Structure-Property Relationships of Inorganic-Organic Hybrid Semiconducting Se-Fe-Cu-CO Polymers

A novel family of inorganic-organic-hybrid SeFe₃(CO)₉-dipyridyl two- and one-dimensional Cu polymers was synthesized via the three-component liquid-assisted grinding (LAG) of [Cu(MeCN)₄]⁺, inorganic cluster [SeFe₃(CO)₉]^2- (1), and rigid conjugated dipyridyls 4,4'-dipyridyl (dpy) and 1,2-bis(4-pyridyl)ethylene (bpee) or flexible conjugation-interrupted dipyridyls 1,2-bis(4-pyridyl)ethane (bpea) and 1,3-bis(4-pyridyl)propane (bpp). They included a cluster-linked 2D polymer, [(μ₄-Se)Fe₃(CO)₉Cu₂(MeCN)(dpy)_1.5] (1-dpy-2D), a cluster-pendant 1D chain, [(μ₃-Se)Fe₃(CO)₉Cu₂(dpy)₃] (1-dpy-1D), cluster-blocked 1D polymers, [(μ₃-Se)Fe₃(CO)₉Cu₂(L)] (1-L-1D, L = bpee, bpea), and a cluster-linked 2D polymer, [(μ₄-Se)Fe₃(CO)₉Cu₂(bpp)₂] (1-bpp-2D). The reversible dimensionality transformations of these three types of polymers accompanied by the change in coordination modes of 1 were achieved by the LAG addition of 1/[Cu(MeCN)₄]⁺ or dipyridyl ligands. These polymers were found to possess tunable low-energy gaps (1.49-1.72 eV) that increased in the order regarding their structural features: cluster-linked 1-dpy-2D and 1-bpp-2D, cluster-blocked 1-bpea-1D and 1-bpee-1D, and cluster-pendant 1-dpy-1D and [(μ₃-Se)Fe₃(CO)₉Cu₂(L)_2.5] (L = bpee, 1-bpee-2D; bpea, 1-bpea-2D), indicative of the importance of the participation of cluster 1. The measured electrical conductivities of 1-bpp-2D, 1-bpea-1D, and 1-dpy-1D were 3.13 × 10^-7, 2.92 × 10^-7, and 2.30 × 10^-7 S·cm^-1, respectively, which were parallel for the trend in their energy gaps, revealing semiconducting behaviors, supported by XPS, XANES, and DFT calculations. The surprising semiconductivity of the conjugation-interrupted bpp-linked 1-bpp-2D was mainly ascribed to electron transport via C-H···O(carbonyl) hydrogen bonds and aromatic C-H···π contacts within its closely packed 2D layers. Water-/light-stable polymers 1-bpp-2D, 1-bpea-2D, and 1-dpy-1D were also demonstrated to exhibit excellent pseudo-first-order photodegradation toward nitroaromatics and organic dyes, where cluster-linked polymer 1-bpp-2D performed the best, as predicted by its structural features and narrow energy gap.