Phyllomanganates transform and concentrate a variety of metals in marine and terrestrial environments through sorption and redox reactions. Water molecules present in the interlayer region of phyllomanganates are assumed to play an important role in the stability, cation exchange, and redox reactions of manganese oxide minerals. The molecular structure of interlayer water remains elusive due to insufficient analytical and computational capabilities for investigating these confined water molecules. This study explores the interlayer water structure of phyllomanganates based on classical molecular dynamics (MD) simulations performed for crystalline chalcophanite group oxides (Me²⁺Mn₃O₇·3H₂O, Me²⁺ = Zn²⁺, Ni²⁺, Mg²⁺, Mn²⁺, or Ca²⁺) as a function of the interlayer water content. As the oxides were dehydrated, MD simulations revealed collapse of the layer spacing in Zn- and Ni-chalcophanite and gradual decrease of the layer spacing in Mg-, Mn-, and Ca-chalcophanite. MD simulations also revealed that the cation-specific reduction in layer spacing with dehydration is controlled by the reorganization of interlayer water molecules, the extent of which strongly depends on the interlayer cations. Water molecules in chalcophanite group oxides occupied the midplane of the interlayer prior to dehydration, with the exception of Ca-chalcophanite which contained two split atomic planes of water molecules near the oxide surface. When Zn- and Ni-chalcophanite were monohydrated per formula unit, water molecules moved directly above or below the interlayer cations, leading to two split atomic planes of water molecules and a minor increase in the c-axis. In monohydrated Mg-, Mn-, and Ca-chalcophanite, water molecules occupied the midplane in the interlayer, with the c-axis reduced. Dehydration of Zn- and Ni-chalcophanite induced the dipole-moment vectors of water molecules to rotate simultaneously and become arranged perpendicular to the (001) basal plane, forming H-bonds between a water molecule and a single Mn octahedral sheet surface. However, in dehydrated Mg-, Mn-, and Ca-chalcophanite, water molecules were induced to rotate in the opposite direction; in this case, the dipole-moment vectors were nearly parallel to the basal plane, and H-bonds formed between a water molecule and two adjacent sheet surfaces. MD simulations with and without Mn⁴⁺-vacancy site disorder demonstrated that vacancy site-disorder causes significant disorder in interlayer cation and water structures. The current study provides atomistic insight into the effects on interlayer water structure of chemical and structural disorders in birnessite-like phyllomanganates.

叶锰酸盐通过吸附和氧化还原反应在海洋和陆地环境中转化和浓缩各种金属。假定存在于叶锰酸盐层间区域的水分子在锰氧化物矿物的稳定性、阳离子交换和氧化还原反应中起重要作用。由于研究这些受压水分子的分析和计算能力不足，夹层水的分子结构仍然难以捉摸。本研究基于对结晶黄铜矿族氧化物 (Me ²⁺ Mn ₃ O ₇ ·3H ₂ O, Me ²⁺ = Zn ) 进行的经典分子动力学 (MD) 模拟，探讨了叶锰酸盐的层间水结构²⁺、Ni ²⁺、Mg ²⁺、Mn ²⁺或Ca ²⁺) 作为层间水含量的函数。随着氧化物脱水，MD 模拟显示 Zn- 和 Ni-黄铜矿的层间距坍塌，而 Mg-、Mn- 和 Ca-黄铜矿的层间距逐渐减小。MD 模拟还表明，脱水时层间距的阳离子特异性减少是由层间水分子的重组控制的，其程度在很大程度上取决于层间阳离子。在脱水之前，黄铜矿组氧化物中的水分子占据中间层的中平面，但钙黄铜矿除外，它在氧化物表面附近含有两个分裂的水分子原子平面。当 Zn- 和 Ni-黄铜矿按分子式单位一水合物时，水分子直接移动到层间阳离子的上方或下方，c轴。在一水合的 Mg-、Mn- 和 Ca-硫磷矿中，水分子占据夹层的中平面，c轴减小。锌和镍黄铜矿的脱水诱导水分子的偶极矩矢量同时旋转并垂直于（001）基面排列，在水分子和单个锰八面体片表面之间形成氢键。然而，在脱水的 Mg-、Mn- 和 Ca-硫磷矿中，水分子被诱导向相反方向旋转；在这种情况下，偶极矩矢量几乎平行于基面，并且在水分子和两个相邻的片表面之间形成 H 键。含和不含 Mn ^{4+ 的}MD 模拟-空位紊乱表明空位紊乱导致层间阳离子和水结构的显着紊乱。目前的研究提供了对类水钠锰酸盐中化学和结构紊乱对层间水结构影响的原子洞察。