Metal–organic Kagome lattices M3(2,3,6,7,10,11-hexaiminotriphenylene)2 (M = Ni and Cu): from semiconducting to metallic by metal substitution

Abstract

Motivated by recent experimental synthesis of a semiconducting metal–organic graphene analogue (J. Am. Chem. Soc., 2014, 136, 8859), i.e., Ni₃(2,3,6,7,10,11-hexaiminotriphenylene)₂ [Ni₃(HITP)₂], a new Kagome lattice, Cu₃(HITP)₂, is designed by substituting the coordination of Ni by Cu. Such substitution results in interesting changes in electronic properties of the M₃(HITP)₂ bulk and two-dimensional (2D) sheets. In Ni₃(HITP)₂, each Ni atom adopts the dsp² hybridization, forming a perfect 2D conjugation, whereas in Cu₃(HITP)₂, each Cu atom adopts the sp³ hybridization, resulting in a distorted 2D sheet. The M₃(HITP)₂ bulks, assembled from M₃(HITP)₂ sheets via both strong π–π interaction and weak metal–metal interaction, are metallic. However, the 2D Ni₃(HITP)₂ sheet is a semiconductor with a narrow band gap whereas the 2D Cu₃(HITP)₂ sheet is a metal. Remarkably, both the 2D M₃(HITP)₂ Kagome lattices possess Dirac bands in the vicinity of the Fermi level. Additional ab initio molecular dynamics simulations show that both sheets exhibit high thermal stability at elevated temperatures. Our theoretical study offers new insights into tunability of electronic properties for the 2D metal–organic frameworks (MOFs).