Vanadium(V) tartrato complexes: Speciation in the H3O +(OH-)/H2VO4-/(2R,3R)- tartrate system and X-ray crystal structures of Na4[V 4O8(rac-tart)2]·12H2O and (NEt4)4[V4O8((R,R)-tart) 2]·6H2O ...

Article abstract of DOI:10.1021/ic062223h

Full title. 3971-3983 Vanadium(V) tartrato complexes: Speciation in the H₃O ⁺(OH^-)/H₂VO₄^-/(2R,3R)- tartrate system and X-ray crystal structures of Na₄[V ₄O₈(rac-tart)₂]·12H₂O and (NEt₄)₄[V₄O₈((R,R)-tart) ₂]·6H₂O (tart = C4H2O6^4-). A study of the aqueous H₃O⁺(OH^-)/H ₂VO₄^-/(2R,3r)-tartrate system has been performed at 273 K in a 1.0 mol/L Na⁺(Cl^-) ionic medium using ⁵¹V NMR spectroscopy. In this relatively complicated system, more than 12 different species were observed. Ligand concentration, vanadate concentration, and pH variation studies were carried out, particularly for the range of pH 5.8-8.0 and for pH 2.4. Chemical shifts, vanadium-ligand stoichiometry, and also composition and formation constants for some, but not all, species are given. Despite some reduction of vanadium-(V) to vanadium(IV) in an acidic medium at pH ≈2.4, the stoichiometries of the principal species in solution at this pH were determined. Electrospray ionization mass spectra for some solutions were obtained and were in accordance with the conclusions drawn from the speciation studies. A series of crystalline vanadium(V) tartrato complexes M₄[V₄O₈(tart)₂]·aq were also prepared and characterized. X-ray diffraction studies of Na ₄[V₄O₈(rac-tart)₂]·12H ₂O (1) and (NEt₄)₄[V₄O ₈((R,R)-tart)₂]·6H₂O (2) revealed unique tetranuclear [V₄O₈(tart)₂]^4- ions for which the {V₄O₄} rings have boat conformations.

Full text of DOI:10.1021/ic062223h

Inorg. Chem. 2007, 46, 3971−3983
+
-
-
Vanadium(V) Tartrato Complexes: Speciation in the H O (OH )/H VO /
3
2
4
(2R,3R)-Tartrate System and X-ray Crystal Structures of
Na [V O (rac-tart) ]
‚
12H O and (NEt ) [V O ((R,R)-tart) ]
‚
6H O (tart
)
4
4
8
-
2
2
4 4
4
8
2
2
4
C H O
)
4
2
6
Peter Schwendt,*,† Alan S. Tracey,‡ Jozef Tatiersky,† Jana G a´ likov a´ ,† and Zdirad Z a´ k§
ˇ
Department of Inorganic Chemistry, Faculty of Natural Sciences, Comenius UniVersity,
Mlynsk a´ dolina, BratislaVa 84215, SloVak Republic, Department of Chemistry, Simon Fraser
UniVersity, Burnaby, British Columbia V5A 1S6, Canada, and Department of Inorganic Chemistry,
Faculty of Natural Sciences, Masaryk UniVersity, Kotl a´ rˇ sk a´ 2, Brno 61137, Czech Republic
Received November 22, 2006
+
-
-/(2R,3R)-tartrate system has been performed at 273 K in a 1.0 mol/L
A study of the aqueous H
3
O (OH )/H
2
VO
4
+
-
51
Na (Cl ) ionic medium using V NMR spectroscopy. In this relatively complicated system, more than 12 different
species were observed. Ligand concentration, vanadate concentration, and pH variation studies were carried out,
particularly for the range of pH 5.8
composition and formation constants for some, but not all, species are given. Despite some reduction of vanadium-
V) to vanadium(IV) in an acidic medium at pH 2.4, the stoichiometries of the principal species in solution at this
−8.0 and for pH 2.4. Chemical shifts, vanadium−ligand stoichiometry, and also
(
≈
pH were determined. Electrospray ionization mass spectra for some solutions were obtained and were in accordance
with the conclusions drawn from the speciation studies. A series of crystalline vanadium(V) tartrato complexes
M
4
[V
4
O
8
(tart)
[V
2
]
‚
aq were also prepared and characterized. X-ray diffraction studies of Na
4
[V
4
O
8
(rac-tart)
2
]
V
‚
4
12H
2
O (1)
rings
4-
and (NEt
4
)
4
4
O
8
((R,R)-tart)
2
]
‚
6H
2
O (2) revealed unique tetranuclear [V
4
O
8
(tart)
2
]
ions for which the
{
O
4
}
have boat conformations.
Introduction
spectroscopy, irrespective of the vanadate/D-tartaric acid
molar ratio, observed only one complex [δ( V) ) -522
ppm] throughout the range of pH 3.0-7.5. A tetranuclear
5
1
The anions of R-hydroxycarboxylic acids take part in many
basic biochemical processes and thus represent an important
group of biogenic ligands. All crystallographically character-
ized R-hydroxycarboxylato complexes of vanadium(V) pos-
sess a dinuclear structure with a {V
(
1) (a) Zhou, Z. H.; Wang, J. Z.; Wan, H. L.; Tsai, K. R. Chem. Res.
Chin. UniV. 1994, 10, 102-106. (b) Smatanov a´ , I.; Marek, J.;
Sˇ van cˇ a´ rek, P.; Schwendt, P. Acta Crystallogr. 1998, C54, 1249-1251.
1
2
O
2
} ring, where the
(
c) Hambley, T. W.; Judd, R. J.; Lay, P. A. Inorg. Chem. 1992, 31,
bridging O atoms derive from the R-hydroxyl groups of the
ligands.
343-345. (d) Wright, D. W.; Humiston, P. A.; Orme-Johnson, W.
H.; Davis, W. M. Inorg. Chem. 1995, 34, 4194-4197. (e) Zhou, Z.
H.; Yan, W. B.; Wan, H. L.; Tsai, K. R.; Wang, J. Z.; Hu, S. Z. J.
Chem. Crystallogr. 1995, 25, 807-811. (f) Zhou, Z. H.; Wan, H. L.;
Hu, S. Z.; Tsai, K. R. Inorg. Chim. Acta 1995, 237, 193-197. (g)
Wright, D. W.; Chang, R. T.; Mandal, S. K.; Armstrong, W. H.; Orme-
Johnson, W. H. J. Biol. Inorg. Chem. 1996, 1, 143-151. (h) Sˇ van cˇ a´ rek,
P.; Schwendt, P.; Tatiersky, J.; Smatanov a´ , I.; Marek, J. Monatsh.
Chem. 2000, 131, 145-154. (i) Djordjevic, C.; Lee, M.; Sinn, E. Inorg.
Chem. 1989, 28, 719-723. (j) Djordjevic, C.; Lee-Renslo, M.; Sinn,
E. Inorg. Chim. Acta 1995, 233, 97-102. (k) Smatanov a´ , I.; Sˇ van cˇ a´ rek,
P.; Marek, J.; Schwendt, P. Acta Crystallogr. 2000, C56, 154-155.
(l) Schwendt, P.; Sˇ van cˇ a´ rek, P.; Smatanov a´ , I.; Marek, J. J. Inorg.
Biochem. 2000, 80, 59-64. (m) Schwendt, P.; Ahmed, M.; Marek, J.
Inorg. Chim. Acta 2005, 358, 3572-3580 and references cited therein.
(n) Kaliva, M.; Raptopoulou, C. P.; Terzis, A.; Salifoglou, A. Inorg.
Chem. 2004, 43, 2895-2905 and references cited therein. (o) Hati,
S.; Batchelor, R. J.; Einstein, F. W. B.; Tracey, A. S. Inorg. Chem.
2001, 40, 6258-6265. (p) Biagioli, M.; Strinna-Erre, L.; Micera, G.;
Panzanelli, A.; Zema, M. Inorg. Chim. Acta 2000, 310, 1-9.
Complexation of vanadium(V) with tartaric acid has been
studied since 1939. Solution studies utilizing UV-vis
2
2
2
3
spectroscopy, conductometry, cryoscopy, IR spectroscopy,
1
13
51
4
5
and H, C, and V NMR spectroscopy, polarography,
5
and cyclic voltammetry have been carried out. From the
very often controversial interpretation of experimental results,
the existence of complexes with n(V)/n(tart ) ratios 4, 2,
n-
4
1, and 0.5 has been proposed. Caldeira et al. using NMR
*
To whom correspodence should be addressed. E-mail: schwendt@
fns.uniba.sk.
†
Comenius University.
Simon Fraser University.
Masaryk University.
‡
§
1
0.1021/ic062223h CCC: $37.00
© 2007 American Chemical Society
Inorganic Chemistry, Vol. 46, No. 10, 2007 3971
Published on Web 04/10/2007

Schwendt et al.
structure with a planar {V
4
O
4
} ring has been suggested for
(NEt
4
)
4
[V
4
O
8
((R,R)-tart)
2
]‚6H
2
O (2). V
2
O
5
(0.18 g, 1.0 mmol)
3
-6
was dissolved in a NEt
4
OH solution (2 mL of a 2.34 mol/L solution,
this complex.
More recently, on the basis of ligand
concentration studies using 5 V NMR spectroscopy, two
1
4.86 mmol), and an aqueous solution of (2R,3R)-tartaric acid was
added (2 mL of a 1 mol/L solution, 2 mmol). The pH of the red
solution was 6.3. For initiation of crystallization, acetone was added.
After 5 days of standing at 276 K, large red plates were isolated.
Anal. Calcd for C40
8.3); N, 4.5 (4.7); V, 16.3 (15.7). IR bands (2000-400 cm ):
632 vs [νas(COO )], 1594 vs, 1352 m [ν (COO )], 1325 m, 1299
s
m, 1171 s, 1097 s [ν(C-O )], 1071 m [ν(C-O )], 1000 s, 957 vs
[ν(VdO )], 930 m, 854 m, 823 m, 797 sh, 777 w, 739 s [ν (VOV)],
656 m [ν
complexes were identified, with the major product being
specified as a 1:1 V/tart complex. It is evident that there is
little agreement between the various studies.
Two types of solid complexes have been obtained by
reactions of vanadates with tartaric acid or tartrates: (a)
5
H N O
96 4 26
V
4
(found): C, 38.3 (38.9); H, 7.7
-1
(
1
-
-
relatively stable red complexes M
2
O‚V
Ca) and (b) unstable yellow
compounds formulated as 3M O‚2V ‚2C ‚aq (M )
2 5
O ‚C
4 4 5
H O ‚aq (M
h
h
1
1
)
Na, K, Rb, Cs, /
2
Mg, /
2
t
as
O
2 5
H O
4 4 5
s
(VOV)], 632 w, 600 w, 546 s [ν(V-Otart)], 533 sh, 510
2
1
2
sh, 466 m, 434 m, 403 m.
2
K, Rb, Cs, / Ca). These results have been confirmed by
Siv a´ k,3 who has proposed a dinuclear structure for yellow
,7
Na [V O ((R,R)-tart) ]‚12H O (3). NaVO (1.22 g, 10.0 mmol)
4
4
8
2
2
3
was dissolved in water (7.5 mL). To the cold solution (273 K) was
added solid (2R,3R)-tartaric acid (0.75 g, 5.0 mmol). This provided
a red solution, which was maintained at 273 K for 2 h, after which
cold ethanol (20 mL) was added. After 14 days at 250 K, red needle-
complexes and a planar tetranuclear structure for red ones.
51
In this study, V NMR spectroscopy was used to
+
-
-
determine speciation in the aqueous H
3 2 4
O (OH )/H VO /
(2R,3R)-tartrate system. Electrospray ionization mass spec-
8 4 32 4
shaped crystals were isolated. Anal. Calcd for C H28Na O V
trometry (ESIMS) was used to substantiate the results of the
speciation analysis. Also, we report the syntheses and
characterization of a series of vanadium(V) tartrato com-
(
(
found): C, 10.3 (10.1); H, 3.0 (2.9); V, 21.9 (21.7). IR bands
2000-400 cm ): 1640 vs [νas(COO )], 1350 s [ν (COO )], 1339
s
-1
-
-
w, 1330 m, 1301 m, 1279 m, 1248 w, 1216 w, 1085 s [ν(C-O )],
h
plexes and the X-ray crystal structures of Na
4
[V
O.
4
O
8
(rac-
1059 m [ν(C-O )], 973 vs [ν(VdO )], 916 w, 851 m, 829 w, 770
h
t
tart) ]‚12H O and (NEt [V ((R,R)-tart) ]‚6H
2
2
4
)
4
4
O
8
2
2
vs [νas(VOV)], 729 sh, 653 s [ν
s
(VOV)], 556 s [ν(V-Otart)], 491
m, 440 m, 407 m.
Experimental Section
Materials and Syntheses. V
K
4
[V
4
O
8
((R,R)-tart)
2
2 3
]‚8H O (4). KVO (1.38 g, 10.0 mmol) was
dissolved in water (7.5 mL). Upon the addition of solid (2R,3R)-
tartaric acid (0.75 g, 5.0 mmol), a red solution was obtained. To
this solution (pH 5.3) was added ethanol until a precipitate started
to appear. Red needles were isolated after 24 h of standing at 276
K. Anal. Calcd for C H K O V (found): C, 10.4 (10.2); H, 2.2
8 20 4 28 4
2.0); V, 22.0 (22.0). IR bands (2000-400 cm ): 1633 vs
2
O
5
was prepared by thermal
VO . KVO
2
‚xH O
decomposition (at 773 K) of previously purified NH
was prepared by thermal decomposition (at 393 K) of KVO
obtained by reaction of V with an aqueous solution of KOH at
pH 8. For preparation of the solutions for the NMR measurements,
NaVO ‚2H O (p.a., Lachema) and (2R,3R)-tartaric acid (p.a.,
4
3
3
3
2 5
O
-
1
(
[
3
2
-
-
ν
as(COO )], 1349 s [ν
)], 1057 m [ν(C-O
m, 851 m, 829 m, 760 vs [νas(VOV)], 652 s [ν
V-Otart)], 438 m, 407 m.
[V (rac-tart) ]‚8H
s
(COO )], 1314 w, 1292 w, 1250 w, 1219
)], 967 vs [ν(VdO )], 917
(VOV)], 553 s [ν-
Lachema) were used. All other chemicals were of reagent grade
and were used as commercially obtained without further purifica-
tion.
w, 1084 s [ν(C-O
h
h
t
s
(
Na
4
4
[V O
8
(rac-tart)
2 2 3
]‚12H O (1). NaVO (1.22 g, 10.0 mmol)
K
4
4
O
8
2
2
O (5). KVO
3
(0.69 g, 5.0 mmol) was
was dissolved in water (7.5 mL). To the cold solution (278 K) was
added under continuous stirring an aqueous solution of rac-tartaric
acid (5 mL of a 1 mol/L solution, 5 mmol). The red solution that
was obtained (pH 5.8) was maintained for a further 2 h at 278 K,
and then ethanol was added until the first turbidity occurred. Dark-
red crystals were isolated after 2 h of standing at 278 K. Anal.
dissolved in water (5 mL), and an aqueous solution of rac-tartaric
acid (2.5 mL of a 1 mol/L solution, 2.5 mmol) was added. The pH
was adjusted to 3.9 using a 5 mol/L KOH solution. Ethanol was
added until the first precipitate was formed. Crystallization at 276
K yielded red plate-shaped crystals. Anal. Calcd for C H K O V
8 20 4 28 4
found): C, 10.4 (10.4); H, 2.2 (2.2); V, 22.0 (22.8). IR bands
(
(
Calcd for C
8
H28Na
O
4 32
V
4
(found): C, 10.3 (10.2); H, 3.0 (2.8); V,
-1
-
-
2000-400 cm ): 1663 vs [νas(COO )], 1347 s [ν
s
(COO )], 1316
)], 1083 s
)], 989 sh, 973
)], 918 w, 850 m, 790 sh, 768 vs [νas(VOV)], 659 m
(VOV)], 557 s [ν(V-Otart)], 515 w, 483 w, 436 m, 414 sh.
NH [V ((R,R)-tart) ]‚9H O (6). To the aqueous solution
of NH VO (4 mL of 0.5 mol/L solution, 2 mmol) was added an
-
1
-
2
1
1
1.9 (22.3). IR bands (2000-400 cm ): 1645 vs [νas(COO )],
m, 1292 m, 1271 m, 1249 w, 1207 w, 1095 m [ν(C-O
ν(C-O )], 1057 m [ν(C-O )], 1045 m [ν(C-O
vs [ν(VdO
h
-
361 s [ν
s
(COO )], 1320 m, 1292 m, 1273 w, 1250 w, 1236 w,
)] (O ) oxygen atom of the
)], 1060
) terminal
oxygen atom), 936 sh, 917 w, 850 m, 766 vs [νas(VOV)], 711 m,
60 m [ν (VOV)], 622 sh, 598 sh, 554 s [ν(V-Otart)] (Otart
coordinated oxygen atom of the tartrato ligand), 517 w, 489 m,
40 m, 414 m.
[
h
h
h
217 w, 1210 w, 1088 m [ν(C-O
h
h
t
hydroxylic group of the tartrato ligand), 1078 s [ν(C-O
m [ν(C-O )], 1049 m [ν(C-O )], 971 vs [ν(VdO )] (O
h
[ν
s
(
h
h
t
t
4
)
4
4
O
8
2
2
4
3
6
s
)
aqueous solution of (2R,3R)-tartaric acid (1 mL of a 1 mol/L
solution, 1 mmol). Crystallization from the red solution (pH 3.9)
was initiated by ethanol. Orange-red plates were isolated after 1
4
day of standing at 276 K. Anal. Calcd for C
C, 11.4 (11.6); H, 4.5 (4.5); N, 6.7 (6.5); V, 24.2 (23.9). IR bands
8 38 4 28 4
H N O V (found):
(
2) Jahr, K. F.; Preuss, F.; Rosenhahn, L. J. Inorg. Nucl. Chem. 1969,
1, 297-302 and references cited therein.
3) Siv a´ k, M. Acta Fac. Rerum Nat. UniV. Comenianae, Chim. 1981, XXIX,
3
-
1
-
+
(
(
(
(
(
(2000-400 cm ): 1606 vs [νas(COO )], 1409 m [δ
d
(NH
)], 1057 m [ν-
)], 916 m, 848 m, 830 w, 756 vs [νas
(VOV)], 554 m [ν(V-Otart)], 483 m, 436 m,
4
)], 1349
-
3
7-45.
s [ν
(COO )], 1314 w, 1214 w, 1081 m [ν(C-O
)], 969 vs [ν(VdO
VOV)], 650 m [ν
s
h
4) Caldeira, M. M.; Ramos, M. L.; Cavaleiro, A. M.; Gil, V. M. S. J.
Mol. Struct. 1988, 174, 461-466.
(
C-O
h
t
-
(
s
5) Khan, A. R.; Crans, D. C.; Pauliukaite, R.; Norkus, E. J. Braz. Chem.
Soc. 2006, 17, 895-904.
407 w.
NMe
was dissolved in a NMe
solution, 2.2 mmol). Then aqueous solutions of (2R,3R)-tartaric acid
6) Bart u˚ sˇ ek, M.; Sˇ ust a´ cˇ ek, V. Collect. Czech. Chem. Commun. 1983,
(
4 4 4 8 2 2 2 5
) [V O ((R,R)-tart) ]‚3H O (7). V O (0.18 g, 1.0 mmol)
48, 2785-2797.
4
OH aqueous solution (2 mL of a 1.1 mol/L
7) Siv a´ k, M. Acta Fac. Rerum Nat. UniV. Comenianae, Chim. 1981, XXIX,
47-57.
3972 Inorganic Chemistry, Vol. 46, No. 10, 2007

Vanadium(V) Tartrato Complexes
Table 1. Crystallographic Data and Refinement Results for 1 and 2
complex
formula
M (g/mol)
space group
a (Å)
1
2
C8H28Na4O32V4
932.02
C40H96N4O26V4
1252.98
P21 (No. 4)
12.225(2)
14.029(3)
18.298(4)
90
108.75(3)
90
2971.6(10)
2
P 1h (No. 2)
10.627(2)
11.392(2)
14.167(3)
88.76(3)
78.53(3)
62.85(3)
1490.9(5)
2
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
3
V (Å )
Z
Fcalcd (g/mL)
temperature (K)
λ (Å)
2.076
120(2)
0.71073
1.397
0.0193
1.400
120(2)
0.71073
0.689
0.0499
0.1173
µ (mm-1)
a
R1 (I > 2σI)
Figure 1. 51V NMR spectrum obtained at 157.68 MHz showing vanadate,
several of its oligomers, and a number of tartrate complexes. Conditions of
the experiment: vanadate, 3.0 mmol/L; (2R,3R)-tartaric acid, 30.0 mmol/
L; pH, 6.5; HEPES buffer, 20 mmol/L; temperature, 278 K; a 1.0 mol/L
b
wR2 (I > 2σI)
0.0530
a
R1 ) ∑|Fo| - |Fc|/∑|Fo|. wR2 ) {∑w(Fo - Fc /∑wFo }1/2.
b
2
2
2
+
-
Na (Cl ) ionic medium.
2
1
mL of a 1 mol/L solution, 2 mmol) and NMe
4
OH (1.8 mL of a
.1 mol/L solution, 1.98 mmol) were added. To the red solution
that decavanadate was not formed, even at low tartrate concentra-
tions at pH 6.5. Solutions were allowed to stand approximately 3
h for equilibration before the measurement. Depending on pH, some
increase of the pH (up to 0.2 pH units) with time occurred as a
result of the reduction of vanadium(V) to vanadium(IV). Reduction
was faster in acidic solutions. By monitoring the changes of the
intensity of the band characteristic for the vanadium(IV) complex
at 762 nm, we estimate that at pH 2.4 up to 10% of the total
vanadium was reduced when the measurement was finished. This
had a negative impact on the speciation procedure, particularly at
low pH. The problem was, however, mitigated to an extent by
cooling the samples to 278 K. To compare our data with those in
(
pH 6.8) was added acetone to initiate crystallization. Small red
needles crystallized from the solution standing at 276 K after 4
days. Anal. Calcd for C24 (found): C, 29.3 (29.8); H,
58 4 23 4
H N O V
-
1
6.0 (6.3); N, 5.7 (5.7); V, 20.7 (21.4). IR bands (2000-400 cm ):
-
-
1
617 vs [νas(COO )], 1485 m, 1335 s [ν
)], 1067 m [ν(C-O )], 958 vs [ν(VdO
m, 825 m, 799 m, 759 vs [νas(VOV)], 704 w, 658 m [ν
03 m, 555 s [ν(V-Otart)], 481 m, 434 w.
Physical Measurements. The IR spectra were recorded on a
s
(COO )], 1302 m, 1094
)], 915 m, 852
(VOV)],
s [ν(C-O
h
h
t
s
6
Nicolet Magna 750 Fourier transform IR spectrometer with either
Nujol mulls or KBr tablets. Elemental analysis (C, H, and N) was
performed on a 1106 CHN analyzer (Carlo Erba, Milano, Italy).
8
the literature, some spectra were measured for solutions at different
Vanadium(V) was determined gravimetrically as V
crucible at 773 K or volumetrically by titration with FeSO
.1 mol/L) using diphenylamine as the indicator. UV-vis spectra
O
2 5
in a platinum
+
-
conditions: 295 K; a 0.6 mol/L Na (Cl ) ionic medium.
4
(c )
Crystal Structure Determination. The intensity data were
collected on a KUMA KM-4 κ-axis diffractometer using a graphite-
monochromatized Mo KR radiation equipped with an Oxford
Cryosystem LT device and corrected for absorption effects using
a ψ scan. The ω-scan technique with different κ and æ offsets for
covering an independent part of reflections in the 2-25° θ range
was used. The cell parameters were refined from all strong
reflections. The data reductions were carried out using the CrysAlis
RED (Oxford Diffraction, Abingdon, U.K.) program. The structures
0
were recorded on a Jasco V-530 UV-vis spectrophotometer at room
temperature. 51V NMR spectra were recorded at 278 or 295 K on
a Varian Mercury Plus 300 MHz spectrometer operating at 78.94
51
MHz ( V) and a Varian Unity Inova 600 MHz spectrometer
51
operating at 157.68 MHz ( V) in 5 mm tubes without locking on
O. Chemical shifts are in ppm relative to a VOCl external
D
2
3
reference, also determined at 278 or 295 K. ESIMS spectra were
recorded for x, y, and z using a direct probe on a Waters ZMD
9
10
were determined by SHELXS-97 and refined by SHELXL-97, and
2
000 mass spectrometer. The mass spectrometer was directly
coupled to a MassLynx data system. Solutions for ESIMS were
prepared by mixing solutions of (2R,3R)-tartaric acid, NaVO , and
NaOH [c(H tart), 0.01 or 0.06 mol/L; c(NaVO ), 0.0018 or 0.01
1
1
the data for publication were prepared by SHELXL and PARST
and the figures by Diamond.12 Crystal data and structure determi-
nation summaries for 1 and 2 are listed in Table 1. Selected bond
lengths and angles for the two compounds are listed in Table 2.
3
4
3
mol/L; pH, 3.0, 4.1, or 4.6]. The pH was measured with a Precision
digital pH meter OP-208/1 (Radelkis, Budapest, Hungary) by use
of a combined semimicro pH electrode HC 139 (THETA ’90). The
log â values for the proton-ligand complexes were estimated by
standard potentiometric procedures.
Results and Discussion
+
-
-
Speciation in the H O (OH )/H VO /(2R,3R)-Tartrate
3
2
4
System. Vanadium, tartrate, and hydrogen ion concentration
studies were undertaken in order to identify the products
formed in solution and to elucidate their stoichiometries.
Preliminary studies at pH 6.5 showed the presence of three
Solutions for the NMR Measurements. Stock aqueous solutions
of 0.15 mol/L NaVO
3 2
‚2H O, 1.00 mol/L (2R,3R)-tartaric acid, 0.20
mol/L HEPES buffer, and 4.00 mol/L NaCl were used for mixing
of solutions for measurement. The pH of the solution was adjusted
by adding a NaOH solution (1 or 0.1 mol/L) or a HCl solution
51
products with V NMR chemical shifts of -503, -524, and
(
only for solutions with pH 2.4; c(HCl), 2 or 0.1 mol/L). All final
(
8) Pettersson, L.; Hedmann, B.; Andersson, I.; Ingri, N. Chem. Scr. 1983,
+
solutions were prepared with c(Na ) ) 1.0 mol/L. The solutions
for the NMR measurements were prepared by combining appropri-
ate amounts from the various stock solutions in the following
order: (2R,3R)-tartaric acid, NaCl, HEPES, (H
NaVO , (NaCl), (HCl), H O. Careful adherence to procedure meant
22, 254-264.
(9) Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467-473.
10) Sheldrick, G. M.; Schneider, T. R. Methods Enzymol. 1997, 277, 319-
(
343.
2
O), (NaOH),
(
11) Nardelli, M. Comput. Chem. 1983, 7, 95-97.
(12) DIAMOND, version 3.1.d; CRYSTAL IMPACT: Bonn, Germany.
3
2
Inorganic Chemistry, Vol. 46, No. 10, 2007 3973

Schwendt et al.
Table 2. Selected Bond Lengths (Å) and Angles (deg) for 1 and for 2
complex
complex
1
2
1
2
V1-O13
1.5970(14)
1.7727(13)
1.8201(12)
1.9270(13)
2.0389(13)
1.5916(14)
1.8304(13)
1.8573(13)
1.8826(12)
2.0375(13)
1.5923(12)
1.8317(12)
1.8413(14)
1.8747(15)
2.0269(13)
1.5995(12)
1.7814(13)
1.8104(13)
1.9314(12)
2.0398(16)
106.98(7)
102.01(6)
98.84(6)
1.618(4)
1.759(4)
1.828(4)
1.963(4)
2.070(4)
1.618(4)
1.854(4)
1.869(4)
1.884(4)
2.059(4)
1.602(4)
1.838(4)
1.882(4)
1.889(4)
2.070(4)
1.617(4)
1.783(4)
1.823(4)
1.962(4)
2.070(4)
105.39(18)
102.61(18)
98.93(16)
110.64(18)
141.79(16)
85.49(16)
93.21(18)
88.32(16)
160.06(16)
77.53(15)
O14-V2-O20
O14-V2-O3
O20-V2-O3
O14-V2-O19
O20-V2-O19
O3-V2-O19
O14-V2-O1
O20-V2-O1
O3-V2-O1
O19-V2-O1
O15-V3-O20
O15-V3-O9
O20-V3-O9
O15-V3-O17
O20-V3-O17
O9-V3-O17
O15-V3-O7
O20-V3-O7
O9-V3-O7
O17-V3-O7
O16-V4-O19
O16-V4-O18
O19-V4-O18
O16-V4-O10
O19-V4-O10
O18-V4-O10
O16-V4-O12
O19-V4-O12
O18-V4-O12
O10-V4-O12
102.32(7)
100.80(6)
100.53(6)
103.18(6)
90.31(6)
150.86(6)
100.74(7)
156.71(5)
78.17(5)
81.29(6)
102.35(6)
100.93(7)
100.00(6)
101.38(6)
90.81(6)
152.44(6)
103.56(6)
153.80(5)
78.81(6)
80.40(6)
105.70(6)
102.43(7)
97.64(6)
107.74(6)
144.11(5)
87.64(6)
94.97(6)
86.59(6)
160.16(5)
77.95(6)
103.51(18)
100.95(19)
98.52(17)
104.01(19)
91.65(17)
149.97(15)
99.32(17)
157.14(17)
78.12(16)
81.58(16)
103.22(19)
100.99(18)
99.74(17)
103.79(18)
91.75(16)
149.44(16)
100.74(17)
155.91(16)
77.96(15)
80.09(16)
107.16(19)
102.18(18)
98.18(17)
108.40(18)
142.20(16)
86.55(15)
93.45(19)
87.53(16)
160.85(15)
77.98(15)
V1-O17
V1-O18
V1-O4
V1-O6
V2-O14
V2-O20
V2-O3
V2-O19
V2-O1
V3-O15
V3-O20
V3-O9
V3-O17
V3-O7
V4-O16
V4-O19
V4-O18
V4-O10
V4-O12
O13-V1-O17
O13-V1-O18
O17-V1-O18
O13-V1-O4
O17-V1-O4
O18-V1-O4
O13-V1-O6
O17-V1-O6
O18-V1-O6
O4-V1-O6
108.34(7)
141.68(6)
87.98(5)
94.96(6)
84.77(6)
160.68(5)
77.88(5)
-
537 ppm. Figure 1 shows a 51V NMR spectrum obtained
is accurately determined relative to the other components.
Also, it has a charge state that is constant at 4-, with it not
being protonated under acidic conditions, which makes it a
good reference for studies under conditions of different
from a 600 MHz spectrometer.
Several product signals are observable in this spectrum
and, in anticipation of the analysis, are identified in the figure.
Also identified are the various oligomeric vanadates that
typically are found. It should be noted that, under the
conditions of this study, decavanadate is not observed in the
NMR spectra. Additionally, line broadening and a change
1
5-17
pH.
Two products are observed in the NMR spectrum at pH
7.9. The one of initial interest is a minor component in rapid
equilibration with the monomer, V . As mentioned, this is
1
in the chemical shift of close to -0.5 ppm of the V
indicated the formation of products in rapid equilibration with
. Similar behavior has been found for R-hydroxycarboxylic
1
signal
possibly two components deriving from an independent
monodentate reaction at the hydroxyl and carboxylate groups.
Because the V/L stoichiometry is identical for the two
situations, it is not possible to separate the two formation
constants at fixed pH, and only an overall formation constant,
V
1
acids and has been assigned to the presence of products
deriving from monodentate carboxylate and hydroxylate
coordination.1 In the case of lactate, the overall formation
3,14
K
f
, is available. Reaction proceeds according to eq 1, but
because [V ] is not known, V provides a reference for V
according to eq 2 so that the two formation constants, K′14
and K , are provided by eq 3, where cV is the total
concentration of V components (cV ) [V ] + [VL])
represented by the mixed signal. The equilibrium unligated
-
1
constant for these products was 0.55 ( 0.05 M at pH
1
4
1
1
4
7
.35. Because of the statistical factor, this value can be
expected to approximately double for the tartrate system.
A major complication in this study was the extreme
sensitivity of product formation to the pH of the medium.
Going from pH 6.5 to 7.0 was sufficient to eliminate the
major product signal at -524 ppm and the minor product
signal at -537 ppm from the NMR spectra. This presented
one advantage in that the product giving rise to the -503
ppm signal could be studied in isolation. For the analysis,
the tetramer was used as the reference compound for two
reasons. The principal one is that this compound gives a
relatively sharp NMR signal, and therefore its concentration
f
1
1
1
1
2-
tartrate concentration, [L ], is obtained from the conserva-
tion equation for total L, so an initial analysis is required in
order to determine ligand stoichiometry for the various
products. Corrections to [L] are then applied as the analysis
proceeds. The two pK
.02 and 3.55 ( 0.02 under the conditions of the NMR
experiments. These values compare well with the literature
a
values of tartaric acid are 2.68 (
0
(15) Elvingson, K.; Baro, A. G.; Pettersson, L. Inorg. Chem. 1996, 35,
3
388-3393.
(
13) Tracey, A. S.; Li, H.; Gresser, M. J. Inorg. Chem. 1990, 29, 2267-
271.
14) Tracey, A. S.; Gresser, M. J.; Parkinson, K. M. Inorg. Chem. 1987,
6, 629-638.
(16) Pettersson, L.; Hedman, B.; Nenner, A. M.; Andersson, I. Acta Chem.
2
Scand. 1985, A39, 499-506.
(
(17) Pettersson, L.; Andersson, I.; Hedman, B. Chem. Scr. 1985, 25, 309-
2
317.
3974 Inorganic Chemistry, Vol. 46, No. 10, 2007

Vanadium(V) Tartrato Complexes
Figure 2. Graphical representation of the formation of the product
giving rise to the -507 ppm signal. The solid line gives the least-squares
fit to a straight line, while the dotted lines represent the 95% confidence
interval. Conditions of the experiments: total vanadate, 6.0 mmol/L;
(
2
2R,3R)-tartaric acid, variable 10-80 mmol/L; pH, 7.95; HEPES buffer,
+
-
0 mmol/L; temperature, 278 K; all solutions, a 1.0 mol/L Na (Cl ) ionic
medium.
values18 of 2.69 and 3.73 at I ) 1.0 mol/L. These low pK
a
values mean that it is not necessary to consider any but the
doubly minus charge state of the ligand unless the pH is
well below 6.
Figure 3. 51V NMR spectra showing the influence of the pH throughout
the range of pH 6.0-8.0 on equilibria in the aqueous vanadate/(2R,3R)-
tartrate system. Conditions of the experiments: total vanadate, 6.0 mmol/
L; (2R,3R)-tartaric acid, 30.0 mmol/L; pH, as indicated; HEPES buffer, 20
mmol/L; temperature, 278 K; all solutions, a 1.0 mol/L Na (Cl ) ionic
medium.
+
-
V + L h VL
[V ][L]K ) [VL]
(1)
(2)
(3)
1
1
f
4
Figure 3 shows the influence of the pH on the 51V NMR
spectra for the range of pH 6.0-8.0. It is evident that, as
the pH becomes lower, the NMR spectra become con-
siderably more complicated. This is in accordance with a
more complicated speciation at the lower pH. Variation of
the vanadate and ligand concentrations at pH 6.5 clearly
showed that the various products have different stoichiom-
etries.
The pH variation studies showed that the -507 ppm signal
shifted to lower field upon acidification from pH 8.0 and
occurred at -503 ppm at pH 6.5. In accordance with this,
the vanadate concentration studies showed that the -503 ppm
signal corresponded to monovanadate species. However, the
ligand concentration study showed that the -503 ppm signal
4
V h V4
[V ] K′ ) [V ]
1
1
14
4
1/4
1/4
cV /[V ] ) (1 + [L]K )/K′
14
1
4
f
A plot of the left side of eq 3 vs [L] then provides both
K′14 and K
1
f
. The values obtained were K′14 ) (3.6 ( 0.5) ×
09 M-3 and K
-1
f
f
) 1.1 ( 0.7 M . The value for K is only
poorly determined, but it and K′14 are in line with expecta-
tions from other studies.1 This value of K′14 is not a true
formation constant in the sense that, at this pH, the signal
3,14
-
2-
from V
Knowing K′14 allows the constant for formation of the -507
ppm product from V to be ascertained even though V is
1 1 1 1
corresponds to V in two ionic states, V and V .
1
4
used as the reference compound. Preliminary studies sug-
gested that the -507 ppm product had VL stoichiometry and
2
had components from both VL (eq 1) and VL (eq 5)
thus is formed as described by eq 1, with KVL replacing K
f
.
products, unlike what was observed at higher pH, where only
VL was observed. Therefore, the concentration corresponding
to the -503 ppm signal, c(-503), is given by eq 6, which
On this basis, eq 4 is obtained, where the product is identified
by its NMR chemical shift.
can be rewritten in terms of the V
4
concentration and
1/4
1/4
c(-507) ) [L][V ] K /K′
14
(4)
formation constants as eq 7, where K14 represents the
4
VL
4
-
-
formation of V
4
1
from 4V .
Figure 2 gives a graphical representation of the experi-
mental results plotted according to eq 4 when the total
vanadate concentration was held constant and the tartrate
concentration varied. A similarly good graph was obtained
when the ligand was maintained constant and the vanadate
2
V + 2L h VL
[V ][L] K ) [VL2]
(5)
(6)
1
2
1
VL2
c(-503) ) [VL] + [VL2]
-
1
concentration varied. KVL had the values 19.7 ( 0.4 M
c(-503)
1
/4
1/4
+ KVL2[L]/K14
and 19.1 ( 0.3 M-1 from the tartrate and vanadate
concentration studies, respectively. There was no indication
that the -507 ppm signal was a composite signal deriving
from more than one component.
) K /K
(7)
VL 14
1/4
[
V ] [L]
4
Formation of the -503 ppm products is sensitive to the
pH. The observations suggested that there is formation of
three complexes, VL , HVL , and HVL
3
-
2-
4-
2
, as described
(
18) Kotrl y´ , S.; Sˇ u˚ cha, L. Handbook of Chemical Equilibria in Analytical
Chemistry; Ellis Horwood Ltd.: Chichester, U.K., 1985.
by eqs 8-12.
Inorganic Chemistry, Vol. 46, No. 10, 2007 3975

Schwendt et al.
V1- + L2- h VL3-
-
2-
3-
Table 3. Formation Constants of (2R,3R)-Tartrate (L) Complexes of
[V ][L ]K ) [VL ] (8)
1
VL
Vanadiuma
3
-
+
2-
formula/notationb
p, q, r
log âpqr(3σ)
-7.87(3)
δV (ppm)c
VL + H h HVL
3
-
+
2-
HVO 2-
-1, 1, 0
0, 1, 0
-1, 2, 0
0, 2, 0
0, 4, 0
0, 5, 0
0, 1, 1
1, 1, 1
1, 1, 2
1, 2, 1
2, 2, 2
3, 4, 2
4, 4, 2
-534
-560
-572
-561
-576
-584
-507
-503
-503
-537
-537
-524
-524
4
[
VL ][H ]K
) [HVL ] (9)
HVL
-
H2VO4
HV2O73
-
-5.03(4)
3.00(6)
10.92(7)
13.61(9)
1.62(3)
7.68(4)
9.36(4)
10.23(19)
18.62(10)
32.55(9)
39.03(9)
HVL + L h HVL24-
2
-
2-
2
-
H2V2O7
V4O124
-
2-
2-
) [HVL24-] (10)
[HVL ][L ]K
V O 5-
HVL2
5
15
3
-
VL
HVL2
HVL2
HV2L
-
c(-503) ) [VL ] + [HVL ] + [HVL 4-]
3-
2-
(11)
4-
2
3
-
H2V2L24
-
-
-
c(-503)
+
5
)
- 1/4 2-
(KVL + K K [H ] +
H3V4L2
VL HVL
4
H4V4L24
[
V4 ] [L ]
+
2-
1/4
14
a
K KHVLKHVL2[H ][L ])/K
(12)
Formation constants are for the following conditions: total vanadate,
VL
6
mmol/L; (2R,3R)-tartaric acid, 30 mmol/L; pH, variable 5.8-8.0; HEPES
+
-
buffer, 20 mmol/L; temperature, 278 K; all solutions, a 1.0 mol/L Na (Cl )
+
ionic medium. b Oxygen stoichiometry is not specified for the tartrato
A plot of the term on the left side of eq 12 vs [H ] gave
a graph with a small amount of curvature. Extrapolation of
the curve to the Y axis gave an intercept of 0.0708 ( 0.0015,
which equals KVL/K14 or KVL ) 42.0 ( 1.1 M . This is
c
3-
complexes because full stoichiometry may be uncertain. Except for VL
,
which is for a pH 7.9 solution, the chemical shifts observed for the tartrate
complexes are for pH 6.5. Because of signal overlap, or possibly rapid
exchange, the signals near -503 ppm and those near -537 ppm are average
values measured for a broad signal.
1/4
-1
in good agreement with the pH 7.9 study where the
-
-
2-
1
proportion of V
1
in total V
1
(V
1
+ V
1
) is close to /
2
the -537 ppm signal corresponded to products of V
stoichiometry. In this event, formation of the -537
ppm products proceeds according to eqs 13 and 14, and their
formation from V can be written as in eq 15. In accordance
2
L and
that at pH 6.5, thus reducing the formation constant of VL
2 2
V L
-
from V
1
by a factor of about 2. An additional correction is
3-
needed if significant protonation of VL occurs at pH 6.5.
4
4-
That there is a HVL
2
component can be seen from a
ligand concentration study. This is demonstrated most readily
by rearranging eq 12 into a form linear in [L ]. The graph
gives both a slope and an intercept when the appropriate
data obtained from tartrate concentration studies are plotted
with this assignment, the agreement between the assumed
stoichiometry and the experimental results, when plotted
according to eq 15, is good (Figure 2s in the Supporting
Information).
2-
2
(
Figure 1s in the Supporting Information). The Y intercept
would be zero if no HVL were formed, while the slope
2V + L h V L
[V ] [L]K ) [V L]
(13)
) [V L ] (14)
2
1
2
1
V2L
2
2-
4
-
would be zero if no HVL
2
were formed.
2
2
2
V + 2L h V L
[V ] [L] K
1
V2L
1
2
2
2 2
There was no evidence that HVL 4
-
2
loses a proton with
an increase in the pH. The formation of HVL
progressively unfavored as the pH is increased with respect
4-
2
becomes
c(-537)
1
/2
) (KV2L + [L]KV2L2)/K14
(15)
1
/2
3
-
2[V ] [L]
4
to VL , and it consequently is not formed to a great extent
at elevated pH, in accordance with a VL product not being
2
Analysis of the pH variation data showed that only one
proton per ligand was taken up during formation of each of
the two -537 ppm products (eqs 16 and 17). Equation 18
gives the conservation equation for the products giving rise
to the -537 ppm signal. This can be combined with eqs 16
and 17, rewritten as eq 19, and the experimental results
plotted graphically (Figure 3s in the Supporting Information).
observed in the pH 7.9 study. The value determined for the
-
pK
a
of HVL2 from the Y intercept of the graph was 6.04.
The formation constants for these and the other products are
summarized in Table 3. The formation constants are written
V L , with H VO
p q r 2 4
, from which the stoichiometry is
defined and for which q is 1 and p and r are 0.
-
in the log âpqr notation defined by H
being the reference, V
1
H + 2V + L h HV2L3-
+
-
2-
The -537 ppm signal is quite broad, and this, coupled
with the comparatively low signal intensity, adds uncertainty
to the analysis. The vanadium concentration study at fixed
tartrate concentration was consistent with this product having
1
+
- 2
3-
[
H ][V ] [L]K
) [HV L ] (16)
1
HV2L
2
+
-
2-
4-
2
H + 2V + 2L h H V L
V
2
stoichiometry. No evidence was obtained for a V
component, which might have been expected because
products of V stoichiometry are frequently formed with
3
1
2
2
2
+
2
- 2
2
) [H V L 4-] (17)
H V L 2 2 2
2
[H ] [V ] [L] K
1
2
2
3
R-hydroxycarboxylic acids and give rise to chemical shifts
c(-537)/2 ) [HV L ] + [H V L 4-]
3-
(18)
near this frequency.1
9,20
2
2
2 2
Analysis of the ligand concentration
study proved somewhat more problematic and suggested that
The intercept of the graph is small but cannot be said to
be 0. From the formation constants for pH 6.5 with 6.0
mmol/L total vanadate and 30 mmol/L (2R,3R)-tartaric acid,
it can be calculated that there is a little over twice as much
(
19) Gorzsas, A.; Andersson, I.; Pettersson, L. J. Chem. Soc., Dalton Trans.
003, 2503-2511.
20) Tracey, A. S. Coord. Chem. ReV. 2003, 237, 113-121.
2
(
3976 Inorganic Chemistry, Vol. 46, No. 10, 2007

Vanadium(V) Tartrato Complexes
c(-537)
)
4
- 1/2 2-
+
2
[V4 ] [L ][H ]
2-
+
1/2
(K
+ K
[L ][H ])/K
14
(19)
HV2L
H V L
2 2
2
of the bisligand than of the monoligand complex in solution.
These studies only provide stoichiometry and cannot deter-
mine whether V L is similar to V L with a second ligand
2 2 2
attached or whether they are completely different products.
There were no indications from any studies that the -524
ppm signal was a composite signal deriving from more than
a single product. The vanadate and tartrate concentration
studies showed that the -524 ppm product had four
vanadium centers and was complexed by two tartrate ligands.
Its formation, therefore, is described by eqs 20 and 21. A
graphical representation of the data, when plotted according
to eq 21, gave an excellent straight line (Figure 4s in the
Supporting Information).
Figure 4. pH dependence of the formation of the tetranuclear products
giving rise to the -524 ppm signal. The intercept corresponds to the
formation of V4L2H3 and the slope to V4L2H2 . The solid line gives the
least-squares fit to a straight line, while the dotted lines represent the 95%
confidence interval. Conditions of the experiments: total vanadate, 6.0
mmol/L; (2R,3R)-tartaric acid, 30 mmol/L; pH, variable 5.81-8.04; HEPES
-
4-
+
-
buffer, 20 mmol/L; temperature, 278 K; all solutions, a 1.0 mol/L Na (Cl )
ionic medium.
4
2
4
V + 2L h V L
[V ] [L] K
) [V L ] (20)
1
4
2
1
V4L2 4 2
2
c(-524)/4 ) [V ][L] KV4L2/K14
(21)
4
The pH study of this product was particularly interesting
because, although it showed that four protons were taken
up during formation of the -524 ppm product, one of the
5-
protons could be released; that is to say, H
V L
3 4 2
can form.
This is described by eqs 22-24.
+
-
2-
4-
4
H + 4V + 2L h H V L
1 4 4 2
+
4
- 4
2- 2
) [H V L 4-] (22)
[
H ] [V ] [L ] K
1
H V L
4
4 2
4
4
2
2
+
-
2-
5-
3
H + 4V + 2L h H V L
1
3
4
2
+
3
- 4 2- 2
) [H V L 5-] (23)
[
H ] [V ] [L ] K
1
H V L
3
4 2
3
4
c(-524)
+
)
(K
+ K
H V L
4 4 2
[H ])/K
14
(24)
H V L
4
-
2- 2
+ 3
3
4
2
4
[V4 ][L ] [H ]
Figure 5. Species distribution diagram calculated for the pH range 6-8.
For the calculations, the concentrations were as follows: total vanadate,
6.0 mmol/L; (2R,3R)-tartaric acid, 30 mmol/L. The formation constants are
A graph of the quantities of eq 24 is shown in Figure 4.
+
-
5-
found in Table 3 and determined for a 1.0 mol/L Na (Cl ) ionic medium.
If the intercept of this graph were 0, no H
3
V
4
5-
L
2
would be
4-
found in solution. If H
the presence of the single proton, then the pK
is 6.48. There are no protons available in H
V
4 4
L
2
and H
3
V
4
L
2
differ only by
fixed at -524 ppm and there was no change in the line shape
with a change in the pH. However, several additional NMR
signals were observed at lower pH.
4
-
a
4 4 2
of H V L
4
-
4
V
4
L
2
unless
it has complexed water. This result therefore suggests that
the coordination about vanadium in an aqueous solution is
not pentacoordinate as observed in the crystalline material
but rather more highly coordinated, perhaps hexacoordinate
As demonstrated by Figure 7, the relative intensities of
these signals are highly dependent on the amount of tartaric
-
acid (H
3
tart + H
4
tart at pH 2.4) in solution. The principle
one of the new signals occurred at -550 ppm. Other signals
occurred at -461, -511, -532, and -539 ppm. Under the
low pH conditions, there was on the order of 10% reduction
of vanadium(V) to vanadium(IV) when the spectra were
measured.
Despite this, it was possible to draw some conclusions
about species stoichiometry. Over the range of tartaric acid
concentrations of 10-60 mmol/L, the V-atom concentration
corresponding to the -524 ppm signal decreased from 1.93
mmol/L at 10 mmol/L tartaric acid to 0.14 mmol/L at 60
mmol/L tartaric acid while the V-atom concentration cor-
(see the discussion of the crystal structure).
A summary of the formation constants measured is given
in Table 3. These values were used to obtain a species
distribution diagram (Figure 5) for the range of pH 6-8 and
calculated for 6 mmol/L total vanadate and 30 mmol/L
(2R,3R)-tartaric acid.
An effort was made to identify species occurring at pH
2.4. A titration from pH 6.01 to 2.55 (Figure 6) suggested
that there was no change in the identity of the product giving
rise to the -524 ppm signal because this signal remained
Inorganic Chemistry, Vol. 46, No. 10, 2007 3977

Schwendt et al.
2
2
V L + 2L h 2V L
[V L ] [L] K ) [V L ]
(25)
4
2
2
2
4
2
2 2
If the product is V
change in the chemical shift from that observed at pH 6.5
for a V product, there is a difference in coordination,
2 2
L , then, as suggested by a -13 ppm
2 2
L
perhaps the V center having octahedral rather than penta-
coordinate geometry. Possibly there is bridging between V
atoms by the tartrate ligands in addition to the normal oxo
bridging, or alternatively there may simply be a change in
the hydration state. A different coordination is expected
because this product was not observable in the NMR spectra
until the pH was below 4. Vanadate itself goes from
tetrahedral to octahedral coordination under acidic conditions
with incorporation of water into the coordination sphere. In
the vanadate case, the change in coordination is accompanied
by a change in the protonation state. Unfortunately, the
charge state of the -550 ppm product is not known.
Figure 6. 51V NMR spectra showing the influence of the pH throughout
the range of pH 2.55-6.01 on equilibria in the aqueous vanadate/(2R,3R)-
tartrate system. Conditions of the experiments: total vanadate, 30 mmol/
L; (2R,3R)-tartaric acid, 60 mmol/L; pH, as indicated; temperature, 278 K;
There is an additional product that appears to have V
2 2
L
+
-
all solutions, a 1.0 mol/L Na (Cl ) ionic medium.
stoichiometry that gives an NMR signal at -511 ppm. This
compound is about a factor of 4 less favored than the -550
ppm product, but its formation with a change in the tartrate
concentration follows closely that of the -550 ppm product.
Some information was also obtained about the stoichiom-
etry of the -539 ppm product. Under conditions where the
-
524 ppm product dropped in concentration by a factor of
about 14, the concentration of the -539 ppm product
followed lockstep with that of the -524 ppm product. This
is demonstrated in Figure 8. The linear correlation suggests
that the -524 and -539 ppm products both have the same
4 2
V/L stoichiometry, i.e., V L . Because protonation/deproto-
nation will generally be fast on the NMR time scale unless
accompanied by a coordination change, it seems likely that
these two tetravanadate complexes differ in their structure.
There is another product that is observed when there is a
large excess of ligand in solution (see Figure 7). This product
gives rise to a very broad signal at -461 ppm, and its
concentration increases rapidly with an increase in the free
ligand concentration, being about 0.13 mmol/L at 40 mmol/L
tartrate and about 0.45 mmol/L at 60 mmol/L tartrate, both
measurements for 3.0 mmol/L total vanadate. For comparison
purposes, the concentration of the -550 ppm product (V
changes from 1.70 to 1.77 mmol/L while that of the -524
ppm product (V ) changes from 0.50 to 0.14 mmol/L, for
the same two ligand concentrations, respectively. Evidently,
the -461 ppm product has a comparatively high L/V
2 2
L )
Figure 7. 51V NMR spectra showing the influence of the (2R,3R)-tartaric
acid concentration on equilibria in the aqueous acidic vanadate/(2R,3R)-
tartrate system for (2R,3R)-tartaric acid concentrations varying throughout
the range of 0-100 mmol/L. Conditions of the experiments: total vanadate,
4 2
L
3
.0 mmol/L; (2R,3R)-tartaric acid, as indicated; pH, 2.4; temperature, 295
+
-
K; all solutions, a 0.6 mol/L Na (Cl ) ionic medium.
2
stoichiometry, perhaps VL .
responding to the -550 ppm signals increased from 0.63 to
There is an additional minor product signal that occurs at
-530 ppm. This signal was only poorly characterized, but
it increases in intensity with an increase in the tartaric acid
concentration in a fashion that suggests it has more than a
1:1 V/L stoichiometry. Two other very low intensity signals
occurred at -575 and -580 ppm. Their intensities did not
vary much over the range of tartaric acid concentrations
above 20 mmol/L, where they accounted for about 2% of
the total vanadium in the solution. However, it is to be noted
that these signals did not occur when no ligand was present
and were very weak at 10 mmol/L tartaric acid. They were
not more fully characterized.
1.77 mmol/L. On the other hand, the -524 ppm signal
increased in intensity much more rapidly than did the -550
ppm signal when the tartaric acid concentration was fixed
and the total vanadate concentration was increased. In fact,
the behavior was consistent with formation of V
as described by eq 25, where it is assumed that the
524 ppm signal corresponds to V , in accordance with
2 2
L from
4 2
V L
-
4 2
L
the pH 6.5 studies and the pH titration (Figure 6). The
experimental data, when plotted graphically according to eq
25, gave a good linear correlation (Figure 5s in the
Supporting Information).
3978 Inorganic Chemistry, Vol. 46, No. 10, 2007

Vanadium(V) Tartrato Complexes
Chart 1. Characteristic Structure of R-Hydroxycarboxylatovanadates
One of a Number of Stereoisomers)
(
Figure 8. Concentration of the -539 ppm shown as a function of the
-
524 ppm product as (2R,3R)-tartaric acid is varied from 10 to 60 mmol/
carboxylate group) bonds and protonation of the carboxylic
groups during the ESIMS process. The most abundant
complexionintheESIMSspectrumwas[V O (tart) (H O) ] .
4 8 2 2 2
L. The solid line represents a linear least-squares fit to the data and the
broken lines the 95% confidence interval. Conditions of the experiments:
total vanadate, 3.0 mmol/L; (2R,3R)-tartaric acid, variable 10-60 mmol/
4-
+
-
L; pH, 2.40; temperature, 295 K; all solutions, a 0.6 mol/L Na (Cl ) ionic
medium.
It was found by the X-ray structure analysis that there is
enough space for accommodation of a bridging water
Table 4. Strongest Signals in the ESIMS Spectrum of the
NaVO3-(2R,3R)-H4tart-NaOH-H2O-CH3OH Solution in Negative
Mode
4-
4 8 2
molecule in each of the two cavities of the [V O (tart) ]
a
ion. The existence of bridging water molecules is not rare
m/z
in structures of R-hydroxycarboxylatovanadium(V) com-
relative
intensity
(%)
designation in
Table 3 and in
the text
plexes (see, e.g., ref 23) and offers some explanation for the
found
4.13
calcd
74.04
assignment
4-
otherwise incomprehensible deprotonation of H
4
V
4
L
2
and
-
5-
7
6
10
100
23
92
51
H2tart2
formation of the H
4
V L
species.
3
2
-
1
1
1
1
2
2
3
16.82 116.95
48.89 149.08
56.05 155.97
65.06 164.98
08.15 208.29
30.86 231.01
13.04 312.94
H2VO4
V1
-
There are some solid tartrato complexes of vanadium(V)
that were not fully characterized. Yellow complexes of
H3tart
[V4O8(tart)2]
[V4O8(tart)2(H2O)2]
4
-
H4V4L24-
4
-
7
I
3
-
supposed composition M
3
[HV
2
O
5
(tart)] could correspond
[V4O8(tart)(Htart)2]
2
-
3-
28
16
[V2O4(H2tart)2]
[V4O8(Htart)2]
V2L2
to the -537 ppm (HV
2
L ) solution species, while the V
2 2
L
2
-
species (δ
V
) -550 ppm) might correspond to the
a
2-
c(NaVO3) ) c(H4tart) ) 10 mmol/L, pH 3.0, solution:methanol ) 9:1
by volume (after measurement of the pH).
[V (H tart)
O
2 4
]
2 2
ion with a dinuclear structure and a {V O }
2
2
central ring (Chart 1). This type of structure is characteristic
for most of the R-hydroxycarboxylatovanadates.
The results of the speciation studies are generally con-
firmed by ESIMS in negative mode. The strongest signals
obtained from acidic solutions (pH 3.0) (Table 4) can be
Synthesis and Characterization of Solid Complexes. In
spite of there being a number of species present in aqueous
solutions, we obtained only complexes of the M
tart)
structure determination.
The complexes Na [V
[V (rac-tart) ]‚12H O (1), and K
4
[V
4
O
8
-
4-
4-
assigned to species derived from the [V
4
O
8
(tart)
) ion, and to tartrate
anions. The V NMR spectrum of the same solution but
2
]
4 4 2
(H V L )
(
2
]‚aq type in the form of crystals suitable for X-ray
2
-
ion, to the [V
2
O
4
(H
2
tart)
2
]
2 2
(V L
5
1
4-
4
O
4 8
((R,R)-tart)
[V
2
]‚12H
2
O (3), Na
]‚8H
4
-
without methanol exhibited signals at -524 ppm (H
4
V
4
4
L
2
-
,
+
O
4 8
2
2
4
4
O
8
((R,R)-tart)
2
,24
2
O
7
7%), -550 ppm (V
2
L
2
, 17%), and -537 (H
2
V
2
L
2
2
3
-
(4) were prepared by modified literature methods, but we
obtained compounds with different numbers of water mol-
ecules in comparison with the published data. The complexes
2
HV L , 6%).
It should be mentioned that vanadium(IV) also forms
21
dinuclear tartrate complexes M
4
[(VO)
2
(tart)
2
2
]‚nH O, where
4 4 8
M [V O ((R,R)-tart)
2 2
]‚nH O [M ) NEt
4 4 4
(2), NH (6), NMe
the fully deprotonated ligand bridges two V centers. The
speciation study of the vanadium(IV) tartrate aqueous system
suggested that there are various dinuclear complexes and also
minor mononuclear species.22
(7)] and K
4
[V (rac-tart)
4
O
8
2
]‚8H O (5) are new. Solid com-
2
plexes are generally photosensitive: exposure under daylight
conditions causes a gradual reduction of vanadium(V), and
a color change from red to brown is observed. The most
stable of the complexes is (NEt ) [V O (R,R-tart) ]‚6H O (2),
4
-
We suppose that the structure of the H
corresponds to the solid-state structure of the [V
4
V
4
L
2
species
4
-
4
8 2
O (tart) ]
4
4
4
8
2
2
ion (vide infra). The 51V NMR spectra of saturated, very
concentrated aqueous solutions of both 1 and 3 exhibited
only one signal at -522 ppm, and the spectra did not change
for at least 1 h. This structure offers the possibility of
which can be stored without decomposition in a refrigerator
for weeks and, surprisingly, also aqueous and acetonitrile
solutions of this complex preserve their color for several
weeks at 276 K and even for several days at room
temperature.
c c
eventual breaking of the V-O (O ) oxygen atom of the
(
21) (a) Forrest, J. G.; Prout, C. K. J. Chem. Soc. A 1967, 1312-1317. (b)
Tapscott, R. E.; Belford, R. L.; Paul, I. C. Inorg. Chem. 1968, 7, 356-
64.
(23) Schwendt, P.; Sˇ van cˇ a´ rek, P.; Kuchta, L.; Marek, J. Polyhedron 1998,
17, 2161-2166.
(24) Siv a´ k, M. Acta Fac. Rerum Nat. UniV. Comenianae, Chim. 1980,
XXVIII, 69-75.
3
(22) Kiss, T.; Bugly o´ , P.; Sanna, D.; Micera, G.; Decock, P.; Dewaele, D.
Inorg. Chim. Acta 1995, 239, 145-153.
Inorganic Chemistry, Vol. 46, No. 10, 2007 3979

Schwendt et al.
conformation. Each V atom is pentacoordinate. The geometry
of the coordination polyhedra can be described in terms of
square pyramids distorted toward trigonal bipyramids. The
τ value (τ ) 0 for ideal square pyramid; τ ) 1 for ideal
2
8
trigonal bipyramid ) is 0.32 for V1, 0.098 for V2, 0.023
for V3, and 0.27 for V4. This arrangement is prevalent for
2
9
pentacoordinated V atoms.
Tetragonal pseudoplanes of the opposite pyramids around
V1 and V2 are nearly parallel (the angle between corre-
sponding planes ≈ 6.5°), and they are nearly perpendicular
to pseudoplanes of the neighboring pyramids around V3 and
V4 (the angles between corresponding planes are ≈ 76°).
The situation is analogous for the pyramids around V3 and
V4. Because the same enantiomeric form of the two tartrate
Figure 9. IR spectra of 3 and 1 (1400-700 cm-1).
4
-
ligands is coordinated in one [V
4 8
O (tart)
2
]
ion, the square
pyramids are mutually shifted in a way that enables weak
interactions between V and O atoms from the opposite
pyramids (V1-O20, V2-O4, V3-O10, and V4-O20;
Figure 10). V atoms thus achieve nearly octahedral coordina-
tion geometry. Because these interactions are weak, the V
atoms deviate considerably from the tetragonal pseudoplanes
(between 0.387 and 0.426 Å).
The {V
O
4 8
} group and eight O donor atoms of ligands
16} core, which can be considered as composed
} tetragonal pyramids. Each of the {VO
pyramids contains one O atom, two O atoms, and two O
atoms of the ligand (O and O ). The bridging O atoms
connect each of the {VO } pyramids with the two neighbor-
ing {VO } pyramids. The bond lengths in the {V 16} core
are within the expected ranges: 1.5946-1.6150 Å for Vd
bonds; 1.7747-1.8792 Å for V-O bonds; 1.8408-
form a {V
of four {VO
4
O
5
5
}
t
b
Figure 10. Structure of the [V4O8(R,R-tart)2]4- anion in 1.
h
c
b
5
The IR spectra of prepared complexes exhibit characteristic
5
4
O
-
-
bands corresponding to νas(COO ), ν
s
(COO ), ν(C-O ), ν-
h
(
VdO ), νas(V-O-V), ν (V-O-V), and ν(V-Otart) vibra-
t
s
O
t
b
tions (see the Experimental Section). The IR spectra of
complexes with rac- and (2R,3R)-tartaric acid are very
similar. The corresponding bands are only slightly shifted,
thus indicating a similar structure of both complexes
(
(
(
(
25) Crans, D. C.; Jiang, F. L.; Chen, J.; Anderson, O. P.; Miller, M. M.
Inorg. Chem. 1997, 36, 1038-1047.
26) Jiang, F. L.; Anderson, O. P. Miller, S. M.; Chen, J.; Mahroof-Tahir,
M.; Crans, D. C. Inorg. Chem. 1998, 37, 5439-5451.
(Figure 9).
27) Tsagkalidis, W.; Rodewald, D.; Rehder, D. Inorg. Chem. 1995, 34,
1943-1945.
Nevertheless, some splitting of the IR bands was observed
28) Murphy, G.; Nagle, P.; Murphy, B.; Hathaway, B. J. Chem. Soc.,
Dalton Trans. 1997, 2645-2652.
in the spectra of rac-tartaric acid complexes when compared
to the spectra of complexes with (2R,3R)-tartaric acid,
probably a result of correlation effects in the unit cell. This
splitting is characteristic, especially in the region of stretching
(29) Maurya, M. R.; Agarwal, S.; Bader, C.; Rehder, D. Eur. J. Inorg.
Chem. 2005, 147-157.
(30) Cavaco, I.; Pessoa, J. C.; Duarte, M. T.; Matias, P. M.; Henriques, R.
T. Polyhedron 1993, 12, 1231-1237.
(31) Manos, M. J.; Tasiopoulos, A. J.; Tolis, E. J.; Lalioti, N.; Woolins, J.
-
1
vibrations of C-O groups (1100-1000 cm ; Figure 9).
h
D.; Slawin, A. M. Z.; Sigalas, M. P.; Kabanos, T. A. Chem.sEur. J.
The complexes prepared with rac- or (2R,3R)-tartaric acid
can be reliably distinguished by means of these bands.
2003, 9, 695-703.
(32) Wulff-Molder, D.; Meisel, M. Acta Crystallogr. 2000, C56,
3
3-34.
Crystal Structures. The crystal structure of 1 consists of
(
33) Arrowsmith, S.; Dove, M. F. A.; Logan, N.; Antipin, M. Y. J. Chem.
Na+ cations, tetranuclear [V
4-
anions, and
4 8
O (rac-tart)
2
]
Soc., Chem. Commun. 1995, 627-627.
(
(
34) Salta, J.; Zubieta, J. Inorg. Chim. Acta 1996, 252, 435-438.
35) Heinrich, D. D.; Folting, K.; Streib, W. E.; Huffman, J. C.; Christou,
G. J. Chem. Soc., Chem. Commun. 1989, 1411-1413.
36) Karet, G. B.; Sun, Z.; Heinrich, D. D.; McCusker, J. K.; Folting, K.;
Streib, W. E.; Huffman, J. C.; Hendrickson, D. N.; Christou, G. Inorg.
Chem. 1996, 35, 6450-6460.
water molecules held together by electrostatic forces and
hydrogen bonds. The triclinic unit cell contains two tetra-
nuclear anions with different enantiomers of tartaric acid,
(
4
-
4-
[
1
V
4
O
8
((R,R)-tart)
represents a typical example of a racemic compound: Na
((R,R)-tart) ][V ((S,S)-tart) ]‚24H O.
The tetranuclear anion (Figure 10) consists of a {V
2
]
4 8 2
and [V O ((S,S)-tart) ] ; the complex
8
-
(37) Priebsch, W.; Rehder, D.; von Oeynhausen, M. Chem. Ber. 1991, 124,
7
61-764.
[V
4
O
8
2
O
4 8
2
2
(
38) Rieskamp, H.; Gietz, P.; Mattes, R. Chem. Ber. 1976, 109, 2090-
4
O
8
}
2096.
4
-
(39) Crans, D. C.; Marshman, R. W.; Gottlieb, M. S.; Anderson, O. P.;
group and two tart ligands. The {V
4 8
O } group is composed
Miller, M. M. Inorg. Chem. 1992, 31, 4939-4949.
40) Carrano, C. J.; Mohan, M.; Holmes, S. M.; de la Rosa, R.;
of four VdO groups that are bridged by four bridging O
t
b
(
Butler, A.; Charnock, J. M.; Garner, C. D. Inorg. Chem. 1994, 33,
atoms. In contrast to what is observed for most tetranuclear
vanadium complexes,25-27 the four V atoms are not coplanar.
The central {V O } ring possesses an approximate boat
4 4
6
46-655.
(
41) Herberhold, M.; Dietel, A. M.; Milius, W. Z. Naturforsch. B: Chem.
Sci. 2003, 58, 299-304.
3980 Inorganic Chemistry, Vol. 46, No. 10, 2007

Vanadium(V) Tartrato Complexes
Table 5. Types of Tetranuclear Vanadium(V) Complexes with Organic Ligandsa
planarity
torsion
angle of
(
coordination
geometry
conformation
b
type
A1
core
l(V-X) (Å)
V
4
)
of V
4
O
4
cycle
compound
(acac)
{V
4
4
4
O
16
O
12
O
16
}
SPY-5 {VO
5
} or
6
2.19-2.32 (X ) O)
Pc (max ( 1°)
P (max ( 1°)
P (max ( 7°)
chair
[V
[V
4
[V
O
6
(OCH
3
)
6
2
]‚2CH
3
CN,26
6
2
OC-6 {VO
}
4
4
4
O
6
O
4
O
4
(OCH
3
)
6
(acac)
2
],
],2
3
5
[
V
{(OCH
{(OCH
2
)
)
3
CCH
CCH
3
}
}
2
(OCH
(OC
3
H
)
5
6
)
2
5
[
V
2
3
3
3
2
]
3
0
{
V
N
4
}
SPY-5, 2×{VO
×{VO } or
OC-6 2×{VO
×{VO
SPY-5 {VO
OC-6 {VO
VO Cl}
3
N
2
}
2.27-2.33 (X ) O)
chair
4
O
8
[V
(OCH
(OCH
(5,5′-Me bpy)
3
)
4
(bpy)
2
],
2
5
4
O
8
3
)
2
(µ
3
-OCH
3
)
2
-
3
1
4
N
2
}
2
2
]‚3CH
3
OH
2
6
}
A2
A3
{V
{V
}
5
} or
6
2.56-2.89
(X ) O, Cl,
or nothing)
all µ-O above
(Ph
4
P)[V
4
O
8
(CH
As)[V
P)[V
[V
(O CCH
tBuCH
3
COO)
4
(NO
3
)],32
(NO
},
the V
plane
4
(Ph
(Ph
4
4
O
8
8
(CH COO)
(CH COO) (Cl)],
(NO )(tca)
Bu) ]‚
COOH‚ BuCH
(H O) ]‚6H
3
4
3
)],33
4
3
{
5
4
4
O
3
4
d,
,
(
NEt
4
O
)
8
2
4
O
8
3
4
]‚H
2
O 35 36
t
[
V
4
2
2
4
t
37
2
2
2
COOK
3
8
4
16
O }
SPY-5 {VO
5
} or
6
2.41, 2.46 (X ) O)
P (max ( 7°)
two µ-O above
the V
K
4
[V
4
O
8
(C
2
O
4
)
4
2
2
2
O
OC-6 {VO
}
4
plane and
two µ-O
below the
4
V plane
3
9
A4
A5
{V
{V
4
4
O
14Cl
2
}
SPY-5 {V
OC-6 {V
SPY-5 {VO
OC-6 {VO
OC-6 {VO
quasi T-4 {VO
2
O
2
7
O
Cl} or
Cl}
} or
2.271, 2.305 (X ) O)
2.487-2.749 (X ) O)
2.273, 2.268 (X ) N)
P
[V
4
4
O (OH)
2
Cl
2
(dmpd)
4
]‚CHCl
3
9
O
16
}
5
NP
boat
boat
this work
6
}
B1
C1
{V
{V
4
O
O
8
N
12
}
3
N
3
}
NP
NP
[V
[V
4
4
O
O
8
{BH(pz)
3
}
4
]‚CH
2
Cl
2
‚2H
2
O40
4
1
4
8
(C
5
)
4
}
3
C
5
}
8 5 5 4
(C H ) ]
a
Abbreviations: acac ) acetylacetonate(1-), Me2bpy ) 5,5′-dimethyl-2,2′-bipyridine, bpy ) 2,2′-bipyridine, Ph4P ) tetraphenylphosphonium(1+),
t
Ph4As ) tetraphenylarsonium(1+), tca ) tiophene-2-carboxylato(1-), NEt4 ) tetraethylammonium(1+), BuCH2COOH ) 3,3-dimethylbutanoic acid, dmpd
b
)
2,2-dimethylpropane-1,3-diolate(2-), BH(pz)3 ) hydridotris(pyrazolyl)borate(1-). X ) atom in the trans position to the double-bonded O atom of the
c
d
2-
VdOt group. P ) planar. NP ) nonplanar. The [V4O8(NO3)(tca)4] anion contains one delocalized electron. The average oxidation state of vanadium
V
IV
is 4.75 (3 × V + 1 × V ).
1
.9328 Å for V-O
h
; 2.0280-2.0542 Å for V-O
c
. Each
structures of this type from CCDC (July 2006) can be
classified into several types.
Type A. The complexes of this type can be considered as
constructed from the {VOE } structural subunits possessing
4
tetragonal-pyramidal geometry (SPY-5). The double-bonded
O atom is always in the apical position; equatorial positions
tartrato ligand possesses trans conformation with torsion
angles 177.07° (for C1-C2-C3-C4) and 176.32° (for C5-
C6-C7-C8) and forms two five-membered chelate rings.
The tartrate anions are bonded as bis(bidentate) ligands,
which is a common coordination mode for this anion. The
crystal structure of 1 is stabilized by numerous hydrogen
bonds between water molecules and between water molecules
2
3
4
are taken by O or, exceptionally, N atoms. The {VOE }
subunits are often mutually arranged in a way that enables
a weak covalent bonding (or weak interaction) between the
V atom and a donor atom X (O or Cl) in the second apical
position (trans position to the double-bonded O atom of the
t b
and O atoms of the anions (O , O , and Otart).
The structure of the chiral compound (Et
4
N)
4
[V
4
O
8
((R,R)-
+
tart)
tart)
2
]‚6H
2
O (2) consists of Et
4
N
cations, [V O ((R,R)-
4 8
4
-
2
]
anions, and molecules of water of crystallization.
t
VdO group). The octahedral (pseudooctahedral) coordina-
4-
The structure of the [V
4
O
8
((R,R)-tart)
2
]
ion is very similar
tion geometry is thus achieved with V-X distances between
2.19 and 2.89 Å (Table 5). The structures classified into A1-
A4 subtypes differ in the mode of arrangement of the
to the structure of the anion in 1. The coordination about
the V atoms is a square-pyramid-like structure distorted
toward a trigonal bipyramid (τ ) 0.30 for V1, τ ) 0.12 for
V2, τ ) 0.11 for V3, and τ ) 0.31 for V4), and the
{VOE
to the V
Types B and C. With ligands that have special structural
properties, the structures of type B ([V {BH(pz) ]‚CH
Cl ‚2H O) and type C ([V (C ]) are profoundly
different from the structures of type A.
4
} subunits and in the positions of µ-O atoms relative
4
plane (Figure 11).
5
arrangement of the {VO } pyramids is analogous to the
arrangement in the structure of 1. Also, here weak interac-
tions occur (l(V‚‚‚O) values are 2.62 and 2.75 Å), which
complete the coordination polyhedron of the central atoms
to a strongly distorted octahedron.
O
4 8
}
3 4
2
-
2
2
4
O
8
5 5 4
H )
4
-
The structure of the [V
4
O
8
(tart)
2
]
ion presented here is
4
-
The [V
4
O
8
((R,R)-tart)
2
]
ions in the structure of 2 are
unique, and although it is classified as type A5, it differs
considerably from the other structures of type A. The four
V atoms do not lie in one plane, and the {V O } ring
4 4
connected by hydrogen bonds, and a two-dimensional (2D)
layered structure is thus formed. Some of the Et
+
4
N cations
are located in cavities that occur in the 2D sheets; the
remainder are situated between the 2D layers.
possesses a boat conformation. There is also another
substantial difference between previously proposed structures
4-
3,4,6
A comparison of the structures of compounds 1 and 2 with
those of other structurally characterized cyclic tetravanadates
that have organic ligands bound to the V atoms and that
contain exclusively or mostly vanadium(V) centers reveals
some structural features (Table 5 and Figure 11). The 15
4 8 2
of the [V O (tart) ]
ion and the structure found by X-ray
diffraction. In contrast to the arrangement in the proposed
4
-
structure, the tart ligands do not bridge between adjacent
V atoms of the {V } ring that are connected by µ-O atoms
4 4
O
but instead coordinate to V1 and V2 or V3 and V4 (Figure
Inorganic Chemistry, Vol. 46, No. 10, 2007 3981

Schwendt et al.
Figure 11. Types of tetranuclear vanadium(V) complexes with organic ligands (see text and Table 5). Ot ) terminal oxygen atom; X ) O or Cl atom trans
t
t
t
37
to the Ot (or nothing in the case of [V4O8(O2CCH2 Bu)4]‚2 BuCH2COOH‚ BuCH2COOK ).
1
0). It is this unique binding mode that imposes the boat
(Grant UK/144/2006). NMR measurements were performed
on the equipment supported by the Slovak State Programme
Project No. 2003SP200280203. We thank Dr. Karel Dole zˇ al
(Faculty of Natural Sciences, Palack y´ University, Olomouc,
Czech Republic) for measurement of the ESIMS spectra.
conformation on the {V } ring.
4 4
O
Acknowledgment. This investigation has been supported
by the Ministry of Education of Slovak Republic (Grant
VEGA 1/4462/07) and Comenius University in Bratislava
3982 Inorganic Chemistry, Vol. 46, No. 10, 2007

Vanadium(V) Tartrato Complexes
Supporting Information Available: X-ray crystallographic files
in CIF format for structures 1 and 2 and graphical representations
of the formation of tartrate complexes (Figures 1s-5s). This
material is available free of charge via the Internet at http://
pubs.acs.org. Crystallographic data (excluding structure factors) for
the structures have been deposited with the Cambridge Crystal-
lographic Data Centre as supplementary publication nos. 622257
and 622258. Copies of the data can be obtained, free of charge,
upon application to CCDC, 12 Union Road, Cambridge CB2 1EZ,
U.K.
IC062223H
Inorganic Chemistry, Vol. 46, No. 10, 2007 3983