Observation of specific intermolecular interactions in the X-ray crystal structure of Cu(I) (1,1,1,3,5,5,5-hepta-fluoropentane-2,4-dionato) (vinyltrimethylsilane)

Article abstract of DOI:10.1016/j.ica.2003.10.022

The determination of the X-ray crystal structure of Cu^(I) (1,1,1,3,5,5,5-heptafluoro-pentane-2,4-dionato) (vinyltrimethylsilane) or Cu(pfac)(VTMS), a close analogue to Cu(hfac)(VTMS), which is the most widely used precursor for copper CVD, gives us an unique insight about the molecular structure of such compounds. In particular, two short F...H distances between CF₃ groups of a molecule and the alkenyl hydrogen atoms of the neighboring molecule reveal intermolecular interactions specifically related to the structure of the VTMS ligand.

Full text of DOI:10.1016/j.ica.2003.10.022

Inorganica Chimica Acta 357 (2004) 1299–1302
www.elsevier.com/locate/ica
Note
Observation of specific intermolecular interactions in the
X-ray crystal structure of Cu(I)
(1,1,1,3,5,5,5-hepta-fluoropentane-2,4-dionato) (vinyltrimethylsilane)
a
a
b
Tai Yuan Chen , Laurent Omnes , Jacqueline Vaisserman , Pascal Doppelt
a,
*
ꢀ
a
ESPCI, Centre dÕEtudes de Chimie Mꢁetallurgique, CNRS UPR 2801, 10 Rue Vauquelin, 75231 Paris Cedex 05, France
b
Laboratoire de Chimie Inorganique et Matꢁeriaux Molꢁeculaires, CNRS 7071, Universitꢁe Pierre et Marie Curie,
4 Place Jussieu, 75252 Paris Cedex 05, France
Received 19 June 2003; accepted 11 October 2003
Abstract
The determination of the X-ray crystal structure of CuðIÞ (1,1,1,3,5,5,5-heptafluoro-pentane-2,4-dionato) (vinyltrimethylsilane) or
Cu(pfac)(VTMS), a close analogue to Cu(hfac)(VTMS), which is the most widely used precursor for copper CVD, gives us an
unique insight about the molecular structure of such compounds. In particular, two short F. . .H distances between CF3 groups of a
molecule and the alkenyl hydrogen atoms of the neighboring molecule reveal intermolecular interactions specifically related to the
structure of the VTMS ligand.
ꢀ 2003 Elsevier B.V. All rights reserved.
Keywords: Cu CVD; Precursor; Intermolecular interaction
1. Introduction
sufficient volatility and deposition of high purity films
via a thermally induced disproportionation reaction [3]:
As a result of the miniaturization race, the semicon-
ductor industry seeks for conductors of low resistivity to
carry the high current density. Copper is an ideal can-
didate for this role as it has a resistivity well below that
of aluminum. Chemical vapor deposition (CVD) is an
adequate process for deposition of copper because it
provides highly conformal films. Therefore, the design
of appropriate precursors is a new field of research for
synthetic chemists. In that context, recent materials
proved to be especially efficient for the deposition of
copper films. In particular, copper (I) complexes in
which copper is coordinated to a fluorinated b-diketone
and the ligand is either an alkyne or an alkene, have
shown great potential [1,2]. Indeed, these species fulfill
most of the requirements of MOCVD processes such as
2ðb-diketonateÞCuIðLÞ ! Cu0 þ CuIIðb-diketonateÞ þ 2L
2
Although several examples of such compounds are
reported in the literature [1,2], little is known about the
relationship between the molecular structure of the
precursors and the CVD deposition process. Here, we
report on the synthesis and the characterization of a new
Cu(I) complex, Cu(pfac)(VTMS) (where pfac ¼ 1,1,1,3,
5,5,5-heptafluoropentane-2,4-dione and VTMS ¼ vinyl-
trimethylsilane), with a particular emphasis of the in-
termolecular interactions revealed by its X-ray crystal
structure.
Among the numerous precursors for copper CVD,
Cu(hfac)(VTMS)
(hfac ¼ hexafluoroacetylacetonate),
trade name Cupraselectꢁ [4], is by far the most widely
used. Recently, a new precursor Cu(hfac)(MHY)ꢁ
(MHY ¼ 2-methyl-1-hexen-3-yne), trade name Giga
Copperꢁ (Merck KGaA product), was synthesized and
gave promising results in terms of deposition tempera-
ture, stability in time, film resistivity and uniformity [2,5].
* Corresponding author. Tel.: +33-1-4079-4528; fax: +33-1-4079-
4425.
E-mail address: pascal.doppelt@espci.fr (P. Doppelt).
0020-1693/$ - see front matter ꢀ 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2003.10.022

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T.Y. Chen et al. / Inorganica Chimica Acta 357 (2004) 1299–1302
Table 1
Although noticeable differences have recently been
ꢂ
Selected bond lengths (A) and angles (ꢂ) related to the X-ray crystal-
lographic molecular structure of Cu(pfac)(VTMS)
reported [6] concerning the properties of Cu(h-
fac)(VTMS) and Cu(hfac)(MHY), such as their volatility
and the deposition rates observed during CVD experi-
ments, no comparison have yet been undertaken between
these two precursors in terms of molecular structure and/
or intermolecular interactions. This lack of information
is mainly due to the difficulty of obtaining a precise X-ray
crystal structure of Cu(hfac)(VTMS). Indeed, the only
structure so far reported [4] simply mentioned a planar
conformation of the Cu(hfac) moiety and the Cu–C
Cu–O(1)
Cu–C(1)
1.967(3)
2.025(6)
1.370(8)
2.025(6)
1.244(6)
1.392(7)
1.385(7)
1.369(6)
1.327(7)
92.5(1)
Cu–O(2)
Cu–C(2)
1.964(3)
2.011(5)
C(1)–C(2)
Cu–C1
O1–C11
Cu–C2
O2–C13
2.011(6)
1.240(6)
1.549(7)
1.880(6)
1.311(6)
1.292(7)
154.5(2)
39.7(2)
C11–C12
C12–C13
C(12)–F(7)
C(14)–F(2)
O(1)–Cu–O(2)
C(1)–C(2)–Si
C11–C14
Si1–C2
C(14)–F(1)
C(14)–F(3)
O(2)–Cu–C(2)
C(1)–Cu–C(2)
ꢂ
ꢂ
(1.99 A) and C@C (1.38 A) bond lengths. On the other
hand, Cu(hfac)(MHY) was fully described [5] as well as
similar compounds such as Cu(tfac)(MHY) and Cu(p-
fac)(MHY). Such difference mainly originates from the
low melting point of Cu(hfac)(VTMS) (mp ¼ 5 ꢂC),
which precludes a good crystallization of the product.
Since Cu(pfac)(MHY) exhibits a higher melting point
than Cu(hfac)(MHY) (mp ¼ 31 and 13 ꢂC, respectively),
it seemed reasonable to envisage a similar effect for
Cu(pfac)(VTMS) versus Cu(hfac)(VTMS). Hence, we
have synthesized Cu(pfac)(VTMS) following the proce-
dure previously reported for similar compounds (see
Section 2). This Cu(I) complex was obtained as a yellow
liquid in a 77% yield which showed a higher melting
point than Cu(hfac)(VTMS), namely 29 ꢂC. In addition,
crystals suitable for X-ray analysis were grown at 5 ꢂC by
sublimation (5 · 10ꢀ2 mBar). The X-ray crystallographic
molecular structure (Fig. 1) is comparable to that re-
ported for Cu(hfac)(VTMS) as the two structures are
both almost perfectly planar like structures of Cu (b-di-
ketone)(L) compounds [5]. The copper–carbon bond
distances (selected bond lengths and angles can be found
124.4(4)
Cu(hfac)(COD) [7–9] (where COD ¼ 1,5-cyclooctadiene)
ꢂ
or 2.011(3) and 2.029(3) A in Cu(hfac)(7-t-BuO-NBD)
(7-t-BuO-NBD ¼ 7-tert-butoxy-2,5-norbornadiene) [10].
ꢂ
The C@C bond length of 1.370(8) A is remarkably close
to the equivalent distance reported for Cu(hfac)(VTMS).
The C(1)@C(2)–Si angle value was found to be 124.4(4)ꢂ,
which is somewhat higher than the expected 120ꢂ.
This distortion can be attributed to the bulky nature
of the Si(Me)3 group which can also be at the origin of
the high dihedral angle between the Cu(C@C) and
C@C–Si plans (99ꢂ instead of the expected value of 90ꢂ).
Remarkably, the F–Csp3 bonds (–CF3, averaged at 1.31
2
ꢂ
A) are slightly shorter than the F(7)–Csp bond
3
2
ꢂ
(1.369(6) A) although F–Csp bonds and F–Csp bonds
ꢂ
are commonly reported to be equal to 1.38 and 1.35 A.
However, this inversion was already observed in the case
of Cu(pfac)(MHY) [5] and short F–Csp3 bonds are
frequently observed in CF3-containing organic com-
pounds [11]. In the three dimension cell, the molecules
adopt a stacked structure with one molecule oriented in
the opposite direction to its neighbor giving a structure
in which short intermolecular distances (dimers) of
ꢂ
in Table 1), 2.025(6) and 2.011(5) A are very similar to
the corresponding distances found in the Cu(hfac)(al-
ꢂ
kene) family (between 2.013(5) and 2.277(7) A) in
ꢂ
3.304(27) A alternate with long intermolecular distances
ꢂ
of 4.224(27) A. The longest intermolecular distance
corresponds to the situation where the –Si(Me)3 groups
of neighboring molecules point towards each other,
giving rise to repulsive forces between bulky groups.
On the other hand the short intermolecular interac-
tions found their origin in the presence of weak hydro-
gen bond between two fluorine of two different CF3
groups and two hydrogen of the C@C bond as repre-
sented in0 Fig. 2. The F. . .H distances, F4. . .H20 and
ꢂ
F1. . .H11 are respectively 2.35(6) and 2.49(3) A show-
ing that these intermolecular interactions are weak in
comparison with those existing in liquid HF
ꢂ
(F. . .H ¼ 1.20 A) but rather close to the shortest C–
ꢂ
F. . .H–C interactions of 2.30 A reported in the literature
[12]. Although the same type of arrangement of the
molecules was observed for Cu(pfac)(MHY), there was
no report of such F. . .H interactions involving the CF3
groups. As a contrary, the shortest F. . .H distance ob-
Fig. 1. Representation of the X-ray crystallographic molecular struc-
ture of Cu(pfac)(VTMS), showing a 30% probability thermal ellip-
soids.
ꢂ
served (2.421(4) A) result from the interaction between

T.Y. Chen et al. / Inorganica Chimica Acta 357 (2004) 1299–1302
1301
tane. 1,1,1,3,5,5,5-Heptafluoroacetylacetone (2.5 g, 16
mmol, ABCR) was added dropwise to the magnetically
stirred solution which contained 2.3 ml (11 mmol) of
vinyltrimethylsilane (VTMS, ABCR). The mixture was
stirred throughout the addition and for a further 30 min.
The brick-red cuprous oxide was suspended in the so-
lution, which had become yellow-green as the reaction
proceeded. Excess Cu2O was filtered off and the pentane
solution purified by flash chromatography under nitro-
gen with a 1.3 in. (diameter) by 5 in. (height) alumina
column (6 g). After chromatography and distillation of
the solvent, Cu(pfac)(VTMS) was obtained as a yellow
liquid in a 77% yield. mp ¼ 29 ꢂC. IR(neat): 3282 (w),
2958 (m), 2899 (w), 1647 (s), 1530 (m), 1478 (m), 1451
(s), 1352 (m), 1271 (s), 1219 (s), 1197 (s), 1155 (s), 1059
(w), 970 (w), 842 (s), 761 (m), 720 (w), 677 (m), 674 (m),
597 (m) cmꢀ1. 1H NMR (CDCl3, 298 K), d (ppm): 0.2 (s,
CH3), 4.65 (m, CH), 4.96 (m, CH2). 13C NMR (CDCl3,
298 K), d (ppm): )1.3 (s, CH3), 90.8 (s, CH), 101.9 (s,
CH2), 117.9 (q, 284 Hz, CF3), 141.8 (d, 230 Hz, CF),
178.4 (q, 34.4 Hz, C@O). 19F NMR (CFCl3 as stan-
dard), d (ppm): )183.9 (d, 17 Hz, CF), )70.7 (d, 17 Hz,
CF3).
Fig. 2. Intermolecular interactions between two hydrogen atoms of the
vinyl group and two fluorine atoms of the CF3 groups in Cu(p-
fac)(VTMS).
2.2. X-ray crystallographic analysis for Cu(pfac)
(VTMS)
the fluorine atom in position 3 on the b-diketone moiety
(i.e. F7) and the hydrogens atoms of the free double
bond. Since the intermolecular interactions identified in
the case of Cu(pfac)(VTMS) are not specifically related
to the structure of the (pfac) ligand (i.e. F7 do not get
involved), one might consider that they most probably
also exist in Cu(hfac)(VTMS). Thus, a change of ligand
from VTMS to MHY not only changes the chemical
nature of the compound but also influences the inter-
molecular interactions. Such differences might have re-
percussion on the behavior of the molecules in the gas
phase and more specifically at the substrate surface
during the deposition process.
Those observations highlight the influence of inter-
actions at the molecular level on the deposition mech-
anism. Hence, further studies are needed to better
understand the relation between the chemical nature of
the precursors and the structural nature of the films,
especially in terms of conformality and contamination
by hetero-atoms such as fluorine atoms.
Accurate cell dimensions and orientation were ob-
tained by least-squares refinements of 25 accurately
centered reflections. No significant variations were ob-
served in the intensities of two checked reflections dur-
ing data collection. The data were corrected for Lorentz
and polarisation effects. Computations were performed
using the PC version of CRYSTAL [13]. Scattering
factors and corrections for anomalous absorption were
found in the literature [14]. The structures were solved
by direct methods (SHELXS) [15,16]. The final refine-
ments were carried out by full-matrix least-squares using
anisotropic displacements parameters for all non-hy-
drogen atoms. Hydrogen atoms were introduced in
calculated positions and only one overall isotropic dis-
placement parameter was refined. Crystal data for
C10H12CuF7O2Si: M ¼ 388:8, monoclinic, Space group
ꢂ
ꢂ
ꢂ
P2/n, a ¼ 13:469(7) A, b ¼ 8:418(6) A, c ¼ 13:613(8) A,
3
ꢀ3
,
ꢂ
b ¼ 95:86(5)ꢂ, V ¼ 1535(2) A , Z ¼ 4, Dc ¼ 1:68 g cm
2
N ¼ 3019, Nind ¼ 2687 (R ¼ 0:05), Nobs ¼ 1622 ððF0Þ >
P
P
2
3rðF0Þ Þ, R ¼ kF0k ꢀ jFcj= jF0j ¼ 0:0441, Rw ¼
P
P
2
2 1=2
½
wðjF0j ꢀ jFcjÞ = wjF0j ꢁ ¼ 0:0534.
2. Experimental
2.1. Synthesis and characterisation of Cu(pfac)(VTMS)
3. Supplementary material
A three neck round-bottom flask was loaded, under
an atmosphere of nitrogen, with 1.6 g (11 mmol) of
Cu2O (Aldrich) and 20 ml of spectroscopic grade pen-
Atomic coordinates, bond lengths, angles and
thermal parameters are available at the Cambridge
Crystallography Data Centre.

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