V. N. Mustyatsa

Aminoguanidinium closo-Borates and Their Reactions with Copper(II) Salts in Aqueous Solutions

Aminoguanidinium hexa-, deca-, and dodecaborates of (AguH)2BnHn· xH2O (Agu = (CN4H6), n= 6, 10, 12; x= 1, 2) composition were synthesized and studied by elemental analysis, magnetic susceptibility, and IR spectroscopy methods. Their reactions with copper(II) salts in aqueous solutions were investigated. A cation–anion interaction was shown to occur in aminoguanidinium closo-borates and to increase in the series B12< B10< B6. Depending on the closo-anion (BnH2–n), the reactions of aminoguanidinium closo-borates with copper(II) salts in aqueous solutions yield either complex compounds (n= 10, 12) or metallic copper (n= 6).

Copper(I) coordination compounds with closo-dodecaborate anion

Copper(I) complexes with a closo-dodecaborate anion were synthesized: Cat[CuB12H12], where Cat = Cs+, Ph4P+, Ph4As+, or RxNH4−x+ (R = Me, Et, Pr, or Bu; x = 3 or 4). The complexes were synthesized from the copper(II)-closo-dodecaborate-sulfur dioxide (sodium sulfite) system. The structure of [Cu2(NCCH3)4B12H12] was determined using X-ray crystallography.

Interaction between a Decahydro-closo-Decaborate(2–) Anion and Aliphatic Carboxylic Acids

Interaction between a closo-decaborate anion B10H2–10and carboxylic acids RCOOH (R = H, CH3, C2H5, iso-C3H7, C4H9) is studied. The mono-, di- tri- and tetrasubstituted products B10H10 – n(OCOR)2–nare formed in sequence with the temperature growth. The reaction follows an essentially regioselective mechanism: only one of all possible isomers forms at every stage of the process. The respective hydroxy-closo-decaborates B10H10 – n(OH)2–nwere prepared by alkaline hydrolysis in aqueous and nonaqueous solutions. All the compounds were identified by chemical analysis and 11B NMR and IR spectroscopy. The crystal structure of [Pb(Bipy)(DMF)(B10H9OH)] · DMF was determined by X-ray diffraction.

Compounds of Undecahydrodecaborate Anion B10H11

Conditions for the synthesis of salts of the B10H11–anion with different cations in the Cat2B10H10+ RCOOH (R = H, CF3; Cat = Me4N+, Et4N+, Bu4N+, Ph4P+, Ph4As+) systems were studied depending on the acid strength (pKa) and size of the cation. It was established that reactions with trifluoroacetic acid give compounds of this anion with any one of the quaternary ammonium, phosphonium, or arsonium cations, while formic acid can only give salts with the largest of these cations.

Structure of the undecahydrodecaborate anion B10H 11 − . Crystal structures of [Ph3PCH2Naph]B10H11 and [Ph3PEt]2B10H10

The crystal structures of [Ph3PCH2Naph]B10H11(I) and [Ph3PEt]2B10H10 (II) are studied (110 K and room temperature, R = 0.0673 and 0.0609 for 4176 and 953 observed reflections in I and II, respectively). It is unambiguously determined that protonation of the B10H102− anion proceeds at one of the faces of the apical belt and results mainly in a significant lengthening of the edges of the centered face [Be-Be, 1.948(4) Å; Ba-Be, 1.770(5) Å and 1.787(5) Å].

The Mechanism of Acid-Catalyzed Nucleophilic Substitution in Decahydro-closo-Decaborate(2–) Anions

The reactions of salts formed by the B10H2–10anion with carboxylic acids were studied. From the model systems Cat2B10H10+ HCOOH (Cat = Et4N+, Bu4N+, Ph4P+, Ph4As+), several intermediates were isolated and characterized. A mechanism was proposed for the replacement of the exo-polyhedral hydrogen atoms in B10H2–10by carboxylate groups in the reactions of Cat2B10H10with carboxylic acids.

Potentiometric sensors with membranes based on ionic liquid tetradecylammonium triethylammonio-closo-dodecaborate

Polymer compositions based on the ionic liquid tetradecylammonium triethylammonium-closododecaborate (TTCD) are proposed as the main components of membranes of potentiometric sensors (ion-selective electrodes) for determining ions [B12H11N(C2H5)3]−. Two types of polymer compositions are considered: conventional, polyvinyl chloride (PVC)-liquid ion-exchanger (solution of TTCD in o-nitrophenyl octyl ether) and another, PVC-TTCD (ionophore-plasticizer). The optimal composition of membranes for both types of electrodes are proposed, and their main electroanalytical parameters, such as selectivity, effect of pH, range of linear response, reproducibility, and stability of potential, were measured. A comparative analysis of the electroanalytical parameters of potentiometric sensors with membranes of two types is given. The detection limits for the electrodes of types I and II are 9 × 10−7 and 4 × 10−7 M. It is shown that [B12H11N(C2H5)3]− anions can be determined by potentiometric titration with indicator electrodes of different types.

Ion-selective electrodes for the determination of closoborate anions

Ion-selective electrodes are proposed on the basis of tetradecylammonium salts for determining [B12H12]2−, [B10H10]2−, and [B10Cl10]2−closoborate anions. Their basic electroanalytical parameters, selectivity, linear response range, detection limit, potential stability, and the pH effect on electrode indications are estimated. The closoborate anions can be arranged in the following series by the selectivity of their determination: [B10Cl10]2− ≫ [B12H12]2− > [B10H10]2−.

Crystal structure of aminoguanidinium hexahydro-closo-hexaborate dihydrate, (CN4H7)2B6H6 · 2H2O

The (HAgu)2B6H6 · 2H2O compound was synthesized and its crystal structure was determined [R = 0.0385 for 2018 reflections with I > 2σ(I)]. The structure consists of HAgu+ cations, centrosymmetric B6H62− anions, and water molecules. The anions have an almost regular octahedral structure. The bond lengths and angles lie within the following narrow ranges: B-B, 1.715–1.726(2) Å; B-H, 1.08–1.14(2) Å; B-B-B, 59.72°–60.29(9)° and 89.63°–90.20(11)°; and B-B-H, 133.2°–137.0(9)°. The HAgu+ cations and water molecules are involved in the O-H⋯O, N-H⋯O, and N-N⋯N hydrogen bonds and participate in numerous (N, O)-H⋯H-B specific interactions with the B6H62− anions, which results in splitting and high-frequency shift of the band of B-H stretching vibrations in the IR spectrum.