Synthesis, Structure, and Magnetic Ordering of Layered (2-D) V-Based Tris(oxalato)metalates

The reaction of K3[MIII(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][MnIIVIII(ox)3]}n (2), {[N(n-Bu)4][VIICrIII(ox)3]}n (3),
{[N(n-Bu)4][VIIVIII(ox)3]}n (4), and an intermediate in the formation of 4, {[N(n-Bu)4][VIIVIII(ox)3(H2O)2]}n·2.5H2O (4a),
while 1-D [VII(ox)(H2O)2]n (5) is obtained by using Na2ox 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, VIII is coordinated with three oxalate
dianions as an approximately D3 symmetric, trigonally distorted octahedron. 1 is paramagnetic [μeff = 2.68 μB at
300 K, D = 3.84 cm-1 (D/kB = 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 VII, S = 3/2 and CrIII, S = 3/2 ions (θ = −116 K) within the 2-D
layers. 4 and 4a magnetically order as ferrimagnets at Tc'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 = −2J

Si·Si-1 − gμB

H·Si) between the VII ions.