Synthesis, Structures, and Spectroscopic Characterization of a Series of N,N'-Dimethyl-2,11-diaza[3.3](2,6)pyridinophane Vanadium(III), -(IV), and -(V) Complexes

Article abstract of DOI:10.1021/ic9510730

Three vanadium-containing complexes, [(L-N₄Me₂)VCl₂](BPh₄) (1), [(L-N₄Me₂)VClO](ClO₄) (2), and [(L-N₄Me₂)VO₂](BPh₄) (3) where L-N₄Me₂ is the tetradentate ligand N,N'-dimethyl-1-2,11-diaza[3.3](2,6)pyridinophane, have been prepared and characterized by X-ray diffraction and electrochemical methods as well as by IR, ¹H-NMR, EPR, and electronic absorption spectroscopy. Complex 1 crystallizes in monoclinic space group P2₁/n (No. 14) with a = 16.940(4) ?, b = 9.902(3) ?, c = 21.936(8) ?, β= 108.21(2)°, V = 3495(2) ?³, and Z = 4, complex 2 in orthorhombic space group P2₁2₁2₁ (No. 19) with a = 10.163(2) ?, b = 13.351(3) ?, c = 14.762(3) ?, V = 2003(1) ?3 and Z = 4, and complex 3 in monoclinic space group P2₁/c (No. 14) with a = 14.349(3) ?, b = 14.040(5) ?, c = 18.131(10) ?, β= 110.62(3)°, V = 3419(2) ?³, and Z = 4. In all these complexes a distorted cis-octahedral coordination geometry is found with the cis coordination sites occupied either by terminal chloro and/or oxo ligands. Thus, a rather unique series of mononuclear complexes has been established where, for example, in reaction with air consecutive replacements of both chloride ions by oxo donors increases the oxidation state of the six-coordinate vanadium ion from III over IV to V while the residual coordination environment remains preserved. Interestingly, in each complex the electronic properties of the cis donor atom set stabilize only one specific oxidation state of the vanadium ion in order to warrant the isolation of the complex.

Full text of DOI:10.1021/ic9510730

Inorg. Chem. 1996, 35, 3533-3540
3533
Synthesis, Structures, and Spectroscopic Characterization of a Series of
N,N′-Dimethyl-2,11-diaza[3.3](2,6)pyridinophane Vanadium(III), -(IV), and -(V) Complexes
Harald Kelm and Hans-Jo1rg Kru1ger*
Institut fu¨r Anorganische und Angewandte Chemie der Universita¨t Hamburg,
Martin-Luther-King-Platz 6, D-20146 Hamburg, Germany
ReceiVed August 18, 1995X
Three vanadium-containing complexes, [(L-N4Me2)VCl2](BPh4) (1), [(L-N4Me2)VClO](ClO4) (2), and [(L-N4-
Me2)VO2](BPh4) (3) where L-N4Me2 is the tetradentate ligand N,N′-dimethyl-2,11-diaza[3.3](2,6)pyridinophane,
1
have been prepared and characterized by X-ray diffraction and electrochemical methods as well as by IR, H-
NMR, EPR, and electronic absorption spectroscopy. Complex 1 crystallizes in monoclinic space group P21/n
(No. 14) with a ) 16.940(4) Å, b ) 9.902(3) Å, c ) 21.936(8) Å, â ) 108.21(2)°, V ) 3495(2) Å3, and Z ) 4,
complex 2 in orthorhombic space group P212121 (No. 19) with a ) 10.163(2) Å, b ) 13.351(3) Å, c ) 14.762(3)
Å, V ) 2003(1) Å3 and Z ) 4, and complex 3 in monoclinic space group P21/c (No. 14) with a ) 14.349(3) Å,
b )14.040(5) Å, c ) 18.131(10) Å, â ) 110.62(3)°, V ) 3419(2) Å3, and Z ) 4. In all these complexes a
distorted cis-octahedral coordination geometry is found with the cis coordination sites occupied either by terminal
chloro and/or oxo ligands. Thus, a rather unique series of mononuclear complexes has been established where,
for example, in reaction with air consecutive replacements of both chloride ions by oxo donors increases the
oxidation state of the six-coordinate vanadium ion from III over IV to V while the residual coordination environment
remains preserved. Interestingly, in each complex the electronic properties of the cis donor atom set stabilize
only one specific oxidation state of the vanadium ion in order to warrant the isolation of the complex.
Introduction
an oxide and two hydroxides. At the axial sites a histidine and
an exogenous ligand (a hydroxide or an azide, depending on
the buffer used for crystallization of the enzyme) are bound to
the vanadium ion. A comparison of the sequences of amino
acids near the vanadium sites in different haloperoxidases
ascribes similar structures to the active sites of the enzymes
from a fungi and an algae source.5 Within this context the
exploration of the basic coordination chemistry of vanadium
provides valuable insights into the role and the structure-
function relationship of the vanadium ion in these enzymes.
Vanadium(V) complexes have been found to act as catalysts
in the oxidation of organic substrates by peroxides (e.g.,
epoxidation of alkenes and hydroxylation of alkanes and
aromates).2,6 Although the mechanisms for these reactions are
still obscure and may involve radicals, the reactive species have
been identified in stoichiometric reactions as mononuclear
peroxovanadium(V) complexes, some of which have been
structurally characterized.2b,6b Interestingly, in recent times, it
has been discovered that peroxovanadium complexes have
insulin-mimetic properties.7
Currently there is considerable interest in investigating
mononuclear vanadium complexes because some haloperoxi-
dasessenzymes that catalyze the peroxide-dependent halogena-
tion of organic substratesshave been shown to contain vana-
dium in their active sites1 and also because peroxovanadium(V)
complexes have been demonstrated to be suitable oxidizing
reagents for a wide variety of organic substrates.2
The active site of marine haloperoxidases is thought to consist
of a V(V)dO in a distorted octahedral geometry with oxygen
and nitrogen atoms as residual donors. From EXAFS measure-
ments3 it is proposed that the donor atom set around the
vanadium consists of one terminal oxide at 1.61 Å, three N/O
donors at the rather short distances of 1.72 Å, and two nitrogen
donors, presumably histidines, at 2.11 Å. Upon reexamination
of the data with new model complexes, it was suggested that
the vanadium site might actually be only five-coordinate.4
A
recent structure determination5 of the haloperoxidase isolated
from the fungus CurVularia inaequalis indeed assigns a trigonal-
bipyramidal coordination geometry to the vanadium ion where
the equatorial coordination sites are presumably occupied by
(6) (a) Mimoun, H.; Mignard, M; Brechot, P.; Saussine, L. J. Am. Chem.
Soc. 1986, 108, 3711. (b) Mimoun, H.; Chaumette, P.; Mignard, M.;
Saussine, L.; Fischer, J.; Weiss, R. NouV. J. Chim. 1983, 7, 467.
(7) (a) Kadota, S.; Fantus, I. G.; Deragon, G.; Guyda, H. J.; Hersh, B.;
Posner, B. I. Biochim. Biophys. Res. Commun. 1985, 147, 259. (b)
Shaver, A.; Ng, J. B.; Hall, D. A.; Lum, B. S.; Posner, B. I. Inorg.
Chem. 1993, 32, 3109.
(8) (a) Kru¨ger, H.-J. Chem. Ber. 1995, 128, 531. (b) Koch, W. O.; Kru¨ger,
H.-J. Angew. Chem. 1995, 107, 2928; Angew. Chem. Int. Ed. Engl.
1995, 34, 2671. (c) Koch, W. O.; Barbieri, A.; Grodzicki, M.;
Schu¨nemann, V.; Trautwein, A. X.; Kru¨ger, H.-J. Angew. Chem. 1996,
108, 484; Angew. Chem., Int. Ed. Engl. 1996, 35, 422. (d) Kru¨ger,
H.-J. Unpublished results.
X Abstract published in AdVance ACS Abstracts, April 15, 1996.
(1) (a) Sigel, H.; Sigel, A., Eds. Metal Ions in Biological Systems Vol.
31: Vanadium and its Role in Life; Marcel Dekker, Inc.: New York,
1995. (b) Butler, A.; Walker, J. V. Chem. ReV. 1993, 93, 1937. (c)
Rehder, D. Angew. Chem., Int. Ed. Engl. 1991, 30, 148. (d) Chasteen,
N. D., Ed. Vanadium in Biological Systems, Kluwer Academic
Publishers; Boston, 1990.
(2) (a) Butler, A.; Clague, M. J.; Meister, G. E. Chem. ReV. 1994, 94,
625. (b) Mimoun, H.; Saussine, L.; Daire, E.; Postel, M.; Fischer, J.;
Weiss, R. J. Am. Chem. Soc. 1983, 105, 3101.
(3) Arber, J. M.; de Boer, E.; Garner, C. D.; Hasnain, S. S.; Wever, R.
Biochemistry 1989, 28, 7968.
(4) Carrano, C. J.; Mohan, M.; Holmes, S. M.; de la Rosa, R.; Butler, A.;
Charnock, J. M.; Garner, C. D. Inorg. Chem. 1994, 33, 646.
(5) (a) Messerschmidt, A.; Wever, R. J. Inorg. Biochem. 1995, 59, 580.
(b) Messerschmidt, A. Personal communication.
(9) List of abbreviations used: L-N4Me2 ) N,N′-dimethyl-2,11-diaza-
[3.3](2,6)pyridinophane; tacn ) 1,4,7-trimethyltriazacyclononane; bipy
) 2,2′-bipyridine; HB(Me2pz)3 ) hydridotris(3,5-dimethylpyrazolyl)-
borate; Me2pzH ) 3,5-dimethylpyrazole; DMF ) dimethylformamide;
THF ) tetrahydrofuran.
S0020-1669(95)01073-1 CCC: $12.00 © 1996 American Chemical Society

3534 Inorganic Chemistry, Vol. 35, No. 12, 1996
Kelm and Kru¨ger
[(L-N4Me2)VCl2](BPh4) (1). Under an atmosphere of pure nitrogen,
a solution of L-N4Me2 (134 mg, 0.5 mmol) and sodium tetraphenylbo-
rate (171 mg, 0.5 mmol) in acetonitrile (25 mL) was added dropwise
to acetonitrile (15 mL) containing [VCl3(THF)3] (187 mg, 0.5 mmol).
After heating the reaction mixture to refluxing temperatures, the initial
violet precipitate dissolved again and a color change from violet to
green occurred. Upon cooling of the reaction mixture to room
temperature, the precipitated white salt was removed by filtration and
the volume of the solution was reduced to about 10 mL. Ether diffusion
into the solution yielded dark green crystals which were separated from
the violet coprecipitate sticking to the glass wall. The green product
was redissolved in 5 mL of acetonitrile. A second ether diffusion
afforded 134 mg (38% yield) of analytically pure product as dark green
crystals. Anal. Calcd for C40H40BCl2N4V: C, 67.72; H, 5.68; N, 7.90.
Found: C, 67.51; H, 5.84; N, 7.96. Absorption spectrum (acetoni-
trile): λmax (ꢀM) 259 (sh, 13 800), 273 (sh, 7270), 375 (588), 450 (sh,
79.9), and 635 (72.1) nm. IR (KBr): 1610, 1578, 1480, 1448, 1428,
1167, 1078, 1031, 748, 732, 707, 612 cm-1 (strong bands only).
Magnetic moment: 2.68 µB.
[(L-N4Me2)VClO](ClO4) (2). Under air, L-N4Me2 (136 mg, 0.51
mmol) in 96% ethanol (10 mL) was added dropwise to a stirred solution
of VCl3 (80 mg, 0.51 mmol) in 96% ethanol (20 mL). The resulting
mixture was refluxed for 15 min and cooled to room temperature before
sodium perchlorate (61 mg, 0.50 mmol) was added to the resulting
turquoise solution. After refluxing the solution for 10 min, the solvent
was completely removed under vacuo. Two consecutive recrystalli-
zations by diffusion of ether into filtered solutions of the residue in
acetonitrile (10 mL) afforded 156 mg of product as light-blue crystals
(65% yield). Anal. Calcd for C16H20Cl2N4O5V: C, 40.87; H, 4.29;
N, 11.92. Found: C, 40.88; H, 4.27; N, 11.89. Absorption spectrum
(acetonitrile): λmax (ꢀM) 257 (7550), 264 (10 800), 356 (45.8), 633
(37.5), and 707 (28.0) nm. IR (KBr): 1610, 1580, 1485, 1449, 1097,
1078, 1027, 982, 968, 879, 815, 624 cm-1 (strong bands only).
Magnetic moment: 1.73 µB.
In our research we extensively employ derivatives of 2,11-
diaza[3.3](2,6)pyridinophane as ligand.8 This macrocycle has
four potential nitrogen donors at its disposal for the complex-
ation of metal ions. Due to its rather small cavity, the
12-membered macrocyclic ring forms preferably cis-octahedral
coordination geometries with metal ions. By protecting four
of the coordination sites at an octahedral metal ion from
nucleophilic reagents, the ligand ensures that any reactivity
occurs only at two defined cis coordination sites. In our efforts
to develop new oxidation catalysts with this type of ligand, we
started to investigate mononuclear vanadium complexes using
N,N′-dimethyl-2,11-diaza[3.3](2,6)pyridinophane (L-N4Me2)9 as
ligand. Here we report on the synthesis and characterization
of three vanadium complexes (1, 2, and 3), of which some may
serve as useful precursors for later studies with peroxides. In
these complexes, the cis coordination sites are occupied by
terminal chlorides and/or oxides. Thus, a complete, structurally
characterized series of compounds was prepared in which
(starting with the dichlorovanadium(III) complex 1) the chlorides
are successively replaced by oxo donors and, concomitantly,
the oxidation state of the vanadium ion is raised each time by
one unit while the residual coordination environment is retained.
Warning: Perchlorate salts are potentially explosive and should be
handled with care.12
[(L-N4Me2)VO2](BPh4) (3). To avoid contamination by traces of
a V(IV)-containing species, the dioxovanadium(V) complex was
prepared anaerobically under exclusion of light, using absolute solvents.
A solution of L-N4Me2 (134 mg, 0.5 mmol) and sodium tetraphenylbo-
rate (342 mg, 1.0 mmol) in acetonitrile (40 mL) was added dropwise
to stirred acetonitrile (15 mL) containing (PPh4)[VCl2O2] (247 mg, 0.5
mmol). After refluxing the initially turbid orange-colored reaction
mixture for 5 min, the solution adopted a yellow color. The precipitate
was then removed by filtration before the volume of the solution was
reduced to ca. 5 mL in vacuo at 50 °C. Slow cooling of the solution
to room temperature resulted in precipitation of most of the produced
tetraphenylphosphonium tetraphenylborate. Ether diffusion to the
residual solution afforded analytically pure product. The total amount
of 260 mg of yellow crystals of 3 corresponds to a yield of 78%. Anal.
Calcd for C40H40BN4O2V: C, 71.65; H, 6.01; N, 8.36. Found: C,
71.52; H, 6.06; N, 8.56. Absorption spectrum (acetonitrile): λmax (ꢀM)
253 (11 500), 261 (12 100), 274 (sh, 3780), 341 (376) nm. 1H NMR
(CD3CN, 200 MHz) δ 3.10 (s, CH3, 6H), 4.42 (JAB ) 15.9 Hz, CH2,
4H), 4.77 (JAB ) 15.9 Hz, CH2, 4H), 6.79-7.03 (m, Ph-H, 12H), 7.17
(B-part, JAB ) 7.81 Hz, 3,5-py-H, 4H), 7.20-7.27 (m, Ph-H, 8H),
2
7.72 (A-part, JAB ) 7.81 Hz, 4-py-H, 2H) ppm. IR (KBr): 1607,
2
1588, 1477, 1438, 1417, 1379, 1161, 1074, 1028, 939, 914, 903, 896,
875, 865, 792, 761, 744, 733, 706, 605 cm-1 (strong bands only).
Physical Methods. 1H-NMR: Varian Gemini 200 MHz. UV-
vis: Varian Cary 5 E. IR: Perkin-Elmer 1700 X FT-IR and Perkin-
Elmer 1720 FT-IR. EPR: Bruker ESP 300E. EPR spectra were
performed at room temperature and at 140 K on a 1 mM sample in
acetonitrile/toluene (v:v ) 1:3) solution. The EPR spectra were
analyzed with the program SimFonia 1.2 of Bruker. Electrochemis-
try: PAR Model 270 Research Electrochemistry Software controlled
potentiostat/galvanostat Model 273A with the electrochemical cell
placed in a glovebox. Electrochemical experiments were performed
on 1 mM acetonitrile solutions containing 0.2 M (Bu4N)ClO4 as
Experimental Section
Preparation of Compounds. The ligand N,N′-dimethyl-2,11-diaza-
[3.3](2,6)pyridinophane (L-N4Me2) was synthesized according to
published procedures with some slight modifications.10 Tetraphen-
ylphosphonium dichlorovanadate(V) was prepared as described11 and
purified with dichloromethane. Acetonitrile was dried over CaH2 and
freshly distilled prior to use. All other chemicals were purchased and
used without further purification.
(10) (a) Bottino, F.; Di Grazia, M.; Finocchiaro, P.; Fronczek, F. R.; Mamo,
A.; Pappalardo, S. J. Org. Chem. 1988, 53, 3521. (b) Alpha, B.;
Anklam, E.; Deschenaux, R.; Lehn, J.-M.; Pietraskiewicz, M. HelV.
Chim. Acta 1988, 71, 1042.
(11) Ahlborn, E.; Diemann, E.; Mu¨ller, A. Z. Anorg. Allg. Chem. 1972,
394, 1.
(12) (a) Wolsey, W. C. J. Chem. Educ. 1973, 50, A335. (b) Raymond, K.
N. Chem. Eng. News 1983, 61 (Dec 5), 4.

[(L-N4Me2)VL1L2]+
Inorganic Chemistry, Vol. 35, No. 12, 1996 3535
Table 1. Summary of Crystal Data, Intensity Collection, and Refinement Parameters for [(L-N4Me2)VCl2](BPh4) (1), [(L-N4Me2)VClO](ClO4)
(2) and [(L-N4Me2)VO2](BPh4) (3)
data
1
2
3
formula
mol wt
crystal dimens, mm
crystal system
space group
Z
C40H40BCl2N4V
709.41
0.3 × 0.4 × 0.5
monoclinic
P21/n (No.14)
4
C16H20Cl2N4O5V
470.20
0.25 × 0.4 × 0.7
orthorhombic
P212121 (No.19)
4
C40H40BN4O2V
670.51
0.3 × 0.3 × 0.8
monoclinic
P21/c (No.14)
4
a, Å
b, Å
c, Å
16.940(4)
9.902(3)
21.936(8)
108.21(2)
3495(2)
10.163(2)
13.351(3)
14.762(3)
(90)
2003(1)
1.559
14.349(3)
14.040(5)
18.131(10)
110.62(3)
3419(2)
â, deg
V, Å3
d
calc, g/cm3
1.348
1.303
diffractometer
temp, K
Hilger & Watts
153
0.71073(Mo KR)
4.72
Syntex P21
293
0.71073(Mo KR)
7.97
Hilger & Watts
153
0.71073(MoKR)
3.32
λ, Å
µ, cm-1
F(000)
1480
964
1408
scan method
ω-2Θ
Θ-2Θ
ω-2Θ
2Θ limits, deg
unique reflcns
reflcns with Fo > 4σ(Fo)
no. of variables (restraints)
GooF on F2 a
2.5 e 2Θ e 55
8061
4 e 2Θ e 50
3510
3 e 2Θ e 55
7914
6120
438
1.057
3024
303(42)
1.089
5672
437
1.067
absolute structure parameter
-0.04(4)
5.02 (11.93)
R(wR2), %a-c
4.25 (9.47)
5.59 (13.66)
2
2
a For all reflections with Fo > 4σ(Fo). b R ) Σ||Fo| - |Fc||/Σ|Fo|. c wR2 ) {Σ[w(Fo - Fc2)2]/Σ[w(Fo )2]}1/2
.
supporting electrolyte; a higher than normal electrolyte concentration
was applied to minimize solution resistance. All potentials were
measured vs a SCE reference electrode at 25 °C. The potentials were
not corrected for junction potentials. A Pt-foil electrode was employed
as the working electrode. Under these conditions the potential for the
ferrocene/ferrocenium ion couple was 0.39 V. Coulometric experiments
were performed by using a Pt-gauze electrode. Magnetic susceptibili-
ties: Johnson Matthey magnetic susceptibility balance. The values for
the diamagnetic susceptibilities of the ligand L-N4Me2 and of the other
components of the complexes were taken from the literature.8a,13
Determinations of the Structures of [(L-N4Me2)VCl2](BPh4) (1),
[(L-N4Me2)VClO](ClO4) (2), and [(L-N4Me2)VO2](BPh4) (3). Single
crystals were obtained by slow diffusion of ether into solutions of
compounds 1, 2, and 3 in acetonitrile. Suitable crystals of 1 and 3
were immersed in oil and then attached to the tips of glass fibers. The
glass fibers were subsequently mounted on goniometer heads in a cool
nitrogen stream at -120 °C. A crystal of 2 was carefully affixed to
the tip of a glass fiber with an adhesive.
Table 1 contains the cell parameters of the crystals and experimental
details on the data collections and the structure refinements. Unit cell
parameters and the final orientation matrices were obtained from least
squares refinement of 25 machine-centered reflections in the range 25°
e 2Θ e 28° (1) or 20° e 2Θ e 25° (2 and 3). The intensities of
three reflections measured every 97 (1 and 3) or 200 reflections (2)
indicated no decay of the crystals during the data collections. The
raw data were processed by the programs XDISK14 or Watshell.14 The
systematic absences uniquely determine the space groups as P21/n,
P212121, and P21/c for 1, 2, and 3, respectively.
SHELXL-93, using F2 of all symmetry-independent reflections except
those with very negative F2-values. All non-hydrogen atoms were
refined anisotropically. Hydrogen atoms were assigned idealized
locations and their isotropic temperature factors were refined. For
compound 2, the perchlorate anion is disordered over two positions.
The largest peaks (holes) in the final difference Fourier maps correspond
to 0.31 (-0.46) e/Å3, 0.50 (-0.21) e/Å3, and 1.44 (-0.63) e/Å3 for
complexes 1, 2, and 3, respectively. The final R factors are given in
Table 1. Positional parameters of the complex cations are listed in
Tables 2-4. Thermal parameters as well as full lists of distances and
angles for all three complexes are provided in the supplementary
material.
Results and Discussion
Synthesis of the Complexes. Reaction of [VCl3(THF)3] with
the tetraazamacrocyclic ligand L-N4Me2 in absolute acetonitrile
under a nitrogen atmosphere and subsequent metathesis with
sodium tetraphenylborate affords green crystals of [(L-N4Me2)-
VCl2](BPh4). The IR spectrum of the complex displays typical
absorptions of a coordinated L-N4Me2. In addition, the occur-
rence of the symmetric and the antisymmetric stretching
vibrations of the cis-VCl2 group as a rather broad band around
375 cm-1 confirms the cis-octahedral geometry of the complex.
The magnetic susceptibility measurement reveals a magnetic
moment of 2.68 µB, which is within the typical range observed
for octahedral mononuclear V(III) complexes with a d2 electron
configuration. As expected, due to the spin-orbit coupling in
a 3T1 ground state, the magnetic moment deviates from the spin-
only value of 2.83 µB. The 1H-NMR spectrum of 1 consists of
five paramagnetically shifted, broad signals in the range between
-20 to 20 ppm, which are attributed to the protons of the
coordinated ligand. The appearance of a purple precipitate
(presumably a dinuclear µ-chloro or µ-oxo bridged complex)
during the synthesis of the mononuclear complex as well as
the rather low yield of 38% indicate the formation of side
products whose exact identities have not yet been established.
However, when the reaction of vanadium trichloride with the
ligand was carried out under air in ethanolic solution, a blue
The positions of the non-hydrogen atoms were determined by
SHELXS 8614 and by Fourier difference maps using the program
SHELXL-93.14 Atomic scattering factors were taken from a standard
source.15 The structural parameters were refined with the program
(13) (a) Hellwege, K.-H.; Hellwege, A. M., Eds. Landolt-Bo¨rnstein, 6th
ed.; Springer Verlag: Berlin, 1967; Vol. II/10. (b) Hellwege, K.-H.;
Hellwege, A. M., Eds. Landolt-Bo¨rnstein New Series; Springer
Verlag: Berlin, 1976; Vol II/8, Supplement 1.
(14) XDISK: X-ray Diffraction Software, Siemens Analytical X-Ray
Instruments, Inc., 1990. Watshell: Kopf, J., Hamburg, 1993. SHELXS-
86: Crystal Structure Solution Program, Sheldrick G. M., Go¨ttingen,
1986. Sheldrick, G. M. In Crystallographic Computing 3; Sheldrick,
G. M., Kru¨ger, C., Goddard, R., Eds.; Oxford University Press:
Oxford, 1985; p 175. SHELXL-93: Crystal Structure Refinement
Program, Sheldrick, G., Go¨ttingen, 1993.
(15) Wilson, A. J. C. International Tables for Crystallography, Volume C;
Kluwer Academic Press: Dordrecht, 1974.

3536 Inorganic Chemistry, Vol. 35, No. 12, 1996
Kelm and Kru¨ger
Table 2. Fractional Atomic Coordinates (x104) and Isotropic
Displacement Parameters (Å2 ×103) with esd’s for the
Non-Hydrogen-Atoms in the Complex Cation of
[(L-N4Me2)VCl2](BPh4) (1)
Table 4. Fractional Atomic Coordinates (×104) and Isotropic
Displacement Parameters (Å2 x 103) with esd’s for the
Non-Hydrogen-Atoms in the Complex Cation of
[(L-N4Me2)VO2](BPh4) (3)
atom
x
y
z
Ueqa or Uiso
atom
x
y
z
Ueqa or Uiso
V(1)
Cl(1)
Cl(2)
N(1)
N(2)
N(3)
N(4)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
C(9)
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
1040(1)
1817(1)
1003(1)
-160(1)
999(1)
1938(1)
302(1)
-113(1)
387(1)
263(2)
778(2)
1391(2)
1487(1)
2126(1)
1581(2)
676(2)
833(1)
83(1)
3070(1)
99(2)
2176(1)
1553(1)
1887(1)
1607(1)
2557(1)
3117(1)
2746(1)
1597(1)
2243(1)
2504(1)
3108(1)
3439(1)
3150(1)
3450(1)
3481(1)
3348(1)
3770(1)
3567(2)
2954(2)
2549(1)
1861(1)
926(1)
19(1)
35(1)
34(1)
26(1)
20(1)
27(1)
26(1)
29(1)
24(1)
36(1)
45(1)
37(1)
24(1)
33(1)
41(1)
35(1)
52(1)
57(1)
50(1)
33(1)
47(1)
42(1)
42(1)
V(1)
O(1)
O(2)
N(1)
N(2)
N(3)
N(4)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
C(9)
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
822(1)
1110(2)
324(2)
-450(2)
1485(2)
2245(2)
553(2)
1918(1)
1892(2)
885(1)
2148(1)
3106(1)
1817(1)
1900(1)
2259(1)
1964(1)
949(1)
2348(2)
2290(2)
2309(2)
2298(2)
2255(2)
2235(1)
2243(2)
1099(2)
620(1)
-98(2)
-456(2)
-100(2)
609(1)
1031(2)
2178(2)
2394(2)
20(1)
33(1)
30(1)
19(1)
21(1)
22(1)
18(1)
27(1)
23(1)
30(1)
34(1)
30(1)
22(1)
26(1)
25(1)
19(1)
25(1)
27(1)
24(1)
18(1)
23(1)
27(1)
33(1)
2908(2)
3341(2)
1703(2)
2426(2)
3811(2)
4088(2)
5015(2)
5143(2)
4364(2)
3457(2)
2543(2)
1540(2)
2229(2)
2618(2)
3258(2)
3470(2)
3027(2)
3115(2)
2531(2)
830(2)
-1085(2)
989(2)
1281(2)
-1410(2)
-1928(2)
-3133(2)
-3468(3)
-2581(3)
-1387(2)
-348(2)
1957(3)
1695(2)
1864(3)
1563(3)
1094(3)
971(2)
-63(2)
924(2)
1272(2)
2225(2)
2797(2)
2399(2)
2941(2)
2016(2)
1234(2)
1161(2)
394(2)
-293(2)
-194(2)
-923(2)
-1245(2)
2747(2)
226(2)
-606(2)
-978(2)
-503(1)
-831(1)
-354(2)
2733(2)
562(3)
567(3)
1564(3)
3070(1)
a The equivalent isotropic thermal parameter Ueq (Å2) is defined as
a The equivalent isotropic thermal parameter Ueq (Å2) is defined as
1
1
Ueq ) /3ΣiΣjUija* a* ai.aj.
Ueq ) /3ΣiΣjUija* a* ai‚aj.
i
j
i
j
Table 3. Fractional Atomic Coordinates (×104) and Isotropic
Displacement Parameters (Å2 × 103) with esd’s for the
Non-Hydrogen-Atoms in the Complex Cation of
[(L-N4Me2)VClO](ClO4) (2)
IR band at 968 cm-1 is tentatively attributed to the VdO
stretching vibration. The magnetic moment of 1.73 µB corre-
sponds to the spin-only value of a d1 electron configuration.
This is typical for vanadyl(IV) complexes where the strong
π-donor capability of the oxo donor lifts the degeneracy of the
t2g-orbitals, thereby prohibiting any strong spin-orbit coupling.
The dioxovanadium(V) complex [(L-N4Me2)VO2](BPh4) was
obtained in a 78% yield by the addition of (PPh4)[VCl2O2] to
acetonitrile containing the ligand L-N4Me2 and 2 equiv of
sodium tetraphenylborate. The reaction has to be carried out
under exclusion of light and moisture or substantial production
of a green byproduct occurs, which cannot be removed from
the product by repeated recrystallization. EPR spectroscopy
attributes the contamination to some vanadyl(IV) species.
1H-NMR spectroscopy of the pure dioxovanadium(V) com-
plex shows that, as expected, the compound is diamagnetic.
Upon coordination, all NMR signals of the ligand protons are
shifted to lower fields. But the most distinctive feature of the
NMR spectrum is the appearance of an AB-coupling pattern
for the diastereotopic methylene protons on the ligand (instead
of the singlet observed for the free ligand) as a consequence of
the fact that the rapid inversions at the amine nitrogen atoms
are revoked by the coordination of the ligand to the metal ion.
This observation further demonstrates that, in solution, the ligand
remains coordinated to the vanadium ion at all times. IR
spectroscopy also confirms coordination of the ligand. The
absence of any characteristic V-Cl stretching vibrations in the
far-IR region and the observation of two VO2-stretching
vibrations at 914 and 903 cm-1 are consistent with the
formulation of 3 as a cis-dioxovanadium(V) complex.
atom
x
y
z
Ueqa or Uiso
V(1)
Cl(1)
O(1)
N(1)
N(2)
N(3)
N(4)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
C(9)
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
8654(1)
8981(1)
9418(3)
10106(3)
8021(3)
6565(3)
7620(3)
10121(5)
8770(5)
8253(5)
6957(6)
6205(5)
6753(4)
6094(4)
5802(4)
6315(5)
5593(5)
6243(6)
7572(6)
8254(5)
9719(5)
11443(5)
6348(5)
3075(1)
2356(1)
2280(2)
4280(3)
4065(2)
2674(2)
4254(3)
4776(4)
4871(3)
5673(4)
5653(4)
4823(4)
4036(3)
3057(3)
3150(4)
4174(3)
4968(4)
5859(4)
5941(4)
5100(3)
5028(4)
3895(4)
1569(3)
2937(1)
4366(1)
2291(2)
3042(3)
1934(2)
2824(2)
3690(2)
2126(3)
1766(3)
1311(3)
1034(3)
1224(3)
1679(3)
1927(3)
3576(3)
3808(3)
4127(4)
4304(4)
4173(4)
3866(3)
3762(3)
3252(4)
2848(4)
37(1)
61(1)
57(1)
45(1)
38(1)
40(1)
37(1)
52(1)
43(1)
52(1)
57(1)
52(1)
40(1)
48(1)
52(1)
43(1)
59(1)
64(2)
56(1)
42(1)
50(1)
66(2)
61(1)
a The equivalent isotropic thermal parameter Ueq (Å2) is defined as
1
Ueq ) /3ΣiΣjUija* a* ai‚aj.
i
j
complex of stoichiometry [(L-N4Me2)VClO](ClO4) was formed
in 65% yield, after addition of sodium perchlorate. IR
spectroscopy confirms coordination of the macrocyclic ligand.
Compared to the spectrum of 1, the rather narrow band at 380
cm-1, corresponding to a V-Cl stretching vibration, indicates
coordination of only one chloride. Further, two intensive IR
bands are observed at 982 and 968 cm-1 for the vanadyl(IV)
complex. On the basis of the finding that for six-coordinate
vanadyl(IV) complexes a VdO stretching frequency is generally
observed around 950 cm-1 while for five-coordinate vanadyl-
The complex [(L-N4Me2)VCl2]+ can be converted to [(L-N4-
Me2)VClO]+ with a 58% yield by treating a solution of 1 in
acetonitrile with aqueous ethanol under air. An analogous way
has been previously pursued in the preparation of the neutral
mononuclear vanadyl complex [(tacn)VX2O] (with X ) Cl, F)
(16) (a) Bonadies, J. A.; Carrano, C. J. J. Am. Chem. Soc. 1986, 108, 4088.
(b) Li, X.; Lah, M. S.; Pecoraro, V. L. Inorg. Chem. 1988, 27, 4657.
(IV) complexes it is found around 980 cm-1 16
, the more intense

[(L-N4Me2)VL1L2]+
Inorganic Chemistry, Vol. 35, No. 12, 1996 3537
Figure 1. Structure of [(L-N4Me2)VCl2]+ showing thermal ellipsoids
at 50% probability and the atom numbering scheme.
Figure 3. Structure of [(L-N4Me2)VO2]+ showing thermal ellipsoids
at 50% probability and the atom numbering scheme.
In complex 1, the average V-Cl distance of 2.298 ( 0.001 Å
is similar to those obtained in other octahedral vanadium(III)
chloride complexes.20,21 As in other metal chloride complexes
with L-N4Me2 as ligand,8,19 the axial V-Namine bonds with an
average length of 2.153 ( 0.001 Å are longer than the equatorial
V-Npy bonds which average to 2.079 ( 0.006 Å. However,
the difference between the axial and the equatorial metal-
nitrogen bond lengths is much less pronounced in complex 1.
In [(L-N4Me2)VClO]+ the V-O bond distance of 1.624 Å is
consistent with a double bond between a six-coordinate vana-
dium(IV) and a terminal oxo function.18,21-23 The lengthening
of the V-Cl bond from 2.298 Å to 2.341 Å despite the higher
oxidation state of the vanadium ion can be explained by the
fact that a weakly π-bonding Cl- and a stronger π-donor O2-
compete for the same d-orbital. In general, the V-Cl bond
lengths in cis-chlorooxovanadium(IV) complexes are somewhat
larger than those found in vanadium(III) complexes containing
a cis-VCl2 unit.18,21-23
Substitution of one Cl- by O2- with concomitant oxidation
of the vanadium also leads to some quite interesting changes
in the coordination of the macrocyclic ligand. While the length
of V-Npy bond trans to the chloride stays approximately the
Figure 2. Structure of [(L-N4Me2)VClO]+ showing thermal ellipsoids
at 50% probability and the atom numbering scheme.
by oxidation of [(tacn)VX3] with air in aqueous methanol
solution.17 Although the vanadyl(IV) complex is quite stable
in most solvents under air, it can be oxidized in a 63% yield to
the dioxovanadium(V) complex by molecular oxygen in the
presence of aqueous tetrahydrofuran. A similar observation has
been made for the complex [(bipy)2VClO]Cl.18
Structures of [(L-N4Me2)VCl2](BPh4) (1), [(L-N4Me2)-
VClO](ClO4) (2), and [(L-N4Me2)VO2](BPh4) (3). Structure
determinations were carried out on single crystals of [(L-N4-
Me2)VCl2](BPh4), [(L-N4Me2)VClO](ClO4), and [(L-N4Me2)-
VO2](BPh4). Perspective views of the complex cations with
the atomic numbering schemes are displayed in Figures 1-3.
A comparison of some selected distances and angles is contained
in Table 5. The overall coordination geometries of all com-
plexes are best described by distorted octahedrons. While
complexes 1 and 3 approach an overall C2V symmetry, the
symmetry of complex 2 is reduced to approximately Cs. As in
some previously reported complexes containing L-N4Me2,8,19
the tetradentate ligand is folded along the Namine-Namine axis,
thus leaving two cis coordination sites available for complex-
ation by the chloro and/or oxo-ligands. The most obvious
distortion from an ideal octahedral coordination geometry is the
substantial deviation of the Namine-V-Namine angle from ideal 180°
to 147° (1 and 2) and 143° (3).
(20) The V-Cl distances in mononuclear octahedral complexes containing
the cis-VIIICl2 unit range from 2.269 to 2.361 Å with a mean at 2.323
Å. (a) Silverman, L. D.; Dewan, J. C.; Giandomenico, C. M.; Lippard,
S. J. Inorg. Chem. 1980, 19, 3379. (b) Folting, K.; Huffman, J. C.;
Bansemer, R. L.; Caulton, K. G.; Martin, J. L.; Smith, P. D. Inorg.
Chem. 1984, 23, 4589. (c) Cotton, F. A.; Duraj, S. A.; Powell, G. L.;
Roth, W. J. Inorg. Chim. Acta 1986, 113, 81. (d) Bultitude, J.;
Larkworthy, L. F.; Povey, D. C.; Smith, G. W.; Dilworth, J. R. J.
Chem. Soc., Dalton Trans. 1986, 2253. (e) Morse, D. B.; Rauchfuss,
T. B.; Wilson, S. R. J. Am. Chem. Soc. 1988, 110, 2646. (f) Kynast,
U.; Bott, S. G.; Atwood, J. L. J. Coord. Chem. 1988, 17, 53. (g)
Henderson, R. A.; Hills, A.; Hughes, D. L.; Lowe, D. J. J. Chem.
Soc., Dalton Trans. 1991, 1755. (h) Cotton, F. A.; Lu, J.; Ren, T.
Inorg. Chim. Acta 1994, 215, 47. (i) Solari, E.; De Angelis, S.; Floriani,
C.; Chiesi-Villa, A.; Guastini, C. Inorg. Chem. 1992, 31, 141. (j)
Sorensen, K. L.; Ziller, J. W.; Doherty, N. M. Acta Crystallogr., Sect.
C 1994, 50, 407.
(21) Kime-Hunt, E.; Spartalian, K.; DeRusha, M.; Nunn, C. M.; Carrano,
C. J. Inorg. Chem. 1989, 28, 4392.
(22) Collison, D.; Eardley, D. R.; Mabbs, F. E.; Powell, A. K.; Turner, S.
S. Inorg. Chem. 1993, 32, 664.
(17) (a) Ko¨ppen, M.; Fresen, G.; Wieghardt, K.; Llusar, R. M.; Nuber, B.;
Weiss, J. Inorg. Chem. 1988, 27, 721. (b) Knopp, P.; Wieghardt, K.;
Nuber, B.; Weiss, J. Z. Naturforsch. 1991, 46B, 1077.
(18) Brand, S. G.; Edelstein, N.; Hawkins, C. J.; Shalimoff, G.; Snow, M.
R.; Tiekink, E. R. T. Inorg. Chem. 1990, 29, 434.
(19) (a) Fronczek, F. R. ; Mamo, A.; Pappalardo, S. Inorg. Chem. 1989,
28, 1419. (b) Sakaba, H.; Kabuto, C.; Horino, H.; Arai, M. Bull. Chem.
Soc. Jpn. 1990, 63, 1822.
(23) The VsCl and VdO distances in mononuclear octahedral complexes
containing the cis-VIVClO unit range from 2.292 to 2.400 Å and from
1.584 to 1.651 Å, with means at 2.347 and 1.599 Å, respectively. (a)
Zah-Letho, J.; Samuel, E.; Dromzee, Y.; Jeannin, Y. Inorg. Chim.
Acta 1987, 126, 35. (b) Priebsch, W.; Rehder, D. Inorg. Chem. 1990,
29, 3013. (c) Willey, G. R.; Lakin, M. T.; Alcock, N. W. J. Chem.
Soc., Chem. Commun. 1991, 1414. (d) Kabanos, T. A.; Keramidas,
A. D.; Papaioannou, A.; Terzis, A. Inorg. Chem. 1994, 33, 845.

3538 Inorganic Chemistry, Vol. 35, No. 12, 1996
Kelm and Kru¨ger
In [(L-N4Me2)VO2]+, the V-O bond lengths average to 1.637
( 0.003 Å and are within the range commonly found in cis-
dioxovanadium(V) complexes with octahedral coordination
geometries.24,25 The slight increase of the average V-O bond
despite the higher nuclear charge on the vanadium ion derives
from the fact that in the cis-dioxo compound both coordinated
oxo groups compete for the same vacant dxy-orbital and,
therefore, the V-O bond order is slightly reduced in comparison
with the previously discussed vanadyl(IV) complex. This
decrease in bond strength is also demonstrated by the decrease
in the VdO stretching vibration frequency from 968 cm-1 in
the vanadyl complex to 914 and 903 cm-1 in the cis-
dioxovanadium(V) complex. A similar reduction of the VdO
bond strength has been observed for other cis-dioxovanadium-
(V) complexes, which distinguish themselves from the corre-
sponding vanadyl(IV) complexes only by the fact that one oxo
function is replaced by a weak π-donor while the residual
coordination environment around the central ion is preserved.18,25
The V-Npy bonds trans to both VdO groups are, with 2.190
( 0.001 Å, as long as the corresponding trans V-Npy bond in
2, again providing evidence for the strong trans influence of
VdO groups. In comparison with compound 2, the average
V-Namine bond length of 2.206 ( 0.005 Å changes only slightly.
The increase from 96.8° (1) to 101.1° (2) to 106.5° (3) for the
angle included by the bondings between the vanadium and the
cis coordinating ligands reflects the stronger electron repulsion
between the shorter VdO bond and the other ligand bonding.
Of all three compounds presented here, the central metal ion
protrudes to the greatest extent out of the macrocyclic cavity
in the dioxovanadium(V) complex, as is manifested in the small
Npy-V-Npy and Namine-V-Namine angles. It is worthwhile to
point out that in complex 3 the axial V-Namine bonds are nearly
as large as the equatorial V-Npy bonds. Considering that the
M-Npy bond determines for the most part the coordination mode
of the macrocycle,8 this finding serves as evidence for the
adaptability of this sterically rigid macrocycle toward individual
complexing conditions given by the size and charge of the metal
ion as well as by the electronic and steric factors of the residual
ligand donors trans to the pyridine nitrogens.
Table 5. Selected Distances and Angles in [(L-N4Me2)VCl2](BPh4)
(1), [(L-N4Me2)VClO](ClO4) (2), and [(L-N4Me2)VO2](BPh4) (3)
1
2
3
V(1)-N(1)
V(1)-N(2)
V(1)-N(3)
V(1)-N(4)
V(1)-Cl(1)
V(1)-Cl(2)
V(1)-O(1)
V(1)-O(2)
2.152(2)
2.084(2)
2.153(2)
2.073(2)
2.2969(8)
2.2990(9)
2.189(4)
2.087(4)
2.196(4)
2.195(3)
2.341(2)
2.211(2)
2.191(2)
2.201(2)
2.189(2)
1.624(3)
1.639(2)
1.634(2)
N(1)-V(1)-N(2)
N(1)-V(1)-N(3)
N(1)-V(1)-N(4)
N(1)-V(1)-Cl(1)
N(1)-V(1)-Cl(2)
N(1)-V(1)-O(1)
N(1)-V(1)-O(2)
N(2)-V(1)-N(3)
N(2)-V(1)-N(4)
N(2)-V(1)-Cl(1)
N(2)-V(1)-Cl(2)
N(2)-V(1)-O(1)
N(2)-V(1)-O(2)
N(3)-V(1)-N(4)
N(3)-V(1)-Cl(1)
N(3)-V(1)-Cl(2)
N(3)-V(1)-O(1)
N(3)-V(1)-O(2)
N(4)-V(1)-Cl(1)
N(4)-V(1)-Cl(2)
N(4)-V(1)-O(1)
N(4)-V(1)-O(2)
Cl(1)-V(1)-Cl(2)
Cl(1)-V(1)-O(1)
O(1)-V(1)-O(2)
77.38(7)
146.80(7)
77.57(7)
99.13(6)
103.09(5)
78.0(1)
146.8(1)
76.1(1)
98.2(1)
75.30(8)
143.02(8)
75.48(8)
101.5(2)
96.36(10)
105.10(9)
75.13(8)
73.34(8)
77.47(7)
81.47(7)
92.31(5)
170.63(5)
78.6(1)
76.0(1)
160.6(1)
98.3(2)
89.08(10)
164.18(9)
75.15(8)
77.58(8)
103.19(6)
98.33(5)
75.6(1)
96.1(1)
105.0(2)
84.6(1)
104.85(10)
97.55(10)
173.45(6)
89.46(5)
174.1(2)
161.93(10)
91.32(9)
96.83(3)
101.1(1)
106.48(11)
same, the V-Npy bond trans to O2- is remarkably elongated to
2.195 Å. This trans influence is a well-known effect found in
complexes containing the strong π donor O2- as ligand. In order
to accommodate the larger V-Npy bond, the vanadium ion in 2
protrudes more out of the macrocyclic cavity than in 1, resulting
in slightly larger V-Namine distances and a decreased Npy-V-
Npy angle. In general, the steric rigidity and the small ring size
of the macrocyclic ligand account for the observation that, in
all complexes with L-N4Me2 as ligand, the metal ion does not
lie on the intersecting line of the least-squares planes of the
two pyridine rings and that, therefore, the angle between both
pyridine planes is normally considerably less than the Npy-
M-Npy angle.8 In complex 2, the asymmetry of the V-Npy
bonds introduces some additional strain onto the coordinated
macrocycle. Thus, within this series of compounds, the angle
between the pyridine planes reaches its minimum with 49.0° in
complex 2 and the displacement of the vanadium ion from the
least-squares planes of the pyridine rings amounts to 0.492 (
0.076 Å, compared to 0.249 ( 0.006 Å and 0.209 ( 0.078 Å
in complexes 1 and 3, respectively.
Such a series of vanadium complexes which differ only in
the oxidation state of the vanadium ion and the donor composi-
tion at two coordination sites is quite rare. With bipy as ligand,
a rather similar series has been obtained in which, however,
only the structures of [(bipy)2VClO]+ and [(bipy)2VO2]+ were
established.18,26 In all other instances, only the vanadium(III)
and the vanadyl(IV) equivalents were obtained.21,22,25 For
example, with the anionic tridentate ligand (HB(Me2pz)3)- only
the complexes [{HB(Me2pz)3}VCl2(DMF)] and [{HB(Me2pz)3}-
VClO(DMF)], but not the corresponding dioxovanadium(V)
complex, were reported.21 On the other hand, in the pair of
compounds [{HB(Me2pz)3}VCl2(Me2pz)] and [{HB(Me2pz)3}-
VClO(Me2pzH)], the protonation of the pyrazolyl ligand varies
in addition to the replacement of one chloride by an oxide.21,22
Electronic Absorption and Electron Paramagnetic Reso-
nance Spectra. The electronic absorption spectra of the three
complexes in acetonitrile are displayed in Figure 4. Assuming
an octahedral ligand field description for complex 1, the
absorption bands at 635 and 450 nm are assigned to the
transitions T1(F) f T2(F) and T1(F) f T1(P), respectively,
based on their low intensities. The third band 3T1(F) f 3A2(F)
lies in the UV region and is obscured by intensive CT bands.
(24) The VdO distances in mononuclear octahedral complexes containing
the cis-VVO2 unit range from 1.613 to 1.670 Å with a mean at 1.636
Å. (a) Scheidt, W. R.; Tsai, C.; Hoard, J. L. J. Am. Chem. Soc. 1971,
93, 3867. (b) Scheidt, W. R.; Collins, D. M.; Hoard, J. L. J. Am. Chem.
Soc. 1971, 93, 3873. (c) Scheidt, W. R.; Countryman, R.; Hoard, J.
L. J. Am. Chem. Soc. 1971, 93, 3878. (d) Drew, R. E.; Einstein, F.
W. B.; Gransden, S. E. Can. J. Chem. 1974, 52, 2184. (e) Isobe, K.;
Ooi, S.; Nakamura, Y.; Kawaguchi, S.; Kuroya, H. Chem. Lett. 1975,
35. (f) Jeannin, Y.; Launay, J. P.; Sedjadi, M. A. S. J. Coord. Chem.
1981, 11, 27. (g) Giacomelli, A.; Floriani, C.; de S. Duarte, A. O.;
Chiesi-Villa,A.; Guastini, C. Inorg. Chem. 1982, 21, 3310. (h) Kojima,
A.; Okazaki, K.; Ooi, S.; Saito, K. Inorg. Chem. 1983, 22, 1168. (i)
Stomberg, R. Acta Chem. Scand., Ser. A 1986, 40, 168. (j) Neves, A.;
Horner, M.; Fenner, H.; Stra¨hle, J. Acta Crystallogr., Sect. C 1993,
49, 1737.
3
3
3
3
(25) Neves, A.; Walz, W.; Wieghardt, K.; Nuber, B.; Weiss, J. Inorg. Chem.
1988, 27, 2484.
(26) (a) Fowles, G. W. A.; Greene, P. T. J. Chem. Soc. (A) 1967, 1869.
(b) Casey, A. T.; Clark, R. J. H. Transition Met. Chem. 1977, 2, 76.

[(L-N4Me2)VL1L2]+
Inorganic Chemistry, Vol. 35, No. 12, 1996 3539
Figure 4. Electronic absorption spectra of [(L-N4Me2)VCl2](BPh4) (1),
[(L-N4Me2)VClO](ClO4) (2), and [(L-N4Me2)VO2](BPh4) (3) in aceto-
nitrile solutions.
3
3
From the position of the T1(F) f T2(F) absorption band,27
the ligand field parameter 10 Dq is estimated to be 17 300 cm-1
,
which is surprisingly larger than the one observed for the cis-
octahedral complex [(bipy)2VCl2]+.26 In agreement with the
spectra of the uncoordinated ligand8a and with those of both
other vanadium complexes, an intense absorption is found
around 260 nm, which is attributed to a π f π* transition. The
other two absorptions at 375 and 273 nm are tentatively assigned
to CT bands.
The visible region of the electronic absorption spectrum of
compound 2 is comprised of three relatively weak absorptions
at 707, 633, and 356 nm, which are, according to Ballhausen
and Gray,28 attributed to the d-d transitions dxy f (dxz,dyz), dxy
2
2
2
f dx -y , and dxy f dz , respectively, assuming approximate
tetragonal geometry with the VdO bond aligned along the
z-axis. As previously mentioned, the value of the magnetic
moment of the complex also indicates a nondegenerate ground
state. The value of 10 Dq ) 15 800 cm-1 can be obtained
directly from the second d-d transition. This value is, as
expected, lower than those observed for the complexes
Figure 5. Cyclic voltammograms (A) of [(L-N4Me2)VCl2](BPh4) (1)
(200 mV/s), (B) of the product obtained by reducing [(L-N4-
Me2)VCl2](BPh4) at -0.77 V (200 mV/s), and (C) of [(L-N4Me2)VClO]-
(ClO4) (2) (50 mV/s) at a Pt-foil electrode in acetonitrile solutions at
25 °C; peak potentials and half-wave potentials vs SCE are indicated.
dioxovanadium(V) complex, while the UV region is dominated
by CT bands at 341 and 274 nm and the two π f π* bands at
261 and 253 nm, which are also found at slightly shifted
wavelengths in the other two complexes.
[(bipy)2VClO]+ (17 400 cm-1 18
) and [(HB(Me2pz)3)VClO(Me2-
with similar cis-octahedral VN4ClO
pzH)] (16 700 cm-1 22
)
coordination environments where, however, in contrast to 2,
all nitrogen donors have π-acceptor capabilities. X-band
electron paramagnetic resonance spectra were obtained for the
complex in acetonitrile/toluene (V/V ) 1:3) at room temperature
and at 140 K. The g and AV values were determined by
simulation of the spectra. At room temperature the solution
spectrum displays eight lines due to the coupling of the S ) 1/2
Electrochemical Properties. The redox chemistry of the
complexes in acetonitrile solutions was investigated by cyclic
voltammetry and by electrolysis. The cyclic voltammograms
are presented in Figure 5.
The vanadium(III) complex 1 can be reduced at -0.57 V vs
SCE. The independence of the cathodic peak current ip,c from
V1/2 shows that the electron transfer is diffusion controlled. At
high scan rates, e.g., V ) 200 mV/s, the separation of the peak
potentials ∆Ep ≈ 90 mV and the ratio of the peak currents,
ip,a/ip,c ≈ 0.9, indicate a somewhat quasi-reversible electron
transfer step. However, lowering the scan rates is accompanied
by a decrease of ip,a/ip,c to about 0.45 at V ) 5 mV/s. Potential
controlled electrolysis at -0.75 V results in the passage of
1.03e- per molecule. Upon reoxidation at -0.35 V, about 90%
of the initially transferred charge is collected. In addition to
the quasi-reversible redox response at -0.57 V, which is vastly
diminished compared to the size of the original reductive current
of the oxidized species, the cyclic voltammogram of the deep-
blue reduced species (Figure 5) reveals a further irreversible
oxidation process at -0.13 V. As a result of the oxidation at
-0.13 V, complex 1 is formed again. As illustrated by reaction
1, the electrochemical results are interpreted to mean that
complex 1 is reduced in a quasi-reversible one-electron reduction
7
electron spin with the vanadium nuclear spin (I ) /2). The
isotropic g and AV values were found to be 1.975 and 90.75
× 10-4 cm-1, respectively. The frozen solution renders a nearly
axial EPR signal. From g| ) 1.955 < g ) 1.983 of the
anisotropic spectrum and from the lack of any observable
superhyperfine coupling to the nuclear spin of the nitrogen
atoms, it can be concluded that the unpaired electron is localized
in the dxy-orbital.29 The somewhat lower g| value compared to
those obtained for [(bipy)2VClO]+ is consistent with the inferior
π-acceptor capabilities of L-N4Me2 compared to bipy.18 The
anisotropic coupling constants AV| and AV were determined to
be 160 × 10-4 and 55 × 10-4 cm-1. These values, as well as
that for AV , are in the common range for vanadyl(IV)
complexes with N4ClO environments.18,22
As expected for d0 metal ions, there are no d-d bands in the
visible region of the electronic absorption spectrum of the
(27) Ballhausen, C. J. Z. Phys. Chem., Neue Folge 1957, 11, 205.
(28) Ballhausen, C. J.; Gray, H. B. Inorg. Chem. 1962, 1, 111.
(29) Kivelson, D.; Lee, S.-K. J. Chem. Phys. 1964, 41, 1896.

3540 Inorganic Chemistry, Vol. 35, No. 12, 1996
Kelm and Kru¨ger
step to [(L-N4Me2)VCl2], which equilibrates with some not
identified species with an irreversible oxidation potential at
-0.13 V.
Scheme 1
methods. The reactions carried out in this investigation are
summarized in Scheme 1. The compounds represent a series
of mononuclear complexes containing six-coordinate vanadium
in the oxidation states III, IV, and V, respectively, where two
chloride ions at two cis-coordination sites are successively
replaced by oxo donors with retainment of the residual donor
environment. This series of complexes provides us with the
rather unique opportunity to examine the influence which the
electronic and steric properties of two cis coordinating ligands
exert on the structure and stability of the vanadium complexes.
The electrochemical results demonstrate quite impressively how
the electronic properties of the cis donors stabilize just one
specific oxidation state of the vanadium ion in a given donor
environment.
In contrast to the 3,5-dimethyl-substituted tris(pyrazolyl)-
borate, which decomposes to some extent in the reaction with
vanadium trichloride,21,22 L-N4Me2 is quite stable and is
therefore well suited for further studies on the basic coordination
chemistry of vanadium. Preliminary studies utilizing the
vanadyl(IV) and the dioxovanadium(V) complexes as oxo-
transfer reagents have shown that compound 2 does not react
with triphenylphosphine under anaerobic conditions, while 3
produces approximately 0.5 equiv of the corresponding phos-
phinoxide. With respect to this reaction, the relatively easy
successive interconversion of complex 1 via 2 to compound 3
by air might prove itself to be very helpful in the development
of catalytically proceeding reactions with oxygen as the terminal
oxidizing reagent. However, since in this reaction the tetra-
nuclear complex [{(L-N4Me2)VO(µ-O)}3VO]3+ is formed as the
main product, it seems that the reaction of 3 with phosphine
does not occur by a simple oxo transfer but instead by a more
complicated, possibly radical-involving mechanism. The further
investigation of this complex and the continuing exploration of
the basic coordination chemistry of vanadium, particularly the
reactivity of the complexes with peroxides, will be reported
elsewhere.
The vanadyl(IV) complex can be oxidized by one electron
at the rather high potential of 1.52 V vs SCE. Also in this
redox reaction, since ∆Ep ) 70 mV and ip,c/ip,a ≈ 1 at a scan
rate of 50 mV/s, cyclic voltammetry assigns quasi-reversibility
to the electron transfer step. While ip,a/V1/2 is approximately
constant over the whole range of scan rates, the ratio of peak
currents is reduced to 0.70 at 5 mV/s. A coulometric oxidation
at 1.72 V reveals a small, but constant, current after the passage
of 1F. When the oxidation of the complex was stopped after
the exact flow of 1e- per molecule, there was no reductive
current observed upon re-reduction at 1.32 V, indicating, as
shown in reaction 2, that the immediate oxidation product, [(L-
N4Me2)VClO]2+, is not stable on a coulometric time scale (20-
30 min) but irreversibly reacts or decomposes to some unknown
product(s). It is interesting to note that a possible intermediate
in the reaction mechanism of vanadium-containing haloperoxi-
dases might consist of a vanadium(V) ion coordinated by an
oxide and a halide. The instability of [(L-N4Me2)VClO]2+
serves as evidence that additional negatively charged ligand
donors, preferably with π-donor properties, are needed to
stabilize a vanadium(V) species with such a ligand donor set.
The effect of an additional charge is demonstrated by the shift
of 160 mV to a lower redox potential for the mononuclear
complex [{HB(Me2pz)3}VClO(Me2pzH)].22 But even here, the
N4ClO coordination environment does not seem to support a
stable vanadium(V) ion. The introduction of anionic oxygen
donors like alkoxides decreases even further the redox potential,
thus finally permitting isolation of the vanadium(V) complex
[{HB(Me2pz)3}VClO(OBut)].4
Acknowledgment. We gratefully acknowledge financial
assistance by the Deutsche Forschungsgemeinschaft and by the
University of Hamburg.
Supporting Information Available: Crystallographic data for the
complexes [(L-N4Me2)VCl2](BPh4), [(L-N4Me2)VClO](ClO4), and [(L-
N4Me2)VO2](BPh4); details of data collections and tabulations of
positional and thermal parameters, interatomic distances and angles,
and calculated hydrogen atom positions; Figure S1, X-band EPR spectra
of [(L-N4Me2)VClO](ClO4) (2) in acetonitrile/toluene (V/V ) 1:3)
solution (a) at room temperature and (b) as frozen glass at 140 K (28
pages). Ordering information is given on any current masthead page.
The cyclic voltammogram of the dioxovanadium(V) complex
3 (not shown) does not display any reversible redox reactions.
Upon reduction, a peak potential was observed at -1.36 V.
Summary. Novel complexes of the tetraazamacrocyclic
ligand L-N4Me2 with vanadium have been prepared and
characterized by X-ray crystallography and other physical
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