Solid-State Reactions of Eicosaborate [B20 H18 ]2− Salts and Complexes

Composites and Materials Prepared from Boron Cluster Anions and Carboranes

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.

Spontaneous Isomerization [trans-B20H18]2– → [iso-B20H18]2– during Cobalt(II) Complexation with Phenanthroline

Abstract

In this work, the cobalt(II) complexation with 1,10-phenanthroline (Phen) in the presence of the [trans-B20H18]2– anion has been studied. At a Co : Phen = 1 : 2 ratio in acetonitrile, a binuclear cobalt(II) complex with bridging chlorine atoms and the boron cluster anion as a counterion [(Phen)2Co(µ-Cl)2Co(Phen)2][trans-B20H18] has been isolated. However, during slow crystallization (within a month), spontaneous isomerization of [trans-B20H18]2– into [iso-B20H18]2– is observed. It has been established by X-ray diffraction analysis that in the crystal of the final compound [(Phen)2Co(µ-Cl)2Co(Phen)2][trans-B20H18]1/3[iso-B20H18]2/3, co-crystallization of both isomeric forms of the octadecahydroeicosaborate anion is observed for the first time. The presence of the iso form of the boron cluster anion is also confirmed by IR spectroscopy data: the spectrum of the product shows a band of stretching vibrations of the BHB bridge groups at 1773 cm–1, which is absent in the trans-form of the boron cluster.

Gold(III) Complexation in the Presence of the Macropolyhedral Hydridoborate Cluster [B20H18]2−

Gold(III) complexation with the octadecahydrido-eicosaborate anion [B20H18]2− was studied for the first time. It was found that when gold(III) complexes [Au(L)Cl2]BF4 (L = bipy, phen) reacted with [B20H18]2−, complexes [Au(L)Cl2]2[B20H18] were isolated. The compounds consisted of a cationic gold(III) complex [Au(L)Cl2]+ and the hydridoborate cluster as a counterion. X-ray diffraction studies revealed weak B–H...Au interactions for both compounds. Note that more reactive anions [BnHn]2− (n = 10, 12) in similar reactions with gold(III) complexes resulted in gold mirror reactions.

Solid-state 1D → 3D transformation of polynitrile-based coordination polymers by dehydration reaction

In crystal structures of two chain coordination polymers [M(tcnopr3OH)₂(H₂O)₂] (M = Ni^II and Co^II; tcnopr3OH^- = [(NC)₂CC(O(CH₂)₃OH)C(CN)₂]^-) based on a N,O or N,N'-bridge polynitrile ligand, the parallel chains are connected via, respectively, C[triple bond, length as m-dash]NH-O and O-HO hydrogen bonds between uncoordinated functional groups of the ligand and coordinated water molecules. Upon heating, both solids undergo dehydration accompanied by degradation of their single crystals. Powder X-ray diffraction showed that non-isostructural triclinic single crystals transformed to isostructural monoclinic compounds. The solid-state reaction yielded 3D coordination polymers [M(tcnopr3OH)₂] (M = Ni^II and Co^II) based on a N,N',O-connected tcnopr3OH^-. Although previously tens of complexes based on tcnopr3OH and similar anions were synthesized and X-ray characterized, none of these contain a tridentate polynitrile ligand. Thus, this study provides evidence that solid-state reactions allow obtaining novel coordination modes of polynitrile ligands. The possible pathways for the transformation of H-bonded networks to 3D coordination polymers are discussed on the basis of the topological approach. Applicability of the topological approach to predict possible networks of solid-state reaction products based on the crystal structures of initial compounds is demonstrated.

Silver(I) and Copper(I) Complexation with Decachloro-Closo-Decaborate Anion

A series of complexation reactions of silver(I) and copper(I) in the presence of a polyhedral weakly coordinating [B10Cl10]2− anion has been carried out. The effect of the solvent and the presence of Ph3P on the composition and structure of the reaction product were studied. Eight novel complexes were obtained and characterized by 11B Nuclear magnetic resonance, Infra-Red, and Raman spectroscopies as well as powder and single-crystal X-ray diffraction techniques. The [B10Cl10]2− anion demonstrated weaker coordinating ability towards coinage metals than [B10H10]2− at similar reaction conditions. The [B10Cl10]2− anion remains unreacted in the copper(I) complexation reaction, while in the absence of competing ligands, we obtained the first complexes containing decachloro-closo-decaborate anion directly coordinated by the metal atom. The bonding between metal atoms and the boron cluster anions was studied using the atomic Hirshfeld surfaces. Besides edge and face coordination of the polyhedral anion, this method allowed us to reveal the Ag–Ag bond in crystal of {Ag2(DMF)2[B10Cl10]}n, the presence of which was additionally supported by the Raman spectroscopy data.

Photochromic System among Boron Hydrides: The Hawthorne Rearrangement

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 B₂₀H₁₈^2- 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 B₂₀H₁₈^2- 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 B₂₀H₁₈^2- photo- and thermal isomerization processes as the Hawthorne rearrangement.