Controlled assembly of [Nb_6-xW_xO₁₉] ^(8-x)- (x = 0-4) Lindqvist ions with (amine)copper complexes

The mixed addenda isopolyanion, [N(CH₃)₄] ₂Na₂[cis-Nb₂W₄O₁₉] ·18H₂O, reacts with Cu(NO₃)₂ in water and in the presence of NH₂CH₂CH₂NH₂ (en) or NH4OH at 60°C to yield a phase that is decorated {[Cu(en) ₂(H₂O)]2-[Nb₂W₄O₁₉] ·2H₂O (1)} or charge-balanced {[Cu(NH₃) ₄-(H₂O)]₂[Nb₂W₄O ₁₉]·8H₂O (2)}, respectively, by (amine)copper complexes. The prolonged heating at 95°C of [N(CH₃) ₄]₆-[Nb₁₀O₂₈]·6H ₂O, [N(CH₃)₄]₂Na₂[cis- Nb₂W₄O₁₉]·18H₂O, or Na ₄K₂[cis-Nb₄W₂O₁₉] ·12H₂O and Cu(NO₃)₂ in a mixed water/amine [en or NH₂CH₂CH₂CH ₂NH₂ (dap)] solution results in the formation of two-dimensional materials with alternate layers of (amine)copper complexes linking Lindqvist [Nb_6-xW_xO₁₉]^(8-x)- (x = 0-4) clusters. These phases include: [Cu(dap)₂] ₃[Nb₄W₂O₁₉]·7H₂O (3), [Cu(dap)₂]₃-[H₂Nb₆O ₁₉]·6H₂O (4), [Cu(dap)₂] ₃[Nb₃W₃O₁₉]·Cl·6H ₂O (5), and [Cu(en)₂]₃[Nb₄W ₂O₁₉]·6H₂O (6). Complexes 4 and 5 result from the decomposition of [Nb₁₀O₂₈]^6- and [cis-Nb₂W₄O₁₉]^4- to [H ₂Nb₆O₁₉]^6- and [fac-Nb ₃W₃O₁₉]^5-, respectively, in alkaline solution. Complex 5 contains an extraframework site that is occupied by Cl _-, but this site is occupied by a water molecule in 3 and is vacant in structures 4 and 6. The results of this study suggest that charge density, cluster charge and symmetry, and cluster-cation pairing are all important parameters in the incorporation of d-electron metals onto the surfaces of [Nb_6-xW_xO₁₉]^(8-x)- (x = 0-4) clusters or into the frameworks of Lindqvist-based complex materials.