Dimensional reduction, as published by Tulsky and Long in 2001, is “a practical Formalism for Manipulating Solid Structures”.[1] The introduction of a dimensional reduction agent can reduce the dimensionality of a metal anion framework by several degrees, from a 3D parent compound all the way to a discrete child compound. In our research[2] we extended the scope of this formalism to metal organic coordination polymers and found similar results.
The use of different types of en-type blocking ligands such as tetramethylethylenediamine (TMEDA), 2,2’-bipyridine (BIPY), 2-(aminomethyl)pyridine (AMPY) and ethylenediamine (EDA) can lead to reduction of the dimensionality of coordination polymers by a degree of one. This effect was observed both for one-dimensional chain polymers, that were reduced to discreet molecular compounds, and for two-dimensional layer structures, that were reduced to one dimensional strands. A reduction by more than one degree of dimensionality could not be observed yet. So far, this dimensional reduction was successfully conducted with Cu(II)aspartate, all stereoisomers of copper(II)tartrate and the copper(II) complex of the tartaric acid derivative dibenzoyl-tartaric acid. The addition of the blocking ligands usually leads to an increase in solubility of the polymer compound, allowing all reactions and crystallisations presented here to be performed in aqueous solutions at room temperature.
[1] E. G. Tulsky and J. R. Long, Chem. Mater. 2001, 13, 1149-1166
[2] M. Kremer, J. v. Leusen and U. Englert, Crystals 2020, 10, 485
All reactions presented in this presentation were performed at room temperature in water as solvent (though ethanol was sometimes used for crystallization). It seems that there are no requirements for temperature or pressure to achieve the dimensional reduction.
Since the phenomenon has only been observed for coordination compounds featuring dicarboxylic acids and some transition metals, it is difficult to predict the behaviour for other ligands or metal types.
The main factor that decides about success or failure of the reaction so far has been the choice of blocking ligand. We employed a catalogue of 7 different en-type ligands and found that it is almost impossible to predict which of them performs well with a given ligand system. A screening of multiple possible en-type ligands is necessary to find the one that leads to the desired effect.
Best wishes
