X11 may be N or C-[(L11)a11-(R11)b11], X12 may be N or C-[(L12)a12-(R12)b12], X13 may be N or C[(L13)a13-(R13)b13], and X14 may be N or C-[(L14)a14-(R14)b14],
X21 may be N or C-[(L21)a21-(R21)b21], X2 may be N or C-[(L22)a22-(R22)b22], and X23 may be N or C-[(L23)a23-(R23)b23],
X29 may be O, S, C(R27)(R28), Si(R27)(R28), or N-[(L29)a29-(R29)b29],
X31 may be N or C-[(L31)a31-(R31)b31], X32 may be N or C-[(L32)a32-(R32)b32], and X33 may be N or C-[(L33)a33-(R33)b33],
X41 may be N or C-[(L4)a41-(R41)b41], X42 may be N or C-[(L42)a42-(R2)b42], X43 may be N or C-[(L43)a43-(R43)b43], and X4 may be N or C-[(L4)a44-(R44)b44],