Structural, Spectroscopic, and Magnetochemical Characterization of the Trinuclear Vanadium(III) Carboxylates [V(3)O(O(2)CR)(6)L(3)](ClO(4)) (R = Various Groups; L = Pyridine, 4-Picoline, 3,5-Lutidine)

Synthetic procedures are described that allow access to the V(3)O(O(2)CR)(6)L(3)](ClO(4)) (R = various groups; L = pyridine (py), 4-picoline (pic) or 3,5-lutidine (lut)) family of complexes. Treatment of VCl(3)(THF)(3) with NaO(2)CR (R = Me, Et) in RCO(2)H/py, pic/MeCN, or CH(2)Cl(2) solution followed by addition of NBu(n)(4)ClO(4) leads to isolation of V(3)O(O(2)CR)(6)L(3)](ClO(4)) salts in 47-95% yields. A similar procedure for R = C(6)H(5), C(6)H(4)-p-OMe, C(6)H(3)-m-Me(2), and C(6)H(4)-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 V(3)O(O(2)CEt)(6)(pic)(3)](ClO(4)) (4) shows the anion to consist of a V(3)O](7+) triangular fragment with a &mgr;(3)-O(2)(-) 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 &mgr;(3)-O atom, but has D(3)(h)() 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) ?, b = 18.323(2) ?, c = 17.470(2) ?, beta = 95.55(1) degrees, V = 4439.7 ?(3), Z = 4. The structure was solved using 2657 unique reflections with F > 3sigma(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 (&mgr;(eff)) per V(3) unit decreases gradually from 4.64 &mgr;(B) at 280 K to 1.76 &mgr;(B) at 5.01 K. The data were fit to the theoretical expression for an isosceles V(III)(3) 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.