An unprecedented class of multichromic single crystals has been
investigated after their initial discovery almost 15~years ago in industry.
Single crystals have been prepared that are crystallographically identical, yet
may be grown colorless, yellow, or green from crystal to crystal, or
surprisingly, multicolored within the same crystal at all viewing angles, where
one would expect that only a single color would exist. The system examined
consisted of Me
$_{2}$
GaCl complexed with
1,4-bis(2,6-diisopropylphenyl)-1,4-diazabutadiene in varying ratios. The work
described is primarily geared towards understanding the factors leading to the
multichromic nature of the complexes. Our results indicate that the most
plausible explanation for the yellow/green mixed crystals is that the yellow
crystals are contaminated with small amounts of an intensely-colored blue
byproduct. In crystal regions where both the yellow and blue compounds are
found, the crystals appear dark green. Identification of the blue byproduct was
confirmed by X-ray diffraction.
