The dilithium silylamide [(Me
2
SiN
t
BuLi)
2
O]
2
shows in the temperature range between ambient temperature and 150 K three solid state phases with transition points at 253 K and 163 K which were characterised by means of X-ray diffraction and solid state NMR spectroscopy. In the high temperature phase the dimeric molecules of [(Me
2
SiN
t
BuLi)
2
O]
2
crystallize in the tetragonal space group
P
4
2
/
nmc
. It can be deducted from X-ray diffraction studies that, at room temperature, the four lithium atoms in [(Me
2
SiN
t
BuLi)
2
O]
2
are statistically distributed on two split positions at a distance of 0.89(1) Å. By cooling below 253 K the crystal transforms into an intermediate phase with space group
P
4
2
/
n
. The symmetry of the molecule is reduced from point symmetry (4) over bar 2
m
(D
2d
) to (4) over bar (S
4
). The split positions of the lithium atoms are found in different planes and their distance is slightly reduced from 0.89 Å to 0.81 Å. Solid state NMR spectroscopic measurements and powder diffraction analysis reveal the existence of a monoclinic low temperature phase below 163 K. From
7
Li MAS and
13
C CP/MAS NMR spectroscopic measurements follows furthermore that the disorder of the lithium atoms in the two higher temperature phases (above 163 K) is due to a local dynamic exchange of the four lithium atoms over eight possible positions in the molecule.
7
Li NMR measurements at variable MAS rates reveal a very small activation energy of 11 KJ/mol for the dynamic process with ex hange rates of the lithium atoms in the order of 5 to 15 K Hz. With respect to the lithium atoms in the order of 5 to 15 KHz. With respect to the lithium motions, the dynamics are intramolecular with an intermolecular coupling process due to van-der-Waals forces.