Crystal chemistry of tetraradial species. Part 4. Hydrogen bonding to aromatic π systems: crystal structures of fifteen tetraphenylborates with organic ammonium cations

Abstract

The aim of this investigation is to provide a classification and examples of N—H …π (and also O—H …π) bonds to the aromatic π systems in organic ammonium tetraphenylborates that would serve as reference for X—H …π(arene) bonds in general. To this end the crystal structures of the tetraphenylborates of the following cations have been determined: Me3NH+, Et3NH+, quinuclidinium, DabcoH+, Et(iso-Pr)2NH+ (monohydrate), (Ph3B)NH[—(CH2)2—]2NHMe+ (Me2CO solvate), Me2NH2+ (MeCN and Et2CO solvates), Et2NH2+, (iso-Pr)2NH2+, azoniacycloheptane, guanidinium (monohydrate), MeNH3+, EtNH3+, and 1-adamantammonium (monohydrate). These structures contain a variety of normal, bifurcated, and trifurcated N—H …π bonds as well as normal O—H …π bonds to the phenyl groups of the anion. The X—H …π bonds will form whenever opportunity arises, even though the result may be unfavourable bonding geometry. Branched bonds and orientational disorder represent compromise solutions in situations where the H(X) hydrogens are presented with competing phenyl acceptors or where the general organization of the crystal structure offers unfavourable bonding conditions to these hydrogens. The distributions of the distances from X or H(X) to the centre of the phenyl-ring skeleton are analyzed in detail, as are also those of the mean X … C and H(X)… C distances to the ring carbons.

Crystal chemistry of tetraradial species. Part 6. Embarras de richesses: lithium cation coordinated by eight O—H … phenyl bonds

“…The geometry of its BC(a), core is, within the statistics, indistinguishable from the corresponding mean geometry (based on many TB anions) reported in ref. 2. The planarity of the phenyl rings is satisfactory (Table C).…”

“…3A). The geometry of this environment is strongly suggestive of 0-H ... secondary and tertiary organic ammonium cations (2,12), the H atoms of a water molecule cannot be placed geometrically, and the results of refining some of the H 2 0 molecules as rigid bodies (using the information from the difference maps) were not sufficiently conclusive. Without unambiguous location of the H(0) atoms the present crystallographic evidence of 0-H ....rr bonding in LiTBw is therefore indirect but (as shown below) no less compelling.…”

“…The L i A H , O coordination in LiTBw is also (for a brief historical review see ref. 2). Reported examples of compared with that in [Li(OH,),](UO,)AsO, (= LiUAw) (7) such bonding have been so sporadic and uncommon that even and also with its nearest formal analog, B e 4 H 2 0 , in simple situations involving one or two X-H ... aromatic)…”

9,10-Bis(7-fluoro-2,5-dioxaheptyl)triptycene

“…The interplanar angles between the arene rings (C3-C8 = A1, C9-C14 = A2 and C15-C20 = A3) on the triptycene are AI^A2 = 116.25 (7), AI^A3 = 121.74 (8) and A2^A3 = 121.68 (8) °. o Hydrogen-bond interactions involve the triptycene arene rings (Bakshi et al, 1994;Gakh et al, 1995).…”

The Basicity of Unsaturated Hydrocarbons as Probed by Hydrogen‐Bond‐Acceptor Ability: Bifurcated NH+⋅⋅⋅π Hydrogen Bonding

“…[31,32] Sometimes one of the acceptors of a bifurcated H-bond is an O-atom, the other an alkyne [19,33,34] or arene. [24,35] Bi-or multifurcated H-bonds are frequently deduced from protein crystallography. [36] The solution phase existence of compounds with bifurcated π-H bonds involving only unsaturated hydrocarbons has not been reported.…”