Semiclathrate hydrate (SCH) is one of the phase change materials suitable for cold storage. The thermodynamic properties of SCHs, such as an equilibrium temperature and a dissociation enthalpy, depend on the size and shape of guest substances. In this study, to reveal the effect of cation size and shape on the thermodynamic properties, tri-n-butylalkylphosphonium bromide (P444R-Br) SCHs, where the alkyl group was n-propyl (R = 3), n-butyl (R = 4), n-pentyl (R = 5), i-butyl (R = i-4), i-pentyl (R = i-5), or allyl (R = Al)), were investigated. The branched alkyl groups (R = i-4 or i-5) raised the equilibrium temperature, whereas the shorter alkyl groups (R = 3 or Al) lowered one. Except for P4445-Br and P444(Al)-Br SCHs, the other P444R-Br SCHs had the same orthorhombic structure. Among the orthorhombic systems in the present study, the semiclathrate hydrate with a higher equilibrium temperature had a larger dissociation enthalpy.

水合半金属酸盐（SCH）是适用于冷藏的相变材料之一。SCH的热力学性质，例如平衡温度和离解焓，取决于客体物质的大小和形状。在这项研究中，揭示阳离子的大小和形状的效果上的热力学性质，三Ñ -butylalkylphosphonium溴（P444R -溴）的SCH，其中烷基是Ñ丙基（R = 3），Ñ丁基（R = 4），正戊基（R = 5），异丁基（R = i-4），i研究了-戊基（R = i-5）或烯丙基（R = Al））。支链烷基（R = i-4或i-5）升高平衡温度，而较短的烷基（R = 3或Al）降低平衡温度。除了P4445-Br和P444（Al）-Br SCH以外，其他P444R-Br SCH都具有相同的正交结构。在本研究的斜方晶系中，平衡温度较高的半水合物水合物具有较大的离解焓。