熔鹽是由陰離子和陽離子所組成的離子化合物，由於是由離子所組成，因此含有很高的導電度，但是熔鹽的熔點通常非常高，導致其應用性大幅的下降。為了改善這個問題，在過去幾年，有學者報導把無機的陽離子設計為有機的陽離子，使熔鹽的晶格對稱性降低便可以使熔點降低，也大幅提升熔鹽的應用性。也因此，在熔鹽的定義上便有了改變。熔點在100oC以下的熔鹽稱為離子液體，在室溫為液態的又稱為室溫離子液體。不論是離子液體還是熔鹽，他們都可依照結構的變化來調控一些他們本身所含有的物理化學性質，我們稱為可調控性。本論文設計三個型態的雙陽離子熔鹽來探討藉由陰陽離子的變化來調控一些物理化學性質。
第一類熔鹽設計為在一個雙陽離子結構中去搭配二個不同的陰離子。我們可發現到這類熔鹽熱行為不同於一般文獻結果，含有NTf2陰離子的熱安定性和PF6陰離子是相似的(一般文獻結果為NTF2陰離子熱安定性高於PF6陰離子)。這類熔鹽提供一個觀念，雙陽離子熔鹽除了可以在陽離子上改變結構進而調控物理化學性質外，也可以利用二種不同陰離子的搭配來調控。
第二類我們設計含磁性過渡金屬為陰離子搭配雙陽離子結構的熔鹽。利用四氯化鈷([CoCl4]2-)和四氯化錳([MnCl4]2-)為陰離子，並使用imidazolium，pyridinium，triethylammonium，triphenylphosphinium設計為雙陽離子，探討其晶體結構，熱安定性，熔點，磁性行為，在各溶劑的溶解度。我們可以發現到雙陽離子熔鹽結構的變化會影響熔鹽本身的物理性質如熱安定性，熔點和磁性。含有triphenylphosphinium和imidazolium官能基的熔鹽含有較高的熱安定性。含有triphenylphosphinium官能基的熔鹽含有較高的熔點，而具有pyriidinium官能基次之。二邊為一樣官能基(symmetrical)的熔點會比二邊不一樣官能基(unsymmetrical)的熔點高。而在磁性直流磁化率量測方面，這些含[CoCl4]2-和[MnCl4]2-陰離子的熔鹽展現反鐵磁的磁性行為，且含[MnCl4]2-陰離子的熔鹽其磁化率會高於含[CoCl4]2-陰離子的熔鹽，我們也發現到利用雙陽離子結構做為熔鹽的陰離子其磁化率會高於用二個單陽離子做陽離子的熔鹽來的高(當陰離子為相同結構)。在溶解度方面，[MnCl4]2-和[CoCl4]2-陰離子的熔鹽均可以溶在高極性溶劑如甲醇和水。
第三類熔鹽則選擇鐵氧鐵陰離子([Fe2Cl6O]2-)並用imidazolium，pyridinium， triphenylphosphinium設計的雙陽離子結構為陽離子來探討其晶體結構，熱性質(熱安定性和熔點)，磁性行為和在各溶劑的溶解度。含有triphenylphosphinium和imidazolium官能基的熔鹽含有較高的熱安定性。在熔點量測方面，含有triphenylphosphinium官能基的熔鹽具有較高的熔點，而含pyriidinium官能基次之。二邊為一樣官能基(symmetrical)的熔點會比二邊不一樣官能基(unsymmetrical)的熔點高。在[Fe2Cl6O]2-陰離子構型方面，由於雙陽離子結構的改變，而會有線型和角形的構型出現，而這些構型在磁性行為上展現了令人感興趣的現象。首先在磁偶合常數的計算上，含一個雙陽離子為陽離子的[Fe2Cl6O]2-熔鹽其磁偶合常數比文獻發表過(為二個單陽離子為陽離子)的高，而且跟文獻不同的是，角型[Fe2Cl6O]2-的磁偶合值會接近或大於線型[Fe2Cl6O]2-的磁偶合值(文獻的討論為角型[Fe2Cl6O]2-的磁偶合值會小於線型[Fe2Cl6O]2-的磁偶合值)。在溶解度方面，這些含[Fe2Cl6O]2-陰離子的熔鹽都可溶在高極性溶劑如甲醇和水。

Molten salts are ionic compounds composed of cations and anions. They exhibit high ionic conductivity. Molten salts usually have high melting points and result in decreasing their application ability. In recent years, scientists reported that designing the organic cations to replace the inorganic cation can lower the melting point of molten salts due to destroying the crystal symmetry; the application ability of molten salts can be also increased. Therefore, the definition of molten salts is also changed. Molten salts are called “ionic liquids” when they are liquids at room temperature or their melting points are below 100oC. Ionic liquids (or generally called molten salts) can be changed their structure to tune some unique physic-chemical properties. This ability has been called “tunability”. This thesis synthesizes three types of dicationic molten salts to investigate that utilize the change of the structure to tune some physic-chemical properties.
The first type of dicationic molten salts which are connected with dicationic moiety is that each dication is associated with two different anions. The thermal stability of these molten salts containing NTf2 anion is close to that containing PF6 anion. This result is different from that previously reported (in early literatures, the thermal stability of NTf2 anion-based molten salt is higher than that of PF6 anion-based ones). This type of dicationic molten salts offer a concept that besides the physic-chemical properties of dicationic molten salts can be tuned by various cationic structures, they can be tuned by two types of anions.
The second type of dicationic molten salt is transition metal-based anion linked with dicationic moiety. [CoCl4]2- and [MnCl4]2- is selected as anions and we use the imidazolium, pyridinium, triethylammonium, and triphenylphosphinium groups as a dicationic moieties. These new tetrachlorocobaltate (II) and tetrachloromanganate (II) ionic compounds containing various counterdications were synthesized and characterized. These salts are soluble in polar solvents such as methanol and water. Physical properties such as thermal stability, melting point, and magnetic susceptibility of these salts depend on the cation or anion structure. The thermal stability of the phosphinium or imidazolium based salts is higher than that of the pyridinium or triethylaminonium analogues. The melting point of these compounds is following the order of triphenylphosphinium > pyridinium > imidazolium dications, and symmetrical dicationic salts > unsymmetrical ones. The magnetic susceptibility (χMT values) of tetrachloromanganate (II) anions-based salts is higher than that of tetrachlorocobaltate (II) anions-based salts. These dicationic salts exhibit weak antiferromagnetic interactions and have higher magnetic susceptibility than that of the previously reported tetrachloromanganate (II) and tetrachlorocobaltate(II) salts with monocationic counterion.
The [Fe2Cl6O]2- anion is used in the third type of dicationic molten salt and incorporated with dicationic moieties designed by imidazolium, pyridinium, and triphenylphosphinium groups. These new (μ-oxo)bis[trichloroferrate(III)] dianions-based ionic compounds that contain various counterdications were synthesized and characterized with regards to their crystal structures, thermal properties, and magnetic susceptibility. These salts are soluble in polar solvents such as methanol and water. The melting point of these compounds is affected by the dication following the order of triphenylphosphinium > pyridinium > imidazolium dications, and symmetrical dicationic salts > unsymmetrical ones. In these compounds, the trichloroferrate dianion exists in either a linear or a bent form, which is affected by the dications. Interestingly, the dicationic diferrate compounds show magnetic coupling constants fairly smaller than those reported in literature for diferrate salts in which monocations are the counterion. Furthermore, unlike the diferrate salts associated with separate monocations, the linear diferrate dicationic compounds show magnetic coupling constant lower than that of bent diferrate dicationic salts.

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