Powder X-ray diffraction. 1.0 boron glass capillaries filled with the corresponding solution of compounds 1-4 were left to dry overnight at room temperature in a vacuum chamber and then stored sealed. X-ray diffraction images were collected at 100 K at XRD1 beamline (Elettra, Trieste, Italy) by spinning the capillary using a wavelength of 0.7000 Å. The software FIT2D was used to obtain experimental XRPD patterns from 2D diffraction images. Calculated XRPD profiles for all four crystal structures were obtained by using the software Mecury.