Chemical reactivity between As and N 2 ,l eading to the synthesis of crystalline arsenic nitride,i sh ere reported under high pressure and high temperature conditions generated by laser heating in ad iamond anvil cell. Single-crystal synchrotron X-rayd iffraction at different pressures between 30 and 40 GPaprovides evidence for the synthesis of acovalent compound of AsN stoichiometry,crystallizing in acubic P2 1 3 space group,inwhich eachofthe two elements is single-bonded to three atoms of the other and hosts an electron lone pair,i n at etrahedral anisotropic coordination. The identification of characteristic structural motifs highlights the key role played by the directional repulsive interactions between non-bonding electron lone pairs in the formation of the AsN structure. Additional data indicate the existence of AsN at room temperature from 9.8 up to 50 GPa. Implications concern fundamental aspects of pnictogens chemistry and the synthesis of innovative advanced materials.

We report the high-pressure structural characterization of an organic polyiodide salt in which ap rogressive addition of iodine to triiodide groups occurs.C ompression leads to the initial formation of discrete heptaiodide units, followed by polymerization to a3Danionic network. Although the structural changes appear to be continuous,t he insulating salt becomes as emiconducting polymer above1 0GPa.T he features of the pre-reactive state and the polymerized state are revealed by analysis of the computed electron and energy densities.T he unusually high electrical conductivity can be explained with the formation of new bonds.Polyiodides (PIs) in crystal form were discovered about 200 years ago. [1] Their structural diversity,which is due to the bonding flexibility of iodine,r emains the subject of continuous interest. [2][3][4] Nowadays,v arious PIs are known, ranging from I 3 À to I 29 3À ,with the general formula I nÀ 2 m+n and n up to 4. Their building blocks consist of I 3 À as adonor and I 2 as an acceptor forming ac harge transfer (CT) complex. CT complexes can interact further to form extended structures with various topologies,u pt oc ubic networks.A st he aggregation of iodine units is somewhat unpredictable,t he design of PIs is not easy.Moreover,the classification of higher units is,thus far,pragmatically based on the distance between iodine atoms,but universal criteria are still lacking.Different theoretical approaches to study bonds in PIs exist, for example,calculations of the potential energy surface and bond order, [5] energy decomposition analysis (EDA), [6] analysis of the electron density and its Laplacian at bond critical points (BCP), [7] theelectron localization function, and the one-electron potential. [8] Furthermore,t he energy den-

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Iodine atoms align into a 1D polymeric polyiodide chain, stabilized with the surrounding phenanthrolinium cations.