<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>The title compounds are hydrothermally synthesized from mixtures of KOH, GeO<sub>2</sub>, Gd(NO<sub>3</sub>)<sub>3</sub>, Tb(NO<sub>3</sub>)<sub>3</sub>, and H<sub>2</sub>O (silver tube, 100 MPa, 400 °C, 5 h).</p> </abstract>