Two Families of Rare-Earth-Substituted Dawson-type Monomeric and Dimeric Phosphotungstates Functionalized by Carboxylic Ligands

Two series of novel organic–inorganic hybrid carboxylated rare-earth-substituted monolacunary Dawson-type phosphotungstate monomers [Hdap] 4 [RE(H 2 O)(Hpic) 3 ][RE(Hpic) 2 (α 2 -P 2 W 17 O 61 )]·21H 2 O [RE = Gd III ( 1 ), Tb III ( 2 ), Dy III ( 3 ), Ho III ( 4 ), Er III ( 5 ), Tm III ( 6 ), Yb III ( 7 ), Y III ( 8 ); Hpic = 2-picolinic acid, dap = 1,2-diaminopropane] and dimers [H 2 dap] 8 [RE 2 (H 2 ox) 2 (ox)(α 2 -P 2 W 17 O 61 ) 2 ]·25H 2 O [RE = Ho III ( 9 ), Er III ( 10 ), Tm III ( 11 ), Yb III ( 12 ), Y III ( 13 ); H 2 ox = oxalic acid] have been hydrothermally synthesized and characterized by elemental analyses, IR spectra, thermogravimetric measurements, and X-ray single-crystal diffraction. The monomeric polyoxoanion skeleton of isomorphic 1 – 8 is constructed from a monolacunary Dawson-type phosphotungstate implanted by a [RE1(Hpic) 2 ] 3+ cation in the polar position and supported by the other [RE 2 (H 2 O)(Hpic) 3 ] 3+ cation on the equatorial belt. Interestingly, two kinds of RE cations separately coordinate to two or three Hpic ligands in the form of N–C–C–O–RE containing five-membered ring fashion. The dimeric polyoxoanion backbone of isomorphic 9 – 13 is built by two mono-RE substituted Dawson-type phosphotungstate fragments [RE(H 2 ox)(α 2 -P 2 W 17 O 61 )] 7– joined together by an ox 2– linker. The visible photoluminescence spectra of solid-state 2, 3, 5, and 10 and the NIR photoluminescence properties for solid-state 5, 10, 7, and 12 at ambient temperature have been carried out, which are mainly derived from the RE 3+ f–f electron transitions. Magnetic susceptibility measurements and fitting results of 3 demonstrate that 3 is a single-molecule magnet.