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 Dy₂Nb₄₈, 103-nuclearity Dy₇Nb₉₆, 200-nuclearity Dy₁₀Nb₁₉₀, and 206-nuclearity Dy₁₄Nb₁₉₂have been made, showing an increasingly large structure evolution from Dy₂Nb₄₈monomer to Dy₇Nb₉₆dimer and to distinct Dy₁₀Nb₁₉₀and Dy₁₄Nb₁₉₂tetramers. Among them, Dy₁₄Nb₁₉₂presents the largest heterometallic PONb and also the PONb with the greatest number of Ln ions reported thus far. Interestingly, both giant Dy₁₄Nb₁₉₂and Dy₁₀Nb₁₉₀molecules can further undergo single-crystal to single-crystal intermolecular aggregations, forming infinite {Dy₁₄Nb₁₉₂}_∞and {Dy₁₀Nb₁₉₀}_∞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.