Building units , metal-oxide frameworks

In zeolites, tetrahedral framework aluminium can be distinguished from non-tetrahedral extra-framework species by means of Al MAS NMR. However, some AlPOs are known to contain 5- or 6-coordinated Al in the framework, which complicates a quantitative determination [4—6]. Quantitative methods for the monitoring of substituting metals Me are, therefore, required. In the case of transition metal ions, possible changes in the oxidation state must also be taken into account, since the charge n of [Me02] building units should directly affect the number of Bronsted acidic sites. 

One feasible method for the exploration of chiral open-framework compounds is the use of chiral chemical units as primary building blocks by coordinating with metal or other assembly methods to form 2-D layer or 3-D open-framework structures with optical activity. A notable example is the enantiomerically pure zinc phosphonate based on a mixed phosphonic acid-phosphine oxide chiral building block reported by Bujoli and coworkers in 2001.[91] The reaction procedures are shown as follows. 

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