A Three-Dimensional M3 AB-Type Hybrid Organic-Inorganic Antiperovskite Ferroelectric: [C3 H7 FN]3 [SnCl6 ]Cl

Since the first perovskite CaTiO₃ was discovered in 1839, the development of perovskite has a history of 180 years. The emergence of solar cells (CH₃ NH₃ )PbI₃ has set off the trend of hybrid organic-inorganic perovskite (HOIP) materials. Since then, various HOIPs have sprung up and been widely used in various material devices. Among them, HOIP ferroelectrics have gained widespread attention. However, antiperovskite, as a twin brother of perovskite, has been neglected although it has similar structure with perovskite. Here, we successfully found that [C₃ H₇ FN]₃ [SnCl₆ ]Cl has a three-dimensional (3D) antiperovskite structure with the formula M₃ AB. Importantly, the compound exhibits obvious ferroelectric properties with an Aizu notation of 622F6 at 391 K. To the best of our knowledge, this is the first 3D hybrid organic-inorganic antiperovskite ferroelectric, which will greatly promote the development of antiperovskite families with more superior physical properties.

Hybrid Organic-Inorganic Antiperovskites

Substitution of A-site and/or X-site ions of ABX₃ -type perovskites with organic groups can give rise to hybrid perovskites, many of which display intriguing properties beyond their parent compounds. However, this method cannot be extended effectively to hybrid antiperovskites. Now, the design of hybrid antiperovskites under the guidance of the concept of Goldschmidt's tolerance factor is presented. Spherical anions were chosen for the A and B sites and spherical organic cations for the X site, and seven hybrid antiperovskites were obtained, including (F₃ (H₂ O)_x )(AlF₆ )(H₂ dabco)₃ , ((Co(CN)₆ )(H₂ O)₅ )(MF₆ )(H₂ dabco)₃ (M=Al³⁺ , Cr³⁺ , or In³⁺ ), (Co(CN)₆ )(MF₆ )(H₂ pip)₃ (M=Al³⁺ or Cr³⁺ ), and (SbI₆ )(AlF₆ )(H₂ dabco)₃ . These new structures reveal that all ions at A, B, and X sites of inorganic antiperovskites can be replaced by molecular ions to form hybrid antiperovskites. This work will lead to the synthesis of a large family of hybrid antiperovskites.

Mix and Match: Organic and Inorganic Ions in the Perovskite Lattice

Materials science evolves to a state where the composition and structure of a crystal can be controlled almost at will. Given that a composition meets basic requirements of stoichiometry, steric demands, and charge neutrality, researchers are now able to investigate a wide range of compounds theoretically and, under various experimental conditions, select the constituting fragments of a crystal. One intriguing playground for such materials design is the perovskite structure. While a game of mixing and matching ions has been played successfully for about 150 years within the limits of inorganic compounds, the recent advances in organic-inorganic hybrid perovskite photovoltaics have triggered the inclusion of organic ions. Organic ions can be incorporated on all sites of the perovskite structure, leading to hybrid (double, triple, etc.) perovskites and inverse (hybrid) perovskites. Examples for each of these cases are known, even with all three sites occupied by organic molecules. While this change from monatomic ions to molecular species is accompanied with increased complexity, it shows that concepts from traditional inorganic perovskites are transferable to the novel hybrid materials. The increased compositional space holds promising new possibilities and applications for the universe of perovskite materials.

Molecular Clusters: Nanoscale Building Blocks for Solid-State Materials

The programmed assembly of nanoscale building blocks into multicomponent hierarchical structures is a powerful strategy for the bottom-up construction of functional materials. To develop this concept, our team has explored the use of molecular clusters as superatomic building blocks to fabricate new classes of materials. The library of molecular clusters is rich with exciting properties, including diverse functionalization, redox activity, and magnetic ordering, so the resulting cluster-assembled solids, which we term superatomic crystals (SACs), hold the promise of high tunability, atomic precision, and robust architectures among a diverse range of other material properties. Molecular clusters have only seldom been used as precursors for functional materials. Our team has been at the forefront of new developments in this exciting research area, and this Account focuses on our progress toward designing materials from cluster-based precursors. In particular, this Account discusses (1) the design and synthesis of molecular cluster superatomic building blocks, (2) their self-assembly into SACs, and (3) their resulting collective properties. The set of molecular clusters discussed herein is diverse, with different cluster cores and ligand arrangements to create an impressive array of solids. The cluster cores include octahedral M₆E₈ and cubane M₄E₄ (M = metal; E = chalcogen), which are typically passivated by a shell of supporting ligands, a feature upon which we have expanded upon by designing and synthesizing more exotic ligands that can be used to direct solid-state assembly. Building from this library, we have designed whole families of binary SACs where the building blocks are held together through electrostatic, covalent, or van der Waals interactions. Using single-crystal X-ray diffraction (SCXRD) to determine the atomic structure, a remarkable range of compositional variability is accessible. We can also use this technique, in tandem with vibrational spectroscopy, to ascertain features about the constituent superatomic building blocks, such as the charge of the cluster cores, by analysis of bond distances from the SCXRD data. The combination of atomic precision and intercluster interactions in these SACs produces novel collective properties, including tunable electrical transport, crystalline thermal conductivity, and ferromagnetism. In addition, we have developed a synthetic strategy to insert redox-active guests into the superstructure of SACs via single-crystal-to-single-crystal intercalation. This intercalation process allows us to tune the optical and electrical transport properties of the superatomic crystal host. These properties are explored using a host of techniques, including Raman spectroscopy, SQUID magnetometry, electrical transport measurements, electronic absorption spectroscopy, differential scanning calorimetry, and frequency-domain thermoreflectance. Superatomic crystals have proven to be both robust and tunable, representing a new method of materials design and architecture. This Account demonstrates how precisely controlling the structure and properties of nanoscale building blocks is key in developing the next generation of functional materials; several examples are discussed and detailed herein.

Self-assembly of ambivalent organic/inorganic building blocks containing Re6 metal atom cluster: formation of a luminescent honeycomb, hollow, tubular metal-organic framework

Reactions in a sealed glass tube between melted pyrazine (pyz) and a Cs(3)Re(6)Q(i)(7)Br(i)Br(a)(6).H(2)O inorganic rhenium cluster compound (Q = S, Se; "i" for inner and "a" for apical positions) containing [Re(6)Q(i)(7)Br(i)Br(a)(6)](3-) units led to the substitution of three apical bromine ligands by three pyrazine groups with the formation of 3 CsBr as a byproduct. The resulting fac-Re(6)Q(i)(7)Br(i)(pyz)(a)(3)Br(a)(3) building unit, based on a Re(6) metal atom cluster, is neutral and noncentrosymmetric and exhibits an ambivalent organic/inorganic nature owing to the opposite disposition of the three apical pyrazine groups versus the three apical bromine atoms. These compounds were characterized by single-crystal and powder X-ray diffraction, elemental and thermal analyses, and luminescence measurements. The crystal structure of fac-Re(6)Q(i)(7)Br(i)(pyz)(a)(3)Br(a)(3).xH(2)O (Q = S (1) and Se (2)) displays an original, neutral metal-organic framework based on the self-assembling of fac-Re(6)Q(i)(7)Br(i)(pyz)(a)(3)Br(a)(3) hybrid building units. The latter are held together by supramolecular interactions: pi-pi, hydrogen bonds (C-H...N, C-H...Br(a), and C-H...Br(i)), and van der Waals contacts. It gives rise to a honeycomb porous structure of parallel hollow open-ended channels wherein the water molecules are located. Their removal does not lead to the collapsing of the structural edifice. The channel walls are constituted by hydrogen atoms from pyrazine as well as apical bromine from the cluster unit. To our knowledge, the structures of 1 and 2 constitute with that of PTMTC (perchlorotriphenylmethyl functionalized by carboxylic group radicals) one of the rare examples of stable open frameworks stabilized by supramolecular interactions between neutral molecules. Moreover, 1 is the first example of luminescent Re(6) compound built up from a noncentrosymmetric Re(6)S(i)(7)Br(i) cluster core.

Strong Magnetic Interactions through Weak Bonding Interactions in Organometallic Radicals: Combined Experimental and Theoretical Study

The magnetic properties of a series of three neutral radical organometallic complexes of general formula [CpNi(dithiolene)]. have been investigated by a combination of X-ray crystal structure analysis and magnetic susceptibility measurements, while the assignment of the exchange coupling constants to the possible exchange pathways has been accomplished with the help of calculations based on density functional theory (DFT). The syntheses and X-ray structures of [CpNi(adt)] (adt=acrylonitrile-2,3-dithiolate) and [CpNi(tfd)] (tfd=1,2-bis(trifluoromethyl)ethene-1,2-dithiolate) complexes are described, while [CpNi(mnt)] (mnt=maleonitriledithiolate) was reported earlier. In the three complexes, we observed strong antiferromagnetic coupling that could not be explained solely by short SS intermolecular contacts. Our calculations indicated that spin density in these complexes is strongly delocalized on the NiS2 moiety, with up to 20% on the Cp ring. As a consequence, CpCp and Cpdithiolene overlap interactions have been identified as responsible for antiferromagnetic couplings. The [CpNi(adt)] complex thus has a value J=-369.5 cm(-1) for an exchange interaction through a pi stacking due to the CpCp overlap.

Balancing framework densification with charged, halogen-bonded-π-conjugated linkages: [PPh4]2{[E-TTF–I2][Re6Se8(CN)6]} versus [PPh4]2[EDT-TTF–I]2{[EDT-TTF–I][Re6Se8(CN)6]}

The ionic character of a set of two redox linkages and strong, directional halogen bonding at the organic-inorganic interface compromise to produce two materials sharing a common two-dimensional net, eventually extended in a third dimension, although two of the six symmetrical halogen bond acceptors ultimately remain uninvolved as a result of charge densification.

New molecular perovskites: cubic C(4)N(2)H(12).NH(4)Cl(3).H(2)O and 2-H hexagonal C(6)N(2)H(14).NH(4)Cl(3)

The room-temperature syntheses and single-crystal structures of C(4)N(2)H(12).NH(4)Cl(3).H(2)O and C(6)N(2)H(14).NH(4)Cl(3) are reported. These novel molecular perovskites contain vertex-sharing octahedral (NH(4))Cl(6) arrays which replicate the octahedral packing in the cubic (SrTiO(3)) and 2-H hexagonal (BaNiO(3)) perovskite structures, respectively. The structures are completed by doubly protonated organic cations and, for the cubic phase, water molecules. Crystal data: C(4)N(2)H(12).NH(4)Cl(3).H(2)O, M(r) = 230.56, orthorhombic, Pbcm (No. 57), a = 6.5279(13) A, b = 12.935(3) A, c = 12.849(3) A, V = 1085.0(4) A(3), Z = 4; C(6)N(2)H(14).NH(4)Cl(3), M(r) = 238.59, trigonal, Pthremacr;c1 (No. 165), a = 16.1616(2) A, c = 22.3496(4) A, V = 5055.5(2) A(3), Z = 18.