Layered hybrid iron fluorides

Funding: We thank the China Scholarship Council and the University of St Andrews for a PhD studentship to T.L. (201606280032) and the China Postdoctoral Science Foundation (2022M710619).The first examples of layered hybrid iron fluorides are reported. In the reactions carried out, the chain compound (H2pipz)FeF5·H2O always occurs as the major phase, with the layered compounds, (H2pipz)3Fe4F18·2H2O and (H2pipz)2Fe3F13·H2O, being isolated from some reactions as major impurities. The latter two compounds feature two-dimensional sheets of corner-and edge-shared FeIIIF6 octahedra, resulting in two distinct layer architectures. The compound (H2pipz)FeF5·H2O, isolated as the major phase, crystallises with a one-dimensional structure exhibiting zig-zag [FeF5]∞ chains. This work opens up the potential for a much wider family of layered hybrid transition-metal fluorides.Publisher PDFPeer reviewe

Structural chemistry of layered lead halide perovskites containing single octahedral layers

Funding: Leverhulme Trust (award No. RPG-2018-065).We present a comprehensive review of the structural chemistry of hybrid lead halides of stoichiometry APbX4, A2PbX4 or AAʹPbX4, where A and Aʹ are organic ammonium cations and X = Cl, Br or I. These compounds may be considered as layered perovskites, containing isolated, infinite layers of corner-sharing PbX4 octahedra separated by the organic species. We first extract over 250 crystal structures from the CCDC and classify them in terms of unit cell metrics and crystal symmetry. Symmetry mode analysis is then used to identify the nature of key structural distortions of the [PbX4]∞ layers. Two generic types of distortion are prevalent in this family: tilting of the octahedral units and shifts of the inorganic layers relative to each other. Although the octahedral tilting modes are well-known in the crystallography of purely inorganic perovskites, the additional layer shift modes are shown to enrich enormously the structural options available in layered hybrid perovskites. Some examples and trends are discussed in more detail in order to show how the nature of the interlayer organic species can influence the overall structural architecture, although the main aim of the paper is to encourage workers in the field to make use of the systematic crystallographic methods used here to further understand and rationalise their own compounds, and perhaps to be able to design-in particular structural features in future work.Publisher PDFPeer reviewe

Unprecedented tin iodide perovskite-like structures featuring ordering of organic moieties

We acknowledge support from the University of St Andrews and the Leverhulme trust (RPG-2018-065).Two unique hybrid tin iodides, with generic compositions A0.5A′0.5SnI3 and A1.5A′0.5SnI4 have been prepared. Each shows ordering of the two organic moieties (A and A′) on distinct crystallographic sites, leading to novel 3D and 2D structure types, respectively.PostprintPeer reviewe

Structural diversity of lead halide chain compounds, APbX3, templated by isomeric molecular cations

We acknowledge support from the University of St Andrews, the China Scholarship Council (studentship to YYG).Three new 1D chain structure type hybrid organic–inorganic lead(II) halides are presented: IQPbBr3, QPbBr3 and QPbI3, templated by large organic cations, isoquinolinium ([IQ+] = protonated isoquinoline) and its isomer quinolonium ([Q+] = protonated quinoline). All three compounds possess the same generic formula as cubic perovskite, ABX3, but adopt different structures. IQPbBr3 adopts a 1D face-sharing single chain hexagonal perovskite structure type, and the other two, QPbBr3 and QPbI3, adopt a non-perovskite structure which is built from 1D edge-sharing octahedral double chains. Crystal structures and preliminary photophysical properties are discussed. Two of them have lower bandgaps than the other reported materials with the same structure type, indicating the value of further exploratory studies for these types of materials.PostprintPostprintPeer reviewe

Complex octahedral tilt phases in the ferroelectric perovskite system LixNa1–xNbO3

We thank STFC for provision of neutron diffraction facilities at ISIS and Dr Aziz Daoud-Aladine for experimental assistance. CALD was supported by an EPSRC DTA studentship (EP/L50579/1).High-temperature phase behavior in the system LixNa1−xNbO3 has been studied by using high-resolution neutron powder diffraction. Each of the three compositions studied in the Na-rich part of the phase diagram (viz., x=0.03,0.08, and 0.12) shows evidence for distinct and complex structural modulations based on different tilting schemes of NbO6 octahedral units. Whilst octahedral tilting is prevalent in the structural chemistry of perovskites the details of the long-range tilt phases are distinct from those previously observed in NaNbO3 itself. A phase with a well-defined fourfold superlattice is observed for the composition Li0.12Na0.88NbO3, and yet more complex phases with modulations based on 20-fold and 30-fold repeats are observed for Li0.03Na0.97NbO3 and Li0.08Na0.92NbO3, respectively. This peculiar structural frustration makes the system LixNa1−xNbO3 a most structurally complex “simple” perovskite.PostprintPostprintPeer reviewe

Variable dimensionality in 'hollow' hybrid tin iodide perovskites

We acknowledge support from the University of St Andrews and the Leverhulme trust (RPG-2018-065).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.Publisher PDFPeer reviewe

Extending the family of hybrid layered fluoride perovskites

We acknowledge support from the University of St Andrews, the China Scholarship Council (201606280032, PhD studentship to TL), and the China Postdoctoral Science Foundation (2022M710619).The family of hybrid layered fluoride perovskites has been extended, based on the only previously reported example (enH2)MnF4 (en = 1,2-diaminoethane), to include further divalent transition metals and longer chain diamines. The compounds (enH2)BF4, (B = Co, Ni) and (bnH2)BF4, (bn = 1,4-diaminobutane, B = Mn, Co) adopt the same space group (P21/c) as (enH2)MnF4, whereas (pnH2)BF4, (pn = 1,3-diaminopropane, B = Mn, Co) adopt the space group Pnma. Key differences in these structure types are shown to depend on the parity of the number of carbon atoms in the linear amine, which may be considered a structure-directing agent. Magnetic measurements on selected samples indicate differences in magnetic order that can be understood in terms of both the transition metal and the molecular species. All samples exhibit antiferromagnetic correlations but can in some cases develop a canted spin ferromagnetic component due to anisotropic exchange interactions. An additional compound, (bn)Ni2F4, has also been isolated, which exhibits a unique layered structure with bn acting as a ligand rather than in cationic formPeer reviewe

New sarcosine-metal halide complexes related to the ferroelectric TSCC

The authors thank the EPSRC for provision of a doctoral studentship to RC (DTG012 EP/K503162-1).There are relatively few sarcosine metal halide complexes. Of these, tris sarcosine calcium chloride (TSCC) ((C3NO2H7)3CaCl2) stands out as an unusual example of a molecular ferroelectric. Here we report the syntheses of eight new related sarcosine-metal halide complexes by slow evaporation. The newly reported materials can be categorised into four different structure types, viz. 3:1 complexes such as (C3NO2H7)3CaBr2, hydrated 3:1 complexes such as (C3NO2H7)3MnI2.2H2O, hydrated 2:1 complexes such as (C3NO2H7)2MgCl2.2H2O, and a 4:1 complex (C3NO2H7)4CaI2.2H2O. The crystal structures of all examples have been determined at multiple temperatures but no evidence is found for any structural transitions to polar phases, either by single crystal X-ray diffraction or by differential scanning calorimetry. The specific compositional reasons behind the apparently unique ferroelectric behaviour of TSCC therefore remain to be ascertained.PostprintPeer reviewe

Structural and dielectric studies of the phase behaviour of the topological ferroelectric La1-xNdxTaO4

We thank the University of St Andrews and EPSRC (via DTG studentships to CALD and JG) for funding,The layered perovskite LaTaO4 has been prepared in its polar orthorhombic polymorphic form at ambient temperature. Although no structural phase transition is observed in the temperature interval 25° C < T < 500 °C, a very large axial thermal contraction effect is seen, which can be ascribed to an anomalous buckling of the perovskite octahedral layer. The non-polar monoclinic polymorph can be stabilised at ambient temperature by Nd-doping. A composition La0.90Nd0.10TaO4 shows a first-order monoclinic-orthorhombic (non-polar to polar) transition in the region 250° C < T < 350 °C. Dielectric responses are observed at both the above structural events but, despite the ‘topological ferroelectric’ nature of orthorhombic LaTaO4, we have not succeeded in obtaining ferroelectric P–E hysteresis behaviour. Structural relationships in the wider family of AnBnX3n+2 layered perovskites are discussed.Publisher PDFPeer reviewe

Perovzalates : a family of perovskite-related oxalates

Authors would like to thank the University of St Andrews (studentship to AJB) and the EPSRC (doctoral studentship to RC: DTG012 EP/K503162-1) for funding.A family of hybrid Perovskite-oxalates (“Perovzalates”) of general composition AILi3MII(C2O4)3 (A = K+, Rb+, Cs+; M = Fe2+, Co2+, Ni2+) are presented. All eight new compounds are isostructural with the previously reported examples NH4Li3Fe(C2O4)3 and KLi3Fe(C2O4)3, crystallising in the rhombohedral space group Rc, with a ∼11.3–11.6 Å, c ∼14.8–15.2 Å. In contrast to other families of “hybrid perovskites” such as the formates, these compounds can be regarded as closer structural relatives to inorganic (oxide) perovskites, in the sense that they contain direct linkages of the octahedral sites via bridging oxygen atoms (of the oxalate groups). It is of note, therefore, that monoatomic cations as large as Cs+ can be incorporated into the perovskite-like A sites of this structure type, which is not feasible in traditional ABO3 perovskites; indeed CsLi3Ni(C2O4)3 appears to exhibit the ‘mostly tightly bound’ 12-coordinate Cs+ ion in an oxide environment, according to a bond valence analysis.PostprintPeer reviewe