The experimental detection and synthesis of pentazole (HN ) and its anion (cyclo-N ) have been actively pursued for the past hundred years. The synthesis of an aesthetic three-dimensional metal-pentazolate framework (denoted as MPF-1) is presented. It consists of sodium ions and cyclo-N anions in which the isolated cyclo-N anions are preternaturally stabilized in this inorganic open framework featuring two types of nanocages (Na N and Na N ) through strong metal coordination bonds. The compound MPF-1 is indefinitely stable at room temperature and exhibits high thermal stability relative to the reported cyclo-N salts. This finding offers a new approach to create metal-pentazolate frameworks (MPFs) and enables the future exploration of interesting pentazole chemistry and also related functional materials.

Over the past decades, there has been an intensive quest for theoretical studies and experimental detection of polynitrogen species (e.g., N 4 Fig. 2). The synthetic details are provided in the Supplementary information (Experimental Section, Fig. S1). Crystal of 1 suitable for single crystal X-ray diffraction (XRD) was obtained by recrystallization in ethyl alcohol (Fig. S2). The crystal structures were resolved and refined by direct methods and full-matrix least-squares methods on F2 using SHELXTL program package, respectively (Table S1-S3).Compound 1 crystallizes in monoclinic C2/c space group with a density of 1.547 g cm −3 at 173 K. There are one independent Li(I) ion, one Na(I) ion, two cyclo-N 5 − anions, and four and two halves water molecules contained in the asymmetric unit of 1 (Fig. 2a). Each lithium ion is connected with two different cyclo-N 5 − anions and two water molecules to form a two-connected tetrahedral configuration, while each sodium ion is coordinated to two adjacent cyclo-N 5 − anions and four water molecules to construct an octahedral structure. The bond length of Li-N and Na-N are in the range of 2.0440(3)-2.0680(3) Å and 2.5406(14)-2.6185(14) Å, respectively (Table S2). The adjacent lithium and sodium ions are connected to each other by cyclo-N 5 − anions to form an inorganic chain {LiNa(H 2 O) 2 (N 5 ) 2 } n , while the lithium and sodium ions are alternating in the hybrid chain strictly (Fig. 2b). The adjacent and parallel hybrid chains are further connected by the bridged water molecules, forming the layered

The experimental detection and synthesis of pentazole (HN 5 )a nd its anion (cyclo-N 5 À )h ave been actively pursued for the past hundred years.T he synthesis of an aesthetic three-dimensional metal-pentazolate framework (denoted as MPF-1) is presented. It consists of sodium ions and cyclo-N 5 À anions in whicht he isolated cyclo-N 5 À anions are preternaturally stabilized in this inorganic open framework featuring two types of nanocages (Na 20 N 60 and Na 24 N 60 ) through strong metal coordination bonds.T he compound MPF-1 is indefinitely stable at room temperature and exhibits high thermal stability relative to the reported cyclo-N 5 À salts. This finding offers anew approach to create metal-pentazolate frameworks (MPFs) and enables the future exploration of interesting pentazole chemistry and also related functional materials.Pentazole (HN 5 )a st he last member in the azole series has been attracting worldwide interest over the past century because of its intriguing aesthetic structure and potential applications as high-performance explosives or propellants. [1, 2] As triking feature of pentazole is that five nitrogen atoms enter ahighly symmetric ring with aromatic character. However,t he inherent instability of the cyclopentazolate anion (cyclo-N 5 À ), arising from its high calculated electron affinity of 5.06 eV and five sterically active free-valence electron pairs in the equatorial plane, [3] has severely hampered pentazole chemistry.D espite arylpentazoles having existed for more than half ac entury, [4] the experimental synthesis of the isolated cyclo-N 5 À salts as well as its parent HN 5 molecule in condensed phases still remains ag reat challenge.Inthis regard, intensive studies have demonstrated that the stability of pentazole ring in the arylpentazoles largely depends on the conjugation of the attached aryl ring featuring as trong electron-detonating group. [5] Theoretical calculations also indicated that the CÀNb ond that links the aryl and pentazole group has arather high dissociation barrier than either the N À Nsingle bond or N = Ndouble bond in the pentazole ring. [6] As ar esult, the biggest challenge in synthesizing ab ulk material containing the isolated cyclo-N 5 À anion is how to selectively cleave the relatively strong CÀ Nbond in the arylpentazoles while keeping the considerably weaker N À Na nd N = Nb onds of the pentazole ring intact.In view of the great attraction and unprecedented challenges in the experimental synthesis of the isolated cyclo-N 5 À anion or its parent HN 5 molecule,significant efforts have been devoted to theoretical studies and experimental detection of the cyclo-N 5 À anion in the solution at the start of this study. [7,8] Several pioneering studies in the experimental detection of cyclo-N 5 À anion were achieved through the negative ion electrospray ionization mass spectrometry (ESI-MS) and collision-induced dissociation (CID) as the analytical tool. [9][10][11] Very recently,the direct formation of cyclo-N 5 À in THF solution was successful through the redu...