Synthesis,structure,and thermal behavior of discrete Co(II),Ag(I),and Pd(II) complexes with 2,3-bis(2-pyridyl)quinoxaline.Insight into coordination modes

摘要

The reactions of 2,3-bis(2-pyridyl)quinoxaline 9bpq)with CoCl_2centre dot6H_2O,Ag9CH_3CN)_4BF_4,and PdCl_2(C_6H_5CN)_2 produce [CoCl_2(bpq)]_2 centre dot2CHCl_3,[Ag(bpq)CH_3CN]_2(BF_4)_2centre dot 2CH_3CN,and [PdCl_2(bpq)],respectively.All the products are discrete 1:1 (metal:bpq)adducts,where the chelation mode lof the bpq is dependent upon the metalatoms.The structure of [CoCl_2(bpq)]_2centre dot 2CHCl_3 is a centrosymmetric Cl-bridged four-membered dimer,[Co_2Cl_2] ,in which the bpq is bonded to the cobalt(II) atom in an anisobidentate mode withthe nitrogen donors of pyridie and pyrazine rings.For [Ag(bpq)CH_3CN]_2(BF_4)_2 centre dot 2CH_3CN,eachbpq ligand connects two tetrahedralsilver(I) ions in a tridentate mode,resulting in a cationic cyclic dimer.The structure of [PdCl_2(bpq)]approximates to a molecular rocking chair withan isobidentate bpq through thenitrogen donors of 2-pyridyl rings.The compunds exhibit significant and characteristic relationships between the structures and their thermalproperties.For [CoCl_2(bpq)]_2 centre dot 2CHCl_3,thesolvate chloroform molecules are safely contained up to 144degC,but drastically evaporate above this temperatue.The striking feature of [Ag(bpq)CH_3CNCN]_2(BF_4)_2 centre dot 2CH_3CN is that the skeletalcyclic dimeris bascally retained after dissociation of the coordianted aceetonitriles in the coordinated acetonitriles in the solid state.