Structural Diversity in Oxoiridates with 1D IrO Chain Fragments and Flat Bands.

A previously unreported series of hexagonal-perovskite-based Rb-oxoiridates, RbIrO, RbIrO, and RbIrO, have been synthesized and structurally analyzed via N-protected single-crystal X-ray diffraction (SC-XRD). These materials exhibit different 1D IrO chain fragments along their axes. IrO octahedra and RbO ( = 6, 8, and 10) polyhedra are their basic building blocks.

s-p Mixing in Stereochemically Active Lone Pairs Drives the Formation of 1D Chains of Lead Bromide Square Pyramids.

In lead(II) halide compounds including virtually all lead halide perovskites, the Pb 6s lone pair results in distorted octahedra, in accordance with the pseudo-Jahn-Teller effect, rather than generating hemihedral coordination polyhedra. Here, in contrast, we report the characterization of an organic-inorganic hybrid material consisting of one-dimensional edge-sharing chains of Pb-Br square pyramids, separated by [Mn(DMF)] (DMF = dimethylformamide) octahedra. Molecular orbital analysis and density-functional theory calculations indicate that square pyramidal coordination about Pb results from the occupancy of the empty ligand site by a Pb lone pair that has both s and p orbital character rather than the exclusively 6s lone pair.

Frustrated and Allowed Structural Transitions at the Limits of the BaAl Type: The (3 + 2)D Modulated Structure of Dy(CuGa).

While elemental substitution is the most common way of tuning properties in solid state compounds, this approach can break down in fantastic ways when the stability range of a structure type is exceeded. In this article, we apply the Frustrated and Allowed Structural Transitions (FAST) principle to understand how structural complexity, in this case incommensurate modulations, can emerge at the composition limits of one common intermetallic framework, the BaAl type. While the Dy-Ga binary intermetallic system contains no phases related to the BaAl archetype, adding Cu to form a ternary system creates a composition region that is rich in such phases, including some whose structures remain unknown.

Entropy-Driven Incommensurability: Chemical Pressure-Guided Polymorphism in PdBi and the Origins of Lock-In Phenomena in Modulated Systems.

Incommensurate order, in which two or more mismatched periodic patterns combine to make a long-range ordered yet aperiodic structure, is emerging as a general phenomenon impacting the crystal structures of compounds ranging from alloys and nominally simple salts to organic molecules and proteins. The origins of incommensurability in these systems are often unclear, but it is commonly associated with relatively weak interactions that become apparent only at low temperatures. In this article, we elucidate an incommensurate modulation in the intermetallic compound PdBi that arises from a different mechanism: the controlled increase of entropy at higher temperatures.

Frustrated and Allowed Structural Transitions: The Theory-Guided Discovery of the Modulated Structure of IrSi.

To the experienced molecular chemist, predicting the geometries and reactivities of a system is an exercise in balancing simple concepts such as sterics and electronics. In this Article, we illustrate how recent theoretical developments can give this combination of concepts a similar predictive power in intermetallic chemistry through the anticipation and discovery of structural complexity in the nominally MnP-type compound IrSi. Analysis of the bonding scheme and DFT-Chemical Pressure (CP) distribution of the reported MnP-type structure exposes issues pointing toward new structural behavior.

Paths to Stabilizing Electronically Aberrant Compounds: A Defect-Stabilized Polymorph and Constrained Atomic Motion in PtGa.

The structures and properties of intermetallic phases are intimately connected to electron count; unfavorable electron counts can result in structural rearrangements or new electrical or magnetic behavior when no such transformation is available. The compound PtGa appears to teeter on the border between these two scenarios with its two polymorphs: a cubic fluorite type form (c-PtGa) and a complex tetragonal superstructure (t-PtGa) whose Pt-Pt connectivity aligns with the 18- n electron counting rule. Here, we investigate the factors underlying this polymorphism.