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Journal of Organometallic Chemistry 596 (2000) 130 – 135
Studies of tetrakis(trifluoroacetate) dirhodium
Part 4. Solventless synthesis of Rh
2
(O
2
CCF
3
)
2
(CO)
4
combined with
Rh
2
(O
2
CCF
3
)
4
, a compound with infinite chains of rhodium atoms
F. Albert Cotton *, Evgeny V. Dikarev, Marina A. Petrukhina
Laboratory for Molecular Structure and Bonding, PO Box 30012, Department of Chemistry, Texas A&M Uniersity, College Station,
TX 77842 -3012, USA
Received 13 September 1999
Abstract
By reaction of Rh
2
(O
2
CCF
3
)
4
and Mo(CO)
6
in an evacuated sealed tube placed in a thermal environment where there is a
thermal gradient (125–120°C), we have obtained a compound in which one Rh
2
(O
2
CCF
3
)
4
unit is sandwiched between two
Rh
2
(O
2
CCF
3
)
2
(CO)
4
units, to give an essentially linear array of six rhodium atoms, with Rh – Rh distances of 2.960(1), 2.790(1)
and 2.412(1) A . These arrays of six rhodium atoms are then linked into infinite chains which lie parallel in the crystal, with Rh
to Rh contacts of 3.062(1) A . The crystals are markedly dichroic and relatively air stable. © 2000 Elsevier Science S.A. All rights
reserved.
Keywords: Rhodium; Trifluoroacetate; Carbonyl; Crystal structure
1. Introduction
Recently we began doing some chemistry that brings
together two novel concepts: (1) the use of a powerful,
two-ended Lewis acid as a structural element and (2)
solventless synthesis.
The two-ended Lewis acid we have chosen is dirhod-
ium(II) tetra(trifluoroacetate) (I). This is, of course,
only one of hundreds of Rh
2
(O
2
CR)
4
and Rh
2
(O
2
CR)
4
-
L
2
compounds [1–3]. It was discovered in 1963 [4], and
a large number of Rh
2
(O
2
CR)
4
L
2
adducts have been
reported. In general, these are easily made by merely
treating Rh
2
(O
2
CR)
4
with the donor and it is usually
possible to obtain crystals of the di-adducts from solu-
tion. The Rh
2
(O
2
CCF
3
)
4
molecule is such a good Lewis
acid that special precautions are necessary to avoid the
formation of the diaqua adduct. As noted in the first
report of its existence [4], Rh
2
(O
2
CCF
3
)
4
is volatile and
can be sublimed without decomposition at temperatures
up to 260°C [5]. Finally, we note that the ‘unliganded’
compound in the solid state [5] is ‘self-liganded’. That
is, it forms infinite chains as shown in II.
* Corresponding author. Tel.: +1-409-845-4432; fax: +1-409-845-
9351.
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII:S0022-328X(99)00609-9