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The macropolyhedral [B19H22]-monoanion 1 and the dianion [B18H21]2- 2 are synthesized in consistent 86-92% yields by the reaction ot [PSH]+[syn-B18H21] with BH3(SMe2) in 1,2-CI2C2H4 at 72°C ['PS' is an abbreviation tor 'Proton Sponge', 1,8-bis-(dimethylamino)naphthalene. 'PSH' is its protonated derivative.] The molecular structures ot 1 and 2 were elucidated as their [PS(BH2)]+ and [PS(BH2)]2- salts 1a and 2a by single-crystal X-ray diffraction studies, in which all atoms were located, and supported by mass spectrometric analyses together with calculations of the cluster molecular geometries (ab ignitio and/or DFT) and of 1 B chemical shifts based on GIAO-DFT shielding tensors. Aciditication ot dianion 2 with CF3COOH in acetonitrile, H2SO4 in dichloromethane, or aqueous HCI results in the clean tormation ot the monoanion [B19H22]- 1. Conversely, shaking a concentrated acetonitrile solution ot 1 in 0.5 M aqueous NaOH cleanly yields the [B19H21]2- dianion 2. Reaction of a dichloromethane solution ot 1 with a 36% aqueous solution ot HCHO in the presence ot H2SO4 quantitatively converts 1 at room temperature to a 1:1 mixture ot the syn- and anti-isomers ot B18H22. This cluster dismantling process is the first example of a syn- to anti-B16H22 isomer conversion. [ABSTRACT FROM AUTHOR]

Treatment of a solution of excess PCl3 and PS (PS = "proton sponge" = 1,8-dimethylamino naphthalene) with arachno-4-CB8H14 (1) in CH2Cl2, followed by hydrolysis of the reaction mixture, resulted in the isolation of the eleven-vertex diphosphacarbaborane nido-7,8,9-P2CB8H10 (2) (yield 34%) as the main product. Other products isolated from this reaction were the phosphacarboranes nido-7,8,9,10-P3CB7H8 (3) (yield 5%) and closo-2,1-PCB8H9 (4) (yield 15%). Compound 2 can be deprotonated by PS in CH2Cl2 or Nail in diethyl ether to give the [nido-7,8,9-P2CB8H9]- (2-) anion, which gives back the original compound, 2, upon re-protonation. Thermal rearrangement of anion 2- (Na+ salt) at 350 °C for 2 h produced the isomeric [nido-7,8,10-P2CB8H9]- (5-) anion, which was isolated as a PPh4+ salt (yield 86%). Multinuclear (¹H, 11B, 31P, and 13C), two-dimensional [11B-11B] COSY, ¹H{11B(selective)}, ¹H{31P(selective)}, and gradient-enhanced ([¹H-13C] HSQC) magnetic resonance measurements led to complete assignments of all resonances which are in excellent agreement with the structures proposed. Coupling constants, ¹J(31P, 13C), ²J(31P,C,¹H), and ¹J(31P,31P), were calculated using the DFT method B3LYP/6311+G(d,p). The molecular geometries of all compounds were optimized ab initio at a correlated level of theory (RMP2(fc)) using the 6-31G* basis set, and their correctness was assessed by comparison of the experimental 11B and 13C chemical shifts with those calculated by the GIAO-SCF/II//RMP2(fc)/6-31G* method. The computations also include the structures and chemical shieldings of the still unknown isomers [nido-7,10,8-P2CB8H9]- (6-) and [nido-7,9,8-P2CB8H9]- (7-). [ABSTRACT FROM AUTHOR]

Wade's rules are a well-established tool for the description of the geometry of inorganic clusters. Among others, they state that a decrease or increase in charge is always accompanied by a change in the number of skeletal electron pairs (SEPs). This work reports the synthesis of the first cationic chalcogenaboranes closo-[12-X-2-IPr-1-EB 11 H 10 ]BF 4 (IPr=1,3-(2,6-iPr 2 C 6 H 3 )-imidazole-2-ylidene; X=H, I; E=S, Se 3 a/b, 4 a/b) featuring the same SEP count as their neutral precursors, EB 11 H 11 , but bearing a positive charge. This ionisation significantly enhances the activity towards the electrophiles. It unlocks reactivity with very weak bases and offers the control of the regioselectivity towards hard/soft bases by the modulation of LUMO. The localisation of the positive charge within the borane cluster has been confirmed experimentally, spectroscopically and theoretically., (© 2025 The Author(s). Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

A series of nido -tricarbollides based on 10,11-X 2 -7-Me 3 N- nido -7,8,9-C 3 B 8 H 8 (X = H, Cl, Br, I) and their protonated, i.e. cationic, counterparts, which have an extra H-bridge over the B10-B11 vector in the nido open pentagonal belt, were prepared. Their structures have been verified by the joint ab initio (DFT)/GIAO(ZORA)/NMR approach, MS and HR-MS spectroscopy, and X-ray diffraction techniques. The iodination process is quite slow and could be monitored by 11 B NMR spectroscopy in conjunction with a computational search for the corresponding reaction pathway. These efforts have revealed the existence of monoiodo nido tricarbollide cationic motifs with an iodine atom in the positions that have features of an asymmetrical bridge over B10(H)-B11(H) in 10,11-H 2 -7-Me 3 N- nido -7,8,9-C 3 B 8 H 8 or B10(I)-B11(H) in 10,11-I,H-7-Me 3 N- nido -7,8,9-C 3 B 8 H 8 . Interestingly, 1,2-(COOH) 2 - closo -1,2-C 2 B 10 H 10 is one of the active acids, which confirms the earlier observation that a dicarboxylic acid based on o -carborane acts as a superacid.

Herein, we present the preparation of a series of electronically and/or sterically distinct borenium-type species based on a simple 2-arylpyridine scaffold. Corresponding arylpyridine was firstly subjected to electrophilic borylation (BBr 3 /i-Pr 2 NEt) and formed BBr 2 chelate was reduced with LiAlH 4 to yield arylpyridine boron dihydride. Elimination of one hydride led to Lewis acidic borenium-like products. Four methods of hydride elimination were evaluated and influence of counterions on reactivity, Lewis acidic and luminescent properties was assessed both experimentally and computationally. Arylpyridine chelates featuring weakly coordinating counterions exhibit fluorescent properties upon UV irradiation. Several general trends were inferred to modulate emission wavelength and fluorescence quantum yield. Based on our observations, we have devised and prepared borenium-type fluorophores with yellow-green fluorescence and quantum yields up to 93 %., (© 2024 Wiley-VCH GmbH.)

The objective of this study is to evaluate the effectiveness of various computational methods in reproducing the experimental heats of formation of boron hydrides using the atomization energy approach. The results have demonstrated that the empirical dispersion combined with the BJ damping function provided too large intramolecular dispersion energies, thereby compromising the accuracy of the outcomes produced by the DFT-D3 methods. Additionally, the CCSD(T) method has reproduced the experimental values only when combined with a basis set optimized for an accurate description of the core-valence correlation effect. Furthermore, the number of multicenter bonds present in the molecules under examination has also reflected their stability, as indicated by the heats of formation. Finally, a five-center two-electron (5c-2e) bond has emerged in B 5 H 9 , by applying the intrinsic bond orbital (IBO) method.

Herein, we report on the synthesis and stereochemistry of mono- and isomeric dinitrile derivatives of [(1,2-C 2 B 9 H 11 ) 2 -3,3'-Co] - ions. The shape and electronic properties of CN groups can apparently surmount the strain associated with the substitution of two vicinal carbon positions. Owing to electron donation to the cage, this results in a substituent-induced rearrangement of one of the carbon atoms to the upper pentagonal ring. The molecular structure of this isomer was confirmed using sc-XRD and DFT chemical computations.

Six-vertex closo-SB 5 Cl 5 (1) and ten-vertex closo-1-SB 9 Cl 9 (2) thiaboranes have been prepared, besides the already known 12-vertex closo-SB 11 Cl 11 (3), from the co-pyrolysis reaction of B 2 Cl 4 with S 2 Cl 2 at 280 °C in vacuo. The compounds are sublimable, off-white solids. Their elemental composition has been determined by high-resolution mass spectrometry. They were further characterized by one- and two-dimensional 11 B NMR spectroscopy and X-ray structure determination for 1 and 3. Ab initio/GIAO/NMR computations support octahedral, bicapped square-antiprismatic, and icosahedral geometries for 1, 2 and 3, respectively, as expected based on their closo-electron counts. 1 is the first isolated example of a neutral polyhedral closo-thiaborane with a cluster size smaller than ten vertices. The solid-state structure of 3 is one of the rare examples of a single-crystal X-ray structure determination of an icosahedral heteroborane reported. The corresponding crystal-packing forces show the different role of chalcogen bonding in these octahedral and icosahedral crystals. In addition, there is a mass-spectrometry evidence for the recurrent formation of further thiaborane homologs of closo-SB n Cl n with n=4, 6, 10, and supra-icosahedral 12., (© 2024 Wiley-VCH GmbH.)

Organic amines are found to be abundant in natural living systems. They also constitute an inestimable family of building blocks available in drug design. Considering the man-made cluster [(1,2-C 2 B 9 H 11 ) 2 -3,3'-Co(III)] - ion ( 1- ) and its application as an emerging unconventional pharmacophore, the availability of the corresponding amines has been limited and those with amino groups attached directly to carbon atoms have remained unknown. This paper describes the synthesis of compounds containing one or two primary amino groups attached to the carbon atoms of the cobaltacarborane cage that are accessible via the reduction of newly synthesized azides or via the Curtius rearrangement of the corresponding acyl azide. This substitution represents the first members of the series of azides and primary amines with functional groups bound directly to the carbon atoms of the cage. As expected, the absence of the linker along with the presence of the bulky anionic polyhedral ion leads to a significant alteration of the chemical and physicochemical properties. On a broader series of amines of the ion 1 - we have thus observed significant differences in the acidity of the amino groups, depending on whether these are attached to the carbon or boron atoms of the cage, or the C-substituted amines contain an aliphatic linker of variable length. The compounds are relevant for potential use as cobalt bis(dicarbollide) structural blocks in medicinal chemistry and material science. Our study includes single-crystal X-ray diffraction (XRD) structures of both amines and a discussion of their stereochemical and structural features.

Borane and heteroborane clusters have been known as neutral or anionic species. In contrast to them, several ten-vertex monocationic nido and closo dicarbaborane-based systems have recently emerged from the reaction of the parent bicapped-square antiprismatic dicarbaboranes with N-heterocyclic carbenes followed by the protonization of the corresponding nido intermediates. The expansion of these efforts has afforded the very first closo -dicationic octahedral phosphahexaborane along with new closo- monocationic pnictogenahexaboranes of the same shapes. All are the products of the one-pot procedure that consists in the reaction of the same carbenes with the parent closo -1,2-Pn 2 B 4 Br 4 (Pn = As, P). Whereas in the case of phosphorus such a monocation appears to be a mixture of stable intermediates, and arsenahexaboranyl monocation has occurred as the final product, all of them without using any subsequent reaction. The well-established DFT/ZORA/NMR approach has unambiguously confirmed the existence of these species in solution, and computed electrostatic potentials have revealed the delocalization of the positive charge in these monocations and in the very first dication, namely within the octahedral shapes in both cases., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Six-vertex closo-TeB 5 Cl 5 (1) and twelve-vertex closo-TeB 11 Cl 11 (2) telluraboranes have been prepared via co-pyrolysis of B 2 Cl 4 with TeCl 4 in vacuo at temperatures between 360 °C and 400 °C. Both compounds are sublimable, off-white solids, and they have been characterized by one- and two-dimensional 11 B NMR and high-resolution mass spectroscopy. Both ab initio/GIAO/NMR and DFT/ZORA/NMR computations support octahedral and icosahedral geometries for 1 and 2, respectively, as expected due to their closo-electron counts. The octahedral structure of 1 has been confirmed by single-crystal X-ray diffraction on an incommensurately modulated crystal. The corresponding bonding properties have been analyzed in terms of the intrinsic bond orbital (IBO) approach. 1 is the first example of a polyhedral telluraborane with a cluster size smaller than 10 vertices., (© 2023 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Modern computational protocols based on the density functional theory (DFT) infer that polyhedral closo ten-vertex carboranes are key starting stationary states in obtaining ten-vertex cationic carboranes. The rearrangement of the bicapped square polyhedra into decaborane-like shapes with open hexagons in boat conformations is caused by attacks of N-heterocyclic carbenes (NHCs) on the closo motifs. Single-point computations on the stationary points found during computational examinations of the reaction pathways have clearly shown that taking the "experimental" NHCs into account requires the use of dispersion correction. Further examination has revealed that for the purposes of the description of reaction pathways in their entirety, i.e., together with all transition states and intermediates, a simplified model of NHCs is sufficient. Many of such transition states resemble in their shapes those that dictate Z -rearrangement among various isomers of closo ten-vertex carboranes. Computational results are in very good agreement with the experimental findings obtained earlier.

Mössbauer and X-ray photoelectron spectroscopies (XPS) are complemented with high-level quantum-chemical computations in the study of the geometric and electronic structure of the paramagnetic salt of the metallacarborane sandwich complex [Fe(1,2-C 2 B 9 H 11 ) 2 ]Cs = FeSanCs. Experimental 57 Fe isomer shifts and quadrupole splitting parameters are compared with the theoretical prediction, with good agreement. The appearance of two sets of Cs(3d) doublets in the XPS spectrum, separated by 2 eV, indicates that Cs has two different chemical environments due to ease of the Cs (+) cation moving around the sandwich complex with low-energy barriers, as confirmed by quantum-chemical computations. Several minimum-energy geometries of the FeSanCs structure with the corresponding energies and Mössbauer parameters are discussed, in particular the atomic charges and spin population and the surroundings of the Fe atom in the complex. The Mössbauer spectra were taken at different temperatures showing the presence of a low-spin Fe atom with S = 1/2 and thus confirming a paramagnetic Fe III species., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

Closo-carborane anions are prominent, whereas the cations of the same are less abundant in the literature. As these ions have similar size and are weakly coordinating, the ionic liquids of these two ions could have important applications in many areas of chemistry. In view of limited number of polyhedral carborane cations available, we revisited the rearrangement of dicarboranyl methyl cation (7-CH 2 7,9-nido-C 2 B 9 H 10 + ) using ab initio molecular dynamics calculations with metadynamics. Our simulations confirmed the concerted mechanism of the rearrangement. We believe this work will resume the interest in its synthesis and carborane cations in general., (© 2022 Wiley Periodicals LLC.)

Among non-covalent interactions, B-H⋯π and C-H⋯π hydrogen bonding is rather weak and less studied. Nevertheless, since both can affect the energetics of protein-ligand binding, their understanding is an important prerequisite for reliable predictions of affinities. Through a combination of high-resolution X-ray crystallography and quantum-chemical calculations on carbonic anhydrase II/carborane-based inhibitor systems, this paper provides the first example of B-H⋯π hydrogen bonding in a protein-ligand complex. It shows that the B-H⋯π interaction is stabilized by dispersion, followed by electrostatics. Furthermore, it demonstrates that the similar C-H⋯π interaction is twice as strong, with a slightly smaller contribution of dispersion and a slightly higher contribution of electrostatics. Such a detailed insight will facilitate the rational design of future protein ligands, controlling these types of non-covalent interactions.

Reactions of the perhalogenated polyhedral pnictogenaboranes closo -1,2-Pn 2 B 4 Hal 4 (Pn = P, As; Hal = Cl, Br) with Lewis bases are presently being studied with a focus on rationalizing the sites of nucleophilic attacks on clusters bearing σ-holes. These σ-holes are localized both on pnictogens and, for Hal = Br, on bromine atoms, as revealed by electrostatic potential (ESP) and intrinsic bond orbital (IBO) analyses. Surprisingly, the attack of the cyclic ether THF on closo -1,2-Pn 2 B 4 Br 4 does not occur on the site with the largest positive partial charge, centered in the middle of the pnictogen-pnictogen vector. Instead, presumably promoted by the positivated bromine substituents, THF inserts into the boron-bromine bonds of the negatively charged boron atoms opposite to the pnictogen atoms to form 4-(4-bromobut-1-oxy)- closo -1,2-Pn 2 B 4 Br 3 ( 1-PB and 1-AsB ) and 4,6-(4-bromobut-1-oxy) 2 - closo -1,2-Pn 2 B 4 Br 2 ( 2-PB and 2-AsB ). 11 B and 31 P chemical shift computations at various levels support the assignments of the signals, which reflect the correctness of the molecular geometries in solutions. The Lewis-acidic perchlorinated analogues closo- 1,2-P 2 B 4 Cl 4 , closo -1,2-As 2 B 4 Cl 4 , and the mixed closo- 1,2-AsPB 4 Cl 4 bear negative charges. These negative charges are revealed by the V s,max values when computing the electrostatic potentials both on the boron and the chlorine atoms. Due to this negative charge, the analogues do not react with THF unless they are heated above 66 °C, where they slowly decompose to borate esters B(OR) 3 without the formation of concrete intermediates. The evaluation of 31 P NMR data of 1-PB has allowed the experimental determination of the coupling constant 1 J ( 31 P(1), 31 P(2)) = |143| Hz in a closo -diphosphaborane for the first time, which agrees well with the computed value of -178 Hz. The pioneering joint experimental vs computational interpretation of 31 P NMR spectra in the area of boron cluster chemistry was decisive for the structural characterization of 1-PB and 2-PB .

Reported herein are mutual rearrangements in the whole series of seven bicapped-square antiprismatic closo -C 2 B 8 H 10 by means of high-quality computations that disprove the earlier postulated dsd (diamond-square-diamond) scheme for these isomerizations. The experimentally existing closo -1,2-C 2 B 8 H 10 was able to be converted to 1,6-, and 1,10-isomers by pyrolysis, and the dsd (diamond-square-diamond) mechanism was offered as an explanation of these processes. However, these computations disprove the postulated dsd scheme for these isomerizations that take place in the ten-vertex closo series. Experimentally observed thermal rearrangements, both in the parent and substituted closo -1,2-C 2 B 8 H 10 , closo -1-CB 9 H 10 - , and closo -B 10 H 10 2- , indirectly support these refined computations. All these processes are based on the new concept of the so-called Z -mechanism, being consistent with a transition state of a boat shape with an open hexagonal belt that results from the initial breakage of three bonds. Such bond breakings and the consequent bond formations bring to mind the shape of the letter Z . In effect, the pattern of multicenter bonding shifts from reactant through a transition state to product. The molecular rearrangements that are available experimentally favour either the axial or equatorial isomers, and this ratio depends on temperature and the type of cluster and its substitution.

Polyhedral boranes and heteroboranes appear almost exclusively as neutral or anionic species, while the cationic ones are protonated at exoskeletal heteroatoms or they are instable. Here we report the reactivity of 10-vertex closo-dicarbadecaboranes with one or two equivalents of N-heterocyclic carbene to 10-vertex nido mono- and/or bis-carbene adducts, respectively. These complexes easily undergo a reaction with HCl to give cages of stable and water soluble 10-vertex nido-type cations with protonation in the form of a BHB bridge or 10-vertex closo-type cations containing one carbene ligand when originating from closo-1,10-dicarbadecaborane. The reaction of a 10-vertex nido mono-carbene adduct with phosphorus trichloride gives nido-11-vertex 2-phospha-7,8-dicarbaundecaborane, which undergoes an oxidation of the phosphorus atom to P = O, while the product of a bis-carbene adduct reaction is best described as a distorted C 2 B 6 H 8 fragment bridged by the (BH) 2 PCl 2 + moiety., (© 2021. The Author(s).)

The electrophilic substitution of icosahedral closo- 1-SB 11 H 11 with methyl iodide has resulted in two B-functionalized thiaboranes, 7,12-I 2 -2,3,4,5,6,8,9,10,11-(CH 3 ) 9 -1- closo -SB 11 and 7,8,12-I 3 -2,3,4,5,6,9,10,11-(CH 3 ) 8 - closo -1-SB 11 , with the former being significantly predominant. These two icosahedral thiaboranes are the first cases of polysubstituted polyhedral boron clusters with another vertex that differs from B and C. Such polyfunctionalizations have increased the earlier observed thiaborane icosahedral barrier, not exhibiting any reactivity toward bases, unlike the parent thiaborane. The search for methylation pathways has revealed that the complete B 11 -methylation is impossible, like in the case of decaborane(14), where this seems to be a result of the positively charged upper parts of these two molecules.

The success of approximate computational methods, such as molecular mechanics, or dispersion-corrected density functional theory, in the description of non-covalent interactions relies on accurate parameterizations. Benchmark data sets are thus required. This area is well developed for organic molecules and biomolecules but practically non-existent for boron clusters, which have been gaining in importance in modern drug as well as material design. To fill this gap, we have introduced two data sets featuring the most common non-covalent interaction of boron clusters, the dihydrogen bond, and calculated reference interaction energies at the "golden standard" CCSD(T)/CBS level. The boron clusters studied interact with formamide, methanol, water and methane at various distances and in two geometrical arrangements. The performance of the tested approximate methods is variable and recommendations for further use are given., (© 2020 Wiley-VCH GmbH.)

9-Br-closo-1,2-C 2 B 10 H 11 has been prepared and its gas-phase structure has been examined by means of gas electron diffraction. The structure of the carbaborane core is similar to the structure of the parent compound, which is of C 2v symmetry. A DFT-based search for the corresponding reaction pathway of the bromination of closo-1,2-C 2 B 10 H 12 revealed that the catalytic amount of aluminum reduces the barrier of the initial attack of the bromination agent toward the negatively charged part of the icosahedral carbaborane, i. e., the first transition state, from about 40 to about 27 kcalmol -1 . The Br-Br bond is weakened by an intermediate binding to the large π-hole on the aluminum atom of AlBr 3 , which is the driving force for the AlBr 3 -catalyzed bromination., (© 2020 The Authors. ChemPlusChem published by Wiley-VCH GmbH.)

The paper reports specific syntheses of methylated decaborane(14), nido -B 10 H 14 ( 1 ), derivatives. The reaction of 1 with an excess of neat MeI and AlCl 3 yields 1,2,3,4-Me 4 - nido -B 10 H 10 ( 2 ) essentially quantitatively when performed at room temperature. Heating the same mixture to 120 °C provides 1-I-2,3,4,5,7,8,10-Me 7 - nido -B 10 H 6 ( 3a ). The formation of analogous 1-CF 3 SO 2 O-2,3,4,5,7,8,10-Me 7 - nido -B 10 H 6 ( 3b ) is achieved by heating 1 or 2 with an excess of MeSO 3 CF 3 in the presence of a catalytic amount of HOSO 2 CF 3 to 120 °C. Compounds 2 and 3 can be deprotonated to yield the corresponding anions [1,2,3,4-Me 4 - nido -B 10 H 9 ] - ( 2 - ), [1-I-2,3,4,5,7,8,10-Me 7 - nido -B 10 H 5 ] - ( 3a - ), and [1-CF 3 SO 2 O-2,3,4,5,7,8,10-Me 7 - nido -B 10 H 5 ] - ( 3b - ). The structure of all the compounds isolated has been unambiguously confirmed by multinuclear ( 11 B and 1 H) NMR measurements, and the structures of 2 - , 3a , 3a - , and 3b have been established by X-ray diffraction analyses. The very high volatility of 2 has made it impossible to apply X-ray diffraction in this case; therefore, its structure has been derived computationally using the ab initio/GIAO/NMR tool. DFT-based computational protocols have also outlined the reason why it is impossible to obtain an octamethyl derivative of 1 experimentally.

The supramolecular recognition of closo,closo-[B 21 H 18 ] - by cyclodextrins (CDs) has been studied in aqueous solution by isothermal titration calorimetry and nuclear magnetic resonance spectroscopy. These solution studies follow up on previous mass-spectrometric measurements and computations, which indicated the formation and stability of CD ⋅ B 21 H 18 - complexes in the gas phase. The thermodynamic signature of solution-phase binding is exceptional, the association constant for the γ-CD complex with B 21 H 18 - reaches 1.8×10 6  M -1 , which is on the same order of magnitude as the so far highest observed value for the complex between γ-CD and a metallacarborane. The nature of the intermolecular interaction is also examined by quantum-mechanical computational protocols. These suggest that the desolvation penalty, which is particularly low for the B 21 H 18 - anion, is the decisive factor for its high binding strength. The results further suggest that the elliptical macropolyhedral boron hydride is another example of a CD binder, whose extraordinary binding affinity is driven by the chaotropic effect, which describes the intrinsic affinity of large polarizable and weakly solvated chaotropic anions to hydrophobic cavities and surfaces in aqueous solution., (© 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

Although 1-Ph - 2-X- closo -1,2-C 2 B 10 H 10 (X = F, Cl, Br, I) derivatives had been computed to have positive values of the heat of formation, it was possible to prepare them. The corresponding solid-state structures were computationally analyzed. Electrostatic potential computations indicated the presence of highly positive σ-holes in the case of heavy halogens. Surprisingly, the halogen•••π interaction formed by the Br atom was found to be more favorable than that of I., Competing Interests: The authors declare no conflict of interest.

Photoswitchable molecules have attracted wide interest for many applications in chemistry, physics, and materials science. In this work, we revisit the reversible photochemical and thermal rearrangements of the two B 20 H 18 2- isomers reported by Hawthorne and Pilling in 1966, whose mechanism had not been understood so far. We investigate the rearrangements by means of a joint experimental and computational study with the outcome that B 20 H 18 2- represents the first boron-based photochromic system ever reported. Both photochemical and thermal isomerizations occur through the same intermediate and involve a diamond-square-diamond (DSD) mechanism. Given the absence within boron chemistry of named chemical reactions as opposed to organic chemistry, we propose to label the B 20 H 18 2- photo- and thermal isomerization processes as the Hawthorne rearrangement.

Chalcogen atoms are a class of substituents capable of generating inner and outer derivatives of boron clusters. It is well known that chalcogenated boron clusters can form strong σ-hole interactions when a chalcogen atom is a part of an icosahedron. This paper studies σ-hole interactions of dicarbaboranes with two exopolyhedral chalcogen atoms bonded to carbon vertices. Specifically, a computational investigation has been carried out on the co-crystal of (1,2-C 2 B 10 H 10 ) 2 Se 4 •toluene and a single crystal of (1,2-C 2 B 10 H 10 ) 2 Te 4 .

The concept of icosahedral barrier has been expanded from the chemistry of carbaboranes to the area of thiaboranes. Both representatives of this barrier, i. e., closo-1,2-C 2 B 10 H 12 and closo-1-SB 11 H 11 , are similar in their electron distribution, which is dominated by positive charge in the midpoint of the C-C vector and on the sulfur atom with experimentally determined dipole moments of 4.50 D and 3.64 D, respectively. This is a driving force for their reactivity as exemplified by their reactions with different carbon functionalities. Icosahedral closo-1-SB 11 H 11 reacts both with an electron sextet containing carbon (in the form of N-heterocyclic carbenes), reported earlier, and with methyl iodide with an electron octet on the carbon. The latter reaction provides hexamethylated thiaborane on the basis of methylation so far unknown in this area of heteroborane chemistry. The computations of the heat of formation (ΔH f 298 ) make it possible to estimate the height of the barrier as well as to propose closo-thiaboranes beyond the barrier. Eleven and twelve vertex thiaboranes with nido electron count are known experimentally for breaking the barrier. These computations also suggest that the larger nido-thiaboranes are promising candidates for the corresponding experimental availability, i. e., the ΔH f 298 of a 13-vertex nido-thiaborane cluster has been computed to be more negative than that of the well-known nido-SB 10 H 11 - cluster (-6.7 and -5.6 kcal mol -1 per vertex, respectively)., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Superconductivity in polycrystalline and thin-film MgB2 is strongly affected by the termination of its surface, but a reliable determination of the surface termination is still a challenging task of surface chemistry. Here, the surface properties of superconducting MgB2 were investigated using a combination of inverse gas chromatography and van der Waals corrected density functional theory calculations. The dispersive surface energy was measured as a function of the surface coverage and its value (58 mJ m-2 to 48 mJ m-2) was verified by high-level non-local EXX + RPA calculations, which predicted that the dispersive contribution to the cleavage energy was 56 mJ m-2. The isosteric adsorption enthalpies of cyclohexane, dioxane, acetone and acetonitrile molecules were measured on an MgB2 sample and compared to the DFT calculated enthalpies for the Mg-terminated MgB2, B-terminated MgB2 and MgO(001) surfaces. The close agreement between theory and experiment for the Mg-terminated surface suggested that the magnesium termination is the dominant surface phase of MgB2. Thus, combining inverse gas chromatography experiments with theoretical calculations may provide information about the surface termination.

The thiaboranes closo-1-SB11H11 (1a) and 12-I-closo-1-SB11H10 (1b) react with 4-(dimethylamino)pyridine under inert conditions upon the formation of the nido-type thiaboranes 9-B{(4-Me2N)C5NH4}2(H)-7-SB10H11 and 9-B{(4-Me2N)C5NH4}2(H)-5-I-7-SB10H10 containing an exoskeletal B-H group. The same type of B-H moiety is also stabilised by one bipyridine molecule in a chelating fashion. These complexes are unstable in solution, and in air and hydrolyse to monodeboronated ionic compounds having [nido-7-SB10H11]- or [5-I-nido-7-SB10H10]- anions which are also products of the reactions of 1a and 1b with other N-bases such as pyridine, ammonia and DABCO. The extrusion of one boron and one sulphur atom takes place when 1a reacts with 2,6-di-tert-butylpyridine to yield decaborane.

Methyl-camouflaged dicarbaboranes closo-1,2- and 1,10-H 2 C 2 B 8 Me 8 have been prepared in high yields either from nido-5,6-H 2 C 2 B 8 H 10 or closo-1,2-H 2 C 2 B 8 H 8 via electrophilic methylation reactions and cluster-rearrangement methods. Prepared were also monosubstituted derivatives of general formulation closo-H 2 C 2 B 8 Me 7 -X (X = I or OTf). The permethylated compounds exhibit extreme air stability in comparison to unprotected counterparts as a consequence of rigid, egg-shaped hydrocarbon structures incorporating inner C 2 B 8 carborane scaffolding. The structures of all compounds isolated were confirmed unambiguously by multinuclear ( 11 B, 1 H, 13 C, and 19 F) NMR measurements, supported by X-ray diffraction analyses and geometry optimization methods on several compounds.

The 12-X- closo-SB 11 H 10 (X = H or I) thiaboranes react with one or two molar equivalents of various N-heterocyclic carbenes (NHCs) to give the deprotonated 12-vertex species of [12-X-SB 11 H 9 ·NHC] - [NHC-H] + composition as kinetic products. The use of one molar equivalent of a sterically more hindered NHC reactant leads to the formation of 12-X-SB 11 H 10 ·NHC adducts with a heavily distorted cage and the nido electron count. Further reaction of 12-I-SB 11 H 10 ·NHC to deboronated 12-X-SB 10 H 9 ·NHC proceeds in acetone to complete the closo- nido reaction pathway under the thermodynamic control. The structures of all compounds have been investigated by NMR spectroscopy and diffraction techniques. The results are supported by theoretical methods.

Carbaboranes 1,2-(EH) 2 -closo-1,2-C 2 B 10 H 10 (E=S, Se) were prepared, in the case of E=Se for the first time. Their semi-experimental equilibrium molecular structures were established by the concerted use of quantum-chemical calculations and gas electron diffraction. A method was developed and implemented to quantify the contribution of experimental data to each refined structural parameter. The accuracy of the experimental structures and those calculated at the MP2 level of theory were gauged by comparison of experimental 11 B NMR chemical shifts with quantum-chemically computed values; the inclusion of electron correlation (GIAO-MP2) provided superior results. For the purpose of geometrical prediction, the remaining group 16 elements were considered, and the icosahedral structures for E=O and Te were also computed; for E=O the same theoretical approach was used as for E=S, and for E=Te a description similar to that for E=Se was employed., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Electrophilic methylation of the closo -1,10-R 2 C 2 B 8 H 8 (1) (R = H or Me) dicarbaboranes at higher temperatures or thermal rearrangement of the 1,6-R 2 C 2 B 8 Me 8 (3) compounds at 400-500 °C generated the B-permethylated derivatives closo -1,10-R 2 C 2 B 8 Me 8 (2) in quantitative (>95%) yields. The compounds exhibit extreme air stability as a consequence of a rigid, egg shaped hydrocarbon structures incorporating inner 1,10-C 2 B 8 carborane core., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Two binary boron hydrides (NH4)2B10H10 and Na2B12H12 and mono- and dicarboxy p- and m-carboranes (namely, 1-(COOH)-closo-1,7-C2B10H11, 1,12-(COOH)2-closo-1,12-C2B10H10 and 1,7-(COOH)2-closo-1,7-C2B10H10) were intercalated into ZnAl-layered double hydroxides (ZnAl-LDH) and into Zn5(OH)8(NO3)2·2H2O. The formed compounds were characterized using elemental analysis, thermogravimetry analysis, X-ray powder diffraction, infrared spectroscopy and solid state NMR. All the intercalated boron compounds are present in the interlayer space of the layered hosts as anions. It is presumed that in the case of B10H102-, B12H122- and 1,12-(COO)2-closo-1,12-C2B10H102-, the guest molecules form a monolayer, whereas in the case of 1-(COO)-closo-1,7-C2B10H111- and 1,7-(COO)2-closo-1,7-C2B10H102- a bilayer arrangement is more probable. In the case of 1,7-(COO)2-closo-1,7-C2B10H102-, the guest molecules are strongly interdigitated resulting in lowering of the interlayer distance. Two different modes of binding were found. Whereas the carboxylate derivatives of p- and m-carboranes are bonded through classical hydrogen bonds, the corresponding parent borane anions interact with the host structures by mainly dihydrogen bonding. In effect, both kinds of hydrogen bonding are mainly of an electrostatic nature. The dihydrogen bond is detected, e.g. in crystal engineering, and represents a driving force for interactions of boranes with biomolecules. Since the latter dicarboxylic acids were found to be superacids, their interactions with the host structures should be stronger than in the case of the benzoic and terephthalic acid intercalates.

Reported are procedures leading to the first types of methyl camouflaged dicarbadecaboranes with fewer than eleven vertices. The compounds contain the closo-1,6-C2B8 scaffolding inside the egg-shaped hepta - decamethyl sheath, which imparts unusually high air and solvolytic stability to all of these compounds.

This paper presents a systematic study of multicenter and classical bonding on a broad series of experimentally known heteroboranes covering closo, nido, arachno and hypho types of cages with incorporated tetrel, pnictogen or chalcogen heterovertices up to the third-row elements. The nature of bonding is studied using a novel quantum-chemical tool, the intrinsic atomic/bond orbital (IAO/IBO) approach, which provides a direct connection between quantum chemistry and chemical concepts. We also discuss how the computed IBO properties are related to molecular observables such as interatomic distances, molecular electrostatic potential surfaces and dipole moments.

11 B NMR chemical shifts of tricoordinated BX 3 and tetracoordinated BX 4 - compounds (X = H, CH 3 , F, Cl, Br, I, OH, SH, NH 2 , and CH═CH 2 ) were computed, and the shielding tensors were explored not only within the nonrelativistic GIAO approach but also by application of both relativistic ZORA computations including spin-orbit coupling as well as scalar nonrelativistic ZORA computations (BP86 level of density functional theory). The contributions of the spin-orbit coupling to the overall shieldings are decisive for X = Br and I in both series. No relationship was found between the 2p orbital occupancies or 1/ΔE (difference between LUMO and suitably occupied MO that can be coupled with LUMO) with the shielding tensors (or their principal values) in the BX 3 series. However, a multidimensional statistical approach known as factor analysis (frequently used in chemometrics) revealed that three factors account for 92% of the cumulative proportion of total variance. The main components of the first factor are occupancies in the 2p x and 2p y orbitals and 1/ΔE; the second factor is mainly the occupancy in the 2p z orbital and the inductive substituent parameters by Taft. Finally, the third factor consists exclusively (98.4%) of the electrostatic potential (V max ), which is directly related to the so-called π-hole magnitudes.

We have prepared nido-7,8,9,11-Sb 2 C 2 B 7 H 9 , the first cluster with simultaneous Sb-B, Sb-C and Sb-Sb atom pairs with interatomic separations with magnitudes that approach the respective sums of covalent radii. However, the length of the Sb-Sb separation in this cluster is slightly less than the sum of the covalent radii. Quantum chemical analysis has revealed that the crystal packing of nido-7,8,9,11-Sb 2 C 2 B 7 H 9 is predominantly dictated by pnictogen (Pn) bonding, an unconventional σ-hole interaction. Indeed, the interaction energy of a very strong Sb 2 H-B Pn-bond in the nido-7,8,9,11-Sb 2 C 2 B 7 H 9 dimer exceeds -6.0 kcal mol -1 . This is a very large value and is comparable to the strengths of known Pn-bonds in Cl 3 Pnπ complexes (Pn = As, Sb).

Close B-Hπ contacts have recently been observed in crystallographic structures of Ir-dithiolene-phosphine complexes containing boron hydride cluster. This finding was interpreted using quantum chemical calculations as a new type of electrostatically driven nonclassical hydrogen bonding. However, such an explanation contradicts the wealth of evidence for unique noncovalent interactions of boron hydrides. Moreover, care must be exercised when computational methods are used to interpret new phenomena. Therefore, here, we cautiously examine the B-Hπ interaction by means of advanced quantum chemistry and disprove the claimed attractive electrostatic nature and rather define it as a nonspecific dispersion-driven contact. In summary, we present evidence that the crystallographically observed B-Hπ contacts do not constitute a novel type of hydrogen bonding of boron hydride clusters.

The electric and magnetic properties of the Li@B 10 H 14 complex, considered as a novel inorganic electride-type system with potential for second-order non-linear optical (NLO) applications, have already been studied. However, the reported C 2v structure is not the global energy minimum and therefore its electronic and magnetic properties need to be revisited. Moreover, by applying more accurate computational protocols (ROHF-CCSD/CCSD(T) and larger basis sets) we show that the model chemistry used earlier (UMP2/6-31+G(d)) is not sufficient for reliable description of the NLO responses of this open-shell doublet complex. The global minimum based on the C s symmetry is significantly (by ca. 25 kcal mol -1 ) more stable than the C 2v structure and it should be viewed as a system with moderate NLO responses. An excess of unpaired electron density is also responsible for the contact and pseudo-contact contributions to the magnetic properties, which was not considered in the earlier work.

The weakly coordinating binary macropolyhedral anion closo,closo-[B 21 H 18 ] - (B21; D 3h symmetry) has been synthesized using a simplified strategy compared to that in the literature. While gas-phase complexes of B21 with β- and γ-cyclodextrin (CD) were detected using ESI FT-ICR spectrometric measurements, α-CD did not bind to the B21 guest. This spectroscopic evidence has been interpreted using quantum-chemical computations, showing that β- and γ-CD are able to interact with B21 due to their larger cavities, in contrast to the smaller α-CD. The hydridic B-H vectors of the B21 anion interact with K + counterions and, via dihydrogen bonding, also with the partially positively charged hydrogens of the CD sugar units in the modeled β- and γ-CD complexes. In summary, it has been shown by combined spectrometric/computational analysis that macropolyhedral boron hydride anions with two counterions can form stable complexes with β- and γ-CD in the gas phase, offering a new perspective for the future investigation of this remarkable anion in the areas of supramolecular and medicinal chemistries.

The reaction between selected X-nido-5,6-C 2 B 8 H 11 compounds (where X = Cl, Br, I) and "Proton Sponge" [PS; 1,8-bis(dimethylamino)naphthalene], followed by acidification, results in extensive rearrangement of all cage vertices. Specifically, deprotonation of 7-X-5,6-C 2 B 8 H 11 compounds with one equivalent of PS in hexane or CH 2 Cl 2 at ambient temperature led to a 7 → 10 halogen rearrangement, forming a series of PSH + [10-X-5,6-C 2 B 8 H 10 ] - salts. Reprotonation using concentrated H 2 SO 4 in CH 2 Cl 2 generates a series of neutral carbaboranes 10-X-5,6-C 2 B 8 H 11 , with the overall 7 → 10 conversion being 75%, 95%, and 100% for X = Cl, Br, and I, respectively. Under similar conditions, 4-Cl-5,6-C 2 B 8 H 11 gave ∼66% conversion to 3-Cl-5,6-C 2 B 8 H 11 . Since these rearrangements could not be rationalized using the B-vertex swing mechanism, new cage rearrangement mechanisms, which are substantiated using DFT calculations, have been proposed. Experimental 11 B NMR chemical shifts are well reproduced by the computations; as expected δ( 11 B) for B(10) atoms in derivatives with X = Br and I are heavily affected by spin-orbit coupling.

Halogen bonds are a subset of noncovalent interactions with rapidly expanding applications in materials and medicinal chemistry. While halogen bonding is well known in organic compounds, it is new in the field of boron cluster chemistry. We have synthesized and crystallized carboranes containing Br atoms in two different positions, namely, bound to C- and B-vertices. The Br atoms bound to the C-vertices have been found to form halogen bonds in the crystal structures. In contrast, Br atoms bound to B-vertices formed hydrogen bonds. Quantum chemical calculations have revealed that halogen bonding in carboranes can be much stronger than in organic architectures. These findings open new possibilities for applications of carboranes, both in materials and medicinal chemistry., (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Reported is an unusual tautomeric behavior within the [nido-5,6-C 2 B 8 H 11 ] - (1a - ) cage that has no precedence in the whole area of carborane chemistry. Isolated were two skeletal tautomers, anions [6-Ph-nido-5,6-C 2 B 8 H 10 -μ 8,9 ] - (2d - ) and [5,6-Me 2 -nido-5,6-C 2 B 8 H 9 -μ 9,10 ] - (3b - ), which differ in the positioning of the open-face hydrogen bridge. Their structures have been determined by X-ray diffraction analyses. The 3b - structure is stabilized by intermolecular interaction involving Et 3 NH + and B8-B9 and H8 atoms in the solid phase; however, its dissolution in CD 3 CN causes instant conversion to the more stable [5,6-Me 2 -nido-5,6-C 2 B 8 H 9 -μ 8,9 ] - (2b - ) tautomer. The dynamic electron-correlation-based MP2/6-31G* computations suggest that the parent [nido-5,6-C 2 B 8 H 11 -μ 8,9 ] - (2a - ) tautomer is 3.9 kcal·mol -1 more stable than the [nido-5,6-C 2 B 8 H 11 -μ 9,10 ] - (3a - ) counterpart and the μ 8,9 structure 2 - is therefore the most stable tautomeric form in the solution, as was also demonstrated by multinuclear ( 1 H, 11 B, and 13 C) NMR measurements on the whole series of C-substituted compounds.

Triethylamine-catalyzed dehydrogenation of carbon-disubstituted dicarbaboranes 5,6-R2-nido-5,6-C2B8H10 [1, where R = H (1a), Me (1b), and Ph (1c)] in refluxing acetonitrile leads to a high-yield (up to 85-95%) formation of a series of dicarbaboranes 1,2-R2-closo-1,2-C2B8H8 (2). The monosubstituted 6-R-nido-5,6-C2B8H11 (3) analogues [where R = Ph (3a), naph (1-naphthyl; 3b), Bu (3c)] afforded 1-R-1,2-closo C2B8H9 (4) isomers [where R = Ph (4a), naph (4b), n-Bu (4c)] as the main products; compounds 4a and 4c were accompanied by 2-R-1,2-C2B8H9 (5) isomers (total yields up to 90%), with the 4/5 molar ratio being strongly dependent on the nature of R (4:1 and 1:1, respectively). All of these cage-closure reactions are supposed to proceed via the stage of the corresponding Et3NH(+) salts of nido anions [5,6-R2-5,6-C2B8H9](-) (1(-)) and [6-R-5,6-C2B8H10](-) (3(-)), which lose H2 and Et3N upon heating (dehydrodeamination). The cage-closure mechanisms leading to closo isomers 2, 4, and 5 have been substantiated by B3LYP/6-31+G* calculations of the reaction profile for a simple 1a(-) → 2a + H(-) conversion. All of the compounds isolated have been characterized by multinuclear ((11)B, (1)H, and (13)C) NMR spectroscopy, mass spectrometry, and elemental analyses, and the structure of 1-Ph-closo-1,2-C2B8H9 (4a) was established by an X-ray diffraction study.

Because of the comparable electron scattering abilities of carbon and boron, the electron diffraction structure of the C2v-symmetric molecule closo-1,2-C2B10H12 (1), one of the building blocks of boron cluster chemistry, is not as accurate as it could be. On that basis, we have prepared the known diiodo derivative of 1, 9,12-I2-closo-1,2-C2B10H10 (2), which has the same point-group symmetry as 1 but in which the presence of iodine atoms, with their much stronger ability to scatter electrons, ensures much better structural characterization of the C2B10 icosahedral core. Furthermore, the influence on the C2B10 geometry in 2 of the antipodally positioned iodine substituents with respect to both carbon atoms has been examined using the concerted application of gas electron diffraction and quantum chemical calculations at the MP2 and density functional theory (DFT) levels. The experimental and computed molecular geometries are in good overall agreement. Molecular dynamics simulations used to obtain vibrational parameters, which are needed for analyzing the electron diffraction data, have been performed for the first time for this class of compound. According to DFT calculations at the ZORA-SO/BP86 level, the (11)B chemical shifts of the boron atoms to which the iodine substituents are bonded are dominated by spin-orbit coupling. Magnetically induced currents within 2 have been calculated and compared to those for [B12H12](2-), the latter adopting a regular icosahedral structure with Ih point-group symmetry. Similar total current strengths are found but with a certain anisotropy, suggesting that spherical aromaticity is present; electron delocalization in the plane of the hetero atoms in 2 is slightly hindered compared to that for [B12H12](2-), presumably because of the departure from ideal icosahedral symmetry.