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[Os(bipy)(CN)4]2- and Its Relatives as Components of Polynuclear Assemblies: Structural and Photophysical Properties
dataset
posted on 2007-11-12, 00:00 authored by Svetlana G. Baca, Harry Adams, Christopher S. Grange, Alec P. Smith, Igor Sazanovich, Michael D. WardA series of diimine-tetracyanoosmate anions [Os(diimine)(CN)4]2- [diimine = 2,2‘-bipyridine (bipy), 2,2‘-bipyrimidine
(bpym), 1,10-phenanthroline (phen), and 4,4‘-tBu2-2,2‘-bipyridine (tBu2bpy)] were prepared and isolated as their
Na+ salts (water soluble) or PPN+ salts (soluble in organic solvents). Several examples were crystallographically
characterized; the Na+ salts form a range of 1D, 2D, or 3D infinite coordination polymers via coordination of the
cyanide groups to Na+ cations in either an end-on or a side-on manner. The [Os(diimine)(CN)4]2- anions are
solvatochromic, showing three MLCT absorptions, which are considerably blue-shifted in water compared to organic
solvents, in the same way as is well-known for the analogous [Ru(diimine)(CN)4]2- anions. Luminescence in the
red region of the spectrum is very weak but (following the expected solvatochromic behavior) is higher energy and
more intense in water. However, by exploiting the effect of metallochromism (ref ), the emission from
[Os(tBu2bpy)(CN)4]2- in MeCN can be very substantially boosted in energy, intensity, and lifetime in the presence
of Lewis-acidic metal cations (Na+, Ba2+, Zn2+), which, in a relatively noncompetitive solvent, coordinate to the
cyanide groups of [Os(tBu2bpy)(CN)4]2-. This has an effect similar in principle to hydrogen bonding of the cyanides
to δ+ protons of water, but very much stronger, such that in the presence of Zn2+ ions in MeCN the 1MLCT and
3MLCT absorptions are blue-shifted by ca. 7000 cm-1, and the luminescence moves from 970 nm (vanishingly
weak) to 610 nm with a lifetime of 120 ns (dominant component). Thus, the binding of metal cations to the cyanides
provides a mechanism to incorporate [Os(diimine)(CN)4]2- complexes into polynuclear assemblies and simultaneously
increases their 3MLCT energy and lifetime to an extent that makes them comparable to much-stronger luminophores
such as Ru(II)-polypyridines.