Packing polymorphism of dicarbonyl-[2-(phenylamino)pent-3-en-4-onato]rhodium(I)

Article abstract of DOI:10.1016/j.jorganchem.2017.09.039

Depending on the crystallization conditions, the interaction between the rhodium metal centres of the separate [Rh(CH₃COCHCN(Ph)CH₃)(CO)₂] molecular units, as described by the interplanar separation and lateral shift of tw

Full text of DOI:10.1016/j.jorganchem.2017.09.039

Journal of Organometallic Chemistry 851 (2017) 235e247
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Packing polymorphism of dicarbonyl-[2-(phenylamino)pent-3-en-4-
onato]rhodium(I)
Hendrik Ferreira a, Marrigje Marianne Conradie a, Petrus H. van Rooyen b,
,
*
Jeanet Conradie a
a Department of Chemistry, PO Box 339, University of the Free State, 9300 Bloemfontein, South Africa
b Department of Chemistry, University of Pretoria, Private Bag X20, Hatfield, 0028, South Africa
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 6 May 2017
Received in revised form
18 September 2017
Accepted 27 September 2017
Available online 29 September 2017
Depending on the crystallization conditions, the interaction between the rhodium metal centres of the
separate [Rh(CH3COCHCN(Ph)CH3)(CO)2] molecular units, as described by the interplanar separation and
lateral shift of two of the units, leads to packing polymorphism of [Rh(CH3COCHCN(Ph)CH3)(CO)2],
which means the same molecule crystallises in different fashions, resulting in different polymorphs (
and ), with a difference in crystal packing. Six different sets of solid state single crystal data of
[Rh(CH3COCHCN(Ph)CH3)(CO)2], show that this complex is polymorphic, forming dinuclear units that
either stack in wire-like chains with weak metallophilic rhodium-rhodium interactions ( -polymorph),
or with packing of the dinuclear units that does not result in rhodium-rhodium chains ( -polymorph). A
a
b
b
Keywords:
Rhodium
a
DFT study on the inter-molecular interactions in different dinuclear [Rh(CH3COCHCN(Ph)CH3)(CO)2]2
models, using different DFT methods, provides an understanding on a molecular level of the rhodium-
rhodium and other inter-molecular interactions between the two separate [Rh(CH3COCHCN(Ph)
CH3)(CO)2] molecules in the dinuclear unit.
DFT
Dicarbonyl
Metal-metal interaction
Packing
© 2017 Elsevier B.V. All rights reserved.
1. Introduction
complexes pack in dinuclear units which form extended linear wire-
like chains of rhodium atoms [8e11]. The extended metal-metal
Polymorphism [1] has been defined by McCrone in 1965 as “a
solid crystalline phase of a given compound resulting from the
possibility of at least two different arrangements of the molecules of
that compound in the solid state” [2]. A few years later, Rosenstein
and Lamy (1969) simplified the definition to “when a substance can
exist in more than one crystalline state it is said to exhibit poly-
morphism” [3]. Polymorphs are also described as “isomers at the
individual crystal level in which the same molecule or salt crystallises
in different fashions, which frequently, but not necessarily, result in
differences in the space group and the cell dimensions”, sometimes
leading to different arrangements (packing) of the molecules in the
solid state [4]. When polymorphism exists as a result of differences in
crystal packing, it is called packing polymorphism. It has been
interactions along the linear chains in the latter case, have been
described as resulting from the overlap of the filled dz2 orbitals and
the empty pz orbitals that lie along the direction of the metal-metal
axis [12]. Similarly to the latter, it has been shown recently that
crystals of the complex [Rh(CH3COCHCN(Ph)CH3)(CO)2] (dicarbonyl-
[2-(phenylamino)pent-3-en-4-onato]rhodium(I)) [13] (see Fig. 1), in
the solid state also pack in linear chains of consecutive unit cells
along the intermolecular rhodium-metal axis in a wire-like structure
(called the b-polymorph), while a related molecule of dicarbonyl-(4-
((2,6-dichlorophenyl)imino)pent-2-en-2-olato)-rhodium did not
show any inter-molecular rhodium-rhodium interaction in the solid
state at all [13]. In this contribution we present an additional packing
polymorphism (the a-polymorph) of the same [Rh(CH3COCHCN(Ph)
observed that the molecules of different [Rh(
complexes in the solid state, either pack in separate dinuclear [Rh(
diketonato)(CO)2]2 dimeric units [5e7], while others of these
b
-diketonato)(CO)2]
CH3)(CO)2] molecule (as in Fig. 1), complemented by a DFT study on
the inter-molecular rhodium-rhodium interactions in four different
dinuclear [Rh(CH3COCHCN(Ph)CH3)(CO)2]2 models.
b-
* Corresponding author.
E-mail address: conradj@ufs.ac.za (J. Conradie).
https://doi.org/10.1016/j.jorganchem.2017.09.039
0022-328X/© 2017 Elsevier B.V. All rights reserved.

236
H. Ferreira et al. / Journal of Organometallic Chemistry 851 (2017) 235e247
crystalline forms (
kappa geometry diffractometer, with duo I
CMOS detector and APEX II [19] control software, using Quazar
multi-layer optics, and monochromated Mo-K radiation, by means
of a combination of and scans. An additional set of data for the
polymorph was collected at 100 K, on a Bruker APEX-II CCD.
a- and
b-polymorphs), on a Bruker D8 Venture
ms sources, a Photon 100
a
f
u
a-
Data reduction was performed using SAINTþ [19] and the in-
tensities were corrected for absorption, using SADABS [19]. The five
crystal structures were solved by intrinsic phasing, using SHELXTS,
and refined by full-matrix least squares, using both SHELXTLþ [20]
and SHELXL-2014þ [20]. In the structure refinement, all hydrogen
atoms were added in the calculated positions and treated as riding
on the atom to which they are attached. All non-hydrogen atoms
were refined with anisotropic displacement parameters; all
isotropic displacement parameters for hydrogen atoms were
calculated as (X ꢂ Ueq) of the atom to which they are attached,
where X ¼ 1.5 for the methyl hydrogens, and X ¼ 1.2 for all other
hydrogens. Crystal data, data collections, structure solutions and
refinement details for all five crystal structures, are available in the
CIFs (with CCDC deposit numbers 1548178, 1558071, 1571132,
1571133 and 1571134).
Fig. 1. Structure of [Rh(CH3COCHCN(Ph)CH3)(CO)2].
2. Experimental
2.1. Synthesis
Reagents were obtained from Sigma-Aldrich. Solid reagents
employed in preparations were used directly without further pu-
rification. Solvents were distilled prior to use. Di-m-chloro-tetra-
carbonyldirhodium(I) was obtained from Sigma-Aldrich.
2.3. Theoretical approach
2.1.1. [CH3COCHCN(HPh)CH3]
Density functional theory (DFT) calculations of this study were
performed with the hybrid B3LYP [21,22] functional, as imple-
mented in the Gaussian 09 program package [23]. Geometries of
the neutral complexes were optimised in the gas phase, using the
6-311G(d,p) basis set on all atoms except rhodium, for which the
def2tzvpp [24] (valens electrons) and SDD (core electrons) basis set
was used. These B3LYP optimised gas phase structures were used to
further conduct a natural bond orbital (NBO) analysis (using the
NBO 3.1 module [25] in Gaussian 09), a fragment analysis, as well as
an electronic density analysis (using Bader's quantum theory of
atoms in molecules (QTAIM) [26e28], as implemented in ADF2013
[29e31]), at the same level of theory.
The single molecular unit of complex [Rh(CH3COCHCN(Ph)
CH3)(CO)2] was optimised by calculation, as well as the
[Rh(CH3COCHCN(Ph)CH3)(CO)2]2 dimeric unit. Further additional
single point calculations were done on the coordinates of such a
dinuclear unit which were obtained from the solid state crystal
The ligand [CH3COCHCN(HPh)CH3] was synthesised using
published methods [14e17] with slight modifications. Acetylace-
tone (5 g, 5.2 ml) was placed in a round bottom flask outfitted with
a condenser for refluxing. Aniline (6.9763 g, 7 ml) and concentrated
hydrochloric acid (5 g, 4.3 ml) was added to the flask whilst stirring
and the mixture was brought to reflux for 5 h. Diethyl ether was
added to the mixture and then placed in the fridge (-5ꢀ C). The
yellow crystalline precipitate was filtered and washed with cold
diethyl ether and recrystallised.
Yield ¼ 50%.1H NMR: 12.493 ppm (s, O-H); 7.388 ppme7.114 ppm
(m, C6H5-N); 5.208 ppm (s, C-H); 2.122 ppm (s, CH3-CN); 2.014 ppm
(s, CH3-CO).
2.1.2. [Rh(CH3COCHCN(Ph)CH3)(CO)2]
The complex [Rh(CH3COCHCN(Ph)CH3)(CO)2] was synthesised
using published methods with slight modifications [18]. The metal,
di-m-chloro-tetracarbonyldirhodium(I) (0.05 g, 0.1286 mmol), was
structure data of this study (a-polymorph at 150 K), as well as on
dissolved in methanol (5 ml). The ligand, [CH3COCHCNHPhCH3]
(0.2572 mmol), also dissolved in methanol (2 ml) was added
dropwise during 10 min whilst stirring. The mixture was left to stir
for 1 h. The mixture was then extracted with n-hexane until the n-
hexane solvent became clear. The solvents were combined and
evaporated under reduced pressure. The precipitated solid was
collected and recrystallised, either from n-hexane at -5 ꢀC, or from
DCM at room temperature (25 ꢀC).
two additional dinuclear models, calculated on the coordinates of a
dinuclear unit obtained from the solid state crystal structure data of
a previous study (b-polymorph at 100 K), as described in Section
3.2.2. The coordinates of the DFT calculations are given in the
Supporting Information.
3. Results and discussion
Yield ¼ 78%. 1H NMR: 7.388 ppme7.061 ppm (m, C6H5-N);
5.298 ppm (s, C-H); 2.195 ppm (s, CH3-CN); 2.141 ppm (s, CH3-CO).
nCO: 2059 cmꢁ1; 1998 cmꢁ1. UV/Vis (CHCl3): lmax ¼ 329 nm
(ε ¼ 5102 molꢁ1 dmþ3 cmꢁ1), 265 nm (ε ¼ 6497 molꢁ1 dmþ3 cmꢁ1).
3.1. X-ray structure
In this section, crystallographic results are presented of the solid
state crystal data of two polymorphs of complex [Rh(CH3COCHCN(Ph)
CH3)(CO)2]; see Table 1 and Table 2 (column 2e6). Data for each
crystalline structure was repeatedly collected at decreasing temper-
atures, to determine whether temperature would transform the
2.2. Crystal structure analysis
The solid state crystal data of two crystals, obtained under
different crystallisation conditions, collected at three different tem-
peratures, for two different crystalline forms of [Rh(CH3COCHCN(Ph)
CH3)(CO)2], is presented here. The first crystalline form, labelled the
structure of each polymorph. The two structures were labelled the
polymorph (with space group P 21/n, data collected at 298 K, 150 K
and 100 K), as well as the -polymorph (with space group I2/a, data
collected at 298 K and 150 K). These experimental results were then
compared to a previously published structure [13] and packing of the
a-
b
a
-polymorph, was obtained from a solution of n-hexane at -5 ꢀC. The
second crystalline form, labelled the
from a solution of DCM at room temperature. Data for both crystals
was collected, both at RT and at 150 K for each of these two
b
-polymorph, was crystallised
same complex (
100 K); see Table 2 (last column of the
able for X-ray diffraction were obtained by slow evaporation from
b
-polymorph with space group I2/a, data collected at
b-polymorphs). Crystals suit-

Table 1
Crystal data and structure refinement of both the a-and b-polymorphs of complex [Rh(CH3COCHCN(Ph)CH3)(CO)2], collected for two crystals at three different temperatures (298 K, 150 K and 100 K).
Polymorph
a
a
a
b
b
Empirical formula
Formula weight
Temperature
C13 H12 N O3 Rh
333.15
298(2) K
C13 H12 N O3 Rh
333.15
150(2) K
C13 H12 N O3 Rh
333.15
100(2) K
C13 H12 N O3 Rh
333.15
298(2) K
C13 H12 N O3 Rh
333.15
150(2) K
Wavelength
0.71073 Å
0.71073 Å
0.71073 Å
0.71073 Å
0.71073 Å
Crystal system
Space group
Monoclinic
P 21/n
Monoclinic
P 21/n
Monoclinic
P 21/n
Monoclinic
I 2/a
Monoclinic
I 2/a
Unit cell dimensions
a ¼ 8.7171(4) Å
b ¼ 12.0141(5) Å
c ¼ 13.1833(6) Å
a ¼ 8.5599(4) Å
b ¼ 11.9808(6) Å
c ¼ 13.1030(7) Å
a ¼ 8.5127(5) Å
b ¼ 11.9666(7) Å
c ¼ 13.0725(8) Å
a ¼ 13.6872(10) Å
b ¼ 9.3364(16) Å
c ¼ 21.350(3) Å
a ¼ 13.4204(14) Å
b ¼ 9.3030(8) Å
c ¼ 21.226(3) Å
a
b
g
¼ 90ꢀ
a
b
g
¼ 90ꢀ
a
b
g
¼ 90ꢀ
a
b
g
¼ 90ꢀ
a
b
g
¼ 90ꢀ
¼ 105.6850(10)ꢀ
¼ 90ꢀ
¼ 105.775(2)ꢀ
¼ 90ꢀ
¼ 105.874(2)ꢀ
¼ 90ꢀ
¼ 95.000(4)ꢀ
¼ 90ꢀ
¼ 95.817(4)ꢀ.
¼ 90ꢀ
Volume
Z
Density (calculated)
Absorption coefficient
F(000)
Crystal size
Theta range for data collection
Index ranges
1329.25(10) Å3
4
1293.16(11) Å3
4
1280.89(13) Å3
4
2717.9(6) Å3
2636.4(5) Å3
8
8
1.665 Mg/m3
1.711 Mg/m3
1.728 Mg/m3
1.628 Mg/m3
1.679 Mg/m3
1.283 mmꢁ1
1.319 mmꢁ1
1.332 mmꢁ1
1.255 mmꢁ1
1.294 mmꢁ1
664
664
664
1328
1328
0.185 ꢂ 0.158 ꢂ 0.148 mm3
2.520 to 28.387ꢀ
ꢁ11 ꢃ h<¼11,
-16 ꢃ k<¼16, -17 ꢃ l<¼17
48660
0.185 ꢂ 0.158 ꢂ 0.148 mm3
2.345 to 25.339ꢀ
ꢁ10 ꢃ h<¼10,
-14 ꢃ k<¼14, -15 ꢃ l<¼15
14021
0.185 ꢂ 0.158 ꢂ 0.148 mm3
3.014 to 25.349ꢀ
ꢁ10 ꢃ h<¼10,
-14 ꢃ k<¼14, -15 ꢃ l<¼15
49469
0.480 ꢂ 0.120 ꢂ 0.110 mm3
2.382 to 26.408ꢀ.
ꢁ17 ꢃ h<¼17, -11 ꢃ k<¼11,
-26 ꢃ l<¼26
0.480 ꢂ 0.120 ꢂ 0.110 mm3
2.392 to 28.536ꢀ
ꢁ17 ꢃ h<¼17, -12 ꢃ k<¼12, -28 ꢃ l<¼28
Reflections collected
33261
41844
Independent reflections
Completeness to theta ¼ 25.242ꢀ
Refinement method
3347 [R(int) ¼ 0.0335]
2370 [R(int) ¼ 0.0252]
2350 [R(int) ¼ 0.0182]
2789 [R(int) ¼ 0.0863]
3342 [R(int) ¼ 0.0632]
100%
99.9%
99.9%
100.0%
100.0%
Full-matrix least-squares on F2
3347/0/165
1.041
Full-matrix least-squares on F2
2370/0/163
1.043
Full-matrix least-squares on F2
2350/0/165
1.134
Full-matrix least-squares on F2
2789/0/165
1.013
Full-matrix least-squares on F2
3342/0/165
1.040
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2sigma(I)]
R indices (all data)
Extinction coefficient
R1 ¼ 0.0214, wR2 ¼ 0.0591
R1 ¼ 0.0318, wR2 ¼ 0.0668
n/a
R1 ¼ 0.0177, wR2 ¼ 0.0440
R1 ¼ 0.0.021, wR2 ¼ 0.0456
n/a
R1 ¼ 0.0146, wR2 ¼ 0.0375
R1 ¼ 0.0152, wR2 ¼ 0.0379
n/a
R1 ¼ 0.0344, wR2 ¼ 0.0582
R1 ¼ 0.0714, wR2 ¼ 0.0662
n/a
R1 ¼ 0.0232, wR2 ¼ 0.0449
R1 ¼ 0.0376, wR2 ¼ 0.0479
n/a
Largest diff. peak and hole
0.348 and -0.470 e.Åꢁ3
0.499 and -0.183 e.Åꢁ3
0.260 and -0.494 e.Åꢁ3
0.472 and -0.463 e.Åꢁ3
0.410 and -0.439 e.Åꢁ3

238
H. Ferreira et al. / Journal of Organometallic Chemistry 851 (2017) 235e247
Table 2
Selected geometrical data (bond lengths in Å and bond angles in degrees) of complex [Rh(CH3COCHCN(Ph)CH3)(CO)2], obtained for both its a- and b-polymorphs, as well as the
optimized DFT calculated data. Data for the two crystals from this study (columns 2 - 6) is compared to the corresponding crystallographic data of a previously published
polymorph, collected at 100 K [13] (column 7). Atom numbering is shown in Fig. 2.
b-
Polymorph
a
-polymorph
b
-polymorph
difference min and
max experimental
parameter
DFT
optimised
molecule
max difference
DFT and experimental
parameter
Temperature
298 K
150 K
100 K
298 K
150 K
100 K
Rh(1)-C(1)
Rh(1)-C(2)
Rh(1)-O(3)
Rh(1)-N(1)
O(3)-C(3)
N(1)-C(5)
N(1)-C(6)
C(4)-C(5)
1.841(2)
1.866(2)
2.0187(14)
2.0501(17)
1.284(3)
1.314(2)
1.448(3)
1.419(3)
1.357(3)
1.847(2)
1.870(2)
2.0239(13)
2.0540(16)
1.292(2)
1.321(2)
1.443(2)
1.417(3)
1.372(3)
87.03(9)
89.57(7)
92.67(7)
90.72(6)
123.76(18)
127.50(18)
126.33(18)
3.4816(3)
1.8439(17)
1.8709(17)
2.0251(11)
2.0557(13)
1.291(2)
1.320(2)
1.444(2)
1.418(2)
1.374(2)
86.98(7)
89.72(6)
92.67(6)
90.63(5)
123.68(14)
127.42(14)
126.37(14)
3.4577(3)
1.827(4)
1.857(4)
2.022(2)
2.054(3)
1.282(4)
1.318(4)
1.437(4)
1.395(5)
1.376(5)
86.54(16)
89.33(13)
93.72(13)
90.41(10)
123.8(3)
128.3(3)
125.4(3)
3.4204(5);
3.4945(5)
1.844(2)
1.868(2)
2.0312(13)
2.0596(15)
1.289(2)
1.320(2)
1.441(2)
1.408(3)
1.380(3)
86.60(9)
89.66(7)
93.26(8)
90.47(6)
124.38(18)
127.57(19)
125.66(18)
3.3272(5);
3.4425(5)
1.841(3)
1.866(2)
2.032(2)
2.058(2)
1.294(2)
1.318(3)
1.448(3)
1.410(3)
1.381(3)
86.5(1)
89.75(8)
93.13(9)
90.55(6)
123.9(2)
127.8(2)
125.7(2)
3.3085(2);
3.4358(2)
0.020
0.014
0.013
0.010
0.012
0.007
0.011
0.024
0.024
0.53
0.42
1.05
0.31
1.31
0.88
0.98
1.855
1.878
2.040
2.092
1.280
1.330
1.439
1.412
1.390
89.0
94.3
89.4
89.4
124.6
127.2
125.8
1.855
0.028
0.021
0.021
0.042
0.014
0.016
0.009
0.017
0.033
2.54
4.98
4.28
1.28
1.51
1.12
0.60
C(3)-C(4)
C(1)-Rh(1)-C(2)
C(2)-Rh(1)-O(3)
C(1)-Rh(1)-N(1)
O(3)-Rh(1)-N(1)
N(1)-C(5)-C(4)
C(3)-C(4)-C(5)
O(3)-C(3)-C(4)
Rh…...Rh
86.79(10)
89.52(8)
93.06(8)
90.62(6)
123.07(19)
128.09(19)
126.38(19)
3.5560(3)
either an n-hexane solution at -5 ꢀC (to yield the
from a DCM solution at RT (to yield the -polymorph). Both poly-
a-polymorph), or
The a-polymorph of [Rh(CH3COCHCN(Ph)CH3)(CO)2] crystal-
b
lised in the P21/n space group, with four molecules per unit cell. The
four bond angles around the rhodium atom deviate slightly (<3ꢀ)
from the normally expected 90ꢀ bond angle for a square planar
morphs exhibit the same experimental properties, such as colour or
UV/vis, IR and 1H NMR spectra as provided in the experimental sec-
tion. The different polymorphs seemed to result from different crys-
tallisation conditions (solvent and temperature) and did not
transform into one another by cooling, since it was found by crys-
tallography that the space group of a specific polymorph stayed the
same upon cooling from 298 K to 150 K or 100 K; see Table 1.
complex, as can be seen from the bond angles of the
a-polymorph
at 150 K (see Table 2, second column of the -polymorphs): namely,
a
bond angle C(1)-Rh(1)-C(2) of 87.03(9)ꢀ, bond angle C(2)-Rh(1)-
O(3) of 89.57(7)ꢀ, bond angle C(1)-Rh(1)-N(1) of 92.67(7)ꢀ and
bond angle O(3)-Rh(1)-N(1) of 90.72(6)ꢀ. The atoms around
rhodium (N1, O3, C1 and C2) as well as rhodium itself all lie in the
same plane, with C1 having the maximum deviation from this
plane of 0.031(2) Å. Similarly, the atoms of the backbone of the
bidentate ligand (O3, C3, C4, C5 and N1) as well as Rh itself, all lie in
another plane (slanted at 0.49ꢀ with respect to the plane through
Rh, N1, O3, C1 and C2), with O3 having the maximum deviation
from that plane of 0.021(1) Å. The angle between the latter plane
and the plane through the phenyl ring is 81.70ꢀ. The separate
molecules form dimers, which are packed about a centre of
symmetry.
3.1.1. Structure
The crystal data and structure refinement of the two
[Rh(CH3COCHCN(Ph)CH3)(CO)2] crystals of this study are sum-
marised in Table 1, while Table 2 compares selected geometrical
data of the two crystals from this study (obtained for both the
and -polymorphs, from data collections at different temperatures)
to the corresponding data of a previously published -polymorph,
collected at 100 K [13]. A molecular diagram of the -polymorph at
a-
b
b
a
150 K, showing the atom labelling used for all six structures, is
illustrated in Fig. 2.
The
lised in the I2/a space group, with eight molecules per unit cell.
The structure of the -polymorph is very similar to that of the a-
b-polymorph of [Rh(CH3COCHCN(Ph)CH3)(CO)2] crystal-
b
polymorph of [Rh(CH3COCHCN(Ph)CH3)(CO)2], as can be seen from
the structure overlay of the two polymorphs, as illustrated in Fig. 3
(top left).
The metal-ligand distances in transition metal complexes are
important in determining the structure and reactivity of the metal
complex. Therefore in Table 2 the bond lengths and bond angles
around the rhodium atom, as well as selected geometrical param-
eters involving the backbone of the bidentate ligand of the
-polymorph obtained crystallographically in this study, are
compared to each other and also to the corresponding parameters
of the previously published structure of the -polymorph, collected
a- and
b
b
at 100 K [13], of complex [Rh(CH3COCHCN(Ph)CH3)(CO)2]. The
maximum difference between the selected bond lengths and bond
angles of both polymorphs obtained at different temperatures, is
only 0.024 Å and 1.3ꢀ respectively. The main difference between the
geometries of the a- and b-polymorphs lies in the orientation of the
phenyl and methyl groups on the ligand, as is clear from the overlay
of the different structures, as presented in Fig. 3 (top left). However,
the orientation of the phenyl and methyl groups on the ligand did
Fig. 2. A perspective drawing of the molecular structure of [Rh(CH3COCHCN(Ph)
CH3)(CO)2] (the
a-polymorph at 150 K), showing the atom numbering scheme. Atomic
displacement parameters (ADPs) are shown at the 50% probability level.

H. Ferreira et al. / Journal of Organometallic Chemistry 851 (2017) 235e247
239
Fig. 3. Overlay of the structures of the
magenta) from this study and
when using the Rh atom, the atoms of the backbone of the bidentate ligand, as well as the carbons of the two carbonyl groups of each structure in the overlay, are indicated. Also
shown (top right) is the overlay of the experimentally obtained structure of the -polymorph (150 K, black) of [Rh(CH3COCHCN(Ph)CH3)(CO)2] with the theoretical mono nuclear
DFT optimised molecule (blue). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
a
-polymorph (298 K, grey),
a-polymorph (150 K, black),
a-polymorph (100 K, green),
b-polymorph (298 K, cyan),
b-polymorph (150 K,
b-polymorph (100 K, red) from a previous study [13], of [Rh(CH3COCHCN(Ph)CH3)(CO)2] with each other. The root means square (RMS) overlay values,
a
not change with temperature for a specific polymorph, see Fig. 3
(bottom).
differences in crystal packing for the same molecule, also leading to
differences in the space group and the cell dimensions of the
different polymorphs.
The molecular pair-wise packing observed for the a-polymorph
3.1.2. Packing
(150 K) is further stabilised by parallel ring1 … ring1 interaction
(ring1 defined by Rh1,O3, C3, C4, C5, N1) at a distance of 4.465(1) Å,
as well as ring1 … ring2 interaction (ring2 defined by C6, C7, C8, C9,
C10, C11) at a distance of 4.607(1) Å between adjacent molecules in
each dimeric unit. Some additional interaction of the type X-Y …
ring-centroid (perpendicular) was observed: for C9-H9 … ring1 the
distance is 2.79 Å and for C1-O1 … ring2 the distance is 3.47 Å.
From the differences found in the solid state packing of all six
crystal structures we can therefore conclude that the interaction of
the rhodium atoms between two adjacent [Rh(CH3COCHCN(Ph)
CH3)(CO)2] molecules can lead to either crystallising as extended
In Fig. 4, packing diagrams are compared of two crystals in this
study, namely of the
group P21/n) and the
group I2/a). Crystals of both polymorphs (
a
b
-polymorph (collected at 150 K, with space
-polymorph (collected at 150 K, with space
and ) form dinuclear
a
b
[Rh(CH3COCHCN(Ph)CH3)(CO)2]2 units in the solid state, with
differing inter-molecular rhodium-rhodium distances which
decrease slightly upon temperature lowering, namely decreasing
from 3.5560(3) (298 K) to 3.4816(3) (150 K) to 3.4577(3) (100 K) for
the
3.3272(5) (150 K) to 3.3085(2) (100 K) for the
given in Å, Table 2). This rhodium-rhodium distance is larger in a
dinuclear unit of the -polymorph at the lowest temperature of
100 K, than in a dimer of the -polymorph at room temperature
(298 K). Consequently, the dinuclear [Rh(CH3COCHCN(Ph)
CH3)(CO)2]2 units of the -polymorphs with shorter inter-
a
-polymorph; and decreasing from 3.4204(5) (298 K) to
b
-polymorph (values
linear chains of metal atoms (b-polymorph), or otherwise under
differing crystallising conditions (such as solvent and temperature),
they do not form infinite metal-metal chains, but crystallise as
a
b
dinuclear units in the solid state (
previously been found that the solid state packing of other related
[M( -diketonato)(CO)2] complexes either displayed extended
linear chains of metal atoms [8e10,32e35] in some instances, or
otherwise they instead formed dinuclear [M( -diketonato)(CO)2]2
a-polymorph) instead. It has
b
molecular rhodium-rhodium distances, rather form extended
linear chains of metal atoms along the a-axis, regardless of tem-
perature; while packing in the solid state of the a-polymorph does
not form any linear chains of rhodium atoms, but only pack in pairs
of dinuclear [Rh(CH3COCHCN(Ph)CH3)(CO)2]2 units. In the case of
the a-polymorph, the formation of linear wire-like chains of inter-
molecular rhodium-rhodium atoms is further impeded, due to the
larger lateral shift (of ca. 0.9 Å) between the two separate molecules
in each dinuclear [Rh(CH3COCHCN(Ph)CH3)(CO)2]2 unit, relative to
a smaller lateral shift of only ca. 0.3e0.4 Å between the molecules of
b
b
units for other complexes [5e7]. However, to our knowledge, no
case of polymorphism has as yet been reported for these related
[M(b-diketonato)(CO)2] complexes, as was found in this study for
complex [Rh(CH3COCHCN(Ph)CH3)(CO)2].
3.2. Computational chemistry
the
b
-polymorph dimer. The difference in crystal packing of the
a
and
b
dimers show that these are therefore packing polymorphs,
3.2.1. Structure of mono nuclear [Rh(CH3COCHCN(Ph)CH3)(CO)2]
The overlay of the theoretical DFT optimised single molecular
unit of [Rh(CH3COCHCN(Ph)CH3)(CO)2], onto the coordinates of the
since dinuclear [Rh(CH3COCHCN(Ph)CH3)(CO)2]2 can exist in more
than one crystalline state. Packing polymorphism is a result of

240
H. Ferreira et al. / Journal of Organometallic Chemistry 851 (2017) 235e247
Fig. 4. Packing diagrams of [Rh(CH3COCHCN(Ph)CH3)(CO)2] of (a) the
a-polymorph (150 K, space group P21/n) along the a (top left) and c* (top right) axis, and of (b) the b-
polymorph (150 K, space group I2/a) along the b (bottom left) and a (bottom right) axis.
experimentally obtained solid state data of the
a
-polymorph
dimeric unit, are described. The four theoretical models will be
referred to hereafter as the DFToptimised dimer 1, DFT single point
2, DFT single point 3 and DFT single point 4 respectively. The first
model, DFT optimised dimer 1, is the gas phase optimised dinuclear
[Rh(CH3COCHCN(Ph)CH3)(CO)2]2 structure, based on the theoretical
coordinates obtained by DFTcalculations for a dimeric molecular unit
in this study. The second, third and fourth models, involve single
point calculations based on crystallographically obtained co-
ordinates, obtained in this and a previous study [13] for dimer
[Rh(CH3COCHCN(Ph)CH3)(CO)2]2, and were chosen so that the lateral
shift between adjacent rhodium atoms in the dimeric unit decreases
consistently, in going from the first model (DFT optimised dimer 1,
lateral shift ¼ 1.590 Å) to the fourth model (DFT single point 4,
lateral shift ¼ 0 Å), where in the latter case, the two rhodium atoms
of adjacent molecular units are aligned directly “on top of each other”
(150 K) of this study, is presented in Fig. 3 (top right). The maximum
difference between the bond lengths and bond angles around
rhodium of any experimental structure and the theoretical DFT
optimised bond lengths and bond angles around rhodium, is
0.042 Å and 4.98ꢀ respectively (See Table 2 last column). This is
comparable with the maximum difference between the selected
bond lengths and bond angles of all six crystal structures obtained
at different temperatures for both polymorphs reported in this
study, namely 0.024 Å and 1.3ꢀ respectively (see Table 2, column 8).
The slightly overestimated DFT calculated metal-ligand bond
lengths are generally observed for gas phase optimisations [36],
and therefore considered insignificant. Similar slightly over-
estimated rhodium-ligand bond lengths for gas phase optimisa-
tions, relative to experimentally obtained solid state crystal data,
have previously been obtained for related rhodium-
complexes [37e39].
b
-diketonato
(with inclination angle
a
¼ 90ꢀ, see Fig. 5), as shown in Fig. 6. The
second model (DFT single point 2) was calculated, based on the
coordinates of the solid state crystal structure data of dimeric unit of
3.2.2. Structure of the [Rh(CH3COCHCN(Ph)CH3)(CO)2]2 dimer
Both the - and -polymorphs of [Rh(CH3COCHCN(Ph)CH3)(CO)2]
the a-polymorph (at 150 K, with the exact experimental lateral shift
of 0.925 Å between adjacent rhodium atoms), while the third model
a
b
thus pack in dimeric units in the solid state. An understanding on a
molecular level of the rhodium-rhodium and other inter-molecular
interactions between the two separate [Rh(CH3COCHCN(Ph)
CH3)(CO)2] molecules in the dinuclear unit is presented here. In this
section the computational chemistry results, calculated on the co-
ordinates of four models of the [Rh(CH3COCHCN(Ph)CH3)(CO)2]2
(DFT single point 3) was based on the coordinates of the dimeric
unit of the b-polymorph (at 100 K, from a previous study [13], with
the exact experimental lateral shift of 0.310 Å between adjacent
rhodium atoms). The fourth model (DFT single point 4) was con-
ducted on the coordinates of the same previously published
b-
polymorph crystal structure (at 100 K, as used for DFT single point

H. Ferreira et al. / Journal of Organometallic Chemistry 851 (2017) 235e247
241
molecular unit, as defined in Fig. 5 [4] and as summarised in Table 3.
The four models are visualised in Fig. 6, indicating the lateral shift
between adjacent rhodium atoms in red. It is clear that the lateral
shift decreases in going from the DFT optimised dimer 1 (1.590 Å) to
DFT single point 2 (0.925 Å) to DFT single point 3 (0.310 Å) to DFT
single point 4 (0 Å), where in the latter, the two rhodium atoms of
adjacent molecular units are aligned directly “on top of each other”
(inclination angle
a
¼ 90ꢀ, see Fig. 5). It is expected that in the parallel
aligned dimers of DFT single point 4, wire-like linear metal-metal
stacking of the [Rh(CH3COCHCN(Ph)CH3)(CO)2]2 units will be fav-
oured, as has also been observed in the three experimental crystal
Fig. 5. Description of inter-molecular distances between two adjacent molecular units
of the dimer [Rh(CH3COCHCN(Ph)CH3)(CO)2]2. The plane through each of the two
molecules is defined by Rh1-O3-N1-C2-C1.
structures of the b-polymorph of [Rh(CH3COCHCN(Ph)CH3)(CO)2]2
(listed in Table 2), as well as in the solid state structure of a related
complex from literature, namely [Rh(acetylacetono)(CO)2] [12].
3), however with the two molecular units being aligned directly
above each other, with the rhodium-rhodium axis near perpendic-
ular to the square plane through the molecules, i.e. with the lateral
shift between the two separate molecular units reduced to near 0 Å
3.2.2.1. Molecular orbitals. The character of the highest occu-
pied molecular orbital (HOMO) of the DFT optimised molecule
[Rh(CH3COCHCN(Ph)CH3)(CO)2] (mono nuclear unit), is distributed
over the backbone of the 2-(phenylamino)pent-3-en-4-onato ligand,
while the HOMO-1 is of mainly dz2 character on rhodium (Fig. 7 left).
The order of these two orbitals is opposite to what has previously
(inclination
a
¼ 90ꢀ, see Fig. 5). The DFT calculated electronic en-
ergies of DFT single point 2 (a-polymorph at 150 K with lateral
shift ¼ 0.925 Å), DFT single point 3 (b-polymorph at 100 K with
lateral shift ¼ 0.310 Å) and DFT single point 4 (with no lateral shift)
are very close to each other (namely 8.42 eV z 8.28 eV z 8.30 eV
respectively), but all of them are ca. 8.3 eV higher than the DFT
optimised dimer 1, see Table 3. The interactions between the two
separate mono nuclear units [Rh(CH3COCHCN(Ph)CH3)(CO)2] in each
model, can collectively be described by the rhodium-rhodium dis-
tances, the interplanar separation between the two units, the lateral
shift between the two individual units, as well as the inclination
been found for complexes [Rh(b-diketonato)(CO)2] [11,40] and
[Ir(acetylacetonato)(CO)2] [41], where the HOMO was of mainly dz2
character on the metal, instead of on the ligand. Interaction between
these two MOs (ligand HOMO and dz2 HOMO-1) from each separate
mono nuclear unit in dinuclear [Rh(CH3COCHCN(Ph)CH3)(CO)2]2,
leads to the top four occupied molecular orbitals of the dinuclear
[Rh(CH3COCHCN(Ph)CH3)(CO)2]2 pair, namely two bonding MOs
(one ligand based and the other rhodium dz2 based) and two anti-
bonding MOs (also one ligand based and the other rhodium dz2
angle
a, between the Rh-Rh vector and the plane through one
Fig. 6. Visualisation of the lateral shift between two adjacent molecular units (indicated in red), in each of the four different DFT models of the dimer [Rh(CH3COCHCN(Ph)
CH3)(CO)2]2, namely 1.590 Å > 0.925 Å > 0.310 Å) > 0 Å, as seen directly from top. (For interpretation of the references to colour in this figure legend, the reader is referred to the web
version of this article.)
Table 3
DFT calculated energies and inter-molecular distances for four different [Rh(CH3COCHCN(Ph)CH3)(CO)2]2 dimer models, with the latter three models based on coordinates
obtained from crystallographic data, while the first model is based on theoretically calculated coordinates for a dimeric molecular unit of the complex.
Complex
Relative electronic energy (eV)
Rh-Rh distance (Å)
Angle
a
(ꢀ)
Interplanar separation (Å)
Lateral shift (Å)
DFT optimised dimer 1
DFT single point 2
0.00
8.42
4.474
3.482
69.8
73.9
4.182
3.357
1.590
0.925
(
a
-polymorph at 150 K)
DFT single point 3
-polymorph at 100 K)
8.28
8.30
3.309
3.309
77.6
90.0
3.294
3.309
0.310
0.000
(
b
DFT single point 4
(with no lateral shift)

242
H. Ferreira et al. / Journal of Organometallic Chemistry 851 (2017) 235e247
Fig. 7. Visualisation of the relative energies of the top four occupied molecular orbitals of the single DFT optimised molecule [Rh(CH3COCHCN(Ph)CH3)(CO)2] (mono nuclear unit)
(left), together with the four dimolecular [Rh(CH3COCHCN(Ph)CH3)(CO)2]2 models calculated in this study. Visualisation of selected MOs of DFT calculations for DFT single point 2
(a-polymorph at 150 K), as representative of the top four MOs of the dimolecular models, are shown on the right.
based), see Fig. 7 (right) for the top four MOs of DFT single point 2
as representative example. Since the dz2 MOs from each
[Rh(CH3COCHCN(Ph)CH3)(CO)2] unit are already are occupied, over-
lapping of these dz2 orbitals do not form a formal bond between the
rhodium centres, but lead to weak intermolecular interactions be-
tween the rhodium centres from adjacent molecules. The dz2 based
bonding orbitals of rhodium stabilise the interaction, or weak met-
allophilic bond, between the two rhodium centres of a dinuclear
[Rh(CH3COCHCN(Ph)CH3)(CO)2]2 unit, while the dz2 based anti-
bonding orbitals destabilise the rhodium-rhodium bond. A balance
between the bonding and antibonding intermolecular orbitals of
mainly dz2 type, determine the strength of the weak intermolecular
interactions between adjacent [Rh(CH3COCHCN(Ph)CH3)(CO)2]
molecules. The energy of the dz2 based bonding orbitals of DFT single
point 3 and DFT single point 4 is more than 0.2 eV lower (more
negative i.e. more stable) than that of the DFT optimised dimer 1
and DFT single point 2 models (Fig. 7), therefore contributing to the
Rh-Rh wire formation observed for both DFT single point 3 and DFT
single point 4 in the solid state. On the other hand, the energies of
the dz2 based antibonding orbitals, increases with decrease in the
lateral shift between the two separate molecular units in dinuclear
[Rh(CH3COCHCN(Ph)CH3)(CO)2]2, see Fig. 7.
interactions between the two rhodium centres in bimolecular
[Rh(CH3COCHCN(Ph)CH3)(CO)2]2 are visualised in Fig. 9.
In the DFT single point 3 model (based on the coordinates of the
b-polymorph at 100 K) where the two molecular units exhibit a large
overlap (with a smaller lateral shift of 0.310 Å), the NBO calculations
generally produced larger donor-acceptor interaction energies E(2)
between a filled (bonding or lone pair) Lewis type NBO on rhodium
of the one molecular unit (which acts as a donor) and an empty
(antibonding or Rydberg) non-Lewis NBO on rhodium of the other
molecular unit (which acts as an acceptor), than the calculated E(2)
for the DFT optimised dimer 1 (with a larger lateral shift of 1.590 Å)
or DFT single point 2 (with lateral shift of 0.925 Å), see Table 4. The
donor NBOs on rhodium, involved in donor-acceptor interactions, are
a CR NBO of mainly s character, a LP NBO of mainly dz2 character, as
well as two BD NBOs, see Fig. 8. The acceptor NBOs on rhodium,
involved in donor-acceptor interactions, are LP* NBOs of mainly pz, py
or px character respectively, see Fig. 8. Selected donor-acceptor in-
teractions between the two molecular units of DFT single point 3 (b-
polymorph at 100 K) are shown in Fig. 9. The slightly lateral shift (of
0.310 Å) between the two units of DFT single point 3, enables
interaction between the filled donor LP on Rh of mainly dz2 character
and the three empty acceptor LP*s on Rh, of mainly pz, py and px
character respectively. This slightly lateral shift also favours donor-
acceptor interactions between the CR on Rh of mainly s character,
and the two 2-centre bond NBOs, namely BD(Rh-Ctrans N) and BD(Rh-
3.2.2.2. Natural bond orbitals (NBO). The inter-molecular in-
teractions between the two molecular units of dimeric
[Rh(CH3COCHCN(Ph)CH3)(CO)2]2 were evaluated by the natural
bond orbitals (NBO) analysis method of Weinhold, since an NBO
analysis provides information about interactions between filled
Lewis type donor NBOs (occupation numbers near 2) and empty
non-Lewis acceptor NBOs (occupation numbers near 0). NBO types
important for the inter-molecular interactions between the two
single molecular units of dimeric [Rh(CH3COCHCN(Ph)CH3)(CO)2]2,
are the following types: the 1-centre core (CR), the 1-centre non-
bonded (lone pair, LP) and the 2-centre bond (BD) NBOs [42,43].
Selected results obtained from the NBO analysis of the four dimeric
models used in this study, are summarised in Table 4, and selected
NBOs are visualised in Fig. 8, while elected donor e acceptor NBO
Ctrans O), with the acceptor LP* on Rh of mainly pz character. The inter-
molecular donor-acceptor interaction energies, E(2), between the
two rhodium atoms of the single molecular units of dimeric
[Rh(CH3COCHCN(Ph)CH3)(CO)2]2, generally decrease in going from
DFT single point 3 to DFT single point 2 to the DFToptimised dimer
1 gas phase model (for example 23.9 kJ molꢁ1 > 11.4 kJ molꢁ1
>
0.7 kJ molꢁ1, for the LP(Rh mainly dz2 ) donor / LP*(Rh mainly pz)
acceptor interaction, also see Table 4 for the other indications), as the
lateral shift between the two single molecular units increases
(namely 0.310 Å < 0.925 Å < 1.590 Å). Similarly, for DFT single point
4, where the lateral shift approaches 0 Å, the interaction energies
E(2) of the donor-acceptor interactions involving the acceptor LP*(Rh

H. Ferreira et al. / Journal of Organometallic Chemistry 851 (2017) 235e247
243
Table 4
Selected second order perturbation theory donor-acceptor interaction energies, E(2) in kJ$molꢁ1, with the calculated natural bond orbital (NBO) occupations, for each of the
four different theoretically calculated DFT models of the dimer [Rh(CH3COCHCN(Ph)CH3)(CO)2]2, with lateral shift between adjacent molecules decreasing from model 1 to
model 4.
Complex
DFT optimised dimer 1 DFT single point 2
DFT single point 3
DFT single point 4
(coordinates of
a
polymorph at 150 K) (coordinates of
b
polymorph at 100 K) (no lateral shift)
E(2)/kJ·molꢁ1
LP(Rh mainly dz2 ) / LP*(Rh mainly pz) 0.7
LP(Rh mainly dz2 ) / LP*(Rh mainly px) 0.8
LP(Rh mainly dz2 ) / LP*(Rh mainly py) 0.2
11.4
4.8
9.7
23.9
8.5
6.6
30.5
3.5
2.5
BD(Rh-Ctrans N) / LP*(Rh mainly pz)
BD(Rh-Ctrans O) / LP*(Rh mainly pz)
CR(Rh mainly s) / LP*(Rh mainly pz)
Occupancy
0.3
0.3
0.1
15.6
7.7
8.1
15.6
15.4
15.2
22.9
22.8
13.8
LP(Rh mainly dz2 )/ee
1.972
1.989
0.061
0.182
0.166
1.960
1.960
1.963
1.989
0.078
0.183
0.168
1.955
1.953
1.957
1.988
0.088
0.184
0.167
1.951
1.949
1.955
1.988
0.090
0.188
0.171
1.949
1.948
CR(Rh mainly s)/ee
LP*(Rh mainly pz)/ee
LP*(Rh mainly px)/ee
LP*(Rh mainly py)/ee
BD(Rh Ctrans N)/ee
BD(Rh-Ctrans O)/ee
Fig. 8. Selected natural bond orbitals of DFT single point 3 (coordinates of the b-polymorph at 100 K, with a slight lateral shift of 0.310 Å between adjacent rhodium atoms). Donor
NBOs: (a) LP on Rh is of mainly s character, (b) LP on Rh is of mainly dz2 character, (c) BD (Rh-Ctrans O), (d) BD (Rh-Ctrans N). Acceptor NBOs: (e) LP* on Rh is of mainly pz character, (f)
LP* on Rh is of mainly py character and (g) LP* on Rh is of mainly px character. The NBO plots utilise a contour of 0.05 e/Å3. Colour code of atoms (online version): Rh (green), C
(black), N (blue), O (red), H (white). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

244
H. Ferreira et al. / Journal of Organometallic Chemistry 851 (2017) 235e247
Fig. 9. Visualisation of selected donor e acceptor NBO interactions between the two rhodium centres in bimolecular [Rh(CH3COCHCN(Ph)CH3)(CO)2]2 of DFT single point 3
(coordinates of the -polymorph at 100 K, with a slight lateral shift of 0.310 Å between adjacent rhodium atoms). (a) LP(Rh of mainly s character) e LP*(Rh of mainly pz character),
b
(b) LP(Rh of mainly pz character) e LP*(Rh of mainly py character), (c) LP (Rh of mainly pz character) e LP*(Rh of mainly px character), (d) LP (Rh of mainly dz2 character) e LP*(Rh of
mainly pz character), (e) LP (Rh of mainly dz2 character) e LP*(Rh of mainly px character) and (f) LP (Rh of mainly dz2 character) e LP*(Rh of mainly py character). The NBO plots utilise
a contour of 0.05 e/Å3. Colour code of atoms (online version): Rh (green), C (black), N (blue), O (red), H (white). (For interpretation of the references to colour in this figure legend,
the reader is referred to the web version of this article.)
of mainly pz character), generally increases relative to the other three
E(2) for DFT single point 3 and DFT single point 2. E(2) of LP(Rh
mainly dz2 ) donor / LP*(Rh mainly px) acceptor decreases from
8.5 eV to 3.5 eV, while E(2) of LP(Rh mainly dz2 ) donor / LP*(Rh
mainly py) acceptor decreases from 6.6 eV to 2.5 eV (when going
from DFT single point 3 to DFT single point 4) see Table 4.
In summary, these identified donor-acceptor interactions thus
support the experimental observation that the [Rh(CH3COCHCN(Ph)
CH3)(CO)2] molecules are packed in pairs in the solid state, either as
models who have a larger lateral shift between the two separate
molecules (for example 30.4 kJ molꢁ1
> >
23.9 kJ molꢁ1
11.4 kJ molꢁ1 > 0.7 kJ molꢁ1, for the LP(Rh mainly dz2 ) donor /
LP*(Rh mainly pz) acceptor interaction of DFT models 4, 3, 2 and 1
respectively, also see Table 4 for the other indications). However, as is
also expected for a ca. 0 Å lateral shift, the donor-acceptor in-
teractions involving the acceptors LP*(Rh of mainly px character) and
LP* (Rh of mainly py character), both decrease dramatically relative to
separate dinuclear [Rh(b-diketonato)(CO)2]2 dimeric units or in
Table 5
Selected topological parameters of the inter-molecular bond-paths for the four dimolecular [Rh(CH3COCHCN(Ph)CH3)(CO)2]2 models of this study, indicating that Rh-Rh bond
paths are only present for models 2 to 4. The critical point (CP) numbers are shown in Fig. 10.
Bond/Ring critical point
Bond type
Atoms involved
inter-atomic distance
/Å
BP length
/Å
Electron density
/e aꢁ0 3
Laplacian of electron density
2r/e aꢁ0 5
r
V
DFT optimised dimer 1
CP# 68/88
hydrogen bond
O-H
2.6314
2.6420
0.0062
0.0228
DFT single point 2
CP# 48
CP# 115/75
CP# 130/61
CP# 113/73
CP# 89/90
rhodium-rhodium
hydrogen bond
hydrogen bond
carbon-hydrogen
hydrogen bond
Rh-Rh
O-H
O-H
C-H
3.4811
2.9315
2.7761
2.9478
2.5858
3.4844
3.0967
2.8373
3.0076
2.6171
0.0113
0.0034
0.0046
0.0033
0.0071
0.0264
0.0153
0.0196
0.0139
0.0281
O-H
DFT single point 3
CP# 90
CP# 93/77
CP# 92/78
CP# 9785
CP# 129/87
DFT single point 4
CP# 87
rhodium-rhodium
hydrogen bond
hydrogen bond
hydrogen bond
hydrogen bond
Rh-Rh
O-H
O-H
O-H
O-H
3.3085
2.7644
2.9263
2.9244
2.8607
3.3109
2.8699
3.2006
3.1336
2.9078
0.0160
0.0048
0.0040
0.0041
0.0041
0.0367
0.0213
0.0181
0.0174
0.0159
rhodium-rhodium
hydrogen bond
Rh-Rh
O-H
3.3085
2.4708
3.3097
2.5016
0.1720
0.0087
0.0383
0.0382
CP# 76/99

H. Ferreira et al. / Journal of Organometallic Chemistry 851 (2017) 235e247
245
dinuclear units that form extended linear wire-like chains of
respectively, were identified via bond critical points, see Fig.10. Due
to symmetry, half of the bond paths are identical to the other half,
except for the rhodium-rhodium bond path.
rhodium, as was indeed found for the
study.
a- and b-polymorphs of this
No rhodium-rhodium bond path was identified for the DFT
optimised dimer 1 with the largest lateral shift of 1.590 Å, indi-
cating no formation of the linear metal-metal chains. However, the
DFT optimised dimer 1 is stabilised by two inter-molecular
hydrogen bonds, thereby favouring the formation of the observed
3.2.2.3. QTAIM. The
interaction
between
the
two
[Rh(CH3COCHCN(Ph)CH3)(CO)2] mono nuclear units in dinuclear
[Rh(CH3COCHCN(Ph)CH3)(CO)2]2 was further analysed, using Bad-
er's quantum theory of atoms in molecules (QTAIM) theory with
selected topological parameters of the inter-molecular bond-paths
for the four dimolecular [Rh(CH3COCHCN(Ph)CH3)(CO)2]2 models
of this study listed in Table 5. The topological analysis of the charge
dinuclear units in the solid state, as observed for the
of this study.
a-polymorphs
For DFT single point 2, DFT single point 3 and DFT single point
4, in addition to inter-molecular hydrogen bonds, rhodium-
density r(r) distribution, as well as the properties of the critical
points (CPs) determined by QTAIM, provides a universal indicator of
bonding between atoms [44]. For the DFT optimised dimer 1, the
DFT single point 2, the DFT single point 3 and the DFT single point
4, a total amount of two, nine, nine and three inter-molecular bonds
rhodium bond paths was identified. The electron density (r) and
the Laplacian of electron density (V2r) at the rhodium-rhodium
bond critical point, increased in value in going from DFT single
point 2 to DFT single point 3 and to DFT single point 4,
Fig. 10. Schematic representation of the inter-molecular bond-paths (BP), indicated by red bond critical points (CP), which are present in the DFT optimised geometry of all four
dimolecular [Rh(CH3COCHCN(Ph)CH3)(CO)2]2 models of this study. The colour range of the bond-paths decreases in frequency, according to the value of the electron density: from
blue (high density) to green to red (low density). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

246
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9780199236565.001.0001.
corresponding to decreasing lateral shift: For example, electron
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and V2r
To conclude, both NBO and QTAIM calculations shed light on
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This work has received support from the South African National
Research Foundation and the Central Research Fund of the Uni-
versity of the Free State, Bloemfontein, South Africa. The High
Performance Computing facility of the University of the Free State,
the Centre for High Performance Computing CHPC of South Africa
and the Norwegian supercomputing program NOTUR (Grant No.
NN4654K), are gratefully acknowledged for computer time. The
authors wish to thank Prof M. Fernandes from the University of the
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Witwatersrand for the data collection at 100 K on the a-polymorph.
Appendix A. Supplementary data
Supplementary data related to this article can be found at
https://doi.org/10.1016/j.jorganchem.2017.09.039.
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