| To meet the urgent demand of energetic materials for weapons and equipment in the future and break through the limit of energy storage and release for traditional CHON energetic materials,energetic metal complexes stand out from many technical approaches by virtue of their high density,high energy,good stability,and adjustable structure.Unfortunately,the solvent molecules in energetic complexes result in poor thermal stability and energy property.Compared with 1D and 2D energetic metal complexes,there are stronger interactions for higher dimension between metals and ligands,which tends to better stability and detonation performance.Therefore,the current research difficulty and focus is that solvent-free and high-dimensional energetic complexes were constructed to improve energy and safety.Herein,we focused on the key issues of balancing the energy and safety of energetic complexes.Twenty new energetic complexes were successfully prepared and characterized by structural regulation using bitetrazole derivatives with abundant coordination sites and luxuriant coordination patterns as energetic ligands.Their structure,thermal stability,detonation performance,mechanical sensitivity,thermal catalysis for ammonium perchlorate（AP）,laser initiation,and combustion characteristic were investigated.This study provides new ideas for constructing high-dimension solvent-free energetic complexes and supports data for promoting their practical application.The work is as follows:（1）Four series of energetic complexes were designed,prepared,and characterized.Based on four bitetrazole derivatives,including H2BTO,H3BTT,H2NBTT,and H3OBTT,twenty new energetic complexes were successfully prepared by regulating electric-rich of ligands to enhance the coordination ability and enrich the coordination modes:[Ln2（BTO）3（H2O）8]n·2H2O（1-4:Ln=La,Ce,Pr,Sm）,[Mn3（BTT）2（H2O）2]n·2H2O（5）,[Cu（HBTT）（H2O）]n·H2O（6）,{[Zn（HBTT）]2-[NH2（CH3）2+]2（H2O）2}·H2O（7）,[Pb3（BTT）2]n（8）,[Pb（NBTT）（H2O）2]n（9）,[Li2（HOBTT）（H2O）]n·2H2O（10）,[Na2（HOBTT）（H2O）2]n·H2O（11）,[K（H2OBTT）]n（12）,[Cs2（HOBTT）]n（13）,[Fe4（OBTT）4（H2O）8]·16H2O（14）,{[Cu（OBTT）]2-[NH2（CH3）2+]2}n（15）,[Ag2（HOBTT）]n（16）,[Cd3（OBTT）2（H2O）2]n·4H2O（17）,[Pb（HOBTT）（H2O）2]n（18）,[Pb（HOBTT）]n（19）,and[Pb3（OBTT）2]n（20）.Among them,7 and14 belong to 0D complexes,complexes 9 displays 1D chain structure,complexes 1,2,3,4,6,10,11,and 18 are 2D layer structures,and others are 3D metal-organic framework structures（EMOFs）.The low-dimensional complexes were restricted by the coordination water molecules to form 3D frame structures.Additionally,there are six solvent-free 3D EMOFs.In detail,complex 8 is a crystal density of 3.344 g cm-3.Interestingly,all eleven theoretically existing coordination sites of each deprotonated BTT3-ligand are involved in coordination,implying a rich coordination mode and excellent coordination ability.EMOF 12 is constructed by the hexadentate ligand H2OBTT-with chelating or bridging five K+.Three solvent-free 3D EMOFs（13,16,and 19）were obtained by an electric-rich HOBTT2-ligand.EMOF 20 with a crystal density of 4.080 g·cm-3 was obtained based on the stronger electric-rich OBTT3-ligand to chelate or bridge eight Pb2+.Moreover,we propose an effective approach for the controllable modulation of the structure models of energetic complexes.Three complexes 18-20 with the same ligand and metal center were designed,which realize dimension enhancement and avoid solvent molecular coordination.This strategy is a breakthrough in constructing high-dimensional solvent-free energetic complexes.（2）The energy and safety of energetic complexes were studied.The thermal stability of energetic complexes was studied by DSC and TG,their mechanical sensitivity was measured by the BMA method,and their detonation performance was calculated by MS software combined with the K-J equation.The results indicated that complexes with high dimensional possess better thermal stability usually.For nine EMOFs,their thermal decomposition peaks are between 300℃and 442℃.The sensitivities of solvent-free EMOFs 8,12,13,and 16 are better than that of RDX and HMX.The sensitivities of complexes 18-20 with the same metal and ligand are different due to different structures.They are sensitive to impact stimuli,but the friction sensitivities are significantly 240 N,84 N,and 10 N,respectively.Their detonation properties are more excellent than that of RDX and HMX.In general,except for the composition of energetic complexes,the effects of solvent molecules and frame structures on energy and safety cannot be ignored.（3）Based on the excellent catalytic activity of Pb（Ⅱ）,Cu（Ⅱ）,Zn（Ⅱ）,and Cd（Ⅱ）,the effects of complexes 6,7,9,15,and 17 on the thermal decomposition of AP were studied.The results show that the catalytic effect of copper energetic complexes 6 and 15 is best,which can dramatically reduce the thermal decomposition temperature and activation energy of AP in the HTD stage by 79.6℃,89.9℃,31.40 k J·mol-1,and 62.16 k J·mol-1,respectively.They are the candidates for combustion catalysts.The mechanism study shows that the HTD stage produces metal oxides along with the decomposition of complexes,which can promote the further decomposition of AP,improve the system energy and release a large number of gas products.（4）The laser initiation of energetic complexes was evaluated by a laser initiation device and a verification board.The results show that both the oxygen balance and the solvent molecule greatly affect the initiation ability of energetic complexes.So the laser response-ability of energetic complexes can be effectively improved by removing the solvent,enhancing the dimension,and improving the oxygen balance.Thus,the initiation threshold of energetic complexes is greatly reduced,and the power capability is significantly enhanced.EMOF 20detonates after laser irradiation at 67.5 ms corresponding to the initiation threshold of 364.5m J.The combustion characteristics of alkali-based energetic complexes 10-13 were studied by laser ignition.Their characteristic flames were red,bright yellow,orange-red,and orange,respectively.Solvent-free 3D EMOF 12 has the longest stable combustion time of 1.400 s.Hence,it is a potential pyrotechnic with high energy,insensitive,and good thermal stability.（5）When solvents are removed by heating,the process and mechanism of EMOF 5 were studied.The frame structure of 5 is heat-resistant 351℃with an exothermic peak temperature of 442℃,implying that the solvent molecules will be removed by heated treatment.The result indicates that EMOF 5 features a breathing effect.In detail,the removal of DMF and free water molecules is accompanied by a transition from a six-coordination to a five-coordination mode of Mn.Moreover,the five-coordination Mn recovers to six-coordination under certain circumstances.The whole process is a single crystal transformation with an intact frame. |
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