K2NiF4-type CaLnCoO(4) (Ln = Sm and Gd) has been synthesized at 1173 or 1223 K in air using citric acid (CA) and ethylene glycol (EG). CaLnCoO(4) (Ln = Sm and Gd) has an orthorhombic structure with the space group Bmab. The average particle sizes are approximately 300 nm for CaSmCoO4 and approximately 170 nm for CaGdCoO4, respectively. The global instability index (GII) indicates that the crystal structure of CaGdCoO4 is more stable than that of CaSmCoO4, CaLnCoO(4) (Ln = Sm and Gd) is a p-type semiconductor and shows paramagnetic behavior above 5 K. The 1/chi-T curve of CaSmCoO4 deviates from the Curie-Weiss law, whereas the 1/chi-T curve of CaGdCoO4 follows the Curie-Weiss law in the temperature range of 5 <= T <= 300 K. From the values of the observed effective magnetic moment (mu(eff)) of CaLnCoO(4) (Ln = Sm and Gd), it is considered that the spin state of the Co3+ ion is low. (c) 2006 Elsevier Ltd. All rights reserved.