American Chemical Society
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Serendipity and Design in the Generation of New Coordination Polymers:  An Extensive Series of Highly Symmetrical Guanidinium-Templated, Carbonate-Based Networks with the Sodalite Topology

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posted on 2004-03-10, 00:00 authored by Brendan F. Abrahams, Adrian Hawley, Marissa G. Haywood, Timothy A. Hudson, Richard Robson, Damian A. Slizys
The serendipitous discovery of a 3D [Cu(CO3)22-]n network with the topology of the 4264 sodalite net in [Cu6(CO3)12(CH6N3)8]·K4·8H2O paved the way for the deliberate engineering of an extensive series of structurally related guanidinium-templated metal carbonates of composition [M6(CO3)12(CH6N3)8]Na3[N(CH3)4xH2O, where the divalent metal M in the framework may be Mg, Mn, Fe, Co, Ni, Cu, Zn, or Cd. A closely related crystalline material with a [Ca(CO3)22-]n sodalite-like framework, but containing K+ rather than Na+, of composition [Ca6(CO3)12(CH6N3)8]K3[N(CH3)4]·3H2O was also isolated. All of these compounds were obtained under the simplest possible conditions from aqueous solution at room temperature, and their structures were determined by single-crystal X-ray diffraction. Pairs of guanidinium cations are associated with the hexagonal windows of the sodalite cages, alkali-metal cations are associated with their square windows, and N(CH3)4+ ions are located at their centers. Structures fall into two classes depending on the metal, MII, in the framework. One type, the BC type (Imm), comprising the compounds for which M2+ = Ca2+, Mn2+, Cu2+, and Cd2+, has a body-centered cubic unit cell, while the second type, the FC type (Fdc), for which M2+ = Mg2+, Fe2+, Co2+, Ni2+, and Zn2+, has a face-centered cubic unit cell with edges on the order of twice those of the BC structural type. The metal M in the BC structures has four close carbonate oxygen donors and four other more distant ones, while M in the FC structures has an octahedral environment consisting of two bidentate chelating carbonate ligands and two cis monodentate carbonate ligands.