Taking advantage of weak and noncovalent interactions based
on dispersion forces as metallophilic and electrophilic
attractions, several efforts were also devoted to assemble
extended arrays of metal complexes, for instance, by using dou-
ble salts of general formula [M]þ[M]–( 160 ). A chain of ligated
metal ions with alternating charges require a judicious choice
of building blocks with particular steric and electronic needs, as
the planarity of the metal complexes involved and the possibility
ofp-stacking as complementary stabilization force. This theme
has been recently reviewed by Doerrer; thus no more room will
be devoted to it hereafter ( 161 ).
Cases of study of double salts in which no metallophilic inter-
action is involved are also known. In this respect, Schlofer and
coworkers first reported an energy transfer studies in Cr(III)-
based complexes of formula [Cr(urea) 6 ][Cr(CN) 6 ]3H 2 O. After-
ward, Kobayashi (162,163), Hauser ( 164 – 166 ), and Kaizu
( 167 – 169 ), reported on quenching studies in Ru(II)/Cr(III) and
Os(II)/Cr(III) mixed double complex salts.
To gain a deeper insight into photoinduced processes in crys-
talline systems, we recently reported on double complex salts
containing more appealing and more luminescent complexes
based on iridium phenylpyridil moieties( 170 ). These compounds
have general formula [Ir–][Irþ] and are formed by two highly
emitting iridium complexes, which possess different emission
colors and complementary charges. Thus, we have combined
the cationic orange-emitting compounds [Ir(dfppy) 2 (bpy)]Cl (1a)
and [Ir(ppy) 2 (bpy)]Cl (2a; dfppy¼4,6-difluorophenylpyridil,
ppy¼2-phenylpyridil, and bpy¼2,2^0 -bipyridil), previously
reported by our group, ( 140 ) with the anionic blue-green-emitting
complexes (n-Bu 4 Nþ)Ir(ppy) 2 (CN) 2 and K[Ir(dfppy) 2 (CN) 2 ]
(2b), reported by Grätzel and coworkers ( 171 ) (see Fig. 9). The
double salts are obtained because the small counter-ions yield
to easily removable water-soluble salts once the metal complexes
are combined. Of course, to have easily detectable and thermody-
namically favored processes, the excited-state energies of the two
F
N N
N NIr FF Ir1FNNN NFIG. 9. X-ray crystal structure of a single crystal and its unit cell
packing for complex 1.
68 CRISTIAN A. STRASSERTet al.