Aggregate assembly of ferrocene functionalized indium-oxo clusters

Abstract

In this study, we synthesized multi-nuclear indium oxide clusters (InOCs) using 1,1'-ferrocene dicarboxylic acid (H₂FcDCA) as the chelating and surface protection ligand. The obtained clusters include the cubane-type heptanuclear InOCs ([In₇]) and the sandwich-type thirteen-nuclear InOCs ([In₁₃]). Notably, [In₁₃] represents the highest nuclear number reported within the InOC family. In addition, the presence of labile coordination sites in these clusters allowed for structural modification and self-assembly. A series of [In₇] clusters with adjustable band gaps have been obtained and the self-assembly of [In₇] clusters resulted in the formation of an Fe-doped dimer, [Fe₂In₁₂], and an imidazole-bridged tetramer, [In₂₈]. Similarly, in the case of [In₁₃] clusters, the coordinated water molecules could be replaced by imidazole, methylimidazole, and even a bridged carboxylic acid, allowing the construction of one-dimensional extended structures. Additionally, part of the H₂FcDCA could be substituted by pyrazole. This flexibility in replacing solvent molecules offered diverse possibilities for tailoring the properties and structures of the InOCs to suit specific applications.

Scheme 1. Aggregate assembly of indium oxide clusters. Color: pink, In; red, O; blue, N; gray, C.

Fig. 1. (a) Structure of 1; (b) the cubane central ion is [In₇(μ₄-O²⁻)₃(μ₃-OCH₃)]¹⁴⁺; (c) coordination environment of 1; (d) 1 accumulates along the c-axis and is filled with TPP⁺. Color: pink, In; green, Fe; red, O; blue, N; gray, C; dark green, Cl; yellow, TPP⁺.

Fig. 2. Molecular structure of compound 2. (a) Assembly of the In atom in 2; (b) two cubane central ions [In₆Fe(μ₄-O²⁻)₃(μ₃-O²⁻)]¹³⁺; (c and d) coordination environment in 2 ; (e) packing structure of 2.

Fig. 3. Molecular structure of compound 3. (a) A and B represent substitution sites. (b and c) 3 with MPP ligand. (d) Packing of 3 along the c-axis. (e and f) Molecular structure of 4. (g and h) Packing structure of 4. (i–l) Cluster assembly in 4. The atom color code: pink, In; green, Fe; red, O; blue, N; gray, C; dark green, Cl.

Fig. 4. Molecular structure of 5: (a) structure of 5; (b) the cubane central ion is [In₁₃(μ₄-O²⁻)₆(μ₂-O²⁻)₆]¹⁵⁺; (c) [In₇(μ₄-O²⁻)₆(μ₃-OCH₃)₆]³⁺ is the Anderson configuration; (d) coordination environment of [In₁₃(μ₄-O²⁻)₆(μ₂-O²⁻)₆]¹⁵⁺. Color: pink, In; green, Fe; red, O; blue, N; gray, C; dark green, Cl.

Fig. 5. (a) [In₁₃] as a secondary building unit: (b) compound 6 (A = B = C = HIm); (c) compound 7 (A= 2-mim, B = DMF, C = H₂O); (d) compound 8 (A = B = MeOH, C = H₂O); (e) compound 9 (A = B = BPDC, C = H₂O. A, B and C represent different substitution sites).

Fig. 6. (a) Energy-level diagram of 1, 3 and 4; (b) 0.4 V-bias photocurrent responses of electrodes derived for 1, 3 and 4 in 0.2 M Na₂SO₄ aqueous solution under repetitive chopped visible light irradiation.

Fig. 7. (a) Reaction rates under different conditions; (b) photocatalytic performance test chart of compound 1; (c) powder XRD patterns for compound 1 before and after photocatalytic reaction.