Polar scatter plot and histogram distributions for halogen bonds. (
a) Polar scatter plot relative to Θ
1 and the normalized halogen (
X) to oxygen distances (
RX···O, where
RX···O ≤
RvdW) are plotted for
X&
Cl (green circles),
XBr (red triangles), and
XI (cyan squares). Both the
x and
y axes of the plot represent
RX···O, with the
y axis aligned along the C
X bond (180°) and the
x axis perpendicular to the C
X bond (90°). The shaded region from 90° to 120° indicates the Θ
1 angles that were excluded from our data set. (
b) Histogram distribution of Θ
1 angles. The number of short
X···O interactions to chlorine (green), bromine (red), and iodine (cyan) halogen atoms, and their sum (gray) are counted and placed into 5° bins of Θ
1 angle and plotted as a 3D histogram. (
c) Histogram distribution of Θ
2 angles. This plot is similar to
b, except the interactions are placed into 10° bins of Θ
2. (
d) Histogram distribution of the dihedral angle Ψ calculated for short halogen bonds involving the O
C group of the peptide backbone.