Structural, spectroscopic, and magnetochemical characterization of the trinuclear vanadium(III) carboxylates [V3O(O(2)CR)(6)L(3)](ClO4) (R=various groups; L=pyridine, 4-picoline, 3,5-lutidine)

Synthetic procedures are described that allow access to the [V3O(O(2)CR)(6)L(3)](ClO4) (R = various groups; L = pyridine (py), 4-picoline (pic) or 3,5-lutidine (lut)) family of complexes. Treatment of VCl3(THF)(3) with NaO(2)CR (R = Me, Et) in RCO(2)H/py, pic/MeCN, or CH2Cl2 solution followed by addition of NBu(4)(n)ClO(4) leads to isolation of [V3O(O(2)CR)(6)L(3)](ClO4) salts in 47-95% yields. A similar procedure for R = C6H5, C6H4-p-OMe, C6H3-m-Me(2), and C6H4-p-Cl but omitting addition of NaO(2)CR provides the corresponding benzoate or substituted-benzoate derivatives in 24-56% yields. The X-ray structure of [V3O(O(2)CEt)(6)(pic)(3)](ClO4) (4) shows the anion to consist of a [V3O](7+) triangular fragment with a mu(3)-O2- ion in the V-3 plane; each triangular edge is bridged by two EtCO(2)(-) groups in their familiar syn,syn modes, and there is a terminal pic group on each V-III completing distorted octahedral geometries at the metal atoms. The cation has imposed C-2 symmetry (isosceles V-3 triangle), the C-2 axis passing through one V atom and the central mu(3)-O atom, but has D-3h virtual symmetry (equilateral V-3 triangle). Complex 4 crystallizes in monoclinic space group C2/c with the following unit cell dimensions at -171 degrees C: a = 13.935(2) Angstrom, b = 18.323(2) Angstrom, c = 17.470(2) Angstrom, beta = 95.55(1)degrees, V = 4439.7 Angstrom(3), Z = 4. The structure was solved using 2657 unique reflections with F > 3 sigma(F) and refined on F to conventional R (R(W)) values of 0.058 (0.066). Variable-temperature, solid-state magnetic susceptibility measurements were made on complex 1 in the 5.01-280 K region in a 1 kG magnetic field. The effective magnetic moment (mu(eff)) per V-3 unit decreases gradually from 4.64 mu(B) at 280 K to 1.76 mu(B) at 5.01 K. The data were fit to the theoretical expression for an isosceles V-3(III) complex, and the fitting parameters were J = -18.0(7) cm(-1), J' = -10.4(4) cm(-1), and g = 1.985, with TIP held constant at 600 x 10(-6) cm(3) mol(-1); J' refers to the unique exchange interaction within the isosceles triangle. The ground state of complex 1 thus has S = 0.