The new compounds N-phenyl-4,4‘-bipyridinium
(PhQ+), N-(4-acetylphenyl)-4,4‘-bipyridinium
(4-AcPhQ+), and
N-(2,4-dinitrophenyl)-4,4‘-bipyridinium
(2,4-DNPhQ+), together with the known ligand
N-methyl-4,4‘-bipyridinium
(MeQ+), have been used to prepare a series of Ru(II)
complex salts
trans-[Ru(NH3)4(LD)(LA)](PF6)3
[LD = NH3
and LA = MeQ+ (1),
PhQ+ (2), 4-AcPhQ+
(3), or 2,4-DNPhQ+ (4);
LD = 4-(dimethylamino)pyridine (dmap)
and LA = PhQ+ (7) or
4-AcPhQ+ (11); LD =
1-methylimidazole (mim) and LA = PhQ+
(8) or 4-AcPhQ+ (12);
LD = 4-(dimethylamino)benzonitrile (dmabn) and
LA = PhQ+ (9) or
4-AcPhQ+ (13); LD =
phenothiazine (PTZ)
and LA = PhQ+ (10) or
4-AcPhQ+ (14)]. These complexes display
intense, visible metal-to-ligand charge-transfer (MLCT) absorptions, due to dπ(RuII) →
π*(LA) excitations. The MLCT energy decreases
as the acceptor
strength of LA increases, in the order MeQ+
< PhQ+ < 4-AcPhQ+ <
2,4-DNPhQ+, and/or as the donor strength
of LD increases, in the order PTZ < dmabn <
NH3 < mim < dmap. X-ray crystal structure
determinations have
been carried out for
[PhQ+]Cl·2H2O and
trans-[Ru(NH3)4(PhQ+)(PTZ)](PF6)3·Et2O
(10·Et2O).
[PhQ+]Cl·2H2O,
chemical formula
C16H17ClN2O2,
crystallizes in the triclinic system, space group P1̄,
with a = 7.675(2) Å, b =
9.895(2) Å, c = 10.175(2) Å, α =
96.003(1)°, β = 104.74(2)°, γ =
90.398(1)°, and Z = 2.
10·Et2O, chemical
formula
C32H44F18N7OP3RuS,
crystallizes in the triclinic system, space group P1̄,
with a = 10.310(3) Å, b =
10.698(2) Å, c = 20.986(4) Å, α =
95.09(2)°, β = 91.49(2)°, γ = 105.53(2)°,
and Z = 2. The dihedral angles
between the two pyridyl rings of the 4,4‘-bipyridinium unit are 19.8°
in [PhQ+]Cl·2H2O and 2.6° in
10·Et2O.
Molecular first hyperpolarizabilities β of the complex salts,
obtained from hyper-Rayleigh scattering measurements
at 1064 nm, are in the range (698−1214) ×
10-30 esu. Static hyperpolarizabilities
β0 derived by using the two-level model are very large, with
trans-[Ru(NH3)4(4-AcPhQ+)(dmap)](PF6)3
(11) having the largest at 410 ×
10-30 esu. When the MLCT absorption is
sufficiently far from the second harmonic at 532 nm, both β and
β0
increase as the absorption energy decreases.
