[Er III (BHT)3] (0.071 g, 0.087 mmol) is dissolved in n-pentane (18.0 g) and dtepy (0.030 g, 0.057 mmol) is added in one portion. The mixture is stirred for ca. 15 minutes until it becomes clear and is left for crystallization at room temperature. Small yellow crystals form within 1-2 days. The identity and purity of the compound is confirmed by powder X-ray diffraction (PXRD) measurements (Figure ). Yield: 30 mg (30%)