Rational Design of Open-Framework Coordination Solids − Synthesis and Structure of [Co5(OH)2{1,2,4,5-(O2C)4C6H2}2(H2O)4]·xH2O

Abstract

A strategy for preparing open-framework coordination solids by hydrothermal synthesis has been developed and tested by the synthesis of a new porous cobalt carboxylate which can A number of groups are developing methods for synthesising open framework materials incorporating transition metals. These strategies include methods which aim to modify premade materials [1Ϫ8] as well as ones designed to construct the framework with the transition metal already incorporated. [9Ϫ19] Amongst the first class are syntheses in which the transition metal is substituted into a preformed zeolite, [1Ϫ3] or a metal complex is encapsulated within zeolite channels (ship-in-a-bottle catalysts) [4Ϫ7] and chemical modification of mesoporous (e.g. MCM-41) materials. [8] The second class includes the synthesis of molybdenum and vanadium phosphates, [9,10] zeolite-like cobalt (alumino) phosphate networks [11] and metal-organic coordination frameworks. [12Ϫ20] It is hoped that these materials will have the stability of zeolites with enhanced catalytic activity.Our recent synthesis [20] of [Co 3 (OH) 2 (C 4 O 4 )·3H 2 O] has shown that microporous transition-metal-containing species can be produced based on metal hydroxide structural members joined together by anionic ligands. These materials can be viewed as being made up from assemblies of tubes with rectangular or diamond-shaped cross sections in which the ligands are the walls of the tube and the metal hydroxide chains form the corners. From the isolation of this material we postulated that the formation of open framework materials could be encouraged by a number a factors and we have now illustrated the usefulness of this theory by the preparation of the title compounds.The factors which are important in the rational synthesis of open framework coordination solids relate to both the types of structural members (i.e. ligands) which can be used and also the way in which the voids can be stabilised during synthesis. The ligand should be capable of forming part of the metal hydroxide backbone and it should have a central [a] 2739 be dehydrated by heating to give a material with coordinatively unsaturated metal ions. Figure 1. Schematic view of the construction of open-framework materials; black areas represent metal-oxo strips, shaded areas represent ligand ''spacer'' regions portion which will act as part of the channel wall (Figure 1). Therefore we should be able to control the dimensions of the channel by choosing ligands with different distances between the donor groups. The channel structure can be stabilised by filling the lacunae with water molecules held in place by hydrogen bonds, particularly to bridging hydroxide ligands but also to coordinated water. The formation of species containing bridging hydroxide ligands is therefore encouraged by the use of high pH conditions for these reactions.The structure [21] (Figure 2) of the title compound is built around a Co 5 (µ 3 -OH) 2 ''bow-tie'' cluster in which two metal triangles have a common vertex. Each triangle has a µ 3 -OH a...

Pillared Hybrid Solids with Access to Coordinatively Unsaturated Metal Sites: An Alternative Strategy

“…However, only a few mixed examples of open-framework solids with access to open metal sites have been reported, including open Zn, Cu, and Tb sites in three distinct metal-organic frameworks, [3,4,7] and Ni and Co sites within separate metal-hydroxycarboxylate solids. [8,9] These open metal coordination sites are typically obtained post-synthesis upon removal of a terminal ligand (such as H 2 O or pyridine) from the metal without irreversible destabilization or collapse of the pore structure. The carboxylate functional groups of the ligands convey much of the structural stability in the above examples.…”

Manganese and Cadmium Benzoate Complexes Having 8-Aminoquinoline Ancillary Ligand

“…Comparison of structure of complexes prepared through solution route or some other related methods is essential to understand nucleation process. It is necessary to choose ligand that has versatility to form different types of metal complexes [27][28][29][30][31][32][33]. There is vast literature on mononuclear and polynuclear metal carboxylate complexes [13][14][15][16][17][18][19][20][21][22][23][24][25]34], thus the metal carboxylate complexes would be suitable for such study.…”

Tetrametallic macrocyclic frameworks constructed from ferrocenedicarboxylato and 2,2′-bipyridine: synthesis, molecular structures and characteristics

“…Up to date, a large number of complexes containing carboxylate ligands have been prepared and most of them are polymeric [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15].…”