Nature of weak inter- and intramolecular interactions in crystals. 5. Interactions Na...H—B in a crystal of sodium salt of charge-compensated nido-carborane [9-SMe2-7,8-C2B9H10]−

Abstract

The character of electron density distribution in the C 2 B 3 open face, the influence of the SMe 2 group on the character of electron density distribution, and the nature of the so dium-anion interaction were studied based on the data of high resolution X ray diffraction study of crystals of the sodium salt of charge compensated nido carborane [9 SMe 2 7,8 C 2 B 9 H 10 ] -and quantum chemical calculations for the Na...H-B bonded dimer, the isolated [9 SMe 2 7,8 C 2 B 9 H 10 ] -anion, and the [7,8 C 2 B 9 H 10 ] 2-dianion. The character of electron density distribution in the C 2 B 3 open face is analogous to the electron distribution in the cyclopentadienyl ligand. In nido carborane, a substantial charge redistribution takes place compared to that observed in the closo analogs. The topological analysis of the electron density distribution function demonstrated that the cation-anion interactions are determined pre dominantly by Na...H-B contacts. The total energy of these contacts in the {[9 SMe 2 7,8 C 2 B 9 H 10 ]Na(thf) 2 } 2 dimer estimated from X ray diffraction data is 11.74 kcal mol -1 .Key words: charge compensated nido carboranes, isolobality, nido carborane salts with alkali metals, quantum chemical calculations, Na...B-H contacts, electron density distribu tion, topological theory of Atoms in Molecules, high resolution X ray diffraction study.Alkali metal salts with anionic 11 vertex nido carbo ranes are widely used as starting compounds in the syn thesis of metallocarboranes. 2-5 However, their structures both in solution and in the solid state remained unknown until very recently. In the last years, it has been demon strated that these salts exist predominantly as contact ion pairs both in crystals 6,7 and in solution. 8 The coordination mode of cations in anionic nido car boranes depends substantially on the cation size. In lithium salts with the charge compensated [9 L 7,8 C 2 B 9 H 10 ] -anions (L = SMe 2 or NMe 3 ) and the [7,8 C 2 B 9 H 10 ] 2-dianions, η 5 coordination at the C 2 B 3 open face of the carborane is the main coordination mode, whereas so dium salts are characterized by exo coordination at the B(10)B(11)B(6) face. 6,7In the case of exo coordination, the sodium-anion interaction can be either analogous to interactions in exo nido Os, Ru, 9,10 and Rh 11 complexes with 3c-2e metal...H-B bonds or occur through an interaction of the sodium cation with the electron density localized at the center of the triangular face and on the boron atoms.Actually, the negative charge in carboranes is distributed not only between the hydrogen atoms of the B-H bonds 12 but also over the surface of the triangular face. 13-15 From the geometric standpoint (Na...B and Na...H distances), 6 both types of interactions in sodium salts with the [9 L 7,8 C 2 B 9 H 10 ] -anion are equally probable. In struc tural studies 16,17 of small and medium sized carborane salts with alkali and alkaline earth metal cations, it was hypothesized that the cations interact predominantly with boron atoms. In contrast, Na...H-B ...

A new look at the structure and reactivity of 10-vertex nido-dicarbaboranes

“…The topology of EDD for nido-5,6-C 2 B 8 H 12 has something in common with that reported for closo-and nido-clusters earlier [8][9][10][11][12][13][14][15][16]. Firstly, the bonding in the cage is realized both via multicenter and two-center bonds of reduced order.…”

“…The works using AIM were reported only for a limited number of boranes and carboranes and concerned mainly closo species [8][9][10][11][12][13][14][15]. For these types of clusters it was shown that stabilization of electron-deficient systems is achieved both by accumulation of electronic charge along the bond paths and by its delocalization over the polyhedron surface.…”

Synthesis of 10‐Methylsulfide and 10‐Alkylmethylsulfonium nido‐Carborane Derivatives: B–H···π Interactions between the B–H–B Hydrogen Atom and Alkyne Group in 10‐RC≡CCH2S(Me)‐7,8‐C2B9H11

“…[14][15][16][17] Another approach includes alkylation of the 9-methylthio derivative of nido-carborane [9-MeS-7,8-C 2 B 9 H 11 ] -to give the corresponding 9-alkylmethylsulfonium derivatives 9-R(CH 2 ) n (Me)S-7,8-C 2 B 9 H 11 . [18][19][20] In contrast to the B-dialkylsulfonium derivatives of other polyhedral boron hydrides where racemization at the sulfur atom already proceeds very fast at ambient temperature, [21] in the case of nido-carborane derivatives 9-R(CH 2 ) n (Me)S-7,8-C 2 B 9 H 11 , the activation barrier is much higher because of an interaction of the sulfur lone pair electrons with the B(9)-B(10) antibonding orbital electrons of the nido-carborane cage [22] , and no racemization is observed up to 333 K. [20] As a result, the asymmetrically substituted nido-carborane derivatives 9-R(CH 2 ) n (Me)S-7,8-C 2 B 9 H 11 exist as mixtures of diastereomers which are not very suitable for medical applications.…”

Studies of Multicenter and Intermolecular Dihydrogen B–H···H–C Bonding in [4,8,8′‐exo‐{PPh3Cu}‐4,8,8′‐(μ‐H)3‐commo‐3,3′‐Co(1,2‐C2B9H9)(1′,2′‐C2B9H10)]

“…[21][22][23][24][25] Experimental data relating to electron density (ED) distribution are limited, to the best of our knowledge, to a metallacarborane of nontransition metals: {Na(thf) 2 [9-SMe 2 -7,8-C 2 B 9 H 10 ]} 2 . [26] QTAIM [27] is a powerful method with which to study various types of chemical bonding. In this method, topological analysis of the three-dimensional ED is carried out to divide space into atomic basins with surfaces of zero electronic flux.…”