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Article ; Online: The Tetrel Bond and Tetrel Halide Perovskite Semiconductors

Pradeep R. Varadwaj / Arpita Varadwaj / Helder M. Marques / Koichi Yamashita

International Journal of Molecular Sciences, Vol 24, Iss 6659, p

2023 Volume 6659

Abstract: The ion pairs [Cs + •TtX 3 − ] (Tt = Pb, Sn, Ge; X = I, Br, Cl) are the building blocks of all-inorganic cesium tetrel halide perovskites in 3D, CsTtX 3 , that are widely regarded as blockbuster materials for optoelectronic applications such as in solar ... ...

Abstract	The ion pairs [Cs + •TtX 3 − ] (Tt = Pb, Sn, Ge; X = I, Br, Cl) are the building blocks of all-inorganic cesium tetrel halide perovskites in 3D, CsTtX 3 , that are widely regarded as blockbuster materials for optoelectronic applications such as in solar cells. The 3D structures consist of an anionic inorganic tetrel halide framework stabilized by the cesium cations (Cs + ). We use computational methods to show that the geometrical connectivity between the inorganic monoanions, [TtX 3 − ] ∞ , that leads to the formation of the TtX 6 4− octahedra and the 3D inorganic perovskite architecture is the result of the joint effect of polarization and coulombic forces driven by alkali and tetrel bonds. Depending on the nature and temperature phase of these perovskite systems, the Tt···X tetrel bonds are either indistinguishable or somehow distinguishable from Tt–X coordinate bonds. The calculation of the potential on the electrostatic surface of the Tt atom in molecular [Cs + •TtX 3 − ] provides physical insight into why the negative anions [TtX 3 − ] attract each other when in close proximity, leading to the formation of the CsTtX 3 tetrel halide perovskites in the solid state. The inter-molecular (and inter-ionic) geometries, binding energies, and charge density-based topological properties of sixteen [Cs + •TtX 3 − ] ion pairs, as well as some selected oligomers [Cs + •PbI 3 − ] n ( n = 2, 3, 4), are discussed.
Keywords	tetrel halide perovskites ; DFT calculations ; MESP and QTAIM analyses ; geometries and energetics ; tetrel bond ; alkali bond ; Biology (General) ; QH301-705.5 ; Chemistry ; QD1-999
Subject code	333 ; 290
Language	English
Publishing date	2023-04-01T00:00:00Z
Publisher	MDPI AG
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: Methylammonium Tetrel Halide Perovskite Ion Pairs and Their Dimers

Pradeep R. Varadwaj / Arpita Varadwaj / Helder M. Marques / Koichi Yamashita

International Journal of Molecular Sciences, Vol 24, Iss 10554, p

The Interplay between the Hydrogen-, Pnictogen- and Tetrel-Bonding Interactions

2023 Volume 10554

Abstract: The structural stability of the extensively studied organic–inorganic hybrid methylammonium tetrel halide perovskite semiconductors, MATtX 3 (MA = CH 3 NH 3 + ... Tt = Ge, Sn, Pb; X = Cl, Br, I), arises as a result of non-covalent interactions between an ... ...

Abstract	The structural stability of the extensively studied organic–inorganic hybrid methylammonium tetrel halide perovskite semiconductors, MATtX 3 (MA = CH 3 NH 3 + Tt = Ge, Sn, Pb; X = Cl, Br, I), arises as a result of non-covalent interactions between an organic cation (CH 3 NH 3 + ) and an inorganic anion (TtX 3 − ). However, the basic understanding of the underlying chemical bonding interactions in these systems that link the ionic moieties together in complex configurations is still limited. In this study, ion pair models constituting the organic and inorganic ions were regarded as the repeating units of periodic crystal systems and density functional theory simulations were performed to elucidate the nature of the non-covalent interactions between them. It is demonstrated that not only the charge-assisted N–H···X and C–H···X hydrogen bonds but also the C–N···X pnictogen bonds interact to stabilize the ion pairs and to define their geometries in the gas phase. Similar interactions are also responsible for the formation of crystalline MATtX 3 in the low-temperature phase, some of which have been delineated in previous studies. In contrast, the Tt···X tetrel bonding interactions, which are hidden as coordinate bonds in the crystals, play a vital role in holding the inorganic anionic moieties (TtX 3 − ) together. We have demonstrated that each Tt in each [CH 3 NH 3 + •TtX 3 − ] ion pair has the capacity to donate three tetrel (σ-hole) bonds to the halides of three nearest neighbor TtX 3 − units, thus causing the emergence of an infinite array of 3D TtX 6 4− octahedra in the crystalline phase. The TtX 4 4− octahedra are corner-shared to form cage-like inorganic frameworks that host the organic cation, leading to the formation of functional tetrel halide perovskite materials that have outstanding optoelectronic properties in the solid state. We harnessed the results using the quantum theory of atoms in molecules, natural bond orbital, molecular electrostatic surface potential and independent gradient models to ...
Keywords	methylammonium tetrel halide perovskites ; ion pair chemistry ; resemblance between the gas and crystalline systems ; charge-assisted hydrogen bonds ; pnictogen bond ; tetrel bond ; Biology (General) ; QH301-705.5 ; Chemistry ; QD1-999
Subject code	290 ; 333
Language	English
Publishing date	2023-06-01T00:00:00Z
Publisher	MDPI AG
Document type	Article ; Online
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Article ; Online: Chalcogen Bonding in the Molecular Dimers of WCh 2 (Ch = S, Se, Te)

Pradeep R. Varadwaj / Arpita Varadwaj / Helder M. Marques / Koichi Yamashita

International Journal of Molecular Sciences, Vol 23, Iss 1263, p

On the Basic Understanding of the Local Interfacial and Interlayer Bonding Environment in 2D Layered Tungsten Dichalcogenides

2022 Volume 1263

Abstract: Layered two-dimensional transition metal dichalcogenides and their heterostructures are of current interest, owing to the diversity of their applications in many areas of materials nanoscience and technologies. With this in mind, we have examined the ... ...

Abstract	Layered two-dimensional transition metal dichalcogenides and their heterostructures are of current interest, owing to the diversity of their applications in many areas of materials nanoscience and technologies. With this in mind, we have examined the three molecular dimers of the tungsten dichalcogenide series, (WCh 2 ) 2 (Ch = S, Se, Te), using density functional theory to provide insight into which interactions, and their specific characteristics, are responsible for the interfacial/interlayer region in the room temperature 2H phase of WCh 2 crystals. Our calculations at various levels of theory suggested that the Te···Te chalcogen bonding in (WTe 2 ) 2 is weak, whereas the Se···Se and S···S bonding interactions in (WSe 2 ) 2 and (WS 2 ) 2 , respectively, are of the van der Waals type. The presence and character of Ch···Ch chalcogen bonding interactions in the dimers of (WCh 2 ) 2 are examined with a number of theoretical approaches and discussed, including charge-density-based approaches, such as the quantum theory of atoms in molecules, interaction region indicator, independent gradient model, and reduced density gradient non-covalent index approaches. The charge-density-based topological features are shown to be concordant with the results that originate from the extrema of potential on the electrostatic surfaces of WCh 2 monomers. A natural bond orbital analysis has enabled us to suggest a number of weak hyperconjugative charge transfer interactions between the interacting monomers that are responsible for the geometry of the (WCh 2 ) 2 dimers at equilibrium. In addition to other features, we demonstrate that there is no so-called van der Waals gap between the monolayers in two-dimensional layered transition metal tungsten dichalcogenides, which are gapless, and that the (WCh 2 ) 2 dimers may be prototypes for a basic understanding of the physical chemistry of the chemical bonding environments associated with the local interfacial/interlayer regions in layered 2H-WCh 2 nanoscale systems.
Keywords	tungsten dichalcogenide dimers ; chalcogen bonding ; energy stability ; natural orbital-based characterizations ; MESP- ; LOL- ; QTAIM- ; RDG- ; IGM- ; and IRI-based analyses ; Biology (General) ; QH301-705.5 ; Chemistry ; QD1-999
Subject code	290
Language	English
Publishing date	2022-01-01T00:00:00Z
Publisher	MDPI AG
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: The Stibium Bond or the Antimony-Centered Pnictogen Bond

Arpita Varadwaj / Pradeep R. Varadwaj / Helder M. Marques / Koichi Yamashita

International Journal of Molecular Sciences, Vol 23, Iss 4674, p

The Covalently Bound Antimony Atom in Molecular Entities in Crystal Lattices as a Pnictogen Bond Donor

2022 Volume 4674

Abstract: A stibium bond, i.e., a non-covalent interaction formed by covalently or coordinately bound antimony, occurs in chemical systems when there is evidence of a net attractive interaction between the electrophilic region associated with an antimony atom and ... ...

Abstract	A stibium bond, i.e., a non-covalent interaction formed by covalently or coordinately bound antimony, occurs in chemical systems when there is evidence of a net attractive interaction between the electrophilic region associated with an antimony atom and a nucleophile in another, or the same molecular entity. This is a pnictogen bond and are likely formed by the elements of the pnictogen family, Group 15, of the periodic table, and is an inter- or intra-molecular non-covalent interaction. This overview describes a set of illustrative crystal systems that were stabilized (at least partially) by means of stibium bonds, together with other non-covalent interactions (such as hydrogen bonds and halogen bonds), retrieved from either the Cambridge Structure Database (CSD) or the Inorganic Crystal Structure Database (ICSD). We demonstrate that these databases contain hundreds of crystal structures of various dimensions in which covalently or coordinately bound antimony atoms in molecular entities feature positive sites that productively interact with various Lewis bases containing O, N, F, Cl, Br, and I atoms in the same or different molecular entities, leading to the formation of stibium bonds, and hence, being partially responsible for the stability of the crystals. The geometric features, pro-molecular charge density isosurface topologies, and extrema of the molecular electrostatic potential model were collectively examined in some instances to illustrate the presence of Sb-centered pnictogen bonding in the representative crystal systems considered.
Keywords	pnictogen bonding ; antimony as pnictogen bond donor ; non-bonded geometry ; directionality ; crystal structure analysis ; ICSD and CSD database analyses ; Biology (General) ; QH301-705.5 ; Chemistry ; QD1-999
Subject code	540
Language	English
Publishing date	2022-04-01T00:00:00Z
Publisher	MDPI AG
Document type	Article ; Online
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Article ; Online: Chalcogen···Chalcogen Bonding in Molybdenum Disulfide, Molybdenum Diselenide and Molybdenum Ditelluride Dimers as Prototypes for a Basic Understanding of the Local Interfacial Chemical Bonding Environment in 2D Layered Transition Metal Dichalcogenides

Pradeep R. Varadwaj / Helder M. Marques / Arpita Varadwaj / Koichi Yamashita

Inorganics, Vol 10, Iss 11, p

2022 Volume 11

Abstract: An attempt was made, using computational methods, to understand whether the intermolecular interactions in the dimers of molybdenum dichalcogenides MoCh 2 (Ch = chalcogen, element of group 16, especially S, Se and Te) and similar mixed-chalcogenide ... ...

Abstract	An attempt was made, using computational methods, to understand whether the intermolecular interactions in the dimers of molybdenum dichalcogenides MoCh 2 (Ch = chalcogen, element of group 16, especially S, Se and Te) and similar mixed-chalcogenide derivatives resemble the room temperature experimentally observed interactions in the interfacial regions of molybdenites and their other mixed-chalcogen derivatives. To this end, MP2(Full)/def2-TVZPPD level electronic structure calculations on nine dimer systems, including (MoCh 2 ) 2 and (MoChCh′ 2 ) 2 (Ch, Ch′ = S, Se and Te), were carried out not only to demonstrate the energetic stability of these systems in the gas phase, but also to reproduce the intermolecular geometrical properties that resemble the interfacial geometries of 2D layered MoCh 2 systems reported in the crystalline phase. Among the six DFT functionals (single and double hybrids) benchmarked against MP2(full), it was found that the double hybrid functional B2PLYPD3 has some ability to reproduce the intermolecular geometries and binding energies. The intermolecular geometries and binding energies of all nine dimers are discussed, together with the charge density topological aspects of the chemical bonding interactions that emerge from the application of the quantum theory of atoms in molecules (QTAIM), the isosurface topology of the reduced density gradient noncovalent index, interaction region indicator and independent gradient model (IGM) approaches. While the electrostatic surface potential model fails to explain the origin of the S···S interaction in the (MoS 2 ) 2 dimer, we show that the intermolecular bonding interactions in all nine dimers examined are a result of hyperconjugative charge transfer delocalizations between the lone-pair on (Ch/Ch′) and/or the π-orbitals of a Mo–Ch/Ch′ bond of one monomer and the d π* anti-bonding orbitals of the same Mo–Ch/Ch′ bond in the second monomer during dimer formation, and vice versa. The HOMO–LUMO gaps calculated with the MN12-L functional were 0.9, ...
Keywords	transition metal dichalcogenides ; chalcogen-centered chalcogen bonding ; nature of non-covalent interactions ; first-principles studies ; geometry ; energy stability ; orbital and charge density analyses ; Inorganic chemistry ; QD146-197
Subject code	541
Language	English
Publishing date	2022-01-01T00:00:00Z
Publisher	MDPI AG
Document type	Article ; Online
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Article ; Online: The Phosphorus Bond, or the Phosphorus-Centered Pnictogen Bond

Pradeep R. Varadwaj / Arpita Varadwaj / Helder M. Marques / Koichi Yamashita

Molecules, Vol 27, Iss 1487, p

The Covalently Bound Phosphorus Atom in Molecular Entities and Crystals as a Pnictogen Bond Donor

2022 Volume 1487

Abstract: The phosphorus bond in chemical systems, which is an inter- or intramolecular noncovalent interaction, occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a covalently or coordinately bonded ... ...

Abstract	The phosphorus bond in chemical systems, which is an inter- or intramolecular noncovalent interaction, occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a covalently or coordinately bonded phosphorus atom in a molecular entity and a nucleophile in another, or the same, molecular entity. It is the second member of the family of pnictogen bonds, formed by the second member of the pnictogen family of the periodic table. In this overview, we provide the reader with a snapshot of the nature, and possible occurrences, of phosphorus-centered pnictogen bonding in illustrative chemical crystal systems drawn from the ICSD (Inorganic Crystal Structure Database) and CSD (Cambridge Structural Database) databases, some of which date back to the latter part of the last century. The illustrative systems discussed are expected to assist as a guide to researchers in rationalizing phosphorus-centered pnictogen bonding in the rational design of molecular complexes, crystals, and materials and their subsequent characterization.
Keywords	pnictogen bonding ; phosphorus as a pnictogen bond donor ; σ- and π-hole interactions ; bonding modes ; sum of the van der Waals radii concept ; geometry analysis ; Organic chemistry ; QD241-441
Subject code	540
Language	English
Publishing date	2022-02-01T00:00:00Z
Publisher	MDPI AG
Document type	Article ; Online
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Article ; Online: The Pnictogen Bond

Arpita Varadwaj / Pradeep R. Varadwaj / Helder M. Marques / Koichi Yamashita

Molecules, Vol 27, Iss 3421, p

The Covalently Bound Arsenic Atom in Molecular Entities in Crystals as a Pnictogen Bond Donor

2022 Volume 3421

Abstract: In chemical systems, the arsenic-centered pnictogen bond, or simply the arsenic bond, occurs when there is evidence of a net attractive interaction between the electrophilic region associated with a covalently or coordinately bound arsenic atom in a ... ...

Abstract	In chemical systems, the arsenic-centered pnictogen bond, or simply the arsenic bond, occurs when there is evidence of a net attractive interaction between the electrophilic region associated with a covalently or coordinately bound arsenic atom in a molecular entity and a nucleophile in another or the same molecular entity. It is the third member of the family of pnictogen bonds formed by the third atom of the pnictogen family, Group 15 of the periodic table, and is an inter- or intramolecular noncovalent interaction. In this overview, we present several illustrative crystal structures deposited into the Cambridge Structure Database (CSD) and the Inorganic Chemistry Structural Database (ICSD) during the last and current centuries to demonstrate that the arsenic atom in molecular entities has a significant ability to act as an electrophilic agent to make an attractive engagement with nucleophiles when in close vicinity, thereby forming σ-hole or π-hole interactions, and hence driving (in part, at least) the overall stability of the system’s crystalline phase. This overview does not include results from theoretical simulations reported by others as none of them address the signatory details of As-centered pnictogen bonds. Rather, we aimed at highlighting the interaction modes of arsenic-centered σ- and π-holes in the rationale design of crystal lattices to demonstrate that such interactions are abundant in crystalline materials, but care has to be taken to identify them as is usually done with the much more widely known noncovalent interactions in chemical systems, halogen bonding and hydrogen bonding. We also demonstrate that As-centered pnictogen bonds are usually accompanied by other primary and secondary interactions, which reinforce their occurrence and strength in most of the crystal structures illustrated. A statistical analysis of structures deposited into the CSD was performed for each interaction type As···D (D = N, O, S, Se, Te, F, Cl, Br, I, arene’s π system), thus providing insight into the typical ...
Keywords	pnictogen bonding ; arsenic as pnictogen bond donor ; inter- and intra-molecular geometry ; directionality ; crystal structure analysis ; ICSD and CSD database analyses ; Organic chemistry ; QD241-441
Subject code	540
Language	English
Publishing date	2022-05-01T00:00:00Z
Publisher	MDPI AG
Document type	Article ; Online
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Article ; Online: The Pnictogen Bond, Together with Other Non-Covalent Interactions, in the Rational Design of One-, Two- and Three-Dimensional Organic-Inorganic Hybrid Metal Halide Perovskite Semiconducting Materials, and Beyond

Arpita Varadwaj / Pradeep R. Varadwaj / Helder M. Marques / Koichi Yamashita

International Journal of Molecular Sciences, Vol 23, Iss 15, p

2022 Volume 8816

Abstract: The pnictogen bond, a somewhat overlooked supramolecular chemical synthon known since the middle of the last century, is one of the promising types of non-covalent interactions yet to be fully understood by recognizing and exploiting its properties for ... ...

Abstract	The pnictogen bond, a somewhat overlooked supramolecular chemical synthon known since the middle of the last century, is one of the promising types of non-covalent interactions yet to be fully understood by recognizing and exploiting its properties for the rational design of novel functional materials. Its bonding modes, energy profiles, vibrational structures and charge density topologies, among others, have yet to be comprehensively delineated, both theoretically and experimentally. In this overview, attention is largely centered on the nature of nitrogen-centered pnictogen bonds found in organic-inorganic hybrid metal halide perovskites and closely related structures deposited in the Cambridge Structural Database (CSD) and the Inorganic Chemistry Structural Database (ICSD). Focusing on well-characterized structures, it is shown that it is not merely charge-assisted hydrogen bonds that stabilize the inorganic frameworks, as widely assumed and well-documented, but simultaneously nitrogen-centered pnictogen bonding, and, depending on the atomic constituents of the organic cation, other non-covalent interactions such as halogen bonding and/or tetrel bonding, are also contributors to the stabilizing of a variety of materials in the solid state. We have shown that competition between pnictogen bonding and other interactions plays an important role in determining the tilting of the MX 6 (X = a halogen) octahedra of metal halide perovskites in one, two and three-dimensions. The pnictogen interactions are identified to be directional even in zero-dimensional crystals, a structural feature in many engineered ordered materials; hence an interplay between them and other non-covalent interactions drives the structure and the functional properties of perovskite materials and enabling their application in, for example, photovoltaics and optoelectronics. We have demonstrated that nitrogen in ammonium and its derivatives in many chemical systems acts as a pnictogen bond donor and contributes to conferring stability, and hence ...
Keywords	pnictogen bonding ; nitrogen as pnictogen bond donor ; intermolecular geometries and directionality ; inorganic-organic hybrid halide perovskites ; ICSD and CSD database analyses ; MESP characterizations ; Biology (General) ; QH301-705.5 ; Chemistry ; QD1-999
Subject code	540
Language	English
Publishing date	2022-08-01T00:00:00Z
Publisher	MDPI AG
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Article ; Online: C70 Fullerene Cage as a Novel Catalyst for Efficient Proton Transfer Reactions between Small Molecules

Pradeep R. Varadwaj / Arpita Varadwaj / Helder M. Marques

Scientific Reports, Vol 9, Iss 1, Pp 1-

A Theoretical study

2019 Volume 14

Abstract: Abstract When acids are supplied with an excess electron (or placed in an Ar or the more polarizable N2 matrix) in the presence of species such as NH3, the formation of ion-pairs is a likely outcome. Using density functional theory and first-principles ... ...

Abstract	Abstract When acids are supplied with an excess electron (or placed in an Ar or the more polarizable N2 matrix) in the presence of species such as NH3, the formation of ion-pairs is a likely outcome. Using density functional theory and first-principles calculations, however, we show that, without supplying an external electron or an electric field, or introducing photo-excitation and -ionization, a single molecule of HCl or HBr in the presence of a single molecule of water inside a C70 fullerene cage is susceptible to cleavage of the σ-bond of the Brønsted-Lowry acid into X− and H+ ions, with concomitant transfer of the proton along the reaction coordinate. This leads to the formation of an X−···+HOH2 (X = Cl, Br) conjugate acid-base ion-pair, similar to the structure in water of a Zundel ion. This process is unlikely to occur in other fullerene derivatives in the presence of H2O without significantly affecting the geometry of the carbon cage, suggesting that the interior of C70 is an ideal catalytic platform for proton transfer reactions and the design of related novel materials. By contrast, when a single molecule of HF is reacted with a single molecule of H2O inside the C70 cage, partial proton transfers from HF to H2O is an immediate consequence, as recently observed experimentally. The geometrical, energetic, electron density, orbital, optoelectronic and vibrational characteristics supporting these observations are presented. In contrast with the views that have been advanced in several recent studies, we show that the encaged species experiences significant non-covalent interaction with the interior of the cage. We also show that the inability of current experiments to detect many infrared active vibrational bands of the endo species in these systems is likely to be a consequence of the substantial electrostatic screening effect of the cage.
Keywords	Medicine ; R ; Science ; Q
Subject code	541
Language	English
Publishing date	2019-07-01T00:00:00Z
Publisher	Nature Publishing Group
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Article ; Online: Halogen Bonding

Pradeep R. Varadwaj / Arpita Varadwaj / Helder M. Marques

Inorganics, Vol 7, Iss 3, p

A Halogen-Centered Noncovalent Interaction Yet to Be Understood

2019 Volume 40

Abstract: In addition to the underlying basic concepts and early recognition of halogen bonding, this paper reviews the conflicting views that consistently appear in the area of noncovalent interactions and the ability of covalently bonded halogen atoms in ... ...

Abstract	In addition to the underlying basic concepts and early recognition of halogen bonding, this paper reviews the conflicting views that consistently appear in the area of noncovalent interactions and the ability of covalently bonded halogen atoms in molecules to participate in noncovalent interactions that contribute to packing in the solid-state. It may be relatively straightforward to identify Type-II halogen bonding between atoms using the conceptual framework of σ-hole theory, especially when the interaction is linear and is formed between the axial positive region (σ-hole) on the halogen in one monomer and a negative site on a second interacting monomer. A σ-hole is an electron density deficient region on the halogen atom X opposite to the R–X covalent bond, where R is the remainder part of the molecule. However, it is not trivial to do so when secondary interactions are involved as the directionality of the interaction is significantly affected. We show, by providing some specific examples, that halogen bonds do not always follow the strict Type-II topology, and the occurrence of Type-I and -III halogen-centered contacts in crystals is very difficult to predict. In many instances, Type-I halogen-centered contacts appear simultaneously with Type-II halogen bonds. We employed the Independent Gradient Model, a recently proposed electron density approach for probing strong and weak interactions in molecular domains, to show that this is a very useful tool in unraveling the chemistry of halogen-assisted noncovalent interactions, especially in the weak bonding regime. Wherever possible, we have attempted to connect some of these results with those reported previously. Though useful for studying interactions of reasonable strength, IUPAC’s proposed “less than the sum of the van der Waals radii” criterion should not always be assumed as a necessary and sufficient feature to reveal weakly bound interactions, since in many crystals the attractive interaction happens to occur between the midpoint of a bond, or the junction region, and a positive or negative site.
Keywords	halogen bonding ; noncovalent interactions ; Type-I ; -II and -III contacts ; σ-hole concepts and controversies ; MESP and electron density models ; crystalline structures ; IGM analysis ; Inorganic chemistry ; QD146-197
Subject code	540
Language	English
Publishing date	2019-03-01T00:00:00Z
Publisher	MDPI AG
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