To understand the formation of our MOFs in more detail, the stoichiometry and the supersaturation of the building blocks were varied to control the growth kinetics and concentration of nuclei formation during crystallization (Figure ). The morphology and size of the crystals changed with the stoichiometry of the building blocks. The ratios of the two building blocks were varied within the range of NiCl2:CSB from 0.5:1 to 4:1. The starting concentration of CSB was 0.6 mM for these experiments. We observed large rod-like crystals (l = 40.4 ± 10.2 μm) when using a metal salt-to-ligand ratio of 0.5:1 (Figure ). When the metal salt-to-ligand ratio is 1:1 both sheafs and spherulites are formed. These sheafs (36.2 ± 6.1 μm) are larger compared to the sheafs obtained when using a metal-to-ligand molar ratio 2:1 (12.0 ± 2.5 μm). Under this condition, the sheafs are metastable and continue to develop into the thermodynamically favorable spherulites (50.4 ± 8.6 μm). Under these conditions, almost all the branches of the fantails are directly attached to the nucleating central rod. It indicates that the surfaces of the central rods become unstable and non-crystallographic branching occurs. The surfaces of the resulting square-branches are more stable as is evident from the single generation of branching (Figure ). These structures bear some similarity to fluorapatite-gelatine reported by These structures have only a first-generation branching. Increasing the metal-to-ligand ratio to 4:1 produced mostly plates (18.6 ± 3.5 μm), half sheafs (12.3 ± 1.1 μm) and sheafs as a minor product (11.6 ± 3.4 μm) (Figure ).