  We show that ZIF-4, a metal-organic framework (MOF) with a zeolitic
structure, undergoes a crystal--amorphous transition on heating to 300
$^\circ$C. The amorphous form, which we term a-ZIF, is recoverable to ambient
conditions or may be converted to a dense crystalline phase of the same
composition by heating to 400 $^\circ$C. Neutron and X-ray total scattering
data collected during the amorphization process are used as a basis for reverse
Monte Carlo refinement of an atomistic model of the structure of a-ZIF. We show
that the structure is best understood in terms of a continuous random network
analogous to that of a-SiO$_2$. Optical microscopy, electron diffraction and
nanoindentation measurements reveal a-ZIF to be an isotropic glass-like phase
capable of plastic flow on its formation. Our results suggest an avenue for
designing broad new families of amorphous and glass-like materials that exploit
the chemical and structural diversity of MOFs.
