Preparation, Molecular and Electronic Structures, and Magnetic Properties of Face-Sharing
Bioctahedral Titanium(III) Compounds: [PPh
4
][Ti
2
(μ-Cl)
3
Cl
4
(PR
3
)
2
]
Linfeng Chen,
²
F. Albert Cotton,*
,²
Kim R. Dunbar,
‡
Xuejun Feng,
²
Robert A. Heintz,
‡
and
Calvin Uzelmeir
‡
Department of Chemistry and Laboratory for Molecular Structure and Bonding, Texas A&M University,
College Station, Texas 77843, and Department of Chemistry, Michigan State University,
East Lansing, Michigan 48824
ReceiVed May 30, 1996
X
Reduction of TiCl
4
with 1 equiv of HSnBu
3
followed by addition of [PPh
4
]Cl and then PR
3
leads to two new
dinuclear titanium(III) compounds, [PPh
4
][Ti
2
(µ-Cl)
3
Cl
4
(PR
3
)
2
] (R ) Et and R
3
) Me
2
Ph), both of which contain
an anion with the face-sharing bioctahedral type structure. Their crystal structures are reported. [PPh
4
][Ti
2
(µ-
Cl)
3
Cl
4
(PEt
3
)
2
]‚2CH
2
Cl
2
crystallized in the triclinic space group P1 h. Cell dimensions: a ) 12.461(1) Å, b )
20.301(8) Å, c ) 11.507(5) Å, R) 91.44°, ) 113.27(1)°, γ ) 104.27(2)°, and Z ) 2. The distance between
titanium atoms is 3.031(2) Å. [PPh
4
][Ti
2
(µ-Cl)
3
Cl
4
(PMe
2
Ph)
2
]‚CH
2
Cl
2
also crystallized in the triclinic space
group P1 h with cell dimensitions a ) 11.635(4) Å, b ) 19.544(3) Å, c ) 11.480(3) Å, R) 100.69(2)°, )
109.70(1)°, γ ) 95.08(2)°, and Z ) 2. The distance between titanium atoms in this compound is 2.942(1) Å.
Variable temperature magnetic susceptibilities were measured for [PPh
4
][Ti
2
(µ-Cl)
3
Cl
4
(PEt
3
)
2
]. Electronic structure
calculations were carried out for a model ion, [Ti
2
(µ-Cl)
3
Cl
4
(PH
3
)
2
]
-
, and another well-known anion, [Ti
2
(µ-
Cl)
3
Cl
6
]
3-
, by employing an ab initio configuration interaction method. The results of the calculations reveal
that the metal-metal interaction in these Ti(III) face-sharing compounds can be best described by strong
antiferromagnetic coulping that leads to a singlet ground state and a thermally accessible triplet first excited state.
Accordingly the measured magnetic data were satisfactorily fitted to a spin-only formula.
Introduction
Titanium has a marked tendency to form cluster species that
possess bridging halogen atoms.
1
One important class of
dinuclear titanium(III) complex are those with a structure of
two fused octahedra that share a common edge. Many such
edge-sharing bioctahedral compounds have been synthesized and
crystallographically characterized.
2
Another important class
comprises those in which two titanium atoms are bridged by
three halogen atoms as to form a face-sharing bioctahedron,
exemplified by the two dinuclear Ti(IV) compounds [(C
6
-
Me
6
)TiCl
3
][Ti
2
(µ-Cl)
3
Cl
6
]
3
and [PCl
4
][Ti
2
(µ-Cl)
3
Cl
6
],
4
both of
which contain a crystallographically characterized bioctahedral
[Ti
2
(µ-Cl)
3
Cl
6
]
-
ion. Dinuclear Ti(III) compounds that exhibit
the face-sharing bioctahedral structure are unknown, except for
the solid state salts, A
3
Ti
2
X
9
(A ) Cs, Rb, Et
2
NH
2
;X ) Cl,
Br),
5-8
which contain a [Ti
2
(µ-X)
3
X
6
]
3-
anion. It has long been
known that the crystal structures of these salts are isomorphous
with that of Cs
3
Cr
2
Cl
9
,
5
but full structural characterization has
never been formally reported.
7
The [Ti
2
Cl
9
]
3-
ion has been
extensively studied for its spectroscopic and, in particular,
magnetic properties.
6-10
Interest in the latter stems from the
high symmetry (D
3h
) of the anion and its simple d
1
-d
1
electronic
configuration, which renders it an ideal candidate for studying
magnetic exchange interaction between two metal centers with
orbitally degenerate local ground states where unquenched
orbital angular momenta are involved.
7-10
Recent studies in this laboratory involving titanium chemistry
have led to a number of new types of titanium compounds.
Herein we report the synthesis and characterization of two new
dinuclear Ti(III) compounds, namely, [PPh
4
][Ti
2
(µ-Cl)
3
Cl
4
(PEt
3
)
2
]
and [PPh
4
][Ti
2
(µ-Cl)
3
Cl
4
(PMe
2
Ph)
2
]. These compounds, which
both contain a [Ti
2
Cl
7
(PR
3
)
2
]
-
anion with the face-sharing
bioctahedral structure, constitute the first Ti(III) compounds of
this type to have been fully characterized by X-ray crystal-
lography. In addition to the synthetic and structural significance,
magnetic properties of these new compounds will also be of
great interest since they provide an instructive comparison to
those of [Ti
2
Cl
9
]
3-
. The variable temperature magnetic sus-
ceptibilities have therefore been measured for one of the
compounds, namely, [PPh
4
][Ti
2
Cl
7
(PEt
3
)
2
]. In conjunction with
²
Texas A&M University.
‡
Michigan State University.
X
Abstract published in AdVance ACS Abstracts, November 1, 1996.
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S0020-1669(96)00636-2 CCC: $12.00 © 1996 American Chemical Society