Electronic properties of substitutional impurities in graphenelike <math> <mrow> <msub> <mi mathvariant='"normal"'>C</mi> <mn>2</mn> </msub> <mi mathvariant='"normal"'>N</mi> </mrow> </math> , <math> <mrow> <mi>t</mi> <mi>g</mi> <mtext>−</mtext> </mrow></math>