Syntheses, Structures And Magnetic Properties Of Coordination Polymers With Pseudohalides And Iner-salt-type Dicarboxylate Coligands

The design and preparation of polynuclear complexes(especially,clusters of high nuclearity and coordination polymers) and coordination polymers have attracted considerable interest because of the desire of obtaining novel supermolecular architectures and their importance in understanding the mechanism of magnetic interaction and the magneto-structural correlation.The pseudohalides ions such as azide,thiocyanate and cyanate are among the most extensively studied bridges,and their abilities in bridging metal ions in various modes,effectively propagating magnetic exchange of different nature,building extended networks with diverse topologies,and generating new magnetic phenomena have been demonstrated by a plethora of studies.In this thesis,we selected transition metal ions as spin carriers,inorganic small molecules such as azide ions,cyanate ions as transmitting magnetic exchange bridging ligands and inner-salt-type ligands as coligands to synthesize magnetic complexes.The ligands used are 1,3-bis(4-carboxylato-1-pyridinium-)propane(L¹), 1-carboxymethylpyridinium-3-carboxylate(L²),1-carboxymethylpyridinium-4-carboxy late(L³).A series of complexes with zero,two and three dimensional structures have been synthesized and characterized by single crystal X-ray analysis,IR,elemental analyses,and some of them have also been characterized by variable-temperature and variable-field magnetic measurements.The main points are as follows:1.Coordination compounds with 1,3-bis(4-carboxylato-1-pyridinium-)propane (L¹) as co-ligands.(a) Four novel Mn(â…¡) coordination polymers with different structures and magnetic properties have been obtained,we have characterized a novel self-catenated 3D network with unprecedented azide-bridged tetramanganese(â…¡) clusters as eight-connecting nodes(compound 1).The formation of the net benefits from the unique combination of azide bridges and zwitterionic dicarboxylate ligands. The discovery of this new net enriches our knowledge of structural topologies,and may suggest the great potential of constructing new highly-connected and/or self-catenated networks from metal-azide clusters.Magnetic measurements show an overall antiferromagnetic behavior.In the chain constructed by metal ions and bridging ligands of compound 2,there are three crystallographically independent Mn (â…¡) ions,and in which metal ions are connected by one azido bridge and two syn-syn carboxylate bridges.Each chain is linked to four others by L¹ ligands to produce a 3D network.The linkers divided the interchain space into small channels,in which perchlorate anions are enclosed.Magnetic measurements indicated that dominant antiferromagnetic coupling exists between neighboring manganese(â…¡) ions in the compound.In the structure of compound 3,metal ions are also connected by one azido bridge and two syn-syn carboxylate bridges to give an 1D uniform chain which is further linked by L¹ ligands to give rise to 2D layer.Interestingly,a mononuclear Mn(â…¡) complex is enclosed in the 2D layer.The coordination sites of Mn2 consist of two oxygen atoms from two water molecules and four nitrogen atoms from four terminal azide ions.Magnetic measurements show dominant antiferromagnetic coupling between neighboring manganese(â…¡) ions in the compound.Compound 4 is a 2D coordination polymer built by the L¹ interlinking 1D manganese(â…¡) azido chains of altemate double EO azido and double syn-anti carboxylate bridges.For compounds 2,3,4,the fit of magnetic data was done by use of appropriate theoretical models.(b) A mononuclear complex was obtained and in the structure of the complex,the metal ion adopts an octahedral coordination geometry completed by three water molecules, one carboxylato oxygen atom from L¹,and two nitrogen atoms from two thiocyanato anions.There are a lot of intermolecular O—H…O hydrogen bonds involving the carboxylate groups and water molecules.These hydrogen bonds lead to a complicated three-dimensional architecture.In addition,there is a lot of S…S interactions between the thiocyanato ions from neighboring complex molecules.2.Coordination polymers with 1-carboxymethylpyridinium-3-carboxylate(L²) as co-ligands.(a) A Co(â…¡) coordination polymers have been obtained,which consists of end-on azido and syn-syn carboxylato mix-brigded M-N₃/COO chains that are further linked by the L² to give rise to 2D layered structure.In its structure,the 1D Co-N₃/COO chain composed of two kinds of Co(â…¡) ions(in a Co(2)…Co(2)…Co(1)…Co(2)…Co(2) sequence) linked by alternate double EO azido (between Co(2) ions) and mixed one EO azido and double syn-syn carboxylato bridges(between Co(2) and Co(1) ions).Magnetic measurements indicated that it shows single-chain magnetic behaviors.(b) A Mn(â…¡) coordination polymers have been obtained,in which the 1D Mn-N₃/COO chain composed of the Mn(â…¡) ions linked by one EO azido and double syn-syn carboxylato bridges and the 1D uniform chains are further linked by the L²to give rise to 2D layered structure.Magnetic measurements show dominant antiferromagnetic coupling between neighboring manganese(â…¡) ions in the compound.3.Coordination compounds with 1-carboxymethylpyridinium-4-carboxylate(L³) as co-ligands.(a) Two Mn(â…¡),Co(â…¡) coordination polymers which are isomorphous have been synthesized and characterized.In the 1D Mn-OCN/COO chain,adjacent metal ions are linked,by one N,N-end-on cyanate bridge and two syn-syn carboxylato bridges and each chain is linked to four others by L³ ligands to produce a 3D network with sra net topology.Magnetic analysis reveal that Mn(â…¡) compound shows antiferromagnetic interactions while Co(â…¡) compound shows ferromagnetic interactions.(b) Two isomorphous mononuclear Mn(â…¡),Co(â…¡) complexes have been obtained in which the six coordination sites are occupied by four oxygens atoms from four water molecules and two oxygen atoms from two carboxylate groups of L³. There is a lot of hydrogen bonds due to the existence of more water molecules and 3D pillared-layer network can been built by hydrogen bonds.