The crystal structures of 16 new alkali metal citrates were determined using powder and/or single crystal techniques. These structures and 12 previously determined citrate structures were optimized using density functional techniques. The central portion of a citrate ion is fairly rigid, while the conformations of the terminal carboxylate groups exhibit no preferences. The citrate–metal bonding is ionic. Trends in metal–citrate coordination are noted. The energy of an O—H…O hydrogen bond is proportional to the square root of the H…acceptor Mulliken overlap population, and a correlation between the hydrogen bond energy and the H…acceptor distance was developed: E (kJ mol⁻¹) = 137.5 (5) − 45.7 (8) (H…A, Å). The hydrogen bond contribution to the crystal energy ranges from 62.815 to 627.6 kJ mol⁻¹ citrate⁻¹ and comprises ∼5 to 30% of the crystal energy. The general order of ionization of the three carboxylic acid groups of citric acid is: central, terminal, terminal, although there are a few exceptions. Comparisons of the refined and DFT‐optimized structures indicate that crystal structures determined using powder diffraction data may not be as accurate as single‐crystal structures.

中文翻译：

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碱金属（第1组）柠檬酸盐的晶体结构。

使用粉末和/或单晶技术确定了16种新的柠檬酸碱金属盐的晶体结构。使用密度泛函技术优化了这些结构和12个先前确定的柠檬酸盐结构。柠檬酸根离子的中心部分是相当刚性的，而末端羧酸根基团的构象没有偏爱。柠檬酸盐-金属键是离子键。注意到金属-柠檬酸盐配位的趋势。O-H…O氢键的能量与H…受体Mulliken重叠种群的平方根成正比，并且氢键能与H…受体距离之间的相关性得到发展：E（kJ mol ^-1） = 137.5（5）− 45.7（8）（H… A， 一种）。氢键对晶体能量的贡献为62.815至627.6kJ mol ^-1 柠檬酸盐^-1，并且占晶体能量的约5至30％。柠檬酸的三个羧酸基团的电离的一般顺序为：中心，末端，末端，尽管有一些例外。精制和DFT优化结构的比较表明，使用粉末衍射数据确定的晶体结构可能不如单晶结构准确。