Noncovalent Synthesis of Hierarchical Zinc Phosphates from a Single Zn4O12P4 Double‐Four‐Ring Building Block: Dimensionality Control through the Choice of Auxiliary Ligands

In contrast to the well‐known reaction of phosphonic acids RP(O)(OH)₂ with divalent transition‐metal ions that yields layered metal phosphonates [RPO₃M(H₂O)]_n, the 2,6‐diisopropylphenyl ester of phosphoric acid, dippH₂, reacts with zinc acetate in methanol under ambient conditions to afford tetrameric zinc phosphate [(ArO)PO₃Zn(MeOH)]₄ ( 1 ). The coordinated methanol in 1 can be readily exchanged by stronger Lewis basic ligands at room temperature. This strategy opens up a new avenue for building double‐four‐ring (D4R) cubane‐based supramolecular assemblies through strong intercubane hydrogen‐bonding interactions. Seventeen pyridinic ligands have been used to synthesize as many D4R cubanes [(ArO)PO₃Zn(L)]₄ ( 2 – 18 ) from 1 . The ligands have been chosen in such a way that the majority of them contain an additional functional group that could be used for noncovalent synthesis of extended structures. When the ligand does not contain any other hydrogen‐bonding donor–acceptor sites (e.g., 2,4,6‐trimethylpyridine (collidine)), zero‐dimensional D4R cubanes have been obtained. The use of pyridine, lutidine, 2‐aminopyridine, and 2,6‐diaminopyridine, however, results in the formation of linear or zigzag one‐dimensional assemblies of D4R cubanes through strong intermolecular C? H???O or N? H???O interactions. Construction of two‐dimensional assemblies of zinc phosphates has been achieved by employing 2‐hydroxypyridine or 2‐methylimidazole as the exo‐cubane ligand on zinc centers. The introduction of an alcohol side chain on the pyridinic ligand in such a way that the ? CH₂OH group cannot participate in intracubane hydrogen bonding (e.g., pyridine‐3‐methanol, pyridine‐4‐methanol, and 3,5‐dimethylpyrazole‐N‐ethanol) leads to the facile noncovalent synthesis of three‐dimensional framework structures. Apart from being useful as building blocks for noncovalent synthesis of zeolite‐like materials, compounds 1 – 18 can also be thermolyzed at approximately 500 °C to yield high‐purity zinc pyrophosphate (Zn₂P₂O₇) ceramic material.