Variable dimensionality in 'hollow' hybrid tin iodide perovskites

Article abstract of DOI:10.1039/d0dt03449e

Two 'hollow' B-site deficient perovskites, (TzH)11(H3PO2)Sn6I23 and (TzH)3Sn2I7 (TzH+ = 1,2,4-triazolium, H3PO2 = hypohosphorous acid), have been prepared. (TzH)11(H3PO2)Sn6I23 is the first example of a 2D layered structure of this type. Leaving the same reaction mixture for an extended time also affords the 3D derivative (TzH)3Sn2I7.

Full text of DOI:10.1039/d0dt03449e

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Variable dimensionality in ‘hollow’ hybrid tin
iodide perovskites†
Cite this: DOI: 10.1039/d0dt03449e
Jason A. McNulty,
Alexandra M. Z. Slawin
and Philip Lightfoot
*
Received 6th October 2020,
Accepted 23rd October 2020
DOI: 10.1039/d0dt03449e
rsc.li/dalton
Two ‘hollow’ B-site deficient perovskites, (TzH)11(H3PO2)Sn6I23 and
In this paper we present two new hybrid Sn iodide perovs-
(TzH)3Sn2I7 (TzH+ = 1,2,4-triazolium, H3PO2 = hypohosphorous kite structures inspired by our previous work using TzH+ as a
acid), have been prepared. (TzH)11(H3PO2)Sn6I23 is the first example structure-directing agent, which has previously led to the dis-
of a 2D layered structure of this type. Leaving the same reaction covery of a wide variety of structural novelty.11–13 Our nominal
mixture for an extended time also affords the 3D derivative target composition was (TzH)SnI3, which we assumed might
(TzH)3Sn2I7.
adopt
a
3D structure related to that observed in
(GuH)0.5(TzH)0.5SnI3. To our surprise the reaction produced a
novel structure type based on a ‘hollow’ B-site deficient perovs-
kite, (TzH)11(H3PO2)Sn6I23 (1). While the B-site deficient per-
ovskite structure has been reported previously,14,15 1 rep-
resents the first example of a layered variant of this family. On
leaving the same reaction mixture for 2 months, a 3D ‘hollow’
perovskite (TzH)3Sn2I7 (2) is the dominant product.
Studies investigating dimensional reduction in organic–in-
organic hybrid perovskite materials, from the 3D ABX3 struc-
ture (A = organic or inorganic monovalent cation, B = Pb2+ or
Sn2+, X = Cl, Br or I), have become prevalent in recent years in
an effort to obtain new materials with tuneable properties.1–3
Many of these materials have generated interest due to their
potential use in solar cells and light-emitting devices (LEDs)
among others.4,5 These studies have primarily focused on lead
halide materials as these have been found to give the highest-
efficiency perovskite solar cells thus far.6,7
However, these materials remain problematic due to the high
toxicity of Pb and, as such, investigations into alternatives are
becoming commonplace.8 The most common examples replace
Pb2+ with Sn2+ due to the similar electronic and optical pro-
perties that can be achieved in these perovskites.9,10 In our pre-
vious work,11 we presented two unusual examples of perovskite
materials incorporating Sn, namely the 3D (GuH)0.5(TzH)0.5SnI3
and 2D (GuH)1.5(Me-ImH)0.5SnI4 (GuH+ = guanidinium, TzH+ =
1,2,4-triazolium and Me-ImH+ = 1-methylimidazolium). Both of
these materials featured unprecedented ordering patterns of
organic cations, suggesting that further study of tin iodide-
based perovskites could result in a diverse range of structure-
types that have not been observed in hybrid perovskite
materials thus far.
Details of the synthesis and characterisation are provided
in the ESI.† In brief, the same reaction mixture produces 1
after ∼1 h and 2 after ∼2 months. The crystal structures of 1
and 2 were determined by single crystal X-ray diffraction at
93 K and 173 K, respectively: crystallographic details given in
Table 1. While the amine and coordinated solvent, H3PO2,
positions in 1 have been identified fully, it has not been poss-
ible to fully assign the C/N positions of TzH+ as partial dis-
order precludes definitive atom assignment. In 2, only the tin
iodide framework has been included in the final refinement;
the level of disorder is higher and although fragments can be
assigned, no satisfactory and complete model of the amine
moieties was found. Nevertheless, CHN analysis supports the
proposed composition, with three intact TzH+ moieties, hence
we conclude there is no degradation of the amine during the
prolonged reaction. Fig. 1 shows the crystal structures of 1 and
2 highlighting the B-site deficiency common to both compo-
sitions and the difference in connectivity between the 2D
layered and 3D structures. For clarity, amine positions have
been omitted. A key distinction between the two structures is
the incorporation of a neutral H3PO2 molecule in 1, which acts
to ‘cap’ and separate the triple perovskite-like blocks.
School of Chemistry and EaStChem, University of St Andrews, St Andrews, Fife,
KY16 9ST, UK. E-mail: pl@st-andrews.ac.uk
†Electronic supplementary information (ESI) available: Synthesis, single crystal
X-ray diffraction, crystallographic data (CIF). CCDC 2026398 (1) and 2026399 (2).
For ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/d0dt03449e
In our previous work11,13 we discussed the significant effect
that ionic size, lone-pair effects and hydrogen-bonding environ-
ments can have on both cationic ordering behaviour and sub-
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Table 1 Crystallographic data and refinement details for 1 and 2
hedral tilting in (GuH)0.5(TzH)0.5SnI3 and the occurrence of con-
siderable octahedral distortions. While it might reasonably be
assumed that a similar distortion would be present in the ‘per-
ovskite unit’ of the network in 1 this is not the case. Instead
conventional tilting of the octahedra occurs to optimise
bonding and accommodate the TzH+ cation, as shown in
Fig. 2a. The accommodation of a TzH+ cation in the ‘hollow’ at
the vacant B-site leads to an unusual coordination environment,
as shown in Fig. 2b. In this environment the central TzH+
cation forms inter-amine hydrogen-bonds to two other TzH+
cations. Due to the space requirements of the N lone-pair, both
of the remaining TzH+ orient with this pointing towards the
central cation. This results in an interaction reminiscent of lone
pair-π stacking (Fig. 2c).16,17 While this type of interaction is
weak, it would be expected to have a slight stabilising effect on
the structure. Perhaps the most interesting amine environment
in 1 is that observed in the interlayer region. TzH+ cations and
H3PO2 molecules are arranged in a bilayer with each H3PO2 co-
ordinated to two TzH+ cations (only one of which is from the
same layer). These are held by strong hydrogen bonds (N–H⋯O
∼2.6–2.8 Å), likely contributing to the stability of this unique
layered B-site deficient structure. In Fig. 2e the coordination of
(H3PO2) to TzH+ cations is shown. This highlights the presence
of partial disorder within TzH+ that precludes full assignment
of C/N positions.
1
2
Temperature
93 K
173 K
Formulaa
C22N33H47PO2Sn6I23
4423.95
3.220
C6N9H12Sn2I7
1335.97
2.801
Formula weight
Density/g cm−3
Crystal system
Space group
Triclinic
P1
Triclinic
P1
ˉ
ˉ
a/Å
b/Å
c/Å
α/°
14.0051(14)
14.7298(13)
22.5350(20)
83.978(5)
85.573(5)
88.147(6)
4608.0(7)
2
6.403(4)
14.2301(10)
14.680(11)
91.42(3)
93.54(3)
90.10(3)
1334.6(13)
2
β/°
γ/°
V/Å3
Z
Measured ref.
Independent ref.
Refined parameters
GOOF
Final R indices (I >
2σ(I))
130 747
36 319
16 815 [R(int) = 0.0869] 4844 [R(int) = 0.1379]
794
1.128
R1 = 0.0593, wR2 =
0.1381
85
1.837
R1 = 0.1758, wR2 =
0.4900
a C/N positions in 1 have not been fully assigned as disorder precludes
definitive atom assignment. While only the tin iodide framework of 2
has been refined, the formula and formula weight has been calculated
based on the assumed (TzH)3Sn2I7 composition.
The mean distortion level (Δd) and bond angle variance
(σ2) of each octahedron in both compositions were calculated
(details are provided in ESI†) and the values shown in Table 2.
It can be noted that the most extreme octahedral distortions in
1 occur for Sn4 and Sn5, which are the two sites in the ‘inner’
layer of the triple perovskite block. Comparison of the struc-
tural distortions of 1 and 2 to previously reported materials is
important in attempting to understand the adoption of the 2D
and 3D structure-types, respectively. While at present there are
five examples of ‘hollow’ B-site deficient tin iodide perovskites
based on the FASnI3 or MASnI3 framework (FA+ = formamidi-
nium and MA+ = methylammonium),14,18,20,21 the crystal struc-
ture of the tin iodide framework of only one of these has thus
far been determined, namely HEAxFA1−xSn0.67 2.33 =
(HEA+
I
hydroxyethylammonium).18 1 is the first of these structure-
types to include resolved amine positions. The mean distortion
level in both
HEAxFA1−xSn0.67 2.33
MA0.55HEA0.63Pb0.63 2.82
1
and
or the related Pb-based composition,
. While a greater distortion is expected
2
is greater than in either
I
I
in Sn-based structures compared to related Pb-based materials
the magnitude of the difference does not solely account for
this. We hypothesise that the presence of only a single small
amine, TzH+, in both 1 and 2 likely results in a greater distor-
tion of the octahedra to optimise the hydrogen-bonding
environments and stabilise the structure. This is in contrast to
the linear HEA+ present in both known materials which appar-
ently somewhat precludes this distortion.
Fig. 1 Inorganic framework of 1 (top) at 93 K and 2 (bottom) at 173 K.
Note the B-site deficiency common to both 1 and 2 (left) and the difference
in connectivity (right) between the layered 2D and 3D structure-types
observed in 1 and 2, respectively. Note that the ‘triple’ perovskite-like blocks
in 1 are partially staggered relative to each other along c (see Fig. 2d).
In summary, we have prepared two new examples of ‘hollow’
B-site deficient tin halide perovskites. In (TzH)11(H3PO2)Sn6I23
we introduce the first 2D layered structure of this type and the
first crystal structure featuring resolved amine positions. In
sequent structural distortions in tin iodide perovskites. In 1,
there are several amine environments of importance and these
are shown in Fig. 2. Previously we discussed the lack of octa-
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Fig. 2 Different amine environments in 1. (a) Octahedral tilting in the ‘perovskite unit’; (b) ‘hollow’ B-site deficient coordination of TzH+ showing
inter-amine hydrogen-bonding and lone pair-π stacking-like interaction; (c) schematic of the lone pair-π stacking interaction; (d) interlayer TzH+
interaction with (H3PO2); (e) strong hydrogen-bonding of TzH+ to (H3PO2). Hydrogen-bonding and the lone-pair-π stacking-like interaction are
shown by the solid orange and dashed green lines, respectively.
Table 2 Summary of calculated bond length distortions (Δd) and bond
angle variance (σ2) for B-site deficient compounds reported here and in
the literature
using a single cation. The versatility of 1,2,4-triazolium as a
structure-directing agent in hybrid perovskites has resulted in
the discovery of several previously unseen structures that likely
would not have been realised otherwise. Moreover, the first
observation of the inclusion of H3PO2 as an active ‘capping’
agent provides food-for-thought in the design of dimensionally-
reduced perovskites. This work prompts further study of the
Composition
B cation
Δd (×10−4
)
σ2
1
Sn1
Sn2
Sn3
Sn4
Sn5
Sn6
Sn1
Sn2
Sn1
Pb1
27.00
19.77
18.48
46.79
32.56
21.86
30.52
18.92
17.47
5.88
14.37
7.32
12.92
24.77 structure-directing effects of both small disc-shaped amines
30.54
8.73
7.62
7.90 lation and control.
1.43
4.98
and hypophosphorous acid in the pursuit of interesting new
structure-types, ultimately with prospects for property manipu-
2
18
HEAxFA1−xSn0.67 2.33
MA0.55HEA0.63Pb0.63 2.82
I
19
I
Conflicts of interest
(TzH)3Sn2I7 we present the first structure of this type templated
by a single organic cation. The occurrence of two distinct com-
pounds in this reaction sequence may be due to a structural
change from 1 to 2 over time, but other processes such as the
delayed precipitation of 2 or the initial presence of both 1 and 2
There are no conflicts to declare.
Acknowledgements
simultaneously followed by dissolution of 1 cannot be ruled We acknowledge support from the University of St Andrews
out. 2 represents the first 3D ‘hollow’ perovskite templated and the Leverhulme trust (RPG-2018-065). The research data
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