title: Carboxylic acid functionalized ortho-linked oxacalix[2]benzene[2]pyrazine: synthesis, structure, hydrogen bond and metal directed self-assembly.
abstract: Cyclooligomerization of 2,6-dichloropyrazine 4 and benzyl 2,3-dihydroxybenzoate 5 under microwave irradiation resulted in a racemic pair of ester functionalized ortho-linked oxacalix[2]benzene[2]pyrazine 6, which was further transformed to the corresponding racemic carboxylic acid functionalized ortho-linked oxacalix[2]benzene[2]pyrazine 3. Both enantiomers of 3 adopt 1,3-alternate conformations with their two carboxylic acid groups pointing to opposite directions in the solid state. Enantiomers of 3 form a step-like one-dimensional supramolecular polymer via intermolecular hydrogen bond interactions between the carboxylic acids for crystals obtained in methanol. No hydrogen bonds were formed between the carboxylic acids for crystals of 3 obtained in pyridine and aqueous guanidine solutions; instead, intermolecular hydrogen bonds between the carboxylic acid groups of 3 and pyridine, as well as guanidinium ions were formed. Under metal-mediated self-assembly conditions, the pyrazinyl nitrogen atoms in 3 interacted with transition metal ions, such as Ag(I), Cu(II) and Zn(II), and resulted in the formation of four new metal-containing supramolecular complexes. Metallomacrocycles 7, 8 and 9 were formed by reactions of 3 with Ag(I) or Cu(II) ions by bridging two ligands 3 in the equatorial region via M-N coordination bonds. A one-dimensional coordination polymer 10 was generated by reaction between ligand 3 and Zn(II) ions, and a cage-based structure is presented in 10 by bridging of the cyclophane units by Zn(2+) ions via Zn-N and Zn-O bonds.
authors.affiliation: Division of Supramolecular Chemistry and Medicinal Chemistry, Key Laboratory of Brain Functional Genomics, MOE, East China Normal University, Shanghai, China.
authors.forename: Ling-Wei
authors.initials: LW
authors.lastname: Kong
authors.forename: Ming-Liang
authors.initials: ML
authors.lastname: Ma
authors.forename: Liang-Chun
authors.initials: LC
authors.lastname: Wu
authors.forename: Xiao-Li
authors.initials: XL
authors.lastname: Zhao
authors.forename: Fang
authors.initials: F
authors.lastname: Guo
authors.forename: Biao
authors.initials: B
authors.lastname: Jiang
authors.forename: Ke
authors.initials: K
authors.lastname: Wen
mesh_terms: D002264:Carboxylic Acids / Q000737:chemistry; D056831:Coordination Complexes / Q000737:chemistry*; D019216:Metals, Heavy / Q000737:chemistry*; D008968:Molecular Conformation; D015394:Molecular Structure; D011719:Pyrazines / Q000138:chemical synthesis / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D002264:Carboxylic Acids; D056831:Coordination Complexes; D019216:Metals, Heavy; D011719:Pyrazines