Syntheses, Structures And Magnetic Properties Of Coordination Polymers With Pyridylbenzoates And Derivatives

In recent years, the research of coordination compounds has become one of the most active fields due to their potential application in luminescent, conductor, magnetism, catalysis and adsorption materials et. al. Pyridylbenzoic acid ligands with fascinating structural diversity and various modes have been used to gain novel coordination architectures. Meanwhile, the azide ion is the most extensively studied bridge owing to its abilities in bridging metal ions in various modes, effectively propagating magnetic exchange of different nature. Thus, azide/carboxylate compounds which consist of azide and carboxylate bridges have different influence on the magnetic properties and structures.In this thesis, a series of complexes with two and three dimensional structures were synthesized by transition metal ions, pyridylbenzoic acid and derivatives and/or inorganic small molecules (azide ions) 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 pyridylbenzoic acid (Hpybz)The pyridylbenzoic acid (Hpybz), which contains both pyridyl and carboxylate, has been explored widely in coordination chemistry, but has seldom reported in magnetochemistry. Based on above consideration, we investigated the coordination chemistry and magnetism of Hpybz.(1) We have synthesized five compounds by the reactions of 4,3-Hpybz and transitional metal ions of Fe(Ⅱ), Co(Ⅱ), Ni(Ⅱ) and Cu(Ⅱ). In isomorphous compounds (1-3), metal ions are linked by the mixed (μ-syn, syn-COO)2(μ-H2O) triple bridges to give dinuclear motifs, which serves as tetrahedral building units and are further linked by 4,3-pybz to give rise to diamond networks. Magnetic studies demonstrated that the (COO)2(H2O) triple bridges induce antiferromagnetic coupling between metal ions in 1 and 2, but compound 3 with the same mixed triple bridges exhibits ferromagnetic coupling, which may be related to orbital countercomplementarity. Compound 4 exhibits a 3D framework with three-fold interpenetrated diamond topology.(2) The three transition-metal coordination compounds (6-8) with 4,3-Hpybz or 4,4'-Hpybz as coligands were synthesized and structurally and magnetically characterized. Compound 6 consists of two-dimensional (2D) coordination networks in which ID [Cu(N3)(COO)]n chains are cross-linked by the 4,3-pybz ligand. Compound 7 exhibits a 3D framework with 2-fold pcu topology in which the dinuclear motifs with mixed (μ-EO-N3)(μ-COO)2 triple bridges are cross-linked by the 4,4'-pybz spacers. Compound 8 also consists of the 2D network in which ID [Mn(EE-N3)]n chains are cross-linked by the 4,4'-pybz ligand. Magnetic studies reveal that compound 7 shows the ferromagnetic interaction and theμ-EE-N3 bridges transmit antiferromagnetic interactions in 8. Compound 6 displays metamagnetic behavior with strong intrachain ferromagnetic interactions and weak interchain antiferromagnetic ones. The magneto-structural correlations have been discussed in comparison with other Cu(Ⅱ) compounds with the similar bridging motif.2. Coordination compounds with zwitterionic pydridylbenzoic acid (L1, L2)(1) We have synthesized five compounds (9-13) by the reactions of L1 (L1= 1-carboxymethyl-4-pyridinio-4-benzoate) and transitional metal ions. Compounds 9 and 10 are isomorphous and zero dimensional structures, which are generated to 3D net by extensive hydrogen bonding interactions. Compounds 11-13 are one dimensional chains, which are generated to 3D net by extensive hydrogen bonding andπ-πinteractions.(2) Three Co(Ⅱ),Ni(Ⅱ),Cu(Ⅱ) coordination compounds (14-16) have been synthesized and characterized. Two isomorphous compounds 14 and 15 exhibit 2D coordination networks in which novel uniform M(Ⅱ) chains with the (μ-EO-N3)(μ-COO)2 triple bridges are cross-linked by L1 ligands. Compound 14 represents a new SCM-based material exhibiting AF ordering, metamagnetic transition, and field-modulated slow dynamics. It is worth noting that the mixed azide and carboxylate bridges induce FM coupling between Co(Ⅱ) ions and thus provide new approaches toward SCM materials with different properties. Compound 15 shows ferromagnetic interactions. Compound 16 exhibits a 3D structure with alternating triple [(μ-EO-N3)2(μ-COO)] and double [(μ-EO-N3)2] bridges. Magnetic measurements indicated dominant ferromagnetic coupling between Cu(Ⅱ) ions.(2) We have described two 1D Cu(Ⅱ) coordination compounds (17,18) derived from the L2 ligand (L2=1-carboxymethyl-3-pyridinio-4-benzoate). The compounds contain the unprecedented anionic basic Cu(Ⅱ) carboxylate clusters of formula [Cu4(OH)2(RCOO)8]2-, which are quadruply interlinked by cationic pyridinium moieties. Magnetic investigations on the compounds revealed antiferromagnetic intra-tetramer interaction through the mixed hydroxo and carboxylato bridges.(3) Four condination compounds (19-22) have been obtained from metal ions and L2 ligand in the presence of azide ions. In two isomorphous compounds 19 and 20, metal ions are linked by the (μ-EO-N3)2 double bridges to give dinuclear motifs, and are further linked into 1D coordination chains by L2 ligand. Similar to compounds 19 and 20, compound 21 is also 1D coordination chains containing dinuclear motifs. Compound 19 shows ferromagnetic coupling between Co(II) ions. Compound 22 exhibits a 2D coordination network with alternating triple [(μ-EO-N3)(μ-COO)2] and double [(μ-EO-N3)2] bridges.3. Coordination compounds with pyridylbenzoic acid N-oxide (4,3-Hopybz, 4,4'-Hopybz)(1) Three coordination compounds (23-25) have been synthesized by pyridylbenzoate N-oxide and metal ions. Compounds 23 and 24 are isostructural but different space group. They consist of 2D coordination networks in which 1D [Cu(OH)(COO)]n chains are cross-linked by the organic ligands. Compound 25 also are a 2D structures linked via the triatomic O-H…O hydrogen bonding bridge to give a 3D architecture. Magnetic measurements revealed antiferromagnetic interaction through the mixed hydroxo and carboxylato bridges in 23.(2) Compounds 26 and 27 contain uniform chain with one EO azide bridge, oneμ2-O bridge and one carboxylate bridge. The chains are interlinked by 4,3-opybz ligands to produce 2D coordination networks. Magnetic analysis reveal that Mn(II) compound shows antiferromagnetic interaction while Cu(II) compound shows ferromagnetic interaction.(3) Four new coordination compounds with azide and the (4,4'-Hopybz) ligand were synthesized, and structurally and magnetically characterized. In the isomorphous compounds 28 and 29, neighboring metal ions are linked by mixed double [(μ1,1-N3)(μ2-COO)] bridges to give a chain of [M(N3)(COO)]n, and each chain is cross-linked by the organic spacers to give a two-dimensional (2D) coordination layer. Compound 30 contains 2D coordination layers in which Mn(II) chains with alternating [(μ1,1-N3)2(μ2-COO)] triple and [(μ2-COO)(μ2-O)] double bridges are interlinked by the organic spacers. Compound 31 contains the linear tetranuclear [Mn4(μ1,1-N3)(μ2-COO)3(μ2-O)2] clusters, which are connected by the ligands to produce a 3D framework with a self-catenated, eight connected net 416·612topology. Magnetically, similar to compound 14, compound 29 also represents a new SCM-based material exhibiting AF ordering, metamagnetic transition, and field-modulated slow dynamics, while Ni(Ⅱ) compound shows metamagnetism with long-range ordering. Compounds 30 and 31 exhibit different antiferromagnetic interactions between Mn(Ⅱ) ions.