An Approach to the Crystal Engineering of Coordination Networks

Abstract

Molecular networks, in principle infinite architectures, are large size molecular assemblies (10-6-10-3 m scale) or hyper molecules composed of molecular components with defined structures and coonectectivity patterns between the components. The construction of molecular networks with predicted and programmed structure may hardly be envisaged through stepwise classical synthesis using covalent linkages. However, the preparation of such higher-order materials may be attained through iterative process based on self-assembly [1-11] of individual tectons [8] (from Greek TEKTON, builder) [3, 4]. In principle, tectons may be organic modules and/or metallic centres bearing in their structure specific informations (molecular algorithms) dealing with the formation processes and the final structure of molecular networks. Thus, molecular tectonics [9], based on molecular programming, deals with the formation of molecular networks in solution or in the solid state. Operational concepts in molecular tectonics are based on molecular recognition (molecular recognition is employed in a rather broad sens including any type of molecular interaction, in particular metal coordination processes) operating at the level of the complementary tectons and on geometrical and topological features allowing the iteration or repetition of the recognition pattern. Based on the nature of interactions involved in the assembling core, one may classify networks into three classes. When the recognition pattern between tecons is mainly based on inclusion processes, inclusion networks are obtained [12]. When the assembling core is formed by hydrgen bonds, the networks obtained may be called hydrogen bonded networks [6-8. 1315] engaging metal cations, the network formed may be nemed coordination networks [16-22]. However, this classification is rather simplistic since many different type of interactions may operate at the same time and in concert.