Two Mixed-Valence Vanadium(III,IV) Phosphonoacetates with 16-Ring Channels: H<sub>2</sub>(DABCO)[V<sup>IV</sup>O(H<sub>2</sub>O)V<sup>III</sup>(OH)(O<sub>3</sub>PCH<sub>2</sub>CO<sub>2</sub>)<sub>2</sub>]·2.5H<sub>2</sub>O and H<sub>2</sub>(PIP)[V<sup>IV</sup>O(H<sub>2</sub>O)V<sup>III</sup>(OH)(O
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Two isostructural mixed-valence vanadium phosphonoacetates H2(DABCO)[VIVO(H2O)VIII(OH)(O3PCH2CO2)2]·2.5H2O (1) and H2(PIP)[VIVO(H2O)VIII(OH)(O3PCH2CO2)2]·2.5H2O (2) have been synthesized. They crystallize in the orthorhombic space group Pnna with a = 7.0479(10) Å, b = 15.307(2) Å, and c = 17.537(3) Å for 1 and a = 7.0465(9) Å, b = 15.646(2) Å, and c = 17.396(2) Å for 2. X-ray single-crystal diffraction reveals that 1 and 2 have a three-dimensional open framework featuring 16-ring ellipsoid channels that are filled with doubly protonated 1,4-diazabicyclo[2,2,2]octanium/piperazinium cations and water molecules. According to the classification in metal−organic frameworks, 1 and 2 contain infinite (−O−V−)∞ chains that are cross-linked by “metalloligand” [VO(H2O)(O3PCH2CO2)2]4- into a 3-D net of the sra topology. The temperature dependence of the magnetic susceptibility of 1 shows that the χmT value in the range of 60−320 K is constant of 1.105 cm3 K mol-1/V2 unit, and upon further cooling, the χmT value rapidly increases to 1.81 cm3 K mol-1 at 2 K. The corresponding effective magnetic moment (μeff)/V2 unit varies from 2.97 μB at 320 K to 3.80 μB at 2 K. The magnetic data in the range of 2−320 K follow the Curie−Weiss law with C = 1.074 cm3 K mol-1 and ϑ = −1.34 K.
