An Insight into nd10 Metal Cyanide‐based Coordination Polymers Through ab‐initio Calculations: Electronic Properties and Optical Response

Abstract

Semiconductors are essential for modern life since they are the basis of many current technologies that are related to better living standards. Some of them, characterized by the periodic assembling of metal cyanides with filled d-shell (nd 10 ) constitute an interesting series of cyanide-based coordination polymers with physical properties such like anomalous anisotropic thermal expansion and quantum confinement effects related to the polymer's width that can be exploited for technological applications. Herein, the electronic structure of nd 10 metal cyanide-based systems were studied both experimentally and through Density Functional Theory. The band gap found for one-dimensional (1D) À MÀ C�NÀ (M=Cu, Ag, Au) and tetrahedral MÀ (C�N) 2 (M=Zn, Cd, Hg) systems can be attributed to Laporteallowed π!π* (Metal to Ligand Charge Transfer mechanism) combined with metal center (d!s,p) electronic transitions. Aurophilic bonding was found on the AuCN structure, and a new forbidden electronic transition associated to its band gap is reported. Computed effective and reduced masses from carriers revealed that carrier mobility and quantum confinement effects are greater in 1D systems.

Computational and Experimental Determination of the Electronic Structure and Optical Properties of Three-Dimensional Zn[M(CN)4] Tetracyanates (M = Ni, Pd, and Pt)

“…Contrary to these results, the PBE functional strongly underestimates the band gap energies by about 2 eV. Unlike other coordination polymers reported, the materials studied herein require a method that better accounts for the electron correlation for an accurate description of the electronic properties. ,, …”

“…11 Considering this difference, the electronic structure and the electronic band gap were calculated by using the hybrid HSE06 density functional since it is known that it produces an accurate description of the electronic properties of cyanide-based coordination polymers. 23,31,32,41 For comparison, the PBE exchange-correlation density functional was also used to calculate the electronic band gap energy (Table 2). Figure 4 shows the electron band structures, the calculated band gap energies, and the path of the transitions.…”

“…Unlike other coordination polymers reported, the materials studied herein require a method that better accounts for the electron correlation for an accurate description of the electronic properties. 32,41,53 The unit cell of the tetracyanate structures was optimized as described in the Materials and Methods section. The relaxed geometries are presented in Table 1.…”

“…This behavior is also observed for other cyanide-based coordination complexes whose constituent metals have closed electronic shells (n)­d (e.g., nitroprussides, AuCN, Cd­(CN) 2 , etc. ). ,,− The charge distributions strongly depend on the coordination environment of metals, the nature of the metals, and the presence of different ligands (NO + , pyridine, etc.). In those cases, the excess charge is also located on the nitrogen ends of cyano ligands at different rates, as a consequence of charge-transfer phenomena (metal–ligand). ,, …”

“…From these results, the minor energy electronic transitions associated with the band gap have an indirect nature (Figure S5). This suggests that the periodic network strongly affects the electronic structure as occurs in analogous tetrahedral cyanide-based Zn polymers. ,, In particular, Zn­[Pd­(CN) 4 ] has the highest band gap energy (5.82 eV), followed by Ni- (5.63 eV) and Pt-containing (5.65 eV) materials; however, this value differs from previous computational results by more than 2 eV . Considering this difference, the electronic structure and the electronic band gap were calculated by using the hybrid HSE06 density functional since it is known that it produces an accurate description of the electronic properties of cyanide-based coordination polymers. ,,, For comparison, the PBE exchange-correlation density functional was also used to calculate the electronic band gap energy (Table ).…”