Crystal Growth & Design
Article
mL of Na2CO3/NaHCO3 (0. , pH = 10) buffer solution, K7HNb6O19·
13H2O (0.25 g, 0.18 mmol), Cu(AC)2·H2O (0.13 g, 0.65 mmol),
Na3AsO4·12H2O (0.013 g, 0.06 mmol), Sb2O3 (0.01 g, 0.03 mmol),
en (0.25 mL), and KCl (0.05 g, 0.67 mmol) was stirred for 3 h, and
the pH of the mixture was necessarily adjusted to 12.5 with KOH (2
M) solution. The mixture was transferred into an 18 mL Teflon-lined
autoclave and heated under autogenous pressure at 140 °C for 5 days
and then left to cool to room temperature. After that, the resulting
solution was filtered and the filtrate was slowly evaporated at room
temperature. Deep purple single crystals were obtained after 10 days.
Yield: 55% based on Nb. Anal. Calcd for C61H534.6Cu15.25K2N61-
Nb48O281.6: Nb, 36.74; Cu, 7.98; K, 0.64; C, 6.04; N, 7.04; H, 4.41.
Found: Nb, 36.58; Cu, 7.95; K, 0.56; C, 6.06; N, 7.00; H, 4.20.
X-ray Crystallography. The single-crystal diffraction data of
compounds 1−3 were obtained on a Bruker Smart-CCD diffrac-
tometer with a Mo Kα radiation (λ = 0.710 73 Å). The data collected
temperatures are 300(2), 211(2), and 200(2) K for compounds 1−3,
respectively. In no data collection was evidence for crystal decay
encountered. The three structures were solved by direct methods and
refined using full-matrix least-squares method on F2 using the
SHELXTL-2014/7 program50,51 incorporated into the program
package Olex2.52 In final refinements, all non-hydrogen atoms were
refined with anisotropic displacement parameters except about 70
water molecules in compound 3, for there are too many atoms to be
refined anisotropically even using the XH software. The hydrogen
atoms of en ligands were placed in idealized positions and refined as
rigid atoms with the relative isotropic displacement parameters, while
hydrogen atoms of water molecules were not found from a difference
Fourier map and not included in the calculation. In addition, there are
also some hydrogens attached on cluster shells of the three
compounds for balancing the charge of the compounds. Unfortu-
nately, these plausible hydrogens cannot be located in the difference
Fourier maps. We also conduct the BVS calculations for attempting to
locate the exact positions of these hydrogens but not successfully. We
think these hydrogens attached on the cluster shells should be
distributed disorderedly. Therefore, the numbers of the proposed H
atoms of the chemical formula of the three compounds are
determined on the basis of the chemical analyses and the charge
balancing requirements of the formula. Some undissolved A- and/or
B-Alerts have been explained as validation reply forms in the CIF files.
One copper complex in compound 1 is severely disordered, and the
disordered model is depicted in Figure s1. Crystal data are listed in
compound 2, and 2021809 for compound 3.
Figure 1. Ellipsoid representation of the bowl-shaped
13.75−
[KNb24O72H9.25
]
anion in compound 1.
bridging Ob atoms from its corresponding {Nb6O19} cluster,
two bridging Ob atoms shared by two {NbO6} octahedra of the
B-group, and a terminal Ot atom, while each Nb of the B-group
is connected to two Ob atoms shared by two adjacent
{Nb6O19} clusters, two Ob atoms shared by two {NbO6}
octahedra of the A-group and two terminal oxygens. There are
only two kinds of oxygens in the {Nb6O30}, which are terminal
oxygens with Nb−Ot distances of 1.72(1)−2.52(1) Å and
bridging oxygens with Nb−Ob distances of 1.93(1)−2.29(1)
Å. Due to the longer distance of the K−O, the K+ is nine-
coordinated with six bridging oxygen atoms and three terminal
oxygen atoms with K−O distances of 2.74(1)−3.14(1) Å.
Single-crystal analysis suggests that compound 1 crystallizes
in the P1
[KNb2 4 O7 2 H9 . 2 5
̅
space group. The asymmetric unit is composed of a
1 3 . 7 5 −
]
, , 2
4. 875 [Cu(en)2 ]2 +
[Cu(en)2(H2O)]2+, and 18.25 lattice water molecules. The
crystallographically independent copper atoms form two
different types of complexes: [Cu(en)2(H2O)]2+ and
[Cu(en)2]2+. The copper center of the former exhibits a
distorted square-pyramidal geometry with four nitrogens
coming from two en and one oxygen coming from a water
molecule with Cu−N distances of 1.92(2)−2.14(4) Å and
Cu−O distances of 2.17(3)−2.7872(2) Å. As for [Cu(en)2]2+,
the copper showing a square-planar geometry is only bonded
to four nitrogens coming from two en ligands with comparable
Cu−N distances. The [Cu(en)2]2+ can be further classified
into three subgroups based on contacts of the copper centers
RESULTS AND DISCUSSION
■
Crystal Structure of Compound 1. Since the three
compounds include almost the same cluster anions, here the
anion of compound 1 is described in detail as an example
(Figure 1). The shape of the cluster is like a “bowl”; it consists
of three {Nb6O19} clusters that serve as the top “bowl” edges
and a cyclic {Nb6O30} fragment serving as the bottom of the
“bowl”. In addition to that, there is a K+ located at the center of
the {Nb6O30} fragment (Figure 1). The “bowl” anion has 24
Nb atoms and interesting coordination patterns. There are
three types of oxygens in the {Nb6O19}: terminal oxygens with
Nb−Ot distances of 1.76(1)−1.86(1) Å, central oxygens with
Nb−Oc distances of 2.25(1)−2.47(1) Å, and bridging oxygens
with Nb−Ob distances of 1.87(1)−2.13(1) Å. It is worth
mentioning that due to the participation of the {Nb6O30}, the
distances of Nb−Ot and Nb−Ob involved in the connections
have been lengthened to a certain extent.
and oxygens from [KNb24O72H9.25]
13.75−. The Cu(3), Cu(4),
Cu(5), and Cu(8) coppers belong to the first subgroup, each
copper of them not only shows interactions with four nitrogens
originating from two en ligands but also has strong contacts
with oxygens from [K0.5Nb24O72H7.75]
13.75−, presenting also a
distorted square-pyramidal geometry. The Cu(6) copper form
the second subgroup, interacting with two oxygens originating
13.75−
from two neighboring [K0.5Nb24O72H7.75
]
as well as four
nitrogens coming from two en ligands. Therefore, Cu(6) serve
13.75−
As for the cyclic {Nb6O30} fragment, its six {NbO6}
octahedra can be divided into two three-member groups: A-
group and B-group (Figure s2). As we can see, each Nb from
the A- and B-groups are connected alternately by sharing two
oxygens. Each Nb of the A-group coordinates with three
as an inorganic bridge joining two [K0.5Nb24O72H7.75
]
to
form a dimer, while Cu(3), Cu(4), Cu(5), and Cu(8)
13.75−
complexes are only supported by [K0.5Nb24O72H7.75
]
to
form the POM-supported complex (Figure 2). The two
remaining Cu(9) and Cu(10) (Cu(11)) complexes belong to
C
Cryst. Growth Des. XXXX, XXX, XXX−XXX