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OH
Ti(OMe)4
and
Ga(NO
3
)
3
O
O
O
Ga
NH
2
H
2
H
2
O
H
2
Et
Ln = La, Nd,
Er, Yb
Et
N
O
O
O
O
Ti
OH
O
O
N
Ln
OH
O
HO
OH
bidentate binding site
for Ti
4+
, Al
3+
, or Ga
3+
K
+
X
-
HO
OH
N
NH
N
HN
O
O
tridentate binding site
for La
3+
or Ca
2+
O
O
Al
S
N
3
R = H, Br
R
Figure 4.10
O-Donor ligands for sequence selective formation of helicates.
dihydroxy-terephthalamide groups to selectively coordinate gadolinium(III) and iron(III)
ions, respectively [26]. Quite recently F.E. Hahn demonstrated that sequence selectivity
could also be achieved using ligand
19
-H
4
with a catechol and its dithiol derivative
as metal binding sites and a mixture of an oxophilic with a thiophilic metal ion [27]
(Figure 4.11).
3-
N
O
Gd
4-
O
O
HN
O
Ti
O
H
O
NH
O
N
O
Fe
O
NH
O
N
H
O
S
Mo
HN
O
S
3
O
Gd
[TiMo(
19
)
3
]
4-
N
O
3
[Gd
2
Fe(
18
)
3
]
3-
Figure 4.11 Ligands for sequence selective formation of heterometallic triple-stranded heli-
cates: trinuclear gadolinium iron complex [Gd
2
Fe(18)
3
]
3
by K.N. Raymond and binuclear
titanium molybdenum complex [TiMo(19)
3
]
4
by F.E. Hahn.
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