2 research outputs found
Structure, Spectra, and DFT Simulation of Nickel Benzazolate Complexes with Tris(2-aminoethyl)amine Ligand
Benzazolate complexes of NiĀ(II),
[NiĀ(pbz)Ā(tren)]ĀClO<sub>4</sub> (pbz = 2-(2ā²-hydroxyphenyl)-benzimidazole
(pbm), <b>1</b>, 2-(2ā²-hydroxyphenyl)-benzoxazole (pbx), <b>2</b>, 2-(2ā²-hydroxyphenyl)-benzothiazole (pbt), <b>3</b>; tren = trisĀ(2-aminoethyl)Āamine), are prepared by self-assembly
reaction and structurally characterized. Theoretical DFT simulations
are carried out to reproduce the features of their crystal structures
and their spectroscopic and photophysic properties. The three complexes
are moderately luminescent at room temperature both in acetonitrile
solution and in the solid state. The simulations indicate that the
absorption spectrum is dominated by two well-defined transitions,
and the electronic density concentrates in three MOs around the benzazole
ligands. The Stokes shifts of the emission spectra of complexes <b>1</b>ā<b>3</b> are determined by optimizing the electronic
excited state
Structure and Spectroscopic Properties of Nickel Benzazolate Complexes with Hydrotris(pyrazolyl)borate Ligand
The reaction of benzazole
ligands 2-(2ā²-hydroxylphenyl)Ābenzimidazole (Hpbm), 2-(2ā²-hydroxylphenyl)Ābenzoxazole
(Hpbx), and 2-(2ā²-hydroxylphenyl)Ābenzothiazole (Hpbt),
with [NiĀ(Tp*)Ā(Ī¼-OH)]<sub>2</sub> (Tp* = hydrotrisĀ(3,5-dimethylpyrazolyl)Āborate),
leads to pentacoordinate nickel complexes [NiĀ(Tp*)Ā(pbz)] (pbz
= pbm (<b>1</b>), pbx (<b>2</b>), pbt (<b>3</b>)).
The structures of <b>1</b>, <b>2</b>, and <b>3</b> were determined by X-ray crystallography. The pentacoordinate nickel
complexes have distorted trigonal bipyramidal geometries with Addisonās
Ļ parameter values of 0.63, 0.73, and 0.61 for <b>1</b>, <b>2</b> and <b>3</b>, respectively. The benzazolates
are bonded in an Ī·<sup>2</sup>(N,O) fashion to the nickel atoms.
DFT calculations are carried out to optimize the structures of the
three complexes giving a good agreement with the X-ray structures.
The <sup>1</sup>H NMR spectra of complexes <b>1</b>ā<b>3</b> exhibit sharp isotropically shifted signals. The complete
assignment of these signals required an application of two-dimensional
{<sup>1</sup>Hā<sup>1</sup>H}-COSY techniques. The experimental
absorption spectra of the three complexes in chloroform solution each
show an intense absorption band in the ultraviolet region ca. 240
nm, followed by three less intense bands, the first two at ā¼295
and ā¼340 nm, and the last more disperse one, at wavelengths
between 360 and 410 nm. The absorption spectra are simulated by TD-DFT
and reproduce the main features of the experimental spectra well.
The analysis of the electronic transitions by inspection of the frontier
molecular orbitals and also the natural transition orbitals allowed
us to characterize and assign the observed bands properly. The three
complexes are moderately blue luminescent at room temperature, both
in the solid state and in solution. Emission spectra at room temperature
display broad structureless bands in chloroform solution at 460, 482,
and 512 nm for complexes <b>1</b>, <b>2</b> and <b>3</b>, respectively, and structured emission in solid state with
Ī»<sub>max</sub> values of 473, 486, and 516 nm. Complexes containing
different donor atoms in the benzazole ligand are furthermore observed
to give different luminescence responses in the presence of ZnĀ(II),
CdĀ(II), HgĀ(II), and CuĀ(II)