Assemblies of Increasingly Large Ln-Containing Polyoxoniobates and Intermolecular Aggregation-Disaggregation Interconversions.

An oxalate-assisted lanthanide (Ln) incorporation strategy is first demonstrated for creating rare high-nuclearity Ln-containing polyoxoniobates (PONbs). With the strategy, a series of high-nuclearity Ln-containing PONbs of 50-nuclearity Dy 2 Nb 48 , 103-nuclearity Dy 7 Nb 96 , 200-nuclearity Dy 10 Nb 190 , and 206-nuclearity Dy 14 Nb 192 have been made, showing an increasingly large structure evolution from Dy 2 Nb 48 monomer to Dy 7 Nb 96 dimer and to distinct Dy 10 Nb 190 and Dy 14 Nb 192 tetramers. Among them, Dy 14 Nb 192 presents the largest heterometallic PONb and also the PONb with the greatest number of Ln ions reported thus far. Interestingly, both giant Dy 14 Nb 192 and Dy 10 Nb 190 molecules can further undergo single-crystal to single-crystal intermolecular aggregations, forming infinite { Dy 14 Nb 192 } ∞ and { Dy 10 Nb 190 } ∞ chains, respectively. The former structural transformation shows a reversible humidity-dependent aggregation-disaggregation process accompanied by a proton conductivity response, while the latter structural transformation is irreversible. These new species largely enrich the very limited members of Ln-containing PONb family and offer rare examples for studying structural transformations between giant molecular aggregates and infinitely extended structures at the atomic level.