We disclose the synthesis and properties of [M(B 11 H 11 ) 2 ] 3− (M = Cu, Ag, Au) with the first gold-based anion [Au(B 11 H 11 ) 2 ] 3− . The nido -[B 11 H 11 ] 4− ligand stabilizes complexes with copper, silver, and gold in the highest known oxidation state +V. The relative stability of [M +V ( nido -B 11 X 11 ) 2 ] 3− , [M +III ( nido -B 11 X 11 )( closo -B 11 X 11 )] 3− , and [M +I ( closo -B 11 X 11 ) 2 ] 3− isomers (X = H, F) was calculated at the DFT level. Unlike for [Cu(B 11 H 11 ) 2 ] 3− and [Au(B 11 H 11 ) 2 ] 3− , in case of [Ag(B 11 H 11 ) 2 ] 3− , we discovered the equilibrium between the kinetically stable [Ag +V ( nido -B 11 H 11 ) 2 ] 3− (η 5 ) and kinetically labile [Ag +I ( closo -B 11 H 11 ) 2 ] 3− (η 2 ) by X-ray diffraction. The isomerization of the Ag complex shows signs of Ag(V)–Ag(I) redox processes. When a crystal is cooled, a phase transition occurs at 110–130 K in which the coordination of the ligands on the silver changes from η 5 to η 2 . The phase transition is reversible and upon heating to 170 K, the η 2 to η 5 coordination is transformed. The reaction of [M(B 11 H 11 ) 2 ] 3− with HF leads to the partial substitution of hydrogen atoms by fluorine atoms to form [M(B 11 H 11−x F x ) 2 ] 3− (M = Cu, Au; x ≈ 4). We synthesized 18 compounds containing [M(B 11 H 11 ) 2 ] 3− (M = Cu, Ag, Au) and their derivatives, followed by structural determination (X-ray crystallography). XANES data confirm the high oxidation state of Cu in K 3 [Cu(B 11 H 11 ) 2 ]·5H 2 O.

Tetracyanidoborates of divalent lanthanides, Ln[B(CN)4]2THF (Ln = Eu (1), Yb (2)), were obtained by a salt metathesis reaction of lanthanide diiodides and ammonium tetracyanidoborate. Unlike known tetracyanidoborates of alkaline-earth metals and trivalent lanthanides, compounds 1 and 2 are 3D metal-organic frameworks (MOFs) with a cubic structure. MOF 1 demonstrates air stability and thermal stability up to 400 degrees C. At 298 K, 1 shows bright broadband photoluminescence (PL) of Eu2+ ions that peaked at 650 nm with 80% absolute quantum yield (QY). When the temperature increases from 77 to 500 K, the maximum of PL spectra of 1 exhibit a blue shift from 13900 to 16350 cm-1. Quantum chemical calculations and X-ray diffraction studies of 1 at 100 and 390 K reveal that observed PL thermochromism is accompanied by changes in the geometry of the Eu-N-C fragment and electronic structure of the [B(CN)4]- anion. Europium-containing MOF 1 exhibits slow relaxation of magnetization at temperatures up to 4 K. The magnetic relaxation dynamics of MOF 1 is dominated by an Orbach-like mechanism with an effective energetic barrier estimated as 16.7 K. Removal of THF from the pores of MOF 1 leads to the same changes in structure and luminescent behavior as heating but significantly reduces its stability in air. The singularity of structural, magnetic, and luminescent behavior, as well as extraordinary stability of europium MOF 1, are due to specifics in europium-tetracyanidoborate bonding. The reported tetracyanidoborates 1 and 2 are the porous 3D MOFs based on divalent lanthanide ions: europium and ytterbium.

We disclose the synthesis and properties of [M(B 11 H 11 ) 2 ] 3− (M = Cu, Ag, Au) with the first gold‐based anion [Au(B 11 H 11 ) 2 ] 3− . The nido ‐[B 11 H 11 ] 4− ligand stabilizes complexes with copper, silver, and gold in the highest known oxidation state +V. The relative stability of [M +V ( nido ‐B 11 X 11 ) 2 ] 3− , [M +III ( nido ‐B 11 X 11 )( closo ‐B 11 X 11 )] 3− , and [M +I ( closo ‐B 11 X 11 ) 2 ] 3− isomers (X = H, F) was calculated at the DFT level. Unlike for [Cu(B 11 H 11 ) 2 ] 3− and [Au(B 11 H 11 ) 2 ] 3− , in case of [Ag(B 11 H 11 ) 2 ] 3− , we discovered the equilibrium between the kinetically stable [Ag +V ( nido ‐B 11 H 11 ) 2 ] 3− (η 5 ) and kinetically labile [Ag +I ( closo ‐B 11 H 11 ) 2 ] 3− (η 2 ) by X‐ray diffraction. The isomerization of the Ag complex shows signs of Ag(V)–Ag(I) redox processes. When a crystal is cooled, a phase transition occurs at 110–130 K in which the coordination of the ligands on the silver changes from η 5 to η 2 . The phase transition is reversible and upon heating to 170 K, the η 2 to η 5 coordination is transformed. The reaction of [M(B 11 H 11 ) 2 ] 3− with HF leads to the partial substitution of hydrogen atoms by fluorine atoms to form [M(B 11 H 11−x F x ) 2 ] 3− (M = Cu, Au; x ≈ 4). We synthesized 18 compounds containing [M(B 11 H 11 ) 2 ] 3− (M = Cu, Ag, Au) and their derivatives, followed by structural determination (X‐ray crystallography). XANES data confirm the high oxidation state of Cu in K 3 [Cu(B 11 H 11 ) 2 ]·5H 2 O.

The unusually high oxidation state + IV of cobalt is stabilized by ligands based on [B11H11](4-) in dark blue colored Cs-4[Co(B11H10.11(OH)(0.75))(2)]4.56H(2)O, K-4[Co(B11H9.19(OH)(1.81))(2)]2H(2)O, Cs-8[Co{(B11H6)(2)(O)(O2BOH)(4)}](2)4H(2)O and K-4[Co{(B11H6)(2)(O2BOH)(5)}]7H(2)O. These compounds were obtained by reacting Co2+ salts with [B11H14](-) under alkaline conditions. In the absence of oxygen, Co(+III) compounds such as the light brownish K-4[Co(B11H11)(CN)(3)]KCl2.5H(2)O are formed. The title compounds were characterized by X-ray crystallography. Cs-8[Co{(B11H6)(2)(O)(O2BOH)(4)}](2)4H(2)O and K-4[Co(B11H11)(CN)(3)]KCl2.5H(2)O were also characterized using IR-, UV-vis and cyclovoltammetry. Magnetic measurements of Cs-4[Co(B11H10.11(OH)(0.75))(2)]4.56H(2)O and ESR measurements of Cs-8[Co{(B11H6)(2)(O)(O2BOH)(4)}](2)4H(2)O show that in these Co(+IV) low-spin d(5) complexes the unpaired electron is on the d(x2-y2), d(xy) (E-2g) orbitals.

A new synthetic method for the synthesis of C-substituted [RC(O)CH2-CB11H11]− carborate anions has been developed. The reaction of [closo-B11H11]2− with terminal alkynes in the presence of a copper catalyst leads to insertion into the boron cluster, and C-substituted [RC(O)CH2-CB11H11]− carborate anions are formed. These reactions are strongly dependent on the reaction conditions, the solvents, and the alkynes used. The alkynes HCCCO2Et, HCCCO2Me, and HCCCONH2 lead to the formation of [NH2C(O)CH2-CB11H11]− as the final product in aqueous ammonia solution. In contrast, the reaction using the alkyne HCCCOMe yields [MeC(O)CH2-CB11H11]−. The products have been fully characterized by multinuclear NMR and IR spectroscopy as well as mass spectrometry. The crystal structures of K[NH2C(O)CH2-CB11H11] and [NEt3CH2Cl][NH2C(O)CH2-CB11H11] have been determined.

Although the formation of thallium hydrogen fluorides TlHxFx+1 (x = 1, 1.5, 2, 3, 5, 6.5, and 7) from TlF and HF was reported in the 1970s, little is known about the corresponding crystal structures. To shed light on the crystal chemistry of the thallium fluorides, we reinvestigated the structure of α-TlHF2, which was obtained by crystallization of TlF from 50% HF at room temperature. We disclose that β-TlHF2 is isostructural with α-MHF2 (M = K, Rb, and Cs), γ-TlHF2 is isostructural with β-MHF2 (M = K and Rb), whereas α-TlHF2 crystallizes in an unusual structure type. During the reaction of TlHF2 with the glass of the microscope slide, crystals of the previously unknown compound Tl2[SiF6]·2TlF were formed. We disclose that the related Tl2[GeF6]·2TlF can be obtained by the crystallization of stoichiometric amounts of Tl2[GeF6] with TlF from water at room temperature. The crystal structures of α-TlHF2, Tl2[SiF6]·2TlF, Tl2[SiF6]·TlCl, Tl2[GeF6]·2TlF, Tl2[GeF6]·TlCl, and Tl2[GeF6] were determined by single-crystal X-ray diffraction analysis. The crystal structures of α-TlF and Tl2[SiF6]·xTlF (x = 0, 1) were redetermined at low temperatures.

A special feature of the small metal-free electrophilic anion [B6X5]− is nitrogen activation through π-backbonding. The π-backbonding predicted by EDA ETS-NOCV and detected by IR spectroscopy as a red shift of the bound N2 vibrational frequency is shown as a cartoon “boxing match” between N2 (blue glove, σ-donation) and [B6Cl5]- (red gloves, π-backdonation). The measured spectrum is shown on the outer surface of the boxing ring. Further information, including interaction with CO and H2O and comparison with [B12X11]−, can be found in the Research Article by J. Warneke and co-workers (DOI: 10.1002/chem.202302247).

Superelectrophilic anions constitute a special class of molecular anions, which show strong binding of weak nucleophiles despite their negative charge. In this study, the binding characteristics of smaller gaseous electrophilic anions of the types [B6X5]- and [B10X9]- (with X = Cl, Br, I) are computationally and experimentally investigated and compared to those of the larger analogues [B12X11]-. The positive charge of vacant boron increases from [B6X5]- via [B10X9]- to [B12X11]-, as evidenced by increasing attachment enthalpies towards typical σ-donor molecules (noble gases, H2O). However, this behavior is reversed for σ-donor-π-acceptor molecules. [B6Cl5]- binds strongest to N2 and CO, even stronger than to H2O. Energy decomposition analysis confirms that the orbital interaction is responsible for this opposite trend. The extended transition state-natural orbitals for chemical valence method shows that the π-backdonation order is [B6X5]- > [B10X9]- > [B12X11]-. This predicted order explains the experimentally observed red shifts of the CO and N2 stretching fundamentals compared to those of the unbound molecules measured by infrared photodissociation spectroscopy. The strongest red shift is observed for [B6Cl5N2]-: 222 cm-1. Therefore, strong activation of unreactive σ-donor-π-acceptor molecules (commonly observed for cationic transition metal complexes) is achieved with metal-free molecular anions.

The crystal structures of (Et4N)(2)C2S6, (Et4N)(2)C2S5, (Et4N)(2)CS4, (Et4N)HCS3, (Et4N)(2)CS3 center dot 2H(2)O and (Et4N)(2)CS4-y center dot yH(2)O (y=0.69) were determined by single-crystal X-ray diffraction analysis at 150 K. For the first time, salts with the C2S52- and HCS3- anions could be synthesized.

Two phosphorous(iii) isocyanates, ClP(NCO)2 and P(NCO)3 were isolated as neat substances and characterized with IR (gas-phase and Ne-matrix), Raman (solid), and 31P NMR spectroscopy. Their vibrational spectra were analyzed in terms of a single conformer with the aid of quantum chemical computations at the B3LYP/6-311+G(3df) level of theory. In line with the theoretically computed favorable syn-configuration of the NCO ligands with the sterically active lone-pair electrons on the central phosphorous atom (nP), low-temperature single-crystal X-ray diffraction (XRD) of solid ClP(NCO)2 reveals a Cs symmetric syn-configuration for both NCO ligands with weak CO (r = 2.9692(4) Å) van der Waals (vdW) interactions. In the binary isocyante P(NCO)3, all the three NCO ligands adopt similar syn-configuration with nP, leading to a propeller-shaped structure with slightly distorted C3v symmetry due to steric repulsion of the NCO ligands and the PO vdW interactions (r = 3.1901(1) Å) in the solid state.

The crystal structures of (Et 4 N) 2 C 2 S 6 , (Et 4 N) 2 C 2 S 5 , (Et 4 N) 2 CS 4 , (Et 4 N)HCS 3 , (Et 4 N) 2 CS 3 ⋅ 2H 2 O and (Et 4 N) 2 CS 4‐y ⋅ yH 2 O (y=0.69) were determined by single‐crystal X‐ray diffraction analysis at 150 K. For the first time, salts with the C 2 S 5 2− and HCS 3 − anions could be synthesized.

The title compound, tetraethylammonium tetrathiorhenate, [(C2H5)4N][ReS4], has, at room temperature, a disordered structure in the space groupP63mc(Z = 2, α-phase). A phase transition to the monoclinic space groupP21(Z = 2, γ-phase) at 285 K leads to a pseudo-merohedral twin. The high deviation from the hexagonal metric causes split reflections. However, the different orientations could not be separated, but were integrated using a large integration box. Rapid cooling to 110–170 K produces a metastable β-phase (P63,Z = 18) in addition to the γ-phase. All crystals of the β-phase are contaminated with the γ-phase. Additionally, the crystals of the β-phase are merohedrally twinned. In contrast to the α-phase, the β- and γ-phases do not show disorder.

Electronic structure, collision-induced dissociation (CID) and bond properties of closo-[B6X6]2- (X = Cl-I) are investigated in direct comparison with their closo-[B12X12]2- analogues. Photoelectron spectroscopy (PES) and theoretical investigations reveal that [B6X6]2- dianions are electronically significantly less stable than the corresponding [B12X12]2- species. Although [B6Cl6]2- is slightly electronically unstable, [B6Br6]2- and [B6I6]2- are intrinsically stable dianions. Consistent with the trend in the electron detachment energy, loss of an electron (e- loss) is observed in CID of [B6X6]2- (X = Cl, Br) but not for [B6I6]2-. Halogenide loss (X- loss) is common for [B6X6]2- (X = Br, I) and [B12X12]2- (X = Cl, Br, I). Meanwhile, X˙ loss is only observed for [B12X12]2- (X = Br, I) species. The calculated reaction enthalpies of the three competing dissociation pathways (e-, X- and X˙ loss) indicated a strong influence of kinetic factors on the observed fragmentation patterns. The repulsive Coulomb barrier (RCB) determines the transition state for the e- and X- losses. A significantly lower RCB for X- loss than for e- loss was found in both experimental and theoretical investigations and can be rationalized by the recently introduced concept of electrophilic anions. The positive reaction enthalpies for X- losses are significantly lower for [B6X6]2- than for [B12X12]2-, while enthalpies for X˙ losses are higher. These observations are consistent with a difference in bond character of the B-X bonds in [B6X6]2- and [B12X12]2-. A complementary bonding analysis using QTAIM, NPA and ELI-D based methods suggests that B-X bonds in [B12X12]2- have a stronger covalent character than in [B6X6]2-, in which X has a stronger halide character.

The supramolecular recognition of closo,closo-[B21H18](-) 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 . B21H18- complexes in the gas phase. The thermodynamic signature of solution-phase binding is exceptional, the association constant for the gamma-CD complex with B21H18- reaches 1.8x10(6) M-1, which is on the same order of magnitude as the so far highest observed value for the complex between gamma-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 B21H18- 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.

Dye-loaded polymer nanoparticles (NPs) emerge as a powerful tool for bioimaging applications, owing to their exceptional brightness and controlled small size. However, aggregation-caused quenching (ACQ) and leakage of dyes at high loading remain important challenges of these nanomaterials. The use of bulky hydrophobic counterions has been recently proposed as an effective approach to minimize ACQ and dye leakage, but the role of counterion structure is still poorly understood. Here, a systematic study based on ten counterions, ranging from small hydrophilic perchlorate up to large hydrophobic tetraphenylborate derivatives, reveals how counterion nature can control encapsulation and emission of a cationic dye (rhodamine B octadecyl ester) in NPs prepared by nanoprecipitation of a biodegradable polymer, poly-lactide-co-glycolide (PLGA). We found that increase in counterion hydrophobicity enhances dye encapsulation efficiency and prevents dye adsorption at the particle surface. Cellular imaging studies revealed that ≥95 % encapsulation efficiency, achieved with most hydrophobic counterions (fluorinated tetraphenylborates), is absolutely required because non-encapsulated dye species at the surface of NPs are the origin of dye leakage and strong fluorescence background in cells. The size of counterions is found to be essential to prevent ACQ, where the largest species, serving as effective spacer between dyes, provide the highest fluorescence quantum yield. Moreover, we found that the most hydrophobic counterions favor dye-dye coupling inside NPs, leading to ON/OFF fluorescence switching of single particles. By contrast, less hydrophobic counterions tend to disperse dyes in the polymer matrix favoring stable emission of NPs. The obtained structure-property relationships validate the counterion-based approach as a mature concept to fight ACQ and dye leakage in the development of advanced polymeric nanomaterials with controlled optical properties.

By means of MP2 and DFT computations we predict gas-phase acidities and liquid-phase (MeCN) acidities of (di)carboxylic acids derived from icosahedral ortho, meta, and para-carboranes. For comparative purpose, we include the benzoic and phthalic acids. Substitution of benzene by a carborane cage - cage effect - strikingly increases the gas-phase acidity (lower GA) for the (di)carboxylic acids, being the ortho isomers always the most acidic, following the order ortho >> meta > para. The computed GA of the dicarboxylic acid derived from ortho-carborane is far lower than sulphuric acid, due to an enhanced stabilization of the carboxylate through an intramolecular OHO bridge connection, also taking place in phthalic acid. The change of GA relative to ortho, meta and para positions of the carboxylic groups - isomer effect - is larger for carboranes. As regards to liquid-phase (MeCN), the computations show that carborane (di)carboxylic acids also show a larger acidity (lower pK(a)) as compared to the phthalic acids and that the dicarboxylic ortho-carborane is also a superacid in the liquid phase (MeCN), due to the OHO bridge connection in the carboxylate, as in the gas phase. Additional computations show how much of this isomeric effect is to be attributed to the electronic delocalization.

Attempted protonation of the [closo-B9H9]2− under the moisture-free conditions did not afford the expected monoanion [closo-B9H10]−, while its reaction with HCl in dichloromethane afforded the first chlorine-containing monoanion [arachno-B9H12-4,8-Cl2]− in a high yield.

Eleven-vertex closo and nido boron clusters with one or two exo-cyano groups were obtained by a series of consecutive cage-opening and cage-closure reactions starting from K2 [closo-B11 H11 ] (K2 1). In the first step, K2 1 reacts with KCN in water at elevated temperatures to yield [7-NC-nido-B11 H12 ]2- (5 a). Oxidation of 5 a with PbO2 gives [NC-closo-B11 H10 ]2- (2). In analogous subsequent reactions, dianion 2 was converted with KCN regioselectively to [7,9-(NC)2 -nido-B11 H11 ]2- (6 a), which was further oxidized to [(NC)2 -closo-B11 H9 ]2- (3). The {nido-B11 } dianions 5 a and 6 a were protonated to yield [7-NC-nido-B11 H13 ]- (5 b) and [7,9-(NC)2 -nido-B11 H12 ]- (6 b). All anions were studied by NMR spectroscopy and, except for 6 b, salts of all anions were characterized by IR and Raman spectroscopy and by elemental analysis. The position of the cyano group(s) in 5 a and 6 a were confirmed by NMR data and single-crystal X-ray diffraction studies on [Ph4 P]2 5 a⋅CH2 Cl2 and [Et4 N]2 6 a. The {closo-B11 } clusters are fluxional in solution. In the crystal of [EMIm]2 2 the BCN vertex is in the 2-position. Two isomers of dianion 3, [2,3-(NC)2 -closo-B11 H9 ]2- and [2,6-(NC)2 -closo-B11 H9 ]2- , were identified in the crystal of its [Et4 N]+ salt. The peak oxidation potentials Epa of anions 1-3, 5 a, 6 a, 5 b, and [nido-B11 H14 ]- (4 b), determined by cyclic voltammetry, increase with increasing number of cyano groups. Increasing Epa in the order 1<2<3 parallels the increasing reactivity toward cyanide anions.