Well-designed Syntheses And Luminescent Properties Of Metal-organic Crystal Networks Based On Flexible Bis(pyridyl)Amine

Metal-organic crystal networks （MOCNs） constructed from bis（pyridyl） ligands haveattracted intensive interests in recent years owing to their alluring structural topologiesand potential applications in photoluminescence, molecular magnet, gas storage,catalysis, as well as chiral separation. Up to now, many outstanding works have beenreported, which provide some useful experiences for designing and synthesizingMOCNs. However, research on the synthesis and property of MOCNs constructed fromflexible unsymmetrical bis（pyridyl） ligands are less concerned owing to the fact that theflexible ligands have many degrees of freedom and hence few conformational restraints,as well as the unpredictable nature of such system. On the contrary, the deformability ofthe flexible unsymmetrical bis（pyridyl） ligands also provides possibility for theassembly of MOCNs with novel topological structures. Therefore, it is still achallenging task to seek for effective synthetic strategies to obtain MOCNs withexpected structures and properties through the rational design of flexible unsymmetricalbis（pyridyl） ligands.We summarized the topological structures and properties of MOCNs based onbis（pyridyl） ligands. According to the principle of crystal engineering andsupramolecular chemistry, we design and synthesize six kinds of flexible unsymmetricalbis（pyridyl） ligands and aim to prepare a series of metal-organic or supramolecularcrystal networks with desired architectures or excellent photoluminescent properties,which then provide some valuable strategies for designing and synthesizing such typesof MOCNs. Accordingly,43metal-organic or supramolecular crystal networks aresynthesized under different solution and hydro（solvo）thermal conditions, which theirarchitectures and properties are also characterized. These researches mainly include thefollowing aspects:1. Three flexible unsymmetrical bis（pyridyl） molecules, namely, N-（pyridin-2-ylmethyl）pyridin-3-amine（2,3-L）, N-（pyridin-4-ylmethyl）pyridin-3-amine（4,3-L） and N-（pyridin-3-ylmethyl）pyridin-2-amine （3,2-L） have been employed toreact with CuI through solvothermal reaction, which then led to the formation of fivenew [Cu₃I₂] or [CuI]_nbased MOCNs,[CuI（2,3-La）]_n（1）（2,3-La=N-（pyridin-2-ylmethyl）-N-（pyridin-3-yl） formamide）,[Cu_1.5I（dmtrz）_0.5（PPh₃）]_n·0.5n（CH₃CN）（2）（Hdmtrz=3,5-dimethyl-4H-1,2,4-triazole）,[Cu₂I₂（2,3-Lb）]_n（3）（2,3-Lb=N-（pyridin-2-ylmethylene）pyridin-3-amine）,[Cu₄I₄（4,3-L）]_n·nH₂O （4） and [CuI（3,2-L）]_n（5）. In1-3,the ligands2,3-La,2,3-Lb, and dmtrz-monoanion are obtained from the in situreaction of2,3-L. Adjacent Cu₂I₂rhomboid dimmers, Cu3I2clusters, as well as the chairlike Cu₄I₄clusters are connected by the above three in situ generated ligands to formdouble chain, linear chain and （4,4） layer structure. The Cu₄I₄cubanes in4act as SUBsand are interlinked by the4,3-L ligands to form2-fold interpenetration （44·62） net. Thedouble-stranded [Cu₂I₂]_nladder in5are linked by the3,2-L molecules into layerstructure. The binding energies of the Cu2p_3/2level in the XPS spectra are typical forCu（I） oxidation state. Moreover, luminescent property investigation shows that only5exhibits a strong blue emission at475nm.2. Twelve silver（I） based MOCNs assemble from AgX （X=NO₃-and ClO₄-） salts andsix flexible unsymmetrical bis（pyridyl） ligands, namely, N-（pyridin-2-ylmethyl）pyridin-3-amine （2,3-L）, N-（pyridin-3-ylmethyl）pyridin-2-amine （3,2-L）, N-（pyridin-4-ylmethyl）pyridin-2-amine （4,2-L）, N-（pyridin-4-ylmethyl）pyridin-3-amine （4,3-L）,N-（pyridin-2-ylmethyl）pyridin-2-amine （2,2’-L）, and N-（pyridin-3-ylmethyl）pyridin-3-amine （3,3’-L） have been obtained, in which6-13exhibit helical chain structure,14presents dinuclear structure,15possesses layer structure,16and17show wavelikechain structure. Moreover, the CD spectrum of9is also studied.3. Solvent reaction of five flexible unsymmetrical bis（pyridyl） ligands of2,2′-L,2,3-L,3,2-L,3,3′-L, and4,3-L with HgX₂（X=Cl^-, Br^-and I^-） salts leads to theformation of fourteen mercury（II） based MOCNs, namely [Hg（2,2′-L）X₂]_n[X=Cl （18）and Br （19）],[Hg（2,3-L）X₂]_n[X=Br （20） and I （21）],[Hg（3,2-L）Cl₂]_n（22）, [Hg（3,3′-L）Cl₂]_n（23）,{Hg[（3,2-HL）]X₃}[X=Br （24） and I （25）],[Hg₂I₆]^2-·2（2,2′-HL）⁺（26）,[HgX₄]^2-·2（3,3′-HL）⁺[X=Br （27） and I （28）],[Hg₃Cl₁₀]^4-·2（4,3-H₂L）²⁺（29）,{Hg₂（4,3-L）[（4,3-HL）]X₅}[X=Br （30） and I （31）].18-23exhibit linear or helical chain motifs assembled from the interconnection betweenHgX₂and bis（pyridyl） ligands.24,25,30and31present mono-or dinuclear structures,in which the Hg（II） cations exist in HgNX₃and Hg₂N₂X₅（X=Br and I） spheres.26-29are obtained as ionic salts composed of protonated bis（pyridyl） ligandsand variousmercury-halide clusters,[HgX₄]^2-（X=Br-and I-）,[Hg₂I₆]^2-,[Hg₃Cl₁₀]^4-. The structuraldiversities and evolutions of these architectures can be attributed to the diversemercury-halide clusters, the ligand conformation （cis-trans, trans-cis, trans-trans） aswell as the noncovalent interactions. Moreover, the binding energies of the Hg4f_7/2level in the XPS spectra present regular decrease from Cl-containing, Br-containing, toI-containing complexes. For the N1s, the different binding energies in the XPS spectracan be attributed to the N atoms with different chemical environments.4. Self-assembly of different inorganic acids （HNO₃and HClO₄） and theaforementioned six flexible unsymmetrical bis（pyridyl） ligands results in the formationof twelve supramolecular networks,（2,2′-H₂L）²⁺·2NO₃^-（32）,（3,2-H₂L）²⁺·2NO₃^-（33）,（4,2-H₂L）²⁺·2NO₃^-（34）,（2,3-H₂L）²⁺·2NO₃^-（35）,（3,3′-H₂L）²⁺·2NO₃^-（36）,（4,3-H₂L）²⁺·2NO₃^-（37）,（2,2′-H₂L）²⁺·2ClO₄^-（38）,（3,2-H₂L）²⁺·2ClO₄^-（39）,（4,2-H₂L）²⁺·2ClO₄^-（40）,（2,3-H₂L）²⁺·2ClO₄^-（41）,（3,3′-H₂L）²⁺·2ClO₄^-（42）,（4,3-H₂L）²⁺·2ClO₄^-（43）. It is interesting to note that anion···π interactions are alldetected in the twelve supramolecular networks. Diverse supramolecular patterns areobtained from the bis（pyridyl） ligands and inorganic acids with the assistance of varioussupramolecular interactions, such as hydrogen bonds, π···π stacking, as well as C-H···π.Moreover, the networks constructed from the perchlorate exhibit strong blue emission atroom temperature.