Tribenzylidenemethane complexes of ruthenium. Synthesis and effects of the diastereoisomerism on the crystal packing

Article abstract of DOI:10.1016/S0022-328X(99)00076-5

Reaction of the tribenzylidenemethane (TBM) dianion with [RuCl₂(C₆H₆)]₂ yields a diastereoisomeric mixture of the metal complexes with formula [Ru(TBM)(C₆H₆)], which can be separated by column chromatography and fractional crystallisation. The crystal structures of both compounds were determined by X-ray diffraction on single crystals. The arrangement of the phenyl rings has a major influence on the build-up of the crystal lattice. The molecule containing the propeller-shaped ligand of C₃ symmetry crystallises in a layer structure with a packing arrangement that is caused by the fragment TBM. The close similarity with the crystal structure of [Ta(TBM)(η⁵-C₅H₅)(CH₃) ₂] shows that the fragment TBM can serve as a synthon for crystal engineering.

Full text of DOI:10.1016/S0022-328X(99)00076-5

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Journal of Organometallic Chemistry 582 (1999) 338–344
Tribenzylidenemethane complexes of ruthenium. Synthesis and
effects of the diastereoisomerism on the crystal packing
Gerhard E. Herberich, Thomas P. Spaniol *
Institut fu¨r Anorganische Chemie, Technische Hochschule Aachen, D-52056 Aachen, Germany
Received 16 October 1998
Abstract
Reaction of the tribenzylidenemethane (TBM) dianion with [RuCl2(C6H6)]2 yields a diastereoisomeric mixture of the metal
complexes with formula [Ru(TBM)(C6H6)], which can be separated by column chromatography and fractional crystallisation. The
crystal structures of both compounds were determined by X-ray diffraction on single crystals. The arrangement of the phenyl rings
has a major influence on the build-up of the crystal lattice. The molecule containing the propeller-shaped ligand of C3 symmetry
crystallises in a layer structure with a packing arrangement that is caused by the fragment TBM. The close similarity with the
crystal structure of [Ta(TBM)(h5-C5H5)(CH3)2] shows that the fragment TBM can serve as a synthon for crystal engineering.
© 1999 Elsevier Science S.A. All rights reserved.
Keywords: Tribenzylidenemethane; Diastereoisomers; Crystal engineering
1. Introduction
2. Synthesis and spectroscopic characterisation
Trimethylenemethane C(CH2)3 (TMM) is a versatile
ligand to transition metals [1]. The synthesis of its
complexes occasionally uses the dianion TMM2− as a
ligand source [2–5]. In analogy, the related dianion of
tribenzylidenemethane [Li(TMEDA)]2[C(CHPh)3] [6,7]
can be used to introduce the ligand TBM [5,8,9]. Tran-
sition metal complexes containing this ligand were used
as catalysts for the polymerisation of olefins [5,8,9]. The
free dianion of TBM is prochiral, but its transition
metal complexes will be chiral. In this paper we show
that the reaction with TBM2− gives the two
diastereomeric isomers of (h6-benzene)(h4-tribenzyli-
denemethane)ruthenium. Here, we also describe the
crystal structures of both compounds with emphasis on
the individual packing arrangements.
Treatment of [RuCl2(C6H6)]2 with [Li(TMEDA)]2-
[C(CHPh)3] in tetrahydrofuran solution gives a mixture
of the two isomers 1a and 1b in moderate yield. In the
lithium dianion, the benzylidene groups are configura-
tionally mobile and the NMR data in solution show
only the propeller-like dianion of C3 symmetry which is
also observed in the crystalline state [7]. In contrast to
this situation, the tribenzylidenemethane ligands are
configurationally fixed in the ruthenium complexes. The
observed product ratio of 3:1 reflects kinetic control
during product formation.
* Corresponding author. Present address: Institut fu¨r Anorganische
Chemie und Analytische Chemie, Johannes Gutenberg-Universita¨t
Mainz, D-55099 Mainz, Germany. Tel.: +49-6131-393918; fax:
+49-6131-395605.
E-mail address: spaniol@mail.uni-mainz.de (T.P. Spaniol)
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00076-5

G.E. Herberich, T.P. Spaniol / Journal of Organometallic Chemistry 582 (1999) 338–344
339
The two diastereoisomers can easily be separated by
fractional crystallisation. Both compounds are yellow
crystalline solids and can be described as derivatives of
the complex [Ru(TMM)(C6H6)] 2 [4]. The symmetries
of the isomers 1a and 1b are reflected in the NMR
spectra. The chemical equivalence of the benzylidene
1
groups in 1a is lost in 1b. In the H-NMR spectra one
resonance is seen for the TMM protons in 1a whereas
in 1b three resonances are found. The good resolution
allows a closer assignment via the coupling constants. It
4
has early been noted that within various JHH couplings
only the w-coupling can easily be detected [10]. In
agreement with this notion one of the TMM protons of
1b is seen a as singlet resonance (3.15 ppm for H1) while
the remaining two protons H2 and H3 at 3.32 and 4.41
Fig. 2. ORTEP plot (30% probability ellipsoids) of 1b.
3. Molecular structures
4
ppm appear as an AB system with J=1.5 Hz.
The structures of both diastereoisomers 1a and 1b
have been determined by X-ray diffraction on single
crystals (Figs. 1 and 2, Tables 1–5); 1a is found with
two crystallographically independent molecules in the
unit cell.
Their molecular structures closely resemble each
other and the core structure is very similar to that
found in the TMM complex 2 [4]. A comparison be-
tween the structures of 1a,b and 2 shows that the
distances between the metal and the C4-carbon atoms
are equal within experimental accuracy. The phenyl
ring substituents do not lead to wider distances. How-
ever, for zirconium complexes the distances between the
C4-fragment of a TMM ligand and the metal were
We assign the low field resonance to H3 as this
proton has a similar environment as the TMM protons
in 1a (4.18 ppm). A recent report describes a TBM
metal complex with the analogous unsymmetrical ar-
rangement of the phenyl rings [9]. In that work, the
ligand was built up in the coordination sphere of the
metal centre. However, for all other transition metal
complexes that were obtained from the dianion of
TBM, only compounds with the symmetrical propeller-
shaped ligand were found [5,8,9].
Table 1
Co-ordinates of non-hydrogen atoms for 1a
a
Atom
x
y
z
Ueq
Ru(1)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
0.0000
0.0000
0.0000
0.0000
−0.01579(5)
−0.1436(5)
−0.1215(4)
−0.1358(3)
−0.0867(4)
−0.0973(5)
−0.1583(5)
−0.2090(5)
−0.1970(4)
0.0914(5)
0.0917(5)
−0.00007(5)
0.1278(5)
0.1076(4)
0.1223(4)
0.1841(4)
0.2027(6)
0.1601(6)
0.0997(5)
0.0804(4)
−0.1071(6)
−0.1083(6)
39.7(2)
35(2)
34(1)
39(1)
50(1)
58(2)
54(2)
54(2)
47(2)
91(4)
88(3)
47.9(2)
39(2)
44(2)
39(1)
46(2)
56(2)
61(2)
56(2)
49(1)
96(4)
108(5)
0.1043(6)
0.1058(5)
0.1862(6)
0.1914(7)
0.1221(8)
0.042(1)
0.0374(6)
0.043(2)
0.1259(9)
0.6667
0.1198(7)
0.2388(5)
0.3419(6)
0.4539(6)
0.4691(8)
0.368(1)
0.2560(6)
0.126(1)
0.085(2)
0.3333
C(9)
C(10)
Ru(2)
C(21)
C(22)
C(23)
C(24)
C(25)
C(26)
C(27)
C(28)
C(29)
C(30)
0.6667
0.3333
0.7901(8)
0.9059(5)
0.9162(6)
1.033(1)
1.1344(8)
1.1254(6)
1.0116(6)
0.575(2)
0.541(1)
0.3607(7)
0.4763(5)
0.5610(6)
0.6634(7)
0.6848(8)
0.6039(8)
0.4999(7)
0.365(2)
0.245(1)
Fig. 1. ORTEP plot (30% probability ellipsoids) of 1a (showing only
one of the crystallographically independent molecules).
a The anisotropic thermal parameters are given in the form of their
2
isotropic equivalents (in 103 A ).
,

340
G.E. Herberich, T.P. Spaniol / Journal of Organometallic Chemistry 582 (1999) 338–344
Table 2
Table 4
,
,
Selected bond distances (A) and angles (°) for 1a
Selected bond distances (A) and angles (°) for 1b
,
Bond length (A)
Ru–C(1)
Ru–C(2)
Ru–C(9)
Ru–C(16)
Ru–C(23)
Ru–C(24)
Ru–C(25)
Ru–C(26)
Ru–C(27)
Ru–C(28)
C(2)–C(1)–C(9)
C(2)–C(1)–C(16)
C(9)–C(1)–C(16)
2.033(3)
2.203(3)
2.194(3)
2.186(3)
2.223(4)
2.214(4)
2.208(4)
2.207(5)
2.208(5)
2.197(5)
110.7(3)
115.0(3)
118.0(3)
Ru1–C(1)
Ru1–C(2)
Ru1–C(9)
Ru1–C(10)
C(1)-C(2)
C(2)–C(3)
C(9)–C(10)
C(9)–C(10)%
2.038(8)
2.196(7)
2.20(1)
2.205(7)
1.449(7)
1.490(9)
1.37(2)
Ru2–C(21)
Ru2–C(22)
Ru2–C(29)
Ru2–C(30)
C(21)–C22)
C(22)–C(23)
C(29)–C(30)
C(29)–C(30)%
2.040(9)
2.215(8)
2.20(1)
2.22(1)
1.435(9)
1.46(1)
1.33(2)
1.45(2)
C(1)–C(2)
C(1)–C(9)
C(1)–C16)
1.426(4)
1.458(5)
1.432(4)
1.401(6)
1.372(6)
1.390(7)
1.374(7)
1.391(8)
1.386(7)
127.7(3)
128.6(3)
127.8(3)
C(23)–C(24)
C(24)–C(25)
C(25)–C(26)
C(26)–C(27)
C(27)–C(28)
C(23)–C(28)
C(1)–C(2)–C(3)
C(1)–C(9)–C(10)
C(1)–C(16)–C(17)
1.41(2)
Bond angles (°)
C(2)–C(1)–C(2)
C(1)–C(2)–C(3)
C(2)–C(3)–C(4)
C(2)–C(3)–C(8)
114.3(3)
123.1(5)
118.2(6)
124.1(5)
C(22)–C(21)–C(22)
C(21)–C(22)–C(23)
C(22)–C(23)–C(24)
C(22)–C(23)–C(28)
115.1(3)
127.7(6)
121.9(6)
120.1(6)
4. Crystal structures
found to be shorter than the corresponding bond
lengths in related TBM ligand [5]. Both
The comparison between both crystal structures
shows the effect that the isomerism has on the relative
orientation of the molecules. It must be noted that the
crystals of 1a and 1b contain the racemic mixtures of
both possible enantiomers. Compound 1a with the pro-
a
crystallographically independent molecules of 1a have a
nearly identical structure within experimental accuracy
(see Table 2). The angles that the phenyl rings form
with the c-axis deviate only slightly with values of ca.
47 and 49°.
Table 5
Crystallographic and selected experimental data for 1a and 1b
Table 3
Coordinates of non-hydrogen atoms for 1b
Compound
1a
1b
a
Atom
x
y
z
Ueq
Formula
C28H24Ru
Prism
Yellow
0.16×0.20×0.64 0.16×0.24×0.56
Trigonal
C28H24Ru
Prism
Yellow
Crystal shape
Crystal colour
Crystal size (mm)
Crystal system
Ru
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
0.15787(3)
0.0121(3)
0.1299(3)
0.1926(3)
0.3248(3)
0.3876(4)
0.3208(5)
0.1896(4)
0.1265(4)
−0.0151(3)
−0.1335(3)
−0.1566(4)
−0.2701(4)
−0.3639(4)
−0.3422(4)
−0.2289(4)
−0.0006(3)
−0.1135(3)
−0.0930(4)
−0.1970(4)
−0.3245(4)
−0.3472(4)
−0.2431(4)
0.1989(5)
0.34867(2) 0.35128(2)
41.3(1)
40.7(8)
41.8(8)
41.7(8)
52.0(9)
62(1)
65(1)
60(1)
51.4(9)
43.5(8)
41.0(8)
55(1)
60(1)
59(1)
61(1)
52.3(9)
42.2(8)
43.4(8)
53.1(9)
63(1)
66(1)
62(1)
51.6(9)
68(1)
64(1)
67(1)
76(1)
80(2)
79(2)
0.2878(2)
0.2648(3)
0.1673(3)
0.1623(3)
0.0746(4)
0.4033(2)
0.4683(2)
0.4889(2)
0.5347(2)
0.5579(3)
0.5370(3)
0.4927(3)
0.4699(2)
0.4023(2)
0.3514(2)
0.2631(2)
0.2218(3)
0.2678(3)
0.3564(3)
0.3973(3)
0.3195(2)
0.2415(2)
0.1558(2)
0.0827(3)
0.0931(3)
0.1771(3)
0.2502(3)
0.2229(3)
0.2507(3)
0.3335(3)
0.3912(4)
0.3649(4)
0.2812(4)
Monoclinic
461.54
P21/c (No. 14)
M (g mol−1
Space group
)
461.54
P31c (No. 159)
Unit cell dimensions
−0.0123(4)
−0.0113(3)
0.0778(3)
0.3936(3)
0.4480(2)
0.4756(3)
0.5249(3)
0.5486(3)
0.5258(3)
0.4769(3)
0.2385(3)
0.2424(2)
0.2307(3)
0.2314(3)
0.2424(3)
0.2510(3)
0.2505(3)
0.3992(4)
0.3141(4)
0.3098(4)
0.3900(5)
0.4743(4)
0.4785(4)
,
a (A)
12.457(7)
12.457(7)
15.95(1)
10.330(2)
13.526(4)
15.402(3)
103.05(3)
4
1.46
7.59
93.89–99.98
,
b (A)
C(8)
C(9)
,
c (A)
i (°)
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
C(17)
C(18)
C(19)
C(20)
C(21)
C(22)
C(23)
C(24)
C(25)
C(26)
C(27)
C(28)
Z
12/3
1.43
7.42
89.00–99.98
zcalc (g cm−3
)
v (Mo–Ka) (cm−1
)
Empirical transmission
Factors
F(000)
Scan range (°)
T (K)
Reflections measured
Indep. refl. obs.
[I]2|(I)]
Final R indices R1, wR2
[I]2|(I)]
Final R indices R1, wR2
All data
Goodness-of-fit
Parameters refined
Residual density
944.0
29
293
6260
2145
944.0
24
293
3398
2379
0.0356, 0.0812
0.0635, 0.1008
0.0253, 0.0537
0.0382, 0.0620
0.2740(5)
0.3579(4)
0.3697(5)
0.2974(6)
1.125
234
1.246, −0.914
1.087
359
0.391, −0.270
0.2115(6)
Maximum, minimum Dz
−3
a The anisotropic thermal parameters are given in the form of their
,
(e A
)
2
isotropic equivalents (in 103 A ).
,

G. E. Herberich, T. P. Spaniol / Journal of Organometallic Chemistry 582 (1999) 338–344
341
Whereas both crystallographically independent
molecules of 1a have nearly identical molecular struc-
tures, their local environment in the crystal lattice is
very different. This is expressed in the molecular coor-
dination [11,12]. We determine the first-neighbouring
molecules on the basis of intermolecular contacts. This
way, we have found coordination numbers of 14 and 18
for the molecules on (0 0 z) and on (2/3 1/3 z) respec-
tively. The different coordination is represented by
projections along the C3-axis (Fig. 5(a) and (b)). For
clarity, Fig. 5(c) shows the positions of the metal cen-
tres only. The geometry of the coordination polyhedron
can be described as a hexagonal prism with a sixfold
capping. The molecule with coordination number 14
(Fig. 5(a)) has contacts with two molecules on the
threefold axis (above and below the original molecules).
After solving this structure, we found that a very
similar arrangement in the solid state was reported for
[Ta(TBM)(h5-C5H5)(CH3)2] 3 [13]. This compound
crystallises in the same space group P31c, which is very
rare [13]. We also note that both compounds do crys-
tallise with nearly identical positions for the metal
atoms and for the carbon atoms of the TBM fragment.
Compared to 3, the atomic co-ordinates for 1a show
that our crystal adopts the opposite polarity. In the
former case, the structural refinement revealed a sub-
stantial amount of inversion twinning (which is not
found here). The peculiar structure of 3 was recognised
and details were discussed [13]. In 3, the imposed
crystallographic C3 symmetry causes the disorder be-
tween the CH3 and the C5H5 groups in spite of their
sterically very different demand. Similarities between
the crystal packing of molecules can often be found in
the molecular enclosure shell but this does not necessar-
ily lead to crystallisation in the same space group [14].
The diastereoisomer 1b shows a considerably differ-
ent packing arrangement (Fig. 6). We observe a molec-
ular co-ordination number of 11, Fig. 7 shows the
molecular enclosure shell. Compared to 1a, the lower
symmetry of 1b allows a more tight packing arrange-
ment, because the phenyl ring ligands can interlock
better with neighbouring molecules. This leads to a
better match of the subunits in the crystal structure.
This effect can be quantified by the values of the
packing coefficient Ck, which are given as the ratio
between the molecular and the crystal volumes [11].
Because an interpretation of these coefficients is useful
on a relative basis, both diastereomeric isomers can be
compared. Here, values of Ck=68.2% for 1b and
65.0% for 1a were determined by the method of Gavez-
zotti [15]. In comparison, the TMM metal complex 2 is
more tightly packed in the solid state (with a value for
Ck of 71.0%), since this molecule has a rather ellipsoidal
shape and no bulky substituents prevent close packing.
The packing of 2 closely resembles that of free benzene,
as shown in Fig. 8 (a) and (b). Such close relationships
Fig. 3. Crystal packing of 1a. SCHAKAL view perpendicular to the
trigonal axis.
peller-like ligand arrangement retains its threefold site-
symmetry in the lattice. This compound crystallises in a
layer structure (Fig. 3). In spite of the polar space
group P31c, all molecules are arranged in an end-to-
end fashion. The three-dimensional arrangement of the
molecules will determine the macroscopic properties of
the crystal. We have determined the unit cell parame-
ters at different temperatures and the results show that
the layer structure is manifested in the strong an-
isotropy of the thermal expansion (Fig. 4).
Fig. 4. Crystal lattice parameters of 1a as a function of temperature.

342
G. E. Herberich, T. P. Spaniol / Journal of Organometallic Chemistry 582 (1999) 338–344
Fig. 5. (a) Crystal packing of 1a. SCHAKAL view parallel to the trigonal axis, showing the coordination of the molecule on (0 0 z). (b) Crystal
packing of 1a. SCHAKAL view parallel to the trigonal axis, showing the coordination of the molecule on (2/3 1/3 z). (c) Same as (b), showing only
the metal atom positions of the coordinating molecules. The view is slightly tilted from the trigonal axis.
between the crystalline packing of the metal complex
and the free ligand have also been observed by Braga
and are especially obvious in the molecular enclosure
shell [16].
strongly directive effect of this fragment may be used to
design other crystal structures with a similar layer
arrangement. This fragment may be employed as a
synthon in crystal engineering [17].
5. Conclusions and outlook
6. Experimental and calculations
The reaction products 1a and 1b show that
diastereoisomers may result when the dianion of TBM
is treated with transition metal halogenides. The prod-
ucts will not necessarily contain only the C3-symmetri-
cal propeller-like ligand.
The close analogy between the crystal structures of
1a and 3 shows that it is the propeller-shaped ligand
TBM which determines how these transition metal
complexes are arranged in the crystal lattice. The
6.1. Synthesis of the (p6-Benzene)(p4-tribenzylidene-
methane) ruthenium isomers 1a and 1b
Experiments were carried out in a dry, oxygen-free
nitrogen atmosphere by means of conventional Schlenk
techniques. Solvents were dried and distilled under
nitrogen prior to use. Alumina for chromatography
(Fa. Woelm, ICN-Adsorbentien) was heated in vacuo
at 300°C and, after cooling, deactivated with deoxy-

G. E. Herberich, T. P. Spaniol / Journal of Organometallic Chemistry 582 (1999) 338–344
343
Fig. 6. SCHAKAL view of the crystal packing of 1b.
genated water (7%). NMR spectra were recorded in
CDCl3 on a Bruker WP-80 PFT spectrometer (1H: 80
MHz) and a Bruker WH-270 spectrometer (13C: 67.88
MHz). The mass spectrum was recorded using a MAT
CH 5-DF (Varian) spectrometer at 70 eV.
[RuCl2(C6H6)]2 [18] (1.81 g, 1.62 mmol) is added with
stirring to [Li(TMEDA)]2[C(CHPh)3] [2] (1.76 g, 3.32
mmol) in THF (100 ml) at −78°C. Stirring is contin-
ued while the mixture was allowed to warm up to r.t.
within 1 h. After removal of all volatiles in vacuo the
residue was dissolved in toluene and the solution was
filtered through a frit with alumina (200 ml). This
process was repeated with toluene–hexane (1:1) as sol-
vent. The solvent was again removed. The residue was
Fig. 8. (a) SCHAKAL view showing the molecular co-ordination of 2.
(b) SCHAKAL view showing the molecular co-ordination of benzene
(co-ordinates are from lit. [26]).
then stirred with hexane (200 ml) overnight. Filtration
and cooling to −30°C gave 1a (0.30 g, 20%) as a
yellow crystalline powder; m.p. (dec.) 232–233°C .
Found: C, 72.9; H, 5.3. C28H24Ru Anal. Calc.: C, 72.9;
H, 5.2%. The mother liquor was concentrated. Chro-
matography over alumina with hexane as eluent gave a
light yellow band. Concentrating the yellow elute and
cooling to −78°C gave 1b (0.10 g, 7.0%) as yellow
crystals; m.p. (dec.) 138–140°C\255°C.
1a: 1H-NMR (ppm): 7.05–7.25 m (3 Ph), 5.13 s
(C6H6), 4.18 s (3 CHPh). 13C-NMR (ppm), J (Hz):
143.6 s (Ci), 129.4 d (158, Cm), 127.5 d (158, Co), 124.2
d (161, Cp); 95.6 s (CC3), 82.5 d (172, C6H6), 61.2 d
(156, 3 CHPh). MS (m/z, Irel. (%)): 461 (83; [M+]), 383
(100; [M+]−C6H6).
1
1b: H-NMR (ppm) 7.0–7.2 m (Ph), 6.7 m (2 Ph),
5.35 s (C6H6), 4.41 d and 3.32 d (4J=1.5 Hz, CHPh),
3.15 s (CHPh); for assignment see text. 13C-NMR
(ppm), J (Hz): 143.2 s, 142.6 s and 141.6 s (Ci), 132.0
Fig. 7. SCHAKAL view showing the molecular co-ordination of 1b.

344
G. E. Herberich, T. P. Spaniol / Journal of Organometallic Chemistry 582 (1999) 338–344
m, 131.0 m, 130.1 m, 127.6 m, 126.5 m and 126.5 m (Co
and Cm), 124.6 m, 124.4 m and 124.2 m (Cp); 96.4 s
(CC3), 83.0 d (173, C6H6), 67.6 d (147, CHPh), 67.1 d
(149, CHPh), 59.7 d (158, CHPh).
volume Vm [15]. Here, we are counting the number of
points that fall inside at least one sphere describing an
atom (using the van der Waals radius). The point mesh
was refined until convergence was reached.
6.2. Determination of the structures of 1a and 1b
Acknowledgements
Data sets were obtained using an Enraf–Nonius CAD4
diffractometer (ꢀ-scan mode, monochromatic Mo–Ka
The authors are indebted to Dr U. Englert for helpful
discussions. Generous support of this work by the Fonds
der Chemischen Industrie is gratefully acknowledged.
,
radiation, u=0.7093 A). The reflections were corrected
for Lp effects using the program MolEN [19] and for
absorption using „-scans [20]. Both structures were
solved by Patterson and Fourier methods. For better
comparison with the structure of 3, the co-ordinates of
1a (Table 1) were transformed into the same asymmetric
unit. The refinement was carried out using the program
SHELXL93 based on F2 [21]. Anisotropic thermal parame-
ters were refined for all non hydrogen atoms. With the
exception of two hydrogen atoms H9 and H10 in 1a,
which were incorporated into calculated positions, all
hydrogen atoms were located and refined with isotropic
thermal parameters. For 1a, the polarity could be deter-
mined unambiguously from the absolute structure
parameter of 0.06(7) [22]. Results are given in Tables 1–5.
Graphical representations of the results were carried out
using the programs ORTEP-III [23] and SCHAKAL [24]. The
unit cell parameters shown in Fig. 4 were determined on
a CAD4 diffractometer with Cu–Ka radiation and 25
centred reflections in the range of (26BqB30°). Crystal-
lographic data for the structural analysis have been
deposited with the Cambridge Crystallographic Data
Centre, CCDC-116616 for 1a and CCDC-116617 for 1b.
Copies of this information may be obtained free of charge
from the Director, CCDC, 12 Union Rd, Cambridge CB2
1EZ, UK (Fax: +44-1223-336-033; e-mail: de-
posit@ccdc.cam.ac.uk; or http://www.ccdc.cam.ac.uk).
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6.3. Coordination numbers
To find out which molecules are forming the enclosure
shell, we calculated the distances between all atoms within
a reference molecule to all remaining atoms which lie
within three unit cells in each direction. If a molecule
contains at least one atom which shows a contact to the
reference molecule, we consider it as being a part of the
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,
A for Ru. Calculations were carried out with the program
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6.4. Packing coefficients
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Packing coefficients were calculated by the numerical
method of A. Gavezzotti by calculating the molecular