Lanthanide complexes of the tetradentate N-donor ligand dihydrobis[3-(2-pyridyl)pyrazolyl]borate and the terdentate N-donor ligand 2,6-bis(1H-pyrazol-3-yl)pyridine: syntheses, crystal structures and solution structures based on luminescence lifetime studies
Abstract
Lanthanide complexes of two polydentate N-donor ligands containing a
mixture of pyridyl and pyrazolyl donors have been prepared.
Dihydrobis[3-(2-pyridyl)pyrazolyl]borate
(L
1
)
-
is a tetradentate ligand with two
bidentate chelating pyridyl/pyrazolyl arms linked by an apical
BH
2
group; 2,6-bis(1H-pyrazol-3-yl)pyridine
(L
2
) is a terdentate chelating ligand reminiscent of
terpyridine. Reaction of L
1
with lanthanide salts gave
complexes of the type
[M(L
1
)
2
X]
n+
; the crystal
structures of
[Eu(L
1
)
2
(dmf
)][ClO
4
]·
2.5CH
2
Cl
2
,
[Tb(L
1
)
2
(NO
3
)]·2CH
2
Cl
2
and
[Tb(L
1
)
2
(H
2
O)][L
1
]·
H
2
O·0.5CH
2
Cl
2
were determined
and all contain two tetradentate ligands L
1
and an ancillary
ligand X [dimethylformamide (dmf), nitrate or water] whose
nature depends on the reaction/recrystallisation conditions to complete
the co-ordination sphere. Luminescence studies of
[Tb(L
1
)
2
(NO
3
)] in water or
D
2
O and MeOH or CD
3
OD showed that in methanol the
solvation number q is ≈1.8, consistent with displacement of
nitrate by the solvent; however in water
q ≈ 4.5, indicating additional displacement of
some of the N-donor heterocyclic rings of L
1
by co-ordinating
water molecules. Reaction of L
2
with lanthanide salts
afforded [M(L
2
)
3
]
3+
, all isolated as
their hexafluorophosphate salts. The crystal structures of three of
these (M = Eu, Gd or Ho) showed that they are
isostructural and isomorphous, with tricapped trigonal-prismatic
nine-co-ordinate geometries similar to that of
[M(terpy)
3
]
3+
(terpy = 2,2′:6′,2″-
terpyridine). Luminescence studies of
[Tb(L
2
)
3
][PF
6
]
3
gave a
solvation number q of 0.6 in methanol, which is small enough to
be accounted for by second-sphere solvation effects alone and therefore
suggests that the nine-co-ordinate structure is retained in methanol
solution. However in water, q is again ≈4.5, due to
displacement of some of the donor groups of the L
2
ligands by
water.
)][ClO
4
]·
2.5CH
2
Cl
2
,
[Tb(L
1
)
2
(NO
3
)]·2CH
2
Cl
2
and
[Tb(L
1
)
2
(H
2
O)][L
1
]·
H
2
O·0.5CH
2
Cl
2
were determined
and all contain two tetradentate ligands L
1
and an ancillary
ligand X [dimethylformamide (dmf), nitrate or water] whose
nature depends on the reaction/recrystallisation conditions to complete
the co-ordination sphere. Luminescence studies of
[Tb(L
1
)
2
(NO
3
)] in water or
D
2
O and MeOH or CD
3
OD showed that in methanol the
solvation number q is ≈1.8, consistent with displacement of
nitrate by the solvent; however in water
q ≈ 4.5, indicating additional displacement of
some of the N-donor heterocyclic rings of L
1
by co-ordinating
water molecules. Reaction of L
2
with lanthanide salts
afforded [M(L
2
)
3
]
3+
, all isolated as
their hexafluorophosphate salts. The crystal structures of three of
these (M = Eu, Gd or Ho) showed that they are
isostructural and isomorphous, with tricapped trigonal-prismatic
nine-co-ordinate geometries similar to that of
[M(terpy)
3
]
3+
(terpy = 2,2′:6′,2″-
terpyridine). Luminescence studies of
[Tb(L
2
)
3
][PF
6
]
3
gave a
solvation number q of 0.6 in methanol, which is small enough to
be accounted for by second-sphere solvation effects alone and therefore
suggests that the nine-co-ordinate structure is retained in methanol
solution. However in water, q is again ≈4.5, due to
displacement of some of the donor groups of the L
2
ligands by
water.
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