On the influence of the titanium source on the composition and structure of novel titanoniobates

Article abstract of DOI:10.1039/C8DT02835D

Systematic variation of the titanium source and the reaction temperature applied during hydrothermal synthesis led to crystallization of four new titanoniobates: {[Ni(cyclam)]₄[Ti₂Nb₈O₂₈]}_n·～28nH₂O (I), K[Ni(cyclam)]₃[TiNb₉O₂₈]·xH₂O; x = 18 (II), x = 14 (III) and x ～ 10 (IV). These are the first titanoniobates with Ni²⁺-centered amine complexes acting as counter cations and additionally, this is the first report of transition metal complexes expanded by monotitanoniobates. While I is obtained using Ti(OⁱPr)₄, II-IV are formed using K₂TiO(C₂O₄)·2H₂O as the educt. The presence of oxalate anions seems to influence the coordination environments of the Ni²⁺ cations that are octahedrally coordinated in I, and in a square-planar environment in II-IV. The titanium source also affects the degree of substitution of Nb^V by Ti^IV. Temperature-dependent syntheses demonstrate that the formation of I does not depend on the reaction temperature, while the formation of II-IV is clearly affected by this parameter. Regarding the arrangement of crystal water molecules, patterns of different dimensionalities ranging from 0D to 3D are formed which can be classified as water clusters. Each compound exhibits a pronounced plateau in the thermogravimetric curves after the removal of crystal H₂O molecules. Rehydration experiments after water removal proved that except for compound III, the re-integration of water was successful.

Full text of DOI:10.1039/C8DT02835D

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On the influence of the titanium source on the
composition and structure of novel
titanoniobates†
Cite this: Dalton Trans., 2018, 47,
15103
Joanna Dopta, Sven Grzanna, Christian Näther
and Wolfgang Bensch
*
Systematic variation of the titanium source and the reaction temperature applied during hydrothermal
synthesis led to crystallization of four new titanoniobates: {[Ni(cyclam)]4[Ti2Nb8O28]}n·∼28nH2O (I),
K[Ni(cyclam)]3[TiNb9O28]·xH2O; x = 18 (II), x = 14 (III) and x ∼ 10 (IV). These are the first titanoniobates
with Ni2+-centered amine complexes acting as counter cations and additionally, this is the first report of
transition metal complexes expanded by monotitanoniobates. While I is obtained using Ti(OiPr)4, II–IV are
formed using K2TiO(C2O4)·2H2O as the educt. The presence of oxalate anions seems to influence the
coordination environments of the Ni2+ cations that are octahedrally coordinated in I, and in a square-
planar environment in II–IV. The titanium source also affects the degree of substitution of NbV by TiIV.
Temperature-dependent syntheses demonstrate that the formation of I does not depend on the reaction
temperature, while the formation of II–IV is clearly affected by this parameter. Regarding the arrangement
of crystal water molecules, patterns of different dimensionalities ranging from 0D to 3D are formed which
can be classified as water clusters. Each compound exhibits a pronounced plateau in the thermo-
gravimetric curves after the removal of crystal H2O molecules. Rehydration experiments after water
removal proved that except for compound III, the re-integration of water was successful.
Received 10th July 2018,
Accepted 27th September 2018
DOI: 10.1039/c8dt02835d
rsc.li/dalton
The first examples of TiIV integration into the PONb struc-
ture were A12[Ti2O2][XNb12O40]·nH2O (A = Na, K; X = Si, Ge) fea-
Introduction
Polyoxometalates (POMs) are anionic metal-oxo clusters that turing the Keggin-type [XNb12O40]16− anions, which are linked
are formed by group V and VI transition metal cations. Due to into chains via [Ti2O2]4+ cations with TiIV in a strongly dis-
their outstanding performance in e.g. catalysis, medicine and torted octahedral environment.8,9 These new compounds also
electrochemistry, the design of novel POMs is an important represent the first PONb Keggin-type ions. In 2003, Nyman
topic in current research.1 Compared to polyoxovanadates, et al. described the synthesis of
a
dititanoniobate
-molybdates and -tungstates, the chemistry of polyoxoniobates [Ti2Nb8O28]8− anion containing compound for the first time.10
(PONbs) is less developed due to the synthetic limitations and A hydrothermal reaction of Nb2O5·xH2O, Ti(OiPr)4, NaOH and
chemical inertness of niobium oxo clusters.2,3 Nevertheless, TMAOH·5H2O yielded Na8[Ti2Nb8O28]·34H2O. Its cluster anion
several novel cluster geometries were discovered in the past exhibits the decaniobate [Nb10O28]6− geometry, where two
decade. In the field of hetero-PONbs, Si or Ge e.g. could be interior NbV positions are substituted by TiIV ions. Molecular
incorporated into Keggin anion containing compounds, e.g. in modeling of the possible isomers revealed that interior cluster
Na16[XNb12O40]·4H2O4 (X = Si, Ge), or transition metal cations positions are favored for substitution, suggesting that repul-
like Ni and V, e.g. in K14Na6[H4Ni10(H2O)8Nb32O102]·73H2O5 or sion is minimized when the number of edges shared by TiO6
Na18[Nb48V8(OH)30O130]·33H2O6 and also lanthanide ions, e.g. octahedra is as large as possible. A few years later, the
in (CN3H6)7K3H17{Eu3(H2O)9Nb48O138(H2O)6}·40H2O.7
“missing link” between the [Ti2Nb8O28]8− anion and
6−
[Nb10O28
]
– the monotitanoniobate anion – was reported.11
The new compound (TMA)7[TiNb9O28]·22H2O offered the
opportunity for more systematic studies on the influence of
substitution on the stability of the decametalate anions.
Integration of Ti into PONb cores may also lead to cluster
geometries different from decametalates or Keggin geometry.
Attempting to crystallize the monotitanoniobate salt, the
[Ti12Nb6O44]10− anion was discovered. This Lindqvist type
Institut für Anorganische Chemie, Christian-Albrechts-Universität zu Kiel,
24118 Kiel, Germany. E-mail: wbensch@ac.uni-kiel.de
†Electronic supplementary information (ESI) available: Crystal structure refine-
ment results, geometric parameters, additional figures of the structures, XRD
patterns, DTA-TG curves, and IR- and UV/Vis spectra. CCDC 1854782, 1854780
and 1854781. For ESI and crystallographic data in CIF or other electronic format
see DOI: 10.1039/c8dt02835d
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“superoctahedron” consists of edge sharing TiO6 octahedra
(2) compounds II and III are the first examples of in-
with NbO5 units capping each face.12 In the aspiring research organic–organic hybrids with [TiNb9O28]7− anions as central
on polyoxotantalates, upon Ti substitution the same cluster structural motifs;
geometries are observed. Using a similar preparation pro-
(3) the choice of the titanium source influences
(a) the number of Ti4+ ions in the cluster;
(b) the geometry of the nickel complex present in the struc-
10−
8−
cedure to Ti-PONbs, [Ti12Ta6O44
]
and [Ti2Ta8O28
]
anions
were obtained.13 The latter is stable in aqueous solution in
contrast to the unsubstituted [Ta10O28]6− anion, which so far is ture and the resulting color of the products; in compound I,
accessible only in non-aqueous solutions14 and, unlike in the cis- and trans-configured isomers coexist;
PONb chemistry, could not even be detected with the aid of
ESI-MS in titanometalate solutions.13
(4) the compounds are obtained within short reaction times
and the reaction temperature influences the formation of com-
Until today, only a single report about a TM (TM = tran- pounds II and III.
sition metal)-substituted titanoniobate is available, which was
synthesized by reacting Cu2+ ions, ethylenediamine, titanium
isopropoxide
Ti(OiPr)4
and
potassium
hexaniobate
Experimental section
Syntheses
K7HNb6O19·13H2O hydrothermally.15 The compound [Cu(en)2]
[Cu(en)2(H2O)2]3[Ti2Nb8O28]·8H2O (en = ethylenediamine) con-
sists of isolated [Ti2Nb8O28]8− clusters charge balanced by All chemicals except K7HNb6O19·13H2O were purchased and
[Cu(en)(H2O)2]2+ and [Cu(en)2]2+ molecules. This was a promis- used without further purification. (Nb2O5: abcr, 99.5% Nb;
ing result, although the employment of other amine molecules KOH: abcr, 85%; Ni(NO3)2·6H2O: Merck, >99%; 1,4,8,11-tetraa-
or other TM cations did not lead to crystalline products under zacyclotetradecane: Alfa Aesar, >98%; Ti(OiPr)4: Merck, 98%;
these reaction conditions.
K2TiO(C2O4)·2H2O: Sigma-Aldrich, 90%, K2C2O4·H2O: Merck,
Through the substitution of NbV ions for TiIV, the pH stabi- 99%, NaHCO3: Gruessing, 99%.) K7HNb6O19·13H2O was syn-
lity of decaniobate derivatives can be strongly affected, a thesized following a literature method.21 Solid reactants were
phenomenon which was also observed for the titanotanta- dispersed in 3 mL of distilled water. The pH value was
lates.13 As mentioned above, only the interior Nb5+ cations are adjusted with 1 M KOH. All reactions were carried out under
substituted by Ti4+. This results in the reduction of the formal hydrothermal conditions in DURAN® glass tubes with an
charge on the μ3-oxo sites, which are the key for the dissociation inner volume of 11 mL.
of [Nb10O28]6− to [Nb6O19]8− in basic media.16 17O NMR experi-
ments of aqueous solutions of dititanoniobate anions proved Synthesis of {[Ni(cyclam)]4[Ti2Nb8O28]}n·∼28nH2O (I)
that the integration of TiIV leads to a stabilization of the mole-
0.2 mmol K7HNb6O19·13H2O, 0.4 mmol Ni(NO3)2·6H2O and
cule and inhibits the base-enhanced dissociation at higher pH
0.4 mmol 1,4,8,11-tetraazacyclotetradecane (cyclam) were dis-
values.17 With the discovery of monotitanoniobate where only a
persed in 3 mL H2O. 0.034 mmol (0.1 mL) Ti(OiPr)4 was added
single NbV is substituted,11 a systematic study was possible and
and the slurry was thoroughly mixed. Afterwards, the pH was
a
similar effect was observed: the dissociation of the
adjusted with 0.2 mL 1 M KOH to 12.2 (after reaction: ∼10.7).
The mixture was reacted at 130 °C for 24 h. Light violet crystals
of I (Fig. S1a†) and colourless X-ray amorphous powder were
obtained. Yield: ∼40 mg (∼83% based on Ti).
C40H140N16Ni4Nb8Ti2O50: calcd in %: C 17.00, H 5.42, N 7.93;
found C 16.55, H 5.01, N 7.63. TG analysis gives a hint that
approx. two water molecules may be emitted during sample
preparation.
[TiNb9O28]7− anion takes place at pH ≥ 12,18 while the
[Nb10O28]6− anion starts to form [Nb6O19]8− already at pH ≥
7.5.19 For each ion, the pKa values were determined, which
increase with a higher substitution degree.18 The experimentally
determined pH-dependencies of oxygen exchange rates could
be understood later by a theoretical approach.20
The chemical properties of PONbs may also be influenced
via integration of TM complexes, but this approach still
remains a challenge and as mentioned above, the examples
are rare. Through their enhanced pH stability, titanoniobate
clusters may be good candidates to introduce TM complexes
into PONb clusters.
Herein, we present three new compounds composed of tita-
noniobate units, {[Ni(cyclam)]4[Ti2Nb8O28]}n·∼28nH2O (I),
K[Ni(cyclam)]3[TiNb9O28]·18H2O (II) and K[Ni(cyclam)]3
[TiNb9O28]·14H2O (III) (cyclam = 1,4,8,11-tetraazacyclotetrade-
cane). In addition to interesting structural features, e.g.
arrangement of water molecules with different dimensional-
ities, these compounds and their syntheses possess several
intriguing features:
Synthesis of K[Ni(cyclam)]3[TiNb9O28]·18H2O (II)
The same method was applied as that for the synthesis of com-
pound I, except that Ti(OiPr)4 was replaced by 0.034 mmol
K2TiO(C2O4)·2H2O. After adding 0.2 mL 1 M KOH to the reac-
tion mixture, the pH value was 11.3 (after reaction: ∼9.5). The
product crystallized as yellow block-like crystals (Fig. S1b†).
Yield: 60 mg (71% based on Ti). C30H108N16Ni3Nb9TiO46: calcd
in %: C 14.57, H 4.40, N 6.80; found C 14.67, H 4.40, N 6.87.
Synthesis of K[Ni(cyclam)]3[TiNb9O28]·14H2O (III)
A few single crystals of compound III were found in a batch of
(1) this is the first time that macrocyclic amine molecules II. The product crystallized as yellow block-like crystals
and Ni2+ ions are incorporated into a titanoniobate network;
(Fig. S1c†). Yield: <1 mg (∼1% based on Ti) under given reac-
15104 | Dalton Trans., 2018, 47, 15103–15113
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tion conditions (see Results) C30H100N16Ni3Nb9TiO42: calcd in Infrared spectroscopy
%: C 15.01, H 4.20, N 7.00; found C 15.10, H 4.30, N 7.17.
We note that all compounds are stable in air for several
weeks.
Infrared spectra were recorded on a Bruker Alpha-P IR spectro-
meter from 4000–400 cm−1 at room temperature.
Ultraviolet–visible spectroscopy
Structure determination
A
UV/Vis two-channel spectrometer Cary
5 from Varian
Data collection was performed using
a STOE Imaging Techtron Pty was used to collect the UV/Vis reflection data
using BaSO4 as a white standard. The data were calculated
Plate Diffraction System (IPDS-2) with MoKα (λ = 0.71073 Å)
and for all compounds, a numerical absorption correction was
performed. The structures were solved with the program
SHELXS-97 22 and refined was performed against F2 using
SHELXL-2014.23 The details of data collection and of the struc-
ture refinements are summarized in Table S1.†
with the Kubelka–Munk relation for diffuse reflectance data.25
Elemental analysis
Elemental analyses were performed on a EURO EA elemental
analyzer (EURO VEKTOR).
All non-hydrogen atoms were refined anisotropically. The
C–H and N–H H atoms were positioned with idealized geome-
try and refined isotropically with Uiso(H) = 1.2Ueq(C,N) using a
riding model. The O–H H atoms were not located but con-
sidered in the calculation of the molecular formula and the
molecular weight. In compound I, there is additional electron
density indicating for disordered water molecules, for which
no reasonable structure model was found. Therefore, the data
were corrected for the disordered solvent using the Squeeze
option in Platon.24 During the SQUEEZE procedure, 140 elec-
trons were collected. The accessible free space was calculated
to be 360.5 Å3 (7.6% of unit cell volume). One of the two
cyclam ligands is disordered and was refined using a split
model. In compound II, the Ti atom is located on the same
position as Nb5 and both atoms were refined with an occu-
pancy of 0.5. The position of the K+ cation is only half occu-
pied and the other half was assigned to disordered water. In
this case the model agrees with elemental analysis and if the
K+ cation is refined with full occupancy much too large displa-
cement parameters are obtained. The low reliability factors
originate from a poor crystal quality and contributions of at
least a second much smaller individual. This kind of twinning
cannot be resolved. In compound III, Nb9/Ti9 and Nb10/Ti10
occupy the same crystallographic positions and were refined
with occupancies of 0.75/0.25 as well as 0.25/0.75 using
restraints (EXYZ and EADP). The K+ cation is also disordered
and was refined using a split model.
Difference thermogravimetry (TG)
A Netzsch STA 409 CD was used to obtain the TG curves under
N2 flow with a heating rate of 4 K min−1
.
Results and discussion
Synthetic aspects
Recently, we used cyclam as a tetradentate ligand for the syn-
thesis of TM-substituted PONbs, resulting in two novel com-
pounds with [Cu(cyclam)]2+ complexes as charge balancing
agents.26 Both compounds could be obtained in a short reac-
tion time. Since the targeted integration of heteroatoms in the
Cu2+/cyclam/Nb5+ system was not yet successful, we replaced
Cu2+ by Ni2+ ions as the TM source. Under similar reaction
conditions to Cu–PONbs, we were able to prepare four novel
titanoniobates {[Ni(cyclam)]4[Ti2Nb8O28]}n·∼28nH2O (I), K[Ni-
(cyclam)]3[TiNb9O28]·xH2O with x = 18 for II, x = 14 for III and
x ≈ 10 for IV. The first experiments were carried out with Ti-
(OiPr)4, which undergoes a hydrolysis in aqueous solution,
forming iPrOH and titanium-oxo/hydroxo species.27 On
heating the reaction mixture solvothermally at 130 °C for 24 h,
I was obtained from the orange-brown colored mother liquor
as violet block shaped crystals (Fig. S1a†). Employing K2TiO-
(C2O4)·2H2O and leaving all other reaction parameters con-
stant, compound II was isolated as block-shaped yellow crys-
tals (Scheme 1, Fig. S1b†).
Several water O atoms were found in the structure of III;
two positions are not fully occupied with s.o.f. = 0.4, two O
atoms have an occupancy of 0.6 and two further O atoms 0.5.
Ten positions of O atoms are fully occupied and one O atom
(O47) is disordered with a ratio of 50 : 50, giving rise to about
fourteen water molecules per formula unit.
CCDC 1854782 (I), CCDC 1854780 (II), and CCDC 1854781
(III) contain the supplementary crystallographic data for this
paper.†
When the red-violet colored mother liquor was evaporated,
crystals of cis-[Ni2(cyclam)2(ox)](NO3)2
batch of II, a very small amount of III was found as yellow
platelet-like crystals (Fig. S1c†). In order to improve the yield
for further characterization, temperature dependent syntheses
from 80 to 180 °C were performed, and fortunately, the yield of
28
were obtained. In a
X-ray powder diffraction
Phase purity of the compounds was checked with X-ray powder
diffraction patterns that were measured with Cu-Kα1 radiation
on a STOE Stadi-P diffractometer (Ge monochromator) with a
Mythen 1 K detector (Fig. S2†).
Scheme 1 Synthesis scheme for the preparation of the title
compounds.
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values ranging from 9 to 13. Applying K2TiO(C2O4)·2H2O as
the titanium source, only X-ray amorphous powders were
obtained for pH = 12–13, while between 9 and 11 only the com-
pounds with the monotitanoniobate anion are obtained. Using
Ti(OiPr)4 as the reactant, at higher pH values the dititanonio-
bate compound I exclusively crystallized, whereas at lower pH
values phase mixtures of the mono- and dititanoniobate com-
pounds I and II are formed. From these results it is obvious
that the formation of the mono- and dititanoniobate anions
do not only depend on the actual pH value but also on the tita-
nium source. Here we want to note that solvothermal reactions
are complex and that changing one parameter inevitably leads
Scheme 2 Influence of the reaction temperature on the formation of
compounds II–IV.
to the alteration of all other parameters.
III could be increased to ∼35 mg (∼43%) at reaction tempera-
tures of 110 °C and lower. During the temperature dependent
investigations (Scheme 2), another type of yellow crystals (IV)
was obtained as very thin yellow platelets (Fig. S1d†), which
were not appropriate for single crystal structure analysis. All
attempts to improve the crystal quality failed. The material was
fully characterized and all analytical data indicate that IV is a
pseudo-polymorph of the compounds II and III with the
general formulae K[Ni(cyclam)]3[TiNb9O28]·xH2O with x ≈ 10
for compound IV.‡
2−
Since the presence of C2O4
seems to influence the
number of Ti4+ cations in the cluster, it is possible that these
anions interact with niobate fragments. In the [VNb12O40{NbO
(CO3)}2]13− and [H10Nb31O93(CO3)]23− anions, the carbonate
ligands are coordinated to Nb5+ via two O2− anions and the
sevenfold coordination is completed by five O2− anions of the
PONb anion in the solid state.29 Therefore, it is imaginable
that such intermediates are present, leading to a preferred
crystallization of one product with a distinct composition.
Further investigations on the influence of C2O42− and other
additives onto the formation of titanoniobates are underway.
We want to note that compound I can also be isolated
under stirring ‘dynamic’ conditions in comparable yields.
Dynamic conditions also lead to formation of II, which crystal-
lizes from the mother liquor, while IV can be recovered from Crystal structures
the same reaction mixture directly by filtration. This demon-
Crystal structure of {[Ni(cyclam)]4[Ti2Nb8O28]}n·∼28nH2O (I).
strates that dynamic conditions are beneficial not only for the
efficient synthesis of iso- but also of heteropolyoxoniobates.
Interestingly, the formation of III could not be observed on
applying stirring conditions.
It is not yet clear why the formation of the dititanoniobate
is favored when Ti(OiPr)4 is employed and the monotitanonio-
bate is dominating when K2TiO(C2O4)·2H2O is applied. But it
is not surprising that the formation depends on the change of
The compound {[Ni(cyclam)]4[Ti2Nb8O28]}n·28nH2O (I) crystal-
lizes in the monoclinic space group C2/m with Z = 2. Ti1, O2,
O8, Ni2, N11, N13, and four water O atoms lie on a crystallo-
graphic mirror plane. Two water O atoms (O7, O17) are located
on the twofold rotational axis and the second crystallographi-
cally independent Ni2+ (Ni2) ion on a center of inversion. The
main structural motif consists of a titanoniobate cluster anion,
which is decorated by Ni2+ centered complexes (Fig. 1).
a single reaction parameter, since in aqueous solutions of the
7−
[TiNb9O28
]
anion the [Ti2Nb8O28]8− cluster is present as a
byproduct.11
On reacting Ti(OiPr)4 and K2TiO(C2O4)·2H2O simul-
taneously in equimolar proportion, solely the [TiNb9O28]7−
containing compounds II and IV were obtained. The formation
of the cis-[Ni2(cyclam)2(ox)](NO3)2 complex, which crystallizes
as
a by-product might influence different coordination
environments of the NiII ion in compound I compared to com-
pounds II–IV.
Carrying out the experiments using Ti(OiPr)4 as a source
and NaHCO3 as an additive (pH = 11.1), only compound IV
crystallized.
To investigate whether the formation of the dititanoniobate
(I) or the monotitanoniobate anions (II–IV) predominantly
depend on the pH value, the syntheses were conducted at pH
‡Analytical data; optical micrographs (Fig. S1†), XRD patterns (Fig. S2†), IR
(Fig. S17†), UV/Vis (Fig. S21†) spectra and DTA-TG curves (Fig. S25†) can be
found in the ESI.†
Fig. 1 Representation of the main structural motif in the structure of I.
Only selected atoms are labeled. H atoms are omitted for clarity. Only
one orientation of the disordered cyclam ligand is shown.
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The anionic unit displays the Nyman-type cluster geometry
[Ti2Nb8O28]8− with Nb5+ and Ti4+ cations octahedrally co-
ordinated by oxygen.10 In analogy to the known decaniobate
geometry,30–33 three octahedra are connected via edge-sharing
and these are attached to another trimer by sharing the edges,
forming a 2 × 3 rectangle. The rectangle is capped by two edge-
sharing octahedra at the top and the bottom, respectively. The
results of bond valence sum (BVS) analysis are in line with oxi-
dation states +5 for Nb, +4 for Ti, and +2 for Ni (Table S2†).
The NbvOt (t = terminal), Nb-μ2-O, Nb-μ3-O and Nb-μ6-O
bonds (Table S3†) are in the range of 1.752(2)–1.768(2) Å, 1.924
(2)–2.0213(19) Å, 2.0787(17)–2.0852(17) Å and 2.3829(3)–2.4305
(19) Å, respectively, a bond length distribution that is known
for other decaniobate compounds.30–33 As expected, the TiO6
octahedron has no terminal TivO bonds. Like in Ti-PONbs,
Ti-POWs and Ti-POMos, terminal TivO bonds were not
observed, and Ti4+ always prefers bonds to bridging O2−
anions, favouring positions with lower distortion.10 This is in
agreement with the structures of layered TiIV/NbV perovskite
materials where Ti4+ octahedra are located in the interior slab
sites.34–37 The Ti-μ2-O, Ti-μ3-O and Ti-μ6-O bond lengths are
1.812(2), 1.962(3)–1.983(3) and 2.1889(17) Å, respectively and
Fig. 2 Coordination spheres around the two crystallographically inde-
pendent Ni2+ ions in the structure of I. The disorder of the cyclam ligand
coordinated to Ni2 is indicated by orange and green lines (left).
Table 1 Comparison of the geometrical parameters of the two crystal-
lographically independent [Ni(cyclam)]2+ complexes in the structure of I
Type of bond /angle
trans-[Ni(cyclam)]2+
cis-[Ni(cyclam)]2+
Ni–N/Å
Ni–O/Å
2.062(3)–2.073(3)
2.087(2) Å
2.058(7)–2.138(6)
2.111(2)
eq. N–Ni–N/O/°
trans N–Ni–N/O/°
85.81(12)–94.19(12)°
180.00°
83.7(2)–99.3(2)°
168.8(2)–174.8(2)°
show the general trend of increasing bond lengths with similar complexes with cis-configured cyclam molecules, e.g.
an increasing number of bridging oxygen atoms.10 The O–Ti–O [Ni2(C2O4)(cyclam)2](ClO4)2.39 The anionic cluster is further
angles (Table S4†) demonstrate a severe deviation from expanded by four trans-[Ni(cyclam)]2+ cations, where the O
ideal geometry (O–Ti–O: 80.93–167.86°). Compared to the atoms of two neighboring clusters occupy the vertices of Ni2+
8−
two literature known [Ti2Nb8O28
(Na8[Ti2Nb8O28]·34H2O10
and
]
containing compounds centered octahedra with cyclam N-donors in axial positions
[Cu(en)2][Cu(en)2(H2O)2]3 (Fig. 2b). The Ni–N and the Ni–O distances (Table 1) match
[Ti2Nb8O28]·8H2O15) there are some slight differences in well with the literature data.42–44 The equatorial N–Ni–N/O
certain bond lengths as displayed in Fig. S3† and summarized angles scatter between 85.81(12)–94.19(12)° and the trans N–
in Table S5.† These differences are most probably caused by Ni–N/O angles are 180.00°, being closer to ideal octahedral
the multiple coordinations of the [Ni(cyclam)]2+ units. The geometry compared to the complex discussed above.
M-μ3-O (M = Ti/Nb) and the Nb-μ6-O bond lengths are slightly
shorter and the Ti-μ6-O distances are longer than reported for ordinated to Ni2 adopts cis-configuration, while the cyclam
the two other compounds.
molecule surrounding Ni1 exhibits trans-configuration,
It is unusual that the disordered cyclam molecule co-
a
The O–Nb–O angles are 75.75–178.15° for Nb1 and which is the most common configuration for metal cation cen-
74.87–171.08° for Nb2 (Table S4†), demonstrating a stronger tered cyclam complexes.45 The coexistence of cis- and trans-
distortion of the NbO6 octahedra which share more edges with isomers in the solid state is rare and was reported only for
neighboring units. Charge compensation in compound I is [Ni2(cyclam)2(μ3-C2O4)]·(ClO4)2·H2O.40
achieved through four Ni2+ centered amine complexes per
Overall, each [Ti2Nb8O28]8− unit is connected to four trans-
formula unit. The octahedral coordination sphere of the two [Ni(cyclam)]2+ and two cis-[Ni(cyclam)]2+ cations and may be
unique Ni2+ ions is formed by the four N atoms of one cyclam viewed as a hexadentate ligand for the complexes. The trans-
molecule and two terminal O2− anions of the [Ti2Nb8O28]8− [Ni(cyclam)]2+ moieties connect the anionic clusters in the ab
cluster.
Each [Ti2Nb8O28
plane into layers (Fig. S4†). The layers are separated by the cis-
unit is decorated by two [Ni(cyclam)]2+ [Ni(cyclam)]2+ complexes, which are arranged in a wave-like
8−
]
molecules via two terminal cluster O atoms in the cis-position. manner (Fig. 3).
The cyclam molecule is disordered over two positions in ratio
H-bonding interactions are observed, which may explain
50 : 50 (Fig. 2a). The Ni–N and the Ni–O bond lengths are some structural peculiarities (Table S7†). The Nb(2)–O(9)–Ni(2)
2.058(7)–2.138(6) Å and 2.111(2) Å, respectively (Table S6†). angle is 134.04(12)° and significantly differs from the ideal
The corresponding values for equatorial N–Ni–N/O angles are value of 180°. This can be explained with the presence of
83.7(2)–99.3(2)° and for the trans N–Ni–N/O angles are 168.8 H-bonds between the N–H and C–H atoms of the cyclam mole-
(2)–174.8(2)°, reflecting a significant distortion of the octa- cule and Nb-μ2-O bridging atoms (N–H⋯O = 2.953(5) Å; <
hedral geometry. Besides the Ni(2)–N(12/13) bond lengths (NHO) = 146.3°; C–H⋯O = 3.391(17) Å; <(CHO) = 163.8°) which
which are shorter (2.058(7)–2.080(5) Å) than most of the lead to a tilting of the cis-[Ni(cyclam)]2+ complex relative to the
reported values but not unprecedented in complexes,28,38–41 all anion (Fig. S5a†). Furthermore, a crystal H2O molecule located
geometrical parameters are in good agreement with those in near the amine molecule is also involved in H-bonding with
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Fig. 3 View of the layers in the structure of I along [100]. H and water
O atoms are omitted for clarity. Only one orientation of the disordered
cyclam ligand is shown. Green polyhedra: NbO6, violet polyhedra: TiO6.
the N–H H atoms, additionally stabilizing the folded geometry
of the cyclam ligand (Fig. S5b†), (N–H⋯O = 3.114(7)–3.122(7)
Å; <(NHO) = 161.3–167.3°). The tilting in the second unique
trans-[Ni(cyclam)]2+ cation is less pronounced (Nb(1)–O(1)–Ni
(1): 166.26(13)°) and only C–H groups are involved in
H-bonding (Fig. S5c†), (C–H⋯O = 3.160(4) Å–3.553(4) Å;
<(CHO) = 112.5–169.0°). One N–H H atom of the trans-config-
ured cyclam molecule interacts with a crystal water molecule
(N–H⋯O = 3.147(4) Å; <(NHO) = 155.6°).
Single crystal structure analysis revealed that there are 22
water molecules per formula unit in the structure of I. The
water H atoms could not be located, but the water O atoms
(O⋯O-distances up to the sum of the van der Waals radii:
3.05 Å, Table S8†) show an unusual arrangement. Following
the notation of Infantes et al.,46,47 the H2O molecules form a
L4(2)4(4)28(14) wallpaper-like layer-type water cluster, i.e. there
are four-membered rings which share water molecules with
two adjacent rings, a second type of four-membered ring sur-
rounded by four other rings and 28-membered rings enclosed
with 14 rings (Fig. 4). Bucket-like 4-membered fragments dec-
orate the 4(4) rings (Fig. S6†). In the 28-membered rings, the
[Ti2Nb8O28]8− anions are located, whereas the cis-[Ni
(cyclam)]2+ molecules are located in the plane formed by the
rings (Fig. S7a†), and the trans-[Ni(cyclam)]2+ molecules are
found below and above these planes (Fig. S7b†).
Fig. 4 Arrangement of the crystal water molecules building a L4(2)4(4)
28(14) type cluster in the structure of I (top, H-bonds dashed lines), and
location of the anions (bottom). C, N and H atoms are not displayed for
clarity. Green: NbO6, violet: TiO6.
Crystal structures of K[Ni(cyclam)]3[TiNb9O28]·18H2O (II)
and K[Ni(cyclam)]3[TiNb9O28]·14H2O (III). K[Ni(cyclam)]3
[TiNb9O28]·18H2O (II) crystallizes in the monoclinic space
group C2/c with four formula units in the unit cell. All atoms
except the central Ti/Nb cations, the K+ cation and a H2O mole-
cule are located at general positions. In the decaniobate
cluster one Nb5+ cation is replaced by a Ti4+ ion (Fig. 5).
Similar to compound I and other titanoniobates, the Ti4+
cation is located on an interior position of the anion, and in II
these positions are occupied with 50% Ti and 50% Nb. For Nb
and Ni, BVS provides oxidation states of +5 and +2, respect-
ively. To calculate the BVS for Ti and Nb on the sites with
mixed occupancy, the R0 values were weighted according to the
Fig. 5 View of the anionic cluster in the structure of compound II.
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occupation factor leading to 4.52 (Table S2†), in accordance
with the average oxidation state for TiIV and NbV on the
interior position. The Nb–O bond lengths in the [TiNb9O28]7−
anion are 1.741(6)–1.763(4) Å for NbvOt, 1.905(4)–2.068(4) Å
for Nb-μ2-O, 2.098(4)–2.116(4) Å for Nb-μ3-O and 2.390(4)–
2.496(4) Å for Nb-μ6-O (Table S9†) and agree with the data for
decaniobates.31 The Ti–/Nb–O bonds with values of 1.815(4)–
1.827(4) Å for μ2- and 1.992(4)–1.999(4) Å for μ3-O atoms differ
only slightly from other [TiNb9O28]7− cluster containing com-
pounds (Table S10†)11 with Ti/Nb-μ6-O bonds with 2.191(4)–
2.208(4) Å matching the reported data. The O–Nb–O angles are
comparable to that observed for I. The negative charge of
7−
[TiNb9O28
]
is compensated through three [Ni(cyclam)]2+
7−
Fig. 7 Arrangement of the KO7 polyhedra (blue) and [TiNb9O28
]
complexes and a K+ cation. In contrast to compound I, the two
anions in the structure of II. The [Ni(cyclam)]2+ cations and water O
crystallographically independent Ni2+ ions are in a square- atoms which are not involved in K–O interactions are omitted. Green:
NbO6, violet: Ti/NbO6, blue: KO7 polyhedra.
planar coordination of four N atoms of the cyclam molecule
(Fig. S8†). The nearest possible axial ligands are cluster O2−
anions at 3.534(4) and 3.669(4) Å, which are too far away for
bonding interactions. The Ni–N bonds (1.923(6)–1.941(6) Å) gen bonding interactions with ligand C–H H atoms (C–H⋯O =
are significantly shorter than those in I, but are in agreement 3.23(1) Å–3.595(9) Å; <(CHO) = 122.7–163.1°).
with the data reported for low-spin NiII amine
The water O atoms in the structure of II form a layered
complexes.38,41,48–51 The angles around Ni2+ (Table S11†) are cluster and considering only fully occupied water O atom posi-
typical of square-planar [Ni(cyclam)]2+ moieties.38,41,48,50–52
tions, a L5(4)L30(18) type cluster along [010] can be identified
Each [TiNb9O28]7− anion is surrounded by six [Ni(cyclam)]2+ (Fig. S13a†). Eight fragments consisting of two O atoms dec-
molecules (Fig. S9†), yielding a layer-like arrangement (Fig. 6).
orate each 30-membered ring. The layers are connected along
The K+ cation is surrounded by five H2O molecules and two the b axis via two H2O molecules (Fig. 13b†), forming a
terminal O atoms of the anion, leading to the coordination 3-dimensional network (Fig. S14†).
number (CN) 7 (Fig. S10a†). The K–O distances scatter from
Because II and III are pseudopolymorphs, mainly the struc-
2.734(12) to 3.054(8) Å (Table S12,† average: 2.874 Å), and are tural differences of K[Ni(cyclam]3[TiNb9O28]·18H2O (III) com-
partially longer than expected (2.81–2.84 Å,53 depending on pared to II are discussed. Compound III crystallizes in the tri-
CN) but they are not unusual.54 The KO7 polyhedra share no clinic space group P1 with two formula units in the unit cell.
ˉ
atoms with each other and are arranged in a wave-like fashion All atoms except Ni3 and Ni4 are located at general positions.
along [010] (Fig. 7, Fig. S11†).
The C–H and N–H H atoms of the cyclam ligands are of the [TiNb9O28
In analogy to II, the Ti4+ and Nb5+ ions in the interior position
]
7− anion are disordered over the same crystal-
involved in intermolecular H bonding interactions with cluster lographic position, but with a different site occupancy of 25%
O atoms (Table S13, Fig. S12†). (N–H⋯O = 2.828(7) Å–3.238(8) (Ti9/Nb10)/75%(Nb9/Ti10). The K+ cation is disordered over
Å; C–H⋯O = 3.194(9)–3.574(9) Å; <(NHO) = 143.1–170.4°; < two positions with a 60 : 40 occupancy. Each of the K+ cations
(CHO) = 131.2–165.0°). Furthermore, H2O also exhibits hydro- is in a different coordination environment of H2O and cluster-
μ2-O atoms. Using a cut-off at 3.2 Å for K–O interactions, K+
(60% occupancy) is surrounded by six H2O molecules and two
O2− anions and two symmetry related face-sharing KO8 poly-
hedra are linked with two [TiNb9O28]7− anions (Fig. 8, top).
The second K+ cation (s.o.f. = 0.4) is coordinated by six H2O
molecules, building distorted edge-sharing octahedra (Fig. 8,
bottom). Geometric parameters for the KOx (x = 8, 6), for the
[Ni(cyclam)]2+ cations and the hydrogen bonding interactions
are listed in Tables S12 and S14.†
Considering only fully occupied water O atoms (O–O dis-
tances: 2.698–3.038 Å (Table S8,† average: 2.791 Å), hexameric
isolated R6 water clusters are found. Taking into account
cluster O atoms being involved in H bonds, an extended water
motif is formed (Fig. 9). Two adjacent cluster anions are linked
via two water molecules along the c axis, which interact with
terminal cluster O atoms building a four-membered ring. A
7−
Fig. 6 Arrangement of the [TiNb9O28
]
anions and [Ni(cyclam)]2+
second arrangement of H2O molecules and cluster O atoms
cations in the structure of compound II. Green polyhedra: NbO6, violet
polyhedra: TiO6.
connect the anions along the a axis, which may be denoted as
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3
3
3
assigned to the A2g
→
3T1g(3P), A2g
→
3T1g(3F) and A2g
→
3T2g d–d transitions, respectively.28,56,57 The signal at 308 nm
is most probably the O → Nb CT transition, which is typically
observed between 200 and 300 nm.7,58–61 But this band is
missing in the absorption spectra of compounds II and III and
in the UV/Vis spectrum of the copper ethylenediamine salt of
the [Ti2Nb8O28]
8− anion.15 Therefore, we assume that the band
3
3
arises from splitting of the A2g → T1g(3P) d–d transition due
to the different coordination geometries of the [Ni(cyclam)]2+
complexes.
In the UV/Vis spectra of II–IV, a single broad band around
455 nm is observed (Fig. S21–23†), which is in accordance with
the yellow color of the compounds. This band is most probably
Fig. 8 Different coordination environments of the disordered K+ cation
in the structure of III; s.o.f = 0.6 (top), 0.4 (bottom) and the arrangement caused by the d–d transition in the low-spin square-planar [Ni
(cyclam)]2+ complex.48
of the resulting K–O polyhedra (blue).
Thermoanalytical investigations and dehydration experiments
Compound I decomposes in at least two steps (Fig. S24†). The
first mass loss of ∼17% is accompanied by an endothermic
signal at a peak temperature (Tp) of 76 °C and can be assigned
to the emission of crystal water molecules (calcd 17.8%). A
plateau is observed ranging from ∼110 to 180 °C, followed by
successive decomposition steps. From ∼200 to 630 °C, the
mass loss of ∼30% may be explained by the emission of the
cyclam molecules (calcd 28.4%). In the DTA curve, two exother-
mic signals are observed at Tp ∼ 250 °C and ∼460 °C
(Fig. S24a†). Beyond 650 °C, no significant mass loss occurs
and the yellow residue recovered after heating the sample to
1000 °C was identified as a mixture of NiTiNb2O8 and
Ni0.5Ti0.5NbO4. The occurrence of exothermic signals during
the decomposition of the sample under an inert atmosphere
Fig. 9 View on the extended water motif along [010] in the structure of
III. O–O distances below the sum of the van der Waals radii shown in
dashed lines. For clarity, the [Ni(cyclam)]2+ and K+ cations are not
shown. Grey polyhedra: Ti/NbO6.
was unexpected. For TG measurements, the sample chamber
is flushed with dry N2. To avoid the desorption of crystal H2O
molecules, the chamber was not evacuated prior to the
measurement. The residual moisture or air impurities may
lead to chemical reactions when decomposing sensitive
samples. We repeated the experiment thoroughly evacuating
the chamber and in the resulting DTA curve, only a single
endothermic event at Tp = 381 °C is present (Fig. S24b†). The
decomposition steps are not well resolved. The first mass loss
until 200 °C of ∼6.2% may be assigned to the residual crystal
R6(2), i.e. there are five hexameric rings which share two O
atoms with adjacent rings (Fig. S15†) and are attached to the
clusters via a H2O molecule.
Spectroscopic investigations
In the IR spectrum of each compound (Fig. S16–19†), charac- H2O molecules. The following steps from 200 to 900 °C are
teristic absorptions of the organic ligands are observed accompanied by a mass loss of ∼33%, but the decomposition
between 3250 and 1000 cm−1 (Table S15†). The O–H stretching is not finished at 1000 °C. In the XRDP (X-ray diffraction
vibrations of the crystal water molecules appear as very broad pattern) of the black powder that was recovered after heating
bands in the characteristic region at 3600–3300 cm−1 55
1000 cm−1, a definite assignment of the signals is difficult Ni0.5Ti0.5NbO4.
.
Below of I to 1000 °C, most reflections are assignable to Ni and
because the N–H and macrocyclic deformation vibrations
In the DTA-TG curves of II the first thermal event is finished
occur in the same region as that of the Nb–O vibrations. The at about 200 °C (Fig. S25†) and the mass loss of 13.1% is in
Nb–Ot absorptions are found at 965, 885 and 857 cm−1 for I, excellent agreement with the removal of crystal water mole-
880 and 864 cm−1 for II and 876 and 857 cm−1 for III. The cules (calcd 13.1%). The DTG and DTA (two endothermic
bands below 800 cm−1 are most probably caused by bridging events, Tp = 89, 126 °C) curves show that the dehydration
M–Ob–M (M = Ti, Nb) vibrations.
process occurs in two not well resolved steps. A distinct
In the UV/Vis spectrum of compound I, the characteristic plateau is observed after the removal of the H2O molecules fol-
transitions of high-spin octahedral Ni2+ complexes are lowed by the next thermal reaction starting at about 270 °C
observed (Fig. S20†). The bands at 354, 554 and 889 nm can be which is accompanied by an endothermic signal in the DTA
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curve at Tp = 393 °C. Upon further heating, the compound reflections of weaker intensity at ∼10° 2θ (Fig. S30†). In the
decomposes in at least two steps and the thermal reaction is XRDP of the recovered material after H2O treatment, a few
not finished at 1000 °C. From 270 to 900 °C the mass loss of reflections of low intensity are present between 6 and 10° 2θ,
24.0% may be explained by the emission of the cyclam mole- which do not match with reflections of the starting material,
cules (calcd 24.3%), and the dark-green residue contains i.e. the dehydration seems to be not reversible. The XRDP of
NiTiNb2O8, (NiNb2O6)0.6667 and NiO but we note that not all dehydrated compound IV is dominated by three broad and
reflections could be assigned.
intense reflections. Interestingly, the XRD pattern of a de-
The TG curve of III is similar to that of II (Fig. S26†) with hydrated sample of compound IV shows some similarity to
two not well resolved thermal events between 50 °C and that of compound II (Fig. S31†). After recovering the sample
∼200 °C, where the mass loss of 10.5% is most likely caused treated in water, the XRDP shows a good crystallinity, but the
by removal of the crystal H2O molecules (calcd for 14H2O = reflections can be clearly assigned to compound II.
10.5%). The mass loss is accompanied by a peak at Tp = 96 °C
On storing the samples at room-temperature, no removal of
and a second signal with low intensity at Tp = 134 °C. The fol- water could be observed, which might be explained by the pro-
lowing endothermic decomposition step (Tp = 400 °C) starts at nounced hydrogen bonding network between the crystal H2O
∼300 °C and ends at ∼550 °C (Δm = −10.5%). A further mass molecules forming water clusters, several H-bonding inter-
decrease is observed between 600 and 900 °C (16.3%), but the actions between cyclam molecules and water or cluster O2−
thermal decomposition is not finished at the highest tempera- anions and close K–Ocluster distances.
ture of 1000 °C. The overall mass loss of 26.8% between 300
pH value stability investigations
and 900 °C is in good agreement with the removal of the
cyclam molecules (calcd 25.0%). In the XRDP of the dark
green residue obtained after heating to 1000 °C, most reflec-
tions could be assigned to NiTiNb2O8, Ni0.5Ti0.5NbO4 and
Nb2O5.
The TG curve of compound IV exhibits a mass loss of 8.2%
caused by the removal of about 11H2O molecules (calcd 8.4%)
(Fig. S27†). The thermal reaction is accompanied by an
endothermal signal at Tp = 138 °C. The second endothermic
event (Tp = 394 °C) and the third decomposition step from
600 °C to ∼900 °C lead to an overall mass loss of 27.5%, indi-
cating the removal of the cyclam molecules (calcd 25.6%). In
analogy to II and III, the decomposition is not finished at
1000 °C. The XRDP of the residue contains reflections of
Ti0.67Nb1.33O4, TiO2 and NiO.
To estimate the pH stabilities of the compounds, samples of I
and II were immersed for 24 h in an aqueous solution of HCl
or KOH at defined pH values. The powder XRD patterns of the
samples (Fig. S32 and S33†) indicate that compound I is stable
between pH 2 and 13. At pH = 14, the compound starts to
decompose, clearly visible by the appearance of additional
reflections. For compound II, a pH stability window from 2 to
13 was determined, while at pH = 14 the reflections start to
diminish indicating decomposition. For pH < 2 both com-
pounds decompose to form X-ray amorphous materials.
Summarizing, the compounds exhibit good pH stability from
pH = 2 to pH = 13.
In the TG curves of the title compounds, distinct plateaus
occur after dehydration. This encouraged us to stop the
Conclusion
decomposition after water removal and investigate whether the Employing [Ni(cyclam)]2+ cations for charge compensation, we
crystal structure is affected and if rehydration recovers the synthesized four novel titanoniobates with NiII in two different
starting material.
spin states and different degrees of substitution of NbV for
For I the decomposition was stopped at 160 °C and the TiIV. These are the first titanoniobates with Ni2+-centered
color turned from violet to brownish. The XRDP of the de- amine complexes and the first transition metal expanded
hydrated material differs significantly from that of the as-syn- monotitanoniobates. The anions are derivatives of the
thesized samples and demonstrates that the water free com- [Nb10O28]
6− decaniobate anion, where one or both interior NbV
pound exhibits a reasonable good crystallinity after H2O positions are substituted with TiIV, yielding the dititanoniobate
removal (Fig. S28†). Immersing the sample in H2O leads to a [Ti2Nb8O28]8− or monotitanoniobate [TiNb9O28
]
anion. In
7−
brownish material exhibiting a similar powder pattern to I compound I, the Ni2+ cation of the [Ni(cyclam)O2]2− complex
before dehydration, but with broader and low intensity reflec- is in a high-spin state. The O2− anions occupy both the trans-
tions typical of a reduced crystallinity.
and the cis-positions in the two crystallographically indepen-
In the XRDP of the dark yellow colored material obtained dent complexes, which is very rare. In compounds II–IV, a low-
after heating compound II to 250 °C, only three very broad spin square-planar coordinated [Ni(cyclam)]2+ cation is
reflections are observed (Fig. S29†). After stirring the sample present. The different spin states of the Ni2+ centers lead to
in H2O, the XRDP matches well with that of the as-synthesized different electronic transitions in the UV/Vis spectra and result
material demonstrating the reversibility of the water removal. in the different colors of the compounds. In the structure of
Compound III was heated to 250 °C that led to partial the title compounds the crystal water molecules are joined by
decomposition of the sample, which is indicated by XRDP H-bonds yielding patterns of different dimensionalities.
measurements, that shows only two not well resolved broad
Beyond the interesting structural characteristics, the
reflections between 6 and 8° 2θ, respectively, as well as two product formation can be controlled to a certain extent.
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Employing Ti(OiPr)4 as a titanium source, {[Ni(cyclam)]4
[Ti2Nb8O28]}n·∼28nH2O (I) with octahedrally coordinated Ni2+
and a disubstituted anion is obtained, while the usage of
K2TiO(C2O4)·2H2O leads to K[Ni(cyclam)]3[TiNb9O28]·xH2O
(II–IV) with a square planar environment around Ni2+ and the
monosubstituted anion. Further experiments demonstrated
that the oxalate anion plays a crucial role in the preferential
crystallization of one distinct compound.
4 M. Nyman, F. Bonhomme, T. M. Alam, J. B. Parise and
G. M. B. Vaughan, Angew. Chem., Int. Ed., 2004, 43, 2787–
2792.
5 Z. Liang, D. Zhang, H. Wang, P. Ma, Z. Yang, J. Niu and
J. Wang, Dalton Trans., 2016, 45, 16173–16176.
6 Y.-T. Zhang, C. Qin, X.-L. Wang, P. Huang, B.-Q. Song,
K.-Z. Shao and Z.-M. Su, Inorg. Chem., 2015, 54, 11083–
11087.
The substitution of NbV for TiIV leads to an enhanced stabi-
lity of the PONb anions in a wider range of the pH scale,
extending the working pH range for future applications. The
good pH stability of the compounds presented here was
demonstrated with XRD experiments.
7 S. Chen, P. Ma, H. Luo, Y. Wang, J. Niu and J. Wang, Chem.
Commun., 2017, 53, 3709–3712.
8 M. Nyman, F. Bonhomme, T. M. Alam, M. A. Rodriguez,
B. R. Cherry, J. L. Krumhansl, T. M. Nenoff and
A. M. Sattler, Science, 2002, 297, 996–998.
Therefore, the study presented here contributes to the sys-
tematic evaluation of the parameters that influence the for-
9 F. Bonhomme, J. P. Larentzos, T. M. Alam, E. J. Maginn
and M. Nyman, Inorg. Chem., 2005, 44, 1774–1785.
mation of such compounds, which is the key for the efficient 10 M. Nyman, L. J. Criscenti, F. Bonhomme, M. A. Rodriguez
design of novel multifunctional materials.
and R. T. Cygan, J. Solid State Chem., 2003, 176, 111–119.
11 C. A. Ohlin, E. M. Villa, J. C. Fettinger and W. H. Casey,
Dalton Trans., 2009, 2677–2678.
12 C. A. Ohlin, E. M. Villa, J. C. Fettinger and W. H. Casey,
Angew. Chem., Int. Ed., 2008, 120, 5716–5718.
13 J.-H. Son and W. H. Casey, Chem. – Eur. J., 2016, 22, 14155–
14157.
Conflicts of interest
There are no conflicts to declare.
14 M. Matsumoto, Y. Ozawa, A. Yagasaki and Y. Zhe, Inorg.
Chem., 2013, 52, 7825–7827.
Acknowledgements
15 Y.-T. Zhang, P. Huang, C. Qin, L.-K. Yan, B.-Q. Song,
Z.-X. Yang, K.-Z. Shao and Z.-M. Su, Dalton Trans., 2014, 43,
9847–9850.
16 E. M. Villa, C. A. Ohlin, E. Balogh, T. M. Anderson,
M. D. Nyman and W. H. Casey, Angew. Chem., Int. Ed.,
2008, 120, 4922–4924.
This work was supported by the State of Schleswig-Holstein.
The authors thank Lisa K. Mahnke for her kind support with
the TOC graphic.
17 E. M. Villa, C. A. Ohlin, J. R. Rustad and W. H. Casey, J. Am.
Chem. Soc., 2009, 131, 16488–16492.
18 E. M. Villa, C. A. Ohlin and W. H. Casey, J. Am. Chem. Soc.,
2010, 132, 5264–5272.
References
1 (a) K. Thompson, Coord. Chem. Rev., 2001, 219–221,
1033–1053; (b) C. Streb, Dalton Trans., 2012, 41, 1651– 19 E. M. Villa, C. A. Ohlin, E. Balogh, T. M. Anderson,
1659; (c) K. V. Rao, P. S. N. Rao, P. Nagaraju, P. S. Prasad
and N. Lingaiah, J. Mol. Catal. A: Chem., 2009, 303, 84–
M. Nyman and W. H. Casey, Angew. Chem., Int. Ed., 2008,
120, 4922–4924.
89; (d) A. Ogata, H. Yanagie, E. Ishikawa, Y. Morishita, 20 J. R. Rustad and W. H. Casey, Nat. Mater., 2012, 11, 223–
S. Mitsui, A. Yamashita, K. Hasumi, S. Takamoto, 226.
T. Yamase and M. Eriguchi, Br. J. Cancer, 2008, 98, 399– 21 M. Filowitz, R. K. C. Ho, W. G. Klemperer and W. Shum,
409; (e) D.-L. Long, R. Tsunashima and L. Cronin, Inorg. Chem., 1979, 18, 93–103.
Angew. Chem., Int. Ed., 2010, 49, 1736–1758; 22 G. M. Sheldrick, SHELXS-97: Program for the Solution of
(f) D. E. Katsoulis, Chem. Rev., 1998, 98, 359–388; Crystal Structures, University of Goettingen, Goettingen, 1997.
(g) C. L. Hill, J. Mol. Catal. A: Chem., 2007, 262, 2–6; 23 G. M. Sheldrick, SHELXL-2014: Program for the Refinement
(h) A. Bijelic, M. Aureliano and A. Rompel, Chem.
Commun., 2018, 54, 1153–1169; (i) S. Herrmann,
of Crystal Structures, University of Goettingen, Goettingen,
2014.
C. Ritchie and C. Streb, Dalton Trans., 2015, 44, 7092– 24 A. L. Spek, Acta Crystallogr., Sect. C: Struct. Chem., 2015, 71,
7104. 9–18.
2 (a) M. Nyman, Dalton Trans., 2011, 40, 8049–8058; 25 G. Kortüm, W. Braun and G. Herzog, Angew. Chem., Int.
(b) M. Nyman and P. C. Burns, Chem. Soc. Rev., 2012, 41, Ed., 1963, 75, 653–661.
7354–7367; (c) B. W. Dale, J. M. Buckley and M. T. Pope, 26 J. Dopta, D.-C. Krause, C. Näther and W. Bensch, Cryst.
J. Chem. Soc. A, 1969, 301–304. Growth Des., 2018, 4130–4139.
3 M. Nyman, J. P. Larentzos, E. J. Maginn, M. E. Welk, 27 U. Schubert, J. Mater. Chem., 2005, 15, 3701–3715.
D. Ingersoll, H. Park, J. B. Parise, I. Bull and F. Bonhomme, 28 L. P. Battaglia, A. Bianchi, A. B. Corradi, E. Garcia-España,
Inorg. Chem., 2007, 46, 2067–2079.
M. Micheloni and M. Julve, Inorg. Chem., 1988, 4174–4179.
15112 | Dalton Trans., 2018, 47, 15103–15113
This journal is © The Royal Society of Chemistry 2018

View Article Online
Dalton Transactions
Paper
29 (a) P. A. Abramov, A. T. Davletgildeeva, N. K. Moroz, 45 Macrocyclic and Supramolecular Chemistry. A lifetime walk in
N. B. Kompankov, B. Santiago-Schübel and M. N. Sokolov,
the Realm of Cyclam, ed. J. Wiley, John Wiley@Sons LTD,
Inorg. Chem., 2016, 55, 12807–12814; (b) R. Tsunashima,
Chichester, 2016.
D.-L. Long, H. N. Miras, D. Gabb, C. P. Pradeep and 46 L. Infantes, J. Chisholm and S. Motherwell, CrystEngComm,
L. Cronin, Angew. Chem., Int. Ed., 2010, 122, 117–120. 2003, 5, 480–486.
30 L. Shen, C.-H. Li, Y.-N. Chi and C.-W. Hu, Inorg. Chem. 47 L. Infantes and S. Motherwell, CrystEngComm, 2002, 4,
Commun., 2008, 11, 992–994. 454–461.
31 J. Niu, G. Wang, J. Zhao, Y. Sui, P. Ma and J. Wang, Cryst. 48 M. Boiocchi, L. Fabbrizzi, F. Foti and M. Vazquez, Dalton
Growth Des., 2011, 11, 1253–1261. Trans., 2004, 2616–2620.
32 E. J. Graeber and B. Morosin, Acta Crystallogr., Sect. B: 49 A.-L. Cheng, N. Liu, J.-Y. Zhang and E.-Q. Gao, Inorg.
Struct. Crystallogr. Cryst. Chem., 1977, 2137–2143. Chem., 2007, 46, 1034–1035.
33 M. Matsumoto, Y. Ozawa and A. Yagasaki, Polyhedron, 50 A. C. Cerdeira, D. Belo, S. Rabaça, L. C. J. Pereira,
2010, 2196–2201.
34 A. R. Drews, W. Wong-Ng, T. A. Vanderah and R. S. Roth,
J. Alloys Compd., 1997, 243–247.
J. T. Coutinho, D. Simão, R. T. Henriques, O. Jeannin,
M. Fourmigué and M. Almeida, Eur. J. Inorg. Chem., 2013,
4612–4618.
35 A. R. Drews, W. Wong-Ng, R. S. Roth and T. A. Vanderah, 51 L. Prasad, S. C. Nyburg and A. McAuley, Acta Crystallogr.,
Mater. Res. Bull., 1996, 31, 153–162. Sect. C: Cryst. Struct. Commun., 1987, 43, 1038–1042.
36 J. Gopalakrishnan, S. Uma and V. Bhat, Chem. Mater., 1993, 52 M. P. Suh, J. W. Jeon, H. R. Moon, K. S. Min and H. J. Choi,
132–136. C. R. Chim., 2005, 8, 1543–1551.
37 Y.-S. Hong, S.-J. Kim, S.-J. Kim and J.-H. Choy, J. Mater. 53 R. D. Shannon, Acta Crystallogr., Sect. A: Cryst. Phys., Diffr.,
Chem., 2000, 10, 1209–1214. Theor. Gen. Crystallogr., 1976, 32, 751–767.
38 E. K. Barefield, A. Bianchi, E. J. Billo, P. J. Connolly, 54 (a) H. Rütter and D. Mootz, Z. Anorg. Allg. Chem., 1991, 73–
P. Paoletti, J. S. Summers and D. G. van Derveer, Inorg.
Chem., 1986, 4197–4202.
82; (b) P. A. Abramov, A. T. Davletgildeeva and
M. N. Sokolov, J. Cluster Sci., 2017, 28, 735–744.
39 H. Liu, W. Gu, X.-L. Tong, Y.-Y. Kou and S.-P. Yan, Acta 55 G. Socrates, Infrared and Raman Characteristic Group
Crystallogr., Sect. E: Struct. Rep. Online, 2006, 62, m2704–
Frequencies, John Wiley@Sons LTD, Manchester, New York,
m2705.
Weinheim, Toronto, Brisbane, Singapore, 2001.
40 H. Liu, W. Gu, G. Xu, Y. Feng, Y. Kou, L. Feng, S. Yan, 56 S. P. Roe, J. O. Hill and R. J. Magee, Monatsh. Chem., 1991,
D. Liao and P. Cheng, Inorg. Chem. Commun., 2007, 10,
1099–1101.
41 E. Pardo, R. Ruiz-García, F. Lloret, M. Julve, J. Cano,
122, 467–478.
57 M. P. Suh, K. S. Min, J. W. Ko and H. J. Choi, Eur. J. Inorg.
Chem., 2003, 1373–1379.
J. Pasán, C. Ruiz-Pérez, Y. Filali, L.-M. Chamoreau and 58 L. Li, Y. Niu, K. Dong, P. Ma, C. Zhang, J. Niu and J. Wang,
Y. Journaux, Inorg. Chem., 2007, 46, 4504–4514. RSC Adv., 2017, 7, 28696–28701.
42 C. Glidewell, G. Ferguson, R. M. Gregson and A. J. Lough, Acta 59 Z. Liang, J. Sun, D. Zhang, P. Ma, C. Zhang, J. Niu and
Crystallogr., Sect. C: Cryst. Struct. Commun., 2000, 174–176. J. Wang, Inorg. Chem., 2017, 56, 10119–10122.
43 C. M. Zakaria, G. Ferguson, A. J. Lough and C. Glidewell, 60 J.-H. Son, C. A. Ohlin, E. C. Larson, P. Yu and W. H. Casey,
Acta Crystallogr., Sect. B: Struct. Sci., 2002, 78–93. Eur. J. Inorg. Chem., 2013, 1748–1753.
44 Y. D. Lampeka, L. V. Tsymbal, A. V. Barna, Y. L. Shuĺga, 61 J.-H. Son, C. A. Ohlin and W. H. Casey, Dalton Trans., 2012,
S. Shova and V. B. Arion, Dalton Trans., 2012, 41, 4118–4125.
41, 12674–12677.
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