The electronic-crystal structure relationship can be further illustrated by the charge density projections with yellow volumes around atoms shown in Fig. . C 8 shows tetrahedral (sp 3 ) shape around the carbon sites, corresponding to the covalent nature of the bonds, similar to diamond. Significant changes are observed for BN: 4H, 6H and 8H polytypes (Figs. ), where charges are mainly centered on nitrogen atoms due to the higher electronegativity of N (= 3.04) compared to B ( =2.03), resulting in polar covalent B-N bonding. In the ternary BC 2 N, the presence of carbon with intermediate electronegativity ( C = 2.55) slightly reduces this behavior with a skewing of the charge envelopes towards C (Figs. ).