Untypical [VOPO₄]^? layer in vanadyl phosphates with variant interlayer gap of double-tiered template

Four new organically templated layered vanadyl(IV) phosphates, (Hcha)VOPO₄·0.5H₂O (cha = cyclohexylamine) (1), (Hchpa)VOPO₄·0.5H₂O (chpa = cycloheptylamine) (2), (Hcha)_0.5(Hchpa)_0.5VOPO₄·0.5H ₂O (3), and (H₂aepip)[(VOPO₄) ₂(H₂O)]·H₂O (aepip = N-(2-aminoethyl)piperazine) (4), have been synthesized under mild hydrothermal conditions and characterized by single-crystal X-ray diffraction, thermogravimetric analysis, magnetic susceptibility, and electron paramagnetic resonance (EPR) spectroscopy. They displayed a large interlayer gap propped up by an unprecedented double-tiered monoamine in vertical angles generating the lightest layered VPO material ever prepared and characterized. The anionic [VOPO₄]^? sheets for all four compounds are constructed by a common secondary building unit consisting of one copper-acetate-type {(V ^IVO)₂(μ₂-PO₄)₄} cluster and two vanadium polyhedra. The d¹ state was confirmed by both magnetic susceptibility studies and EPR spectra. Moreover, compounds 1 and 4 showed antiferromagnetism with T_N at 30 K, the highest ever observed in layered vanadyl phosphates. The structural relationship, template arrangement, magnetic property, thermal stability, and correlation between interlayer gaps and densities are discussed. Compounds 1?3 crystallized in the monoclinic space group P2₁/c (no. 14) with Z = 8, whereas compound 4 crystallized in the orthorhombic space group Pbca (no. 61) with Z = 4. Crystal data of 1, a = 16.3461(9) Å, b = 14.2641(8) Å, c = 9.4037(5) Å, β = 94.519(1)^o, V = 2185.8(2) ų; 2, a = 17.0773(5) Å, b = 14.3449(4) Å, c = 9.4251(3) Å, β = 93.976(1)^o, V = 2303.3(1) ų; 3, a = 16.6765(4) Å, b = 14.2927(3) Å, c = 9.4120(3) Å, β = 95.389(1) ^o, V = 2233.5(1) ų; 4, a = 14.2517(9) Å, b = 9.4012(6) Å, c = 24.442(2) Å, V = 3274.8(4) ų.