Crystal Structures of L2AlH (5) and LAl(NMe2)2 (7).
Complexes 5 and 7 were characterized further by X-ray
crystallography, and the molecular structures are presented
in Figures 3 and 4. Table 1 contains important
bond parameters of compounds 5 and 7, and crystallographic
data for the structural analyses are listed in
Table 2. The X-ray structure reveals that in 5 the aluminum
is five coordinate and in a distorted trigonal bipyramidal
geometry with N1 and N4 in axial positions and
N2, N3, and H in the equatorial plane. The N1-Al1-N4
axis is almost linear [N1-Al1-N4 175.80(5)] in which
the Al-N bond lengths of 2.08(13) A˚ for Al-N1 and
2.100(13) A˚ for Al1-N4 are almost the same. The equatorial
Al1-N1 and Al1-N3 having almost the same bond
lengths. [Al1-N2 1.94(13) A˚ , Al1-N3 1.93(13) A˚ ]. The
deviation from the ideal trigonal-bipyramidal geometry
can be described by an angle of 73.94(26) between the
least-squares plane of N1, Al, N4, H and the equatorial
plane. Clearly, the deviation from ideal trigonal-bypyramidal
geometry arises from the steric requirements of
the two chelating ligands. The axial Al-N bond lengths
are in good agreement with those which are observed in
similar five coordinate aluminum complexes14 where
Al-N bond lengths are found in the range from
2.051(18) A˚ to 2.179(7) A˚ . Colorless compound 7 crystallizes
in the monoclinic space group P21/n, with one
monomer in the asymmetric unit from n-hexane at -78
C. The coordination polyhedron around the aluminum
atom features a distorted tetrahedral environment and
the metrical parameters associated with the PN2 ligand
are quite similar to those of 2 and 3. The Al-N3 and
Al-N4 bond distances are comparable to those reported
in structurally characterized Al-bound terminal NMe2
groups.15 The Al-N1 and Al-N2 bond lengths
(1.937(12)-1.950(12) A˚ ) are longer than the Al-N3 and