Synthesis Of Tridentate Betaine Derivatives,Their Applications In Studying Weak Hydrogen Bonding Interactions And Coordination To Metal Ions

Bearing naked carboxylate groups and quarternary ammonium groups, betaine derivatives?prototype?CH₃?₃N⁺CH₂CO₂^-? are structurally analogous to amino acid in zwitterionic form. The structural characters of these kinds of compounds enable them being good hydrogen bonding acceptor and weak hydrogen bonding donor, and thus exhibit variety of hydrogen bonding types in solid state. On the other hand, the naked carboxylate groups of the compounds have strong ligating ability towards metal ions, and readily form coordination compounds with various metal salts.In present study, two tridentate betaine derivatives tri-?4-carboxypridinium-ethyl?-amine?L1? and tri-?3-carboxypridinium-ethyl?-amine?L2? were synthesized and characterized by IR,¹H NMR,EA,TG methods. As we known, they are the first synthesized tridentate betaine derivatives. L1·2H₂O?1?,?L1·3H⁺?·3Cl O₄^-·2H₂O?2?,?L1·3H⁺?·H₂O·3NO₃^-?3?,?C₆H₄O₂??HCl?4? were prepared and subjected to single crystal X-Ray diffraction structure analysis to study the hydrogen bonding interactions in them.Reacting L1 and 1,5-bis?3-carboxypyridinium?-N-methyl–diethylamine?L3? with various metal salts, five coordination compounds, namely, [Mn?L1?3H⁺?₂ ??H₂O?₂??Cl-?₂?5?,[Ag5?L1?₂?H₂O?3]?2H₂O?5Cl O₄^-?6?,[Cu L1?H₂O?4] ?2Cl O₄^-?6H₂O?7?, [Er L1?H₂O?₂] ?5H₂O?3Cl O₄^-?8?, [Ce?L2?₂?H₂O?]??H₂O???Cl O₄^-?3?9? were prepared and their single crystals were obtained. The molecular and crystal structures of resulted compounds have been determined by single X-Ray diffraction structure analysis method, and their thermal stability were demonstrated with TG.The results show that,?1? In 1-4, strong hydrogen bonds O-H???O and weak hydrogen bonds such as C-H???O,O-H????,C/N-H???Cl not only strongly affect the conformation of the molecule, but also play a thumb role in the packing patterns of the molecules in the solid state. In 1, the basic hydrogen bonded unit is a 108-membered ring, however, in 2 a 2D folding double-ladder, in 3 1D wave-like chains and in 4 a 2D plane were constructed.?2? The main coordination modes of carboxylates in L1 are three-atom bridging mode?6, 8? and monodentate mode?5, 7?. In 6, Ag??? ions are bridged by carboxylates forming Ag-Ag structure and in 8, rare earth element Er??? ions are bridged to a 3D channel structure. In 7, two Cu??? are connected by a pair of monodentate ligands to form a 36-membered ring.?3? The coordination modes of metal ions can greatly influence the crystal structure. For instance,with the same coordination modes of carboxylates in compound 5 and 7, different metal ions Mn??? and Cu??? lead to different crystal structures. Besides, lanthanide ions?8? can build more complicated frameworks compared with transition metals?6?, with the factors such as high and variable coordination number.?4? comparing with bidentate derivatives, the one more carboxylate of tridentate derivative can participate in the coordination as well as forming various hydrogen bonds, thus leading to more complicated crystal networks.