  Metal--organic frameworks (MOFs) are a family of chemically diverse
materials, with applications in a wide range of fields covering engineering,
physics, chemistry, biology and medicine. Research so far has focused almost
entirely on crystalline structures, yet a clear trend has emerged shifting the
emphasis onto disordered states of MOFs, including "defective by design"
crystals, as well as amorphous phases such as glasses and gels. Here we
introduce a MOF liquid, a strongly associated liquid obtained by melting a
zeolitic imidazolate framework (ZIF), with retention of chemical configuration,
coordinative bonding modes, and porosity of the parent crystalline framework.
We combine in-situ variable temperature X-ray, ex-situ neutron pair
distribution function experiments, and first principles molecular dynamics
simulations to study the melting phenomenon and the nature of the liquid
obtained, focusing on structural characterization at the molecular scale,
dynamics of the species, and thermodynamics of the solid--liquid transition.
