Three Transition-Metal Substituted Polyoxotungstates Containing Keggin Fragments: From Trimer to One-Dimensional Chain to Two-Dimensional Sheet

Three novel transition-metal substituted polyoxotungstates based on Keggin fragments, Cs 3 K 3 [Co(H 2 O) 6 ] 2 [Co(H 2 O) 3 (α-GeW 11 CoO 38 ) 3 ]·30H 2 O ( 1 ), K 18 {[Mn(H 2 O) 3 ] 2 [Mn(H 2 O) 2 ][(B-β-SiW 9 O 33 (OH))Mn 3 (H 2 O)(B-β-SiW 8 O 30 (OH))] 2 }·16H 2 O ( 2 ), and K 8 [Cd(H 2 O) 3 ] 2 [Cd 4 (H 2 O) 2 (B-α-SiW 9 O 34 ) 2 ]·20H 2 O ( 3 ), have been synthesized by reaction of dilacunary Keggin precursors K 8 [γ-GeW 10 O 36 ]·6H 2 O/K 8 [γ-SiW 10 O 36 ]·12H 2 O with transition-metal salts at ambient temperature and characterized by inductively coupled plasma (ICP) analyses, IR spectra, UV spectra, and single-crystal X-ray diffraction. The polyoxoanion of 1 is a novel trimer constructed from three mono-Co II substituted Keggin fragments [α-GeW 11 CoO 38 ] 4− linked by six W−O−Co/W bridges and a capping [Co(H 2 O) 3 ] 2+ bridge. 2 displays the one-dimensional chain built by tetrameric {[Mn(H 2 O) 3 ] 2 [Mn(H 2 O) 2 ][(B-β-SiW 9 O 33 (OH))Mn 3 (H 2 O)(B-β-SiW 8 O 30 (OH))] 2 } 18− units, which is the first one-dimensional silicotungstate containing asymmetric sandwich-type moieties constructed from [B-β-SiW 9 O 34 ] 10− and [B-β-SiW 8 O 31 ] 10− fragments. 3 utilizes the two-dimensional sheet established by tetra-Cd II substituted sandwich-type [Cd 4 (H 2 O) 2 (B-α-SiW 9 O 34 ) 2 ] 12− units and [Cd(H 2 O) 3 ] 2+ linkers, representing the first two-dimensional (3,6)-topological network with a Schläfli symbol of 3 6 4 6 5 3 built by sandwich-type Keggin units in polyoxometalate chemistry. Magnetic susceptibility measurements indicate antiferromagnetic exchange interactions within Co II ions in 1 and within Mn II ions in 2 . The best least-squares fitting values for 2 are J = −1.16 cm −1 and g = 2.13 based on the isostropic spin model. Furthermore, the room-temperature solid-state photoluminescence of 3 displays two emission bands, which are derived from O → Cd ligand-to-metal charge transfer transitions and O → W ligand-to-metal charge transfer transitions, respectively.