Second‐sphere Coordination of [Pt(bipy)(NH<inf>3</inf>)<inf>2</inf>]²⁺ by Dibenzo‐crown Ethers. Solution Spectroscopic Studies and the Crystal and Molecular Structures of [Pt(bipy)(NH<inf>3</inf>)<inf>2</inf>.dibenzo‐30‐crown‐10] [PF<inf>6</inf>]<inf>2</inf>.0.6 H<inf>2</inf>O and [Pt(bipy)(NH<inf>3</inf>)<inf>2</inf>.dibenzo‐24‐crown‐8] [PF<inf>6</inf>]<inf>2</inf>

Abstract

In addition to hydrogen bonding and Coulombic forces, charge transfer interactions stabilise the 1:1 adducts formed between [Pt(bipy)(NH3)2] 2+ and a series of dibenzo‐3n‐crown‐n (n = 6–12) ethers as evidenced by 1H NMR and UV‐visible spectra in solution and by X‐ray crystal structures (for n = 8 and 10) in the solid state. Mutual diamagnetic (ring current) shielding by the aromatic systems of host and guest results in dramatic upfield shifts of certain aromatic proton resonances on adduct formation, especially when n = 10 or 11. A broad charge‐transfer absorption band at 350 nm attains its maximum intensity at n = 11 though stability constant measurements indicate optimum binding when n = 10. X‐ray diffraction studies reveal that, when n = 8, only one of the crown ether benzo‐rings interacts with the bipyridyl ligand in a charge‐transfer sense. However, when n = 10, the macrocycle is sufficiently large and flexible to allow both benzo‐rings to enter into stabilising interactions with the bipyridyl ligand such that the platinum complex is encapsulated by the host in a U‐shaped cavity. Copyright © 1985 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim