Structural studies of nickel complexes of the unsymmetrical tridentate ligand N-phenyl-N-(2-pyridyl)formamidinate

Article abstract of DOI:10.1016/S0020-1693(03)00112-9

We describe the preparation and structural characterization of six nickel complexes with the unsymmetrical formamidine HPhPyF (N,N′-phenylpyridylformamidine). These six compounds include one dinuclear species Ni₂(PhPyF)₄ (1), two mononuclear complexes: cis-[Ni(HPhPyF)₂(MeCN)₂][BF₄]₂ (3) and Ni(HPhPyF)Br₂ (6), and three trinuclear compounds: Ni₃(PhPyF)₄(MeCN)₂(BF₄) ₂ (2), [Ni₃(PhPyF)₄Cl]Cl (4), and Ni₃(PhPyF)₄Cl₂ (5). In the dinuclear species 1, the two nickel atoms are surrounded by four formamidinate ligands. Each is pseudo-octahedral and there is long separation (≈3.41 ?) between them. One mononuclear compound, cis-[Ni(HPhPyF)₂(MeCN)₂][BF₄]₂ (3) has a distorted octahedral geometry, the other Ni(HPhPyF)Br₂ (6) contains a Ni atom in a pseudo-tetrahedral environment. All three trinuclear compounds contain a linear chain of three Ni^II atoms wrapped by four PhPyF anions, but each has a different axial environment. There are two axially coordinated MeCN in 2, only one axial Cl anion for 4 and two axial Cl anions for 5. In 2, 4, and 5, the Ni₃⁶⁺ chains are symmetrical with relatively long Ni?Ni separations in the range 2.44-2.51 ?.

Full text of DOI:10.1016/S0020-1693(03)00112-9

Inorganica Chimica Acta 351 (2003) 183ꢁ190
/
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Structural studies of nickel complexes of the unsymmetrical tridentate
ligand N-phenyl-N-(2-pyridyl)formamidinate
F. Albert Cotton *, Peng Lei, Carlos A. Murillo *
Department of Chemistry and Laboratory for Molecular Structure and Bonding, P.O. Box 30012, Texas A&M University, College Station,
TX 77842-3012, USA
Received 2 January 2003; accepted 28 January 2003
Abstract
We describe the preparation and structural characterization of six nickel complexes with the unsymmetrical formamidine
HPhPyF (N,N?-phenylpyridylformamidine). These six compounds include one dinuclear species Ni2(PhPyF)4 (1), two mononuclear
complexes: cis-[Ni(HPhPyF)2(MeCN)2][BF4]2 (3) and Ni(HPhPyF)Br2 (6), and three trinuclear compounds: Ni3(Ph-
PyF)4(MeCN)2(BF4)2 (2), [Ni3(PhPyF)4Cl]Cl (4), and Ni3(PhPyF)4Cl2 (5). In the dinuclear species 1, the two nickel atoms are
˚
3.41 A) between them. One
surrounded by four formamidinate ligands. Each is pseudo-octahedral and there is long separation (:
/
mononuclear compound, cis-[Ni(HPhPyF)2(MeCN)2][BF4]2 (3) has a distorted octahedral geometry, the other Ni(HPhPyF)Br2 (6)
contains a Ni atom in a pseudo-tetrahedral environment. All three trinuclear compounds contain a linear chain of three NiII atoms
wrapped by four PhPyF anions, but each has a different axial environment. There are two axially coordinated MeCN in 2, only one
axial Cl anion for 4 and two axial Cl anions for 5. In 2, 4, and 5, the Ni36ꢀ chains are symmetrical with relatively long Ni
/
ꢀ ꢀ ꢀ
/
Ni
˚
separations in the range 2.44ꢁ2.51 A.
/
# 2003 Elsevier Science B.V. All rights reserved.
Keywords: Nickel compounds; Linear trinickel compounds; Unsymmetrical formamidine; Crystal structures
1. Introduction
Metalꢁmetal interactions in dinuclear paddlewheel
compounds have been intensively investigated and are
well understood [1]. Recently, increasing attention has
been given to the chemistry of the metal complexes with
larger numbers of metal atoms in linear arrays [2]. Thus,
a large number of complexes with linear trimetal units
anionic nitrogen based ligands, such as DPhIP (the
anion of 2,6-di(phenylimino)piperidine) [8] and BPAP
(the dianion of bisphenylaminopyridine) [9], shown in
Scheme 2, have also been used to support linear trimetal
units.
/
A very detailed study of Ni3(dpa)4Cl2 [5b] from this
laboratory led to the conclusion that there is no metalꢁ
metal bonding even though the nickelꢁnickel separa-
2.43 A). Instead, there is
/
/
˚
tions are relatively short (:
/
have been synthesized [2ꢁ7]. The majority of these
/
antiferromagnetic coupling between the terminal five-
coordinated nickel atoms, each of which has two
unpaired electrons. The central nickel atom is d8,
square-planar and diamagnetic. Peng and coworkers
[10] have done extensive work on the preparation of
multinuclear nickel compounds with five, seven, nine
nickel atoms in a linear array using oligo-pyridyl amino
ligands. Their results indicate that antiferromagnetic
interactions are similar to those in the trinickel unit and
they decrease as might be expected with increasing chain
length.
complexes characterized to date are supported by the
anion of dipyridylamine (dpa) and have the formula
M3(dpa)4X2 (MꢂCr [3], Co [4], Ni [5], Cu [6], Rh [7],
/
Ru [7]), where X is usually an anion, such as Clꢃ,
occupying axial positions. The typical structure of a
M3(dpa)4X2, molecule is shown in Scheme 1. Some other
* Corresponding authors.
E-mail addresses: cotton@tamu.edu (F. Albert Cotton),
murillo@tamu.edu (C.A. Murillo).
0020-1693/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0020-1693(03)00112-9

184
F. A. Cotton et al. / Inorganica Chimica Acta 351 (2003) 183ꢁ190
/
Scheme 1.
More recently, the one-electron oxidation of Ni3-
(dpa)4Cl2was reported [11]. The NiÃNi distances in the
oxidized compound Ni3(dpa)4(PF6)3 (ꢀ
much shorter than those in the unoxidized species (ꢀ
/
˚
2.28 A) are
/
/
˚
2.43 A), and are consistent with three-center metalꢁ
/
metal bonding and a formal bond order of 0.5.
In this work, we report syntheses and structural
studies of a series of nickel complexes including mono-
nickel, dinickel and trinickel complexes supported by the
anion of the unsymmetrical N,N?-phenylpyridylforma-
midine HPhPyF. A schematic drawing of the formami-
dine is shown in Scheme 3.
Scheme 3.
2.2. Preparations
2.2.1. Preparation of Ni2(PhPyF)4 (1)
A flask was charged with HPhPyF (396 mg, 2.00
mmol) dissolved in 30 ml of THF. The solution was
2. Experimental
cooled to ꢃ78 8C, and 1 equiv. of MeLi was added
/
slowly. The solution was removed from the cold bath,
stirred until it reached room temperature. The mixture
was then added via cannula to a flask containing
anhydrous Ni(py)4Cl2 (670 mg, 1.50 mmol). The reac-
tion mixture was refluxed for 12 h. The volume was then
reduced to approximately 10 ml, and upon addition of
40 ml of hexanes a deep-brown precipitate formed. The
solid was collected by filtration, and washed thoroughly
with ether. After drying, the solid was dissolved in 15 ml
of CH2Cl2, and then 40 ml of hexanes was added to
precipitate the product. The mixture was filtered, and
the solid was briefly dried under vacuum. Finally, the
product was dissolved in 15 ml of CH2Cl2, and layered
with 40 ml of hexanes. Large, dark-blue crystals of
Ni2(PhPyF)4 formed in a week. Yield: 52%.
2.1. General procedures
All manipulations were carried out under an atmo-
sphere of dry nitrogen using standard Schlenk techni-
ques. Solvents were purified prior to use by distillation
over appropriate drying agents in a nitrogen atmo-
sphere. The compounds HPhPyF [12], Ni(py)4Cl2 [13]
and Ni(PPh3)2Br2 [14] were synthesized as previously
described. Anhydrous NiCl2, NiBr2 and AgBF4 were
purchased from Strem. The former was refluxed in
thionyl chloride prior to use. Methyllithium (1.6 M in
ether) was obtained from Acros. Magnetic measure-
ments were done at room temperature on a magnetic
susceptibility balance (Johnson Matthey Chemicals
Limited).
Scheme 2.

F. A. Cotton et al. / Inorganica Chimica Acta 351 (2003) 183ꢁ
/
190
185
2.2.2. Preparation of Ni3(PhPyF)4(MeCN)2(BF4)2 (2)
and [Ni(HPhPyF)2(MeCN)2](BF4)2 (3)
The ligand HPhPyF (396 mg, 2.00 mmol) was
dissolved in 15 ml of THF and deprotonated with 1
2.2.5. Preparation of Ni(HPhPyF)Br2 (6)
To a flask charged with HPhPyF (396 mg, 2.00 mmol)
and Ni(PPh3)2Br2, 10 g of naphthalene was added. The
mixture was quickly heated to 145 8C with gently
stirring. A dark-purple, crystalline precipitate formed.
After 10 min of stirring at 145 8C, the reaction mixture
was allowed to cool to room temperature. The solid was
equiv. of MeLi at ꢃ78 8C. After the temperature of the
/
solution had slowly risen to room temperature, the THF
was removed under vacuum. Then, 40 ml of MeCN was
used to dissolve the residue and the solution was
transferred to a flask containing NiBr2 (378 mg, 1.50
mmol). The yellow mixture was stirred for 3 h at room
temperature. To this mixture AgBF4 (584 mg, 3.00
mmol) was added, and the mixture was refluxed for 12
h, and then filtered. The filtrate was reduced to half of
its original volume and 60 ml of Et2O was added. A
washed with copious amounts of ether, then 2ꢄ
benzene.
/
10 ml of
The remaining solid was dissolved in 20 ml of acetone,
and an insoluble portion was removed by filtration. The
resulting acetone solution was layered with 40 ml of
hexanes. Dark-purple crystals formed in a week. Yield:
58%.
blackꢁbrown solid formed. This was collected by
/
filtration, washed twice with 20 ml of Et2O, and then
dried briefly under vacuum. Finally, the solid was
dissolved in 20 ml of MeCN, and the solution was
layered with ether (40 ml). Three-weeks later, several
2.3. Crystallographic studies
Data were collected on a Bruker SMART 1000 CCD
area detector system. In each case, a suitable crystal was
attached to the tip of a quartz fiber with a small amount
of grease and transferred to a goniometer, where the
crystal was kept in a stream of cold nitrogen. Cell
parameters were obtained using SMART software [15].
Data were corrected for Lorentz and polarization effects
using the program SAINTPLUS [16]. Absorption correc-
tions were applied using SADABS [17].
dark-red,
block-shaped
crystals
of
Ni3(Ph-
PyF)4(MeCN)2(BF4)2 (2) were obtained along with
some blue needle-like crystals of [Ni(HPh-
PyF)2(MeCN)2](BF4)2 (3). The crystals were separated
manually. The yield for compound 2 was about 2% and
that of 3 was 40%.
The positions of heavy atoms were found by the direct
methods programmed in SHELXS-97 [18]. Subsequent
cycles of least-square refinement followed by difference
Fourier syntheses revealed the positions of the non-
hydrogen atoms. All hydrogen atoms were placed in
idealized positions.
Crystallographic data and structure refinement details
for all the structures reported in this work are listed in
Table 1. All space groups were uniquely determined by
systematic absences, and refinements proceeded
straightforwardly.
2.2.3. Preparation of [Ni3(PhPyF)4Cl]Cl (4)
To the ligand HPhPyF (396 mg, 2.00 mmol) in 40 ml
of THF was added 1 equiv. of MeLi at ꢃ78 8C. The
/
deprotonation was essentially complete when the tem-
perature of the mixture rose to room temperature. The
THF solution was transferred to a flask containing
Ni(py)4Cl2 (1.34 g, 3.00 mmol). The reaction mixture
was refluxed for 15 h and then filtered. The volume of
the resulting solution was reduced to approximately 10
ml. Ether (50 ml) was added to this mixture. The solid
was collected by filtration, washed with copious
amounts of ether, and then dissolved in 15 ml of THF.
Addition of hexanes produced a precipitate which was
isolated by filtration. Finally, the solid was dissolved in
15 ml of CH2Cl2, and layered with 40 ml of hexanes.
3. Results and discussion
3.1. Synthetic considerations
Blackꢁ
weeks along with a lot of dark-blue crystals of 1. The
yield of the trinuclear compound 4 was ꢀ8%. Magnetic
/
red crystals of Ni3(PhPyF)4Cl]Cl formed within 2
We were surprised to encounter a great deal of
difficulty in preparing trinickel compounds with the
PhPyF ligand. From a purely preparative point of view,
here our report is far from satisfactory, but the existence
of these compounds of structural interest has been
established.
/
susceptibility at room temperature: 3.08 mB.
2.2.4. Preparation of Ni3(PhPyF)4Cl2 (5)
A simple and commonly-used method to prepare
linear trimetal chain complexes is to react the lithium
salt of the ligand with a stoichiometric amount of the
The method of preparation was similar to that of 4,
except that a threefold excess of Ni(py)4Cl2 was used.
After 3 weeks, very dark red (almost black) crystals of
Ni3(PhPyF)4Cl2 formed along with the some dark-blue
crystals of 1. The yield for the trinickel compound 5 was
anhydrous metal halides [2ꢁ6]. However, we found
/
anhydrous nickel halides (chloride and bromide) to be
very unreactive toward the lithium salt of HPhPyF. No
ꢀ/5%.
reaction takes place when LiPhPyF and NiX2 (XꢂCl,
/

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F. A. Cotton et al. / Inorganica Chimica Acta 351 (2003) 183ꢁ190
/
Table 1
Crystallographic data and refinement details
1
2
3
4
5×
/
CH2Cl2
6
Empirical formula
Formula weight
Space group
C48H40N12Ni2 C52H46B2F8N14Ni3
902.34
P21/n
C28H28B2F8N8Ni
708.91
Pbcn
C48N40Cl2N12Ni3
1031.95
P4/ncc
C49H42Cl4N12Ni3
1116.88
P43212
C12H11Br2N3Ni
415.77
P21/c
1216.78
I41/a
˚
a (A)
13.5762(7)
10.4773(5)
29.800(2)
96526(1)
4211.4(4)
1.423
18.7409(7)
18.7409(7)
29.8937(15)
20.911(2)
10.5688(4)
14.0333(11)
13.461(2)
13.461(2)
24.334(7)
14.8822(6)
14.8822(6)
43.382(4)
133441(11)
13.3396(11)
8.1227(6) A
96.556(2)
41436.4(2)
1.923
˚
b (A)
˚
c (A)
b (8)
3
V (A )
˚
10499.3(8)
1540
3101.4(4)
1.518
4409.5(16)
1.554
9608.4(9)
1.544
Dcalc (g cmꢃ3
)
Z
T (K)
4
213(2)
8
213(2)
4
213(2)
4
213(2)
8
213(2)
4
213(2)
b
R1 a, wR2 [I ꢁ
/2s(I)]
0.0276, 0.0693 0.0539, 0.1294
0.0338, 0.0727 0.0683, 0.1411
0.0464, 0.1299
0.0552, 0.1441
1.065
0.0706, 0.1544
0.1513, 0.2006
1.094
0.0639, 0.1539
0.0766, 0.1636
1.152
0.0273, 0.0658
0.0416, 0.0775
1.009
Rl a, wR2 (all data)
Quality of fit c
b
1.034
1.177
a
R1ꢂ
/
ajjFojꢃ
wR2ꢂ
[a[w(Fo2ꢃ
Quality of fitꢂ
[a[w(Fo2ꢃ
/
jFcjj/ajFoj.
2 2
/
2 2 12
//
/
Fc ) ]/aw(Fo ) ], wꢂ
/
1/[s2(Fo2)ꢀ
Nparameters)] based on all data.
/
(aP)2ꢀ
/
bP], where Pꢂ
/
[max(0 or Fo2)ꢀ2(Fc2)]/3.
/
b
c
/
/
Fc2)2]/(Nobs
ꢃ
/
Br) are mixed in THF even during an extended period of
reflux. It seemed clear that either some other source of
nickel(II) was required, or more forcing conditions were
needed if an anhydrous nickel halide had been used as a
starting material. When 2 equiv. of AgBF4 were added
to precipitate the bromide ions from NiBr2 in an attempt
to make the nickel(II) ion more readily accessible to
Naphthalene has been proven to be a good reaction
medium for the preparation of multinuclear metal chain
complexes with the number of metal atoms extending
from 3 to 9 as shown by Peng and coworkers [10]. In
those reactions, naphthalene allows the reaction tem-
perature to rise as high as about 185 8C, which is critical
to generate the target compounds having many metal
atoms in a linear array. However, the naphthalene
reaction medium could not be used for the preparation
of trinickel compounds with the anion PhPyF since a
thermogravimetric analysis of HPhPyF showed that the
ligand decomposes at approximately 153 8C. The reac-
tion of HPhPyF with NiCl2, Ni(py)4Cl2 and
Ni(PPh3)2Br2 in naphthalene using KOBu? as a base at
145 8C did not yield isolable products. When no base
was added, the reaction of HPhPyF with Ni(PPh3)2Br2
in naphthalene gave a mononickel species, Ni(HPh-
PyF)Br2, in which a neutral ligand HPhPyF is found to
be chelating the nickel atom, with the two bromide
atoms filling the remaining two positions of a distorted
tetrahedron.
LiPhPyF,
the
trinuclear
complex,
Ni3(Ph-
PyF)4(MeCN)2(BF4)2 (2) was obtained but the isolated
yield was minute. The major product of this reaction, 3,
was a mononuclear nickel complex of octahedral
structure1 containing the neutral ligand, with the
formula of [Ni(HPhPyF)2(MeCN)2][BF4]2.
In a search for other suitable Ni(II) sources to prepare
trinickel complexes by reaction with the anion of
HPhPyF, Ni(py)4Cl2 was examined. The reaction was
carried out with Ni(py)4Cl2 and LiPhPyF in the
stoichiometric ratio of 3:4 necessary to form a trinuclear
compound. However, under such conditions only the
dinuclear species Ni2(PhPyF)4 (1) was obtained. This
compound appears to be thermodynamically very
stable. Since 1 is deficient in Ni, relative to the Ni36ꢀ
species, twice as much Ni(py)4Cl2 was used. In this way,
a small amount of the trinickel complex [Ni3(Ph-
PyF)4Cl]Cl (4) was isolated, but a significant amount
of the dinuclear compound 1 was again obtained. When
a larger excess of Ni(py)4Cl2 (approximately threefold)
was used, a different trinickel species, Ni3(PhPyF)4Cl2
(5), was isolated, but, again, 1 was present as the major
product. The reactions of LiPhPyF and Ni(py)4Cl2 are
summarized in Scheme 4.
The difficulty in preparing the Ni36ꢀ chain com-
pounds described here contrasts with the ease of
preparing the Cr36ꢀ analogs. Those have been synthe-
sized relatively straightforwardly by reaction of CrCl2
and unsymmetrical formamidinates [19].
3.2. Structural studies
The molecular structure of the dinuclear compound
Ni2(PhPyF)4 is shown in Fig. 1. It crystallizes in the
space group P21/n with all atoms of the molecule
occupying general positions. Each ligand uses two
nitrogen atoms to chelate one nickel atom while the
third nitrogen atom spans to the other nickel atom.
Each nickel atom has a very distorted octahedral
1
The crystal structure of this compound showed an octahedral
arrangement with two neutral HPhPyF ligands chelating to the nickel
atom and two MeCN molecules cis to each other.

F. A. Cotton et al. / Inorganica Chimica Acta 351 (2003) 183ꢁ
/
190
187
Scheme 4.
before in the compounds V2(dpa)4 [20b] Mo2(D-
PhIP)4(BF4)2.
For the following discussion of trinickel complexes, it
is important to compare some previously determined
trinickel chain, Ni36ꢀ, structures with those being
reported here. For this purpose, critical dimensions for
two such molecules are listed in Table 2 along with those
for the new compounds 2, 4, and 5.
The
molecular
structure
of
Ni3(Ph-
PyF)4(MeCN)2(BF4)2 (2) is shown in Fig. 2. The
compound crystallizes in the I41/a space group with a
C2 axis perpendicular to the linear trinickel chain and
going through the central nickel atom. The chain is
wrapped by four ligands in a transoid relationship and
two MeCN molecules occupying the axial positions. The
counterions are BF4ꢃ. The distance from the terminal
nickel atom to the nitrogen atom of MeCN is 2.028(4)
˚
NMeCN
Fig. 1. The molecular structure of Ni2(PhPyF)4 (1) with ellipsoids
shown at the 45% probability level. Hydrogen atoms are omitted for
A. This is relatively short compared to the NiÃ
/
˚
distance (:
Ni(PhPyF)2(MeCN)2(BF4)2 (3), and is indicative of a
strong metalꢁligand interaction. The nickelꢁnickel
separation is slightly longer (0.04 A) than that in
Ni3(dpa)4Cl2, but the NiÃN distances follow the same
N distances for
/
2.11 A) in the mononuclear compound cis-
˚
clarity. Selected bond distance (A): Ni(1)Ã
/
N(3), 2.091(1); Ni(1)Ã
/
N(4),
N(8),
2.116(1); Ni(1)Ã
/
N(5), 2.181(1); Ni(1)Ã
/
N(7), 2.097(1); Ni(1)Ã
/
/
/
2.185(1); Ni(1)ÃN(12), 2.094(1).
/
˚
/
geometry, and the nickelꢁ
about 3.41 A, indicating there is no metalꢁmetal
/
nickel separation is long,
trend as those in Ni3(dpa)4Cl2, The NiÃ
/
˚
/
the central nickel atoms arc considerably shorter than
those for the terminal ones with average values in
bonding. There are two kinds of structural motifs
commonly expected for dimetal complexes with four
tridentate ligands and the general formula M2L4. In one
type the two metal atoms form a direct bond and thus
there is a short separation while the third donor atom on
each L ligand is dangling as in Cr2(dpa)4 [2a]. The
addition of a third metal atom to the dimetal unit is then
possible by taking advantage of the third dangling
nitrogen donor. In the second type, the structural motif
for M2L4 is that seen here in the structure of Ni2(Ph-
PyF)4. There is no dangling nitrogen donor as all of 12
nitrogen atoms in the four ligands coordinate to the
metal atoms and two distorted octahedra are formed.
Such a compound is thermodynamically very stable,
and, it is very difficult to introduce an additional metal
atom. This accounts for the low yield of trinickel
complexes and the common presence of dinickel species
in these reactions. This structural motif has been seen
Ni3(PhPyF)4(MeCN)22ꢀ being 1.888[3] and 2.089[3] A,
˚
respectively. These values are almost identical to those
in Ni3(dpa)4Cl2. This strongly suggests that they may
have a similar electronic structure. Based on the earlier
results for Ni3(dpa)4Cl2, the trinickel chain in
Ni3(PhPyF)4(MeCN)22ꢀ can be interpreted as having
two five-coordinate terminal nickel atoms, each posses-
sing two unpaired electrons while the central nickel
atom is d8, square-planar, and diamagnetic. There is
probably antiferromagnetic coupling between the term-
inal magnetic centers, but this has not been investigated
because of the low yield of compound 2.
The core structure of [Ni3(PhPyF)4Cl]Cl (4) (Fig. 3)
reveals a linear Ni36ꢀ chain supported by a set of four
PhPyF anions. The compound crystallizes in the space
group P4/ncc with a C4 axis passing through the
trinickel chain. There is only one Cl anion in an axial

188
F. A. Cotton et al. / Inorganica Chimica Acta 351 (2003) 183ꢁ190
/
Table 2
Comparison of important parameters in the neutral linear trinickel compounds
Mean values a
Ni3(dpa)4Cl2 (TBA)2Ni3(BPAP)4 Ni3(PhPyF)4Cl2 (5)
[Ni3(PhPyF)4Cl]Cl (4) Ni3(PhPyF)4(MeCN)2(BF4)2 (2)
˚
Ni (A)
˚
X axial (A)
˚
N, central (A)
˚
N outer, (A)
Ni
NiÃ
NiÃ
NiÃ
/
ꢀ ꢀ ꢀ
/
2.43[8]
2.34[6]
1.88[9]
2.10[7]
2.368[1]
2.5075(10), 2.5027(10) 2.443(3), 2.454(3)
2.469(5)
2.0284(4)
1.889[3]
2.090[3]
40.5
/
ꢁ/
2.317[2]
1.893[5]
2.100[5]
40.4
2.331(5)
1.911(7)
/
1.906[7]
1.917[5]
30
/
1.921(6) 2.129(7)
30
Overall torsion angle (8) 51.0
Ref.
[5c]
[9]
this work
this work
this work
a
Numbers within square brackets are e.s.d.s. of average values.
groups are at other end. Despite this, the NiÃ
/Ni
distances of 2.443(3) A and 2.454(3) A are not sig-
nificantly different and comparable to those in 2 and
Ni3(dpa)4Cl2, suggesting an absence of direct bonding
between nickel atoms. Space-filling models of the two
ends of [Ni3(PhPyF)4Cl]ꢀ are shown in Fig. 4. It is clear
that the axial Cl anion fits on the end having pyridyl
ring while there is not enough space for a Cl anion at the
other end because of a hydrogen atoms on the phenyl
rings.
The pattern of NiÃ/N distances in 4 is quite different
from that in Ni3(dpa)4Cl2, Ni3(PhPyF)4Cl2 (5) and
[Ni3(PhPyF)4(CH3CN)2](BF4)2 (2). In 4 there is only
one outer nickel atom that is five-coordinate, and for
˚
that one the NiÃ
/
N distances are 2.129(7) A. The NiÃ
/N
distances for the other four-coordinated outer nickel
˚
atom are 1.921(6) A, and for the center four-coordinated
Fig. 2. Perspective view of Ni3(PhPyF)4(MeCN)22ꢀ in 2. Atoms are
drawn at 45% probability level and hydrogen atoms are omitted for
clarity.
˚
N distance are all 1.911(7) A. The
nickel atom the NiÃ
/
central and the outer nickel atom devoid of axial
ligation are d8 and square-planar, and would be
expected to be diamagnetic while the other outer nickel
atom attached to a Cl anion should possess two
unpaired electrons. This is consistent with magnetic
measurement of compound 4 at room temperature,
which shows a magnetic moment of 3.08 mB.
Compound 5, Ni3(PhPyF)4Cl2, crystallizes in the
space group P43212 with the entire molecule on a
general position. The structure (Fig. 5) consists of two
Fig. 3. A drawing of the cation Ni3(PhPyF)4Clꢀ in 4 showing a vacant
axial site. Ellipsoids are drawn at the 45% probability level and
hydrogen atoms are omitted.
˚
position with the distance of 2.331(5) A to the nickel
atom; the other Cl anion, required to balance the
charge, is not coordinated. The ligand arrangement is
quite different from that in 2, with all the ligands
pointing in the same direction. Thus, all the pyridine
rings are at one end of the molecule while all the phenyl
Fig. 4. Space-filling models showing the two ends of
[Ni3(PhPyF)4Cl]ꢀ in 4. Note that the a-hydrogen atoms of the phenyl
rings in b obstruct the possible approach of a Cl anion forcing an
empty axial site.

F. A. Cotton et al. / Inorganica Chimica Acta 351 (2003) 183ꢁ
/
190
189
Fig. 6. A drawing of the cation in 3 with ellipsoids drawn at the 45%
probability level. Hydrogen atoms are omitted. Selected bond distance
Fig. 5. A drawing of the molecular structure of Ni3(PhPyF)4Cl2 (5).
Ellipsoids are drawn at 45% probability level with hydrogen atoms
omitted for clarity.
˚
(A): Ni(1)Ã
/
N(1), 2.113(2); Ni(1)Ã
/
N(3): 2.099(2); Ni(1)ÃN(4), 2.113(2).
/
square pyramidal Ni(II) atoms at each end of the
trinickel chain and one square-planar, central Ni(II)
atom. The ligands are cisoid to each other, whereas in 2
they are transoid. The Ni
/
ꢀ ꢀ ꢀ
and 2.5027(10) A. These values are 0.07 A longer than
N distances
/
Ni distances are 2.5075(10)
˚
˚
those in the Ni3(dpa)4Cl2 analogue. The NiÃ
/
are similar to those in Ni3(PhPyF)4(MeCN)22ꢀ and
Ni3(dpa)4Cl2. Once again, the central nickel atom can be
regarded as having a low-spin, square-planar geometry;
while the two outer nickel atoms are in a triplet state,
but because of the low yield magnetic measurements
have not been made.
In all three new trinickel compounds, the PhPyF
ligands are twisted. The torsion angles from one
terminal nickel atom to the other terminal nickel atom
range from 30 to 40.58. Individual values are given in
Table 2. The compounds with the smaller torsion angles
of 308 are (TBA)2Ni3(BPAP)4 9 and 4. The former does
not show axial coordination while the latter has only
one axial coordination site occupied. The others have
two axially coordinated ligands. This is consistent with
observations made on Cr36ꢀ compounds [19].
Fig. 7. The molecular structure of Ni(HPhPyF)Br2 (6) showing the
pseudo-tetrahedral environment. Ellipsoids are drawn at the 45%
probability level with hydrogen atoms omitted. Selected bond dis-
˚
tances (A): Ni(1)Ã
/
N(1), 1.982(2); Ni(1)Ã
/
N(3), 1.959(2); Ni(1)ÃBr(1),
/
2.3402(5); Ni(1)Ã
/
Br(2), 2.3719(5).
201 047, respectively. Copies of CIFs are available free
of charge from The Director, CCDC, 12 Union Road,
Cambridge, CB2 1EZ, UK (fax: ꢀ44-1223-336-033;
/
email: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).
The structures of the mononuclear compounds 3 and
6 are given in Figs. 6 and 7, respectively. In the former,
there are two neutral formamidines chelating the Ni
atom which is also coordinated by two cis acetonitrile
molecules. Compound 6 possesses one chelating for-
mamidine and two Br anions creating a roughly tetra-
hedral environment around the nickel atom. This
structure is reminiscent of that of Co(Hdpa)Cl2 [21].
Acknowledgements
We thank the National Science Foundation and the
NIRT (Nanoscale Science and. Engineering (NIRT
Grant DMR-0103455) and the Telecommunications
and Information Task Force at Texas A&M University.
4. Supplementary material
References
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/
Atoms, second ed., Oxford University Press, Oxford, 1993.

190
F. A. Cotton et al. / Inorganica Chimica Acta 351 (2003) 183ꢁ190
/
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