Design, Synthesis And Characterization Of New Magnetic Systems With Mixed Bridges Based On Tetrazolate Ligands

In recent years, molecular magnetic materials having interesting magnetic properties have fascinated chemists and physicists alike. Connecting paramagnetic centers by short bridges, in combination with incorporating different organic coligands to adjust the bridging structure and dimensionality, is a general strategy to design such materials. Using two or more short bridging groups which can transmit magnetic coupling effectively is an important way to design new molecular magnetic materials. In this thesis, new mixed bridging systems have been designed and synthesized, and we have investigated the magneto-structural correlation based on structural and magnetic characterization to gain new molecular magnets, especially single-chain magnets (SCMs).Using pyridine tetrazole Oxide, zwitterionic tetrazolate and bifunctional carboxylate and tetrazolate zwitterionic organic ligands,29transition metal coordination polymers containing azide, azide-tetrazolate and azide-tetrazolate-carboxylate bridges have been prepared. All these compounds have been structurally characterized; and some of them have been magnetically characterized. This dissertation covers the following parts:1. Syntheses, structures and magnetic properties of coordination polymer with new mixed double azide-tetrazolate bridging systemUsing4-(1H-tetrazol-5-yl)pyridine N-oxide tetrazolate as ligand, two complexes with double mixed (μ-EO-azide)(μ-tetrazolate) bridges,[M(pnotz)(N3)2(H2O)2]·H2O, M=Co(Ⅱ)(1), M=Ni(Ⅱ)(2), have been synthesized and structurally characterized. Magnetically, the double mixed (μ-EO-azide)(μ-tetrazolate) bridges induce strong ferromagnetic interactions in the two compounds. Furthermore, this isostructural series of ferromagnetic-chain-based compounds has allowed us to observe distinct bulk properties that are dependent upon the natures of the Co(Ⅱ) and Ni(Ⅱ) ions: compound1with the strong magnetic anisotropy displays the coexistence of antiferromagnetic ordering, metamagnetism, and SCM behavior with slow dynamics; compound2displays the coexistence of antiferromagnetic ordering, metamagnetism and frequency-dependent below2.5K under the field. The mononuclear compound3is generated to three dimensional net by extensive hydrogen bonding interactions. 2. Syntheses, structures and magnetic properties of coordination polymer with bifunctional carboxylate and tetrazolate zwitterionic organic ligandsThe bifunctional zwitterionic ligands bearing both carboxylate and tetrazolate(1) We repot the first Mn(II) compounds with the azide-carboxylate-tetrazolate tricomponent heterobridges using1-(carboxylatomethyl)-3-(5-tetrazolato)pyridinim (a3-ptz) and1-(carboxylatoethyl)-4-(5-tetrazolato)pyridinim (ae4-ptz) as ligands, and the coordination compounds are formulated as [Mn3(a3-ptz)2(N3)4(H2O)2]·4H2O (9),[Mn3(ae4-ptz)2(N3)4(H2O)3]·3.5H2O (10). Both9and10are3D coodination polymers bansd on linear trinuclear units with the (EO-N3)(COO)(tetrazolate) bridges. The trinclear units are interconnected by single EE-N3bridges into2D networks in9but into1D in10. Magnetic analyses indicate that tricomponent bridges transmit antiferromagnetic coupling between Mn(Ⅱ) ions.(2) We have synthesized five compounds (11-15) by the reactions of a3-ptz and1-(carboxylatomethyl)-4-(5-tetrazolato)pyridinim (a4-ptz) with transitional metal ions. Compound11is zero dimensional structure, which is generated to three dimensional net by extensive hydrogen bonding interactions. Compounds12is three dimensional net connected Na(Ⅰ) by azide ions and a4-ptz. Compounds13-14are one dimensional chains, which are generated to3D net by extensive hydrogen bonding and π-π interactions. Compound15is two dimensional self-penetration networks connected by organic ligands.(3) Using a4-ptz as coligand with transitional metal Cu(Ⅱ),Ni(Ⅱ), Co(Ⅱ) ions, we got the first coordination systems (16-18) with tricomponent (azide)(tetrazolate)(carboxylate) cobridging motifs. The compounds16and18contain isostructural2D coordination networks in which the1D [M(CN4)(N3)(COO)]n chains are interlinked by the organic spacers. Magnetic analyses indicate that the tricomponent bridges induce ferromagnetic coupling in all the Cu(Ⅱ), Ni(Ⅱ), and Co(Ⅱ) compounds. The isostructural series of ferromagnetic-chain-based Cu(Ⅱ), Ni(Ⅱ), and Co(Ⅱ) compounds has allowed us to observe distinct bulk properties that are dependent upon the natures of the different spin carriers:with the isotropic Cu(Ⅱ) ion, the compound exhibits a paramagnetic phase of the ferromagnetic chains without long-range magnetic order above2K; with the weakly anisotropic Ni(Ⅱ) ion, the compound displays antiferromagnetic ordering and field-induced metamagnetism without slow dynamic relaxation; and with strong anisotropic Co(Ⅱ)ion, the compound exhibits magnetization dynamics typical of single-chain magnets. This work illustrates a simple heterobridging approach to achieving ferromagnetic coupling and designing SCM materials.3. Regulation of magnetism in the double azide-tetrazolate and tricomponent azide-tetrazolate-carboxylate heterobridges systems with mixed metal Mixed Co(Ⅱ)/Ni(Ⅱ) metal molecular magnetic material systems with double azide-tetrazolate and tricomponent azide-tetrazolate-carboxylate heterobridges have been discussed systematically. Magnetic analyses indicate that the single-ion spin and magnetic anisotropy effect the bulk properties of the isostructural materials. The magnetism of compounds4-8containing double azide-tetrazolate heterobridges change regularly with Co(Ⅱ) ions decrease and the compounds19-24containing tricomponent azide-tetrazolate-carboxylate heterobridges follow the same tendency. Compound4-7display the coexistence of antiferromagnetic ordering, metamagnetism, and SCM behavior with slow dynamics. Compound19-23exhibit coexistence of antiferromagnetic ordering and magnetization dynamics single-chain magnets.4. Syntheses, structures and properties of coordination polymer with inner-salt-type organic ligands(1) We have synthesized the compounds25and26by the reactions of inner-salt-type N-methyl-4-pyridinium tetrazolate ligand with transitional metal ions. Compound25is a one-dimensional chain that has alternating basal-basal and basal-apical azide briges. Magnetic analyses confirm that a strong intradimeric ferromagnetic interaction through the double basal-basal EO-azide bridges and a weak interdimeric antiferromagnetic coupling through the basal-apical EO-azide bridges. Magnetism and photofluorescent properties of some of the compounds have been investigated. Compound26exhibits a novel three-dimensional Mn(Ⅱ)-azide network with (10,3)-b topology, in which the dimeric [Mn(p,-EO-N3)2Mn]2+fragment is linked to four identical motifs by means of four single EE-azide bridge. Magnetic analyses indicate that compound26exhibits ferromagnetic and antiferromagnetic interactions through the double EO and single EE-azide bridges, respectively. (2) We have described one unprecedented trinuclear Co(Ⅱ) coordination compound27formulated as [Co3Na2(mptz)4(N3)8(H2O)7] with tricomponent (azide)(tetrazolate)2cobridging motifs [Co3(mptz)4(N3)6], derived from the N-methyl-4-pyridinium tetrazolate ligand. The trinuclear motifs are interlinked by EE-azide and Na(Ⅰ) ions and which are generated to three dimensional net by extensive hydrogen bonding interactions.(3) Two2D Cu(Ⅰ) coordination compounds (28and29) have been synthesized and characterized. Photofluorescent properties of the two compounds have been investigated.