LAUSR

Abstract Conditions necessary for the formation of isostructural sodium heteropoly decatungstolanthanidates(III) with Peacock–Weakley type anion Na 9 [Ln(W 5 O 18 ) 2 ]·35H 2 O (Ln = Gd, Er) in Ln(NO 3 ) 3 –Na 2 WO 4 –HNO 3 –H 2 O solutions with a ratio ν (Ln):  ν (W) = 1:10, acidified up to Z  =  ν (H + )/ ν (WO 4 2− ) = 0.80, were established. The synthesized salts were characterized by Single Crystal X-ray analysis, FT-IR spectroscopy, and scanning electron microscopy. The correlation between structural parameters and the charge of Ln-heteroatom nuclei was determined. Comparison of structural parameters for isostructural neutral salts Na 9 [Ln(W 5 O 18 ) 2 ]·35H 2 O (Ln = Eu, Gd, Tb, Dy, Ho, Er) allowed us to establish linear dependences between decreasing lengths of Ln—O b (W) bonds and interatomic distances O⋯O in Peacock–Weakley type heteropoly anions, and the nuclear charge of Ln–heteroatom. Graphic Abstract Two isostructural sodium heteropoly decatungstolanthanidates(III) with Peacock–Weakley type anion Na 9 [Ln(W 5 O 18 ) 2 ]·35H 2 O (Ln = Gd, Er) have been synthesized from Ln(NO 3 ) 3 –Na 2 WO 4 –HNO 3 –H 2 O solutions, acidified up to Z  =  ν (H + )/ ν (WO 4 2− ) = 0.80, and characterized by single-crystal X-ray diffraction, FT-IR spectroscopy, and scanning electron microscopy.