In contrast, 4HMS presents a rather different situation. Overall, we observe that all four groups are constrained to a preferred orientation which allows for a stable dipole-charge interaction to form between the chelator hydroxamate groups and Zr 4+ . While there are some differences among the angular distributions of different groups, the peaks are localized in two defined regions ranging from one to two radians in the Zr 4+ -O-N angles and from two to three radians in the Zr 4+ -O-C angles.