The optimized unit cell of p-BCN consists of six atoms (2B, 2N, and 2C), with a B/C/N ratio of 1:1:1, forming a pentagonal 3 layered 2D monolayer. The first, second, and third layers consist of B (or N), purely C, and N (or B) atoms inside a rectangular cell, respectively. This monolayer belongs to C 2 2 symmetry (space group 4) in the pentagonal crystal family. The fully relaxed structure (Fig. ) consists of lattice constants a=3.69 Å and b=3.66 Å, which fairly agree with previous reports . Expanding the unit cell into a larger supercell, one can see four distinct irregular pentagonal Cairo tiles (labeled by I-IV in Fig. ), having different bond lengths and bond angles between atoms. We consider two C atoms located in different positions form different bond angles and bond lengths with other atoms. We mark the positions of these two atoms as C1 and C2 in the unit cell to remove the obscure visualization. Although the previous report has not shown this fact, here, we have presented the detailed bond analysis (Table ). The bond length plays a direct role in the stability and physical and chemical properties. The shorter bond length allows to have stronger structure. Comparatively, the B-N (1.43 Å) is the shortest and strongest quasi-sp 3 hybridized bond. This particular bond in p-BCN is even shorter than in the h-BN monolayer (1.45 ). Moreover, the thickness of the p-BCN monolayer, calculated by subtracting the topmost and lowermost vertical positioning of atoms, is 1.36 Å. This thickness is larger than other 2D penta structures including the penta-graphene (1.20 Å ) but lesser than those of penta-BP 5 (2.50 Å ) and penta-CN 2 (1.52 Å ).