Tetrel Bonds in Infinite Molecular Chains by Electronic Structure Theory and Their Role for Crystal Stabilization

Intermolecular bonds play a crucial role in the rational design of crystal structures, dubbed crystal engineering. The relatively new term tetrel bonds (TBs) describes a long-known type of such interactions presently in the focus of quantum chemical cluster calculations. Here, we energetically explore the strengths and cooperativity of these interactions in infinite chains, a possible arrangement of such tetrel bonds in extended crystals, by periodic density functional theory. In the chains, the TBs are amplified due to cooperativity by up to 60%. Moreover, we computationally take apart crystals stabilized by infinite tetrel-bonded chains and assess the importance of the TBs for the crystal stabilization. Tetrel bonds can amount to 70% of the overall interaction energy within some crystals, and they can also be energetically decisive for the taken crystal structure; their individual strengths also compete with the collective packing within the crystal structures

Dimensionality of Intermolecular Interactions in Layered Crystals by Electronic-Structure Theory and Geometric Analysis

Two-dimensional (2D) and layered structures gained a lot of attention in the recent years (“post-graphene era”). The chalcogen cyanides S­(CN)₂ and Se­(CN)₂ offer themselves as interesting model systems to study layered inorganic crystal structures; both are built up from cyanide molecules connected by chalcogen bonds (ChBs). Here, we investigate ChBs and their cooperativity directly <i>within</i> the layers of the S­(CN)₂ and Se­(CN)₂ crystal structures and, furthermore, in putative O­(CN)₂ and Te­(CN)₂ crystal structures derived therefrom. Moreover, we determine the energetic contributions of ChBs <i>within</i> the layers to the overall stabilization energy. To compare these structures not only energetically but also geometrically, we derive a direction-dependent root mean square of the Cartesian displacement, a possible tool for further computational investigations of layered compounds. The molecular chains connected by ChBs are highly cooperative but do <i>not</i> influence each other when combined to layers: the ChBs are nearly orthogonal in terms of energy when connected to the same chalcogen acceptor atom. Layers built up from ChBs account for 41% to 79% of the overall interaction energy in the crystal. This provides new, fundamental insight into the meaning of ChBs, and therefore directed intermolecular interactions, for the stability of crystal structures

Cooperativity of Halogen, Chalcogen, and Pnictogen Bonds in Infinite Molecular Chains by Electronic Structure Theory

Halogen bonds (XBs) are intriguing noncovalent interactions that are frequently being exploited for crystal engineering. Recently, similar bonding mechanisms have been proposed for adjacent main-group elements, and noncovalent “chalcogen bonds” and “pnictogen bonds” have been identified in crystal structures. A fundamental question, largely unresolved thus far, is how XBs and related contacts interact with each other in crystals; similar to hydrogen bonding, one might expect “cooperativity” (bonds amplifying each other), but evidence has been sparse. Here, we explore the crucial step from gas-phase oligomers to truly infinite chains by means of quantum chemical computations. A periodic density functional theory (DFT) framework allows us to address polymeric chains of molecules avoiding the dreaded “cluster effects” as well as the arbitrariness of defining a “large enough” cluster. We focus on three types of molecular chains that we cut from crystal structures; furthermore, we explore reasonable substitutional variants in silico. We find evidence of cooperativity in chains of halogen cyanides and also in similar chalcogen- and pnictogen-bonded systems; the bonds, in the most extreme cases, are amplified through cooperative effects by 79% (I···N), 90% (Te···N), and 103% (Sb···N). Two experimentally known organic crystals, albeit with similar atomic connectivity and XB characteristics, show signs of cooperativity in one case but not in another. Finally, no cooperativity is observed in alternating halogen/acetone and halogen/1,4-dioxane chains; in fact, these XBs <i>weaken</i> each other by up to 26% compared to the respective gas-phase dimers

Cooperativity of Halogen, Chalcogen, and Pnictogen Bonds in Infinite Molecular Chains by Electronic Structure Theory

Halogen bonds (XBs) are intriguing noncovalent interactions that are frequently being exploited for crystal engineering. Recently, similar bonding mechanisms have been proposed for adjacent main-group elements, and noncovalent “chalcogen bonds” and “pnictogen bonds” have been identified in crystal structures. A fundamental question, largely unresolved thus far, is how XBs and related contacts interact with each other in crystals; similar to hydrogen bonding, one might expect “cooperativity” (bonds amplifying each other), but evidence has been sparse. Here, we explore the crucial step from gas-phase oligomers to truly infinite chains by means of quantum chemical computations. A periodic density functional theory (DFT) framework allows us to address polymeric chains of molecules avoiding the dreaded “cluster effects” as well as the arbitrariness of defining a “large enough” cluster. We focus on three types of molecular chains that we cut from crystal structures; furthermore, we explore reasonable substitutional variants in silico. We find evidence of cooperativity in chains of halogen cyanides and also in similar chalcogen- and pnictogen-bonded systems; the bonds, in the most extreme cases, are amplified through cooperative effects by 79% (I···N), 90% (Te···N), and 103% (Sb···N). Two experimentally known organic crystals, albeit with similar atomic connectivity and XB characteristics, show signs of cooperativity in one case but not in another. Finally, no cooperativity is observed in alternating halogen/acetone and halogen/1,4-dioxane chains; in fact, these XBs <i>weaken</i> each other by up to 26% compared to the respective gas-phase dimers

Significant Lanthanoid Substitution Effect on the Redox Reactivity of the Oxygen-Storage Material BaYMn₂O_5+δ

The redox characteristics of oxygen storage materials BaLnMn₂O_5+δ, with Ln = La, Nd, Gd, and Y, were investigated employing the reductive water dissolution by the deoxygenated δ = 0 form. The Ln = La, Nd, and Gd compounds were found to show a capability to produce hydrogen gas through the water dissolution at 500 °C, whereas the Ln = Y compound was unreactive to water. It was also revealed that the reactivity obviously depends upon the Ln species: the larger the ionic size of Ln³⁺, the higher reactivity the BaLnMn₂O_5.0 samples exhibit. The experimentally derived thermodynamic parameters of the BaLnMn₂O_5+δ series were compared to those obtained by first-principles calculations

Ammonothermal Synthesis, Crystal Structure, and Properties of the Ytterbium(II) and Ytterbium(III) Amides and the First Two Rare-Earth-Metal Guanidinates, YbC(NH)₃ and Yb(CN₃H₄)₃

We report the oxidation-controlled synthesis of the ytterbium amides Yb­(NH₂)₂ and Yb­(NH₂)₃ and the first rare-earth-metal guanidinates YbC­(NH)₃ and Yb­(CN₃H₄)₃ from liquid ammonia. For Yb­(NH₂)₂, we present experimental atomic displacement parameters from powder X-ray diffraction (PXRD) and density functional theory (DFT)-derived hydrogen positions for the first time. For Yb­(NH₂)₃, the indexing proposal based on PXRD arrives at <i>R</i>3̅, <i>a</i> = 6.2477(2) Å, <i>c</i> = 17.132(1) Å, <i>V</i> = 579.15(4) ų, and <i>Z</i> = 6. The oxidation-controlled synthesis was also applied to make the first rare-earth guanidinates, namely, the doubly deprotonated YbC­(NH)₃ and the singly deprotonated Yb­(CN₃H₄)₃. YbC­(NH)₃ is isostructural with SrC­(NH)₃, as derived from PXRD (<i>P</i>6₃/<i>m</i>, <i>a</i> = 5.2596(2) Å, <i>c</i> = 6.6704(2) Å, <i>V</i> = 159.81(1) ų, and <i>Z</i> = 2). Yb­(CN₃H₄)₃ crystallizes in a structure derived from the [ReO₃] type, as studied by powder neutron diffraction (<i>Pn</i>3̅, <i>a</i> = 13.5307(3) Å, <i>V</i> = 2477.22(8) ų, and <i>Z</i> = 8 at 10 K). Electrostatic and hydrogen-bonding interactions cooperate to stabilize the structure with wide and empty channels. The IR spectra of the guanidinates are compared with DFT-calculated phonon spectra to identify the vibrational modes. SQUID magnetometry shows that Yb­(CN₃H₄)₃ is a paramagnet with isolated Yb³⁺ (4f¹³) ions. A <i>CONDON 2.0</i> fit was used to extract all relevant parameters