Controlling Nuclearity and Stereochemistry in Vanadyl(V) and Mixed Valent VIV/VV Complexes of Oxido-Pincer Pyridine-2,6-dimethanol Ligands

Article abstract of DOI:10.1002/zaac.201800352

The coordination chemistry of three oxido-pincer ligands 2,6-(HOCR₂)₂(pyridine) (H₂L) based on 2,6-pyridinedimethanol [R = H (H₂pydim), Me (H₂pydip), Ph (H₂pyphen)] towards vanadium(V) was explored. Reaction of NH₄VO₃ with the protoligands H₂L gave the dinuclear complexes [(L)OV(μ-O)VO(L)]. Mononuclear anionic species [VO₂(L)]^–, which were isolated as alkaline metal salts were obtained from reactions of [VO(acac)₂] (acac^– = acetylacetonate) and H₂L under basic conditions and addition of HCl to these species allowed to isolate the unprecedented oxido chlorido complexes [VOCl(L)] for pydip and pyphen. Cyclic voltammograms of the dinuclear [V₂O₃(L)₂] and mononuclear [VOCl(L)] complexes show reversible V^V/V^IV reduction waves, while corresponding waves of the anionic [VO₂(L)]^– are completely irreversible. The mixed-valent V^IV/V^V species [V₂O₃(L)₂]^·– were characterized by EPR and UV/Vis spectroelectrochemistry revealing a delocalized system with a 15 line EPR spectrum and an intervalence charge transfer (IVCT) band for the bulky pyphen ligand but localized radicals in case of the pydim and pydip derivatives (8 line EPR, no IVCT). DFT calculated structures of the three derivatives show an V–O–V arrangement for [V₂O₃(pyphen)₂]^·– of about 145° ideally suited for delocalization, whereas for [V₂O₃(pydip)₂]^·– an angle of 128° was found.

Full text of DOI:10.1002/zaac.201800352

Journal of Inorganic and General Chemistry
DOI: 10.1002/zaac.201800352
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
Controlling Nuclearity and Stereochemistry in Vanadyl(V) and
Mixed Valent VIV/VV Complexes of Oxido-Pincer Pyridine-2,6-
dimethanol Ligands
Sara Nitsche,[a] Simon Schmitz,[a] Kathrin Stirnat,[a] Aaron Sandleben,[a] and Axel Klein*[a]
Dedicated to Prof. Dr. Wolfgang Bensch on the Occasion of his 65th Birthday
Abstract. The coordination chemistry of three oxido-pincer ligands reversible VV/VIV reduction waves, while corresponding waves of the
2,6-(HOCR2)2(pyridine) (H2L) based on 2,6-pyridinedimethanol anionic [VO2(L)]– are completely irreversible. The mixed-valent
[R
= H
(H2pydim), Me (H2pydip), Ph (H2pyphen)] towards VIV/VV species [V2O3(L)2]·– were characterized by EPR and UV/Vis
vanadium(V) was explored. Reaction of NH4VO3 with the protoli-
gands H2L gave the dinuclear complexes [(L)OV(μ-O)VO(L)]. Mono-
nuclear anionic species [VO2(L)]–, which were isolated as alkaline bulky pyphen ligand but localized radicals in case of the pydim and
metal salts were obtained from reactions of [VO(acac)2] (acac– = acet- pydip derivatives (8 line EPR, no IVCT). DFT calculated
ylacetonate) and H2L under basic conditions and addition of HCl to structures of the three derivatives show an V–O–V arrangement for
these species allowed to isolate the unprecedented oxido chlorido com-
plexes [VOCl(L)] for pydip and pyphen. Cyclic voltammograms of whereas for [V2O3(pydip)2]·– an angle of 128° was found.
the dinuclear [V2O3(L)2] and mononuclear [VOCl(L)] complexes show
spectroelectrochemistry revealing a delocalized system with a 15 line
EPR spectrum and an intervalence charge transfer (IVCT) band for the
[V2O3(pyphen)2]·– of about 145° ideally suited for delocalization,
plexes as luminescent materials,[3,11–14] luminescent probes in
Introduction
biology,[15,16] or acid catalysts for DNA hydrolysis.[17]
Tridentate ligands of the so called pincer type (Scheme 1)
combine the possibility to prepare highly stable transition
metal complexes with defined stereochemistry with almost un-
limited possibilities for ligand derivatization and fine tuning of
the complexes properties. This has allowed the rational design
of such complexes for applications in catalysis or molecular
sensing.[1,2] Initially coined for ECE donor combinations with
E = N, S, P or O, and comprising a central M–C bond,[1] the
expression pincer ligands has meanwhile been extended to any
combination of donor atoms from the periodic table.[2] The
most widely used oxo-pincer ligand is pyridine-2,6-dicarboxyl-
ate (pydic2–, see Scheme 1) and due to its high acidity pyr-
idine-2,6-dicarboxylic acid H2pydic is always deprotonated
upon binding to metals and the ligand pydic2– forms com-
plexes with almost any transition metal.[3–5] As expected from
the HSAB concept,[6,7] early d-block elements or lanthanides
are preferred for binding to pydic2– and many complexes have
found very interesting applications, e.g. vanadium complexes
as model compounds for amavadine,[8–10] or lanthanide com-
Scheme 1. Oxo-pincer ligands based on pyridine dicarboxylic acid
(H2pydic) or pyridine dimethanol (H2pydim).
In contrast to this, pyridine-2,6-dimethanol (H2pydim) or its
2,6-(methylene) substituted derivatives (H2RRЈpydim)
(Scheme 1) have been found to coordinate in its protonated or
deprotonated forms (H2pydim, Hpydim–, or pydim2–) de-
pending on the “hardness” of the metal and charge require-
ments. In complexes with the so called late transition metals
CoII,[18–23] NiII,[20,23,24] CuII,[20,22,23,25–34] ZnII,[20,32,33,35] or
PtII,[20,36] frequently the protonated forms were found
as in [M(H2pydim)2]2+ (M
=
Co, Ni, Cu, Zn),[21–23]
* Prof. Dr. A. Klein
Phone: +49-2214704006
E-Mail: axel.klein@uni-koeln.de
ORCID:
[Cu(H2pydim)(Hpydim)](ClO4),[26] [Cu2(η2,μ-Hpydim)2(η3-
H2pydim)2]2+,[23,27] and [MCl2(H2pydim)2] (M = Pd
or
[36]
[a] Institut für Anorganische Chemie
Department für Chemie, Universität zu Köln
Greinstraße 6
Pt [37]). In the central part on the d-block the partly deproton-
ated ligand Hpydim– is found in coordination polymers of
MnII,[39–41] tetranuclear [Mn2Ln2] (Ln = Dy, Gd) clusters,[42]
or complexes of ReV.[43,44] Examples for complexes
of early transition metals contain exclusively the fully depro-
50939 Köln, Germany
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/zaac.201800352 or from the au-
thor.
Z. Anorg. Allg. Chem. 0000, ᭿,0–0
1
© 0000 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
tonated ligand dianion pydim2–, as e.g. [(OR)2M(μ2-pydim)[(μ- UV/Vis absorption spectroscopy, electrochemistry (cyclic vol-
pydim)M(OR)2]2 (M = Ti, OR = OiPr, Oneop; Zr, OtBu),[45] in tammetry) and spectroelectrochemistry in combination with
[M(μ-pydim)(OR)3]2 (M/OR = Nb/OEt, Ta/Oneop),[45] in DFT calculations to probe for their electronic properties. Our
[Ti(RRЈpydim)2], [Ti(RRЈpydim)X2] (R = RЈ = Ph, H; X = Cl study thus connects scattered previous reports and deepens the
or OiPr),[46] [Ti(Cp*)(X)(pydim)], [Ti(Cp*)(LЈ)(pydim)]+ (Cp* understanding on the structures, reactivity, and spectroscopic
= pentamethylcyclopentadienide; X = Me, OH; LЈ = H2O, and electrochemical properties of these interesting complexes.
MeCN),[47] Na[VO2(pydim)],[48] [Ta(Cp*)(Me)(pydim)(X)]
(X = OTf, H2O),[49] [MoO2(pydim)].[50]
Results and Discussion
If the two substituents are not identical or were both part of
an asymmetric ring system (e.g. menthyl, see Scheme 1) chiral
ligands are obtained. Complexes of early transition metals con-
taining such chiral oxido pincer ligands have been used in
enantioselective transformations. E.g. the mononuclear tita-
nium complex [Ti(1-tBu2pydim)(OiPr)2] is able to catalyze the
asymmetric epoxidation of E-α-phenylcinnamyl alcohol (41%
ee) using tBuOOH.[51] Dinuclear V and Mo compounds, con-
taining the chiral menthyl-substituted derivative (menpydim)
shown in Scheme 1, are able to catalyse asymmetric
epoxidation of 1-hexene.[52] The cationic complexes
Syntheses, Analyses, and NMR Spectroscopy of the
Complexes
We prepared the dinuclear complexes [V2O3(L)2] (H2L =
H2pydim, H2pydip, H2pyphen) by reacting 1 equiv. ammonium
metavanadate with 1 equiv. protoligand (protonated ligand)
H2L in alcohol in good to excellent yields (route a in
Scheme 2, details in the Experimental Section). From EI-MS,
1H, and 51V NMR spectroscopy their dinuclear character is
unequivocally revealed. E.g. the splitting of the methylene,
[Zr(menpydim)(Bn)L]+ (Bn = Benzyl, L = OEt2 or BArF )
have been used for diastereoselective olefin insertion reac-
tions.[53]
1
3
methyl, and phenyl H NMR signals for all three compounds
reveals the diastereotopic character of these protons.
Alternative preparations for such dinuclear complexes have
been reported, e.g. [V2O3(menpydim)2] was prepared from
H2menpydim (Scheme 1) and [VO(OiPr)3] in CH2Cl2 solution
(Scheme 2, route b),[52] and [V2O3(L1)2] (H2L1 = 2,2Ј-dihy-
In this contribution we report on the synthesis of oxido va-
nadium(V) complexes with the pyridine-2,6-dimethanol li-
gands H2pydim, H2pydip, and H2pyphen depicted in
Scheme 2. Previous reports on VV complexes of the pyridine-
2,6-dimethanol ligand show that depending on the reaction
conditions the binuclear complex [V2O3(pydim)2],[52] the an-
droxyazobenzene) was prepared using [VO(acac)2] (acac–
=
acetylacetonate) with concomitant aerial oxidation from VIV to
VV (Scheme 2, route c).[54] Very recently, the complex
ionic mononuclear complex [VO2(pydim)]–,[48] and the poly-
[V2O3(L2)2] [H2L2
= 6,6Ј-(pyridine-2-ylmethylazanediyl)-
[48]
meric [HVO2(pydim)]x
can be formed. We thus varied in
bis(methylene)bis(2,4-di-tBu-phenol)] was synthesized in the
same way.[55] We tried the latter method also for our com-
plexes, however, the corresponding yields using method a
were largely superior. In contrast to this, the recently reported
reaction of H2pydim and NH4VO3 in water under acidic
our study the steric demand of the ligand, varied previously
reported synthesis methods, optimized them, added new meth-
ods and even found conditions allowing the interconversion of
different complex species including the unprecedented oxido
chlorido complexes [VOCl(L)]. In addition, we studied the dif-
ferent complex species in detail using 51V NMR spectroscopy,
conditions yielded
a
product described as polymeric
[HVO2(pydim)]x and the dinuclear complex was not ob-
served.[48]
The 51V shifts of δ = –513 ppm for [V2O3(pydim)2],
–539 ppm for [V2O3(pydip)2] and –566 ppm for
[V2O3(pyphen)2] (Table 1) put the three new complexes in a
line with the previously reported –533 ppm for
[V2O3(menpydim)2].[53] Generally, 51V shifts (51V; I = 7/2, nat.
abundance 99.75%) of VV compounds can vary over a huge
range from –1000 to +2600 ppm,[56] however vanadates(V)
usually show values ranging from –400 to –700 ppm. The di-
nuclear complexes lie in the same range as [VO4]3– (δ =
–530 ppm), which is in line with the expected high overall
shielding from the coordination of “hard” electronegative li-
gands (O or N donor functions).[56]
Compounds of the formulae M[VO2(L)] (M = K or Na;
H2L = H2pydim, H2pydip, H2pyphen) containing anionic mo-
nonuclear V complexes were obtained from reactions using
[VO(acac)2] as precursor, the protoligands H2L and the ad-
dition of the corresponding alkaline metal hydroxide (route d).
Furthermore, reacting the complexes [V2O3(L)2] with MOH in
MeOH (route e) gave the same products. When stirring the
salt-like compounds M[VO2(L)] in [D4]MeOH 51V NMR
Scheme 2. Preparation routes and conversion reactions of vanadyl(V)
complexes with ONO pincer ligands. a: H2L, (NH4)VO3, MeOH, re-
flux, 18 h; b: H2L, [VO(OiPr)3], CH2Cl2, room temperature, 2 h;[52]
c: H2L, [VO(acac)2], air, MeOH, room temperature, 6 h;[54] d: H2L,
[VO(acac)2], air, MeOH, room temperature, 12 h (compare refer-
ence[54]). e: [V2O3(L)2], 2MOH, MOH (M = alkaline metals), MeOH,
room temperature, 12 h; f: M[VO2(L)], [D4]MeOH (NMR experi-
ment); g: Na[VO2(L)], HCl, CH3CN/CH3OH (1:1), room temperature,
1 h; h:. [VOCl(L)], [D4]MeOH (NMR experiment).
Z. Anorg. Allg. Chem. 0000, 0–0
www.zaac.wiley-vch.de
2
© 0000 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
a)
Table 1. 51V NMR spectroscopic data /ppm of vanadium complexes
.
δ = 51V
δ = 51V
δ = 51V
b)
[V2O3(pydim)2]
[VO2(pydim)]–
–
–513
–511
–
[V2O3(pydip)2]
[VO2(pydip)]–
[VOCl(pydip)]
–564
–530
–435
[V2O3(pyphen)2]
[VO2(pyphen)]–
[VOCl(pyphen)]
–566
–528
–433
b)
a) Measured in CDCl3. [b] Measured in [D4]MeOH.
showed the slow conversion to the dinuclear complexes pected dinuclear complex entities and overall square-pyrami-
[V2O3(L)2] (route f).
dal coordination.[60] The arrangement around the bridging O2
The same behavior had been reported before for the above atom with V–O2–V angles of 117.1(3)° for the pydip complex
mentioned system [V2O3(L1)2] (L1 = 2,2Ј-dihydroxyazoben- and 129.5(6)° for the pyphen derivative revealing a syn-angu-
zene)[54] and for the reaction of [HVO2(pydim)]x with NaOH lar configuration.[61–64] Essential bond lengths show compar-
yielding the structurally characterized Na[VO2(pydim)]· able values to other syn-angular configured oxido-bridged
4H2O.[48]
complexes with similar ligand systems (details in Tables S1
Finally, treating solutions of the anionic complexes and S2, Supporting Information).[61–70]
[VO2(L)]– with gaseous HCl, allowed to isolate the novel neu-
When calculating the molecular structures using density
tral chlorido complexes [VOCl(L)] for L = pydip and pyphen functional methods (DFT), geometry optimization for
(route g). In situ NMR experiments gave evidence for the ini- [V2O3(pydip)2] in THF using the COSMO approximation gave
tial formation of the dinuclear complexes [V2O3(L)2] in line essentially three minima as defined by their bridging V–O–V
with the observations for the system [VO2(L1)]–.[54] Interest- angles at around 130, 155, and 180°, thus far larger than the
ingly, for the pydim complex the reaction with HCl failed to experimental value (Figure S8, Supporting Information) and
give the chlorido complex. Instead, as already reported by indicative for a rather flexible (floppy) V–O–V unit. For
Howard et al.,[48] the solution turned blue indicating the for- [V2O3(pyphen)2] only one but a rather broad minimum was
mation of VO2+ and the protonated ligand H3pydim+ was ob- found at a V–O–V angle of around 150° (Figure S8). Figure 1
1
served in H NMR (recrystallized from MeOH). The two new shows the two DFT-calculated structures with the minimum
chlorido complexes show markedly low-field shifted 51V reso- angle. For both complexes all calculated structures exhibit very
nances (Table 1) in line with the presence of the chlorido li- similar essential bond parameters around the V atoms (Table
gand causing lower overall shielding compared to O or N li- S3, Supporting Information), which are also in line with the
gands.[56] At the same time, these unprecedented oxido experimental data (Table S2, Supporting Information). The cal-
chlorido complexes [VOCl(L)] containing the tridentate li- culated O=V–O–V=O torsion angles are 74, 86, and 85°,
gands pydip2– and pyphen2– undergo slow transformation into respectively, for the pydip complex and 56° for the pyphen
the dinuclear complexes [V2O3(L)2] with a full conversion in complex. Reported values for both V–O–V angles and
approximately one day. We assume that the remaining open O=V···V=O torsion angles vary largely in crystal structures of
coordination site in these pentacoordinate complexes allows related complexes and were probably largely governed by
them to undergo Cl– Ǟ OH– ligand exchange or Cl– Ǟ OH2 crystal packing and with them also the basal N–V–Obridge
hydrolysis with subsequent condensation to form the dinuclear angles. E.g. V–O–V angles of reported complexes range from
oxido-bridged dimers. Our assumption is supported by reports 107 to 180°,[61,62,64] in line with our DFT-optimized structures
on VV [VOCl(L)] complexes with tetradentate bisphenolate- having several and/or broad minimum V–O–V angles.
diamine ligands,[55,57] or VIV complexes [VOCl(L3)(L4)] con-
taining two bidentate ligands (L3 = curcumine; L4 = α-di-
imines),[58] or the VIII complex [VOCl(L5)]+ containing the
Absorption Spectroscopy
tetradentate neutral N,NЈ-dimethyl-2,11-diaza-[3.3](2,6)pyrid-
inophane ligand, L5,[59] which are all stable in this respect,
very probably due to the hexacoordinate character.
UV/Vis absorption spectra of the three protoligands
H2pydim, H2pydip, and H2pyphen show intense absorption
peaks in the UV region which are assigned to π–π* transitions
of the pyridine system. These bands are slightly red-shifted for
the vanadium complexes and some weak additional absorp-
tions were observed at the edge to the visible region 300–
500 nm (Figure 2 and Table 2), explaining the yellow color of
the complexes. These absorptions can be assigned to li-
gand(oxido)-to-metal(VV) LMCT transitions.[63,67,71,72]
Crystal and Molecular Structures from Single Crystal XRD
and DFT Calculations
From the protoligands H2pydip and H2pyphen and from the
corresponding dinuclear complexes [V2O3(pydip)2] and
[V2O3(pyphen)2]·2CHCl3 single crystals were obtained from
saturated solutions. Unfortunately, the quality of the data is
very low in all cases with very high Rint values, very low good-
ness-of-fit and poor R1 and wR2 values which are probably due
Cyclic Voltammetry
The electrochemical behavior of the protoligands H2L and
to low quality of the crystals (see Supporting Information). the vanadyl(V) complexes was studied by cyclic voltammetry
Nevertheless, the obtained structures were in line with the ex- in CH3CN or CH2Cl2 solutions, respectively, with nBu4NPF6
Z. Anorg. Allg. Chem. 0000, 0–0
www.zaac.wiley-vch.de
3
© 0000 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
Figure 1. DFT-optimized molecular structures of [V2O3(pydip)2] (top left,) and [V2O3(pyphen)2] (top right) at the minimum angle of 130° for
the pydip complex and 150° for the pyphen derivative. Schematic drawings of the edge-sharing square pyramids (bottom).
recorded for corresponding [V2O3(L)2] complexes from
roughly 0 V to –1.5 V (vs. ferrocene/ferrocenium).[73] This
points to a non-extensive π-backbonding of the pyridine-2,6-
dimethanol ligands to facilitate the VV reduction. Further
irreversible reduction waves correspond to reduction of the li-
gands, which are shifted to more positive potentials by about
0.3 V compared with the protoligands H2L.
In contrast to the increasing redox potentials of the dinuclear
complexes [V2O3(L)2] from pydim to pyphen, the redox poten-
tials of the mononuclear complexes [VO2(L)]– and [VOCl(L)]
show cathodic shifting from the pyphen to the pydim deriva-
tives. As expected, the potentials of the anionic dioxidovanadi-
um(V) complexes [VO2(L)]– are far lower compared with
those of the neutral oxido chlorido [VOCl(L)] derivatives, they
are strongly depending on the ligand and the reduction pro-
cesses occur irreversible, in line with reports on related com-
plexes.[73] Very probably the radical dianions [VO2(L)]·2– un-
dergo rapid decomposition including protonation and conden-
sation reactions. The reduction of the unprecedented neutral
oxido chlorido complexes [VOCl(L)] occurs reversibly or par-
tially reversible (Table 3).
Figure 2. UV/Vis absorption spectra of [VOCl(pyphen)],
[V2O3(pyphen)2], K[VO2(pyphen)], and H2pyphen in CH2Cl2.
as the supporting electrolyte. Table 3 summarizes the redox
potentials (referenced to the ferrocene/ferrocenium redox cou-
ple). The ligands exhibit irreversible reductions beyond (lower
than) –3 V. The dinuclear complexes [V2O3(L)2] show a first
reversible reduction wave at around –1 V. For the pydim and
pydip derivatives second reversible reduction waves were
found at around –2 V (plots in the Supporting Information).
These reductions are one-electron steps as revealed by parallel
EPR and UV/Vis/NIR Spectroelectrochemistry and DFT
Calculations
The dinuclear complexes [V2O3(L)2] (H2L = H2pydim,
measurement of weighted ferrocene samples and we assign H2pydip, H2pyphen) were reduced in THF solution using co-
them to vanadium-based redox couples [VV(μ-O)VV]/[VV(μ- baltocene and X-band EPR spectra were recorded (Figure 3).
O)VIV] and [VV(μ-O)VIV]/[VIV(μ-O)VIV]. The potentials are For comparison the monomeric VIV complex [VO(acac)2]
solvent sensitive and lie rather at the cathodic end of the range (acac– = acetylacetonate) was studied under the same condi-
Z. Anorg. Allg. Chem. 0000, 0–0
www.zaac.wiley-vch.de
4
© 0000 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
a)
Table 2. UV/Vis absorption maxima of protoligands and VV complexes
.
Compound
λ1 (ε)
λ2 (ε)
λ3 (ε)
λ4 (ε)
Solvent
H2pydim
208 (22.0)
212 (21.2)
218 (20.6)
208 (19.1)
206 (25.3)
223 (22.3)
231 (18.3)
204 (25.4)
220 (20.3)
225 (23.8)
234 (27.5)
264 (6.3)
272 (34.0)
265 (8.3)
261 (12.9)
270 (9.9)
269 (10.1)
261 (11.8)
265 (13.6)
277 (12.5)
274 (19.1)
280 (17.3)
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
[V2O3(pydim)2]
K[VO2(pydim)]
H2pydip
[V2O3(pydip)2]
K[VO2(pydip)]
[VOCl(pydip)]
H2pyphen
[V2O3(pyphen)2]
K[VO2(pyphen)]
[VOCl(pyphen)]
321 (11.2)
284 (2.5)
404 (1.9)
307 (7.8)
280 (5.7)
405 (0.8)
388(2.2)
355(2.4)
320 (4.1)
305 (3.2)
323 (7.1)
383 (0.5)
389 (0.4)
442 (0.4)
a) Wavelengths λ in nm (extinction coefficients ε in 1000 m–1·cm–1).
a)
Table 3. Selected redox potentials of protoligands and VV complexes
.
Compound
E1 /V
E2 /V
E3 /V
Solvent
H2pydim
H2pydip
H2pyphen
–
–
–
–
–
–
–3.30 (irr)
–3.21 (irr)
–3.13 (irr)
–2.96 (irr)
–2.98 (irr)
–2.94 (irr)
–
–3.16 (irr)
–
–2.01 (irr)
–2.33 (irr)
–
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH2Cl2
CH3CN
CH2Cl2
CH3CN
CH2Cl2
CH2Cl2
CH3CN
CH2Cl2
[V2O3(pydim)2]
[V2O3(pydip)2]
[V2O3(pyphen)2]
[V2O3(pyphen)2]
Na[VO2(pydim)]
Na[VO2(pydip)]
Na[VO2(pyphen)]
Na[VO2(pyphen)]
[VOCl(pydip)]
[VOCl(pyphen)]
[VOCl(pyphen)]
–0.79 (rev)
–0.92 (rev)
–1.15 (rev)
–0.90 (rev)
–1.90 (irr)
–1.35 (irr)
–0.84 (prev)
–1.10 (irr)
–0.73 (rev)
–0.54 (rev)
–0.66 (prev)
–1.98 (rev)
–2.14 (rev)
–
–
–2.91 (irr)
–2.45 (irr)
–1.47 (prev)
–1.88 (irr)
–2.15 (rev)
–2.51 (irr)
–2.45 (irr)
a) From measurements in 0.1 m solvent/nBu4NPF6 solutions; potentials were referenced to the ferrocenium/ferrocene redox couple. Scan rate =
100 mV·s–1, rev = reversible, prev = partially reversible, irr = irreversible.
tions. Assuming the radical anionic complexes [V2O3(L)2]·– with tridentate ONO2– ligands based on hydroxy phenoxy hy-
after one-electron reduction the pydim and pydip derivative drazides,[64,78,80,81] salenes,[62] carboxy-salicylaldiminates,[82]
and [VO(acac)]2 show eight line spectra with isotropic g val- or azophenolates,[83,84] and also the [OVIV(μ-Ooxido)(μ-
ues below 2 and a 51V hyperfine splitting (HFS) a(V) of about
90 G (Table 4). This is in line with the nuclear spin of I = 7/2 (NЈNONNЈ)3–
of the 51V isotope (nat. abundance 99.75%) and means that on methyl)aminomethyl)-phenolates,[85,86]
O
phen)VVO]·2+
complexes
2,6-bis(phenoxymethyl-N,N-dimethylamino-
or complexes
containing
pentadentate
the timescale of the EPR experiment the unpaired electron is [(L)OVIV(µ-O)VVO(LO]·3+ complexes containing neutral
localized on one vanadium atom representing a VIV d1 spin S NЈNNЈ ligands of the 2,6-bis[benzimidazol-2Ј-yl]pyridine
= ½ system. In contrast to this, [V2O3(pyphen)2]·– affords a 15 or -amine type,[87] tris(2-pyridylmethyl)amine,[88] or 1,4,7-tri-
line spectrum with a similar g value but a reduced a(V) by azacyclononane derivatives.[77]
approximately 50%. This means that the unpaired electron in
The different behavior of the complexes stems from their
this system is delocalized over both vanadium atoms. Accord- molecular structures. For delocalization of the unpaired spin
ing to the classification for mixed-valent systems of Robin and across both vanadium atoms an overlapping of the singly occu-
Day,[74] the dinuclear pydim and pydip complexes represent pied dxy orbitals at the central VVI atoms with the px orbital
class I complexes with a localized electron at one atom, while of the oxido-bridge is necessary. The overlap depends on the
the pyphen derivative represents either a class III complex with arrangement of the V–O–V moiety. Perfect overlap and class
a complete delocalization over both atoms or class II with eas- III delocalized systems are expected for a linear arrangement
ily accessible electron transfer between the two atoms of dif- (V–O–V) and a torsion angle (O=V···V=O) of 180°.[64,77]
ferent oxidation number.
Bending in the xy and yz planes also allows the possibilities of
The EPR parameters for the pydim and pydip derivative are spin-delocalization (class III and class II) but any torsion
similar to those of related mononuclear O=VIV com- would hamper delocalization and lead to localized spins. At
plexes[59,61,63,75–78] and comparable dinuclear compounds with the same time, it is clear that correlation of molecular struc-
class I valence-isolated [OVIV(μ-O)VVO] units.[61,62,68,77,79] tural data of the parent [OVV(μ-O)VVO] complexes from sin-
Similar valence delocalized (class II or III) behavior gle crystal XRD with the EPR behavior of the one-electron
as found for [V2O3(pyphen)2]·– has been previously reported reduced [OVIV(μ-O)VVO]·– radicals cannot be straightforward
for the radical anionic complexes [(L)OVIV(µ-O)VVO(LO]·– since in the solid state packing forces possibly lead to defor-
Z. Anorg. Allg. Chem. 0000, 0–0
www.zaac.wiley-vch.de
5
© 0000 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
mation of the OV(μ-O)VO core compared with structures in
solution and one-electron reduction might lead to even larger
deformations. This has been nicely worked out on the mixed-
valence complexes [(HL)OVIV(μ-O)VVO(HL)]·– with ONO2–
= hydroxybenzoylhydrazones of acetylacetone (HL1) and ben-
zoylacetone (HL2) respectively, which showed valence delo-
calization at room temperature and localization at 77 K in
glassy frozen solution. DFT calculations of the parent [OVV(μ-
O)VVO] complexes in solution gave similar structural param-
eters as found from single crystal XRD but the bond angles
for the singly reduced [OVIV(μ-O)VVO]·– radicals were calcu-
lated to 177.5 and 180° respectively, thus markedly different
from the parent state for the complex based on acetylacetone
(HL1) and identical for the benzoylacetone (HL2) deriva-
tive.[64]
DFT calculated optimized structures for the reduced com-
plexes [V2O3(L)2]·– (H2L = H2pydip, H2pyphen) in THF solu-
tion (details in the Supporting Information) gave also large
V–O–V angles and Table 5 clearly shows that only the DFT
optimized structure of the [V2O3(L)2]·– radical anions allows
correlation with the EPR behavior.
Upon chemical reduction of [V2O3(pyphen)2] in THF solu-
tion by titration using solutions of cobaltocene in THF, the
intense UV band at 275 nm more than doubles in intensity and
undergoes a slight blue-shift (Figure 4) in line with the re-
duction occurring at the central V atom shifting this π–π* ab-
sorption only slightly in energy but making it more allowed.
Instead of the two assumed LMCT absorptions at 320 and
380 nm in the spectrum of the reduced species only one blue-
shifted band at 355 nm is observed in line with a VVǞVIV
reduction.
Figure 3. X-band EPR spectra of [VO(acac)2]2 and the one-electron
reduced dinuclear complexes [V2O3(L)2]•– (H2L = H2pydim, H2pydip,
H2pyphen) in THF.
The two new weak and broad absorption band appearing in
the visible region with maxima at 695 and 520 nm might be
Table 4. EPR data of reduced dinuclear complexes [V2O3(L)2]•– a)
.
Compound
giso
a(V) /G
a(V) /cm–1
Lines
assigned to the B2Ǟ2E and B2Ǟ2B1 ligand field transitions
assuming a distorted octahedral arrangement of the d1 VIV
atom.[89] The third absorption corresponding to the expected
2B2Ǟ2A1 can be found as a shoulder at 400 nm or lies below
the LMCT bands. The absorption energies reported for the LF
transitions of VO(SO4) in aqueous solution were 770, 625, and
333 nm, respectively,[89] underlining the higher ligand strength
2
2
[V2O3(pydim)2]·–
[V2O3(pydip)2]·–
1.980
1.989
88
97
49
81.4ϫ10–4
90.1ϫ10–4
45.5ϫ10–4
8
8
15
[V2O3(pyphen)2]·– 1.988
a) Generated through in situ reduction of [V2O3(L)2] in THF using
cobaltocene. Hyperfine coupling a, isotropic g values, and number of
lines.
Table 5. Selected structural data of dinuclear parent [OVV(μ-O)VVO] vanadium complexes from single crystal XRD – DFT calculated structural
a)
data of solvated molecules – and EPR behavior of their monoreduced [OVIV(μ-O)VVO]·– radical complexes.
a)
b)
Compound
Bond angle V–O– Torsion angle
Distance V···V /Å Overall OVOVO
EPR lines
Reference
V /°
O=V···V=O /°
structure
[V2O3(pydip)2] (XRD)
[V2O3(pydip)2] (DFT)
[V2O3(pydip)2]·– (DFT)
[V2O3(pyphen)2] (XRD)
[V2O3(pyphen)2] (DFT)
[V2O3(pyphen)2]·– (DFT)
117.1(1)
137.7
128.2
129.5(5)
151.0
144.9
81.4(4)
75.5
73.2
48.7(6)
57.6
53.5
3.076(2)
3.34
3.30
3.247(4)
3.46
3.48
syn-angular
syn-angular
syn-angular
syn-angular
syn-angular
syn-angular
this work
this work
this work
this work
this work
this work
8
15
c)
[V2O3(HL1)2] (XRD)
115.0(2)
175.7
180
101.6(3)
–
3.027(2)
–
anti-angular
anti-angular
anti-linear
anti-linear
[64]
[64]
[64]
[64]
[V2O3(HL1)2]·– d) (DFT)
[V2O3(HL2)2] c) (XRD)
[V2O3(HL2)2]·– d) (DFT)
15
15
e)
e)
180.00(3)
3.572(1)
e)
e)
180
–
–
a) Structures of parent [V2O3(L)2] and reduced [V2O3(L)2]·– complexes were optimized (more data in the Supporting Information). b) From
one-electron reduced complexes [V2O3(L)2]·–. c) (HL)2– = hydroxybenzoylhydrazones of acetylacetone (HL1) and benzoylacetone (HL2). d)
Geometry optimization on B3LYP/6-311++G** level using the UB3LYP functional.[64] e) Not provided.
Z. Anorg. Allg. Chem. 0000, 0–0
www.zaac.wiley-vch.de
6
© 0000 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
only measure the full spectrum of the mixed-valent complex
[V2O3(pyphen)2]·– but also embark on detailed quantum chem-
ical calculations.
Conclusions
The reaction of ammonium metavanadate NH4VO3 with the
protoligands H2L of three oxido-pincer ligands 2,6-(HOCRRЈ)
2(pyridine) based on 2,6-pyridinedimethanol [R = RЈ = H
(H2pydim); R = RЈ = Me (H2pydip); R = RЈ = Ph (H2pyphen)]
gave the dinuclear complexes [(L)OV(μ-O)VO(L)] in 54 to
91% yield. Mononuclear anionic species [VO2(L)]–, which
were isolated as alkaline metal salts were obtained from reac-
tions of [VO(acac)2] (acac– = acetylacetonate) with H2L under
basic conditions in very good yields. Addition of anhydrous
HCl to these compounds allowed to isolate the unprecedented
oxido chlorido complexes [VOCl(L)] for pydip and pyphen,
whereas the same reaction for pydim showed the formation of
VO2+ and the protonated ligand H3pydim+ was isolated. This
is remarkable, since all isolated species including the oxido
chloride complexes contain exclusively the completely depro-
Figure 4. UV/Vis absorption spectra of [V2O3(pyphen)2] during re-
duction using cobaltocene in THF. Note that the spectra were
recorded for the visible region (insert) using a concentrated solution
(2ϫ10–2 m), while the full scale spectra were recorded on a dilute
sample (5ϫ10–4 m). This explains the slight incongruence of the two
plots: while for the insert an isosbestic point at 440 nm is observed, in
the spectra for the lower concentration this feature is missing.
of the pyridine-2,6-dimethanol ligand. The most interesting tonated ligands L2–. In situ NMR experiments for the reaction
feature is the band growing upon reduction at energies lower of [VO(acac)2] with H2L gave evidence for the initial forma-
than 1000 nm.
tion of the dinuclear complexes [V2O3(L)2]. At the same time,
Due to spectrometer limitations we were not able to record the oxido chlorido complexes [VOCl(L)] undergo slow trans-
the maximum of this band but we can assign this to an interval- formation into the dinuclear complexes [V2O3(L)2] with a full
ence charge transfer (IVCT) band of the mixed valent conversion in approximately one day. We assume that the re-
[OVIV(μ-O)VVO]·– system in line with further reported VIV(μ- maining open coordination site in these pentacoordinate
O)VV complexes.[64,68,77–88] E.g., the complex [V2O3(L)2] con- [VOCl(L)] complexes allows them to undergo Cl– Ǟ OH– li-
taining a ONO2– Schiff base ligand condensed from anthra- gand exchange or Cl– Ǟ OH2 hydrolysis with subsequent con-
nilhydrazide and 2-hydroxy acetophenone shows after electro- densation to form the dinuclear oxido-bridged dimers. All
1
lytic reduction an absorption band at 675 nm, which was as- these interconversions can be easily studied using H and 51V
2
signed to the ligand field B2Ǟ2E transition and an additional NMR and UV/Vis absorption spectroscopy. The molecular
absorption in the NIR at 979 nm, which was assigned to an structures of the dinuclear complexes of [V2O3(pydip)2] and
IVCT transition.[81] The corresponding IVCT band of the com- [V2O3(pyphen)2] were studied both from single crystal XRD
plex [V2O3(L6)2]·+ (L6 = 1,4,7-triazacyclononane-N-acetate) and DFT geometry optimizations. The calculations show sev-
was observed at 1070 nm, while for [V2O3(L7)2]·+ (L7 = N-(2- eral possible minima for both complexes with characteristic
hydroxybenzyl)-1,4,7-cyclononane) a long-wavelength absorp- V–O–V angles markedly higher (130–180°) than the experi-
tion at 710 nm was assigned to the low-energy LF transition mentally found ones (ca. 117° for pydip and ca. 130° for
2B2Ǟ2E and an IVCT band is missing.[77]
pyphen) but with the essential bond parameters around the
Importantly, the first of these two complexes shows a 15 square pyramidal configured V atoms being very similar. This
line EPR spectrum corresponding to a delocalized VIV/VV sys- is in line with a very floppy character of the V–O–V group in
tem, while the latter displays the 8 line spectrum for a localized such complexes in line with values ranging from 107 to 180°
case. For the two complexes with pydim and pydip also no reported for similar complexes. Cyclic voltammetry of the mo-
IVCT bands were observed in line with the localized character nonuclear [VOCl(L)] and dinuclear [V2O3(L)2] complexes re-
of the [OVIV(μ-O)VVO]·– complexes. The long-wavelength ab- vealed reversible VV/VIV redox couples, while the reduced
sorptions are found at 660 nm for pydip and at 650 nm for [VO2(L)]·2– undergo rapid decomposition, resulting in irrevers-
pydim and were assigned to the low-energy LF transitions. The ible behavior. The mixed-valent VIV/VV species [V2O3(L)2]·–,
earlier mentioned mixed-valent complexes [V2O3(HL1)2]·– and generated through one-electron reduction from the neutral par-
[V2O3(HL2)2]·– with (HL)2– representing the deprotonated hy- ent complexes were characterized by EPR and UV/Vis spectro-
droxybenzoylhydrazones of acetylacetone (HL1) and benzo- electrochemistry revealing a delocalized system (15 line EPR,
ylacetone (HL2) display long-wavelength absorption maxima intervalence charge transfer (IVCT) band) for the bulky
at 828 and 838 nm, respectively, and TD-DFT calculations pyphen ligand but localized radicals in case of the pydim and
show that essentially three IVCT transitions are responsible for pydip derivatives (8 line EPR, no IVCT). DFT calculated
the absorptions in the range 600–1000 nm, probably obscuring structures of the three derivatives [V2O3(L)2]·– show an
the ligand field transitions.[64] So, in future work we will not V–O–V arrangement for [V2O3(pyphen)2]·– of about 145° ide-
Z. Anorg. Allg. Chem. 0000, 0–0
www.zaac.wiley-vch.de
7
© 0000 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
ally suited for delocalization, while for [V2O3(pydip)2]·– an an-
gle of about 128° was found.
ether and MeCN) were dried using a MBRAUN MB SPS-800 solvent
purification system.
Synthesis of 2,6-Bis(1-hydroxy-1-methyl-ethyl)pyridine (H2pydip):
H2pydip was synthesized using a modified literature procedure.[54] An
amount of a 3 m solution of MeMgBr (16.5 mL, 49.4 mmol) was added
dropwise via syringe to an ice-cold solution of dimethyl(pyridine-2,6-
dicarboxylate) (1.93 g, 9.88 mmol) in 250 mL THF. The clear dark red
solution has been warmed to room-temperature and after stirring for
20 h, the yellow suspension was quenched with an aqueous saturated
NaCl solution. After separation of the organic and aqueous phases, the
latter was extracted with CH2Cl2 (3ϫ50 mL). The collected organic
phases were dried with MgSO4 and finally the solvent was evaporated
to leave yellow oil. This was dissolved in diethyl ether and HCl gas
was passed thorough. After a few seconds a yellow solid precipitated.
The precipitate was washed with diethyl ether. NaOH (10 mL, 1 m)
was added to the solid and the mixture was stirred for 5 h at room
temperature. Saturated NaCl solution was added and after extraction
with CH2Cl2 and drying over MgSO4 the solvent was evaporated yield-
ing a yellow oily product. The product was washed with n-hexane
several times and finally recrystallized from diethyl ether. Yield:
1.23 mg, (6.28 mmol, 64%) of a light yellow solid. C11H17NO2 (MW
= 195.26 g·mol–1): calcd. C 67.66, H 8.78, N 7.17%; found: C 67.18,
Experimental Section
Instrumentation: Elemental analysis was obtained with a HEKAtech
CHNS EuroEA 3000 Analyzer. NMR spectra were recorded with a
Bruker Avance II 300 MHz spectrometer (1H: 300.13 MHz, 51V:
29.9 MHz) equipped with a BBO ATM 5 mm probe head with z-gradi-
ent (1H/19F X 2H) using a triple resonance 1H,19F,BB inverse probe
1
1
head. The unambiguous assignment of the H was obtained from H
1
NOESY and H COSY experiments. All 2D NMR experiments were
performed using standard pulse sequences from the Bruker pulse pro-
gram library. Chemical shifts were relative to TMS (1H and 13C) or
VOCl3 (51V). EI-MS spectra (positive) were measured with a Finnigan
MAT 900 S instrument. UV/Vis/NIR absorption spectra were measured
with Varian Cary50 Scan or Shimadzu UV-3600 photo spectrometers.
EPR spectra were recorded in the X-band with a Bruker System
ELEXSYS 500E equipped with a Bruker Variable Temperature Unit
ER 4131VT (500 to 100 K or an Oxford Instruments helium-cryostat
(300 to 4 K); the g values were calibrated using a dpph sample. Elec-
trochemical experiments were carried out in 0.1 m nBu4NPF6 solutions
using a three-electrode configuration (glassy carbon working electrode,
Pt counter electrode, Ag/AgCl pseudo reference) and an Autolab
PGSTAT30 potentiostat and function generator. The ferrocene/ferro-
cenium couple (FeCp2/FeCp2+) served as internal reference. UV/Vis/
NIR spectroelectrochemical measurements were performed with an op-
tically transparent thin-layer electrochemical (OTTLE) cell.[90,91]
1
H 9.21, N 7.26%. H NMR (300.13 MHz, CDCl3), δ = 7.73 (t, 1 H,
4py), 7.33 (d, 2 H, 3,5py), 1.53 (s, 12 H, CH3). 1H NMR
(300.13 MHz, CD3OD): δ = 7.76 (t, 1 H, 4py), 7.45 (d, 2 H, 3,5py),
1.54 (s, 12 H, CH3). UV/Vis (CH3CN): λmax = 208, 261 nm.
Synthesis
of
2,6-Bis(1-hydroxy-1,1-diphenylmethyl)pyridine
(H2pyphen): H2pyphen was synthesized using a modified literature
procedure.[106,107] Magnesium turnings (1 g, 40 mmol) were stirred in
50 mL THF and bromobenzene (4.1 mL, 38.5 mmol), dissolved in
50 mL THF, was added dropwise. After addition, the reaction was
heated under reflux for 30 min, then cooled down to room temperature.
While the ice-cold solution was stirring, a suspension of 1.5 g
(7.7 mmol) dimethyl(pyridine-2,6-dicarboxylate) in 20 mL THF was
added slowly and the mixture was stirred for 6 h at room temperature.
After quenching with 50 mL of water, the solution was filtered and
then extracted three times using CH2Cl2. The organic phase was dried
with MgSO4 and the solvent was evaporated leaving a red-brownish
oil, which was dissolved in acetone. Overnight colorless needles crys-
tallized at 4 °C. Yield: 2 g (2.33 mmol, 58%) of a colorless solid.
C31H25NO2 (MW = 443.19 g·mol–1): calcd. C 83.95, H 5.68, N 3.16%;
Single Crystal Structure Determination: The measurements were
performed at 293(2) K using graphite-monochromatized Mo-Ka radia-
tion (λ = 0.71073 Å) on IPDS II (STOE and Cie.). The structures were
solved by direct methods using SIR 2014[92] and refined by full-matrix
least-squares techniques against F2 with SHELXL-2018/3[93] within
WinGX-2014.[94,95] The numerical absorption corrections (X-RED
V1.22; Stoe & Cie, 2001) were performed after optimizing the crystal
shapes using X-SHAPE V1.06 (Stoe & Cie, 1999).[96,97] The non-
hydrogen atoms were refined with anisotropic displacement param-
eters. Hydrogen atoms were included by using appropriate riding mod-
els. Details are provided in Tables S1 and S2 (Supporting Information).
Crystallographic data (excluding structure factors) for the structures in
this paper have been deposited with the Cambridge Crystallographic
Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK.
Copies of the data can be obtained free of charge on quoting the de-
pository numbers CCDC-1860509 (H2pydip), CCDC-1860510
(H2pyphen·acetone), CCDC-1860511 ([V2O3(pydip)2]), and CCDC-
1860512 ([V2O3(pyphen)2]·2CHCl3) (Fax: +44-1223-336-033; E-Mail:
deposit@ccdc.cam.ac.uk, http://www.ccdc.cam.ac.uk)
1
found: C 82.81, H 5.63, N 3.12%. H NMR (300.13 MHz, CD2Cl2):
δ = 7.62 (t, 1 H, 4py), 7.09 (d, 2 H, 3,5py), 7.21–7.35 (m, 20 H, Ph).
1H NMR (300.13 MHz, CDCl3): δ = 7.62 (t, 1 H, 4py), 7.36–7.09 (m,
22 H, Ph, 3,5Py). 1H NMR (300.13 MHz, CD3OD): δ = 7.65 (t, 1
H, 4py), 7.27–7.14 (m, 22 H, Ph, 3,5py). UV/Vis (CH3CN): λmax
=
261 nm.
Synthesis of the Dinuclear Complexes [V2O3(L)2] (H2L = H2pydim,
H2pydip, H2pyphen) – General Method. The protoligand H2L
(1 equiv.) and 1.1 equiv. of ammonium metavanadate were suspended
in methanol and heated under reflux for 18 h. In the case of [V2O3(py-
dim)2] and [V2O3(pydip)2] the resulting reaction mixture was filtered
at elevated temperatures and the clear yellow- or orange-colored fil-
trate was evaporated to dryness. For [V2O3(pydim)2] the resulting ma-
terial was carefully washed with water and for [V2O3(pydip)2] the ma-
terial was recrystallized from CH2Cl2 at 4 °C. The complex
[V2O3(pyphen)2] precipitated as a yellow solid from the reaction mix-
ture. The microcrystalline yellow brownish solid was dissolved in
CHCl3, filtered and the yellow complex crystallized at 4 °C.
Quantum Chemical DFT Calculations: Ground state electronic
structure calculations on the complexes were done on the base of den-
sity-functional theory (DFT) methods using the TURBOMOLE[98]
program package and TMoleX 4.2 user interface.[99] For relaxed geom-
etry optimization the structures of the uncharged complexes as well as
the radical anionic species and scanning of the V–O–V angle the struc-
tures were calculated at def-SV(P)[100]/B3LYP level.[101–103] All calcu-
lations were done using a Conductor-like Screening Model (COSMO)
for solvent interactions implemented in TURBOMOLE.[104,105]
Materials: Commercially available reagents (solvents and the
H2pydim ligand) from Fluka, Sigma–Aldrich, or Acros were used
[V2O3(pydim)2]: Yield: 66 mg (0.13 mmol, 77%) of a dark-green so-
without further purification. Solvents (CH2Cl2, THF, toluene, diethyl lid. C14H14N2O7V2 (MW = 424.15 g·mol–1): calcd. C 39.64, H 3.33, N
Z. Anorg. Allg. Chem. 0000, 0–0
www.zaac.wiley-vch.de
8
© 0000 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
1
6.60%; found: C 39.50, H 3.90, N 6.29%. H NMR (CD3OD, ppm):
δ = 8.11 (t, 2 H, 2 H, 4py), 7.53 (d, 4 H, 3,5py), 6.08 (d, 4 H, CH2),
5.74 (d, 4 H, CH2). 51V NMR (29.9 MHz, CD3OD): δ = –513. EI-
MS: m/z = 425 [V2O3(pydim)+H]+. UV/Vis (CH3CN): λmax = 202,
272, 321 nm.
CD3OD): δ = 7.96 (t, 1 H, 4py), 7.27–7.14 (m, 22 H, 3,5py, Ph). 51V
1
NMR (29.9 MHz): δ = –534. H NMR (300 MHz, CDCl3): δ = 7.77
(t, 1 H, 4py), 7.25–6.93 (m, 22 H, 3,5py, Ph). 51V NMR (29.9 MHz,
CDCl3): δ = –428. UV/Vis (CH2Cl2): λmax = 225, 274, 314 nm.
Synthesis of M[VO2(L)] from the Dinuclear Complexes
[V2O3(L)2] – General Method. Methanol solutions of the dinuclear
complexes [V2O3(L)2] were stirred together with two equivalents of
alkaline metal hydroxide overnight at room temperature. After this the
solvent was removed under reduced pressure and the resulting brown
solids were washed with water. Yields were 66% for K[VO2(pydim)],
63% for Na[VO2(pydip)] and 78% for K[VO2(pyphen)] and thus gen-
erally lower than those found from the synthesis starting with
[VO(acac)2].
[V2O3(pydip)2]: Yield: 308 mg, (0.57 mmol, 54%) of a green solid.
C22H30N2O7V2 (MW = 536.37 g·mol–1): calcd. C 49.26, H 5.64, N
5.22%; found: C 48.96, H 5.43, N 5.20%. 1H NMR (300 MHz,
CD3OD): δ = 8.15 (t, 2 H, 4py), 7.51 (d, 4 H, 3,5py), 1.82 (s, 12 H,
CH3), 1.63 (s, 12 H, CH3). 51V NMR (29.9 MHz, CD3OD): δ =
1
–539 ppm. H NMR (300 MHz, CDCl3): δ = 7.91 (t, 2 H, 4py), 7.17
(d, 4 H, 3,5py), 1.86 (s, 12 H, CH3), 1.61 (s, 12 H, CH3). 51V NMR
(29.9 MHz, CDCl3):
δ
=
–564 ppm. EI-MS: m/z
=
537
[V2O3(pydip)2)+H]+, 278 [VO2(pydip)+2H]+, 262 [VO(pydip)+2H]+.
Synthesis of the Neutral Mononuclear Complexes [VOCl(L)]
(H2L = H2pydip, H2pyphen) – General Procedure: The compounds
Na[VO2(L)] were dissolved in a mixture of CH3CN and CH3OH (1:1)
and anhydrous hydrochloric acid gas was passed through the solution
for 1 h while stirring. The color changed from brown to orange and
red. The complexes [VOCl(pydip)] and [VOCl(pyphen)] precipitated
slowly from these solutions.
UV/Vis (CH3CN): λmax = 206, 270, 405 nm.
[V2O3(pyphen)2]: Yield: 433 mg, (0.42 mmol, 91%) of a yellow solid.
C62H46N2O7V2 (MW = 1032.92 g·mol–1): calcd. C 71.60, H 4.93, N
2.71%; found: C 72.09, H 4.49, N 2.61%. 1H NMR (300 MHz,
CDCl3): δ = 7.91 (t, 2 H, 4py), 7.4 (d, 4 H, 3,5py), 7.21–7.35 (m, 40
H, Ph). 51V NMR (29.9 MHz, CDCl3): δ = –433 ppm. EI-MS: m/z =
1033 [V2O3(pyphen)2+H]+. UV/Vis (CH2Cl2): λmax = 231, 277, 315,
325 nm.
[VOCl(pydip)]: Yield: 56 mg (0,19 mmol, 59%) of a yellow solid.
C11H15ClNO3V (MW = 295.64 g·mol–1): calcd. C 44.69, H 5.11, N
4.74%; found: C 44.66, H 5.18, N 4.78%. 1H NMR (300 MHz,
CD3OD): δ = 8.60 (t, 1 H, 4py), 8.06 (d, 2 H, 3,5py), 1.69 (s, 12 H,
CH3). 51V NMR (29.9 MHz, CD3OD): δ = –460. 1H NMR (300 MHz,
CDCl3): δ = 8.05 (t, 1 H, 4py), 7.25 (d, 2 H, 3,5py), 1.86 (s, 12 H,
CH3). 51V NMR (29.9 MHz, CDCl3): δ = –435. EI-MS: m/z = 262
[VO(pydip)+2H]+. UV/Vis (CH3CN): λmax = 261, 295, 355 nm.
Synthesis of the Compounds M[VO2(L)] (M = Alkaline Metal; H2L
= H2pydim, H2pydip, H2pyphen) – General Method: Following a
published method,[54] the protoligands H2L (1 equiv.) were suspended
in 30 mL of methanol and two equivalents of alkaline metal hydroxide
were added. The resulting solution was added to 10 mL of a methanol
solution of [VO(acac)2] in the ratio 1:1 proportional to the ligand. The
mixture was stirred overnight at room temperature and after that the
solvent removed under reduced pressure. The resulting brown solids
were washed with water. The yields range from 70 to 88% with respect
to the used [VO(acac)2].
[VOCl(pyphen)]: Yield: 49 mg (0,09 mmol, 25%) of an orange solid.
C31H23ClNO3V (MW = 543.91 g·mol–1): calcd. C 68.46, H 4.26, N
2.58%; found: C 68.51, H 4.18, N 2.58%. 1H NMR (300 MHz,
CDCl3): δ = 7.99 (t, 1 H, 4py), 7.42 (d, 2 H, 3,5py), 7.62–7.29 (m, 20
H, Ph). 51V NMR (29.9 MHz, CDCl3): δ = –433. EI-MS: m/z =
548 [VO2(pyphen)+H+Na]+, 544 [VOCl(pyphen)+H]+, 478
[VO(pyphen)+2H]+. UV/Vis (CH2Cl2): λmax = 234, 297, 348, 373 nm.
Na[VO2(pydim)]: Yield: 204 mg (0.84 mmol, 84%) of a brown solid.
C7H7NNaO4V (MW = 243.07 g·mol–1): calcd. C 34.59, H 2.90, N
5.76%; found: C 34.29, H 2.88, N 5.71%. 1H NMR (300 MHz,
CD3OD): δ = 8.00 (t, 1 H, 4py), 7.43 (d, 2 H, 3,5py), 5.48 (s, 4 H,
CH2). 51V NMR (29.9 MHz, CD3OD): δ = –513.
Supporting Information (see footnote on the first page of this article):
Further figures showing experimental crystal and molecular structures
(XRD), DFT-calculated molecular structures, NMR spectra, UV/Vis
absorption spectra and cyclic voltammograms along with tables on
the experimental crystal and molecular structures and DFT-calculated
structural data.
K[VO2(pydim)]: Yield: 190 mg (0.73 mmol, 73%) of a brown solid.
C7H7NKO4V (M = 259.18 g·mol–1): calcd. C 32.44, H 2.72, N 5.40%;
found: C 32.33, H 2.71, N 5.43%. 1H NMR (300 MHz, CD3OD): δ =
8.01 (t, 1 H, 4py), 7.48 (d, 2 H, 3,5py), 5.48 (s, 4 H, CH2). 51V NMR
(29,9 MHz, CD3OD): δ = –512.
Acknowledgements
Cs[VO2(pydim)]: Yield: 123 mg (0.35 mmol, 70%) of a brown solid.
C7H7NCsO4V (MW = 352.98 g·mol–1): calcd. C 23.82, H 2.00, N
3.97%; found: C 23.91, H 2.11, N 4.01%. 1H NMR (300 MHz,
CD3OD): δ = 7.99 (t, 1 H, 4py), 7.42 (d, 2 H, 3,5py), 5.47 (s, 4 H,
CH2). 51V NMR (29.9 MHz, CD3OD): δ = –511. UV/Vis (CH3CN):
λmax = 265 nm.
We thank Dr. Ingo Pantenburg (University of Cologne) for crystal data
collection.
Keywords: Oxido pincer ligands; Vanadyl; Electrochemistry;
Mixed-valent; EPR spectroscopy; Spectroelectrochemistry
Na[VO2(pydip)]: Yield: 70 mg (0.22 mmol, 88%) of a brown solid.
C11H15NNaO4V (M = 315.28 g·mol–1): calcd. C 44.16, H 5.05, N
4.68%; found: C 44.09, H 5.11, N 4.61%. 1H NMR (300 MHz,
CD3OD): δ = 8.03 (t, 1 H, 4py), 7.40 (d, 2 H, 3,5py), 1.60 (s, 12 H,
CH3). 51V NMR (29.9 MHz, CD3OD): δ = –537.
References
[1] J. T. Singleton, Tetrahedron 2003, 59, 1837–1857.
[2] P. S. Chase, R. A. Gossage, G. van Koten, in G. van Koten, R. A.
Gossage (Eds.) The Privileged Pincer-Metal Platform: Coordi-
nation Chemistry & Applications, in Top. Organomet. Chem.
2016, 54, 1–16.
K[VO2(pyphen)]: Yield: 490 mg (0.87 mmol, 87%) of a brown solid.
C31H23KNO4V (MW = 536.56 g·mol–1): calcd. C 66.07, H 4.11, N
2.49%; found: C 66.09, H 4.18, N 2.53%. 1H NMR (300 MHz,
Z. Anorg. Allg. Chem. 0000, 0–0
www.zaac.wiley-vch.de
9
© 0000 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
[3] S. Xiang, D.-X. Bao, J. Wang, Y.-C. Li, X.-Q. Zhao, J. Lu- [36] F. D. Rochon, A. L. Beauchamp, C. Bensimon, Can. J. Chem.
minesc. 2017, 186, 273–282.
1996, 74, 2121–2130.
[37] T. Kawato, H. Koyama, H. Kanatomi, Y. Muramoto, Inorg.
Chim. Acta 1991, 183, 107–112.
[38] S. Onaka, L. Hong, M. Ito, T. Sunahara, H. Imai, K. Inoue, J.
Coord. Chem. 2005, 58, 1523–1530.
[4] M. J. Celestine, J. L. Bullock, S. Boodram, V. H. Rambaran,
A. A. Holder, Rev. Inorg. Chem. 2015, 37, 57–67.
[5] A. M. Kirillov, G. B. Shul’pin, Coord. Chem. Rev. 2013, 257,
732–754.
[39] C. Boskovic, W. Wernsdorfer, K. Folting, J. C. Huffman, D. N.
Hendrickson, G. Christou, Inorg. Chem. 2002, 41, 5107–5118.
[40] A. Bhattacharjee, Y. Miyazaki, M. Nakano, J. Yoo, G. Christou,
D. N. Hendrickson, M. Sorai, Polyhedron 2001, 20, 1607–1613.
[41] J. Yoo, E. K. Brechin, A. Yamaguchi, M. Nakano, J. C. Huff-
man, A. L. Maniero, L.-C. Brunel, K. Awaga, H. Ishimoto, G.
Christou, D. N. Hendrickson, Inorg. Chem. 2000, 39, 3615–
3623.
[42] T.-X. Lan, W.-S. Gao, C.-N. Chen, H.-S. Wang, M. Wang, Y.-
H. Fan, New J. Chem. 2018, 42, 5798–5805.
[43] X. Chen, F. J. Femia, J. W. Babich, J. Zubieta, Inorg. Chim. Acta
2000, 308, 80–90.
[44] J. W. Babich, W. Graham Coco, S. Barrow, A. J. Fischman, F. J.
Femia, J. Zubieta, Inorg. Chim. Acta 2000, 309, 123–136.
[45] T. J. Boyle, M. L. Neville, D. T. Yonemoto, T. M. Alam, L. Jan,
J. Coord. Chem. 2015, 68, 1616–1632.
[46] K. V. Zaitsev, M. V. Bermeshev, S. S. Karlov, Y. F. Oprunenko,
A. V. Churakov, J. A. K. Howard, G. S. Zaitseva, Inorg. Chim.
Acta 2007, 360, 2507–2512.
[47] R. Fandos, B. Gallego, A. Otero, A. Rodriguez, M. J. Ruiz, P.
Terreros, C. Pastor, Organometallics 2007, 26, 2896–2903.
[48] R. J. Fites, A. T. Yeager, T. L. Sarvela, W. A. Howard, G. Zhu,
K. Pang, Inorg. Chim. Acta 2006, 359, 248–256.
[49] A. Conde, R. Fandos, A. Otero, A. Rodrıguez, Organometallics
2007, 26, 1568–1570.
[6] J. A. Davies, F. R. Hartley, Chem. Rev. 1981, 81, 79–90.
[7] R. G. Pearson, Inorg. Chem. 1988, 27, 734–740.
[8] M. Aureliano, F. Henao, T. Tiago, R. O. Duarte, J. J. G. Moura,
B. Baruah, D. C. Crans, Inorg. Chem. 2008, 47, 5677–5684.
[9] M. V. Kirillova, M. L. Kuznetsov, P. M. Reis, J. A. L. da Silva,
J. J. R. Frausto da Silva, A. J. L. Pombeiro, J. Am. Chem. Soc.
2007, 129, 10531–10545.
[10] D. Rehder, Metallomics 2015, 7, 730–742.
[11] J.-C. G. Bünzli, Acc. Chem. Res. 2006, 39, 53–61.
[12] T. Le Borgne, J.-M. Bénech, S. Floquet, G. Bernadinelli, C. Ali-
prandini, P. Bettens, C. Piguet, Dalton Trans. 2003, 3856–3868.
[13] S. Tanase, P. M. Gallego, R. de Gelder, W. T. Fu, Inorg. Chim.
Acta 2007, 360, 102–108.
[14] E. Furet, K. Costuas, P. Rabiller, O. Maury, J. Am. Chem. Soc.
2008, 130, 2180–2183.
[15] M. L. Cable, J. P. Kirby, K. Sorasaenee, H. B. Gray, A. Ponce,
J. Am. Chem. Soc. 2007, 129, 1474–1475.
[16] A. Picot, A. D’Aleo, P. L. Baldeck, A. Grichine, A. Duperray,
C. Andraud, O. Maury, J. Am. Chem. Soc. 2008, 130, 1532–
1533.
[17] H. Katada, H. Seino, Y. Mizobe, J. Sumaoka, M. Komiyama, J.
Biol. Inorg. Chem. 2008, 13, 249–255.
[18] D. Valigura, C. Rajnák, J. Moncol, J. Titisˇa, R. Bocˇa, Dalton
Trans. 2017, 46, 10950–10956.
[19] A. Scheurer, J. Korzekwa, T. Nakajima, F. Hampel, A. Buling,
C. Derks, M. Neumann, L. Joly, K. Petukhov, K. Gieb, P. Müller,
K. Kuepper, K. Meyer, Eur. J. Inorg. Chem. 2015, 1892–1901.
[20] A. Klein, S. Elmas, K. Butsch, Eur. J. Inorg. Chem. 2009, 15,
2271–2281.
[21] V. T. Yilmaz, S. Hamamci, C. Thöne, Polyhedron 2004, 23, 841–
848.
[22] O. Andac, S. Guney, Y. Topcu, V. T. Yilmaz, W. T. A. Harrison,
Acta Crystallogr., Sect. C 2002, 58, m17–m20.
[23] V. T. Yilmaz, S. Guney, O. Andac, W. T. A. Harrison, J. Coord.
Chem. 2003, 56, 21–32.
[24] S. Winter, W. Seichter, E. Weber, J. Coord. Chem. 2004, 57,
997–1014.
[25] A. Klein, K. Butsch, S. Elmas, C. Biewer, D. Heift, S. Nitsche,
I. Schlipf, H. Bertagnolli, Polyhedron 2012, 31, 649–656.
[26] S. Winter, W. Seichter, E. Weber, Z. Anorg. Allg. Chem. 2004,
630, 434–442.
[27] T. C. Stamatatos, G. C. Vlahopoulou, C. P. Raptopoulou, A.
Terzis, A. Escuer, S. P. Perlepes, Inorg. Chem. 2009, 48, 4610–
4612.
[28] G. C. Vlahopoulou, D. I. Alexandropoulos, C. P. Raptopoulou,
S. P. Perlepes, A. Escuer, T. C. Stamatatos, Polyhedron 2009, 28,
3235–3242.
[50] J. M. Berg, R. H. Holm, Inorg. Chem. 1983, 22, 1768–1771.
[51] J. M. Hawkins, K. B. Sharpless, Tetrahedron Lett. 1987, 28,
2825–2828.
[52] S. Bellemin-Laponnaz, K. S. Coleman, P. Dierkes, J.-P. Masson,
J. A. Osborn, Eur. J. Inorg. Chem. 2000, 1645–1649.
[53] R. M. Gauvin, J. A. Osborn, J. Kress, Organometallics 2000, 19,
2944–2946.
[54] S. Dutta, P. Basu, A. Chakravorty, Inorg. Chem. 1993, 32, 5343–
5348.
[55] M. Debnath, M. Dolai, K. Pal, S. Bhunya, A. Paul, H. M. Lee,
M. Ali, Dalton Trans. 2018, 47, 2799–2809.
[56] D. Rehder, Coord. Chem. Rev. 2008, 252, 2209–2223.
[57] S. Barroso, A. M. Coelho, P. Adão, M. J. Calhorda, A. M. Mar-
tins, Dalton Trans. 2017, 46, 9692–9704.
[58] S. Banerjee, I. Pant, I. Khan, P. Prasad, A. Hussain, P. Kondaiah,
A. R. Chakravarty, Dalton Trans. 2015, 44, 4108–4122.
[59] H. Kelm, H.-J. Krüger, Inorg. Chem. 1996, 35, 3533–3540.
[60] D. C. Crans, M. L. Tarlton, C. C. McLauchlan, Eur. J. Inorg.
Chem. 2014, 4450–4468.
[61] M. Sutradhar, A. J. L. Pombeiro, Coord. Chem. Rev. 2014, 265,
89–124.
[62] P. B. Chatterjee, K. Bhattacharya, M. Chaudhury, Coord. Chem.
Rev. 2011, 255, 2150–2164.
[63] N. Biswas, D. Patra, B. Mondal, S. Bera, S. Acharyya, A. K.
Biswas, T. K. Mukhopadhyay, A. Pal, M. G. B. Drew, T. Ghosh,
Dalton Trans. 2017, 46, 10963–10985.
[64] D. Patra, S. Paul, I. Majumder, N. Sepay, S. Bera, R. Kundu,
M. G. B. Drew, T. Ghosh, Dalton Trans. 2017, 46, 16276–
16293.
[65] A.-C. Schmidt, M. Hermsen, F. Rominger, R. Dehn, J. H. Teles,
A. Schäfer, O. Trapp, T. Schaub, Inorg. Chem. 2017, 56, 1319–
1332.
[66] Z. Kazemi, H. A. Rudbari, V. Mirkhani, M. Sahihi, M. Mogh-
adam, S. Tangestaninejad, I. Mohammadpoor-Baltork, A. A. Ka-
jani, G. Azimi, Eur. J. Med. Chem. 2017, 135, 230–240.
[67] V. A. Nikolakis, P. Stathopoulos, V. Exarchou, J. K. Gallos, M.
Kubicki, T. A. Kabanos, Inorg. Chem. 2010, 49, 52–61.
[68] P. B. Chatterjee, S. Bhattacharya, A. Audhya, K.-Y. Choi, A.
Endo, M. Chaudhury, Inorg. Chem. 2008, 47, 4891–4902.
[29] A. K. Gupta, J. Kim, Acta Crystallogr., Sect. C 2003, 59, m262–
m264.
[30] M. Koman, M. Melník, T. Glowiak, Cryst. Res. Technol. 2002,
37, 119–124.
[31] M. Koman, M. Melnik, J. Moncol, Inorg. Chem. Commun. 2000,
3, 262–266.
[32] E. C. Escudero-Adan, J. Benet-Buchholz, A. W. Kleij, Inorg.
Chem. 2008, 47, 410–412.
[33] J. D. Crowley, K. D. Hänni, D. A. Leigh, A. M. Z. Slawin, J.
Am. Chem. Soc. 2010, 132, 5309–5314.
[34] F. M. Al-Sogair, B. P. Operschall, A. Sigel, H. Sigel, J. Schnabl,
R. K. O. Sigel, Chem. Rev. 2011, 111, 4964–5003.
[35] E. Katsoulakou, D. Dermitzaki, K. F. Konidaris, E. E. Moushi,
C. P. Raptopoulou, V. Psycharis, A. J. Tasiopoulos, V. Bekiari,
E. Manessi-Zoupa, S. P. Perlepes, T. C. Stamatatos, Polyhedron
2013, 52, 467–475.
Z. Anorg. Allg. Chem. 0000, 0–0
www.zaac.wiley-vch.de 10
© 0000 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
[69] B. Mondal, T. Ghosh, M. Sutradhar, G. Mukherjee, M. G. B.
[87] S. Ghosh, K. K. Nanda, A. W. Addison, R. J. Butcher, Inorg.
Chem. 2002, 41, 2243–2249.
[88] R. A. Holwerda, B. R. Whittlesey, Inorg. Chem. 1998, 37, 64–
68.
[89] C. J. Ballhausen, H. B. Gray, Inorg. Chem. 1962, 1, 111–122.
[90] W. Kaim, J. Fiedler, Chem. Soc. Rev. 2009, 38, 3373–3382.
[91] M. Krejcˇík, M. Danˇek, F. Hartl, J. Electroanal. Chem. 1991,
317, 179–187.
[92] M. C. Burla, R. Caliandro, B. Carrozzini, G. L. Cascarano, C.
Cuocci, C. Giacovazzo, M. Mallamo, A. Mazzone, G. Polidori,
J. Appl. Crystallogr. 2015, 48, 306–309.
[93] G. M. Sheldrick, Acta Crystallogr., Sect. A 2008, 64, 112–122.
[94] G. M. Sheldrick, SHELXL, Acta Crystallogr., Sect. C 2015, 71,
3–8.
[95] L. J. Farrugia, J. Appl. Crystallogr. 2012, 45, 849–854.
[96] STOE X-RED, Data Reduction Program, Version 1.22/Win-
dows, STOE & Cie, Darmstadt, 2001.
[97] STOE X-SHAPE, Crystal Optimization for Numerical Absorp-
tion Correction, Version 1.06/Windows, STOE & Cie, Darm-
stadt, 1999.
[98] TURBOMOLE 7.0, TURBOMOLE GmbH 2015.
[99] C. Steffen, K. Thomas, U. Huniar, A. Hellweg, O. Rubner, A.
Schroer, J. Comput. Chem. 2010, 31, 2967–2970.
[100] A. Schafer, H. Horn, R. Ahlrichs, J. Chem. Phys. 1992, 97,
2571–2577.
Drew, T. Ghosh, Polyhedron 2008, 27, 2193–2201.
[70] T. Jakusch, A. Melman, M. P. Sigalas, T. Kiss, A. D. Keramidas,
T. A. Kabanos, Inorg. Chem. 2008, 47, 11698–11710.
[71] P. Sarkar, M. K. Mondal, A. Sarmah, S. Maity, C. Mukherjee,
Inorg. Chem. 2017, 56, 8068–8077.
[72] D. Patra, N. Biswas, B. Kumari, P. Das, N. Sepay, S. Chatterjee,
M. G. B. Drew, T. Ghosh, RSC Adv. 2015, 5, 92456–92472.
[73] P. Galloni, V. Conte, B. Floris, Coord. Chem. Rev. 2015, 301–
302, 240–299.
[74] M. B. Robin, P. Day, Adv. Inorg. Chem. Radiochem. 1967, 9,
247–422.
[75] A. Apostolopoulou, M. Vlasiou, P. A. Tziouris, C. Tsiafoulis,
A. C. Tsipis, D. Rehder, T. A. Kabanos, A. D. Keramidas, E.
Stathatos, Inorg. Chem. 2015, 54, 3979–3988.
[76] B. D. Howes, C. Kühlmeyer, R. Pogni, R. Basosi, Magn. Reson.
Chem. 1999, 37, 538–544.
[77] D. Schulz, T. Weyhermüller, K. Wieghardt, B. Nuber, Inorg.
Chim. Acta 1995, 240, 217–229.
[78] S. P. Dash, S. Roy, M. Mohanty, M. F. N. N. Carvalho, M. L.
Kuznetsov, J. C. Pessoa, A. Kumar, Y. P. Patil, A. Crochet, R.
Dinda, Inorg. Chem. 2016, 55, 8407–8421.
[79] A. Sarkar, S. Pal, Eur. J. Inorg. Chem. 2009, 622–627.
[80] R. Dinda, P. Sengupta, M. Sutradhar, T. C. W. Mak, S. Ghosh,
Inorg. Chem. 2008, 47, 5634–5640.
[101] C. T. Lee, W. T. Yang, R. G. Parr, Phys. Rev. B PRB 1988, 37,
785–789.
[102] A. D. Becke, J. Chem. Phys. 1993, 98, 5648–5652.
[103] A. D. Becke, J. Chem. Phys. 1993, 98, 1372–1377.
[104] A. Klamt, J. Phys. Chem. 1995, 99, 2224–2235.
[105] A. Klamt, V. Jonas, T. Bürger, J. C. W. Lohrenz, J. Phys. Chem.
A 1998, 102, 5074–5085.
[106] E. Gómez, V. Santes, V. de la Luz, N. Farfán, J. Organomet.
Chem. 2001, 622, 54–60.
[107] E. Gómez, R. Flores, G. Huerta, C. Alvarez-Toledano, R. A. To-
scano, V. Santes, N. Nava, P. Sharma, J. Organomet. Chem.
2003, 672, 115–122.
[81] R. Dinda, P. Sengupta, S. Ghosh, T. C. W. Mak, Inorg. Chem.
2002, 41, 1684–1688.
[82] S. Mondal, P. Gosh, A. Chakravorty, Inorg. Chem. 1997, 36, 59–
63.
[83] S. Dutta, P. Basu, A. Chakravorty, Inorg. Chem. 1993, 32, 5343–
5348.
[84] J. Chakravarty, S. Dutta, A. Chakravorty, J. Chem. Soc., Dalton
Trans. 1993, 2857–2858.
[85] A. Mondal, S. Basak, S. Sarkar, D. Chopra, R. Das, K. K. Rajak,
Eur. J. Inorg. Chem. 2006, 1824–1829.
[86] A. Mondal, S. Sarkar, D. Chopra, T. N. G. Row, K. Pramanik,
Received: August 11, 2018
K. K. Rajak, Inorg. Chem. 2005, 44, 703–708.
Published online: ᭿
Z. Anorg. Allg. Chem. 0000, 0–0
www.zaac.wiley-vch.de 11
© 0000 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
S. Nitsche, S. Schmitz, K. Stirnat, A. Sandleben,
A. Klein* ......................................................................... 1–12
Controlling Nuclearity and Stereochemistry in Vanadyl(V) and
Mixed Valent VIV/VV Complexes of Oxido-Pincer Pyridine-
2,6-dimethanol Ligands
Z. Anorg. Allg. Chem. 0000, 0–0
www.zaac.wiley-vch.de 12
© 0000 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim