Fig. 3. Molecular model for POM single-cluster self-assembled nanostructures.

(A) Single-cluster nanowire. (B) Single-cluster nanoring. (C) Building block of a nanowire structure in which two POM clusters are linked head to head by Ac⁻. (D) Building block of a nanoring structure in which POM clusters are linked head to tail by HAc. (E) Single-cluster nanowire structure model at low pH in which POM clusters are linked by HAc in the head-to-head configuration. (F) Comparison of Mülliken charges on metal M and surface oxygen O_M coordinating M in a single POM cluster P₂W₁₇M (M = Zn, La, Ce), as well as hydrogen bond length established between O_M and hydroxyl oxygen of HAc (O_M-O) and binding energy of HAc to single POM cluster calculated by the density functional theory. With the increasing acidity of M, O_M becomes less negatively charged, and its ability to establish a hydrogen bond with HAc is diminished. Color code: M, blue; W, gray; O, red; and C, cyan.