Metal–Ligand Complexes as Molecular Metal-Ion Reservoirs for Highly Promoted Growth of β-Co(OH)2 Microplates

Highly developed single crystals of metal hydroxide can be achieved through a controlled release of metal ions in the growth phase. We report an alternative protocol for the synthesis of β-Co(OH)2 microplates by utilizing ethylenediamine-cobalt (En-Co) complexes as molecular reservoirs of Co2+ ions for a promoted crystal growth. Through a hydrothermal treatment, highly developed β-Co(OH)2 microplates could be obtained with a lateral size varying from 0.2 to 20 μm. Our mechanism study revealed that the Co2+ ions encapsulated by En ligands were protected from precipitation under ambient alkaline conditions but could be thermally released in a kinetically controlled manner. It is demonstrated that the amount of En in the system is responsible for the controlled release of Co2+ ions from stable En-Co complexes, which tunes the size of β-Co(OH)2 crystals. These large β-Co(OH)2 microplates exhibited a few unusual physical characteristics as to ordinarily grown platelets.