Interrelationships between the tetrahedral and planar polymorphs of bis(3-ethylamino-1-phenyl-but-2-en-1-ono)nickel(II) and structural comparisons with related CoII, NiII, CuII, and ZnII complexes

Article abstract of DOI:10.1039/c7ce00638a

Conditions for the crystallization and interconversion of the green and brown polymorphs of bis(3-ethylamino-1-phenyl-but-2-en-1-ono)nickel(ii) (Ni(B-Et)₂), which contain planar and tetrahedral complexes in accord with previous magnetic and spectroscopic studies, have been determined. Additionally, the series of β-diketoamine-containing complexes, M(B-Et)₂ and M(B-Bn)₂, (M = Co^II, Ni^II, Cu^II, Zn^II) obtained from condensation of benzoylacetone (B) with either ethylamine (Et) or benzylamine (Bn) followed by treatment with [MCl₄]^2- under basic conditions has been prepared and their structures characterized crystallographically. In contrast to Ni(B-Et)₂, Ni(B-Bn)₂ has been crystallized only in the planar form. M(B-Et)₂ and M(B-Bn)₂ (M = Co or Zn) have similar, nearly tetrahedral structures, while Cu(B-Et)₂ and Cu(B-Bn)₂ have structures that are decidedly intermediate between tetrahedral and planar. Despite the abilities of these complexes to exist in tetrahedral, planar, or intermediate structures in solution, it has not been possible to induce much structural variation in crystalline forms. While two polymorphs of Zn(B-Bn)₂ have been obtained, both have similar, tetrahedral structures. Only Ni(B-Et)₂ crystallizes in both planar and tetrahedral forms. None of the complexes formed cocrystals with fullerenes or solvates in which structural variation as seen in Ni(B-Et)₂ occurred.

Full text of DOI:10.1039/c7ce00638a

View Article Online
View Journal
CrystEngComm
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: X. B. Powers, K. B.
Ghiassi, J. T. Greenfield, M. Olmstead and A. L. Balch, CrystEngComm, 2017, DOI: 10.1039/C7CE00638A.
This is an Accepted Manuscript, which has been through the
Volume 18 Number 1 7 January 2016 Pages 1–184
Royal Society of Chemistry peer review process and has been
accepted for publication.
CrystEngComm
Accepted Manuscripts are published online shortly after
www.rsc.org/crystengcomm
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
HIGHLIGHT
Tiddo J. Mooibroek, Antonio Frontera et al.
Towards design strategies for anion–π interactions in crystal engineering
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
rsc.li/crystengcomm

Page 1 of 30
CrystEngComm
View Article Online
DOI: 10.1039/C7CE00638A
Interrelationships Between the Tetrahedral and Planar Polymorphs of Bis(3-ethylamino-1-
phenyl-but-2-en-1-ono)nickel(II) and Structural Comparisons with Related CoII, NiII, CuII,
and ZnII Complexes
Xian B. Powers, Kamran B. Ghiassi, Joshua T. Greenfield, Marilyn M. Olmstead,* Alan L.
Balch*
Department of Chemistry, University of California, One Shields Avenue, Davis, CA, U. S. A.
E-mail: albalch@ucdavis.edu; Fax +1 (530) 752 2820; Tel +1 (530) 752 0941.
1

CrystEngComm
Page 2 of 30
View Article Online
DOI: 10.1039/C7CE00638A
Abstract
Conditions for the crystallization and interconversion of the green and brown polymorphs of
bis(3-ethylamino-1-phenyl-but-2-en-1-ono)nickel(II) (Ni(B-Et)2), which contain planar and
tetrahedral complexes in accord with previous magnetic and spectroscopic studies, have been
determined. Additionally, the series of β-diketoamine-containing complexes, M(B-Et)2 and
M(B-Bn)2, (M = CoII, NiII, CuII, ZnII) obtained from condensation of benzoylacetone (B) with
either ethylamine (Et) or benzylamine (Bn) followed by treatment with [MCl4]2- under basic
conditions has been prepared and their structures characterized crystallographically. In contrast
to Ni(B-Et)2, Ni(B-Bn)2 has been crystallized only in the planar form. M(B-Et)2 and M(B-Bn)2
(M = Co or Zn) have similar, nearly tetrahedral structures, while Cu(B-Et)2 and Cu(B-Bn)2 have
structures that are decidedly intermediate between tetrahedral and planar. Despite the abilities of
these complexes to exist in tetrahedral, planar, or intermediate structures in solution, it has not
been possible to induce much structural variation in crystalline forms. While two polymorphs of
Zn(B-Bn)2 have been obtained, both have similar, tetrahedral structures. Only Ni(B-Et)2
crystallizes in both planar and tetrahedral forms. None of the complexes formed cocrystals with
fullerenes or solvates in which structural variation as seen in Ni(B-Et)2 occurred.
2

Page 3 of 30
CrystEngComm
View Article Online
DOI: 10.1039/C7CE00638A
Introduction
Cocrystallization of transition metal complexes and other molecules with C60 can produce
significant alterations in the geometry of the complex. For example, in solution dicobalt
octacarbonyl, Co2(CO)8, exists as three, dynamically interconverting isomers (the bridged C2v
isomer along with the D3d and D2d isomers that lack carbonyl bridges).1,2,3,4 Crystallization of
Co2(CO)8 from solution results in isolation of the doubly-bridged C2v isomer.5,6 In the presence
of C60, solutions of Co2(CO)8 produce black crystals that contain the unbridged D3d-Co2(CO)8
isomer along with C60 molecules.7 In this solid, D3d-Co2(CO)8•C60, molecules of D3d-Co2(CO)8
are situated in the octahedral holes formed by close packing of the C60 molecules. In another
example, cocrystallization of Hg{Co(CO)4}2 with C60 results in a structural rearrangement from
the staggered D3d form into one that allows the Hg{Co(CO)4}2 molecule with idealized C2v
symmetry to embrace the neighboring fullerene in crystalline Hg{Co(CO)4}2•C60•toluene.8
Similarly, cocrystallization of the oxo-bridged dimer, µ-O{FeIII(OEP)}2, with C60 results in
bending of the Fe-O-Fe bonds from the nearly linear situation in the pristine crystals
(172.16(17)° in the triclinic form and 176.2(2)° in the monoclinic polymorph9) to 150.18(11)°
and 151.89(11)° in the two independent molecules in C60•µ-O{FeIII(OEP)}2•C6H6.10 In a
slightly different vein, cocrystallization of bis(ethylenedithio)tetrathiafulvalene (ET) with C70
with produces two different solvates, C70•ET•C6H6 and 2C70•2ET•CS2, that show different
degrees of folding and twisting of the ET molecules away from planarity.11 These crystals also
show clearly different overlap between the ET and fullerene molecules.
In this context, we became interested in the series of complexes shown in Scheme 1, where B
refers to the benzoylacetone backbone and R refers to the substituent on the parent amine. On
the basis of spectroscopic and magnetic data, the bis(β-ketoamino)metal(II) complexes, M(B-R)2
3

CrystEngComm
Page 4 of 30
View Article Online
DOI: 10.1039/C7CE00638A
with M = NiII or CoII, are known to exist as an equilibrating mixture of planar and tetrahedral
forms in solution.12,13 It was particularly interesting to note that Everett and Holm observed that
Ni(B-Et)2 crystallized as a green, diamagnetic solid, but after heating in vacuum for 0.5 hr. at
100 ° it transformed into a brown paramagnetic form. These observations indicated a structural
transformation from a planar (diamagnetic) form into a tetrahedral (paramagnetic, µβ = 3.1 B.M.)
form. Additionally, copper complexes of this sort are known to be quite plastic and can have
structures that are intermediate between planar and tetrahedral. Thus, we explored the premise
that the four-coordinate complexes M(B-R)2, shown in Scheme 1, might cocrystallize with
fullerenes and that in such cocrystallizations, the geometry of the M(B-R)2 molecule might
change to accommodate the presence of the fullerene. Several related planar, four-coordinate
macrocyclic complexes of nickel, cobalt, and copper are known to readily cocrystallize with
various fullerenes.14-16 Indeed, Ni(OEP) (OEP is the dianion of octaethylporphyrin) has been
shown to be useful in forming suitable crystals of endohedral fullerenes for single crystal X-ray
diffraction studies and has allowed the structures of many of these endohedral fullerenes to be
determined.17-20
Scheme 1. Formation of Bis(β-ketoamino)metal(II) Complexes M(B-R)2.
4

Page 5 of 30
CrystEngComm
View Article Online
DOI: 10.1039/C7CE00638A
Results and Discussion
Samples of M(B-Et)2 and M(B-Bn)2 (M = Co, Ni, Cu, and Zn) were prepared using the
method shown in Scheme 1 as outlined previously.12,13 The original method of ligand formation
called for heating of the amine and β-diketone at 100° C for several hours in the presence of
calcium sulfate. The volatility of ethylamine seemed problematic, but we found that heating an
aqueous solution of ethylamine with the β-diketone in toluene in the presence of magnesium
sulfate produced the ligand in good yield. We prepared the M(B-Bn)2 complexes because we
expected that the two additional phenyl substituents could act to assist in forming π−π
interactions with the fullerene during cocrystallization.21 Unfortunately, we were unable to
obtain cocrystals of any of these eight M(B-R)2 complexes with either C60 or C70.
The Structures of the Green and Brown Polymorphs of Ni(B-Et)2.
Although Everett and Holm reported obtaining only the green diamagnetic polymorph of
Ni(B-Et)2 upon crystallization from heptane, we have found that both polymorphs of Ni(B-Et)2
can be selectively
obtained by modification of the recrystallization temperature.
Recrystallization from heptane by cooling a hot solution of the complex to 0 °C affords the green
diamagnetic polymorph, while recrystallization by cooling a hot solution of the complex to 30 °C
gives the brown paramagnetic form. A concomitant mixture can be obtained through
recrystallization at room temperature. Crystallographic data for these polymorphs, along with
those of related four-coordinate complexes considered here, are presented in Table 1. Table 2
contains selected bond distances and angles for these complexes. In addition, the table lists the
dihedral angle between the planes of the two β-ketoamino ligands in each complex and their τ4
values. The τ4 value is a measure of the degree of planar or tetrahedral geometry for four-
5

CrystEngComm
Page 6 of 30
View Article Online
DOI: 10.1039/C7CE00638A
coordinate complexes.22 For a perfectly tetrahedral complex it will be 1.0, while for a perfectly
planar complex it will be 0.
The green polymorph of Ni(B-Et)2 has a planar structure, as expected from earlier work
that determined that it was diamagnetic. Figure 1 shows two views of the molecule. The
ligands, which themselves are planar (except for the positioning of the peripheral phenyl and
ethyl groups) are in a trans arrangement. This arrangement places the ethyl groups on the
nitrogen atoms far apart and minimizes the steric strain that would occur in the cis isomer.
Figure 1. Two views of the molecular structure of green, planar Ni(B-Et)2 drawn with 50%
thermal contours. Hydrogen atoms are omitted for clarity.
6

Page 7 of 30
CrystEngComm
View Article Online
DOI: 10.1039/C7CE00638A
Table 1
Crystal Data for M(B-R)2 complexes
Ni(B-Et)2
planar
Ni(B-Et)2
tetrahedral
Ni(B-Bn)2
Co(B-Et)2
Co(B-Bn)2
chemical formula
color
C24H28N2NiO2
green
C24H28N2NiO2
brown
C34H32N2NiO2
green
C48H56Co2N4O4
orange
C34H32CoN2O2
orange
559.54
0.71073
orthorhombic
P21212
90(2)
formula weight
radiation source, λ (Å)
crystal system
space group
T (K)
435.19
435.19
559.32
0.71073
monoclinic
P21/c
870.82
0.71073
triclinic
0.71073
triclinic
0.71073
triclinic
–
–
–
P1
P1
P1
90(2)
90(2)
90(2)
90(2)
a (Å)
9.509(5)
9.826(5)
12.281(6)
87.621(8)
70.731(7)
74.265(8)
1041.2(9)
2
7.5160(5)
12.6431(9)
13.1097(14)
118.470(2)
101.607(2)
95.514(2)
1045.70(15)
2
7.5225(3)
25.9549(12)
6.9974(3)
90
12.6021(17)
13.2685(18)
14.856(2)
102.934(2)
94.203(2)
117.9330(18)
2092.7(5)
4
15.1696(16)
16.2061(17)
5.6087(6)
90
b (Å)
c (Å)
α (deg)
β (deg)
98.5330(10)
90
90
γ (deg)
90
V (Å3)
1351.09(10)
2
1378.8(3)
2
Z
dcalc (g cm-3)
µ (mm-1)
1.388
1.382
1.375
1.382
1.348
0.954
0.95
0.753
0.842
0.656
F(000)
460
460
588
916
586
0.410 x 0.150 x
0.100
0.210 x 0.170 x
0.150
0.210 x 0.120 x
0.090
0.110 x 0.100 x
0.050
0.230 x 0.090 x
0.050
crystal size (mm3)
Flack abs. struct. par
reflections collected
n/a
n/a
n/a
n/a
0.011(12)
23476
28983
34968
22633
35987
data/parameters/restraints 6833 / 266 / 0
6904 / 266 / 0
0.0524
4497 / 179 / 0
0.0191
13854 / 531 / 0
0.0428
4637 / 179 / 0
0.0286
R(int)
0.0400
R1 [I > 2σ(I)]a
wR2 (all data)a
0.0368
0.0220
0.0330
0.0478
0.0263
0.1059
0.0680
0.0971
0.1249
0.0671
largest difference peak
and hole (e Å-3)
1.405 and -0.706
0.488 and -0.322
0.554 and -0.674
1.625 and -0.776
0.360 and -0.261
7

CrystEngComm
Page 8 of 30
View Article Online
DOI: 10.1039/C7CE00638A
Table 1 (continued)
Crystal Data for M(B-R)2 complexes
Zn(B-Et)2
α-Zn(B-Bn)2
β-Zn(B-Bn)2
Cu(B-Et)2
Cu(B-Bn)2
chemical formula
color
C24H28N2O2Zn
colorless
441.85
C34H32N2O2Zn
colorless
565.98
C34H32N2O2Zn
colorless
565.98
C24H28CuN2O2
brown
C34H32CuN2O2
brown
formula weight
radiation source, λ (Å)
crystal system
space group
T (K)
440.02
0.71073
monoclinic
P21/n
564.15
0.71073
0.71073
orthorhombic
P21212
0.71073
monoclinic
P21/n
0.71073
monoclinic
P21
triclinic
–
P1
90(2) K
7.3939(10)
12.6055(17)
13.2996(18)
116.469(2)
105.648(2)
93.280(2)
1045.6(2)
2
90(2)
90(2)
90(2)
90(2)
a (Å)
15.2491(19)
16.231(2)
5.5977(7)
90
13.8756(12)
14.6124(13)
14.7723(13)
90
12.813(2)
7.2285(13)
23.157(4)
90
9.4162(7)
10.2399(8)
14.8195(11)
90
b (Å)
c (Å)
α (deg)
β (deg)
90
112.4210(10)
90
90.407(2)
90
106.6690(10)
90
γ (deg)
90
V (Å3)
1385.4(3)
2
2768.8(4)
4
2144.8(7)
4
1368.86(18)
2
Z
dcalc (g cm-3)
µ (mm-1)
1.403
1.357
1.358
1.363
1.369
1.197
0.92
0.921
1.04
0.832
F(000)
464
592
1184
924
590
0.150 x 0.140 x
0.010
0.150 x 0.130 x
0.130
0.110 x 0.110 x
0.100
0.160 x 0.120 x
0.110
crystal size (mm3)
Flack abs. struct. par
reflections collected
0.420 x 0.170 x 0.150
0.036(9)
23276
n/a
n/a
n/a
0.023(10)
23334
15597
44087
30346
data/parameters/restraint
s
6341 / 295 / 0
0.026
4641 /179 / 0
0.0201
8437 / 354 / 0
0.0304
6026 / 266 / 0
0.0427
9053 / 355 / 1
0.0303
R(int)
R1 [I > 2σ(I)]a
wR2 (all data)a
0.0455
0.1201
0.0226
0.0359
0.0383
0.0332
0.0656
0.0961
0.1077
0.0746
largest difference peak
and hole (e Å-3)
0.488 and -
2.346
0.402 and -0.195
1.047 and -0.793
0.931 and -0.524
0.391 and -0.345
!/!
!
!
!
! ! !! !!!
a R1 = ! !" ! !" ; wR2 =
! !
! !"
! ! !!
Table 2
8

Page 9 of 30
CrystEngComm
View Article Online
DOI: 10.1039/C7CE00638A
Selected Bond Distances and Angles for M(B-R)2 Complexes
Ni(B-Et)2
Planar
Ni(B-Et)2
Ni(B-Bn)2
Co(B-Et)2
Co(B-Et)2
Co(B-Bn)2
Tetrahedral
Molecule 1
Molecule 2
Distances
(Å)
M-O1
M-O2
M-N1
1.8401(14)
1.8414(14)
1.9510(14)
1.9506(13)
1.9124(7)
1.9141(7)
1.9467(8)
1.9551(8)
1.8373(9)
1.9344(14)
1.9284(14)
1.9764(16)
1.9732(16)
1.9346(14)
1.9325(14)
1.9636(17)
1.9720(17)
1.9203(11)
1.9603(13)
1.9396(11)
M-N2
Angles (°)
177.22(5)
92.69(5)
87.72(5)
87.35(5)
92.38(5)
177.08(5)
122.87(3)
94.33(3)
108.19(3)
121.34(3)
95.65(3)
115.14(3)
86.62
180.
113.75(6)
97.67(6)
113.76(6)
114.91(6)
97.66(6)
120.12(7)
87.32
117.72(6)
96.79(6)
108.99(7)
119.67(6)
97.39(6)
117.08(7)
86.05
115.45(7)
96.07(5)
119.38(5)
O1-M-O2
O1-M-N1
O2-M-N1
O1-M-N2
O2-M-N2
N1-M-N2
92.09(4)
87.91(4)
180
112.10(8)
84.72
Dihedral
angle (°)
0.040
0.821
0
0.886
0.870
0.860
τ4
9

CrystEngComm
Page 10 of 30
View Article Online
DOI: 10.1039/C7CE00638A
Table 2 continued
Selected Bond Distances and Angles for M(B-R)2 complexes
Zn(B-
Cu(B-Et)2 Cu(B-Bn)2
α-Zn(B-Bn)2 β-Zn(B-Bn)2
Et)2
P21212
P21/n
Distances
(Å)
M-O1
M-O2
M-N1
1.9456(15)
1.949(2)
1.9404(11)
1.9625(11)
1.9435(11)
1.9883(13)
1.9934(13)
1.9094(13)
1.9069(14)
1.9481(16)
1.9504(16)
1.9214(14)
1.9166(17)
1.970(2)
1.965(2)
1.796(8)
1.9695(13)
M-N2
1.9800(18)
Angles(°)
114.25(7)
101.2(2)
103.2(3)
117.13(7)
97.60(8)
122.33(19)
86.69
112.71(7)
96.46(5)
119.22(5)
110.85(5)
96.66(5)
117.11(5)
104.37(5)
97.04(5)
129.91(5)
80.73
142.71(6)
95.34(6)
95.47(6)
96.86(6)
95.42(6)
143.31(7)
52.56
155.18(8)
92.81(8)
90.97(8)
91.08(7)
93.48(7)
160.51(8)
34.5
O1-M-O2
O1-M-N1
O2-M-N1
O1-M-N2
O2-M-N2
N1-M-N2
114.35(8)
84.57
Dihedral
angle (°)
τ4
0.855
0.862
0.801
0.525
0.314
10

Page 11 of 30
CrystEngComm
View Article Online
DOI: 10.1039/C7CE00638A
The brown polymorph of Ni(B-Et)2 has a tetrahedral structure, which is illustrated in
Figure 2. Again, the core of the β-ketoamino ligand is planar, but the two ligands are aligned so
that the dihedral angle between them is 86.62 °. Tetrahedral complexes with two chelating,
bidentate ligands are chiral, but crystals of the brown polymorph of Ni(B-Et)2 are
centrosymmetric and contain a racemate.
The structural parameters obtained in the
crystallographic work agree rather well those predicted on the basis of computations on the
related compound, bis-[3-(methylimino)prop-1-enyloxy]Ni(II).23
Figure 2. A view of the molecular structure of one enantiomer in the brown polymorph of Ni(B-
Et)2 drawn with 50% thermal contours. Hydrogen atoms are omitted for clarity.
11

CrystEngComm
Page 12 of 30
View Article Online
DOI: 10.1039/C7CE00638A
Interconversions of the Green and Brown Polymorphs of Ni(B-Et)2.
The two polymorphs have different melting points. The planar form melts at 117 - 119
°C, while the tetrahedral polymorph melts at a higher temperature, 163 – 167 °C. After the
planar polymorph was melted and then cooled to room temperature, the resulting solid was
brown in color and had a melting point of 163 - 167°C. Thus, melting of the green, planar
polymorph transforms it into the brown, tetrahedral form. This transformation has also been
demonstrated by examination of the X-ray powder diffraction pattern of the sample before and
after melting as shown in Figure 3.
Figure 3. Powder X-ray diffraction patterns for (a) crystals of tetrahedral Ni(B-Et)2, (b) a sample
of planar Ni(B-Et)2 after melting and solidification, and (c) crystals of planar Ni(B-Et)2.
12

Page 13 of 30
CrystEngComm
View Article Online
DOI: 10.1039/C7CE00638A
Everett and Holm noted that upon heating in vacuo at 100 °C for 0.5 hours, the
crystalline green diamagnetic solid (Ni(B-Et)2) converted to a brown crystalline paramagnetic
solid with the same elemental composition. This observation was tested by heating a single
crystal of planar Ni(B-Et)2 under vacuum for 30 minutes, then mounting the crystal on the
diffractometer to determine its unit cell. The unit cell of the crystal remained unchanged,
indicating no geometric transformation occurred. Additionally, no color change was observed.
However, we were able to effect the conversion of planar Ni(B-Et)2 to tetrahedral Ni(B-Et)2 by
heating several planar crystals in the same vessel, under the same conditions, for approximately
two hours. A color change from green to brown was observed for the sample.
To test the conversion conditions further, a crystal of the tetrahedral form was placed in
the vicinity of the planar crystal, and the heating process repeated. The green crystal underwent a
color change from green to brown, consistent with the observation of Everett and Holm. This
experiment was then conducted in the presence of other compounds in the series, as shown in
Figure 4. In the presence of Ni(B-Et)2, Cu(B-Et)2, Zn(B-Et)2, and either polymorph of Zn(B-
Bn)2, the planar Ni(B-Et)2 crystal converted to the tetrahedral form. This conversion did not
occur in the presence of Co(B-Et)2, Co(B-Bn)2, Ni(B-Bn)2, or Cu(B-Bn)2. We also attempted to
induce the conversion by placing the planar Ni(B-Et)2 near a variety of samples (e.g. the free
ligands, Co(acac)3, a molecular sieve, magnesium metal, decolorizing carbon, NaCl, and
anthracene); no conversion was observed.
13

CrystEngComm
Page 14 of 30
View Article Online
DOI: 10.1039/C7CE00638A
Figure 4. (a-e) Images of Ni(B-Et)2 crystals before heating. (a) planar Ni(B-Et)2; (b) planar
Ni(B-Et)2 and Co(B-Et)2; (c) planar Ni(B-Et)2 and Cu(B-Et)2; (d) planar Ni(B-Et)2 and Zn(B-
Et)2; (e) planar Ni(B-Et)2 and α-Zn(B-Bn)2. (f-j) Images of Ni(B-Et)2 crystals after heating for
0.5 hr. (f) planar Ni(B-Et)2; (g) planar Ni(B-Et)2 and Co(B-Et)2; (h) tetrahedral Ni(B-Et)2 and
Cu(B-Et)2; (i) tetrahedral Ni(B-Et)2 and Zn(B-Et)2; (j) tetrahedral Ni(B-Et)2 and α-Zn(B-Bn)2.
A similar experiment was conducted where a crystal of Zn(B-Et)2 was placed a few
millimeters from a crystal of planar Ni(B-Et)2; the Zn(B-Et)2 crystal was carefully removed and
the vial heated under vacuum for 30 minutes. The planar Ni(B-Et)2 crystal converted to the
tetrahedral form (as depicted in Figure 4(i)). This observation suggests that small particulates
may fragment off of the Zn(B-Et)2 crystal and act as a seeds, thus inducing the geometric
transformation of planar Ni(B-Et)2 in the solid state. To confirm this, we then coated the Zn(B-
Et)2 crystal in an oil (Paratone, mineral, or silicone), and heated the coated Zn(B-Et)2 crystal
along with a crystal of planar Ni(B-Et)2 under vacuum for 30 minutes. The conversion of the
nickel complex no longer occurred.
14

Page 15 of 30
CrystEngComm
View Article Online
DOI: 10.1039/C7CE00638A
The Structure Ni(B-Bn)2.
Only one crystalline form of Ni(B-Bn)2 was found. Ni(B-Bn)2, which crystallized as
green blocks, has a planar, centrosymmetric structure as shown in Figure 5. As with the planar
form of Ni(B-Et)2, the complex crystallizes as the trans isomer. As the data in Table 2 show, the
bond distances and angles within the planar molecules, Ni(B-Et)2 and Ni(B-Bn)2, are similar.
Figure 5. Molecular structure of Ni(B-Bn)2 drawn with 50% thermal contours. Hydrogen atoms
are omitted for clarity.
The Structures of the Tetrahedral Complexes M(B-Et)2 and M(B-Bn)2 (M = Co or
Zn).
Figure 6 shows a comparison of the structures of the orange crystals of Co(B-Et)2 and
Co(B-Bn)2. Co(B-Et)2 crystallizes in a centrosymmetric space group with two molecules in the
asymmetric unit, but as the data in Table 2 and in Figure 6 show, the two molecules have very
similar structures. The major difference between them involves the positioning of the ethyl
15

CrystEngComm
Page 16 of 30
View Article Online
DOI: 10.1039/C7CE00638A
groups. Additionally, Co(B-Bn)2 has a similar tetrahedral structure. However, it undergoes
spontaneous resolution and only one enantiomer is present in any one crystal. These findings are
consistent with the observations made on other bis(β-ketoamino)cobalt(II) complexes, which
revealed that only when R = H was the planar form found in the solid state.13 Larger substituents
produced only tetrahedral complexes.
Figure 7 shows a comparison of the structures of Zn(B-Et)2 and Zn(B-Bn)2. Colorless
Zn(B-Bn)2 crystallizes as two different polymorphs. The core structures of colorless Zn(B-Et)2
and both polymorphs of Zn(B-Bn)2 are similar. The α-polymorph of Zn(B-Bn)2 crystallizes as
colorless blocks and is isostructural with Co(B-Bn)2. Consequently, any one crystal of α-Zn(B-
Bn)2 contains only one enantiomer of the complex. β-Zn(B-Bn)2 crystallizes as colorless
parallelepipeds which contain a racemate. The major difference between the two polymorphs of
Zn(B-Bn)2 involves the positioning of the benzyl groups. The calculated densities and melting
points of these two polymorphs do not differ. Unlike the set of nickel polymorphs, it is not
possible to induce a phase transition from one form to the other upon heating at temperatures
below their melting point. The structure of Zn(B-Et)2 suffers from disorder in the position of N2
The distances is reported in Table 2 refer to the major site (N2A) with 0.56 fractional occupancy.
16

Page 17 of 30
CrystEngComm
View Article Online
DOI: 10.1039/C7CE00638A
Figure 6. Comparison of the structures of the two independent enantiomers of Co(B-Et)2 that are
found in one crystal (top two drawings) with the structure of Co(B-Bn)2 (bottom drawing)..
Drawn with 50% thermal contours. Hydrogen atoms are omitted for clarity.
17

CrystEngComm
Page 18 of 30
View Article Online
DOI: 10.1039/C7CE00638A
Zn(B-Et)2
α-Zn(B-Bn)2
β-Zn(B-Bn)2
Figure 7. Comparison of the structure of one enantiomer of Zn(B-Et)2 with those of the two
polymorphs of Zn(B-Bn)2. Drawn with 50% thermal contours. Hydrogen atoms are omitted for
clarity.
18

Page 19 of 30
CrystEngComm
View Article Online
DOI: 10.1039/C7CE00638A
The Structures of the Copper Complexes Cu(B-Et)2 and Cu(B-Bn)2. The structures
of these two complexes are compared in Figure 8. Cu(B-Et)2 crystallizes as a racemate in a
centrosymmetric space group, while Cu(B-Bn)2 undergoes spontaneous resolution and
crystallizes in an enantiomorphic space group. In each case, the structure is intermediate
between planar and tetrahedral. For Cu(B-Et)2, the dihedral angle between the ligand planes is
52.56° and τ4 value is 0.525, while for Cu(B-Bn)2 the corresponding dihedral angle is 34.5° and
the τ4 value is 0.314. Despite repeated attempts to obtain other crystalline forms of these copper
complexes, only the two crystalline forms reported here have been obtained.
Figure 8. Comparison of the structure of one enantiomer of Cu(B-Et)2 (top) with the structure of
Cu(B-Bn)2 (bottom drawing).
19

CrystEngComm
Page 20 of 30
View Article Online
DOI: 10.1039/C7CE00638A
Efforts were made to modify the geometry of each complex through solvate formation or
cocrystallization. Solvate formation can influence molecular geometry, as shown for example in
the structures of the dimers Au2(µ-dppe)2X2 (X = Br, I).24,25 These molecules involve two
planar, three-coordinate gold centers with variable Au•••Au separations (ranging from 3.1 to 3.8
Å) that change (along with their photo luminescence) depending upon the particular type of
solvate molecules that are incorporated into the crystal. To incorporate a solvate molecule into
crystals of M(B-Et)2 and M(B-Bn)2, recrystallization was attempted using dichloromethane,
toluene, benzene, mesitylene, and pentane. In all cases, except mesitylene, unsolvated crystals of
the complex resulted. In the case of mesitylene and Cu(B-Bn)2, the ligand dissociated and
recrystallized. Attempts to cocrystallize all compounds through slow vapor diffusion were
unsuccessful. Cocrystallizations were attempted with bis(ethylenedithio)tetrathiafulvalene (ET),
tetracyanoquinodimethane (TCNQ), anthracene, C60, and C70. In all cases, the metal complexes
and cocrystallization agents crystallized individually. Attempts to modify the geometry of the
Cu(B-R)2 and Ni(B-R)2 complexes by doping into colorless Zn(B-R)2 were unsuccessful and led
only to the crystallization of the individual metal complexes.26,27
Conclusions
The series of β-diketoamine containing complexes, M(B-Et)2 and M(B-Bn)2, (M= CoII,
NiII, CuII, ZnII) has been synthesized and their structures characterized crystallographically.
Conditions for the crystallization and interconversion of the green and brown polymorphs of
Ni(B-Et)2, which contain planar and tetrahedral complexes in accord with previous magnetic and
spectroscopic studies, have been determined. Ni(B-Bn)2 has been crystallized only in the planar
20

Page 21 of 30
CrystEngComm
View Article Online
DOI: 10.1039/C7CE00638A
form. M(B-Et)2 and M(B-Bn)2 (M = Co or Zn) have similar, nearly tetrahedral structures, while
Cu(B-Et)2 and Cu(B-Bn)2 have structures that are decidedly intermediate between tetrahedral and
planar. Despite the abilities of these complexes to exist in tetrahedral, planar, or intermediate
structures in solution, it has not been possible to induce much structural variation in crystalline
forms. While two polymorphs of Zn(B-Bn)2 have been obtained, both have similar, tetrahedral
structures. Only Ni(B-Et)2 crystallizes in both planar and tetrahedral forms. The green, planar
form can be converted to the brown, tetrahedral form by heating without melting at 100 °C. At a
molecular level this structural change probably involves rotation of one ligand relative to
another, as occurs in solution.12 At the crystal level, the process is facilitated by the availability
of suitable seed crystals. None of the complexes formed cocrystals with fullerenes.
EXPERIMENTAL
General and materials
All manipulations were carried out using standard Schlenk or glovebox techniques under a dry
nitrogen atmosphere. Unless otherwise noted, solvents were purchased from commercial
suppliers and used without further purification. Solvents were deoxygenated by sparging with
nitrogen gas. Benzoylacetone (98 %) and ethylamine hydrobromide (98%) were purchased from
TCI America and used without further purification. Potassium tert-butoxide (98%), benzylamine
(99%), and ethylamine (70 wt % solution in water) were purchased from Sigma Aldrich and used
without further purification. P-toluenesulfonic acid monohydrate was purchased from Sigma
Aldrich, and heated under vacuum at 130 °C for two hours to generate the dehydrated product.
Tert-butyl alcohol was purchased from Fisher Scientific, dried over 3 Å molecular sieves for two
21

CrystEngComm
Page 22 of 30
View Article Online
DOI: 10.1039/C7CE00638A
days, and stored at 30 °C. The tetraethylammonium metal bromide salts [Et4N]2[CoBr4],
[Et4N]2[NiBr4], [Et4N]2[CuBr4], and [Et4N]2[ZnBr4] were synthesized according to literature
methods.28
Synthesis
(Z)-3-(ethylamino)-1-phenylbut-2-en-1-one (B-Et)
Method 1.
In a three-neck round bottom flask with a reflux condenser attached, toluene (30 mL) and a 70
wt% solution of ethylamine in water (1.0 mL) were added to benzoylacetone (1.280 g, 2.89
mmol) and magnesium sulfate (0.435 g, 3.61 mmol). After stirring at 100 °C for three hours, the
mixture was allowed to cool to room temperature under nitrogen, and then filtered in air. The
yellow filtrate was concentrated in vacuo and purified by column chromatography (hexanes:
ethyl acetate 9:1), yielding B-Et as a yellow oil (yield 0.979 g, 66%).29
Method 2.30
Using a Dean-Stark apparatus, p-toluenesulfonic acid (0.349 g, 2.03 mmol) and benzoylacetone
(1.598 g, 9.851 mmol) were dissolved in toluene (100 mL), charged with a 70 wt% solution of
ethylamine in water (1.5 mL), and vigorously refluxed for 3 hours. The mixture was cooled to
room temperature and filtered in air. The yellow filtrate was concentrated in vacuo and purified
by column chromatography (hexanes: ethyl acetate 9:1), yielding B-Et as a yellow oil (yield
0.392 g, 21%).
(Z)-3-(benzylamino)-1-phenylbut-2-en-1-one (B-Bn) B-Bn was obtained as a white crystalline
solid utilizing a procedure similar to the Method 1 synthesis of B-Et, using benzoylacetone
(1.561 g, 9.62 mmol), magnesium sulfate (0.867 g, 7.20 mmol), and benzylamine (1.5 mL) in
toluene (30 mL). The solid was recrystallized from hexanes (1.278 g, 70%). Alternatively,
22

Page 23 of 30
CrystEngComm
View Article Online
DOI: 10.1039/C7CE00638A
Method 2 could be employed with p-toluenesulfonic acid (0.105 g, 0.610 mmol), benzoylacetone
(1.226 g, 7.56 mmol), toluene (100 mL), and benzylamine (1.5 mL, 13 mmol). Recrystallization
from hexanes afforded the product (yield 0.539 g, 28%).31
Co[C6H5COCHC(NCH2CH3)CH3]2, (Co(B-Et)2)
t
t
A colorless solution of BuOK (0.301 g, 2.68 mmol) in dry BuOH (30 mL) was added to B-Et
(0.508 g, 2.68 mmol). The resulting yellow solution was heated at 50 °C for 10 minutes, then
added to [Et4N]2[CoBr4] (0.852 g, 1.33 mmol). The light blue suspension turned bright orange
over 2 minutes, and was stirred vigorously for three hours at 30 °C. Tert-butyl alcohol was
removed under vacuum and n-heptane (30 mL) was added to the solid. The slurry was filtered
through a fine Schlenk frit, and orange needles suitable for X-ray diffraction were obtained from
recrystallization in n-heptane (yield 0.090 g, 15%). Mp: 185–188 °C. FTIR (cm-1): 2962, 2928,
1699, 1585, 1564, 1503, 1483, 1455, 1404, 1390, 1347, 1301, 1285, 1273, 1240, 1179, 1154,
1128, 1116, 1086, 1069, 1025, 966, 920, 872, 850, 792, 748, 693, 685, 624, 582, 537, 461, 416.
Ni[C6H5COCHC(NCH2CH3)CH3]2 (Ni(B-Et)2)
t
Ni(B-Et)2 was obtained analogously to the procedure of Co(B-Et)2 using BuOK (0.303 g, 2.70
mmol), B-Et (0.512 g, 2.70 mmol), and [Et4N]2[NiBr4] (0.851 g, 1.33 mmol) in tBuOH (30 mL).
Crystals suitable for X-ray diffraction of both green needles (planar Ni(B-Et)2) and brown blocks
(tetrahedral Ni(B-Et)2) were obtained from the filtrate (yield 0.205 g, 35%). Planar Ni(B-Et)2
was converted to tetrahedral Ni(B-Et)2 upon melting. Planar Ni(B-Et)2 mp: 117 -119 °C. FTIR
(cm-1): 2975, 2957, 2926, 1588, 1570, 1510, 1472, 1451, 1419, 1363, 1341, 1307, 1275, 1228,
1176, 1155, 1100, 1064, 1024, 999, 957, 921, 878, 843, 792, 755, 708, 694, 647, 617, 593, 569,
505, 479, 434, 404. Tetrahedral Ni(B-Et)2 mp: 163 - 167°C. FTIR (cm-1): 3060, 3029, 1585,
1566, 1499, 1479, 1463, 1447, 1401, 1342, 1333, 1301, 1288, 1253, 1210, 1176, 1112, 1083,
23

CrystEngComm
Page 24 of 30
View Article Online
DOI: 10.1039/C7CE00638A
1069, 1026, 998, 923, 911, 881, 838, 807, 792, 755, 740, 696, 653, 618, 595, 574, 555, 458, 425,
406.
Cu[C6H5COCHC(NCH2CH3)CH3]2 (Cu(B-Et)2)
t
Cu(B-Et)2 was obtained analogously to the procedure of Co(B-Et)2 using BuOK (0.301 g, 2.68
mmol), B-Et (0.464 g, 2.45 mmol), and [Et4N]2[CuBr4] (0.788 g, 1.22 mmol) in tBuOH (30 mL).
Brown blocks suitable for X-ray diffraction were obtained from recrystallization in n-heptane
(yield 0.251 g, 47%). Mp: 129–131 °C. FTIR (cm-1): 2969, 2922, 2864, 1590, 1573, 1505, 1482,
1456, 1409, 1367, 1337, 1286, 1235, 1179, 1153, 1141, 1115, 1096, 1067, 1026, 997, 953, 920,
870, 849, 790, 738, 687, 624, 582, 5422, 476, 452, 420.
Zn[C6H5COCHC(NCH2CH3)CH3]2 (Zn(B-Et)2)
t
Zn(B-Et)2 was obtained analogously to the procedure of Co(B-Et)2 using BuOK (0.295 g, 2.62
mmol), B-Et (0.490 g, 2.59 mmol), and [Et4N]2[ZnBr4] (0.833 g, 1.30 mmol) in tBuOH (30 mL).
Colorless blocks suitable for X-ray diffraction were obtained from recrystallization in n-heptane
(yield 0.155 g, 20%). mp: 172-175 °C. FTIR (cm-1): 2929, 2205, 2095, 2072, 2049, 2015, 2000,
1968, 1567, 1482, 1457, 1382, 1347, 1301, 1284, 1241, 1179, 1154, 1131, 1118, 1088, 1025,
998, 962, 921, 871, 851, 792, 695, 620, 582, 455.
Co[C6H5COCHC(NCH2C6H5)CH3]2 (Co(B-Bn)2)
t
t
A colorless solution of BuOK (0.225 g, 2.01 mmol) in dry BuOH (30 mL) was added to B-Bn
(0.501 g, 2.00 mmol). The colorless solution was heated at 50 °C for 10 minutes, then added to
[Et4N]2[CoBr4] (0.637 g, 1.00 mmol), forming a bright orange suspension. The suspension was
stirred vigorously for three hours at 30 °C. Tert-butyl alcohol was removed under vacuum and n-
heptane (30 mL) was added to the solid. The orange slurry was filtered through a fine Schlenk
frit, and orange parallelepipeds suitable for X-ray diffraction were obtained from the filtrate
24

Page 25 of 30
CrystEngComm
View Article Online
DOI: 10.1039/C7CE00638A
(yield 0.086 g, 15%) Mp: 156–160 °C. FTIR (cm-1): 3060, 3029, 1585, 1566, 1499, 1479, 1463,
1447, 1401, 1342, 1333, 1301, 1288, 1253, 1210, 1176, 1112, 1083, 1069, 1026, 998, 923, 911,
881, 838, 807, 792, 755, 740, 696, 653, 618, 595, 574, 555, 458, 425, 406.
Ni[C6H5COCHC(NCH2C6H5)CH3]2 (Ni(B-Bn)2)
Ni(B-Bn)2 was obtained analogously to the procedure of Co(B-Bn)2 using tBuOK (0.226 g, 2.01
t
mmol), B-Bn (0.508 g, 2.02 mmol), and [Et4N]2[NiBr4] (0.633 g, 1.00 mmol) in BuOH (30
mL). Green blocks suitable for X-ray diffraction were obtained from recrystallization in n-
heptane (yield 0.060 g, 10%). Mp: 192–195 °C. FTIR (cm-1): 3059, 3022, 1588, 157-, 1558,
1511, 1494, 1484, 1455, 1445, 1416, 1343, 1327, 1310, 1260, 1123, 1094, 1069, 1028, 983, 926,
909, 891, 842, 814, 789, 769, 726, 714, 693, 617, 582, 561, 511, 481, 450, 416, 405.
Cu[C6H5COCHC(NCH2C6H5)CH3]2 (Cu(B-Bn)2)
Cu(B-Bn)2 was obtained analogously to the procedure of Co(B-Bn)2 using tBuOK (0.226 g, 2.01
t
mmol), B-Bn (0.504 g, 2.01 mmol), and [Et4N]2[CuBr4] (0.646 g, 1.00 mmol) in BuOH (30
mL). Brown blocks suitable for X-ray diffraction were obtained from recrystallization in n-
heptane (yield 0.230 g, 42%). mp: 186–188 °C. FTIR (cm-1): 3028, 1587, 1570, 1512, 1483,
1459, 1415, 1345, 1310, 1290, 1256, 1219, 1181, 1117, 1088, 1067, 1026, 999, 970, 926, 903,
885, 840, 795, 753, 723, 688, 617, 596, 574, 544, 474, 456, 406.
Zn[C6H5COCHC(NCH2C6H5)CH3]2 (Zn(B-Bn)2)
Zn(B-Bn)2 was obtained analogously to the procedure of Co(B-Bn)2 using tBuOK (0.237 g, 2.11
t
mmol), B-Bn (0.501 g, 2.00 mmol), and [Et4N]2[ZnBr4] (0.643 g, 1.00 mmol) in BuOH (30
mL). Colorless blocks of α-Zn(B-Bn)2 and colorless parallelepipeds of β-Zn(B-Bn)2 suitable for
X-ray diffraction were obtained concomitantly from recrystallization in n-heptane (yield 0.123 g,
22%). α-Zn(B-Bn)2 mp: 172-175 °C. FTIR (cm-1): 3060, 2957, 2169, 1585, 1565, 1483, 1457,
25

CrystEngComm
Page 26 of 30
View Article Online
DOI: 10.1039/C7CE00638A
1339, 1307, 1286, 1271, 1250, 1214, 1177, 1153, 1116, 1066, 1027, 955, 928, 888, 852, 797,
712, 685, 624, 578, 542, 487, 458, 433. β-Zn(B-Bn)2 Mp: 172-175 °C. FTIR (cm-1): 3061, 2956,
2848, 1585, 1564, 1483, 1459, 1411, 1349, 1339, 1306, 1287, 1250, 1214, 1177, 1153, 1115,
1063, 1026, 999, 954, 928, 888, 852, 797, 712, 697, 685, 617, 578, 541, 487, 485, 433.
Physical Measurements
IR spectra were recorded on a Bruker Alpha FT-IR spectrometer using attenuated total
reflectance (ATR). Melting point determinations were obtained using a Thomas-Hoover
capillary melting point apparatus and are uncorrected.
Crystal Structure Determination
X-ray data were collected using a Bruker AXS Smart diffractometer with an APEX-II CCD
Detector, equipped with a molybdenum fine-focused sealed tube and a CRYO Industries low-
temperature apparatus. All data sets were reduced with Bruker SAINT and were corrected for
absorption using SADABS.32 Structures were solved and refined using SHELXT and SHELXL-
2014, respectively.33,34
Powder X-ray Diffraction
Powder X-ray analysis was performed at room temperature using a Rigaku MiniFlex 600
equipped with a Cu-Kα X-ray source (λ= 1.5418 Å) and a D/teX Ultra high-speed silicon strip
detector (with a Ni Kβ filter). The sample was prepared on a Si510 single-crystal zero-background
holder that was rotated during collection at 60 rpm, and the pattern was collected in continuous
sweep mode from 5-50° 2θ at 2.0° 2θ/min, with an integration step size of 0.01° 2θ.
ACKNOWLEDGEMENTS
We thank the National Science Foundation for financial support (Grant CHE-1305125 to A.L.B.
and M.M.O.) and the Department of Education for a GAANN fellowship to X.B.P.
26

Page 27 of 30
CrystEngComm
View Article Online
DOI: 10.1039/C7CE00638A
ASSOCIATED CONTENT
Supporting Information: X-ray crystallographic files in CIF format for M(B-Et)2 and M(B-Bn)2,
(M = CoII, NiII, CuII, ZnII). This material is available free of charge via the Internet at
http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: albalch@ucdavis.edu (A.L.B.)
*E-mail mmolmstead@ucdavis.edu (M.M.O.)
Notes
The authors declare no competing financial interest.
REFERENCES
(1)
(2)
(3)
(4)
(5)
(6)
(7)
G. Bor, Spectrochim. Acta, 1963, 19, 2065-2073.
K. Noack, Helv. Chim. Acta, 1964, 47, 155-1563.
G. Bor and K. J. Noack, J. Organomet. Chem., 1974, 64, 367-372.
G. Bor, U. K. Dietler and K. Noack, Chem. Commun., 1976, 914-916.
G. G. Sumner, H. P. Klug and L. E. Alexander, Acta Crystallogr., 1964, 17, 732-742.
P. C. Leung and P. Coppens, Acta Crystallogr., 1983, B39, 535-542.
T. Y. Garcia, J. C. Fettinger, M. M. Olmstead and A. L. Balch, Chem. Commun., 2009,
7143-7145.
27

CrystEngComm
Page 28 of 30
View Article Online
DOI: 10.1039/C7CE00638A
(8)
(9)
F. L. Bowles, M. M. Olmstead, C. M. Beavers and A. L. Balch, Chem. Commun., 2013,
49, 5921-5923.
B. Cheng, J. D. Hobbs, P. G. Debrunner, J. Erlebacher, J. A. Shetnutt and W. R. Scheidt,
Inorg. Chem., 1995, 33, 102.
(10) H. M. Lee, M. M. Olmstead, G. G. Gross and A. L. Balch, Cryst. Growth Des., 2003, 3,
691-697.
(11) K. B. Ghiassi, M. M. Olmstead and A. L. Balch, Chem. Commun., 2013, 49, 10721-
10723.
(12)
G. W. Everett Jr. and R. H. Holm, J. Am. Chem. Soc., 1965, 87, 2117-2127.
(13) G. W. Everett Jr. and R. H. Holm, J. Am. Chem. Soc., 1966, 88, 2442–2451.
(14) M. M. Olmstead, D. A. Costa, K. Maitra, B. C. Noll, S. L. Phillips, P. M. Van Calcar and
A. L. Balch, J. Am. Chem. Soc., 1999, 121, 7090-7097.
(15) P. D. W. Boyd, M. C. Hodgson, C. E. F. Rickard, A. G. Oliver, L. Chaker, P. J. Brothers,
R. D. Bolskar, F. S. Tham and C. A. Reed, J. Am. Chem. Soc., 1999, 121, 10487-10495.
(16) J. U. Franco, J. C. Hammons, D. Rios and M. M. Olmstead, Inorg. Chem., 2010, 49,
5120-5125.
(17) S. Stevenson, G. Rice, T. Glass, K. Harich, F. Cromer, M. R. Jordan, J. Craft, E. Hadju,
R. Bible, M. M. Olmstead, K. Maitra, A. J. Fisher, A. L. Balch and H. C. Dorn, Nature,
1999, 401, 55-57.
(18) B. Q. Mercado, C. M. Beavers, M. M. Olmstead, M. N. Chaur, K. Walker, B. C.
Holloway, L. Echegoyen and A. L. Balch, J. Am. Chem. Soc., 2008, 130, 7854-7855.
(19) T. Zuo, L. Xu, C. M. Beavers, M. M. Olmstead, W. J. Fu, D. Crawford, A. L. Balch and
H. C. Dorn, J. Am. Chem. Soc., 2008, 130, 12992-12997.
28

Page 29 of 30
CrystEngComm
View Article Online
DOI: 10.1039/C7CE00638A
(20) Y. Zhang, K. B. Ghiassi, Q. Deng, N. A. Samoylova, M. M. Olmstead, A. L. Balch and
A. A. Popov, Angew. Chem. Int. Ed., 2015, 54, 495-499.
(21) A. L. Balch, V. J. Catalano, J. W. Lee and M. M. Olmstead, J. Am. Chem. Soc., 1992,
114, 5455-5457.
(22) L. Yang, D. P. Powell and R. P. Houser, Dalton Trans., 2007, 955–964.
(23) A. G. Starikov, R. M. Minyaev and V. I. Minkin, Rus. J. Gen. Chem., 2009, 79, 1793–
1801.
(24) S. H. Lim, M. M. Olmstead and A. L. Balch, J. Am. Chem. Soc., 2011, 133, 10229-
10238.
(25) S. H. Lim, M. M. Olmstead and A. L. Balch, Chem. Sci., 2013, 4, 311-318.
(26) A. Chakravorty, Inorg. Chem., 1965, 4, 127-128.
(27) C. R. R. Adolf, S. Ferlay, N. Kyritsakas and M. W. Hosseini, J. Am. Chem. Soc., 2015,
137, 15390 - 15393.
(28) N. S. Gill and R. S. Nyholm, J. Chem. Soc., 1959, 3997-4007.
(29) M. de la Cal, B. I. Cristobal, P. Cuadrado, A. M. Gonzalez and F. J. Pulido, Synth.
Commun., 1989, 19, 1039-1045.
(30) X. He, Y. Yao, X. Luo, J. Zhang, Y. Liu, L. Zhang and Q. Wu, Organometallics, 2003,
22, 4952-4957
(31) G. Karthikeyan and P. T. Perumal, Can. J. Chem., 2005, 83, 1746-1751.
(32) SAINT and SADABS; Bruker AXS Inc.: Madison, WI, 2014.
(33) G. M. Sheldrick, Acta Crystallogr., Sect. A, 2015, 71, 3-8.
(34) G. M. Sheldrick, Acta Crystallogr., Sect. C, 2015, 71, 3-8.
29