Heteroleptic mer-[Cr((NNN)-N-boolean AND-N-boolean AND)(CN)(3)] complexes: synthetic challenge, structural characterization and photophysical properties
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Show full item recordEditorial
Royal Society of Chemistry
Date
2022-02-17Referencia bibliográfica
Dalton Trans., 2022,51, 4297-4309. DOI: [10.1039/d2dt00126h]
Sponsorship
Swiss National Science Foundation (SNSF); European Commission 200020_178758 206021_183324Abstract
The substitution of three water molecules around trivalent chromium in CrBr3·6H2O with the tridentate
2,2’:6’,2’’-terpyridine (tpy), N,N’-dimethyl-N,N’-di(pyridine-2-yl)pyridine-2,6-diamine (ddpd) or 2,6-di
(quinolin-8-yl)pyridine (dqp) ligands gives the heteroleptic mer-[Cr(L)Br3] complexes. Stepwise treatments
with Ag(CF3SO3) and KCN under microwave irradiations provide mer-[Cr(L)(CN)3] in moderate yields.
According to their X-ray crystal structures, the associated six-coordinate meridional [CrN3C3] chromophores
increasingly deviate from a pseudo-octahedral arrangement according to L = ddpd ≈ dpq ≪ tpy; a
trend in line with the replacement of six-membered with five-membered chelate rings around CrIII.
Room-temperature ligand-centered UV-excitation at 18 170 cm−1 (λexc = 350 nm), followed by energy
transfer and intersystem crossing eventually yield microsecond metal-centered Cr(2E → 4A2) phosphorescence
in the red to near infrared domain 13 150–12 650 cm−1 (760 ≤ λem ≤ 790 nm). Decreasing the
temperature to liquid nitrogen (77 K) extends the emission lifetimes to reach the millisecond regime with a
record of 4.02 ms for mer-[Cr(dqp)(CN)3] in frozen acetonitrile.