Unsolvated homo- and heterometallic highly fluorinated β-diketonate complexes of copper(II)

Article abstract of DOI:10.1016/j.poly.2018.09.048

The unsolvated Cu(II) complex with bis(pentafluorobenzoyl)methanide ligand (L, C₆F₅COCHCOC₆F₅^?) is prepared and crystallized as [CuL₂] (1) using gas phase sublimation-deposition at 150 °C. The X-ray crystallographic characterization confirmed the centrosymmetric mononuclear structure of 1 with a square planar geometry around Cu(II) (Cu–O_av 1.9149(8) ?). The reaction of 1 with sodium hexafluoroacetylacetonate [Na(hfac)] in a solvent-free environment afforded [Na₂Cu₂L₄(hfac)₂] (2), the first heterometallic Na–Cu β-diketonate characterized by single-crystal X-ray diffraction. In the centrosymmetric tetranuclear structure of 2, a dimeric [Na(hfac)]₂ unit is sandwiched between two CuL₂ units. The L-ligands function as chelating-bridging between Cu and Na through one of their O-atoms. The hfac ligands are chelating-bridging between Cu and Na and between Na(1) and Na(1A) through both O-atoms. In addition to the five primary Na–O interactions (av. 2.4109(17) ?), three secondary Na–F contacts (av. 2.6006(15) ?) contribute to the overall distorted square antiprismatic coordination environment for Na. The geometry of Cu is square pyramidal with Cu–O(L) distances averaging at 1.922(14) ? and Cu–O(hfac) of 2.3021(15) ?. Thermal decomposition of 2 yields a mixture of NaCuF₃, Na₂CuF₄ and NaF, when conducted at 230 °C in argon at ambient pressure.

Full text of DOI:10.1016/j.poly.2018.09.048

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Polyhedron 157 (2019) 33–38
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Unsolvated homo- and heterometallic highly fluorinated b-diketonate
complexes of copper(II)
⇑
⇑
Janell M. Crowder, Haixiang Han, Zheng Wei, Evgeny V. Dikarev , Marina A. Petrukhina
Department of Chemistry, University at Albany, State University of New York, Albany, NY 12222, USA
a r t i c l e i n f o
a b s t r a c t
The unsolvated Cu(II) complex with bis(pentafluorobenzoyl)methanide ligand (L, C6F5COCHCOC6Fꢀ5 ) is
prepared and crystallized as [CuL2] (1) using gas phase sublimation-deposition at 150 °C. The X-ray crys-
tallographic characterization confirmed the centrosymmetric mononuclear structure of 1 with a square
planar geometry around Cu(II) (Cu–Oav 1.9149(8) Å). The reaction of 1 with sodium hexafluoroacetylace-
tonate [Na(hfac)] in a solvent-free environment afforded [Na2Cu2L4(hfac)2] (2), the first heterometallic
Na–Cu b-diketonate characterized by single-crystal X-ray diffraction. In the centrosymmetric tetranu-
clear structure of 2, a dimeric [Na(hfac)]2 unit is sandwiched between two CuL2 units. The L-ligands func-
tion as chelating-bridging between Cu and Na through one of their O-atoms. The hfac ligands are
chelating-bridging between Cu and Na and between Na(1) and Na(1A) through both O-atoms. In addition
to the five primary Na–O interactions (av. 2.4109(17) Å), three secondary Na–F contacts (av. 2.6006
(15) Å) contribute to the overall distorted square antiprismatic coordination environment for Na. The
geometry of Cu is square pyramidal with Cu–O(L) distances averaging at 1.922(14) Å and Cu–O(hfac)
of 2.3021(15) Å. Thermal decomposition of 2 yields a mixture of NaCuF3, Na2CuF4 and NaF, when con-
ducted at 230 °C in argon at ambient pressure.
Article history:
Received 1 August 2018
Accepted 18 September 2018
Available online 26 September 2018
Keywords:
Copper
Sodium
X-ray diffraction
Fluorinated ligands
Heterometallic complexes
Ó 2018 Elsevier Ltd. All rights reserved.
1. Introduction
metal centers that are apt to additional coordination [5]. The elec-
tron-withdrawing nature of fluorinated ligands further enhances
Fluorinated b-diketonates are valued for their high volatility
and solubility, superior mass-transport properties, and improved
thermal stability relative to the non-fluorinated analogues [1].
Consequently, they are utilized extensively in various chemical
vapor deposition (CVD) processes for the deposition of metal,
metal oxide, and fluorine-doped metal oxide thin films and as pre-
cursors to metal fluorides and oxyfluorides [1b,1c,2]. A great num-
ber of transition metal fluorinated b-diketonates has been
synthesized and interrogated as CVD precursors, as summarized
in a recent comprehensive review [1b].
Fluorinated Cu(II) b-diketonates are some of the more thor-
oughly studied transition metal compounds of this type due to
the critical application of copper metal in the manufacture of inte-
grated circuits [2b,3] and the need for volatile sources of Cu(II) for
the metal–organic CVD (MOCVD) production of superconducting
cuprate YBCO films [2a,4]. Copper b-diketonate complexes without
exogenous ligands are of particular interest for the above applica-
tions as well as due to the presence of coordinatively unsaturated
the Lewis acidity of the metal center and increases the tendency
of the metal to bind to ancillary ligands [6]. Several partially
fluorinated Cu(II) b-diketonates without exogenous ligands have
been structurally characterized by X-ray crystallography [7], but
it is of note that only two fully fluorinated Cu(II) b-diketonates
have been reported, namely [Cu(hfac)2] [8] and [Cu(pfh)2]
(pfh = 1,1,1,5,5,6,6,6-octafluoro-2,4-hexanedionate) [9].
Understanding the influence of electron-withdrawing fluori-
nated ligands on metal complexation has led to advances in many
fields. An area of growing interest is the use of fluorinated b-dike-
tonates in the synthesis of unsolvated heterometallic compounds
of Na or Li with transition or rare earth metals which, when pre-
pared with the proper metal stoichiometry, are used as single-
source MOCVD precursors for heterometallic fluorides [10]. When
studying the catalytic performance of copper(II) b-diketonate com-
plexes in ring expansion and rearrangement reactions of vinyl
derivatives, it was found that the most fluorinated, and thus the
most electrophilic, complexes outperformed the lesser- or non-flu-
orinated counterparts [7i,11]. Fluorinated Cu(I) carboxylates have
likewise shown impressive photoluminescent properties and
structural diversity driven by changes in the degree of ligand fluo-
rination and bulkiness [12]. Furthermore, the structural study of
⇑
Corresponding authors.
E-mail addresses: edikarev@albany.edu (E.V. Dikarev), mpetrukhina@albany.edu
(M.A. Petrukhina).
https://doi.org/10.1016/j.poly.2018.09.048
0277-5387/Ó 2018 Elsevier Ltd. All rights reserved.

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J.M. Crowder et al. / Polyhedron 157 (2019) 33–38
fluorinated coordination complexes and organofluorine com-
pounds has advanced the understanding of the role of fluorine in
supramolecular packing as it relates to the design of advanced
functional materials, enhanced doping, crystal engineering, and
molecular recognition processes in medicinal chemistry [13].
These remarkable properties and applications stimulate continued
interest in synthesis and study of highly electrophilic homo- and
heterometallic b-diketonates.
Herein, we target the isolation of the unsolvated Cu(II) complex
[CuL2] (1) with highly-fluorinated bis(pentafluorobenzoyl)metha-
nide ligands followed by testing its ability to serve as a metallo-
ligand or ligand-transfer reagent. We used high volatility and
coordinatively unsaturated ability of the above copper complex
to synthesize [Na2Cu2L4(hfac)2] (2), the first heterometallic
Na–Cu b-diketonate characterized by X-ray crystallography.
2. Results and discussion
2.1. Synthesis and crystal growth
The preparation of unsolvated [CuL2] (1) in the single-crys-
talline form suitable for X-ray crystallographic characterization
began with the synthesis of benzene-solvated [CuL2]ꢁ3(C6H6)
adduct as previously reported [14], except that anhydrous starting
reagents and dry solvents were employed in an oxygen-free and
moisture-free environment (see Supporting Information (SI) for
more details). Superstitial benzene was removed by heating in
vacuo, and single crystals of 1 were grown using a small-scale sub-
limation-deposition method at 150 °C in 3 days. This procedure
was optimized to produce bulk crystals of 1 in ca. 80% yield, allow-
ing the effective use of 1 in subsequent reactions. The purity of
bulk crystalline product was confirmed by comparing the X-ray
powder diffraction pattern to the one calculated from the single
crystal data (see Fig. S11 and Table S9). The preparation of 1 in
the unsolvated form was a critical step which allowed the explo-
ration of its synthetic potential in further reactions. The avidity
of 1 for additional coordination has been illustrated by the forma-
tion of [CuL2(H2O)] (3) crystallized from regular hexanes via slow
evaporation of the solvent at room temperature (see SI for the
details). This experimental evidence further reinforced the need
to use the high-quality anhydrous solvents or solvent-free condi-
tions when 1 is utilized as a new metallo-ligand.
For the next step, bulk crystals of 1 were combined with sodium
hexafluoroacetylacetonate [Na(hfac)] in a 1:1 molar ratio and the
mixture was sealed under vacuum in a small glass ampule. The
ampule was heated at 120 °C for 7 days resulting in the formation
of bright teal green product, [Na2Cu2L4(hfac)2] (2), in nearly quan-
titative yield. The purity of the bulk crystalline product was con-
firmed by X-ray powder diffraction analysis (see Fig. S12 and
Table S10). The X-ray quality single crystals of 2 were grown at
slightly lower temperature in a 110 °C oven with ca. 5 °C tempera-
ture gradient in 10 days (yield 60–80%). To the best of our knowl-
edge, the only other known Na–Cu heterometallic b-diketonate
derivative is b-diketonatofluoroalkoxide [NaCu{OCH(CF3)2}2
(thd)]m (thdH = 2,2,6,6-tetramethylheptane-3,5-dione) [15]. This
mixed-ligand complex, comprised of fluoroisopropoxide and non-
fluorinated b-diketonate ligands, was characterized by elemental
analysis, IR, and mass spectrometry; however, an X-ray crystallo-
graphic investigation was not reported.
Fig. 1. Molecular structure of 1. Color scheme: copper – blue; oxygen – red; carbon
– grey; fluorine – green. Hydrogen atoms are omitted. Carbon atoms C(7), C(8) and
C(9) deviate slightly from the Cu–O(L) plane by 0.127, 0.300 and 0.259 Å,
respectively. (Color online.)
contains only one bis(pentafluorobenzoyl)methanide ligand (L).
The copper coordination environment is square planar with Cu–O
(1) and Cu–O(2) bond distances of 1.9063(8) and 1.9236(7) Å,
respectively. These distances are within the range of those
reported for related Cu(II) diketonate structures (Table 1)
[7c,8,14,16]. The pentafluorophenyl groups of L are twisted relative
to the metal–oxygen coordination plane with dihedral angles of
36.4 and 68.9° between the [O(1)–O(2)–O(1A)–O(2A)] plane and
the planes created by the aromatic rings D and E (Fig. 1). Further-
more, the planes formed by rings D and E are nearly orthogonal
with an angle of 87.1°. For comparison, the pentafluorophenyl
groups in [CuL2]ꢁ3(C6H6) [14] are similarly twisted, whereas the
dibenzoylmethanato (dbm) ligands in [Cu(dbm)2] [16] (the non-
fluorinated analogue of 1) are nearly coplanar with the metal–oxy-
gen plane. The X-ray single-crystal data and structure refinement
parameters of 1 are given in Table S5, and the thermal ellipsoid
plot is shown in Fig. S5. Bond angles for 1 are listed in Table S6,
and an alternative view of 1, illustrating the planarity of the
Cu–O core and the twisted nature of L, is shown in Fig. S6.
In the solid state, the molecules of 1 form the columns down the
crystallographic a-axis with intermolecular C–Fꢁ ꢁ ꢁpF interactions
between C(15)–F(10) of one molecule and pentafluorophenyl ring
D of the adjacent molecule (Fig. S7), and the distances and angles
are similar to those previously reported [7c,17]. The distance
Table 1
Comparison of interatomic distances between 1 and related structurally characterized
copper diketonates.
Cu–O distances (Å)
O–C distances (Å)
[CuL2] (1) [a]
1.9063(8), 1.9236(7)
1.932(2), 1.923(2) [b]
1.9104(13), 1.9295(14)
1.9100(19), 1.9216(18)
1.892(3), 1.914(3)
1.2714(12), 0.2681(12)
1.265(3), 1.270 (3)
1.265(3), 1.268(3)
1.271(3), 1.271(3)
1.274(5), 1.266(5)
1.259(2), 1.264(3)
[CuL2(H2O)] (3) [a]
[CuL2]ꢁ3(C6H6) [14]
[CuL02] [7c]
[Cu(dbm)2] [16]
[Cu(hfac)2] [8]
2.2. X-ray crystallographic study
1.914(2), 1.924(2)
The unsolvated mononuclear complex [CuL2] (1) (Fig. 1) crystal-
ꢀ
lizes in the centrosymmetric space group P1 with the copper atom
[a] This work.
[b] Cu–O(L) distances. L0 = C6H5COCHCOC6Fꢀ5 . dhm = C6H5COCHCOC6Hꢀ5 .
residing on the inversion center. The asymmetric unit therefore

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J.M. Crowder et al. / Polyhedron 157 (2019) 33–38
35
between F(10) and the plane of ring D is 3.089 Å and between F(10)
and ring D centroid (CgD) is 3.201 Å. The C(15)–F(10)–CgD angle is
151.3°. The highly twisted orientation of the pentafluorophenyl
rings permits intermolecular pF–pF interactions between pentaflu-
orophenyl groups of neighboring molecules in adjacent columns in
both the b- and c-axis directions (Fig. 2). Ring D of one molecule
interacts with ring D0 of a second molecule located in the neighbor-
ing column (moving across to the next column in the b-direction
and down one molecule in the a-direction). Ring E of one molecule
interacts with ring E0 of a second molecule directly across to the
adjacent column in the c-direction. Each pair of interacting rings
have an offset face-to-face (off) alignment with separations of
3.467 and 3.293 Å between the Dꢁ ꢁ ꢁD0 and Eꢁ ꢁ ꢁE0 planes, respec-
tively. These separations are on par with those reported for other
perfluoroaryl pF–pF interactions (3.23–3.62 Å) [14,18].
The Na–Cu heterometallic b-diketonate compound (2) crystal-
lizes in the space group P1. It possesses a centrosymmetric
Fig. 3. Molecular structure of 2. Only the Na, Cu and O atoms of the asymmetric
unit are labeled. Interactions between sodium and fluorine atoms are indicated by
dashed lines. Color scheme: copper – blue; sodium – purple; oxygen – red; fluorine
– green. Hydrogen atoms are omitted. (Color online.)
ꢀ
tetranuclear molecular structure with two neutral electrophilic
Na(hfac) units at the center terminated by a neutral CuL2 unit on
each end (Fig. 3). Both L ligands of the CuL2 unit act as bridging
to sodium atoms through one oxygen each (O(2) and O(4)). The
second oxygen atom of each L ligand (O(1) and O(3)) is purely
chelating to Cu. Each hfac ligand is chelating-bridging through
both of its oxygen atoms – between Na(1) and Cu(1) through O
(5) on one side and between Na(1) and Na(1A) through O(6) on
the other. The X-ray single-crystal data and structure refinement
parameters of 2 are given in Table S5, and the thermal ellipsoid
view of the asymmetric unit is presented in Fig. S8. The full list
of bond distances and bond angles for 2 can be found in Table S7.
Considering the coordination environment of copper (Fig. 4), it
can be seen that the Cu(II) center exhibits square pyramidal coor-
dination formed by oxygen atoms. The purely chelating Cu–O(L)
bonds (av. 1.9109(14) Å) are slightly shorter than the chelating-
bridging Cu–O(L) bonds (av. 1.9416(14) Å). The Cu–O chelating-
bridging bond with O(5) (2.3021(15) Å) of the hfac ligand, located
in the axial coordination position, is significantly longer due to the
Jahn-Teller effect [19]. This distance is comparable to the Cu–O
(H2O) distance (2.289(4) Å) observed in 3 for water coordinated
Fig. 4. Fragment of the solid-state structure of 2 showing the square pyramidal
coordination environment of the copper atom. Ring F = C(1)–C(2)–C(3)–C(4)–C(5)–C
(6); ring G = C(10)–C(11)–C(12)–C(13)–C(14)–C(15); ring H = C(16)–C(17)–C(18)–C
(19)–C(20)–C(21); ring I = C(25)–C(26)–C(27)–C(28)–C(29)–C(30).
in the apical position and to other reported Cu–O distances for oxy-
gen atoms located in the apical position of square pyramidal cop-
per [5c,7b,8,20]. The Cu–O(L) coordination environment in 2 is
less planar compared to 1 because the pentafluorophenyl groups
are pushed outward to make room for the hfac ligand. The copper
atom moves above the O(L) plane by 0.162 Å, while C(7), C(8), C(9),
C(22), C(23) and C(24) atoms deviate by 0.136–0.506 Å below the
plane resulting in a slightly curved (boat) arrangement of the L
ligands away from the hfac ligand coordinated to Cu. As in 1, the
pentafluorophenyl groups are twisted relative to the basal oxygen
coordination plane with dihedral angles of 80.5, 61.4, 32.6 and
54.1° between the [O(1)–O(2)–O(4)–O(3)] plane and each of the
planes created by pentafluorophenyl rings F, G, H and I (Fig. 4).
Considering the sodium center, a fragment of the solid-state
structure of 2 depicting its coordination environment is shown in
Fig. 5. As previously mentioned, one oxygen atom from each of
the L ligands is bridging between sodium and copper with Na–O
distances of 2.4986(17) Å and 2.5112(16) Å for Na(1)–O(2) and
Na(1)–O(4), respectively. Both oxygen atoms of the hfac ligand, O
(5) and O(6), serve as chelating-bridging. Na and Cu are bridged
by O(5) with the Na(1)–O(5) distance of 2.3390(16) Å, and Na(1)
and Na(1A) are bridged by O(6) with the Na(1)–O(6) distance of
2.3355(17) Å. Due to the inversion symmetry operation, Na(1)
and Na(1A) are also bridged by O(6A) at 2.3702(16) Å. In addition
Fig. 2. (a) Crystal packing in the structure of 1 showing the columnar arrangement
of molecules down the a-axis and the intermolecular off pF–pF interactions between
pentafluorophenyl groups indicated by dashed orange (CgDꢁ ꢁ ꢁCgD0) and purple
(CgEꢁ ꢁ ꢁCgE0) lines; CgX represents the centroid of ring X. (b) Space-filling model
showing a single instance of the Eꢁ ꢁ ꢁE0 off pF
–pF paired interaction. Color scheme:
copper – blue; oxygen – red; fluorine – green. Hydrogen atoms are omitted. (Color
online.)

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J.M. Crowder et al. / Polyhedron 157 (2019) 33–38
is 3.029 Å and the C(12)–F(7)ꢁ ꢁ ꢁ
pF(centroid) angle is 144.5° [7c,17].
The distance between F(7) and the plane of the C6F5 ring is 2.970 Å.
Two instances of intermolecular C–Hꢁ ꢁ ꢁF–C short contacts are
observed in 2, although none are present in 1. The H(8) and H(23)
atoms of the L ligands interact with F(4) and F(1) of neighboring
molecules at the distances of 2.641 and 2.639 Å, respectively. The
angles of interaction are 150.0 and 141.5° for C(8)–H(8)ꢁ ꢁ ꢁF(4) and
C(23)–H(23)ꢁ ꢁ ꢁF(1). These distances and angles are consistent with
the previously reported C–Hꢁ ꢁ ꢁF interactions [17a,18c,18d,23].
Although C–Hꢁ ꢁ ꢁF–C and C–Fꢁ ꢁ ꢁ
pF interactions are weak, it has been
shown that they can influence crystal packing when stronger inter-
actions are not present [13].
2.3. Thermal decomposition study
Thermal decomposition of 2 has been investigated in the range
of temperatures from 150 to 280 °C with the time varying from 0.5
to 24 h. No decomposition was observed below 180 °C when the
sample was heated for up to 24 h. Weak signals from the target
decomposition products, NaCuF3 and Na2CuF4, were detected by
X-ray powder diffraction analysis following experiments con-
ducted at 200 and 215 °C for short periods of time (30 min), but
all NaCuF3 was lost when compound 2 was heated at 210 °C for
4 h. The strongest X-ray powder diffraction signals corresponding
to decomposition products NaCuF3 and Na2CuF4 were observed
when utilizing 230 °C for a short time. Specifically, it was found
that heating 2 for 30 min at 230 °C under argon at ambient pres-
sure results in the formation of a mixture of NaCuF3, Na2CuF4
and NaF (see Fig. S13 and Table S11 for X-ray powder diffraction
pattern and Le Bail fit of unit cell parameters compared to the lit-
erature values). Decomposition at 230 °C for 2 h resulted in the loss
of NaCuF3; and decomposition at 230 °C for 24 h resulted in the
loss of both NaCuF3 and Na2CuF4. Decomposition at temperatures
over 230 °C caused loss of all mixed-metal products.
Fig. 5. Fragment of the solid-state structure of
2 showing the coordination
environment of the sodium atom. For clarity, only half of each ligand is shown
when the other half is chelating-bridging to copper or to the other sodium atom.
R = CF3.
to the five primary interactions with oxygen atoms, three fluorine
atoms, F(10), F(20), and F(26), interact with sodium at distances of
2.6307(16), 2.5062(15) and 2.6648(16) Å. These values are smaller
than the sum of the van der Waals radii [21] and are on par with
Naꢁ ꢁ ꢁF interactions reported in literature (ranging from 2.3 to
3.0 Å) [10b,22]. Therefore, the sodium atom coordination can be
described as distorted square-antiprismatic composed of five
oxygens and three fluorine atoms.
The formation of a mixture of decomposition products is con-
gruous with the gas-phase composition of 2 observed by DART-
MS (direct analysis in real time mass spectrometry) (Fig. S2, Tables
S3 and S4) in which various heterometallic ion fragments with Na-
Cu ratios of 1:1, 2:1 and 1:2, such as [NaCuL(hfac)]+, [Na2CuL2(-
hfac)]+ and [NaCu2L3(hfac)]+, are present along with several
homometallic fragments containing Cu and L.
In the solid state, the molecules of 2 pack in rows keeping the
same orientation within each row (Fig. 6). In contrast to 1, no
pF–pF interactions are formed. However, similar to 1, an intermolec-
3. Conclusions
ular C–Fꢁ ꢁ ꢁpF interactions occur between C(12)–F(7) of ring G and
pentafluorophenyl ring I [C(25)–C(26)–C(27)–C(28)–C(29)–C(30)]
In this work, we prepared the unsolvated complex [CuL2] (1) in
of the neighboring molecule where the F(7)ꢁ ꢁ ꢁ
pF(centroid) distance
bulk crystalline form using gas-phase sublimation-deposition
Fig. 6. Packing diagram of 2 rendered as space-filling models. Only [Na2Cu2O8] cores are shown for clarity. Color scheme: copper – blue; sodium – purple; oxygen – red.
(Color online.)