Electrochemical Exploration of Active Cu-Based Atom Transfer Radical Polymerization Catalysis through Ligand Modification

“…39−41 This includes the dicopper(I) complexes [Cu 2 (L 3 ) 2 ] 2+ (a double helicate structure) 42 as well as the non-helical [(Ph 3 P)ICu(L 3 )CuI(PPh 3 )] 43 and [(Ph 3 P) 2 Cu(L 3 )Cu(PPh 3 ) 2 ] 2+ complexes. 44 Crystallographic analysis of [CuL 1 ](ClO 4 ) 2 and [CuL 2 ]-(ClO 4 ) 2 revealed them to be identical to their previously published structures, 15,18,19 and the crystal structures of [CuL 1 ](ClO 4 ) 2 , [CuL 2 ](ClO 4 ) 2 , and [CuL 3 ](ClO 4 ) 2 are compared in Figure 4. Despite their apparent similarity, they exhibit quite different coordination geometries and physical properties (Table 1) due to stereochemical changes at the ethylenediamine/diimine N-donors (N2 in Figure 3).…”

Artificial Chemical Nuclease and Cytotoxic Activity of a Mononuclear Copper(I) Complex and a Related Binuclear Double‐Stranded Helicate

“…In addition, there is a strong intramolecular ππ‐stacking interaction in the helicate, which arises from the stacking of two phenanthroline moieties from adjacent L 2 ligands, at a centroid‐centroid distance of 3.759 Å (Figure S2). We have previously reported that this type of non‐covalent interaction has a stabilizing effect on the structure of helicates, and consequently on the redox stability of the Cu(I) centers [47] …”

Helical Copper Redox Mediator with Low Electron Recombination for Dye-Sensitized Solar Cells

“…where L is the ligand. Di ́az 21 and Lemus 22 calculated the equilibrium constant (K) by NMR measurements, and the calculated value is about 10 −3 . The equilibrium makes the components and electrochemical properties rather complicated.…”