Search Results (16)

Homopolyatomic cations of the main group elements and of the element sulfur, in particular, are used as tutorial examples to teach structure and bonding in inorganic chemistry. So far, the cations [S₄]²⁺, [S₈]²⁺, [S₁₉]²⁺, [S₅]^•+, and [S₈]^•+ are known experimentally. In this report, the generation and crystal structure determination of the salt Na₂[S₂₀]₂[B₁₂Cl₁₂]₃, containing the new homopolyatomic sulfur cation [S₂₀]²⁺, is reported. The structure of the latter cation consists of two seven-membered homocycles, which are bridged by a six-membered sulfur chain. This structure is strongly related to that of [S₁₉]²⁺. The heptasulfur rings show pronounced bond alternation. Comparison with the experimental structures of [S₇X]⁺ (X = I, Br) and the application of quantum chemical calculations show unambiguously that the observed structural features are intrinsic properties of the cationic cyclo-heptasulfur moieties. The latter can occupy different conformations, which only slightly differ in energy. Charge delocalization and negative hyperconjugation contribute to the stability of the observed structures. The discovery of the [S₂₀]²⁺ cation fits well into range of known homopolyatomic sulfur cations, which can be classified by their averaged oxidation state of sulfur. Full article

In this work, a series of boronated amidines based on the closo-dodecaborate anion and amino acids containing an amino group in the side chain of the general formula [B₁₂H₁₁NHC(NH(CH₂)_nCH(NH₃)COOH)CH₃], where n = 2, 3, 4, were synthesized. These derivatives contain conserved α-amino and α-carboxyl groups recognized by the binding centers of the large neutral amino acid transporter (LAT) system, which serves as a target for the clinically applied BNCT agent para-boronophenylalanine (BPA). The paper describes several approaches to synthesizing the target compounds, their acute toxicity studies, and tumor uptake studies in vivo in two tumor models. The promising compound [B₁₂H₁₁NHC(NH(CH₂)₂CH(NH₃)COOH)CH₃]*3H₂O demonstrates low toxicity (LD₅₀ in a range from 150 to 300 mg/kg) and excellent solubility and also shows selective uptake in experimental melanoma in laboratory mice (T/N ratio remained >3 up to 60 min post-injection, with a maximum T/N of 6.2 ± 2.8 at 45 min). Full article

The modification of carborane anion monocarba-closo-dodecaborate (1) with perfluoroalkyl groups enhances its solubility in fluorinated ethers. This novel approach achieves a degree of solubility that is unattainable by using traditional lipophilic modifications or boro–vertex functionalizations of 1. A spectroscopic analysis in combination with DFT calculations confirmed that these new anions retain their weakly coordinating nature and exhibit moderate chemical stability. Full article

By reacting nitrilium derivative of the closo-dodecaborate anion, Bu₄N[B₁₂H₁₁N≡CR] (where R = Me, Et, nPr, iPr, p-tolyl), with lithium aluminum hydride (LiAlH₄), N-alkylammonium derivatives of the closo-dodecaborate anion, and Bu₄N[B₁₂H₁₁NH₂CH₂R], were obtained. The reduction reaction procedure was optimized, achieving yields close to quantitative (90–95%). The structure of the compound Bu₄N[B₁₂H₁₁NH₂CH₂CH₃] was determined using X-ray structural analysis. It was found that substituting lithium aluminum hydride (LiAlH₄) with sodium borohydride (NaBH₄) leads to the same products but only upon heating, while the reaction with LiAlH₄ proceeds at room temperature. Full article

A series of Schiff base derivatives, namely N-(4-methoxyphenyl)-1-(1-methylbenzimidazol-2-yl)methanimine (L¹), 4-methoxy-N-[(1-methylbenzimidazol-2-yl)methyl]aniline (L²), and 2-[(E)-(1-propylbenzimidazol-2-yl)iminomethyl]phenol (L³), were synthesized. These compounds feature different linker groups, including –CH=N–, –CH₂–NH–, and –N=CH–, respectively. During the process of zinc(II) and cadmium(II) complexation in the presence of the closo-dodecaborate [B₁₂H₁₂]^2– anion, it was observed that ligand L³ underwent degradation. Consequently, two compounds were isolated, [Zn(Bz-NH₂)₂(CH₃COO)₂] and (HBz-NH₂)₂[B₁₂H₁₂]∙2CH₃CN, both containing 1-propyl-2-aminobenzimidazole (Bz-NH₂), which is a degraded fragment of the ligand. Several new zinc(II) and cadmium(II) coordination compounds were synthesized and characterized using various physicochemical analysis methods, including elemental analysis, IR, and UV spectroscopy. Additionally, X-ray diffraction and Hirshfeld surface analysis were performed for compounds [Cd(L²)₂(CH₃CN)(H₂O)][B₁₂H₁₂], [Zn(Bz-NH₂)₂(CH₃COO)₂], and (HBz-NH₂)₂[B₁₂H₁₂]∙2CH₃CN, as well as for ligand L². Full article

Here, we present composites and materials that can be prepared starting with boron hydride cluster compounds (decaborane, decahydro-closo-decaborate and dodecahydro-closo-dodecaborate anions and carboranes). Recent examples of their utilization as boron protective coatings including using them to synthesize boron carbide, boron nitride, metal borides, metal-containing composites, and neutron shielding materials are discussed. The data are generalized demonstrate the versatile application of materials based on boron cluster anions and carboranes in various fields. Full article

Tl[CB₁₁H₁₂] was prepared with a reaction of Tl₂[CO₃] with the acid of the monocarba-closo-dodecaborate anion (H₃O)[CB₁₁H₁₂] in aqueous solution as prismatic colorless single crystals by isothermal evaporation from the clear brine. It crystallizes in a monoclinic primitive structure with the space group P2₁/c (a = 685.64(3) pm, b = 1978.21(9) pm, c = 1006.89(5) pm, β = 132.918(3)° for Z = 4), which can be derived from the halite-type arrangement if the closo-carbaborate cages are considered as spheres. Due to the different atoms in the [CB₁₁H₁₂]⁻ anion, Tl[CB₁₁H₁₂] features interesting C–H^δ+ ∙∙∙ ^δ−H–B interactions near to non-classical hydrogen bridges (“dihydrogen bonds”) and exhibits considerably different luminescence properties compared to regular closo-hydroborates, such as Tl₂[B₁₀H₁₀], Tl₂[B₁₂H₁₂] and Tl₃Cl[B₁₂H₁₂]. Tl[CB₁₁H₁₂] shows strong photoluminescence (PL) at 390 nm, while the excitation bands for this broad band are located at 245 and 280 nm. It is caused by an interconfigurational [Xe]4f¹⁴5d¹⁰6s² (³P₁) to [Xe]4f¹⁴5d¹⁰6s¹6p¹ (¹S₀) transition, which is also known as lone-pair luminescence. The quantum yield is rather low (<10 %), which is likely caused by the rather large Stokes shift. In addition, temperature-dependent emission spectra were recorded to determine the thermal quenching curve and the respective quenching temperature. Full article

Novel fluorescent 7-methoxy- and 7-(diethylamino)-coumarins modified with azido-group on the side chain have been synthesized. Their photophysical properties and single crystals structure characteristics have been studied. In order to demonstrate the possibilities of fluorescent labeling, obtained coumarins have been tested with closo-dodecaborate derivative bearing terminal alkynyl group. Cu^I catalyzed Huisgen 1,3-dipolar cycloaddition reaction has led to fluorescent conjugates formation. The absorption–emission spectra of the formed conjugates have been presented. The antiproliferative activity and uptake of compounds against several human cell lines were evaluated. Full article

This review systematizes data on the coordination ability of mono- and disubstituted derivatives of boron cluster anions and carboranes in complexation with transition metals. Boron clusters anions [B_nH_n]^2–, monocarborane anions [CB_nH_n–1]^–, and dicarboranes [C₂B_nH_n–2] (with non-functionalized carbon atoms) (n = 10, 12) containing the B–X exo-polyhedral bonds (X = N, O, S, Hal) are discussed. Synthesis and structural features of complexes known to date are described. The effect of complexing metal and substituent attached to the boron cage on the composition and structures of the final complexes is analyzed. It has been established that substituted derivatives of boron cluster anions and carboranes can act as both ligands and counterions. A complexing agent can coordinate substituted derivatives of the boron cluster anions due to three-center two-electron 3c2e MHB bonds, by the substituent functional groups, or a mixed type of coordination can be realized, through the BH groups of the boron cage and the substituent. As for B-substituted carboranes, complexes with coordinated substituents or salts with non-coordinated carborane derivatives have been isolated; compounds with MHB bonding are not characteristic of carboranes. Full article

The preparation of novel nitrilium derivatives of closo-dodecaborate anion [B₁₂H₁₁NCR]⁻, R = n-C₃H₇, i-C₃H₇, 4-C₆H₄CH₃, 1-C₁₀H₇ is described. Target compounds were obtained in good yields (up to 73%). The synthesis of target borylated nitrilium derivatives was characterised by the simplicity of the chemical apparatus and the absence of the necessity for the purification of desired compounds. The crystal structures of previously obtained [B₁₂H₁₁NCCH₃]⁻ and novel [B₁₂H₁₁NCC₃H₇]⁻ were established with the help of X-ray structure analysis. DFT-analysis of several nitrilium derivatives [B₁₂H₁₁NCR]⁻, R = CH₃, C₃H₇, 4-CH₃C₆H₄ was carried out. The main peculiarities of the C≡N bond of the exo-polyhedral substituent were revealed in terms of bond lengths, bond orders and atomic charges. The LUMO orbitals of the systems considered were examined for understanding of the electrophilic nature of the nitrilium derivatives of the closo-dodecaborate anion. Full article

In this work, we present an electrochemical study of the boron cage monomercaptoundecahydro-closo-dodecaborate [B₁₂H₁₁SH]²⁻ in solution and in a self-assembled monolayer over a polycrystalline gold electrode. Cyclic voltammetry of the anion [B₁₂H₁₁SH]²⁻ in solution showed a shift in the peak potentials related to the redox processes of gold hydroxides, which evidences the interaction between the boron cage and the gold surface. For an Au electrode modified with the anion [B₁₂H₁₁SH]²⁻, cyclic voltammetry response of the probe Fe(CN)₆³⁻/Fe(CN)₆⁴⁻ showed a ΔEp value typical for a surface modification. Electrochemical impedance spectroscopy presented R_tc and C_dl values related to the formation of a self-assembled monolayer (SAM). A comparison of electrochemical responses of a modified electrode with thioglycolic acid (TGA) reveals that the boron cage [B₁₂H₁₁SH]²⁻ diminishes the actives sites over the Au surface due to the steric effects. Differential capacitance measurements for bare gold electrode and those modified with [B₁₂H₁₁SH]²⁻ and (TGA), indicate that bulky thiols enhance charge accumulation at the electrode–solution interface. In addition to electrochemical experiments, DFT calculations and surface plasmon resonance measurements (SPR) were carried out to obtain quantum chemical descriptors and to evaluate the molecular length and the dielectric constant of the Boron cage. From SPR experiments, the adsorption kinetics of [B₁₂H₁₁SH]²⁻ were studied. The data fit for a Langmuir kinetic equation, typical for the formation of a monolayer. Full article

In the present work, a convenient and straightforward approach to the preparation of borylated amidines based on the closo-dodecaborate anion [B₁₂H₁₁NCCH₃NHR]−, R=H, Alk, Ar was developed. This method has two stages. A nitrile derivative of the general form [B₁₂H₁₁NCCH₃]⁻ was obtained, using a modified technique, in the first stage. On the second stage the resulting molecular system interacted with primary amines to form the target amidine products. This approach is characterised by a simple chemical apparatus, mild conditions and high yields of the final products. The mechanism of the addition of amine to the nitrile derivative of the closo-dodecaborate anion was studied, using quantum-chemical methods. The interaction between NH₃ and [B₁₂H₁₁NCCH₃]⁻ ammonia was chosen as an example. It was found that the structure of the transition state determines the stereo-selectivity of the process. A study of the biological properties of borylated amidine sodium salts indicated that the substances had low toxicity and could accumulate in cancer cells in significant amounts. Full article

Oligonucleotide conjugates with boron clusters have found applications in different fields of molecular biology, biotechnology, and biomedicine as potential agents for boron neutron capture therapy, siRNA components, and antisense agents. Particularly, the closo-dodecaborate anion represents a high-boron-containing residue with remarkable chemical stability and low toxicity, and is suitable for the engineering of different constructs for biomedicine and molecular biology. In the present work, we synthesized novel oligonucleotide conjugates of closo-dodecaborate attached to the 5′-, 3′-, or both terminal positions of DNA, RNA, 2′-O-Me RNA, and 2′-F-Py RNA oligomers. For their synthesis, we employed click reaction with the azido derivative of closo-dodecaborate. The key physicochemical characteristics of the conjugates have been investigated using high-performance liquid chromatography, gel electrophoresis, UV thermal melting, and circular dichroism spectroscopy. Incorporation of closo-dodecaborate residues at the 3′-end of all oligomers stabilized their complementary complexes, whereas analogous 5′-modification decreased duplex stability. Two boron clusters attached to the opposite ends of the oligomer only slightly influence the stability of complementary complexes of RNA oligonucleotide and its 2′-O-methyl and 2′-fluoro analogs. On the contrary, the same modification of DNA oligonucleotides significantly destabilized the DNA/DNA duplex but gave a strong stabilization of the duplex with an RNA target. According to circular dichroism spectroscopy results, two terminal closo-dodecaborate residues cause a prominent structural rearrangement of complementary complexes with a substantial shift from the B-form to the A-form of the double helix. The revealed changes of key characteristics of oligonucleotides caused by incorporation of terminal boron clusters, such as the increase of hydrophobicity, change of duplex stability, and prominent structural changes for DNA conjugates, should be taken into account for the development of antisense oligonucleotides, siRNAs, or aptamers bearing boron clusters. These features may also be used for engineering of developing NA constructs with pre-defined properties. Full article

High boron content systems were prepared by the peripheral functionalisation of 1,3,5-triphenylbenzene (TPB) and octavinylsilsesquioxane (OVS) with two different anionic boron clusters: closo-dodecaborate (B₁₂) and cobaltabisdicarbollide (COSAN). TPB was successfully decorated with three cluster units by an oxonium ring-opening reaction, while OVS was bonded to eight clusters by catalysed metathesis cross-coupling. The resulting compounds were spectroscopically characterised, and their solution-state photophysical properties analysed. For TPB, the presence of COSAN dramatically quenches the fluorescence emission (λ_em = 369 nm; Φ_F = 0.8%), while B₁₂-substituted TPB shows an appreciable emission efficiency (λ_em = 394 nm; Φ_F = 12.8%). For octasilsesquioxanes, the presence of either COSAN or B₁₂ seems to be responsible for ∼80 nm bathochromic shift with respect to the core emission, but both cases show low emission fluorescence (Φ_F = 1.4–1.8%). In addition, a remarkable improvement of the thermal stability of OVS was observed after its functionalisation with these boron clusters. Full article

The synthesis and structural characterization of new derivatives of [B₁₂H₁₂]²⁻ is of fundamental interest and is expected to allow for extended applications. Herein we report on the synthesis of a series of amidine, amide, urea and isocyanate derivatives based on the amino-closo-dodecaborate anion [B₁₂H₁₁NH₃]⁻. Their structures have been confirmed by spectroscopic methods, and nine crystal structures are presented. Full article