Neutral mixed-ligand complexes of platinum(II) and palladium(II) with α-diimine and dioxolenes

(2,2′-Bipyridine-κ2N,N′)(2,3-naphthalenediolato-κ2O,O′)palladium(II) and (2,2′-biquinoline-κ2N,N′)(2,3-naphthalenediolato-κ2O,O′)palladium(II)

“…In the present study, we have prepared two cis-coordinated ternary complexes of Pd II , namely the title complexes [Pd-(bpy)(nad)], (I), and [Pd(biq)(nad)], (II), with the aromatic ligands bpy, 2,2 H -biquinoline (biq) and 2,3-naphthalenediol (nad), and determined their structures. The same complexes were synthesized previously by a different method for electrochemical studies into their use as photosensitizers in inorganic photochemistry (Kamath et al, 1989). Structures have been determined for complexes of nad with Si (Holmes et al, 1985;Strohmann et al, 1991;Tacke et al, 1991Tacke et al, , 1993Sperlich et al, 1993), Fe (Ju È stel et al, 1999), Ge (Tacke et al, 1994), Rb (Yang et al, 1997), Mo (Mondal et al, 1988;El-Hendawy et al, 1989;Kang et al, 1989) and Sb (Holmes et al, 1987).…”

Exploring excited states of Pt(ii) diimine catecholates for photoinduced charge separation

“…Previously, CT transitions in Pt(II) catecholates have been shown to display negative solvatochromism; namely, the shift of the MMLL'CT band maximum to lower energy with decreasing solvent polarity. 16,20 This behaviour is clearly exemplified for 1 in Fig. 5, where electronic absorption spectra recorded in a range of solvents are displayed.…”

“…This band is characteristic of Pt(II) catecholates, with its' absence in the spectrum of {(COO i Pr) 2 bpy}PtCl 2 allowing primary assignment to a ligand-to-ligand charge transfer (LL'CT). 16,17,20,43 However, since the electronic transition between catechol and diimine ligands is known to also involve orbital contributions from the metal centre, the process may be more accurately labelled as a mixed metal-ligand-to-ligand charge transfer (MMLL'CT). 21 It is noted that the change in catechol ligand between 1 and 2 is manifest in the electronic absorption spectra.…”

“…14,15 Whilst transition metal catecholates have been widely studied, Pt(II) catecholate chemistry has been rather less explored. [16][17][18][19][20][21][22][23][24][25] Previously reported Pt(II) catecholates commonly feature α,α′-diimines such as substituted bipyridines or phenanthrolines, in conjunction with simple dioxolenes, for example pyrocatechol, 3,5-di-tert-butyl catechol or 4-tert-butyl catechol. These Pt(II)-centred complexes are characterised by the broad, moderately intense, low-energy electronic absorption, being predominantly of a ligand-to-ligand charge transfer nature (LL'CT).…”

Ground State Nuclear Magnetic Resonance Chemical Shifts Predict Charge-Separated Excited State Lifetimes

“…A distinguishing feature of these chromophores is the presence of a dichalcogenolene → diimine ligand-to-ligand charge transfer (LL′CT) band in the visible region of the spectrum (Figure ). − With the exception of 1-O,O′ catecholate complex, , these complexes display phosphorescent emission with LL′CT excited state lifetimes that are dominated by nonradiative rate constants, which are markedly greater than the radiative rate constants. , The chromophoric π-systems, 1-O,O′ and 2-S,S , both possess effective C 2 v symmetry when neglecting the presence of the t -Bu substituents. In the C 2 v point group, the HOMO and LUMO for 1-O,O′ and 2-S,S both possess b 1 symmetry.…”