Coordination Polymers With Mixed Azide And Carboxylate Bridges From Zwitterionic Ligands:Structural And Magnetic Design

In recent years, the research of complexes functional materials has become one of the most active fields due to their favorable potential application in the fields of luminescent, adsorption, magnetism, catalysis et. al. The main research content of this thesis is complexes molecular magnetic materials. The azide ions and the carboxylate ions which usually act as short bridges and bridge metal ions to constrct molecular magnetic materials, are the most extensively studied bridges owing to their abilities in bridging metal ions in various modes, and effectively propagating magnetic exchange of different nature.In this thesis, a series of complexes from zero to three dimensional structures were synthesized by self-assembly of paramagnetic transition metal ions, azide ions and zwitterionic compounds and characterized by single crystal, IR, elemental analyses, X-ray analysis, and most of them have also been characterized by variable-temperature and variable-field magnetic measurements. The main points are as follows:1. Coordination polymers based on clusters with mixed carboxylate and azide (or cyanate) bridgesFour coordination polymers with mixed (μ-EO-N3)2(μ-COO)/(μ-NCO)2(μ-COO) bridges based on linear trinuclear/tetranuclear clusters were synthesized and structurally characterized, and their magnetic properties have been studied. The complexes were obtained from the assembly of azide/cyanate ions, Mn(II)/Co(II) ions and zwitterionic dicarboxylate ligands (1,2-bis(4-carboxylatopyridiniuum-1-methy lene)benzene(L1)/1,4-bis(4-carboxylatopyridinium-l-methylene)benzene (L2))-Magnetic study shows the mixed bridges transmit antiferromagnetic (AF) interactions between Mn(II) ions and ferromagnetic (FM) intractions between Co(II) ions.(1) Two isomorphous Mn(II)(1) and Co(II)(2) coordination polymers [M3(L)2(N3)6(H2O)2]·2H2O (M=Mn (1), Co (2)) based on linear trinuclear clusters with azide and a zwitterionic dicarboxylate ligand1,2-bis(4-carboxylatopyridinium-l-methylene)benzene (L1) as ligands were synthesized and structurally characterized. The metal ions are bridged by (μ-EO-N3)2(μ-COO)(EO=end on) into trinuclear units, and the trinuclear units are further linked into1D double cahin structure. The magnetic properties revealed that the mixed (EO-N3)2(COO) bridges transmit AF and FM coupling in1(J=-3.20cm-1) and2(J=7.5cm-1), respectively. The nature of magnetic coupling changes from AF to FM on going from Mn(Ⅱ) to Co(Ⅱ). This can be related to the change in the relative numbers of AF and FM contributions as the ligand-field configuration is changed from t2g3eg2(Mn(Ⅱ)) to/t2g5e2(Co(Ⅱ)). Additionally, a Mn(Ⅱ) coordination polymer (3) based on linear trinuclear clusters with cyanate and a zwitterionic dicarboxylate ligand1,4-bis(4-carboxylatopyridinium-l-methylene)benzene (L2) as coligands has also been synthesized, structurally characterized. The Mn(Ⅱ) ions are bridged by mixed (μ-NCO)2(μ-COO) bridges into trinuclear units, and the trinuclear units are further linked into1D chains. Magnetic studies demonstrate that the magnetic coupling through the mixed (EO-N3)2(COO)/(μ-NCO)2(μ-COO) bridges in1and3(J=-5.63cm-1) are both AF, and is FM in2. It is also noted that the magnetic coupling transmitted by (μ-NCO)2(μ-COO) bridges is stronger than that of (EO-N3)2(COO) bridges.(2) AMn(Ⅱ) coordination compound{[Mn4(L2)(N3)8(H2O)4(CH3OH)2]·[L1]}n (4) based on tetranuclear clusters with L and azide ion as ligands was synthesized and structurally and magnetically characterized. The tetranuclear unit in4is with (u-EO-N3)2as central bridges and (μ-EO-N3)2(μ-COO) as peripheral bridges and are linked into1D chain by L2. An expression based on classical spins approximation of magnetic susceptibility for linear tetranuclear systems of has been deduced and applied to4, which indicates (μ-EO-N3)2bridges transmit FM coupling (J1=1.18cm-1) and the mixed (μ-EO-N3)2(μ-COO) bridges transmit AF coupling (J2=-2.24cm-1).2. High-dimensional coordination polymers based on AF chains with mixed carboxylate and azide bridges5-7are coordination polymers with mixed carboxylate and azide bridges based on1D chains. Mn(Ⅱ) ions are both bridged by mixed (μ-EO-N3)(μ-COO)2bridges in5and6, while Mn(Ⅱ) ions in7are bridged by (μ-EO-N3)(μ-COO) and (μ-EE-N3) bridges. Magnetic analysis shows the magnetic coupling transmitted by mixed bridges is all AF in5-7and the magnitude is similar with that of in1.7shows spin-frustration behaviors.8is a Co(Ⅱ) complex based on1D alternating chain with double EO and double EE azide bridges, magnetic study shows FM and AF interactions transmitted by double EO and double EE azide bridges respectively.(1) We have obtained three compounds (5-7) which based on1D chains by the reactions of L2(nutral)/1-carboxymethylpyridinium-4-carboxylate (L3, with an electronic charge), azide ions and Mn(II) ions. Both [Mn2(L2)(N3)2(OAc)2(H2O)6]n (5) and [Mn(L3)(N3)]n·H2O (6) consist of1D uniform polymeric chains and the chains are interlinked by long organic ligands into2D and3D structure respectively. In5and6, Mn(II) ions are both bridged by mixed (u-EO-N3)(μ-COO)2bridges. Magnetic studies on5(J1=-4.5) and6(J1=-1.93) reveal that the mixed triple bridges induce AF coupling between Mn(II) ions. Compound [Mn2(L2)(H20)0.5(N3)8]n (7) features the magnetic A-chain formed from isosceles triangular units with singleμ-EE-N3and double (μ-EO-N3)(μ-COO) bridges (EE=end-to-end). The A-chains are interlinked by long organic ligands into a3D framework with novel net topology and three-fold interpenetration. The magnetic properties of7(J1=-1.74) indicate the presence of spin frustration characteristic of△-chains with AF interactions.(2) A new Co(II) coordination polymer [Co2(N3)4(L4)]n (8) with azide and a quadritopic ligand, TPOM=tetrakis(4-pyridyloxymethylene)(L4) methane, was synthesized and characterized structurally and magnetically. The compound exhibits a3D framework in which Co(II) chains with alternating double EO and double end-to-end EE azide bridges are linked by the tetrapyridyl ligand in a bowl-shaped conformation. Magnetic studies demonstrated that the alternating double EO and double EE azide bridges induce FM (J1=19.2cm-1) and AF (J2=-30.6cm-1) interactions along the chain.3. Single-chain magnets (SCMs) based on FM chains with mixed carboxylate and azide bridgesWe have obtained four isomorphous coordination polymers [M(L3)(N3)]n·H2O (M=Fe(Ⅱ)(9),Co(Ⅱ)(10),Ni(Ⅱ)(11) and Zn(Ⅱ)(12)). The magnetic coupling transmitted by (μ-EO-N3)(μ-COO)2bridges are all FM. It is noted that9-11stand for the first series of isomorphous SCMs. A solvent-modulated SCM ([Co3(L5)2(N3)4(H2O)2]n·2H2O (13)) has been obtained. In the structure of13, Co(II) ions are bridged by (μ-EO-N3)(μ-COO)2and (μ-EO-N3)2bridges. The mixed bridges and double EO-azide bridges transmit FM interaction.13shows SCM behaviours whenever it is hydrated or dehydrated and the SCM behaviours is reversible. In {[Co2(L2)(N3)4]·2[DMF]}n (14), the uniform Co(II) chains with mixed (μ-EO-N3)2(μ-COO) triple bridges are cross-linked by L2to generate2D coordination layers. It was demonstrated that the triple bridges mediate FM coupling and that the compound represents a new example of the rare systems exhibiting the coexistence of antiferromagnetic ordering, metamagnetism, and slow magnetic dynamics.(1) A consecutive series of isomorphous compounds with different paramagnetic metal ions,[M(II)(L3)(N3)]·H2O [M=Fe (9), Co (10), Ni (11) and Zn (12)], have been synthesized from azide and the zwitterionic ligand L3. The structure of the four copounds are the same as that of6. The magnetic properties of9,10and11have been studied. The triple bridges (μ-EO-N3)(μ-COO)2transmits FM coupling in all these three compounds and the magnitude of the FM coupling increases in the order Fe(Ⅱ)<Co(Ⅱ)<Ni(Ⅱ).9-11represent the first family of isomorphous homospin single-chain magnets (SCMs) with different metal ions. Only a few homospin Fe(Ⅱ) SCM and no homospin Ni(Ⅱ) SCM have been reported to date. For9Fe(Ⅱ),10Co(Ⅱ) and11Ni(Ⅱ), the blocking temperature and the activation energy (△τ) for magnetization relaxation increasing in the order Ni(Ⅱ)<Co(Ⅱ)<Fe(Ⅱ). According to the energetic analysis on the static and dynamic data, the uniaxial magnetic anisotropy increases in the same order, emphasizing the great importance of anisotropy in determining SCM properties. It is also indicated that the increase of the number of unpaired d electrons from Ni(Ⅱ) to Fe(Ⅱ) also contributes much to the enhancement of the energy barriers (△ξand△τ) and the relaxation time.(2) We have obtained a new SCM (13) by the reactions of1-carboxymethylpridi nium-3-carboxylate (L5), azide ions and Co(Ⅱ) ions.13is based on ID alternating chains. In the1D chains, Col and Co2are bridged by mixed (μ-EO-N3)(μ-COO)2bridges and Col and Col are bridged by (μ-EO-N3)2bridges. The metal ions are linked into an ID chain with the bridges alternating in the double-triple-triple sequence. Magnetic studies on13demostrated SCM behaviors. Further studies on magnetic behaviors change modulated by water molecules has also been done. Upon desolvation, the system (13') transforms into an AF phase with metamagnetic character and midfied slow magnetic relaxation. It is noted that both the process of de/resolvation and the magnetic behaviors are reversible.(3) We have synthesized a compound (14) by the self-assembly of L2, azide and Co(II) ions. In compound14, the uniform Co(II) chains with mixed (μ-EO-N3)2(μ-COO) triple bridges are cross-linked by the long chain organic ligands to generate2D coordination layers. It was demonstrated that the triple bridges mediate FM coupling and that the compound represents a new example of the rare systems exhibiting the coexistence of antiferromagnetic ordering, metamagnetism, and slow magnetic dynamics.4. First exploration on magnetic modulation of mixed-metal SCMs with mixed carboxyalte and azide bridges.The magnetic change of three types of mixed-metal SCMs systems has been studied. The first type is the mix of the anistropic and diamagnetic metal ions, for example Co(Ⅱ)-Zn(Ⅱ) system; the second type is the mix of the anistropic and isotropic metal ions, for example Co(Ⅱ)-Mn(Ⅱ) and Fc(Ⅱ)-Mn(Ⅱ) systems; the third type of is the mix of two different anistropic metal ions, for example Fe(Ⅱ)-Ni(Ⅱ), Co(Ⅱ)-Ni(Ⅱ) and Fe(Ⅱ)-Co(Ⅱ) systems. The magnetic study on Co(Ⅱ)-Ni(Ⅱ) system shows that it is realistic to increase the woking temperature of SCM.(1) Mixed-metal Co(Ⅱ)-Zn(Ⅱ) system (15-17). We are aimed at finding the change pattern of the static and dynamic magnetic behaviors of mixed-metal coordination polymers by bringing in diamagnetic metal ions in the anisotropic system. The research indicates that the SCM behaviours gradually disapper with the Zn(Ⅱ) content increasing in expectation. In accordance with this change, the△τ (△τ is the energy barrier to reverse the magnetization) and TB(blocking temperature) values are gradually lowered.(2) Mixed-metal Co(Ⅱ)-Mn(Ⅱ)(18-20) and Fe(Ⅱ)-Mn(Ⅱ) systems (21-23). With Mn(Ⅱ) content increases, anisotropic Co(Ⅱ) and Fe(Ⅱ) ions are gradually replaced by isotropic Mn(Ⅱ) ions, the intrachain magnetic coupling changes gradually from ferromagnetic to antiferromagnetic. The alternating magnetic susceptibilities out-of-phase signals change from frequency-depedent behaviours to showing no signal. And the△τ andTB values are gradually lowered. (3) Mixed-metal Fe(Ⅱ)-Ni(Ⅱ)(24-25), Co(Ⅱ)-Ni(Ⅱ)(26-31), Fe(Ⅱ)-Co(Ⅱ)(32-37) systems. For Fe(Ⅱ)-Ni(Ⅱ)(24-25) system, with Ni(Ⅱ) or Co(Ⅱ) content increases, the magnetic behavior changes monotonically. With Ni(Ⅱ) or Co(Ⅱ) content increases, the△τandTB values are gradually lowered. In addition, the isothermal magnetization at2K shows the more Ni(Ⅱ) content, the smaller of the saturation value at50kOe and remnant magnetization and coercive field.Mixed-metal Co(Ⅱ)-Ni(Ⅱ) system (26-31). The magnetic study indicates that TB shows unexpectly after rising to drop with x increases. When x=0.21, TB is the maxmum. When x>0.21, TB is lowering. In accordance with this change, the other magnetic values also show similar change, such as△τ,△ξ, To (relaxation time), and so on. Due to the complexity of the system and being short of logical theory model, we can not give clear explanation on the specific physical mechanism.Mixed-metal Fe(Ⅱ)-Co(Ⅱ) system(32-37). The change of TB in this system with Co(Ⅱ) content increasing is contrary to the one of Co(Ⅱ)-Ni(Ⅱ) system. The magnetic study indicates that the TB shows after the first decline rise with x increases. When x=0.5, TB is the minimum. When x>0.50, TB is increasing. In accordance with this change, the other magnetic values also show similar change, such as△τ,△ξ and so on. The specific physical mechanism of this unexpected behaviours is under studying.