Structural Studies of Rare Earth/Transition Metal Complex Ion Systems as a Basis for Understanding Their Thermal Decomposition to Mixed Oxides

Thermal decomposition in air of the series of complexes [Co(NH 3 ) 6 ][Ln(dipic) 3 ] · x  H 2 O, [Cr(en) 3 ][Ln(dipic) 3 ] · y  H 2 O and [Cr(urea) 6 ][Ln(dipic) 3 ] · z  H 2 O (Ln = La – Lu, excluding Pm but plus Y; dipic = 2,6‐pyridinedicarboxylate) to give oxide phases has been examined. The products were characterised by powder X‐ray diffraction, magnetic and surface area measurements. From the Co‐containing species, either Co 3 O 4 + Ln 2 O 3 or perovskite (CoLnO 3 ) products result, while the Cr‐containing species provide CrLnO 4 phases in addition, the monazite form of CrNdO 4 being detected for the first time in this way. Underpinning consideration of the solid state decomposition mechanisms, single‐crystal X‐ray structure de‐terminations have been performed on [Co(NH 3 ) 6 ][Ln(dipic) 3 ] · n  H 2 O across the Ln series, defining differing phases (alltriclinic P $\bar {1}$ ) for n = 5 (encompassing Ln = La–Pr), n = 8(.5) (Ln = Tm – Eu) and n = 10 (Ln = Pr – Er, including Y), and also on one of the low‐temperature decomposition products, [Co(NH 3 ) 6 ]Cl · dipic · 2 H 2 O ( 1 ). The structure of 1 provides evidence that conventional π‐stacking of the dipicolinate anions may be of some importance in determining the solid state array, whereas consideration of all structures involving [Ln(dipic) 3 ] 3– anions indicates that “edge‐to‐face” interactions between dipicolinate ligands of adjacent complex anions may also be determinants of the formation of sheet‐like arrays of the trianions commonly observed in these compounds. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)