Structural studies of two isoelectronic tetrakis isocyano complexes

Article abstract of DOI:10.1007/s10870-009-9648-3

Two isoelectronic tetrakis isocyano compounds, tetra(p-isocyanoanisole) nickel(0) and tetra(p-isocyanoanisole)copper(I) hexafluorophosphate were synthesized from nickel bis cyclooctadiene and copper (I) tetra acetonitrile hexafluorophosphate and the isonitrile, respectively, and their structures were determined. The nickel complex crystallizes in the orthorhombic space group P2₁2₁2₁ with a = 9.6709(8), b = 15.2324(13), c = 19.0955(16) A and Z = 4. The copper salt forms crystals with a tetragonal setting in P4/n with a = b = 15.8206(5), c = 6.5848(4) A and Z = 2. Both complexes exhibit the approximate tetrahedral coordination environment expected for 18 valence electron complexes with soft σ-donor π-acceptor ligands. Packing in the nickel complex is dominated by weak π-π stacking, C-H...;π_phenyl, and C-H...;π interactions towards the isonitrile carbon and nitrogen atoms, and several slightly stronger C-H...;O interactions. In the copper complex the presence of the PF₆ anion allows for the formation of stronger C-H...;F interactions, and these in combination with π-π stacking and C-H...;O hydrogen bonds dominate the packing.

Full text of DOI:10.1007/s10870-009-9648-3

J Chem Crystallogr (2010) 40:289–295
DOI 10.1007/s10870-009-9648-3
ORIGINAL PAPER
Structural Studies of Two Isoelectronic Tetrakis Isocyano
Complexes
•
Cynthia L. Perrine Matthias Zeller
•
•
•
John Woolcock Timothy M. Styranec
Allen D. Hunter
Received: 15 June 2009 / Accepted: 1 October 2009 / Published online: 10 November 2009
Ó Springer Science+Business Media, LLC 2009
Abstract Two isoelectronic tetrakis isocyano compounds,
tetra(p-isocyanoanisole)nickel(0) and tetra(p-isocyanoani-
sole)copper(I) hexafluorophosphate were synthesized from
nickel bis cyclooctadiene and copper (I) tetra acetonitrile
hexafluorophosphate and the isonitrile, respectively, and
their structures were determined. The nickel complex crys-
tallizes in the orthorhombic space group P212121 with
Keywords Homoleptic isonitrile complexes Á
18 VE complexes Á Isonitriles Á Ni(0) complexes Á
Cu(I) complexes
Introduction
˚
a = 9.6709(8), b = 15.2324(13), c = 19.0955(16) A and
Z = 4. The copper salt forms crystals with a tetragonal set-
˚
ting in P4/n with a = b = 15.8206(5), c = 6.5848(4) A and
Transition metal carbonyl complexes are among the most
investigated classes of organometallic complexes and are
the textbook examples of r-donor p-acceptor ligands. They
are convenient starting materials in the preparation of a
huge number of low valent transition metal compounds,
and many of their derivatives are used as homgeneous
catalysts in both laboratory as well as industrial settings.
The first metal carbonyl complex ever reported, and one of
the most famous to this date, is nickel tetracarbonyl,
Ni(CO)4. Being a tetrahedral charge neutral complex it is
the example of an 18 valence electron low valent metal
complex with soft r-donating p-accepting ligands. Because
it is a highly volatile and toxic liquid, the verification of its
solid state structure by X-ray diffraction was a challenge.
High quality data [1, 2] were obtained only about 10 years
ago, thus over a century after its original discovery by
Ludwig Mond in 1890 [3].
Z = 2. Both complexes exhibit the approximate tetrahedral
coordination environment expected for 18 valence electron
complexes with soft r-donor p-acceptor ligands. Packing in
the nickel complex is dominated by weak p–p stacking,
C–HÁÁÁpphenyl, and C–HÁÁÁp interactions towards the isonitrile
carbon and nitrogen atoms, and several slightly stronger
C–HÁÁÁO interactions. In the copper complex the presence of
the PF6 anion allows for the formation of stronger C–HÁÁÁF
interactions, and these in combination with p–p stacking and
C–HÁÁÁO hydrogen bonds dominate the packing.
C. L. Perrine Á M. Zeller Á T. M. Styranec Á A. D. Hunter (&)
Department of Chemistry, YSU Structure and Chemical
Instrumentation Center, Youngstown State University,
One University Plaza, Youngstown, OH 44555-3663, USA
e-mail: adhunter@ysu.edu
Tetrakis nickel(0) complexes have been investigated for
their chemical and electrochemical properties. One of the
most intriguing properties of these complexes is their tet-
rahedral star shape, and with properly chosen coordinating
ligands they are expected to have degrees of conjugation
down their arms and across their central vertices. Our
interest in such highly symmetric tetrahedral low valent
compounds prompted us to investigate Ni(0) isonitrile and
their isoelectronic Cu(I) complexes as model compounds
for more complicated systems, e.g., multifunctional ligands
such as 1,4-bisisocyano benzene. In the current contribution
J. Woolcock
Department of Chemistry, Indiana University of Pennsylvania,
975 Oakland Ave, Indiana, PA 15705, USA
C. L. Perrine
Division of Pediatric Pulmonology, Case Western Reserve
University, BRB 8th Floor, LC 4948, Cleveland,
OH 44106, USA
123

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J Chem Crystallogr (2010) 40:289–295
ambient temperature and washed under nitrogen with a
10% solution of Na2CO3 (3 9 100 ml) and with H2O
(1 9 100 ml). The organic layer is dried over anhydrous
MgSO4. The MgSO4 is filtered off, washed with CH2Cl2
(3 9 20 ml), and all volatile materials are removed in vacuo
from the combined filtrates (e.g., high vacuum manifold
at room temperature). Crystallization of the resulting light
brown solid from pentane at 4 °C gavewhite–yellow needles.
The crystals are dissolved in a 2:1 hexane/CH2Cl2 mixture
(ca 40 ml). The solution is filtered through a neutral alumina
column (0.5 m) using a 2:1 hexane/CH2Cl2 mixture
(ca. 150 ml) and all volatile materials are removed from the
filtrate in vacuo. The solid was again crystallized from pen-
tane at 4 °C to give a 21% yield (1.84 g, 13.8 mmol) of the
product as white–yellow needles exhibiting a pronounced
isonitrile smell. The crystals start to melt at room temperature
and have to be stored under nitrogen at -20 °C to avoid rapid
decomposition. No spectroscopic properties were recorded
due to the sensitivity of the compound. The identity of the
compound was verified by its conversion into the Ni(0) and
Cu(1?) tetraisocyanide complexes, see below.
Scheme 1 Synthesis of compounds 1, 2 and 3
Tetra(p-isocyanoanisole)nickel(0) (2)
we would like to present the synthesis and structure of
two isoelectronic homoleptic isonitrile complexes, tetrakis
(p-isocyanoanisole)nickel(0) and tetrakis(p-isocyanoani-
sole)copper(I) hexafluorophosphate (Scheme 1).
Diethylether (25.0 ml) is added to bis(1,5-cyclooctadi-
ene)nickel(0) (0.580 g, 2.12 mmol, Strem 98?%). The
bis(1,5-cyclooctadiene)nickel(0) does not completely dis-
solve. p-Methoxy isocyanobenzene (1) (1.41 g, 10.6 mmol)
is dissolved in diethylether (40 ml), is added dropwise to the
mixture at 0 °C, and the solution is stirred for 2 h at ambient
temperature to form a yellow precipitate. The solid is filtered
off under nitrogen, and rinsed with hexanes (3 9 10 ml). All
the volatile materials are removed in vacuo to obtain an 87%
crude yield (0.53 g, 0.896 mmol) of the bright yellow solid.
Recrystallization from THF at -20 °C yielded yellow crys-
tals suitable for single-crystal diffraction.
Experimental
Synthesis
All reactions were performed under an inert atmosphere of
dry nitrogen using standard Schlenk techniques. All solvents
were freshly dried before use by distillation from calcium
hydride (CH2Cl2) or sodium benzophenone (THF, Et2O).
Spectroscopic Properties
p-Isocyanoanisole (1)
13C {1H} NMR (100.565 MHz, CDCl3): 165.373 (d,
1J(13C, 14N) = 4.73 Hz, CN), 157.770 (s, Ph-C), 126.653
(s, Ph-C), 123.371 (s, Ph-C), 114.146 (s, Ph-C), 55.473
(s, CH3-C). 1H NMR (399.905 MHZ, CDCl3): 6.982
(d, 3J(1H,1H) = 8.40 Hz, 8H, Ph-H), 6.337 (d, 3J(1H,1H) =
8.40 Hz, 8H, Ph-H), 3.034 (s, 12H, CH3). IR (toluene,
CaF2): 2,017 cm-1 (s, m isonitrile).
The isocyanide was prepared using a method based on a
published procedure by Hanack et al. [4] Para-formamido-
anisole [5] (10.0 g, 66.15 mmol), CH2Cl2 (200 ml), and tri-
ethylamine (45.85 ml, 33.29 g, 0.329 mol) are combined in a
nitrogen purged 250 ml three-necked round bottom flask
equipped with a nitrogen adapter, reflux condenser, dropping
funnel, and magnetic stirring bar. Trichloromethyl chloro-
formate (‘‘diphosgene’’) (3.9 ml, 6.54 g, 33.0 mmol) is
placed into a dropping funnel containing CH2Cl2 (46 ml).
The diphosgene solution is added dropwise over a 15 min
period and then the solution is heated to reflux of the solvent
for an additional 2 h. The solution is allowed to cool to
Tetra(p-isocyanoanisole)copper(I) hexafluorophosphate
(3)
Tetrahydrofuran (25.0 ml) is added to tetrakis(acetonitrile)
copper(I) hexafluorophosphate (0.41 g, 1.1 mmol, Strem
98?%). Para-methoxy isocyanobenzene (1) (0.62 g,
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J Chem Crystallogr (2010) 40:289–295
291
Table 1 Crystal data and structure refinement of 2 and 3
2
3
Empirical formula
Moiety formula
Formula weight
Solvent
C32H28N4NiO4
Ni(C8H7NO)4
591.29
C32H28CuF6N4O4P
[Cu(C8H7NO)4]?[PF6]-
741.09
Diethylether
Block, yellow
100(2) K
Tetrahydrofuran/diethylether
Block, colourless
100(2) K
Cryst. habit, color
Temperature
Crystal system
Space group
Orthorhombic
P212121
Tetragonal
P4/n
˚
a = 9.6709(8) A
˚
a = b = 15.8206(5) A
Unit cell dimensions
˚
b = 15.2324(13) A
˚
c = 6.5848(4) A
˚
c = 19.0955(16) A
3
3
˚
2813.0(4) A
˚
1648.12(12) A
Volume
Z
4
2
Density (calculated)
Absorption coefficient
F(000)
1.396 g cm-3
0.734 mm-1
1.493 g cm-3
0.788 mm-1
756
1,232
Crystal size
0.4 9 0.4 9 0.2 mm
1.71–28.28°, 100%
-12 B h B 12,
-20 B k B 20,
-24 B l B 25
0.30 9 0.30 9 0.21 mm
1.82–30.58°, 100%
-22 B h B 22,
-22 B k B 22,
-9 B l B 9
18,867
h range for data collection, completeness
Index ranges
Reflections collected
28,954
Independent reflections
Reflections with I [ 2 r(I)
Absorption correction
6,979 [R(int) = 0.0474]
6,048
2,528 [R(int) = 0.0238]
2,387
Semiempirical from multi scans
0.860, 0.740
Semiempirical from multi scans
Max. and min. transmission
Data/restraints/parameters
Goodness-of-fit on F2
0.850, 0.633
6,979/0/374
2,528/0/119
1.050
1.120
Final R indices [I [ 2r (I)]
R indices (all data)
R1 = 0.0382, wR2 = 0.0787
R1 = 0.0488, wR2 = 0.0823
0.054(10), 3,067 Friedel pairs
R1 = 0.0392, wR2 = 0.0976
R1 = 0.0409, wR2 = 0.0987
Absolute Structure Parameter
Largest diff. peak and hole
–
-3
-3
˚
0.733 and -0.236 e 9 A
˚
0.565 and -0.214 e 9 A
4.6 mmol) is dissolved in tetrahydrofuran (40 mL), is added
dropwise to the mixture at 0 °C, and the solution is stirred
for 5 h at ambient temperature. Reduction in volume and
careful addition of diethyl ether induced crystallization. The
sample was first cooled to 4 °C, then to -20 °C to yield
colourless to slight beige crystals in 86% (0.705 g,
0.95 mmol) yield suitable for single-crystal diffraction.
3.833 (s, 12H, CH3). 31P NMR (161.98 MHZ, CDCl3):
1
144.2 (septet, J(19F,31P) = 711.1 Hz, 1P).
Diffraction data were collected using a Bruker AXS
SMART APEX CCD diffractometer at 100(2) K using
monochromatic Mo Ka radiation with the omega scan
technique. The unit cells were determined using SMART
and SAINT? and the data were corrected for absorption
using SADABS [6–8]. The structures were solved by direct
methods and refined by full matrix least squares against F2
with all reflections using SHELXTL [6–8]. Non-hydrogen
atoms were refined anisotropically. All H atoms were
placed in calculated positions with C–H distances of 0.95
Spectroscopic Properties
13C {1H} NMR (100.618 MHz, CDCl3): 160.67 (s, Ph-C),
145.91 (s, broad, CN), 128.60 (s, Ph-C), 177.51 (s, Ph-C),
115.19 (s, Ph-C), 55.79 (s, CH3-C). 1H NMR
(400.150 MHZ, CDCl3): 7.758 (d, 3J(1H,1H) = 9.03 Hz,
8H, Ph-H), 7.104 (d, 3J(1H,1H) = 9.03 Hz, 8H, Ph-H),
˚
and 0.98 A for aromatic and methyl H atoms respectively.
H atoms were refined with Uiso(H) = 1.2 Ueq(Carom) or 1.5
Ueq(Cmethyl) of the adjacent carbon atom. Methyl hydrogen
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J Chem Crystallogr (2010) 40:289–295
˚
Table 2 Selected bond lengths (A) and angles (°)
For 2
Ni1-C41
Ni1-C31
Ni1-C11
Ni1-C21
C11-N1
C21-N2
C31-N3
C41-N4
N1-C12
N2-C22
N3-C32
N4-C42
1.840(2)
1.846(2)
1.847(2)
1.852(2)
1.169(3)
1.173(3)
1.171(3)
1.181(3)
1.392(3)
1.395(3)
1.392(3)
1.398(3)
C11-Ni1-C21
C31-Ni1-C11
C31-Ni1-C21
C41-Ni1-C11
C41-Ni1-C21
C41-Ni1-C31
N1-C11-Ni1
N2-C21-Ni1
N3-C31-Ni1
N4-C41-Ni1
C11-N1-C12
C21-N2-C22
C31-N3-C32
C41-N4-C42
103.26(10)
109.66(9)
112.24(10)
114.37(10)
114.25(10)
103.28(10)
177.7(2)
174.3(2)
176.41(19)
173.6(2)
170.0(2)
163.4(2)
176.9(2)
160.0(2)
For 3
P1-F2
1.6043(19)
1.6046(19)
1.6051(9)
1.9521(15)
1.152(2)
F2-P1-F1
F2-P1-F3
F1-P1-F3
F3-P1-F3
F3-P1-F3i
F3-P1-F3i
F2-P1-F3ii
F3-P1-F3ii
180.000(1)
90.04(4)
89.96(4)
179.92(8)
90.003(1)
90.0
P1-F1
P1-F3
Cu1-C1
N1-C1
Fig. 1 ORTEP style representation of 2, ellipsoids at 50% probabil-
ity. Hydrogen labels are omitted for clarity
N1-C2
1.3988(18)
C1iii-Cu1-C1
C1iv-Cu1-C1
C1-Cu1-C1v
C1-N1-C2
N1-C1-Cu1
106.70(9)
90.04(4)
90.000(1)
110.88(5)
110.87(5)
178.87(16)
175.48(13)
atoms were allowed to rotate around the C–C bond at a
fixed angle to best fit the experimental electron density.
Crystal data and experimental details are listed in Table 1.
Symmetry codes: (i) -y ? 3/2, x, z; (ii) y, -x ? 3/2, z; (iii) -x ? 3/2,
-y ? 1/2, z; (iv) y ? 1/2, -x ? 1, -z; (v) -y ? 1, x - 1/2, -z
˚
Table 3 Intermolecular interactions for 2 ([A] and angles (°))
Donor-HÁÁÁacceptor
D-H
HÁÁÁA
DÁÁÁA
D-HÁÁÁA
C17-H17ÁÁÁO2i
0.95
0.95
0.98
0.98
0.95
0.95
0.98
0.95
0.95
0.95
0.95
0.95
2.55
2.53
2.89
2.71
2.87
2.86
2.86
2.82
2.86
2.76
2.77
2.74
3.480(3)
3.471(3)
3.797(4)
3.601(3)
3.790(4)
3.806(3)
3.810(3)
3.523(3)
3.805(3)
3.556(3)
3.451(3)
3.674(2)
166
170
154
152
163
173
164
132
171
142
129
167
C33-H33ÁÁÁO4ii
C48-H48AÁÁÁC11iii
C48-H48AÁÁÁN1iii
C27-H27ÁÁÁC18iv
C24-H24ÁÁÁC11v
C28-H28BÁÁÁC44vi
C13-H13ÁÁÁC31v
C44-H44ÁÁÁC31iv
C37-H37ÁÁÁC11iv
C16-H16ÁÁÁCg3vii
C34-H34ÁÁÁCg2viii
Symmetry codes: (i) -x, 1/2 ? y, 3/2 - z; (ii) -x, -1/2 ? y, 3/2 - z;
(iii) -1 - x, -1/2 ? y, 3/2 - z; (iv) -x, -1/2 ? y, 3/2 - z; (v) -x,
1/2 ? y,3/2 - z;(vi)1/2 ? x,3/2 - y,2 - z,(vii)-1/2 ? x,3/2 - y,
1 - z; (viii) 1 - x, -1/2 ? y, 3/2 - z
Fig. 2 ORTEP style representation of 3, ellipsoids at 50% probabil-
ity. Hydrogen labels and labels of symmetry dependent atoms are
omitted for clarity
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J Chem Crystallogr (2010) 40:289–295
293
Fig. 3 Packing view of 2, view
down the b-axis. Ellipsoids are
at 50% probability. Orange
dashed lines symbolize C–HÁÁÁp
interactions towards isonitrile
groups and phenyl p systems.
Blue dashed lines are C–HÁÁÁO
hydrogen bonds, and red dashed
lines represent pÁÁÁp interactions
between phenyl rings (red
spheres are centroids of
aromatic rings C32–C37 and
C42–C47; centroid to centroid
˚
distance is 3.4955(9) A,
symmetry operator for
C42–C47: (ix) 1 ? x, y, z).
(color figure online)
˚
Table 4 Intermolecular interactions for 3 ([A] and angles [deg])
Donor-HÁÁÁacceptor
D-H
HÁÁÁA
DÁÁÁA
D-HÁÁÁA
C4-H4ÁÁÁO1v
C6-H6ÁÁÁF3
C3-H3ÁÁÁC1vi
0.95
0.95
0.95
2.54
2.47
2.85
3.4455(18)
3.1686(17)
3.756(2)
160
131
160
Symmetry codes: (v) 1 - x, 1 - y, 2 - z, (vi) 1 - y, -1/2 ? x, 1 - z
Results and Discussion
Ni(0) complexes were often prepared using nickel tetra-
carbonyl as the starting material. Its high toxicity has a,
however, led to its substitution by other Ni(0) complexes
with weakly coordinated ligands. In recent years bis(1,5-
cyclooctadiene)nickel(0) (Ni(COD)2) has established itself
as a common starting material for Ni(0) compounds and a
variety of complexes were synthesized this way such as
NiL4, NiL2, and NiL2(UN) (e.g., L = phosphine, arsine,
stibine, nitrogen base, or isocyanide, and UN = olefin,
acetylene, or azide). [9] Ni(COD)2 has been found to be an
exceptionally good starting material for homoleptic iso-
cyanide nickel(0) complexes. [10, 11] Treatment of
bis(1,5-cyclooctadiene)nickel(0) with para-methoxy iso-
cyanobenzene (1) gave the homoleptic isocyano complex
(2) in excellent yield. The equivalent reaction of tetra-
kis(acetonitrile) copper(I) hexafluorophosphate provided
the isoelectronic copper hexafluorophosphate complex (3).
Both complexes were characterized by multinuclear NMR
and IR spectroscopy, and single crystals suitable for X-ray
Fig. 4 Packing view of 3, view down the c-axis. Ellipsoids are at 50%
probability. Color coding similar to Fig. 3: Orange dashed lines:
C–HÁÁÁp interactions; blue dashed lines are C–HÁÁÁO/F hydrogen bonds,
and red dashed lines represent pÁÁÁp interactions between phenyl rings
(red spheres are centroids of aromatic rings C2–C7; centroid to centroid
˚
distance is 3.5910(9) A, symmetry operator for the second phenyl ring:
(vii) 1 - x, 1 - y, 1 - z). (Color figure online)
crystallographic analysis were obtained from THF-diethyl
ether mixtures.
Ortep style plots of the two compounds are given in
Figs. 1 and 2, the most important crystallographic data are
summarized in Tables 1, 2, and 3. The compounds are both
123

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J Chem Crystallogr (2010) 40:289–295
approximately tetrahedral as expected for 18 valence
electron low valent metal complexes, but the shape of the
p-anisole isocyanide ligand—it is neither linear nor does it
have threefold rotational symmetry—does not allow for the
formation of exactly tetrahedral complexes in a crystallo-
graphic or symmetry sense. Tetra(p-isocyanoanisole)
nickel(0) (2) crystallized in a chiral orthorhombic setting in
P212121 with one crystallographically independent mole-
cule located on a general position. The molecule is
approximately tetrahedral, but the C–Ni–C angles do differ
somewhat from the ideal value of 109.5°. The smallest
value found is 103.26(10)°, with the largest at 114.37(10)°.
The Ni–C:N–C units are slightly bent, especially at the
nitrogen atoms: the Ni–C:N angles are with 173.6(2)–
177.7(2)° relatively close to the ideal 180°, the C:N–C
angles are on average 167.6°, and the smallest angle has a
value of only 160.0(2)° (Table 2). This is, however, still
within the usual range found for the three previously
reported structures of Ni(0) isonitrile complexes. [11] The
dominated by rather weak interactions such as p–p stack-
ing interactions between phenyl rings, C–HÁÁÁp interactions
towards aromatic p-systems, C–HÁÁÁp interactions towards
isonitrile carbon and nitrogen atoms, and several slightly
stronger C–HÁÁÁO interactions (Table 3; Fig. 3). In 3 the
presence of the hexafluoro phosphate anion allows for the
formation of stronger C–HÁÁÁF interactions in addition to
the interactions also found in 2.. There is still one C–HÁÁÁC
interaction towards the carbon atoms of the isonitrile
functional group, but this rather weak interaction is prob-
ably simply a result of the directional forces of the much
stronger C–HÁÁÁF interactions, and it is these in combina-
tion with C–HÁÁÁO hydrogen bonds and strong p–p stacking
interactions that dominate the packing of the copper
complex salt 3 (Table 4; Fig. 4).
Supplementary Material
˚
Ni–C distances in (2) range from 1.840(2) to 1.852(2) A,
which is slightly larger but comparable to those found for
˚
other Ni tetraisonitrile complexes (1.828–1.841 A for the
CCDC-736014 & 736015 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge at http://www.ccdc.cam.ac.uk/conts/retrieving.
html [or from the Cambridge Crystallographic Data Center
(CCDC), 12 Union Road, Cambridge CB2 1EZ, UK; fax:
?44(0)1223-336033; email: deposit@ccdc.cam.ac.uk].
three previously reported structures of Ni(0) complexes
˚
[11], 1.831–1.839 A for the single structurally described
square planar Ni(II) tetraisonitrile salt) [12].
Tetra(p-isocyanoanisole)copper(I) hexafluorophosphate
(3), while also not perfectly tetrahedral, has higher crys-
tallographic symmetry. It crystallizes in the tetragonal
setting P4/n with the PF6 anion located on the fourfold axis
at , , z with four of the six fluoride anions being
crystallographically related by this axis. The cationic
copper complex is located on the fourfold inversion axis
with the Cu(I) center at ’, , 0, thus leading to the
presence of only one crystallographically independent
isonitrile ligand. The angles at the metal center for 3 are
closer to the ideal 109.5° than in 2 with values between
106.70(9)° and 110.87(5)° (Table 3). The same is observed
for the Ni–C:N and C:N–C angles, which are much
closer to the ideal 180° than in nickel complex 2
(178.87(16) and 175.48(13)°, respectively). The Cu–C
Acknowledgments MZ was supported by NSF grant 0111511, CLP
by ACS PRF grant 37228-B3, JCW by ACS PRF grant 37228-B3-
SRF, and the diffractometer was funded by NSF grant 0087210, by
Ohio Board of Regents grant CAP-491, and by YSU.
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˚
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C:N and N–C bond lengths vary not significantly for
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˚
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˚
˚
1.152(2) A. N–C bond lengths are 1.392(3)–1.398(3) A
˚
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¨
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range as observed for all other structurally described
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Intermolecular interactions in 2 and 3 are somewhat
similar, but still distinctively different. Packing in 2 is
123

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¨
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123