Countercation-Controlled Nuclearity of Zr/Hf Peroxo Oxalates

Understanding fundamental differences between zirconium and hafnium chemistry contributes to our fundamental understanding of the periodic table and leads to devising necessary separations for high-precision nuclear and microelectronics applications, developing water-based nanolithographic processes, and creating new robust metal–organic frameworks for catalysis and separations. Here we crystallize a rich matrix of polynuclear Zr and Hf species differentiating in complexation with peroxide and oxalate in mild acid, where the countercations influence polymerization. Hf only complexes oxalate, yielding polymeric {(N­(CH3)4)4[Hf2(OH)2(C2O4)5]} n , dimeric Na6[Hf2(OH)2(C2O4)6], and Li2K4[Hf2(OH)2(C2O4)6] and mononuclear K4Hf­(C2O4)4, Rb4Hf­(C2O4)4, and Cs4Hf­(C2O4)4. Zr complexes both peroxide and oxalate to yield the ring structures (N­(CH3)4)6[Zr6(O2)6(OH)6(C2O4)6], Li12[Zr8(O2)12(OH)4(C2O4)8], K18[Zr12(O2)18(OH)6(C2O4)12], and Rb24[Zr16(O2)24(OH)8(C2O4)16]. The Zr ring nuclearity increases with countercation size, while Hf polymerization decreases with increasing countercation size. The Zr rings feature nine-coordinate face-sharing polyhedra in both solution and the solid state, unprecedented in Zr coordination complexes. These studies describe differentiating the coordination chemistry of Zr/Hf, exploiting simple aqueous reagents that could be further developed for aqueous synthesis of materials as well as challenging chemical separations.