Mineralization routes to polyphosphides: Cu2P20 and Cu5InP16

Article abstract of DOI:10.1002/anie.200705540

(Figure Presented) Mineralization chemistry: Cu₂P₂₀ and Cu₅InP₁₆ were synthesized by a mineralization reaction from the elements and binary starting materials. Cu₂P₂₀ is the first representative retaining the structural features of violet or fibrous phosphorus in a binary compound (see picture). Cu₅InP ₁₆ displays a previously unseen layered polyphosphide substructure built up of six-membered rings connected via four phosphorus bridges.

Full text of DOI:10.1002/anie.200705540

Communications
DOI: 10.1002/anie.200705540
Phosphorus Chemistry
Mineralization Routes to Polyphosphides: Cu2P20 and Cu5InP16**
Stefan Lange, Melanie Bawohl, Richard Weihrich, and Tom Nilges*
The element chemistry of phosphorus is one the most
complex but also one of the most exciting of all chemical
elements. Both the element and the binary and ternary
derivatives show a great diversity in terms of reactivity,
structural chemistry, and physical properties,[1] such as
polymorphism, magnetism, and superconductivity, and are
applied, for example, as thermoelectrics, catalysts, or in
precipitation hardening. Four allotropic modifications of
phosphorus are known to date at standard conditions,
namely white, violet, fibrous, and black phosphorus, besides
the amorphous red phosphorus.[2–6]
phosphorus,[13] making this phosphorus modification com-
mercially available[14] and accessible for applications. Both
compounds have been synthesized by a kinetically controlled
reaction route using main group metal halides such as SbI3 or
SnI4 as reaction promoters (mineralizers). The general
reaction principle is closely related to the well-known concept
of mineralization reactions described by Schäfer.[15]
Phosphides and polyphosphides such as Zn3P2, Cu3P,
LiCu2P2, and Li7Cu5P8 are considered to be promising
materials for electrodes in rechargeable batteries,[16–19] and a
carbon–phosphorus composite was successfully tested as an
electrode material.[20] The ongoing interest in new energy
storage materials on the one hand and the still not completely
solved material and engineering problems with present
battery systems on the other hand are stimulating the
development of new synthesis routes to new materials.
Polyphosphides with anisotropic subunits (2D layers) are
potential candidates for intercalation reactions, as shown in
case of black phosphorus. Herein we report on the CuI-
mediated synthesis of Cu2P20 and Cu5InP16 as well as on their
structures and physical properties.
White phosphorus comprises molecular P4 units, and black
phosphorus is a layered compound, whereas violet and
fibrous phosphorus are characterized by polymeric phospho-
rus stands of tubular [P20]2ꢀ units connected via P2 bridges.
Structural fragments of these units have been identified in
amorphous red phosphorus by vibrational spectroscopy and
in KP15 by structural analysis.[7] Some theoretically predicted
allotropes[8] featuring polymeric phosphorus units were
successfully isolated from a copper halide matrix.[9a] P15Se
and P19Se are two examples of heteroatomic polymer chains
that have similar but not identical structural motifs to
X-ray powder diffraction and EDX analyses for both
polyphosphides substantiated the phase purity of the bulk
phases and the composition of the single crystals selected for
the structure determinations.[21] The crystal structure of
Cu2P20 was solved from single-crystal X-ray data at room
temperature (Figure 1, top).[22a] Tubular [P20]2ꢀ units are
stacked parallel to each other and connected through
[P20]2ꢀ [9b]
In the past decades elemental phosphorus was
.
used to prepare a plethora of binary and multinary phos-
phides and polyphosphides.[1] Thermodynamically and also
kinetically controlled reactions[10] were developed to derive
new compounds from elemental phosphorus. Surprisingly
none of the developed methods led to a binary derivative of
violet or fibrous phosphorus with retention of the polyphos-
phide substructure. Only one ternary compound featuring a
[P20]2ꢀ unit, the direct subunit of the element structure,
embedded in a copper(I) halide matrix, was reported.[11]
Recently we prepared the novel polyphosphide AgSbP14,
ꢀ
tetrahedrally coordinated copper(I) ions; the Cu P bond
ꢀ
lengths range between 2.271(3) and 2.317(3) Š. The P P
bond lengths (2.154(4)–2.322(3) Š) within the tubular [P20]2ꢀ
unit lie in the range reported for covalently bonded phos-
phorus (2.15–2.30 Š).[1b] The [P20]2ꢀ unit, built up by P2
dumbbells, P3 units, and P8 units, can be regarded as a
fragment of the polymeric structure of violet or fibrous
phosphorus. Baudler introduced a set of rules,[23] which were
extended by Häser, to describe the unique and complex
phosphorus substructures in terms of subunits and their
links.[8] According to these rules the [P20]2ꢀ unit can be written
as 11([P8]P2[P3]P2[P3]P2[) and can be regarded as a con-
densation of a [P8]P2[ and two [P3]P2[ fragments. Both
fragments are two of the possible repeating units of the
Baudler set for polymers. A high Baudler index of 9, which is
derived from the number of five-membered rings minus the
number of three-membered rings, is a good indicator of a
highly stable polymer unit. The close relationship to violet
and fibrous phosphorus can easily be derived from the
Baudler/Häser scheme 11([P8]P2[P9]P2[) for violet phospho-
rus by abstraction of the P2 link located in the [P9] unit. A
[P3]P2[P3] fragment for each strand (Figure 2) results.
ꢀ
the first pure inorganic material containing a covalent Sb P
interaction,[12] and developed a low-pressure route to black
[*] Dr. S. Lange, M. Bawohl, Priv.-Doz. Dr. T. Nilges
Institut für Anorganische und Analytische Chemie
Corrensstrasse 30, 48149 Münster (Germany)
Fax: (+49)251-83-36636
E-mail: nilges@uni-muenster.de
Homepage:
http://www.uni-muenster.de/Chemie.ac/nilges/welcome.html
Dr. R. Weihrich
Institut für Anorganische Chemie
Universität Regensburg
Universitätsstrasse 31, 93040 Regensburg (Germany)
[**] This work was supported by the DFG (Grant NI 1095/1-1 and WE
4284/1-1). We thank Dr. R.-D. Hoffmann and Dipl.-Chem. W.
Hermes for magnetic susceptibility measurements, and Prof. Dr. R.
Pöttgen for continuous support.
The parallel stacking of the polyphosphide strands is
forced by the cations coordinating one three-bonded (3b)P
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author.
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Chemie
Figure 2. Structure relationships between Cu2P20, violet P,[4] fibrous P,[5]
and (CuBr)10Cu2P20.[11] The orientation of the tubular units relative to
each other and the Baudler nomenclature is given.
compared with the average MPA of 0.29 a.u. for the remain-
ing bonds. We hope to be able to break this slightly activated
bond by intercalation or electrochemical reactions, to reduce
the tubular polyphosphide strand to a [P5ꢀ] unit, which would
correspond to a polymer of the Bauder set unit [P3]P2[.
The mineralization concept was successfully transferred
to ternary polyphosphides, which substantiated the high
potential of the general method. Cu5InP16 crystallizes mono-
clinic in the space group C2/c.[22b] It contains a previously
unknown polyphosphide substructure built up by P6 rings in
the chair conformation, connected to each other in 1-, 2-, 5-, 6-
position through (2b)P bridges. Alternatively, the polyphos-
phide substructure can be described by condensed corrugated
P14 and P6 rings, which form a polyphosphide layer. This
unique arrangement has not previously been found in
polyphosphide chemistry, but it has a topological pendant in
ultraphosphate chemistry as regards the phosphorus sub-
structure.[27] NiP4O11 and MgP4O11 show similar but not
identical 14/6 ring subunits.[28] The polyphosphide layers in
Cu5InP16 are connected through a tetrahedrally coordinated
Cu and through a [3+1] coordinated mixed occupied Cu/In
position (Figure 1, bottom).
Figure 1. Crystal structures of Cu2P20 (top) and Cu5InP16 (bottom).
Anisotropic displacement parameters at 95% probability. Cu and Cu/
In coordination spheres are illustrated by polyhedra.
position (P18) and the bridging two-bonded (2b)P atoms P19
and P20. Cu2P20 represents the direct link between the
element chemistry and the huge field of phosphides and
polyphosphides. Despite a plethora of polyphosphides de-
scribed so far, no binary polyphosphide has been reported in
which the structural features of the tubular element allotropes
are retained. Cu2P20 is diamagnetic, in good agreement with
the two d10 ions connecting the covalently bonded polyphos-
phide substructure.[24] Band structure calculations at the DFT
level (GGA) revealed that Cu2P20 is a semiconductor with a
band gap of 1.58 eV, which is consistent with the dark red/
violet color of the compound.[25]
Both Cu2P20 and Cu5InP16 can be regarded as electron-
precise compounds with Cu+, In3+, (2b)Pꢀ, and (3b)P0
resulting in Cuþ2 [(3b)P108(2b)P2ꢀ] and Cuþ5 In3+[(3b)P00(2b)Pꢀ2 ]
following the Zintl–Klemm concept.
Our studies confirm that the mineralization principle,
which is based on the use of small amounts of metal halides as
reaction promoters, is a powerful tool in polyphosphide
chemistry. The application of the method ranges from
element chemistry (low-pressure route to black phosphorus)
over binary compounds such as Cu2P20, the first example of a
polyphosphide with complete retention of the structural
features of the element, to ternary compounds with previ-
ously unknown polyphosphide substructures (Cu5InP16). It
can also be used to make some of the elements such as Hg, Pb,
Sb, Bi, or Te, which are known to be less or nonreactive with
Within the polyphosphide substructure a “weak” bond is
located between P17 and P18 in the P8 unit. Compared to that
[4]
ꢀ
ꢀ
in violet (d(P P) = 2.30 Š) or fibrous phosphorus (d(P P)
2.31 Š), this bond in slightly elongated to 2.322(3) Š.[26] From
Mulliken population analyses (MPA) of the polyphosphide
substructure, we found the highest overlap of 0.31 a.u. for the
ꢀ
(2b)P positions to the neighboring P positions (d(P P) ca.
2.15 Š). A MPA of 0.25 a.u. is observed for this “weak” bond
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5655

Communications
Schmidt, Angew. Chem. 1967, 79, 32 3;Angew. Chem. Int. Ed.
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phosphorus, more accessible as starting materials for the
synthesis of new compounds. These elements and do not form
binary phases with phosphorus and only a handful of ternary
compounds of Hg or Te have been stabilized as phosphide
halides,[29] BaP4Te2,[30] and Ti2PTe2.[31] Recently we reported
on AgSbP14, the first purely inorganic compound with a
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ꢀ
covalent Sb P interaction, and we have preliminary exper-
imental evidence for a compound in which Pb is the only
cationic species stabilizing a polyphosphide substructure.
Currently we are looking to increase the number of miner-
alization agents and trying to generalize and transfer the
principle to other polyanionic frameworks. A first successful
step was the transfer of this principle to polytellurides.[32]
[13] S. Lange, P. Schmidt, T. Nilges, Inorg. Chem. 2007, 46, 4028 –
4035.
[14] Black Phosphorus is commercially available: http://www.chem-
pur.de. See also: T. Nilges, M. Kersting, T. Pfeiffer, J. Solid State
Chem. 2008, DOI: 10.1016/j.jssc.2008.03.008.
[15] H. Schäfer, Chemische Transportreaktionen in Monographien zu
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[17] M.-P. Bichat, T. Politova, J. L. Pascal, F. Favier, L. Monconduit, J.
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Experimental Section
Cu2P20 was synthesized by the reaction of Cu3P and red P (Chempur,
99.999 + %) in the molar ratio of 1= :92= in evacuated silica ampoules.
3
3
A total of 300 mg of powdered starting materials were placed in the
ampoule together with CuI (4 mg, Sigma Aldrich, 98%) as mineral-
ization promoter. Cu3P was prepared from the elements at 1023 K in
evacuated silica ampoules and checked for phase purity by X-ray
powder diffraction and EDX analyses. The starting materials were
heated to 820 K within 10 h and kept at that temperature for one
week. Cu2P20 was obtained as a dark red powder, on top of which
needle-shaped crystals grew. When the reaction was carried out
without adding CuI under the above-mentioned conditions, a mixture
of Cu2P7 and elemental phosphorus was obtained.
Cu5InP16 was synthesized by reacting Cu (Chempur, 99.999%, In
(Chempur, 99.99%) and red P (Chempur, 99.999 + %) in a molar
ratio of 5:1:16 in evacuated silica ampoules. CuI (10 mg) was added to
a total of 500 mg of starting materials. After an initial heating step to
550 K for 8 h, the mixture was kept at 823 K for 14 days.
[18] H. Schlenger, H. Jacobs, Acta Crystallogr. Sect. B 1972, 28, 327.
[19] H. Schlenger, H. Jacobs, R. Juza, Z. Anorg. Allg. Chem. 1971,
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[20] C.-M. Park, H.-J. Sohn, Adv. Mater. 2007, 19, 2465 – 2468.
[21] X-ray powder diffraction data were collected by using a Stoe
STADIP powder diffractometer fitted with CuKa1 radiation (l =
1.54051 Š), germanium monochromator, transmission geometry,
298 K, 7.0 < 2q < 70.08, linear 58 PSD (Braun). A comparison of
calculated and measured powder diffractograms of the samples
is given in the Supporting Information. Lattice parameters
derived from the powder data were used for the single-crystal
structure determinations. Semiquantitative EDX analyses were
performed by using a Leica 420i scanning electron microscope
(Zeiss) fitted with an energy-dispersive detector unit (EDX,
Oxford). Cu, In, and GaP were used as standards for calibration.
A voltage of 20 kV was applied to the samples. Data were
averaged for more than five independent measurements col-
lected from crystals separated from different reaction batches.
Cu2P20 (in atom%): Cu 9(2), P 91(2); calcd: Cu 9.1, P 90.9;
Cu5InP16: Cu 24(2), In 5(2), P 72(2); calcd: Cu 22.7, In 4.6, P 72.7.
Cu2P20 is sensitive to hydrolysis in air after several days. Samples
were stored under an argon atmosphere. Cu5InP16 is stable in air
for several months and can stored without the need for an inert
gas atmosphere.
Received: December 4, 2007
Revised: February 23, 2008
Published online: June 23, 2008
Keywords: coinage metals · indium · mineralization reactions ·
.
phosphorus · polyphosphides
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[27] An overview on the topological relationship between polyphos-
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[32] Examples with polytelluride substructures are Ag10Q4X3
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Angew. Chem. Int. Ed. 2008, 47, 5654 –5657ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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