Hydride Encapsulation by a Molecular Main-Group-Metal Cluster:  Single-Crystal Neutron Diffraction Structure of [{Ph(2-C₅H₄N)N}₆HLi₈]⁺

Abstract

The new very-intense vertical-axis Laue diffractometer (VIVALDI) at the Institut Laue-Langevin has been used to probe the single-crystal structure of [(t-Bu2AlMe2)2Li]-[{Ph(2-C5H4N)N}6HLi8]+, with data proving that the molecular main-group-metal cluster cation component incorporates interstitial hydride. Variations in nitrogen coordination mode and distortion of the metal core are in accord with octahedral hydride coordination (H−Li = 1.92(2), 2.04(2), 2.07(2) Å), two metal centers being nonbonding with respect to hydride (H···Li = 2.86(2) Å).

Metal‐Hydride Bonding in Higher Alkali Metal Boron Monohydrides

“…-[{PhN(2-C 5 H 4 N)} 6 -HLi 8 ] + , [5,6] X-ray analysis revealed encapsulation of the hydride center by a pseudocubic arrangement of alkali metal ions, each face of which was straddled by a bidentate amido ligand. The omission of lithium from the cluster has been noted, with the observation of neutral {PhN(2-C 5 H 4 N)} 6 HLi 7 and, of particular import in understanding the geometrical constraints of these systems, the use of hppH (= 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine) [7] has recently allowed the comparison of [(hpp) 6 HLi 8 ] + with its hydride-free parent cluster [(hpp) 6 Li 8 ] 2+ .…”

“…The omission of lithium from the cluster has been noted, with the observation of neutral {PhN(2-C 5 H 4 N)} 6 HLi 7 and, of particular import in understanding the geometrical constraints of these systems, the use of hppH (= 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine) [7] has recently allowed the comparison of [(hpp) 6 HLi 8 ] + with its hydride-free parent cluster [(hpp) 6 Li 8 ] 2+ . [8] Variation of hydride coordination in the field of Li 7/8 cubanes has been reported, with linear µ 2 -[Am = CyN(2-C 5 H 4 N), Cy = cyclohexyl], octahedral µ 6 -, capped-octahedral µ 7 -, and cubic µ 8 -bonding seen.…”

“…+ [10] and [{Et 3 B(tBu)Li(Et 3 BH)} 2 Li] -[(hpp) 6 HLi 8 ] + , [9] and lead to the view that [Et 3 BH] -might act as an intermediate in hydride capture. This has been subsequently established by DFT methods, which indicated the direct abstraction of hydride from tBuLi through a transition state based on an Et 3 B·tBuLi adduct in preference to the degradation of an in situ generated tetraalkylborate intermediate (Scheme 1).…”

High-speed neutron Laue diffraction comes of age

“…[2][3][4][5][6]. For example, the existence of the hydrogen atoms around the Co cluster in the 8200 Å 3 unit cell of [H 4 Co 4 (C 5 Me 4 Et) 4 ] was proven from a three-day collection (using the blue plates) on a crystal of just 0.6 mm 3 in volume (Fig 2).…”

“…In just a few hours it has yielded detailed atomic structural information on large organic molecules, e.g., Refs. [2][3][4][5][6], shown 2-D magnetic ordering in astounding clarity [7], revealed new magnetic structures [8], allowed full data collection from small crystals inside anvil pressure cells [9], and followed variations of bond lengths with temperature in fine detail [10].…”