Two mixed-valence vanadium(III,IV) phosphonoacetates with 16-ring channels: H2(DABCO)[V(IV)O(H2O)V(III)(OH)(O3PCH2CO2)2].2.5H2O and H2(PIP)[V(IVO)(H2O)V(III)(OH)(O3PCH2CO2)2].2.5H2O

Two isostructural mixed-valence vanadium phosphonoacetates H2(DABCO)V(IV)O(H2O)V(III)(OH)(O3PCH2CO2)2].2.5H2O (1) and H2(PIP)V(IV)O(H2O)V(III)(OH)(O3PCH2CO2)2].2.5H2O (2) have been synthesized. They crystallize in the orthorhombic space group Pnna with a = 7.0479(10) A, b = 15.307(2) A, and c = 17.537(3) A for 1 and a = 7.0465(9) A, b = 15.646(2) A, and c = 17.396(2) A 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-diazabicyclo2,2,2]octanium/piperazinium cations and water molecules. According to the classification in metal-organic frameworks, 1 and 2 contain infinite (-O-V-)(infinity) 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 chi(m)T value in the range of 60-320 K is constant of 1.105 cm3 K mol(-1)/V2 unit, and upon further cooling, the chi(m)T value rapidly increases to 1.81 cm3 K mol(-1) at 2 K. The corresponding effective magnetic moment (mu(eff))/V2 unit varies from 2.97 mu(B) at 320 K to 3.80 mu(B) 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 Theta= -1.34 K.