Luminescent Properties of Lanthanide Nitrato Complexes with Substituted
Bis(benzimidazolyl)pyridines
Stéphane Petoud
Jean-Claude G. Bünzli
Kurt J. Schenk
Claude Piguet
10.1021/ic961305a.s001
https://acs.figshare.com/articles/journal_contribution/Luminescent_Properties_of_Lanthanide_Nitrato_Complexes_with_Substituted_Bis_benzimidazolyl_pyridines/3617784
The protonated form of the ligand
2,6-bis(1‘-methylbenzimidazol-2‘-yl)pyridine crystallizes as
its perchlorate salt
(HL<sup>1</sup>)ClO<sub>4</sub> (<b>1</b>) in the
orthorhombic system <i>Pbca</i>, with <i>a</i> =
13.976(3) Å, <i>b</i> = 14.423(3) Å, <i>c</i> =
19.529(4) Å, <i>Z</i>
= 8. The proton is located on one benzimidazole N-atom, and the
two N-methyl substituents lie on the same
side of the pyridine N-atom (cisoid conformation). New 1:1 nitrato
complexes of composition
[Eu(NO<sub>3</sub>)<sub>3</sub>(L<i><sup>i</sup></i><sup></sup>)](solv‘)<i><sub>y</sub></i> have been isolated with L<sup>4</sup>
(<b>4</b>), L<sup>6</sup> (<b>5</b>), L<sup>7</sup>
(<b>6</b>), and L<sup>8</sup> (<b>7</b>), and their structural
and photophysical properties
are compared with those of the previously reported complexes
[Eu(NO<sub>3</sub>)<sub>3</sub>(L<sup>1</sup>)(MeOH)]
(<b>2</b>) and
[Eu(NO<sub>3</sub>)<sub>3</sub>(L<sup>3</sup>)]
(<b>3</b>). The crystal and molecular structure of
[Eu(NO<sub>3</sub>)<sub>3</sub>(L<sup>7</sup>)(MeCN)]·2.5MeCN
at 180 K (<b>6a</b>, triclinic, <i>P</i>1̄, <i>a</i>
=
12.137(2) Å, <i>b</i> = 14.988(3) Å, <i>c</i> =
16.926(3) Å, α = 114.52(3)°, β = 98.28(3)°,
γ = 103.99(3)°, <i>Z</i> = 2) shows
a decacoordinated Eu<sup>III</sup> ion to six O-atoms from the
nitrates, three N-atoms from L<sup>7</sup>, and one N-atom from
a
coordinated MeCN. The metal-centered luminescence arising upon
ligand excitation in the solid state is analyzed
in terms of nephelauxetic effects of the ligand and crystal field
splitting of the <sup>7</sup>F<sub>1</sub> level. Quantum yields
of 10<sup>-3</sup>
and 10<sup>-4</sup> M solutions in MeCN are substituent
dependent and may be rationalized by taking into account
several
factors, including the energy of the ligand singlet and triplet levels
and the arrangement of the ligands in the first
coordination sphere. We also show that the quantum yield of the
ligand-centered luminescence decreases in the
order L<sup>1</sup> >
[La(NO<sub>3</sub>)<sub>3</sub>(L<sup>1</sup>)]MeOH
>
[La(L<sup>1</sup>)<sub>3</sub>](ClO<sub>4</sub>)<sub>3</sub>.
1997-03-26 00:00:00
protonated form
nephelauxetic effects
substituent
ligand excitation
L 8
L 7
L 4
MeCN
180 K
HL 1
photophysical properties
quantum yields
Lanthanide Nitrato Complexes
7 F 1 level
order L 1
cisoid conformation
perchlorate salt
triplet levels
crystal field splitting
Luminescent Properties
MeOH
complex
ligand singlet
decacoordinated Eu III ion
coordination sphere
system Pbca
luminescence
ClO 4