The methylgallium-2-carboxylatobenzimidazolato hexamer, [MeGa·C 8 H 4 N 2 O 2 ] 6 ·C 6 H 6 ·(Me 2 C 6 H 4 ) 2 ; synthesis and X-ray crystal structure

• Published in: Canadian journal of chemistry Vol. 77; no. 4; pp. 434 - 438
• Main Authors: Rettig, Steven J, Storr, Alan, Trotter, James
• Format: Journal Article
• Language: English
• Published: 01-04-1999
• ISSN: 0008-4042; 1480-3291
• DOI: 10.1139/v99-064

The room-temperature reaction of Me
3
Ga with benzimidazole 2-carboxylic acid in xylene solvent has yielded a novel crystalline hexameric gallium compound with "MeGa" moieties bridged by the doubly depronotated ligand precursor. Crystals of [MeGa(4,5-benzimidazolato-2-carboxylato)]
6
·(C
6
H
6
)·(m-Me
2
C
6
H
4
)
2
are monoclinic, a = 18.091(2), b = 17.094(2), c = 13.2215(5) Å, Z = 2, space group C2/m. The structure was solved by direct methods and refined by full-matrix least-squares procedures to R (F, I [Formula: see text] 3σ(I)) = 0.064 (R
w
(F
2
, all data) = 0.134). The hexameric Ga complex contains a six-membered ring of Ga atoms, bridged by the benzimidazolate ligands with the benzo rings projecting alternately above and below the Ga plane, thus forming a ball-shaped molecule. The complex could have ideal D
3d
symmetry, but it contains an encapsulated molecule of benzene, which distorts the regularity of the Ga
6
hexagon, and reduces the symmetry of the complex to the crystallographically observed C
2h
. The coordination geometry at each of the two independent GaO
2
N
2
C centres approximates a trigonal bipyramid, with a N
2
C trigonal plane, and the O atoms above and below; average dimensions are Ga-O = 2.176(2), Ga-N = 1.973(3), Ga-C = 1.927(5) Å, O-Ga-O = 165°. The unit cell also contains four m-xylene solvent molecules (outside the molecular cage).Key words: gallium, crystal structure, benzene intercalate, benzimidazolecarboxylic acid.