Linear negative thermal expansion in Pd(acac)2

For network forming materials, the wine-rack structure motif is known to facilitate anisotropic structural responses to temperature and pressure variation. Here we propose that linear negative thermal expansion in Pd(acac)(2) can be rationalised through intermolecular interactions that can be mapped on a wine-rack network. By comparison with isomorphous Cu(acac)(2), the decisive role of intermolecular interactions in Pd(acac)(2) for the emergence of collective responsive structural properties is shown. Our results suggest that concepts that have previously been used to understand the responsive behaviour of framework forming materials such as metal-organic frameworks can be transferred to coordination compounds and molecular crystals, underlining that the challenge of enforcing collective structural responsiveness is coupled to the control of distinct, directional chemical interactions.