Synthesis, structure, and magnetic ordering of layered (2-D) V-based tris(oxalato)metalates

The reaction of K₃[M^III(ox)₃] ·3H₂O [M = V (1), Cr; ox = oxalate], Mn(II)/V(II), and [N(n-Bu)₄]Br in water leads to the isolation of 2-D V-based coordination polymers, {[N(n-Bu)₄][Mn^IIV ^III(ox)₃]}_n, (2), {[N(n-Bu)₄][V ^IICr^III(ox)₃]}_n (3), {[N(n-Bu) ₄][V^IIV^III(ox)₃]}_n (4), and an intermediate in the formation of 4, {[N(n-Bu)₄][V ^IIV^III(ox)₃(H₂O)₂]} _n·2.5H₂O (4a), while 1-D [V^II(ox)(H ₂O)₂]_n (5) is obtained by using Na ₂ox and [V(OH₂)₆]SO₄ in water. The structures of 1-5 have been investigated by single crystal and/or powder X-ray crystallography. In 1, V^III is coordinated with three oxalate dianions as an approximately D₃ symmetric, trigonally distorted octahedron. 1 is paramagnetic [μ_eff = 2.68 μ_B at 300 K, D = 3.84 cm^-1 (D/k_B = 5.53 K), θ = -1.11 K, and g = 1.895], indicating an S = 1 ground state. 2 exhibits intralayer ferromagnetic coupling below 20 K, but does not magnetically order above 2 K, and 3 shows a strong antiferromagnetic interaction between V^II, S = 3/2 and Cr^III, S = 3/2 ions (θ = -116 K) within the 2-D layers. 4 and 4a magnetically order as ferrimagnets at T_c's, taken as the onset of magnetization, of 11 and 30 K, respectively. The 2 K remanent magnetizations are 2440 and 2230 emu·Oe mol^-1 and the coercive fields are 1460 and 4060 Oe for 4 and 4a, respectively. Both 4 and 4a clearly show frequency dependence, indicative of spin-glass-like behavior. The glass transition temperatures were at 6.3 and 27 K, respectively, for 4 and 4a. 1-D 5 exhibits antiferromagnetic coupling of -4.94 cm^-1 (H = -2JΣ_i=1ⁿS_i·S_i-1 gμ_BΣ_i=0ⁿH·S_i) between the V^II ions.