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)C R)(6)L(3)](ClO4) (R = various groups; L = pyridine (py), 4-picoline (p ic) 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 solu tion followed by addition of NBu(4)(n)ClO(4) leads to isolation of [V3 O(O(2)CR)(6)L(3)](ClO4) salts in 47-95% yields. A similar procedure fo r R = C6H5, C6H4-p-OMe, C6H3-m-Me(2), and C6H4-p-Cl but omitting addit ion of NaO(2)CR provides the corresponding benzoate or substituted-ben zoate derivatives in 24-56% yields. The X-ray structure of [V3O(O(2)CE t)(6)(pic)(3)](ClO4) (4) shows the anion to consist of a [V3O](7+) tri angular fragment with a mu(3)-O2- ion in the V-3 plane; each triangula r edge is bridged by two EtCO(2)(-) groups in their familiar syn,syn m odes, and there is a terminal pic group on each V-III completing disto rted octahedral geometries at the metal atoms. The cation has imposed C-2 symmetry (isosceles V-3 triangle), the C-2 axis passing through on e 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 refi ned on F to conventional R (R(W)) values of 0.058 (0.066). Variable-te mperature, solid-state magnetic susceptibility measurements were made on complex 1 in the 5.01-280 K region in a 1 kG magnetic field. The ef fective magnetic moment (mu(eff)) per V-3 unit decreases gradually fro m 4.64 mu(B) at 280 K to 1.76 mu(B) at 5.01 K. The data were fit to th e theoretical expression for an isosceles V-3(III) complex, and the fi tting 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' ref ers to the unique exchange interaction within the isosceles triangle. The ground state of complex 1 thus has S = 0.