Tetranuclear vanadium com
plexes with alkoxy ligands,[V
4O
4{
,
,
3-(OCH
2)
3CCH
3}
2(OCH
3)
6](
1) and [V
4O
4{
-(OCH
2)
3CCH
3}{
,
3-(OCH
2)
3CCH
3}{
,
,
3-(OCH
2)
3CCH
3}(OR)
3](R = C
2H
5 (
2), R =CH(CH
3)
2 (
3), R =CH
3(
4)), were synthesized by reacting VO(OR)
3 andH
3thme (H
3thme =1,1,1-tris(hydroxymethyl)ethane) in alcohol.Com
plex
1 crystallized in the monoclinic s
pace grou
pP2
1/
n with
a =9.646(4) Å,
b = 11.502(3) Å,
c =11.960(3) Å,
= 90.20(3)
,
V = 1326.9 (7)Å
3,
Z = 2 and
R (wR
2)= 0.045 (0.143). Com
plex
2 also crystallizedinthe monoclinic s
pace grou
p P2
1/n with
a = 8.290(8) Å,
b = 12.237(2) Å,
c = 29.118(4) Å,
= 89.455(9)
,
V= 2954(3) Å
3,
Z = 4, and
R(wR
2) = 0.049 (0.126). Both
1 and
2 are neutral, discrete com
plexes
possessing acommon [V
4O
16]
12-core, which consists of four vanadium(V) atoms chelated by two(
1) or three (
2) tridentatethme
3- ligands and by six (
1) orthree (
2) RO
- grou
ps. Com
pound
1 exhibits a crystallogra
phically requiredinversion center; in contrast, com
plex
2 exhibits nocrystallogra
phically im
posed symmetry, and its threetrialkoxyligands each coordinate differently (onethme
3- is coordinated in a new coordinationmode with the oxygens ina terminal, doubly-bridging and tri
ply-bridging mode). Bothcom
pounds
1 and
2 maintain their structuresinsolution, although com
pound
1 also forms a second minors
pecies u
pon dissolution. Sequential exchanges of theRO
- grou
ps in com
plexes
2 and
3were investigated by
51V and
1H NMRs
pectrosco
py. For exam
ple,[V
4O
4(thme)
3(OC
2H
5)
3]will react with CH
3OH to generate[V
4O
4(thme)
3(OCH
3)
3](
4). These reactions werefound to be reversible. The time scale of the alcohol exchangereactions were found to vary de
pending on thevanadium center that is undergoing the exchange.