Synthesis And Characterization Of Inclusion And Coordination Compounds Of Bidentate Betaine Derivatives Containing Aromatic Rings

As zwitterionic compounds, the molecules of betaine derivatives (prototypeMe3N+CH2COO-) are electroneutral and bear both–N+R3cations and–COO-anionson them. The existence of naked carboxylate groups–COO-enables these kinds ofcompounds be good ligands towards metal ions and excellent hydrogen bondacceptors.In present study, six bidentate bataine derivatives which contain various kinds ofaromatic ring systems, namely,9,10-bis(4-carboxy-pyridinium)anthracene (L1),9,10-bis(3-carboxy-pyridinium)anthracene (L2),1,4-bis(4-carboxy-pyridinium)Naphthalene (L3),1,5-bis(3-carboxy-pyridinium)naphthalene (L4),4,4’-bis(4-carboxy-pyridinium)diphenyl (L5) and4,4’-bis(3-carboxy-pyridinium)diphenyl (L6) have been synthesized, and among them L4, L5and L6are firstsynthesized ones. By reacting these compounds with various metal salts and smallorganic guests, single crystals of six metal coordination compounds, namely,{[Ce(L1)1.5(H2O)2]·3(NO3)·6(H2O)}n(1),{[Pr(L2)2(H2O)4]2·6ClO4·8H2O·L2}n(2),{[Ag2L2(DMSO)2(H2O)2]·2ClO4}n（3）{[Cu2(L2)2(DMSO)(H2O)5]·2DMSO·10H2O·Cl·3ClO4}n(4),{[ZnL2(Cl)2]·DMSO·2H2O}n(5),{{[Mn(L5)2(H2O)2]·2ClO4·8H2O·L5}n(11), and three hydrogen bonded inclusion compounds, namely,(L3·DMSO·2H2O)n(7),[L3·(C10H10N2)0.5·2H2O]n(8) and (L3·C6H8N2·H2O)n(9),have been obtained and characterized by IR spectrum, TG and single crystal X-raydiffraction structure analysis method.The results show that:(1) In the coordination compounds of third row transitionmetal ions, the carboxylate groups usually act in a monodentate coordination mode,however, the syn-syn and chelate/one atom bridging modes are preferred in rare earthcoordination compounds as exampled in1, owing to the larger radii of Ln(III) ions. Inaddition, because the4f orbitals of Ln(III) ions are involved in coordination bondingthe coordination number of Ln(III) ions are usually high.(2) Both in3and4the metalions are bridged by L2molecules forming zig-zag chains. However, in4the aqualigands on Cu(II) atoms of one chain linked to the pendent oxygen atoms of thecarboxylate groups on the neighboring chain constructing one-dimensional ribbonstructures.(3) Unlike other compounds, in5the counter Cl-anions are involved in coordination, and both carboxylate groups of L2molecule moledendately ligate toZn(II) atom, thus forming a bucket-like discrete coordination molecule. By π–πinteractions between the aromatic rings, the molecules of5are arranged to a layerpattern.(4) In11, the central Mn(II) atom is coordinated by two carboxylate groupseach from a molecule of L5forming a discrete coordination cation, Hydrogen bondsbetween the lattice water molecules, aqua ligands and coordination free carboxylategroups link the cartions to a layer containing tunnels. On the other hand, coordinationfree L5molecules are linked by hydrogen bonds between water molecules andcarboxylate groups to zig-zag chains, which penetrate different lays thus resulting athree-dimensional structure.(5) Compounds7,8and9are inclusion compounds withL3and water molecules forming host framework, and organic small molecules DMSO,4,4’-bypyridyl and benzene-1,3-diamine as guest entities. In both7and8, adopting“U” conformation and oppositely aligned L3molecules are linked by hydrogen bondsbetween carboxylate groups and water molecules producing tubes. The neighboringtubes are agglutinated by π–π stacking thus generating the host framewoke, and DMSOor4,4’-bipyridyl molecules are hosted inside the tubes. There are no significantinteraction between the guest molecules and the host framework other than van deWaals interactions. However, in9one of the-NH2groups on benzene-1,3-diaminemolecule forms strong hydrogen bond with the carboxylate group of L3molecule,which destroys the tube structure, and another kind of inclusion compound is resulted.