Dense inorganic-organic coordination polymers with a perovskite-like architecture exhibit fascinating properties such as multiferroic behaviour, semiconductivity and tunable mechanical properties. For solid-state perovskites, there are rigid-body guidelines to explain the stability and formation of structural features that allow for tuning properties over a wide range. In inorganic-organic perovskites, however, crystal engineering is a more challenging task due to the higher bonding complexity.  Particularly, entropic effects originating from the relatively low densities and hydrogen bonding interactions have long been underestimated in such frameworks. In this presentation I will discuss the crystal chemistry and dynamic properties of inorganic-organic hybrid perovskites. The focus will be laid on entropy in inorganic-organic perovskites and how our understanding of such effects has developed over the past years.[1]

[1] K. T. Butler, A.Walsh, A. K. Cheetham, G. Kieslich, Chem. Sci. 2016, DOI: 10.1039/C6SC02199A