Synthesis and characterization of the [Ni6Ge13(CO) 5]4- and [Ge9Ni2(PPh 3)]2- Zintl ion clusters

Article abstract of DOI:10.1016/j.poly.2005.07.031

Reactions between K₄Ge₉, Ni(CO)₂(PPh ₃)₂, and 2,2,2-crypt in ethylenediamine solutions give two different products depending on reaction conditions. The [Ni₆Ge ₁₃(CO)₅]^4- ion (1) is formed at low temperatures (～40°C) and short reaction times whereas the [Ge ₉Ni₂(PPh₃)]^2- ion (2) forms at higher temperatures (～118°C). Both complexes were isolated as [K(2,2,2-crypt)]⁺ salts and characterized by single-crystal X-ray diffraction, electrospray mass spectrometry (ESI-MS) and NMR studies ( ¹³C and ³¹P). 1 has a hypo-closo cluster electron count (Wades Rules) and adopts an interpenetrating biicosahedral structure with 17 vertices and 2 interstitials, which is unique in transition metal Zintl ion clusters. 2 also has a hypo-closo cluster electron count but displays an open, nido-like 10-vertex structure with a Ni interstitial. The composition of 2 was established through ESI-MS studies and corrects an earlier report that characterized the cluster as [Ge₁₀Ni(PPh₃)]^2- with an interstitial Ge.

Full text of DOI:10.1016/j.poly.2005.07.031

Polyhedron 25 (2006) 521–529
www.elsevier.com/locate/poly
Synthesis and characterization of the [Ni6Ge13(CO)5]4ꢀ
and [Ge9Ni2(PPh3)]2ꢀ Zintl ion clusters
*
Emren N. Esenturk, James Fettinger, Bryan Eichhorn
Department of Chemistry and Biochemistry, University of Maryland, College Park, MD 20742, United States
Received 3 June 2005; accepted 21 July 2005
Available online 31 August 2005
Abstract
Reactions between K4Ge9, Ni(CO)2(PPh3)2, and 2,2,2-crypt in ethylenediamine solutions give two different products depending
on reaction conditions. The [Ni6Ge13(CO)5]4ꢀ ion (1) is formed at low temperatures (ꢁ40 ꢀC) and short reaction times whereas the
[Ge9Ni2(PPh3)]2ꢀ ion (2) forms at higher temperatures (ꢁ118 ꢀC). Both complexes were isolated as [K(2,2,2-crypt)]+ salts and char-
acterized by single-crystal X-ray diffraction, electrospray mass spectrometry (ESI-MS) and NMR studies (13C and 31P). 1 has a
hypo-closo cluster electron count (Wades Rules) and adopts an interpenetrating biicosahedral structure with 17 vertices and 2 inter-
stitials, which is unique in transition metal Zintl ion clusters. 2 also has a hypo-closo cluster electron count but displays an open,
nido-like 10-vertex structure with a Ni interstitial. The composition of 2 was established through ESI-MS studies and corrects an
earlier report that characterized the cluster as [Ge10Ni(PPh3)]2ꢀ with an interstitial Ge.
ꢁ 2005 Elsevier Ltd. All rights reserved.
Keywords: Polygermanide; Zintl; Icosahedron
1. Introduction
anes and are predicted by Wades rules [14] whereas oth-
ers, such as [Sn9Pt2(PPh3)]2ꢀ, seem to violate Wadeꢀs
structure prediction principles [15]. The latter complex
has 20 cluster electrons with 10 surface vertices, which
corresponds to a hypo-closo system in a Wade type anal-
ysis. The observed structure is not the anticipated
closed, deltahedral type but a more open, nido-like
framework [16] with fewer Sn–Sn contacts that pre-
dicted. This structural variance presumably results from
the steric demands of the centered Pt atom and the weak
nature of the Sn–Sn bonds. For comparison, the closely
related [Sn9Ni2(CO)]3ꢀ, which has a smaller Ni intersti-
tial, adopts the expected closo structure in accord with
its 21 electron, 2n + 1 configuration [15].
Interest in ‘‘ligand-free’’ transition metal derivatives
of Zintl ions has received much attention of late due
to their close relationship to nanoparticles and fuller-
cages [1–4], their remarkable molecular and electronic
structures [5,6] and their utility in preparing low temper-
ature alloys and intermetallics [7,8]. In particular, group
14 Zintl ions (i.e., Ge94ꢀ, Sn94ꢀ, Pb94ꢀ) react with labile
transition metal precursors to give high symmetry clus-
ters that often contain centered transition metals. These
include the [M@Pb12]2ꢀ and [M@Pb10]2ꢀ ions where
M = Ni, Pd, Pt [9–11], and the recently reported
[Pd2@Ge18]4ꢀ and [Ni3@Ge18]4ꢀ clusters [12,13]. The
structures of these clusters depend on both the steric
demands of the constituent elements and the cluster
electron count. Many have structures similar to the bor-
Our initial studies with group 14 Zintl ions involved
the use of MLn subunits that did not contribute elec-
trons to cluster bonding and were not expected to alter
the cluster electron count or Zintl ion precursor frame-
*
work structure. For example, the 9-vertex, 22-electron
Corresponding author.
E-mail address: eichhorn@umd.edu (B. Eichhorn).
4ꢀ
nido-Sn9
complex forms the expected 10-vertex,
0277-5387/$ - see front matter ꢁ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2005.07.031

522
E.N. Esenturk et al. / Polyhedron 25 (2006) 521–529
22-electron closo-[Sn9M(CO3)]4ꢀ series of complexes
(M = Cr, Mo, W) [17]. The first transition metal poly-
germanide was prepared from the reaction between
2.3. Synthesis
2.3.1. Preparation of [K(2,2,2-crypt)]4[Ni6Ge13(CO)5] Æ
1.5en (1)
4ꢀ
Ge9 and Ni(CO)2(PPh3)2 in ethylenediamine solvent.
The product was characterized as [K(2,2,2-crypt)]2-
[Ge9(l10-Ge)Ni(PPh3)] on the basis of X-ray analysis
and Wadeꢀs electron counting principles [18]. By inserting
an interstitial Ge instead of an interstitial Ni atom, one
achieves a nido electron count that is consistent with
the observed nido-like structure. With the discovery [15]
of the isostructural [Sn9Pt2(PPh3)]2ꢀ ion that violates
Wades rules, we were prompted to reinvestigate the
identity of the [Ge9(l10-Ge)Ni(PPh3)]2ꢀ ion by way of
electrospray mass spectrometry (ESI-MS) and a new sin-
gle-crystal X-ray analysis. During the course of our inves-
tigation, we discovered a new type of transition metal
Zintl cluster, [Ge13Ni6(CO)5]4ꢀ, that possesses an inter-
penetrating biicosahedral structure [19,20]. Herein we
report the synthesis and characterization of this cluster
in addition to the correct structure and composition of
the [Ge9Ni2(PPh3)]2ꢀ ion that was previously described
[18] as the [Ge9(l10-Ge)Ni(PPh3)]2ꢀ ion. The interconver-
sion of these complexes and their relationships to other
transition metal group 14 Zintl complexes are described.
In a vial K4Ge9 (54 mg, 0.07 mmol), 2,2,2-crypt
(100 mg, 0.27 mmol), and [Ni(CO)2(PPh3)2] (84 mg,
0.14 mmol) were dissolved in 4 ml of en yielding a red/
brown mixture. This mixture was heated (35 ꢀC <
T < 45 ꢀC) and stirred for about 15 min. and filtered
through a hot filter. After a week small thin black
crystals of [K(2,2,2-crypt)]4[Ni6Ge13(CO)5] Æ 1.5en pre-
cipitated. Yield: ꢁ20 mg (ꢁ30%). EDX Ge:Ni:K =
3.8:1.7:1. ESI-MS data: (m/z, ion) 1850 [K(2,2,2-
crypt)Ni6Ge13(CO)5]1ꢀ
(CO)4]1ꢀ 1296 [Ni6Ge13]1ꢀ
Ge9Ni2(CO)]1ꢀ; 838 K[Ge9Ni2(CO)]1ꢀ; 810 K[Ge9Ni2]1ꢀ
770 [Ge9Ni2]1ꢀ; 677 K[Ge4Ni4(CO)4]1ꢀ
;
1821 [K(2,2,2-crypt)Ni6Ge13-
1214 [K(2,2,2-crypt)-
;
;
;
.
2.3.2. Preparation of [K(2,2,2-crypt)]2[Ni2Ge9(PPh3)] Æ
en (2)
In a vial K4Ge9 (54 mg, 0.007 mmol), 2,2,2-crypt
(100 mg, 0.27 mmol), and [Ni(CO)2(PPh3)2] (84 mg,
0.14 mmol) were dissolved in 4 ml of en yielding a red/
brown mixture. This mixture was boiled and stirred
for about 15 min, and filtered through a hot filter. After
3–4 days block-shaped black crystals of [K(2,2,2-
crypt)]2[Ni2Ge9(PPh3)] Æ en started to precipitate. Yield:
ꢁ20 mg (ꢁ30%). EDX analysis on crystals showed pres-
ence of K, P, Ge, and Ni. ESI-MS data: (m/z, ion)
1447 [K(2,2,2-crypt)Ni2Ge9(PPh3)]ꢀ1, 1072 K[Ni2Ge9-
2. Experimental
2.1. General data
All reactions were performed in a nitrogen atmo-
sphere drybox (Vacuum Atmosphere Co.). The
31P{1H} NMR spectrum was recorded on a Bruker
DRX400 spectrometer at 162 MHz. Electrospray Mass
Spectra (ESI-MS) were obtained by direct injection of
DMF solutions into a Finnigan mass spectrometer.
Samples were detected in the negative ion mode. An
AMRAY 1820K scanning electron microscope with a
potential of 20 kV was used for energy dispersive
X-ray (EDX) studies.
(PPh3)]ꢀ1, 838 K[Ni2Ge9(CO)]ꢀ1, 810 K[Ni2Ge9]ꢀ1
.
2.3.3. Interconversion studies
Conversion of 1 to 2. In a dry box, 36 mg of [K(2,2,2-
crypt)]4[Ni6Ge13(CO)5] crystals were dissolved in 4 ml
DMF. ESI-MS data were recorded to confirm the
presence of [Ni6Ge13(CO)5]ꢀ and [K(2,2,2-crypt)]-
[Ni6Ge13(CO)5]ꢀ, [Ni2Ge9(CO)]ꢀ and [Ni2Ge9]ꢀ ions be-
fore the interconversion experiments. 3 mg of PPh3 was
added to the starting solution and the reaction mixture
was stirred for 30 min at ꢁ118 ꢀC. The resulting ESI-
MS spectra showed signals of K[Ni2Ge9(PPh3)]ꢀ and
[Ni2Ge9(PPh3)]ꢀ ions.
Attempted conversion of 2 to 1. In dry box, 20 mg of
[K(2,2,2-crypt)]2[Ni2Ge9(PPh3)] Æ en crystals were dis-
solved in 4 ml DMF. ESI-MS data were recorded to
confirm the presence of [Ni2Ge9(PPh3)]ꢀ and
[K(2,2,2-crypt)][Ni2Ge9(PPh3)]ꢀ ions before the inter-
conversion experiment. The solution was placed in a
Schlenk flask, the head gases evacuated and the flask
back filled with CO gas. The reaction mixture was stir-
red for 3 h under the CO atmosphere. The resulting
ESI-MS spectra showed decomposition of the starting
material but did not show the formation of 1 or the
[Ni2Ge9(CO)]ꢀ ion.
2.2. Chemicals
Melts of nominal composition K4Ge9 was made by
fusion (at high temperature) of stoichiometric ratios of
the elements. The chemicals were sealed in evacuated,
silica tubes and heated carefully with a natural gas/oxy-
gen flame. CAUTION: the synthesis of polygermanides
can result in explosive mixtures and all fusion reactions
should be conducted behind a blast shield inside of a
well functioning hood. 4,7,13,16,21,24-Hexaoxa-1,
10-diazobicyclo[8,8,8]-hexacosane (2,2,2-crypt) and Ni-
(CO)2(PPh3)2 were purchased from Aldrich. Anhydrous
ethylenediamine (en) and dimethylformamide (DMF)
were purchased from Fisher, vacuum distilled from
K4Sn9, and stored under dinitrogen.

E.N. Esenturk et al. / Polyhedron 25 (2006) 521–529
523
2.4. Crystallographic studies
that were all near heavy atoms while the remainder of
the map was featureless indicating that the structure is
both correct and complete.
2.4.1. [K(2,2,2-crypt)]4[Ni6Ge13(CO)5] Æ 1.5en (1)
A black plate with approximate orthogonal dimen-
sions 0.260 · 0.196 · 0.101 mm3 was placed and opti-
cally centered on the Bruker SMART CCD system at
ꢀ80 ꢀC. The initial unit cell was indexed using a least-
squares analysis of a random set of reflections collected
from three series of 0.3ꢀ wide x-scans. Data frames were
collected [Mo Ka] with 0.2ꢀ wide x-scans, 40 s per frame
and 909 frames per series. Five data series were collected
at varying / angles (/ = 0ꢀ, 72ꢀ, 144ꢀ, 216ꢀ, 288ꢀ), and
finally, a partial repeat of the first series, 300 frames,
for decay purposes. The crystal to detector distance
was 4.903 cm, thus, providing a complete sphere of data
to 2hmax = 55.0ꢀ. A total of 96582 reflections were col-
lected and corrected for Lorentz and polarization effects
and absorption using Blessingꢀs method as incorporated
into the program SADABS [21] with 27463 unique
(Rint = 0.0330).
3. Results and discussion
K4Ge9 and Ni(CO)2(PPh3)2 react in ethylenediamine
(en) in the presence of 2,2,2-crypt to give two different
products that depend on reaction conditions. At
moderate temperatures (30 ꢀC < T< 40 ꢀC), the [Ni6-
Ge13(CO)5]4ꢀ ion (1) formed as the [K(2,2,2-crypt)]+ salt
in moderate yield. The [K(2,2,2- crypt)]+ salt of 1 forms
small, thin dark brown crystals is air and moisture sen-
sitive in solution and the solid state. The salt is highly
soluble in DMF and CH3CN and forms dark brown
solutions. The 19-atom cluster has a fused biicosahedral
capsule-like structure with 17 Ge/Ni vertices and 2 cen-
tered Ni atoms. The structure and properties of this
cluster will be discussed in subsequent sections.
System symmetry, lack of systematic absences and
intensity statistics indicated the centrosymmetric tri-
clinic space group P1 (no. 2). The structure was deter-
At higher temperatures (T ꢁ 118 ꢀC), the same reac-
tion yields the [Ge9Ni2(PPh3)]2ꢀ ion (2) in moderate
yields, which crystallizes as large, block-like dark
brown crystals of the [K(2,2,2-crypt)]+ salt. The struc-
ture of the anion has 1 Ni and 9 Ge vertices with a
centered Ni atom and will also be discussed in subse-
quent sections. Both complexes have been character-
ized by single-crystal X-ray diffraction, NMR
spectroscopy (13C and 31P where appropriate), Energy
dispersive X-ray analysis (EDX), electrospray ioniza-
tion mass spectrometry (ESI-MS) and infrared spec-
troscopy. Both salts are highly soluble in DMF and
CH3CN and decompose upon exposure to air in the
solid state or in solution.
A proposed scheme for the interconversion of anions
1 and 2 is illustrated in Scheme 1. The transformation
involves the initial formation of the cluster anion
[Ni6Ge13(CO)5]4ꢀ (1) followed by an irreversible conver-
sion to [Ge9Ni2(PPh3)]2ꢀ (2). This conclusion is based
on the following results and observations:
ꢀ
mined by direct methods with the successful location
of the heavy atom cluster and a few potassium atoms
using the program XS [22]. The structure was refined
with XL [22]. A multitude of least-squares difference-
Fourier cycles were required to locate the remaining
non-hydrogen atoms. All non-hydrogen, full occu-
pancy, atoms were refined anisotropically. All of the
hydrogen atoms were placed in calculated positions.
Various disorders were found for the potassium crypt-
and cations and each was optimized independently. A
full and half occupancy ethylenediamine molecules were
located and also optimized. The final difference-Fourier
map possessed several large peaks that were all near
heavy atoms while the remainder of the map was fea-
tureless indicating that the structure is both correct
and complete. An empirical correction for extinction
was also attempted but found to be negative and there-
fore not applied.
(i) The same Ni precursor, Ni(CO)2(PPh3)2, is used in
the synthesis of 1 and 2. However, anion 1 is iso-
lated from reactions conducted at relatively lower
temperatures (35–40 ꢀC) and short reaction times
whereas the formation of 1 is favored at high tem-
peratures and long reaction times.
(ii) Electrospray mass spectra of DMF solutions of 1
(see following section) show anion 1 as well as,
[Ge9Ni2(CO)]ꢀ and [Ge9Ni2]ꢀ, that result from
fragmentation of the parent. These ions have the
same Ge9Ni2 core composition of 2.
2.4.2. [K(2,2,2-crypt)]2[Ni2Ge9(PPh3)] Æ en (2)
A black block with approximate orthogonal dimen-
sions 0.152 · 0.139 · 0.068 mm3 was mounted as above
and cooled ꢀ100 ꢀC. The data collection was performed
as described above. A total of 75805 reflections were
collected and corrected for Lorentz and polarization ef-
fects and absorption using Blessingꢀs method as incorpo-
rated into the program SADABS with 17295 unique
(Rint = 0.0615).
The structure was solved and refined using the SHEL-
XTL program package [22] as described above. An empir-
ical correction for extinction was also attempted but
found to be negative and therefore not applied. The final
difference-Fourier map possessed several large peaks
(iii) Addition of PPh3 to en solutions of pure [K(2,2,2-
crypt)]4[Ni6Ge13(CO)5] results in the formation
of 2 after ꢁ30 min of reaction at 118 ꢀC. The
ESI-MS spectra of these solutions show signals

524
E.N. Esenturk et al. / Polyhedron 25 (2006) 521–529
Scheme 1.
corresponding to K[Ge9Ni2(PPh3)]1ꢀ and [Ge9Ni2-
mass envelopes arising from the multiple isotopes of
Ge and Ni have been simulated to facilitate assignments
and verify nuclearities. The spectrum for K[Ge9-
Ni2(PPh3)]1ꢀ is shown in Fig. 1 as an example and the
remaining spectra and simulations are given in the Sup-
porting Information. The spectrum of 1 (Fig. S1) shows
weak signals of the [K(2,2,2-crypt)]-coordinated molecu-
lar ion of [Ni6Ge13(CO)5]ꢀ along with the decarbonyl
(PPh3)]1ꢀ ions, that coincide with those of the
authentic sample.
(iv) Reactions between 2 and carbon monoxide result
in cluster decomposition but do not regenerate 1
or result in the formation of [Ge9Ni2(CO)]ꢀ
according to ESI-MS analysis.
ꢀ
While these experiments show that 2 can be generated
loss products Ni6Ge13ðCOÞ4ꢀ, Ni6Ge13ðCOÞ2 and li-
from 1 under appropriate conditions, they do not pre-
gand-free binary ion Ni6Ge13ꢀ. Paꢀtterns of new com-
clude the direct formation of 2 from Ge9
and
pounds, Ge9Ni2(CO)ꢀ and Ge9Ni ꢀare also observed
4ꢀ
2
Ni(CO)2(PPh3)2.
as well as peaks for the Ge4Ni4ðCOÞ4 cluster ion paired
Indeed, the synthesis of closely related clusters such as
[Sn9Pt2(PPh3)]2ꢀ appear to form directly from Sn94ꢀ with
sequential addition of Pt fragments (NMR analysis) [15]
and do not seem to involve intermediates akin to 1. More-
over, the proposed mechanism for the formation of the
closely related [Ni3@Ge18]4ꢀ involves direct insertion of
Ni into a Ge9 cluster and a subsequent coupling [13].
to K+ and [K(2,2,2-crypt)]+.
The negative ion electrospray mass spectrum of DMF
solution constituted from crystalline [K(2,2,2-crypt)]2-
[Ge9Ni2(PPh3)] shows an intense signal for the K[Ge9-
Ni2(PPh3)]1ꢀ molecular ion with the expected mass
envelope (Fig. 1). As is common for these types of Zintl
ions, the potassium-coordinated ion pair, K[Ge9-
Ni2(PPh3)]1ꢀ, appears as the parent ion, (m/z 1072.1)
and the fully charged anion is not observed. The
ligand-free Ge–Ni cluster anion K[Ge9Ni2]1ꢀ was also
observed as well as the CO substituted cluster, K[Ge9-
Ni2(CO)]1ꢀ, which presumably results from a trace
contamination in the sample.
3.1. Mass spectrometry
The electrospray mass spectrum for each sample was
recorded in the negative ion mode from DMF solutions
of crystalline [K(2,2,2-crypt)]+ salts. The distinctive

E.N. Esenturk et al. / Polyhedron 25 (2006) 521–529
525
The [Ni6Ge13(CO)5]4ꢀ anion possesses Cs point sym-
metry with a symmetry plane defined by Ge1, Ge8, Ge19
and the bridging carbonyl (Fig. 2). The anion is a
17-vertex deltahedral cluster defined by 13 Ge atoms
and 4 Ni atoms. The cluster is centered by two addi-
tional interstitial Ni atoms. Each of the 4 vertex Ni
atoms has a terminal CO ligand bound in a radial fash-
ion with an additional bridging CO spanning the Ni2–
Ni3 edge. The 17-atom deltahedron possesses 126 total
valence electrons and has 32 cluster electrons according
to Wades rules of electron counting [14]. According to
Wades Rules, each of the Ge atoms contributes 2 elec-
trons whereas each Ni(CO) vertex unit and interstitial
Ni contributes zero electrons. The bridging CO ligand
and the cluster charge contribute 2 and 4 electrons,
respectively, to give 32 cluster electrons
13 ꢂ 2ðGeÞ þ 2ðCOÞ þ 4ðchargeÞ ¼ 32e.
The 17-vertex, 32 electron cluster corresponds to a
hypo-closo electron count and is consistent with the
closed, deltahedral structure type.
Fig. 1. ESI-mass spectrum of the K[Ge9Ni2(PPh3)]1ꢀ molecular ion.
The inset shows the simulated mass envelope.
3.2. Solid-state structures
The [Ni6Ge13(CO)5]4ꢀ structure can be viewed as two
interpenetrating icosahedral units (Ih1 and Ih2) that
share the central Ge3Ni2(CO)2 penagonal ring and the 2
interstitial Ni atoms of the biicosahedral cluster (see
Fig. 2(b)). Ih1 has a composition Ge7Ni6(CO)5 where
Ni7 is interstitial and Ni13 occupies a vertex. Ih2 has a
Ge9Ni4(CO)2 composition where Ni7 occupies a vertex
and Ni13 occupies the interstitial site. This type of inter-
penetrating biicosahedral structure is new for transition
metal Zintl clusters but is known in some of Teoꢀs bime-
tallic Au–Ag and trimetallic Au–Ag–M; M = Pt, Pd, Ni
supraclusters. In particular, the structure of 1 is highly
The [Ni6Ge13(CO)5]4ꢀ (1) and [Ge9Ni2(PPh3)]2ꢀ (2)
anions crystallize as the [K(2,2,2-crypt)]+ salts with tri-
ꢀ
clinic crystal symmetry, space group P1. The former
has 1.5en solvate molecules per formula unit. A sum-
mary of the crystal data is given in Table 1, and selected
bond distances are given in Tables 2 and 3, respectively.
A previous report of the [K(2,2,2-crypt)]2[Ge9Ni2(PPh3)]
structure was incorrectly characterized as having an an-
ion formula [Ge10Ni(PPh3)]2ꢀ. We correct this interpre-
tation here and present a new refinement of the crystal
structure from new X-ray data.
Table 1
Summary of crystallographic data for the [Ni6Ge13(CO)5]4ꢀ and [Ge9Ni2(PPh3)]2ꢀ ions
Empirical formula
Compound formula
Formula weight
[K(2,2,2-crypt)]2[2] Æ en
C78.5H150Ge13K4N9.5Ni6O29
3143.41
193(2)
0.71073
triclinic
[K(2,2,2-crypt)]4[1] Æ 1.5en
C56H95Ge9K2N6Ni2O12
P
1924.28
173(2)
0.71073
triclinic
Temperature (K)
˚
Wavelength (A)
Crystal system
ꢀ
ꢀ
Space group
P1
P1
˚
a (A)
15.2287(4)
16.1988(4)
26.1824(7)
92.7560(10)
91.3490(10)
11.2730(10)
6006.0(3)
12.9083(11)
13.0373(11)
23.569(2)
96.546(2)
104.757(2)
96.868(2)
3764.7(6)
2
˚
b (A)
˚
c (A)
a (ꢀ)
b (ꢀ)
c (ꢀ)
3
˚
Volume (A )
Z
2
Dcalc (g/cm3)
1.738
1.698
Absolute coefficient (mmꢀ1
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2r(I)]a
R indices (all data)a
a
)
4.319
27463/2340/1437
1.118
R1 = 0.0549; wR2 = 0.1794
R1 = 0.0839; wR2 = 0.1936
4.212
17295/5/790
1.029
R1 = 0.0428; wR2 = 0.1007
R1 = 0.0834; wR2 = 0.1111
P
2
2
2
2
The function minimized during the full-matrix least-squares refinement was
wðFo ꢀ Fc Þ where w ¼ 1=½r2ðFo Þ þ ð0:050 ꢃ PÞ þ 1:3423 ꢃ Pꢄ
and P ¼ maxðFo2; 0Þ þ 2 ꢃ Fc Þ=3.
2

526
E.N. Esenturk et al. / Polyhedron 25 (2006) 521–529
Table 2
Table 3
Selected bond distances (A) and angles (ꢀ) for the [Ge13Ni6(CO)5]4ꢀ ion
Selected bond distances (A) and angles (ꢀ) for the [Ge9Ni2(PPh3)]2ꢀ ion
˚
˚
Ge(1)–Ni(2)
Ge(1)–Ni(7)
Ge(4)–Ni(3)
Ge(4)–Ni(7)
Ge(4)–Ni(9)
Ge(5)–Ni(7)
Ge(8)–Ni(2)
Ge(8)–Ni(7)
Ge(1)–Ge(4)
Ge(1)–Ge(5)
Ge(4)–Ge(5)
Ge(4)–Ge(10)
Ge(5)–Ge(10)
Ge(5)–Ge(11)
Ge(8)–Ge(15)
Ge(10)–Ge(11)
Ni(2)–Ni(7)
2.668(1)
2.474(1)
2.610(1)
2.438(1)
2.557(1)
2.431(1)
2.508(1)
2.381(1)
2.658(1)
2.906(1)
2.892(1)
2.735(1)
2.659(1)
2.706(1)
2.703(1)
2.862(1)
2.606(1)
2.742(1)
2.771(1)
2.564(1)
2.637(1)
2.610(1)
2.497(1)
2.522(1)
2.574(1)
2.595(1)
2.666(1)
2.575(1)
2.605(1)
2.499(1)
2.638(1)
2.820(1)
2.749(1)
2.741(1)
2.675(1)
2.777(1)
2.808(1)
2.772(1)
1.694(8)
1.859(8)
1.712(8)
1.898(8)
1.715(8)
1.750(8)
Ni(1)–P(1)
2.121(1)
2.381(1)
2.371(1)
2.370(1)
2.359(1)
2.350(1)
2.433(1)
2.368(1)
1.847(4)
1.843(4)
1.840(4)
2.640(1)
2.608(1)
2.634(1)
2.722(1)
2.733(1)
2.594(1)
2.633(1)
2.692(1)
2.788(1)
2.642(1)
2.656(1)
2.657(1)
2.808(1)
2.692(1)
2.635(1)
Ge(1)–Ni(1)
Ge(3)–Ni(1)
Ge(9)–Ni(1)
Ni(1)–Ni(2)
Ge(1)–Ni(2)
Ge(2)–Ni(2)
Ge(3)–Ni(2)
P(1)–C(1)
P(1)–C(2)
P(1)–C(3)
Ge(1)–Ge(2)
Ge(1)–Ge(8)
Ge(2)–Ge(3)
Ge(2)–Ge(5)
Ge(2)–Ge(6)
Ge(3)–Ge(4)
Ge(4)–Ge(9)
Ge(4)–Ge(7)
Ge(4)–Ge(5)
Ge(5)–Ge(7)
Ge(5)–Ge(6)
Ge(6)–Ge(7)
Ge(6)–Ge(8)
Ge(7)–Ge(8)
Ge(8)–Ge(9)
Ni(2)–Ni(12)
Ni(3)–Ni(9)
Ni(7)–Ni(13)
Ni(7)–Ni(9)
Ni(9)–Ni(13)
Ge(8)–Ni(9)
Ge(10)–Ni(7)
Ge(10)–Ni(9)
Ge(10)–Ni(13)
Ge(14)–Ni(12)
Ge(14)–Ni(13)
Ge(15)–Ni(9)
Ge(16)–Ni(13)
Ge(10)–Ge(16)
Ge(10)–Ge(17)
Ge(14)–Ge(15)
Ge(14)–Ge(19)
Ge(15)–Ge(16)
Ge(16)–Ge(17)
Ge(16)–Ge(19)
Ge(17)–Ge(19)
Ni(2)–C(2)
Ni(2)–Ge(1)–Ni(1)
Ni(1)–Ge(1)–Ge(8)
Ni(1)–Ge(1)–Ge(2)
Ge(8)–Ge(1)–Ge(2)
Ni(2)–Ge(2)–Ge(3)
Ge(3)–Ge(2)–Ge(1)
Ge(3)–Ge(2)–Ge(5)
Ge(1)–Ge(2)–Ge(5)
Ni(2)–Ge(4)–Ge(3)
Ge(3)–Ge(4)–Ge(9)
Ge(9)–Ge(4)–Ge(7)
Ge(9)–Ge(4)–Ge(5)
Ge(7)–Ge(4)–Ge(5)
Ge(9)–Ni(2)–Ge(1)
Ge(1)–Ni(2)–Ni(1)
Ge(1)–Ni(2)–Ge(3)
Ge(1)–Ni(2)–Ge(7)
Ni(1)–Ni(2)–Ge(7)
Ge(3)–Ni(2)–Ge(8)
Ni(2)–Ni(1)–Ge(3)
P(1)–Ni(1)–Ni(2)
P(1)–Ni(1)–Ge(9)
P(1)–Ni(1)–Ge(3)
C(1)–P(1)–Ni(1)
59.82(2)
92.35(3)
82.29(2)
108.20(2)
55.56(2)
89.45(2)
68.03(2)
107.92(2)
56.16(2)
82.94(2)
76.38(2)
109.40(2)
57.60(2)
94.80(3)
60.75(2)
103.73(3)
128.30(3)
148.06(3)
157.16(3)
60.08(2)
177.23(4)
122.79(4)
117.45(4)
119.34(1)
112.37(1)
100.69(2)
102.21(2)
117.79(1)
Ni(2)–C(230)
Ni(3)–C(3)
Ni(3)–C(230)
Ni(9)–C(9)
Ni(12)–C(12)
Ni(2)–Ge(1)–Ni(3)
Ge(4)–Ge(1)–Ge(5)
Ge(4)–Ge(5)–Ge(6)
Ge(1)–Ni(7)–Ni(13)
Ge(5)–Ni(7)–Ge(8)
Ge(6)–Ni(7)–Ni(9)
Ge(4)–Ni(9)–Ge(16)
Ge(6)–Ge(11)–Ge(17)
Ge(8)–Ni(13)–Ge(15)
Ge(16)–Ni(13)–Ni(12)
Ge(19)–Ni(13)–Ni(7)
Ge(16)–Ni(17)–Ge(18)
C(230)–Ni(2)–Ge(6)
C(3)–Ni3–C(23)
54.80(3)
62.44(3)
97.67(3)
173.03(4)
173.04(4)
169.49(4)
122.46(4)
157.25(4)
65.11(3)
171.06(4)
176.55(4)
106.81(3)
140.70(2)
106.10(4)
127.50(3)
81.40(2)
C(2)–P(1)–Ni(1)
C(2)–P(1)–C(1)
C(3)–P(1)–C(2)
C(3)–P(1)–C(1)
C(9)–Ni(9)–Ge(8)
Ni(3)–C(230)–Ni(2)
˚
As expected, Ni–CO(terminal) contacts (avg. 1.718(8) A)
are shorter than the Ni–CO(bridge) contacts (avg.
1.879(8) A). The structure is slightly flattened along
reminiscent of the sss rotamer of the [(PPh3)10Au13Ag12-
Br8]+ triicosahedral cluster [20].
˚
The Ge–Ge, Ni–Ni, and Ni–Ge bond distances are in
the range of 2.658(1)–2.894(1) A (avg. 2.746(4) A),
the Ge8–Ge14 and Ge8–Ge5 vectors. This distortion is
best illustrated by the differences between the 6 diagonal
distances in each icosahedral subunit. In both of the ico-
sahedral cages, diagonal distances involving Ge8, (Ge8–
˚
˚
˚
˚
2.450(1)–2.771(1) A (avg. 2.624(4) A), and 2.381(1)–
˚
˚
2.668(1) A (avg. 2.522(5) A), respectively (see Table 2).

E.N. Esenturk et al. / Polyhedron 25 (2006) 521–529
527
Fig. 2. (a) ORTEP drawing of the [Ni6Ge13(CO)5]4ꢀ anion. Ni is yellow, Ge is blue, C is gray and oxygen is red. A fully labeled drawing is given in
the Supporting material. (b) The two interpenetrating icosahedral subunits, Ih1 and Ih2.
˚
˚
Ge5 = 4.812(1) A for Ih1, and Ge8–Ge17 = 4.878(2) A
for Ih2) are shorter than the other 5 diagonals in the
˚
respective subunits (5.087(5) A, avg. for Ih1, and
5.115(4) A avg. for Ih2).
˚
The Ge–Ge bond distances for the anion
1
˚
(2.6335(9)–2.9064(11); 2.750(6) A avg.) are similar to
those in other polygermenide clusters such as [K(2,2,2-
crypt)]3[P(C6H5)3Ge9], where Ge–Ge distances vary
˚
from 2.53 to 3.27 A [23–25]. The Ni–Ge (2.3808(9)–
˚
˚
2.6681(11) A; 2.523(5) A av.) and Ni–Ni (2.450(1)–
˚
˚
2.771(1) A, 2.624(4) A av.) contacts are similar to the
˚
reported compounds (2.470–2.691 and 2.553–2.721 A,
respectively) [26].
As mentioned previously, the structure of the [Ge9-
Ni2(PPh3)]2ꢀ ion, (2), was incorrectly reported to have
the formula [Ge10Ni(PPh3)]2ꢀ in which the interstitial
atom was refined as Ge. The formula has been
unequivocally established by ESI-MS studies and the
structure re-determined. The structure (Fig. 3) is iden-
tical to that previously reported except for the identity
of the centered atom. The anion has virtual C3v point
symmetry and is isoelectronic and isostructural to
[Sn9Pt2(PPh3)]2ꢀ [15]. It is defined by nine surface Ge
Fig. 3. ORTEP drawing of the [Ge9Ni2(PPh3)]2ꢀ ion, (2). Ni is yellow,
Ge is blue, C is gray, P is purple and H is turquoise.
atoms, one interstitial Ni atom and
a capping
[Ni(PPh3)] fragment. The cluster is a 10-vertex 20-elec-
tron hypo-closo system that has an open, nido-like
structure. For comparison, it is isostructural to the
24-electron 10-vertex [Sb7Ni3(CO)3]3ꢀ ion that adopts a
nido-type architecture [27]. Note that replacing the
centered Ni atom with a Ge atom would add 4 electrons
to cluster bonding and would be consistent with the
observed structure. Although this does not occur, this
electron counting rationale gave rise to the erroneous
assignment in the original publication [18].
The centered Ni atom has nine Ni–Ge contacts in the
˚
range of 2.342(6)–2.447(6) A. The 3 Ni–Ge bonds to Ni1
˚
average 2.37(2) A. The Ge–Ge contacts are in the range
˚
2.594(1)–2.808(1) A and are typical of polygerminide
cages.

528
E.N. Esenturk et al. / Polyhedron 25 (2006) 521–529
3.3. NMR spectroscopic studies
like C3v structure of 2 despite having 5 fewer electrons
than the 22-electron closo-[Ni@Pb10]2ꢀ cluster. While
many of Zintl clusters of the group 14 elements and their
transition metal derivatives adopt Wadian like struc-
tures, there are now several examples that do not. It is
certain that more exceptions will be discovered as re-
search continues.
The 13C NMR spectrum of [Ni6Ge13(CO)5]4ꢀ
(DMSO-d6, 25 ꢀC) shows carbonyl resonances at
194.6, 217.9, 224.9 ppm, which is consistent with the so-
lid state structure.
The room temperature 31P NMR spectrum of [Ge9-
Ni2(PPh3)]2ꢀ crystals shows only free triphenylphos-
phine in DMF solution (d = ꢀ5.1 ppm), suggesting that
PPh3 ligand dissociation is fast on the NMR time scale.
This observation is somewhat surprising in view of the
static nature of the PPh3 ligand in the isoelectronic, iso-
structural [Sn9Pt2(PPh3)]2ꢀ ion and the electron deficient
nature of the cluster.
Acknowledgments
We dedicate this manuscript to Professor Malcolm
Chisholm on the occasion of his 60th birthday. This
material is based upon work supported by the National
Science Foundation under Grant No. 0401850.
4. Conclusions
Appendix A. Supplementary data
In our original report, the centered atom of 2 was
modeled as both Ni and Ge with ultimate selection of
the latter. Due to the similarities in the scattering factors
of Ni and Ge, the refinement of the X-ray data did not
allow for the discrimination between the two models.
The assignment of a centered Ge atom was primarily
based on electron counting principles (Wades rules)
and striking structural similarities to other clusters of
the same nuclearity (e.g., [Sb7Ni3(CO)3]3ꢀ). With the
discovery of [Sn9Pt2(PPh3)]2ꢀ, we were prompted to
reinvestigate the Ni–Ge system and the identity of 2.
The higher precision CCD data reported here and, more
importantly, the ESI-MS data unequivocally identify the
ion as [Ge9Ni2(PPh3)]2ꢀ with a centered Ni atom. The
non-deltahedral nido-like structures of these hypo-closo
clusters are presumably due to steric demands of the
centered metal atom.
Crystallographic data for the compounds have been
deposited with the Cambridge Crystallographic Data
Centre, CCDC Nos. 273776 (1) and 273777 (2). Copies
of this information may be obtained free of charge from
The Director, CCDC, 12 Union Road, Cambridge, CB2
1EZ, UK (fax: +44 1223 3360333 or e-mail: deposit@
ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk). Supple-
mentary data associated with this article can
be found, in the online version, at doi:10.1016/j.poly.
2005.07.031.
References
[1] T.F. Fassler, S.D. Hoffmann, Angew. Chem. Int. Ed. 43 (2004)
6242.
[2] L. Yong, S.D. Hoffmann, T.F. Fassler, Z. Anorg. Allg. Chem.
630 (2004) 1977.
During our re-investigation of the synthesis of 2, we
found that the [Ni6Ge13(CO)5]4ꢀ ion, 1, was formed at
lower temperatures and shorter reaction times. While
we have shown that 2 can be formed from 1 (Scheme 1),
it seems quite possible that it also forms directly from
[3] T.F. Fassler, Angew. Chem. Int. Ed. 40 (2001) 4161.
[4] J.M. Goicoechea, S.C. Sevov, Inorg. Chem. 44 (2005) 2654.
[5] S. Neukermans, E. Janssens, Z.F. Chen, R.E. Silverans, P.V.
Schleyer, P. Lievens, Phys. Rev. Lett. 92 (2004).
[6] R.B. King, T. Heine, C. Corminboeuf, P.V. Schleyer, J. Am.
Chem. Soc. 126 (2004) 430.
4ꢀ
Ge9 and the Ni(CO)2(PPh3)2. The biicosahedral struc-
ture of 1 is unique to Zintl ion chemistry but is a known
feature in bimetallic clusters of the coinage metals [20].
The recently reported [Pd2@Ge18]4ꢀ and [Ni3@(Ge9)2]4ꢀ
cluster anions also in this general class of compounds.
The former is an 18 vertex, 2 focus, 40 electron cluster
with the expected closo architecture (2n + 2 cluster elec-
trons per focus) whereas the latter does not easily fit into
a Wadian description. Interestingly, neither forms icosa-
hedral structures and are structurally distinct from 1.
Recently, we have shown that ligand-free deltahedral
clusters of Pb and Sn that are compositionally similar to
the ligand-free ions identified here. For example,
[Ni@Pb10]2ꢀ and the gas phase [Ni@Pb10]1ꢀ ions are
[7] M.J. Moses, J.C. Fettinger, B.W. Eichhorn, Science 300 (2003)
778.
[8] R.C. Haushalter, C.M. OꢀConnor, J.P. Haushalter, A.M. Umarji,
G.K. Shenoy, Angew. Chem. Int. Ed. 23 (1984) 169.
[9] E.N. Esenturk, B. Eichhorn, J. Fettinger (to be published).
[10] E.N. Esenturk, J. Fettinger, B. Eichhorn, Chem. Commun. (2005)
247.
[11] E.N. Esenturk, J. Fettinger, Y.F. Lam, B. Eichhorn, Angew.
Chem. Int. Ed. 43 (2004) 2132.
[12] J.M. Goicoechea, S.C. Sevov, J. Am. Chem. Soc. 127 (2005)
7676.
[13] J.M. Goicoechea, S.C. Sevov, Angew. Chem. Int. Ed. 44 (2005)
4026.
[14] K.J. Wade, Adv. Inorg. Chem. Radiochem. 18 (1976) 1.
[15] B. Kesanli, J. Fettinger, D.R. Gardner, B. Eichhorn, J. Am.
Chem. Soc. 124 (2002) 4779.
ꢀ1
centered 10-vertex clusters [10] similar to Ge9Ni2 (or
[Ni@Ge9Ni]ꢀ1). The later presumably adopts the nido-
[16] S. Lee, Inorg. Chem. 31 (1992) 3063.

E.N. Esenturk et al. / Polyhedron 25 (2006) 521–529
529
[17] B. Kesanli, J.C. Fettinger, D.R. Gardner, B.W. Eichhorn, Chem.
Eur. J. (2001) 5277.
[23] C. Belin, H. Mercier, V. Angilella, New J. Chem. 15 (1991)
931.
[18] D.R. Gardner, B.W. Eichhorn, J. Fettinger, Angew. Chem. Int.,
Ed. Engl. 35 (1996) 2852.
[24] L. Yong, S.D. Hoffmann, T.F. Fassler, Z. Anorg. Allg. Chem.
631 (2005) 1149.
[19] B.K. Teo, H. Zhang, Y. Kean, H. Dang, X.B. Shi, J. Chem. Phys.
99 (1993) 2929.
[25] C. Downie, Z.J. Tang, A.M. Guloy, Angew. Chem. Int. Ed. 39
(2000) 338.
[20] B.K. Teo, H. Zhang, Coord. Chem. Rev. 143 (1995) 611.
[21] G.M. Sheldrick, Universitat Gottingen, Gottingen, Germany,
1996.
[26] A. Ceriotti, F. Demartin, B.T. Heaton, P. Ingallina, G. Longoni,
M. Manassero, M. Marchionna, N. Masciocchi, J. Chem. Soc.,
Chem. Commum. (1989) 786.
[22] G.M. Sheldrick, Siemens Analytical X-ray Instruments, Inc.,
Madison, WI, 1994.
[27] S. Charles, B.W. Eichhorn, S.G. Bott, J. Am. Chem. Soc. 115
(1993) 5837.