The Hydrothermal Synthesis of Transition Metal Complex Templated Octamolybdates

Abstract

Abstract The hydrothermal reaction of an aqueous ammonium heptamolybdate solution with cobalt or copper metal salts in the presence of imidazole (imi) or pyrazole (pz) in the temperature range 120–180 °C and at autogenous pressure yields four fully oxidized metal‐complex‐templated octamolybdates, namely [{Cu I (imi) 2 } 4 (imi) 2 Mo 8 O 26 ] · 4H 2 O ( 1 ), (Himi) 2 [{Cu II (imi) 2 } 2 Mo 8 O 27 ] ( 2 ), [{Co II (pz) 4 } 2 (pz) 2 Mo 8 O 26 ] ( 3 ), and [{Cu II (pz) 4 } 2 Mo 8 O 26 ] · 2H 2 O ( 4 ). The single‐phase nature of the solids was established by single‐crystal and powder X‐ray diffraction, thermal analysis, and spectroscopic techniques. Compounds 1 , 3 , and 4 are neutral composite solids – 1 is a discrete molecular unit while 3 and 4 are 2D sheets. Compound 2 consists of anionic chains with imidazolium counter cations. The influence of the metal complex and temperature of the hydrothermal reaction on the formation of the different hybrid solids built of octamolybdate clusters is discussed. We also provide plausible mechanisms for the self‐assembly of the crystals in terms of supramolecular organization between metal complexes and soluble molybdenum precursors in the initial stages of the reaction. The magnetic properties of 2 , 3 , and 4 confirm the presence of Cu and Co in the divalent state with no appreciable long‐range order down to 5 K, whereas 1 is diamagnetic.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)