Cyclodiphosphazanes: options are endless

Cyclodiphosphazanes, also known as diazadiphosphetidines, are saturated inorganic ring systems containing alternating trivalent phosphorus and nitrogen atoms. With a rigid planar structure and moderately stable P-N bonds, cyclodiphosphazanes have shown versatility not only in coordination chemistry as both neutral and anionic ligands but also as useful scaffolds in supramolecular chemistry, resulting in a plethora of molecules with interesting structural features. Recent reports on their utility in generating several 3D-coordination polymers including those with sodalite structures, cyclodiphosphazane based N-heterocyclic carbenes and stable biradicaloids highlight the versatility of these novel phosphorus-nitrogen cyclic compounds. This review describes mainly the coordination chemistry of cyclodiphosphazanes as neutral ligands and their applications besides recent advances in cyclodiphosph( iii )azane chemistry. The key points on the empirical model proposed to highlight the coordinating ability of cyclodiphosphazanes to build soft-soft MOFs and an analysis of pertinent structural features are also presented. This short review describes the transition metal chemistry of cyclodiphosphazanes.