Synthesis, Structural Characterization, and Intercalation Chemistry of Two Layered Cadmium Organophosphonates

Abstract

The crystal structures of two cadmium organophosphonate monohydrates, Cd(O3PCH3)·H2O and Cd(O3PC6H5)·H2O, were solved by single-crystal X-ray diffraction. Cd(O3PCH3)·H2O is orthorhombic, space group Pna21 with Z = 4 and a = 17.763(6), b = 5.008(2), and c = 5.912(3) Å, V = 525.9(5) Å3. The structure consists of layers of Cd atoms octahedrally coordinated by five phosphonate oxygen atoms and a water molecule. The methyl groups lie above and below the approximately planar CdO layer, and makes van der Waals contacts between layers. The structure of Cd(O3PC6H5)·H2O was refined in orthorhombic space group Pmn21, Z = 2, a = 5.860(4), b = 14.459(14), c = 5.054(3) Å, V = 428.2(6) Å3. It is isostructural with previously reported Mn(O3PCH3)·H2O and Zn(O3PCH3)·H2O. The layers in this structure are similarly constructed from octahedral coordination of Cd atoms by oxygen atoms. Both compounds dehydrate at elevated temperatures with no significant structural degradation. The dehydrated Cd(O3PCH3) intercalates amines both from vapor and from nonaqueous solutions. As a result, a wide range of amine intercalation compounds (propylamine to n-octadecylamine) have been prepared. The intercalation reaction is shape-selective and is restricted to amines with no branching at the α-carbon position. This result is rationalized on the basis of steric restriction of the accessibility to the metal atoms. Such restriction is imposed by the methyl groups of the phosphonate which prevent amines that have α-branching from forming a Cd-N coordination bond. Dehydrated Cd(O3PC6H5)·H2O is also capable of intercalating very weakly basic alkanethiols. © 1993, American Chemical Society. All rights reserved.