A variable Ag-Cr-Oxalate channel lattice: [M(x)Ag(0.5)(-)(x)(H(2)O)(3)]@[Ag(2.5)Cr(C(2)O(4))(3)], M = K, Cs, Ag.
A variable Ag-Cr-Oxalate channel lattice: [M(x)Ag(0.5)(-)(x)(H(2)O)(3)]@[Ag(2.5)Cr(C(2)O(4))(3)], M = K, Cs, Ag.
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可变Ag-Cr-草酸盐通道晶格：[M(x)Ag(0.5)(-)(x)(H(2)O)(3)]@[Ag(2.5)Cr(C(2)O(
作者：
P. Dean;D. Craig;I. Dance;Vanessa Russell;M. Scudder
阿尼奥（3）水溶液与M（3）[Cr（ox）（3）]水溶液以大于或等于3：1的摩尔比反应，导致大的、樱桃黑色的、光稳定的晶体的快速生长，所述晶体不是Ag（3）[Cr（ox）（3）]，而是[M（0.5）（H（2）O）（3）]@[Ag（2.5）Cr（ox）（3）]（ox（2）（-）=草酸盐，C（2）O（4）（2）（-）; M = Na、K、Cs、Ag或Ag和第1族元素的混合物）。这些晶体的结构包含一个不变的通道框架，组成为[[Ag（2.5）Cr（ox）（3）]（-）（0.5）]（无穷大），由Ag原子通过中心对称的[Cr-O（2）C（2）O（2）-Ag]（2）双桥连接的[Cr（ox）（3）]配位单元构成。骨架组成[Ag（2.5）Cr（ox）（3）]（-）（0.5）的出现是因为一个Ag位于2重轴上。在通道内有一个明确定义和有序的六个水分子，彼此之间和一些草酸O原子之间有很强的氢键。这种不变的通道加水的结构容纳组1阳离子，和/或银阳离子，在不同的位置和可变的比例，但总是由通道水和一些草酸O原子协调。因此，这些晶体的通式为[M（x）Ag（0.5-x）（H（2）O）（3）]@[Ag（2.5）Cr（ox）（3）]。报道了五种具有这种结构的晶体，其组成为1 Ag（0.5）[Ag（2.5）Cr（ox）（3）]（H（2）O）（3），2 Cs（0.19）银（0.31）[Ag（2.5）Cr（ox）（3）]（H（2）O）（3），3 K（0.28）Ag（0.22）[Ag（2.5）Cr（ox）（3）]（H（2）O）（3）、4 Cs（0.41）Ag（0.09）[Ag（2.5）Cr（ox）（3）]（H（2）O）（3）和5 Cs（0.43）Ag（0.07）[Ag（2.5）Cr（ox）（3）]（H（2）O）（3）。所有的晶体都属于空间群C2/c，a约为18.4，B约为14.6，c约为12.3，β约为113度。通过用过量的阿尼奥（3）处理Li（3）[Cr（ox）（3）]，从水中获得具有相同晶体结构（1）的纯Ag（3）[Cr（ox）（3）]（H（2）O）（3）。所有这些化合物的完全脱水发生在30至100摄氏度之间，衍射损失，但在环境温度下暴露于H（2）O（g）的再水合导致原始衍射图案的恢复。在单晶体中，这种可逆的脱水-水化发生时没有视觉上明显的晶体变化，但机械强度损失。我们假设一个一般的机制，运输水分子沿着的渠道，与当地的部分崩溃的渠道框架，伴随着弯曲，但很少打破主机Ag-O和Cr-O键，这是很容易逆转。
Reaction of aqueous AgNO(3) with aqueous M(3)[Cr(ox)(3)] in >or=3:1 molar ratio causes the rapid growth of large, cherry-black, light-stable crystals which are not Ag(3)[Cr(ox)(3)], but [M(0.5)(H(2)O)(3)]@[Ag(2.5)Cr(ox)(3)] (ox(2)(-) = oxalate, C(2)O(4)(2)(-); M = Na, K, Cs, Ag, or mixtures of Ag and a group 1 element). The structure of these crystals contains an invariant channeled framework, with composition [[Ag(2.5)Cr(ox)(3)](-)(0.5)]( infinity ), constructed with [Cr(ox)(3)] coordination units linked by Ag atoms through centrosymmetric [Cr-O(2)C(2)O(2)-Ag](2) double bridges. The framework composition [Ag(2.5)Cr(ox)(3)](-)(0.5) occurs because one Ag is located on a 2-fold axis. Within the channels there is a well-defined and ordered set of six water molecules, strongly hydrogen bonded to each other and some of the oxalate O atoms. This invariant channel plus water structure accommodates group 1 cations, and/or Ag cations, in different locations and in variable proportions, but always coordinated by channel water and some oxalate O atoms. The general formulation of these crystals is therefore [M(x)Ag(0.5-x)(H(2)O)(3)]@[Ag(2.5)Cr(ox)(3)]. Five different crystals with this structure are reported, with compositions 1 Ag(0.5)[Ag(2.5)Cr(ox)(3)](H(2)O)(3), 2 Cs(0.19)Ag(0.31)[Ag(2.5)Cr(ox)(3)](H(2)O)(3), 3 K(0.28)Ag(0.22)[Ag(2.5)Cr(ox)(3)](H(2)O)(3), 4 Cs(0.41)Ag(0.09)[Ag(2.5)Cr(ox)(3)](H(2)O)(3), and 5 Cs(0.43)Ag(0.07) [Ag(2.5)Cr(ox)(3)](H(2)O)(3). All crystallize in space group C2/c, with a approximately 18.4, b approximately 14.6, c approximately 12.3 A, beta approximately 113 degrees. Pure Ag(3)[Cr(ox)(3)](H(2)O)(3), which has the same crystal structure (1), was obtained from water by treating Li(3)[Cr(ox)(3)] with excess AgNO(3). Complete dehydration of all of these compounds occurs between 30 and 100 degrees C, with loss of diffraction, but rehydration by exposure to H(2)O(g) at ambient temperature leads to recovery of the original diffraction pattern. In single crystals, this reversible dehydration-hydration occurs without visually evident crystal change, but with loss of mechanical strength. We postulate a general mechanism for transport of water molecules along the channels, associated with local partial collapses of the channel framework, with concomitant bending but little breaking of the host Ag-O and Cr-O bonds, which is readily reversed.