Computational Study of Polarizabilities and Second Hyperpolarizabilities of Inorganic Transition Metal Thiometalates and Metalates in Solution Page: 4,711
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J. Phys. Chem. A 2000, 104, 4711-4717
Computational Study of Polarizabilities and Second Hyperpolarizabilities of Inorganic
Transition Metal Thiometalates and Metalates in Solutiont
Thomas R. Cundari,*,1 Henry A. Kurtz, and Tie Zhou
Department of Chemistry, Computational Research on Materials Institute (CROMIUM), University of Memphis,
Memphis, Tennessee 38152-6060
Received: October 28, 1999; In Final Form: December 21, 1999
A systematic study of nonlinear optical (NLO) properties of inorganic transition metal (TM) thiometalates
and metalates is reported. Polarizabilities (c) and second hyperpolarizabilities (y) are calculated in solution
within the polarizable continuum model. It is found that NLO properties of anionic inorganic complexes can
be successfully modeled in solution, when this cannot be done so in the gas phase. Solvent effects are found
to significantly increase ac and y. The effects are stronger on y (up to 80%) than on ac (up to 40%) and
stronger on TM thiometalates than on metalates. For ac, solvent effects are found to be more important than
electron correlation effects. For y, the two effects are similarly important. Solvent effects on ac and y caused
by subordinate factors other than the dominant electrostatic solute-solvent interactions were studied and
assessed to be negligible. Upon solvation, large TM and ligand modification effects on ac and y are found.
One oxo-to-sulfido substitution results in an increase in ac by 38 au and y by 10 000 au.Introduction
With the progress in computational modeling of nonlinear
optical (NLO) properties, many important effects (e.g., basis
set, electron correlation, solvent, intermolecular interaction, etc.)
regarding NLO properties have been studied separately by
different researchers mainly focusing on specific and/or proto-
typical small organic and organometallic molecules.2 However,
systematic studies of NLO properties of inorganic complexes
are comparatively very rare.3 As an initial effort to fill this void,
we have recently studied NLO properties of all the existing
transition metal (TM) metalates, [MO4]q- (M: transition metals
of groups 4-8 and the first to third transition series, except for
Fe; q: charge).4 Metalates are simple molecular models for
inorganic NLO materials, such as lithium niobate and barium
titanate,5 which belong to the first NLO materials in use. To
our knowledge, no experimental studies of the NLO properties
of thiometalate species have been reported. Computations on
organic systems suggest that oxygen - sulfur replacements can
enhance NLO properties.6 For this reason, we undertook an
evaluation of oxygen - sulfur replacements on NLO properties
of inorganic species. Systematic research focusing on families
of chemically and structurally correlated complexes contributes
to understanding the relationship between NLO properties and
chemical structure and properties, which is important for the
design of novel NLO materials.
On the basis of the initial results for [MO4]q-,4a we found
that NLO properties of neutral and sometimes less negatively
charged inorganic species can be reliably modeled in the gas
phase. However, there is a systematic overestimation of polar-
izabilities (ct) and second hyperpolarizabilities (y) for highly
negatively charged species as a consequence of the inherent
difficulties in treating such species quantum mechanically in
the gas phase. It is often the case that their valence electrons
t Part of the special issue "Electronic and Nonlinear Optical Materials:
Theory and Modeling".
* Address correspondence to this author.
10.1021/jp9938381 CCC: $19.00are not bound to atomic or molecular orbitals, and thus they
are not stable, gas-phase entities. Therefore, quantum calcula-
tions on isolated highly negatively charged species in a vacuum
using extended basis sets, including diffuse polarization func-
tions, give rise to magnifications in ac and particularly in y.7
These are highly dependent on the electron density distribution
in the outer and fringe region. The supermolecule approach with
ligation of counterions (e.g., alkali metal cations) has proven
to be successful in solving problems with modeling the NLO
properties of anionic inorganic complexes.4b
Another way to solve this problem is prompted by our interest
in modeling NLO properties of anionic species in a solution
environment as well as studying the resulting solvent effects
on NLO properties of inorganic TM complexes. This is of
interest because a study of solvent effects on NLO properties
helps fill in the gap between quantum mechanical calculations
done mostly for isolated molecules and the experimental
measurements performed mostly in condensed phase (solution,
solid). The screening of electron-electron repulsions on the
anionic solute by a high dielectric solvent results in bound
molecular orbitals. The (hyper)polarizabilities of this stable form
can then be reliably calculated by current techniques.
Thus, as a further step in a systematic study of the NLO
properties of inorganic TM complexes, this present research was
extended from TM metalates, [MO4]q-, to all known TM
thiometalates, [MS4]q- (M: transition metals of groups 5-7
and the first to third transition series; q: charge), and from the
gas-phase isolated systems to solution. The research employed
a sophisticated solvation model technique, the polarizable
continuum model (PCM).8-12 Recently, some works on solvent
effects on (hyper)polarizabilities for some prototypical organic
molecules using the PCM technique have been reported.'3-16
However, to our knowledge, this present work is the first
systematic study of solvent effects on NLO properties of
inorganic complexes. In addition, reliable modeling of NLO
properties for a series of TM thiometalates versus metalates in
2000 American Chemical SocietyPublished on Web 03/08/2000
4711
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Cundari, Thomas R., 1964-; Kurtz, Henry A. & Zhou, Tie. Computational Study of Polarizabilities and Second Hyperpolarizabilities of Inorganic Transition Metal Thiometalates and Metalates in Solution, article, March 8, 2000; [Washington, D.C.]. (https://digital.library.unt.edu/ark:/67531/metadc107806/m1/1/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT College of Arts and Sciences.