Crystal Structure and Electronic Properties of New Compound Zr6.5Pt6Se19

Article abstract of DOI:10.1021/acs.inorgchem.0c00522

A new ternary nonstoichiometric Zr_6.5Pt₆Se₁₉ has been discovered as a part of effort to dope Zr into the layered transitional metal chalcogenide PtSe₂. With a new structure type (oC68), it is the first Pt-based ternary chalcogenide with group 4 elements (Ti, Zr, and Hf). The crystal structure adopts the orthorhombic space group Cmmm with lattice parameters of a = 15.637(6) ?, b = 26.541(10) ?, c = 3.6581(12) ?, and V = 1518.2(9) ?³. This unusual structure consists of several building units: Chains of edge-sharing selenium trigonal prisms and octahedra centered by zirconium atoms, chains of corner-shared square pyramid, and square planar centered by Pt atoms. The condensation of these building blocks forms a unique structure with bilayered Zr_5.54Pt₆Se₁₉ slabs stacking along the b direction and large channels parallel to the c direction within the bilayered slabs. Band structure calculations suggest that partial occupancy of Zr atoms creates a pseudo gap at the Fermi level and is likely the main cause for the stability of this new phase.

Full text of DOI:10.1021/acs.inorgchem.0c00522

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Article
Crystal Structure and Electronic Properties of New Compound
Zr6.5Pt6Se19
Hanlin Wu, Huifei Zhai, Sheng Li, Maurice Sorolla, II, Gregory T. McCandless, Daniel Peirano Petit,
Julia Y. Chan, and Bing Lv*
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ABSTRACT: A new ternary nonstoichiometric Zr6.5Pt6Se19 has been discovered as
a part of effort to dope Zr into the layered transitional metal chalcogenide PtSe2.
With a new structure type (oC68), it is the first Pt-based ternary chalcogenide with
group 4 elements (Ti, Zr, and Hf). The crystal structure adopts the orthorhombic
space group Cmmm with lattice parameters of a = 15.637(6) Å, b = 26.541(10) Å, c
= 3.6581(12) Å, and V = 1518.2(9) Å3. This unusual structure consists of several
building units: chains of edge-sharing selenium trigonal prisms and octahedra
centered by zirconium atoms, chains of corner-shared square pyramid, and square
planar centered by Pt atoms. The condensation of these building blocks forms a
unique structure with bilayered Zr5.54Pt6Se19 slabs stacking along the b direction and
large channels parallel to the c direction within the bilayered slabs. Band structure
calculations suggest that partial occupancy of Zr atoms creates a pseudo gap at the
Fermi level and is likely the main cause for the stability of this new phase.
unique PtSe5 square pyramids and layered stacking along the b
axis and large channels parallel to the c directions in the
structure. The detailed structural description, chemical
bonding analysis, and band structure calculations are also
described in this paper.
1. INTRODUCTION
The transition metal chalcogenide PtSe2 recently has attracted
interest after the discovery of type II Dirac semimetal
behavior,1 negative longitudinal magnetoresistance,2 quantum
oscillations,3 thickness and quantum confinement modulated
semimetal to semiconductor transformation,4,5 and photo-
catalytic activity.6 First-principles calculations suggest that
transition metal (TM) doped PtSe2 exhibits versatile spintronic
behavior depending on the nature of the dopant TM atoms7
and topological phase transition caused by broken inversion
symmetry with Te substitution.8 Chemical doping has also
been proven to be an effective tool to change carrier
concentration9 and Fermi level10 and induce superconductivity
in the transition metal chalcogenides.11 However, the
investigation of new materials and phase behavior in systems
of the type TM−Pt−Se, where TM = group IVB−group VIIIB
transition metals, has been largely neglected. Indeed, only a
few reports on group VB ternary compounds, such as
Nb8PtSe20,12 Ta2PtSe7,13 and Ta2Pt3Se8,14 have been reported.
Given the rich structural diversity and various bonding features
in the Pt-based pnictide system,15−21 it is reasonable to
speculate that phases in combinations of the electron-rich
group IVB elements will form, with different structure features
as the alkali and alkaline earth ternary Pt-based chalcoge-
nides.22−26 During the course of doping studies of transition
metal chalcogenide ZrSe2, we discovered a new ternary Pt-
based layered chalcogenide, nonstoichiometric Zr6.5Pt6Se19,
with a new structure type (oC68). It is the first Pt-based
ternary compound as a group IVB and chalcogenide, with
2. EXPERIMENTAL SECTION
2.1. Material Synthesis, Crystal Growth and Composition
Analysis. The starting materials used were Zr pieces (99.9%, Alfa
Aesar), Pt powder (99.95%, Alfa Aesar), and Se shots (99.999%, Alfa
Aesar). The ZrSe2 precursor was first synthesized through solid-state
reaction by sealing stoichiometric Zr pieces and Se shots in a clean
fused silica tube under a vacuum and then heated at 950 °C for 2
days. The obtained powders were ground and pressed into a pellet,
followed by the same heat treatment two times to ensure
homogeneity. The compound was initially found as impurities during
the chemical doping studies for PtxZrSe2 (0.1 ≤ x ≤ 1.5) above 900
°C and later on was isolated successfully as small needle-shaped
crystals on the wall of the alumina crucible container when the
reaction temperature was above 1020 °C. Small crystals are selected
for the X-ray single crystal diffraction. The refined chemical
composition from single crystal diffraction is subsequently confirmed
by both SEM energy-dispersive X-ray spectroscopy (SEM-EDX) and
inductively coupled plasma mass spectrometry (ICP-MS) measure-
Received: February 18, 2020
https://dx.doi.org/10.1021/acs.inorgchem.0c00522
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ments. Since the characteristics of the X-ray energy spectra of Zr Lα
(2.044 keV) and Pt Mα (2.048 keV) are nondistinguishable, the
SEM-EDX is mainly used to check the presence of the chemical
species, and ICP-MS is our main tool to precisely determine the
chemical composition. The determined Zr/Pt/Se ratio is
6.1(5):5.72(7):19, very close to the refined chemical composition
from X-ray single crystal diffraction.
The attempts to synthesize an X-ray powder pure phase are also
carried out with different starting ratios of Zr/Pt/Se = 6.5:6:19 (as
refined Zr occupancy ratio) and Zr/Pt/Se = 9:6:19 (as Zr position
fully occupied stoichiometric ratio) but unfortunately give poor yields.
It is mainly due to the presence of the competing phases of ZrSe2 and
PtSe2 in the powder during the synthesis. On the other hand, larger
size crystals, up to 3 mm in length, were successfully synthesized when
the assembly was heated at 1150 °C for 2 days and slowly cooled to
600 °C at a rate of 3 °C/h. Single crystal refinement from different
batches of crystals with different starting Zr (6.5 ≤ x ≤ 9) ratios
shows very similar Zr partial occupancies; therefore, we conclude the
title compound is indeed a nonstoichiometric compound.
2.2. X-ray Crystallography. Phase identification and crystal
structure were determined by single crystal X-ray diffraction. Single
crystals were mounted on a Bruker D8 Quest Kappa single-crystal X-
ray diffractometer equipped with a Mo Kα IμS microfocus source (λ =
0.71073 Å) operating at 50 kV and 1 mA with a HELIOS optics
monochromator and a CPAD detector. The collected data set was
integrated with Bruker SAINT and scaled with Bruker SADABS
(multiscan absorption correction).27 A starting model was obtained
using the intrinsic phasing method in SHELXT,28 and atomic sites
were refined anisotropically using SHELXL2014.29 Crystallographic
parameters and refinement details for Zr6.5Pt6Se19 are provided in
Table 1. Atomic coordinates, equivalent anisotropic displacement
method30 in the atomic sphere approximation (ASA) and (2) the full-
potential linearized augmented plane wave (FP-LAPW) method as
implemented in the WIEN2K code.31 For the LMTO method, the
Barth−Hedin local exchange correlation potential was implemented.32
Radii of the atomic spheres and interstitial empty spheres were
obtained as implemented in the TB-LMTO-ASA program. The
tetrahedron method was selected for the k-space integration.33 The
calculations utilized as basis sets Zr 5s/(5p)/4d/(4f), Pt 6s/6p/5d/
(5f), and Se 5s/5p/(5d) (downfolded orbitals in parentheses).34,35
Reciprocal space integrations were performed using 305 irreducible k-
points. The chemical bonding analyses were investigated using the
crystal orbital Hamilton population (COHP)36 technique as
implemented in the TB-LMTO-ASA 4.7 program package. For the
WIEN2K method, the exchange and correlation energies were treated
within the density functional theory (DFT) using the Perdew−
Burke−Ernzerhof generalized gradient approximation (GGA).37 The
self-consistencies were carried out using 1000 k-points (10 × 10 × 10
mesh) in the irreducible Brillouin zone. Spin orbit coupling effects are
considered for the calculation. The computational results from both
methods are compared and consistent with each other.
3. RESULTS AND DISCUSSION
3.1. Structural Description. The crystal structure of the
title compound Zr6.5Pt6Se19 is shown in Figure 1a. It
crystallizes in a new structure type (oC68) in the
centrosymmetric orthorhombic space Cmmm with lattice
parameters a = 15.637(6) Å, b = 26.541(10) Å, and c =
3.6581(12) Å. To the best of our knowledge, it is the only
ternary, group 4 (Ti, Zr, and Hf), Pt-based chalcogenide. It is a
bilayer structure composed of Zr and Pt polyhedra expanded
along the ac plane and stacked along the b axis. The two slabs
are related by inversion symmetry. However, within the bilayer
slab, it appears to have stronger anisotropy along the a axis and
thus is consistent with the quasi-1D morphology along the a
axis in the grown crystals. The local environments of the
different Pt atoms [with two crystallographic sites Pt1 (8p) and
Pt2 (4i)], Zr atoms [with two crystallographic sites Zr1 (4j)
and Zr2 (8q)], and Se atoms are shown in Figure 1b−e, and
their associated coordination and stacking are discussed below.
Pt1 atoms form a very unusual five coordinated PtSe5 square
pyramid with the connecting Se1, Se2, and Se5 atoms (Figure
2b). This is very different from square planar or octahedral
coordination commonly observed in the Pt-related chalcoge-
nides such as PtSe2,38 Li2Pt3Se4,23 Na2Pt4Se6,26 and
Table 1. Crystallographic Details for Zr6.5Pt6Se19
temperature
wavelength
298 K
0.71073 Å
space group
Cmmm (No. 65)
unit cell dimensions
a = 15.637(6) Å, b = 26.541(10) Å,
c = 3.6581(12) Å
volume
Z
absorption coefficient
F(000)
1518.2 (9) Å3
2
52.422 mm−1
2748
crystal size
θ range for data
collection
0.01 × 0.02 × 0.46 mm3
3.02° to 30.51°
12
reflections collected
5916
Nb8PtSe20 compounds. As far as we know, only one ternary
transition metal Pt chalcogenide, Ta2Pt3Se8,14 has similar PtSe5
square pyramid coordination reported, and this is the first time
the square pyramid coordination has been established in the
group 10 platinum-group metal in an inorganic solid state
independent reflections
1381 [R(int) = 0.040]
1381/1/62
data/restraints/
parameters
goodness-of-fit on F2
1.094
final R indices [I >
2σ(I)]
R1 = 0.0256, wR2 = 0.0604
14
compound. In the Ta2Pt3Se8 compound, the PtSe5 square
pyramids are interconnected with the TaSe6 trigonal prism
forming a three-dimensional network. In our new compound
Zr6.5Pt6Se19, the PtSe5 square pyramids are corner-shared
through a common apical Se atom constructing the Pt2Se2/2Se8
unit. The resulting Pt2SeSe8 units share edges along the basal
Se atoms building the Pt2SeSe8/2 chain. This Pt2Se5 chain
(Figure 1b) grows along the crystallographic c axis. The Se5
atom is located at the apex of the PtSe5 square pyramid with a
slightly longer Pt−Se distance [2.693 (1) Å] than the basal
plane Pt−Se bonding distances within the square nets [2.493
(1) Å for Pt1−Se1(×2) and 2.485 (1) Å for Pt1−Se2(×2)]
and is reasonably comparable with the Pt−Se distances in the
Ta2Pt3Se8 compound [2.465(4)−2.583(5) Å]. The distortions
of the basal plane are reflected by the angles Se1−Pt1−Se1,
94.39(4)°, and Se1− Pt1−Se2, 84.56(3)°.
R indices (all data)
largest diff. peak and
hole
R1 = 0.0301, wR2 = 0.0623
1.24 and −1.60 e Å−3
parameters, occupancies, and some selected interatomic distances are
included in Tables 2 and 3. More detailed selected interatomic angles
are provided in Supporting Information Table S1. Integrated
precession images along different planes are also shown in Figure
S1, where the green circles indicate the indexed Bragg reflections. No
indication of superstructure is observed in the title compound.
Powder X-ray diffraction measurements were collected from 5° < 2θ <
90° on a Rigaku Smartlab Diffractometer.
2.3. Electronic Band Structure Calculations. Electronic
structure calculations were performed using two different methods:
(1) the Stuttgart TB-LMTO-ASA program employing the tight-
binding (TB) version of the linear muffin-tin orbital (LMTO)
B
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Table 2. Atomic Coordinates and Equivalent Isotropic Displacement Parameters (Ueq) of Zr6.5Pt6Se19
a
atom
Wyckoff site
symm
x
y
z
occ.
Ueq (Å2)
Zr1
Zr2
Zr3
Zr4
Pt1
Se1
Se2
Pt2
Se3
Se4
Se5
Se6
4j
m2m
..m
mmm
m2m
..m
..m
..m
m2m
..m
..m
1/2
0.17937(4)
0
0.07771(7)
0.13126(3)
0
1/2
1/2
1/2
1/2
0
1/2
1/2
0
0
0
0
0
0.768(2)
0.0222(3)
0.0093(2)
0.026(1)
8q
2d
4j
8p
8q
8q
4i
8p
8p
4i
0.354(3)
0.305(2)
1/2
0.24143(17)
0.13027(2)
0.06667(3)
0.19274(3)
0.13162(2)
0.06710(3)
0.19607(3)
0.14847(5)
0
0.027(1)
0.33056(2)
0.32143(5)
0.31242(4)
0
0.11283(4)
0.11287(4)
1/2
0.00973(9)
0.0129(2)
0.0106(2)
0.0132(1)
0.0119(2)
0.0114(2)
0.0144(2)
0.0157(3)
m2m
mmm
2b
1/2
a
Ueq is defined as one-third of the trace of the orthogonalized Uij tensor.
with those reported Zr−Se distances in Cs4Zr3Te16,39
Table 3. Selected Interatomic Distances (Å) in Zr6.5Pt6Se19
41
EuZrSe3,40 and Ce2ZrSe5 compounds. Each Zr1 atom is
Zr−Se
partially occupied (∼77%). Neighboring Zr0.77Se6 octahedra
share edges along the equatorial Se atoms forming the Zr0.77Se4
chain (Figure 1d) that propagates along [001]. The octahedra
formed by Zr1 atoms are highly distorted (see selected bond
angles in Table S1) due to the neighboring Pt2Se5 chain. The
geometric distortions about the metal atoms are consistent
with the chemical inequivalence of the Se atoms. Each Se2,
Se3, and Se4 atom is bound to three metal atoms. The Se1 and
Se5 atoms bridge two Pt atoms and two Zr atoms, while the
Se6 atom connects four Zr1 atoms. In contrast, the Zr2 atoms
are fully occupied and are six-coordinated to the Se atoms in a
trigonal prismatic fashion. The adjacent ZrSe6 units are edge-
shared along the basal Se atoms forming the ZrSe4 chain
(Figure 1e) that expands along [001]. The Se−Se distances
between the adjacent layers range from 3.539(2) to 3.663(2)
Å. These values are slightly bigger than the Se−Se distance
across the van der Waals’ gap of PtSe2, 3.329(4) Å, but smaller
than that of ZrSe2, 3.782(3) Å.
The Pt2Se5 unit formed by Pt1 atoms is edge-shared with the
neighboring ZrSe6 octahedra by Zr1 atoms and condenses to
construct the Zr0.77Pt2Se6 chain (Figure 2a). The stacking and
condensation of the Zr0.77Pt2Se6 chains, PtSe4 units, and two
ZrSe4 chains build a unique Zr2.77Pt3Se10 monolayered slab
(Figure 2b) along the a direction. The Zr0.77Pt2Se6 chains are
edge-shared to the apical Se atoms of the ZrSe4 chains. The
two and opposite sides of the distorted PtSe4 square planar
units are shared with the two ZrSe4 chains along the basal Se
atoms. These two ZrSe4 chains are related by a mirror-plane
symmetry. Two Zr2.77Pt3Se10 monolayered slabs join through
edge-sharing of the equatorial Se atoms of the Zr0.77Se6
octahedra. Thus, the Zr5.54Pt6Se19 bilayered slab is constructed.
Two different Zr atoms, Zr3(2d) and Zr4(4j), lie in between
the Zr5.54Pt6Se19 bilayered slabs. Both Zr3 and Zr4 atoms are
not fully occupied, with occupancy only 0.354(3) for Zr3 and
0.305(2) for Zr4, respectively. The Zr3 atoms are located
within the channels of the bilayered slabs. On the other hand,
the Zr4 atoms are sandwiched between the neighboring
bilayered slabs. Although the Zr−Se contacts outside the slabs
are long (between ∼3 and 3.2 Å), the corresponding Zr−Se
interactions are not to be neglected based on band structure
calculations. Consequently, Zr6.5Pt6Se19 can be viewed as a
pseudo-two-dimensional structure. If all of the Zr sites are fully
occupied, one would expect a stoichiometric Zr9Pt6Se19
compound. Interestingly, a simple formal valence description
Zr1−Se1
Zr1−Se5
Zr1−Se6
Zr2−Se1
Zr2−Se2
Zr2−Se3
Zr2−Se4
Zr3−Se3
Zr4−Se2
Zr4−Se4
Zr4−Se5
(×2)
(×2)
(×2)
(×1)
(×1)
(×2)
(×2)
(×8)
(×2)
(×4)
(×2)
Pt−Pt
2.808(1)
2.622(2)
2.757(2)
2.806(1)
2.644(1)
2.707(1)
2.718(1)
3.1032(9)
3.205(2)
3.035(3)
3.071(4)
Pt1−Pt1
Pt2−Pt2
(×2)
(×2)
Pt−Se
3.658(1)
3.658(1)
Pt1−Se1
Pt1−Se2
Pt1−Se5
Pt2−Se3
Pt2−Se4
(×2)
(×2)
(×1)
(×2)
(×2)
Zr−Zr
2.4930(9)
2.4849(8)
2.693(1)
2.459(1)
2.458(1)
Zr1−Zr1
Zr2−Zr2
Zr3−Zr3
Zr4−Zr4
(×2)
(×2)
(×2)
(×2)
3.658(1)
3.658(1)
3.658(1)
3.658(1)
The Pt2 atom forms a slightly distorted PtSe4 square planar
coordination with the Se3 and Se4 atoms (Figure 1c), as
commonly observed in Pt-related compounds. These PtSe4
units stack in an eclipsed manner along [001]. The bonding
distances [2.459 Å for Pt2−Se3(×2) and 2.458 (1) Å for Pt2−
Se4(×2)] are comparable to those in the basal plane with Pt1−
Se distances. All the Pt−Se bond distances for both Pt1 and
Pt2 atoms are generally smaller than the 6-coordinated Pt−Se
38
distances such as in PtSe2 and comparable to the 4-
23
coordinated Pt−Se distances such as in Li2Pt3Se4 and
Na2Pt4Se6.26
Two of the Zr atoms [Zr1 (4j) and Zr2 (8q)] are found to
be six-coordinated as expected. The Zr1 atoms form distorted
octahedra with the neighboring Se1, Se5, and Se6 atoms,
whereas the Zr2 atoms have trigonal prismatic coordination
with the surrounding six Se1, Se2, Se3, and Se4 atoms. All the
Zr−Se bond distances [2.622(2)−2.808(1) Å] are consistent
C
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Figure 1. (a) The crystal structure of Zr6.5Pt6Se19 projected along the c axis. Different building units by Zr and Pt coordination polyhedra are
highlighted for clarity. (b) Pt2Se5 chain formed by corner and edge-shared Pt(1)Se5 square pyramid for Pt1 atoms. (c) PtSe4 square planar units for
Pt2 atoms surrounded by four Se atoms. (d) Zr0.77Se4 chain formed by edge-shared ZrSe6 octahedra for Zr1 atoms, and Zr1 has a partial occupancy
of 0.768(2). (e) ZrSe4 chain formed by edge-shared ZrSe6 trigonal prisms for Zr2 atoms.
Figure 2. (a) The Zr0.77Pt2Se6 chain formed by the condensation of the Pt2Se5 and the Zr0.77Se4 chains. (b) The stacking sequence in the
Zr2.77Pt3Se10 monolayered slab displayed in two different isometric views.
Figure 3. (a) Density of states (DOS) of the hypothetical Zr9Pt6Se19 phase (210e−) with fully occupied Zr sites. Weighted average crystal orbital
Hamilton population (−COHP) of the (b) Zr−Se and (c) Pt−Se interactions. The Fermi level (EF) is set at 0 eV. The total electron count of
200e− is denoted by dashed lines. Qualitative molecular orbital diagrams of the main d-block in the idealized (d) PtSe4 (D4h) and (e) PtSe5 (C4v)
units with a d8 electronic configuration.
for the compound Zr6.5Pt6Se19 is Zr4+, Pt2+, and Se2− and
yielded a net charge balance of the compound of [6.5 × 4 + 6
× 2 + 19 × (−2) = 0].
3.3. Band Structure Analysis. To examine the role of the
partial occupancies of the Zr atoms in the stability of
Zr6.5Pt6Se19, electronic structure calculations have been
performed. The calculations are based on the hypothetical
Zr9Pt6Se19 compound with all the Zr atoms fully occupied. As
shown in the density of states (DOS) plot (Figure 3a), the
Fermi level of the hypothetical 210-electron phase lies along
the shoulder of a high-DOS peak. In contrast, there is a
pseudogap with an ultralow-DOS corresponding to a total
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electron value of 200e−. The removal of 10e−, such as in the
partial occupancies of Zr atoms, provides a great electronic
stability. Thus, the 200e− Zr6.5Pt6Se19 is more favorable than
the 210e− Zr9Pt6Se19 phase. The crystal orbital Hamilton
populations (COHP) also provide a rationale for the partial
occupancies of the Zr atoms. As shown in Figure 3b, the Zr−
Se interactions are optimal in Zr6.5Pt6Se19; the antibonding
states are empty while the bonding states are fully occupied.
This is not the case for Zr9Pt6Se19, where the Fermi level lies in
antibonding Zr−Se states. The integrated −COHP
(−ICOHP) up to the Fermi level (200e−) of the nearest-
neighbor Zr−Se and Pt−Se interactions in Zr6.5Pt6Se19 is
enumerated in Table 4. The Zr−Se interactions are the major
geometry are frequent in solid-state compounds, as we
discussed before, it is quite uncommon in Pt-based selenides.
Typically, the Pt atoms in these compounds are coordinated in
either square-planar or octahedral fashion. In organometallics,
there are only a few Pt-based molecules with square pyramidal
configuration and are based on Pt(+4).42−44 However, the
Pt1(+4) oxidation state leads to a highly electron-deficient
(Zr4+)6.5(Pt14+)4(Pt22+)2(Se2−)19 phase. In contrast, the Pt1-
(+2) assignment points to an electron-precise compound,
consistent with the Fermi level lying in a pseudogap with
ultralow DOS. Hence, Zr6.5Pt6Se19 can be formulated as
(Zr4+)6.5(Pt2)6(Se2−)19.
Qualitative orbital analysis of square planar PtSe4 and
square-based pyramidal PtSe5 units coupled with the electronic
structure calculations of the solid-state compound also offer a
rationale for the stability of (Zr4+)6.5(Pt2+)6(Se2−)19. Figure 3d
and e illustrate the main d-block orbitals of the idealized units
of PtSe4 (D4h) and PtSe5 (C4v), respectively, with d8 electronic
configuration. In both cases, the ordering of the energy levels
of the MOs are the same: x2 − y2 > z2 > xz = yz = xy. Strong σ-
antibonding states (based from the x2 − y2 orbitals) are present
in the lowest unoccupied molecular orbitals of both the PtSe4
and PtSe5 units. In the solid-state compound, these strong Pt−
Se σ-antibonding interactions are located above −0.2 eV
(Figure 3c). These are unoccupied in Zr6.5Pt6Se19 but partially
filled in the hypothetical Zr9Pt6Se19 phase. As such, the absence
of strong Pt−Se σ-antibonding interactions favors the
formation of Zr6.5Pt6Se19. Meanwhile, only weak antibonding
Pt−Se states (based from the z2 orbitals) are involved in the
highest occupied molecular orbitals of both the PtSe4 and
PtSe5 units. Due to the polarized z2 orbital, the antibonding
interaction between Pt and the apical Se orbitals in the PtSe5
unit is rather weak. Compared with the Pt1−Se distances
involving the basal Se atoms (2.485 to 2.493 Å), Pt1−Se5
separation along the apical Se position is longer (2.693 Å),
which further weakens the antibonding interaction along these
orbitals. In the solid-state material, these weak antibonding
Pt−Se interactions based on the z2 orbitals are located just
below the Fermi level of Zr6.5Pt6Se19 (−1.7 to −4.2 eV). Thus,
the partial occupancies of the Zr atoms enhance the electronic
stability of Zr6.5Pt6Se19 by preventing the filling up of strong
Pt−Se σ-antibonding states.
Table 4. Integrated Crystal Orbital Hamilton Population
(−ICOHP) up to Total Electron Count of 200e−
−ICOHP (eV/
N per unit
%
interaction d (Å)
bond)
cell
contribution
Pt1−Se1
Pt1−Se2
Pt1−Se5
Pt2−Se3
Pt2−Se4
Zr1−Se1
Zr1−Se5
Zr1−Se6
Zr2−Se1
Zr2−Se2
Zr2−Se3
Zr2−Se4
Zr3−Se3
Zr4−Se2
Zr4−Se4
Zr4−Se5
2.493
2.485
2.693
2.459
2.458
2.808
2.622
2.757
2.806
2.644
2.707
2.717
3.103
3.206
3.035
3.071
2.65
2.70
1.26
2.86
3.03
1.41
2.14
1.53
1.82
2.47
2.08
2.18
1.10
0.85
1.28
1.13
2
2
1
2
2
2
2
2
1
1
2
2
8
2
4
2
8.2
8.4
2.0
8.9
9.4
4.4
6.6
4.7
2.8
3.8
6.4
6.8
13.6
2.6
7.9
3.5
contributors (∼63%) to the −ICOHP values due to their
frequency. As such, the Zr atoms have a vital part to play in the
chemical bonding in Zr6.5Pt6Se19. The significant Zr−Se
interactions are also reflected in the DOS plot where the Zr
atoms effectively mix with the Se atoms below the Fermi level
(−1.7 to −8 eV). Thus, the partial occupancy of the Zr atoms
plays a crucial role in the electronic stability of Zr6.5Pt6Se19.
To shed light on role of the Zr atoms in the chemical
bonding in Zr6.5Pt6Se19, COHP has been calculated, with
results shown in Figure 3b and Supporting Information. As can
be seen in Figure 3b, if all the Zr sites are fully occupied, the
Fermi level will fill part of the antibonding states, which will
destabilize the PtSe chains. Once Zr sites follow experimental
occupancies, all the Pt−Se bonds and Zr−Se bonds are
optimal; i.e., the antibonding states are unfilled while bonding
states stay below the Fermi level. The −ICOHP up to the
Fermi level for the respective nearest-neighbor interactions in
Zr6.5Pt6Se19 have been computed (Table 4).
4. CONCLUSIONS
In summary, a new ternary chalcogenide Zr6.5Pt6Se19, with a
new structure type is reported with a nonstoichiometric ratio.
It consists of PtSe5 square pyramid, PtSe4 plane, and ZrSe6
octahedra/trigonal prism building blocks and forms a unique
layered structure along the b direction. Band structure
calculations show that the partial occupancies of the Zr
atoms create a pseudogap at the Fermi level, optimize the Pt−
Se bonding state, and thus enhance the electronic stability for
the compound.
With the absence of any Zr−Zr and Se−Se bonds, the
zirconium and selenium atoms adopt their usual oxidation
states: Zr(+4) and Se(−2). The oxidation state of the Pt2
atom is +2, following the typical d8 electronic configuration for
a transition metal in a square planar coordination environment.
For a square-based pyramidal geometry (as in the case of the
Pt1 atom), both the d6 and d8 electronic configurations are
common. As such, Pt1 can either be in +2 or +4 oxidation
states. Although transition metals with five-coordination
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.inorgchem.0c00522.
■
sı
The selected interatomic angles, integrated precession
images along different planes and COHP plot for Zr−Se,
Pt−Se, and Zr−Pt interactions for Zr6.5Pt6Se19 model
(PDF)
E
https://dx.doi.org/10.1021/acs.inorgchem.0c00522
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
pubs.acs.org/IC
Article
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Gity, F. Quantum confinement-induced semimetal-to-semiconductor
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Accession Codes
CCDC 1981675 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
data_request@ccdc.cam.ac.uk, or by contacting The Cam-
bridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
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AUTHOR INFORMATION
Corresponding Author
■
Bing Lv − Department of Physics, The University of Texas at
Dallas, Richardson, Texas 75080, United States; orcid.org/
0000-0002-9491-5177; Email: blv@utdallas.edu
Authors
Hanlin Wu − Department of Physics, The University of Texas at
Dallas, Richardson, Texas 75080, United States; orcid.org/
0000-0002-7920-3868
Huifei Zhai − Department of Physics, The University of Texas at
Dallas, Richardson, Texas 75080, United States
Sheng Li − Department of Physics, The University of Texas at
Dallas, Richardson, Texas 75080, United States
Maurice Sorolla, II − Department of Chemistry, University of
Houston, Houston, Texas 77204, United States; orcid.org/
0000-0003-2190-5223
Gregory T. McCandless − Department of Chemistry and
Biochemistry, The University of Texas at Dallas, Richardson,
Texas 75080, United States
Daniel Peirano Petit − Department of Physics, The University
of Texas at Dallas, Richardson, Texas 75080, United States
Julia Y. Chan − Department of Chemistry and Biochemistry, The
University of Texas at Dallas, Richardson, Texas 75080, United
States; orcid.org/0000-0003-4434-2160
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Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.inorgchem.0c00522
(15) Lv, B.; Jawdat, B. I.; Wu, Z.; Li, S.; Chu, P. C. W.
Superconductivity in the Ternary Compound SrPt10P4 with Complex
New Structure. Phys. Rev. Mater. 2017, 1, 064801.
Notes
(16) Lv, B.; Jawdat, B. I.; Wu, Z.; Sorolla, M.; Gooch, M.; Zhao, K.;
Deng, L.; Xue, Y.-Y.; Lorenz, B.; Guloy, A. M.; Chu, P. C. W.
Synthesis, Structure, and Superconductivity in the New-Structure-
Type Compound: SrPt6P2. Inorg. Chem. 2015, 54, 1049−1054.
(17) Takayama, T.; Kuwano, K.; Hirai, D.; Katsura, Y.; Yamamoto,
A.; Takagi, H. Strong Coupling Superconductivity at 8.4 K in an
Antiperovskite Phosphide SrPt3P. Phys. Rev. Lett. 2012, 108, 237001.
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Pressure and Doping Studies of the Superconducting Antiperovskite
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(19) Li, S.; Liu, X.; Sorolla, II M.; McCandless, G. T.; Wu, H.; Zhai,
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Zr3.55Pt4Sb4 Compound. Inorg. Chem. 2019, 58, 12017−12024.
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The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work at University of Texas at Dallas is supported by US
Air Force Office of Scientific Research Grant No. FA9550-15-
1-0236 and FA9550-19-1-0037. This project is also partially
funded by NSF- DMREF- 1921581, and the University of
Texas at Dallas Office of Research through the Core Facility
Voucher Program. J.Y.C. also acknowledges partial support
from NSF DMR-1700030.
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