Low-dimensional metal halides have been the focus of intense investigations in recent years following the success of hybrid lead halide perovskites as optoelectronic materials. In particular, the light emission of low-dimensional halides based on the 5s2 cations Sn2+ and Sb3+ has found utility in a variety of applications complementary to those of the three-dimensional halide perovskites because of its unusual properties such as broadband character and highly temperature-dependent lifetime. These properties derive from the exceptional chemistry of the 5s2 lone pair, but the terminology and explanations given for such emission vary widely, hampering efforts to build a cohesive understanding of these materials that would lead to the development of efficient optoelectronic devices. In this Perspective, we provide a structural overview of these materials with a focus on the dynamics driven by the stereoactivity of the 5s2 lone pair to identify the structural features that enable strong emission. We unite the different theoretical models that have been able to explain the success of these bright 5s2 emission centers into a cohesive framework, which is then applied to the array of compounds recently developed by our group and other researchers, demonstrating its utility and generating a holistic picture of the field from the point of view of a materials chemist. We highlight those state-of-the-art materials and applications that demonstrate the unique capabilities of these versatile emissive centers and identify promising future directions in the field of low-dimensional 5s2 metal halides.

Efficient Lone-Pair-Driven Luminescence: Structure-Property Relationships in Emissive 5s2 Metal Halides.

Molecular interaction between mercury and selenium in neurotoxicity

Solid-state-lighting (SSL) technologies are gradually replacing conventional lighting sources due to their advantages in energy efficiency and reduced environmental impact. As such, developing high-performance luminescent materials to be used in SSL devices for lighting related applications has become a very hot topic in the past decade. These luminescent materials can be designed as either phosphors or emissive layers for light-emitting diodes (LEDs) or organic light-emitting diodes (OLEDs). This article provides a brief overview on the recent research and development of a variety of luminescent inorganic-organic hybrid semiconductor material classes. The structural characteristics and luminescent properties of representative examples of each material family will be discussed and summarized.

Luminescent inorganic-organic hybrid semiconductor materials for energy-saving lighting applications

Weak interionic interactions in 2-bromoimidazolium derivatives

The 3 centre-4 electrons (3c-4e) and the donor/acceptor or charge-transfer models for the description of the chemical bond in linear three-body systems, such as I3– and related electron-rich (22 shell electrons) systems, are comparatively discussed on the grounds of structural data from a search of the Cambridge Structural Database (CSD). Both models account for a total bond order of 1 in these systems, and while the former fits better symmetric systems, the latter describes better strongly asymmetric situations. The 3c-4e MO scheme shows that any linear system formed by three aligned closed-shell species (24 shell electrons overall) has reason to exist provided that two electrons are removed from it to afford a 22 shell electrons three-body system: all combinations of three closed-shell halides and/or chalcogenides are considered here. A survey of the literature shows that most of these three-body systems exist. With some exceptions, their structural features vary continuously from the symmetric situation showing two equal bonds to very asymmetric situations in which one bond approaches to the value corresponding to a single bond and the second one to the sum of the van der Waals radii of the involved atoms. This indicates that the potential energy surface of these three-body systems is fairly flat, and that the chemical surrounding of the chalcogen/halogen atoms can play an important role in freezing different structural situations; this is well documented for the I3– anion. The existence of correlations between the two bond distances and more importantly the linearity observed for all these systems, independently on the degree of their asymmetry, support the state of hypervalency of the central atom.

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The nature of the chemical bond in linear three-body systems: from i3- to mixed chalcogen/halogen and trichalcogen moieties.

[H3O · (Dibenzo-18-crown-6)][Te2Br9] and [H5O2][Te2Cl9] · 2 C4H8O2: Two New Oxonium Halotellurates(IV) Containing a Novel Type of [Te2X9]– Anions

Tiefrote Kristalle der Zusammensetzung [H3O][TeBr5] · 3 C4H8O2 (1) wurden aus einer gesattigten Losung von TeBr4 in wasserhaltigem 1,4-Dioxan dargestellt. In der Verbindung (Raumgruppe P21/m, a = 8.922(4) A, b = 13.204(7) A, c = 9.853(5) A, β = 91.82(4)° bei 150 K) konnte erstmals ein quadratisch-pyramidales [TeBr5]− -Anion isoliert werden. Dessen Koordinationspolyeder wird durch eine schwache Wechselwirkung mit einem 1,4-Dioxan-Molekul zu einem verzerrten Oktaeder vervollstandigt. Die [H3O]+-Kationen sind durch 1,4-Dioxan-Molekule zu Ketten verknupft. Die Saure ist bei Raumtemperatur nur in ihrer Mutterlauge stabil. [H3O]2[SeBr6] (2) (Raumgruppe Fm3m, a = 10.421(1) A bei 170 K) ist eine hochsymmetrisch kristallisierende Bromoselen(IV)-saure, mit der es gelang, ein nur sehr schwach durch Br-Atome des Anions koordiniertes [H3O]+-Ion zu isolieren. Die anionische Einheit besteht aus freien, unverzerrt oktaedrischen [SeBr6]2−-Ionen. Die Kristallstruktur ist isotyp zu K2[PtCl6]. Die Verbindung zeigt eine fur Halogenochalkogen(IV)-sauren bemerkenswerte thermische Stabilitat. Beide Oxoniumsalze wurden durch vollstandige Rontgenstrukturanalysen charakterisiert. Uber schwingungsspektroskopische Untersuchungen an 2 wird berichtet.



New Oxonium Bromochalcogenates(IV) — Synthesis, Structure, and Properties of [H3O][TeBr5] · 3 C4H8O2 and [H3O]2[SeBr6]



Dark red crystals of the composition [H3O][TeBr5] · 3 C4H8O2 (1) were isolated from a saturated solution of TeBr4 in 1,4-dioxane containing a small amount of water. In this compound (space group P21/m, a = 8.922(4) A, b = 13.204(7) A, c = 9.853(5) A, β = 91.82(4)° at 150 K) a square pyramidal [TeBr5]− anion has been isolated for the first time. The coordination sphere of the anion is completed to a distorted octahedron by weak interaction with a dioxane molecule of the cationic system. The [H3O]+ cations are connected to chains by dioxane molecules. At room temperature the compound is stable only in its mother liquor. Crystalline [H3O]2[SeBr6] (2) (space group Fm3m, a = 10.421(1) A at 170 K) is a bromoselenous acid of high symmetry. The [H3O]+ ion is only weakly coordinated by Br atoms of the anion. The anions are isolated octahedral [SeBr6]2− units. The structure is isotypic to the K2[PtCl6] structure. Despite being a halogenochalcogen(IV) acid, 2 exhibits a remarkable thermal stability. Both oxonium compounds were characterized by single-crystal X-ray structure analyses. Vibrational spectra of 2 are reported.

Neue Oxonium‐Bromochalkogenate(IV) — Darstellung, Struktur und Eigenschaften von [H3O][TeBr5] · 3C4H8O2 und [H3O]2[SeBr6]

Aus einer gesattigten Losung von SeCl4 in 98% igem Ethanol konnten durch Zugabe von Morpholin blasgelbe Kristalle der Verbindung [C4H10NO]2[SeOCl4] (1) gewonnen werden (Raumgruppe Pnma, a = 7.731(5) A, b = 21.053(16) A, c = 9.725(8) A bei 150 K). In 1 liegt ein Teilhydrolyseprodukt der Chloroselenate(IV), das quadratisch pyramidale [SeOCl4]2−-Anion, als Morpholiniumsulzvor. Die Anionen sind uber schwache Se… Cl-Wechselwirkungen zu Ketten verknupft. Die Morpholinium-Kationen bilden Wasserstoffbruckenbindungen zu Cl-Atomen der Anionen aus.



[C4H10NO]2[Se2Br10] (2) kann aus einer gesattigten Losung von SeBr4 in 47% iger wasriger Bromwasserstoffsaure durch Zugabe von Morpholin in Form roter Kristalle erhalten werden (Raumgruppe P21/c, a = 8.357(2) A, b = 17.656(6) A, c = 8.495(2) A, β = 95.49(2)° bei 150 K). Die [Se2Br10]2 -Anionen bestehen aus zwei kantenverknupften verzerrten SeBr6-Oktaedern. Intermolekulare Anion-Anion-Wechselwirkungen verknupfen die Anionen zu einem zweidimensionalen Netzwerk.



[(CH3)2CHC(NH2)(OH)][Te3Cl13] · (CH3)2CHCN (3) wurde aus einer Losung von TeCl4 in iso-Butyronitril/konz. HCl dargestellt (Raumgruppe P1, a = 8.718(2) A, b = 11.030(2) A, c = 15.756(4) A, α = 84.49(2)°, β = 79.24(2)°, γ = 86.10(2)° bei 170 K). Die [Te3Cl13]−-Anionen bestehen aus drei cis-kanten-verknupften verzerrten Oktaedern und sind uber Cl … Cl Wechselwirkungen zu einem zweidimensionalen Netzwerk verknupft. Als Kationen treten protonierte Isobuttersaure-amid-Molekule auf. 1, 2 und 3 wurden durch vollstandige Rontgenstrukturanalysen charakterisiert. Uber Raman-spektroskopische Untersuchungen an 1 und 2 wird berichtet.



Stabilization of Oxohalogeno and Halogenochalcogenates(IV) by Proton Acceptors - Synthesis, Structures and Properties of [C4H10NO]2[SeOCl4], [C4H10NO]2[Se2Br10] and [(CH3)2CHC(NH2)(OH)][Te3Cl13] · (CH3)2CHCN



Pale yellow crystals of the compound [C4H10NO]2[SeOCl4] (1) were isolated by adding morpholine to a saturated solution of SeCl4 in 98% ethanol (space group Pnma, a = 7.731(5) A, b = 21.053(16) A, c = 9.725(8) A at 150 K). The square pyramidal [SeOCl4]2 anion in this morpholinium salt is a partial hydrolysis product of chloroselenates(IV). The anions are connected to chains by weak Se … Cl interactions. The morpholinium cations form hydrogen bonds to Cl atoms of the anions.



The red compound [C4H10NO]2[Se2Br10] (2) was synthesised by adding morpholine to a saturated solution of SeBr4 in 47% hydrobromic acid (space group P21/c, a = 8.357(2) A, b = 17.656(6) A, c = 8.495(2) A, β = 95.49(2)° at 150 K). The [Se2Br10]2− anions consist of two edge sharing distorted octahedra. Intermolecular interactions connect the anions to a two-dimensional network.



[(CH3)2CHC(NH2)(OH)][Te3Cl13]·(CH3)2CHCN (3) was isolated from a solution of TeCl4 in iso-butyronitrile/conc. HCl (space group P1, a = 8.718(2) A, b = 11.030(2) A, c = 15.756(4) A, α = 84.49(2)°, β = 79.24(2)°, γ = 86.10(2)° at 170 K). The [Te3Cl13]− anions consist of three distorted cis-edge sharing octahedra. A two-dimensional anionic network is formed by Cl…Cl interactions. The cation is a protonated iso-butyric amide. 1, 2 and 3 were characterized by single-crystal X-ray structure analyses. Raman spectra of 1 and 2 are reported.

Stabilisierung von Oxohalogeno‐ und Halogenochalkogen(IV)‐Säuren durch Protonenakzeptoren – Darstellung, Struktur und Eigenschaften von [C4H10NO]2[SeOCl4], [C4H10NO]2[Se2Br10] und [(CH3)2CHC(NH2)(OH)][Te3Cl13] · (CH3)2CHCN

New Oxonium Bromochalcogenates(IV) ‐ Synthesis, Structure, and Properties of (H3O)(TeBr5)×3 C4H8O2 and (H3O)2(SeBr6).

Stabilization of Oxohalogeno and Halogenochalcogenates(IV) by Proton Acceptors ‐ Synthesis, Structures, and Properties of (C4H10NO)2(SeOCl4) , (C4H10NO)2(Se2Br10) and ((CH3)2CHC(NH2)(OH))(Te3Cl13)×(CH3) 2CHCN.

S. Hasche

Papers

[H3O · (Dibenzo-18-crown-6)][Te2Br9] and [H5O2][Te2Cl9] · 2 C4H8O2: Two New Oxonium Halotellurates(IV) Containing a Novel Type of [Te2X9]– Anions

Neue Oxonium‐Bromochalkogenate(IV) — Darstellung, Struktur und Eigenschaften von [H3O][TeBr5] · 3C4H8O2 und [H3O]2[SeBr6]

Stabilisierung von Oxohalogeno‐ und Halogenochalkogen(IV)‐Säuren durch Protonenakzeptoren – Darstellung, Struktur und Eigenschaften von [C4H10NO]2[SeOCl4], [C4H10NO]2[Se2Br10] und [(CH3)2CHC(NH2)(OH)][Te3Cl13] · (CH3)2CHCN

New Oxonium Bromochalcogenates(IV) ‐ Synthesis, Structure, and Properties of (H3O)(TeBr5)×3 C4H8O2 and (H3O)2(SeBr6).

Stabilization of Oxohalogeno and Halogenochalcogenates(IV) by Proton Acceptors ‐ Synthesis, Structures, and Properties of (C4H10NO)2(SeOCl4) , (C4H10NO)2(Se2Br10) and ((CH3)2CHC(NH2)(OH))(Te3Cl13)×(CH3) 2CHCN.