Synthesis of two new group 13 benzoato-chloro complexes: A structural study of gallium and indium chelating carboxylates

Article abstract of DOI:10.1016/j.ica.2010.08.026

Two new heteroleptic chelated-benzoato gallium (III) and indium (III) complexes have been prepared and structurally characterized. The molecular structures of [GaCl₂(4-Mepy)₂(O₂CPh)]·4- Mepy (1) and [InCl(4-Mepy)₂(O₂CPh)2]·4-Mepy (2) have been determined by single-crystal X-ray diffraction. The gallium compound (1) is a distorted octahedron with cis-chloride ligands co-planar with the chelating benzoate and the 4-methylpyridines trans to each other. This is the first example of a Ga(III) structure with a chelating benzoate. The indium compound (2) is a distorted pentagonal bipyramid with two chelating benzoates, one 4-methylpyridine in the plane and a chloride trans to the other 4-methylpyridine. The indium bis-benzoate is an unusual example of a seven-coordinate structure with classical ligands. Both complexes, which due to the chelates, could also be described as pseudo-trigonal bipyramidal, include a three-bladed motif with three roughly parallel aromatic rings that along with a solvent of crystallization and electron-withdrawing chloride ligand(s) stabilize the solid-state structures.

Full text of DOI:10.1016/j.ica.2010.08.026

Inorganica Chimica Acta 365 (2011) 54–60
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Synthesis of two new group 13 benzoato–chloro complexes: A structural study
of gallium and indium chelating carboxylates
b,
⇑⇑
c
c
d
Stan A. Duraj a, , Aloysius F. Hepp
, Robert Woloszynek , John D. Protasiewicz , Michael Dequeant ,
⇑
Tong Ren e
a Department of Chemistry, Cleveland State University, Cleveland, OH 44115, USA
b NASA Glenn Research Center, MS 302-1, 21000 Brookpark Road, Cleveland, OH 44135, USA
c Department of Chemistry, Case Western Reserve University, Cleveland, OH 44106, USA
d Department of Chemistry, Hendrix College, Conway, AR 72032, USA
e Department of Chemistry, Purdue University, West Lafayette, IN 47907, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Two new heteroleptic chelated-benzoato gallium (III) and indium (III) complexes have been prepared and
structurally characterized. The molecular structures of [GaCl2(4-Mepy)2(O2CPh)]ꢀ4-Mepy (1) and [InCl(4-
Mepy)2(O2CPh)2]ꢀ4-Mepy (2) have been determined by single-crystal X-ray diffraction. The gallium com-
pound (1) is a distorted octahedron with cis-chloride ligands co-planar with the chelating benzoate and
the 4-methylpyridines trans to each other. This is the first example of a Ga(III) structure with a chelating
benzoate. The indium compound (2) is a distorted pentagonal bipyramid with two chelating benzoates,
one 4-methylpyridine in the plane and a chloride trans to the other 4-methylpyridine. The indium bis-
benzoate is an unusual example of a seven-coordinate structure with classical ligands. Both complexes,
which due to the chelates, could also be described as pseudo-trigonal bipyramidal, include a three-bladed
motif with three roughly parallel aromatic rings that along with a solvent of crystallization and electron-
withdrawing chloride ligand(s) stabilize the solid-state structures.
Received 15 April 2010
Accepted 16 August 2010
Available online 31 August 2010
Keywords:
Gallium
Indium
Structure
Benzoate
Carboxylate
Chelate
Published by Elsevier B.V.
1. Introduction
of 4-methylpyridine or c-picoline solvent (ligands) has yielded
complexes that most readily provide single crystals suitable for
X-ray diffraction studies. Previously, reaction of sodium benzoate
with Ga2Cl4 in 4-methylpyridine resulted in isolation and struc-
tural characterization of the first oxo-centered main group trinu-
clear carboxylate, [Ga3(l3-O)(l-O2CC6H5)6(4-MeC5H5N)3](GaCl4)
[9]. Similarly, oxidation of indium powder with benzoyl peroxide
In recent years, there has been an intense and ongoing interest
in the study of gallium and indium complexes for use as potential
precursors for electronic materials via chemical spray pyrolysis or
chemical solution deposition [1–4]. Ideally, such precursors should
be readily prepared from inexpensive starting materials, be easily
handled or preferably air-stable, and decompose cleanly for chem-
ically-driven processing to be economically viable [5,6]. In our on-
going research, we are preparing derivatives of gallium and indium
chlorides with chalcogenide ligands, determining their single-
crystal structures and studying further reactions to produce new
precursors for solid-state materials [6–9]. For example, oxidative
addition of lower-valent Ga and In chlorides (or metal) via addition
of carboxylate (RCOꢁ) or dithiocarbamate (S2C-NRꢁ) ligands by
produced the first example of a mononuclear eight-coordinate in-
dium (III) benzoate, In(g
2-O2CC6H5)3(4-MeC5H5N)2 [10]. In this re-
port, we detail two further examples of structurally characterized
examples of mixed-ligand chelated–benzoato complexes prepared
by this straightforward synthetic approach with classical ligands.
We discuss the structures and compare them to other molecular
and metal–organic framework structures of indium and gallium.
2
2
reaction with the respective chalcogenide-bonded dimers affords
compounds that are amenable to characterization, particularly
complexes that are stabilized by pyridine-like ligands [1–10]. Use
2. Experimental
2.1. Materials and methods
⇑
Corresponding author. Tel.: +1 216 687 2454; fax: +1 216 687 9892.
Corresponding author. Tel.: +1 216 433 3835; fax: +1 216 433 6106.
All manipulations were performed either in an MBRAUN Lab-
master 130 drybox or utilizing standard Schlenk techniques under
an atmosphere of nitrogen. All solvents were distilled from sodium
benzophenone ketyl just prior to use. Celite was purchased from
⇑⇑
E-mail addresses: s.duraj@csuohio.edu (S.A. Duraj), Aloysius.F.Hepp@nasa.gov
(A.F. Hepp), protasiewicz@case.edu (J.D. Protasiewicz), dequeant@hendrix.edu
(M. Dequeant).
0020-1693/$ - see front matter Published by Elsevier B.V.
doi:10.1016/j.ica.2010.08.026

S.A. Duraj et al. / Inorganica Chimica Acta 365 (2011) 54–60
55
ACROS and heated under vacuum for 24 h prior to use. All glass-
ware used was flame-dried and stored in an oven prior to use. Solu-
tions were transferred via stainless steel cannulae and/or syringes.
Gallium (II) chloride (99.999%) and indium (I) chloride (99.995%)
(both from Alfa Aesar) were purchased in argon-filled ampoules
and transferred in an inert atmosphere glove box. Benzoyl peroxide
((C6H5CO2)2 – Aldrich) was deaerated under vacuum at room tem-
perature prior to use.
ered on the filtrate via cannula. Colorless single crystals, suitable
for X-ray diffraction studies were isolated from the resulting fil-
trate after standing for 3 weeks at room temperature.
2.4. X-ray crystallographic study of 1 and 2
X-ray intensity data from previously described single crystals
were measured at 300 K on a Bruker SMART1000 CCD-based
X-ray diffractometer system using Mo K
used for data collection were cemented to a quartz fiber with
epoxy glue. Data were measured using scans of 0.3° per frame
a (k = 0.71073 Å). Crystals
2.2. Preparation of [GaCl2(4-Mepy)2(O2CPh)]ꢀ4-Mepy (1)
x
for 10 s for both 1 and 2 so that a hemisphere (1271 frames) was
collected with a final resolution of 0.75 Å. No decay was indicated
by the recollection of the first 50 frames at the end of data collec-
tion. The frames were integrated with the Bruker SAINTÓ software
package [11] using a narrow-frame integration algorithm, which
also corrects for the Lorentz and polarization effects. Absorption
corrections were applied using SADABS [12,13] supplied by Sheldrick
Gallium (II) chloride (0.302 g, 0.996 mmol) and a 2:1 excess of
benzoyl peroxide (0.480 g, 1.98 mmol) were added to a Schlenk
flask charged with a stirbar in a drybox. The flask was sealed with
a septum, removed from the drybox, and taken to a fume hood
where the flask was placed under nitrogen. 4-methylpyridine
(10 mL) was slowly added via cannula with rapid stirring. The solu-
tion immediately turned a deep crimson red color and the solution
was allowed to stir at room temperature for 48 h. During the
course of the reaction, the solution gradually changed from crim-
son red to orange in color. The reaction mixture was then filtered
through a pad of Celite. An equal amount of hexanes was layered
on the filtrate via cannula. Colorless single crystals, suitable for
X-ray diffraction studies were observed at the solvent interface
after standing for 72 h at room temperature.
[14]. Structures were solved and refined using the Bruker SHELXTL
Ó
ꢀ
(version 5.1) software package [14,15] in space groups of P1 (1)
and P21/n (2). All non-hydrogen atoms were derived from the di-
rect method solution. With all non-hydrogen atoms being aniso-
tropic and hydrogen atoms being isotropic, the structure was
refined to convergence by least squares method on F2, SHELXL-97,
incorporated in SHELXTL.PC V 5.03 [14]. Crystallographic data are gi-
ven in Table 1, selected bond lengths and angles are given in
Table 2.
2.3. Preparation of [InCl(4-Mepy)2(O2CPh)2]ꢀ4-Mepy (2)
Indium (I) chloride (0.150 g, 0.998 mmol) and benzoyl peroxide
(0.240 g, 0.998 mmol) were added to a Schlenk flask charged with a
stirbar in a drybox. The flask was sealed with a septum, removed
from the drybox and taken to a fume hood where the reaction flask
was placed under nitrogen. 4-Methylpyridine (10 mL) was slowly
added via cannula with rapid stirring, and a cloudy solution was
evident. The solution was allowed to stir for 7 days at room tem-
perature. The reaction mixture was filtered through a pad of Celite
to yield a colorless solution. An equal amount of hexanes was lay-
3. Results and discussion
3.1. Synthesis of compounds 1 and 2
The synthesis of both compound 1 and 2 can be simply de-
scribed as oxidative addition, see (1) and (2), respectively, below,
Table 2
Select bond distance (Å) and angles (°) for compounds 1 and 2.
Ga(1)–O(1)
Ga(1)–O(2)
2.099(2)
2.102(3)
In(1)–O(1)
In(1)–O(2)
In(1)–O(3)
In(1)–O(4)
2.274(3)
2.292(4)
2.212(3)
2.417(4)
Table 1
Summary of X-ray diffraction data.
Ga(1)–N(1)
Ga(1)–N(2)
Ga(1)–Cl(1)
Ga(1)–Cl(2)
O(1)–C(1)
2.099(3)
In(1)–N(1)
In(1)–N(2)
In(1)–Cl(2)
O(1)–C(13)
O(2)–C(13)
O(3)–C(20)
O(4)–C(20)
2.312(4)
2.286(4)
2.4132(15)
1.261(6)
1.259(6)
Compound
1
2
2.111(3)
2.2455(11)
2.2365(11)
1.288(4)
1.271(4)
Empirical formula
Molecular weight
Crystal system
Space group
a (Å)
C
25H26Cl2GaN3O2
C32H31ClInN3O4
671.87
541.11
triclinic
P1 (No. 2)
monoclinic
P21/n (No. 14)
13.1565 (13)
8.2116 (8)
28.796 (3)
90
94.460 (2)
90
3101.6 (5)
4
ꢀ
O(2)–C(1)
1.248(6)
1.249(6)
10.5987 (13)
11.3705 (15)
12.6660 (17)
104.525 (2)
101.976 (3)
111.981 (2)
1290.7 (3)
2
b (Å)
c (Å)
O(1)–Ga(1)–N(1)
O(1)–Ga(1)–O(2)
N(1)–Ga(1)–O(2)
O(1)–Ga(1)–N(2)
N(1)–Ga(1)–N(2)
O(2)–Ga(1)–N(2)
O(1)–Ga(1)–Cl(2)
N(1)–Ga(1)–Cl(2)
O(2)–Ga(1)–Cl(2)
N(2)–Ga(1)–Cl(2)
O(1)–Ga(1)–Cl(1)
N(1)–Ga(1)–Cl(1)
O(2)–Ga(1)–Cl(1)
N(2)–Ga(1)–Cl(1)
Cl(2)–Ga(1)–Cl(1)
O(2)–C(1)–O(1)
85.47(10)
62.83(10)
87.21(11)
86.64(11)
171.04(12)
85.43(11)
159.73(8)
93.01(9)
96.92(8)
92.92(10)
95.30(8)
92.62(10)
158.09(8)
92.32(10)
104.96(4)
117.6(4)
O(3)–In(1)–O(1)
O(3)–In(1)–N(2)
O(1)–In(1)–N(2)
O(3)–In(1)–O(2)
O(1)–In(1)–O(2)
N(2)–In(1)–O(2)
O(3)–In(1)–N(1)
O(1)–In(1)–N(1)
N(2)–In(1)–N(1)
O(2)–In(1)–N(1)
O(3)–In(1)–Cl(2)
O(1)–In(1)–Cl(2)
N(2)–In(1)–Cl(2)
O(2)–In(1)–Cl(2)
N(1)–In(1)–Cl(2)
O(3)–In(1)–O(4)
O(1)–In(1)–O(4)
N(2)–In(1)–O(4)
O(2)–In(1)–O(4)
N(1)–In(1)–O(4)
Cl(2)–In(1)–O(4)
O(2)–C(13)–O(1)
O(4)–C(20)–O(3)
162.40(15)
82.98(14)
83.94(14)
134.10(14)
56.99(12)
140.78(14)
86.83(14)
81.50(14)
90.28(15)
81.33(14)
97.07(11)
95.43(11)
93.44(11)
93.60(10)
174.91(10)
55.57(13)
135.57(13)
138.45(14)
79.23(13)
85.11(14)
94.37(10)
119.6(5)
a
(°)
(b) (°)
c
(°)
V (Å3)
Z
Dcalc (g cmꢁ3
)
1.392
1.30
556
1.439
0.89
1368
l
(mmꢁ1
)
F
Crystal size (mm)
h range for collection (°)
No. collected
0.38 ꢂ 0.23 ꢂ 0.09 0.31 ꢂ 0.14 ꢂ 0.08
2.2–22.3
6882
2.5–22.2
15 267
No. ind. (Rint
Tmax, Tmin
)
4505 (0.029)
1.000, 0.537
0.044
5462 (0.054)
1.000, 0.580
0.053
R [F2 > 2
r
(F2)]
wR(F2)
0.084a
0.119b
Largest difference in peak and hole 0.48, ꢁ0.41
1.17, ꢁ0.47
(e Åꢁ3
)
Goodness-of-fit (GOF) on F2
1.000
753 437
0.999
753 438
CCDC deposit no.
2
w ¼ 1=½r2ðFo2Þ þ ð0:0202PÞ ꢃ; whereP ¼ ðFo2 þ 2F2c Þ=3.
a
120.2(5)
2
w ¼ 1=½r2ðFo2Þ þ ð0:0584PÞ ꢃ; whereP ¼ ðFo2 þ 2F2c Þ=3.
b

56
S.A. Duraj et al. / Inorganica Chimica Acta 365 (2011) 54–60
with the cleavage of the peroxide bond and subsequent electron
transfer producing benzoate ligands and oxidizing the In and Ga
centers to produce trivalent metal complexes.
coordination of metal carboxylates can be found in a classic mono-
graph [18].
The angle formed by the chelating benzoate in 1, O1–Ga–O2, is
62.83(10)°, andissignificantlylargerthantheaverageangleforcom-
pound 2 of 56.28(13)° but is comparable to an average angle of
62.6(1)° for three structurally-characterized chelating carboxylates
previously reported [19–21]; a more thorough consideration of in-
dium carboxylate-chelate bonding angles is given below. The previ-
ously reported chelating carboxylates include a four-coordinate
doubly-chelating dicarboxylate organometallic complex [19] and
two compounds stabilized by chelating hetrocyclic ligands, one with
(pyrazolyl)borate [20] and the other with benzoxazole [21].
Previously, we prepared a trimeric basic carboxylate (com-
pound 5) with syn–syn bridging benzoates [18] obtained through
a similar reaction involving sodium benzoate instead of benzoyl
peroxide [9]; see reaction (3). The source of the central oxygen
atom is likely water from the sodium benzoate.
Ga2Cl4 þ H5C6CðOÞO-OCðOÞC6H5
! 2GaCl2ð4-MepyÞ2ðO2CC6H5Þ
ð1Þ
ð2Þ
InCl þ H5C6CðOÞO-OCðOÞC6H5 ! InClð4-MepyÞ2ðO2CC6H5Þ2
The starting material for reaction (1) is actually more accurately
described as a Ga(I)Ga(III) species: Ga+[GaCl4]ꢁ. The reaction most
likely proceeds through an intermediate ethane-like formally
Ga(II) complex, Ga2Cl4(c-pic)2 (3). An unsuccessful attempt to pro-
duce a gallium basic carboxylate [9], resulted in the isolation and
structural characterization of the Ga(II) dimer [7]. In the same
study, an attempt to produce a mixed-metal Ga–Ni species re-
sulted in the isolation of the solvated mixed-oxidation state salt,
[GaCl2(c
-pic)4]+[GaCl4]ꢁ (4) [7]. The isolation and structural char-
2Ga2Cl4 þ 6NaCO2C6H5
acterization of 1 brings to five the number of related structures
from the reaction of benzoate-containing reagents and Ga2Cl4 in
! ½Ga3ð
l
3-OÞðl
-O2CC6H5Þ6ð4-MepyÞ3ꢃ½GaCl4ꢃ
ð3Þ
c-picoline, reinforcing the utility of Ga2Cl4 as an extremely versa-
The Ga–O bond distances of the bridging benzoates in 5 ranged
from 1.959 (5) to 2.006 (9) Å, with an average distance of
1.985(6) Å [9]. This is shorter than the average Ga–O bond distance
for the chelating benzoate found in 1 of 2.101(3) Å. These intermo-
lecular distances are comparable to those found in the three che-
lating carboxylates [19–21] that range from 2.042(2) to
2.127(3) Å, with the four-coordinate organometallic dimeric com-
pound having the shortest average bond length (2.049(2) Å) [19].
Of the four structurally-characterized chelating gallium carboxyl-
ates, only the (pyrazolyl)borate compound had asymmetrical coor-
tile entry into Ga coordination chemistry.
The oxidizing potential of benzoyl peroxide is amply demon-
strated in reaction (2). We had previously exploited this chemistry
when we prepared the first example of an eight-coordinate indium
benzoate, In(O2CC6H5)3(4-Mepy)2, by oxidation of indium metal
powder with a 3:2 excess of benzoyl peroxide in c-picoline [10].
The use of the indium (I) chloride starting material provides a site
for further chemistry to be utilized for preparation of mixed-metal
complexes or clusters [5,6].
dination of the carboxylate moiety (DGa–O = 0.079(3) Å) [20].
3.2. Structural features of compound 1
This can be contrasted to the surprisingly complex structure of
methylgallium diacetate, H3C–Ga(O2CCH3)2 [22]. This structure in-
cludes dative, bridging, and mono-dentate acetate coordination
resulting in Ga–O bond distances ranging from 1.873(3) to
2.219(3) Å. As noted previously [17], several reports of related orga-
nometallic indium compounds, dimethyl [23] and diethyl [24] ace-
tate include simultaneously bridging and chelating acetate
coordination. A much more straightforward Ga acetate mono-den-
tate interaction is found in a neutral acetato tetraphenylporphyrin
complex (Ga(OAc)(tpp) with Ga–O bond length of 1.874(4) Å [25],
very similar to the mono-dentate Ga–O bond length of 1.873(3) Å
[22].
A key structural feature of 1 is the chelating benzoate ligand;
compound 1 (shown in Fig. 1) is the first example of such a struc-
turally characterized gallium benzoate. A recent review of mono-
nuclear six-coordinated Ga compounds did not include a single
example of a homoleptic, tris-bidentate or chelating-carboxylate
structure [16]. A structural and theoretical study by Barron et al.
demonstrated that chelated-group 13 carboxylate structures (par-
ticularly Al) are not energetically favorable, relative to bridged on
mono-dentate coordination [17]. A very thorough discussion of
A further example of a lengthened M–O bond for a chelating
versus bridging carboxylate group is demonstrated by a series of
silver complexes (AgO2CR)2 where a dimer (R = C(Me)@C(Me)H)
with bridging carboxylates is stabilized as a monomer by the addi-
tion of triphenylphosphine ligands: [AgO2CR(PPh3)2] (R = CH2CN,
CH2CH2@C(H)CH2, and C(Me)@C(Me)H) with a subsequent average
increase of 0.235(3) Å for a chelated versus bridging Ag–O bond
length [26].
The carboxylate moiety in 1 is fairly symmetrical with an aver-
age C–O bond length of 1.280(4) Å. This is comparable to an aver-
age C–O bond length of 1.274(5) Å for the bridging carboxylates of
methylgalliumdiacetate [22], 1.25(2) Å for the bridging benzoates
of compound 5 [9], 1.255(2) Å for the chelating acetate of the benz-
oxazole [21], and 1.254(6) Å for compound 2 of this study. A recent
study of solvent-free synthesis of a bismuth carboxylate reported a
C–O bond range of 1.249(2)–1.301(2) Å for dimeric substituted
benzoates with multiple coordination modes [27].
The 2.105(3) Å average Ga–N bond length for the ligated pico-
lines is comparable to 2.105(5) Å for 4 [7] and 2.085(9) Å for 5
[9]. This is slightly longer than Ga–N bond length of 2.058(4) Å
for the (pyrazolyl)borate [20] and 2.034(2) Å for the benzoxazole
[21] compounds. It is longer than the Ga–N (picoline) bond length
Fig. 1. ORTEP diagram and atomic labeling scheme of first coordination sphere of
[GaCl2(O2CPh)(4-Mepy)2]ꢀ4-Mepy (1) (hydrogen atoms and the co-crystallized
picoline not shown for clarity).

S.A. Duraj et al. / Inorganica Chimica Acta 365 (2011) 54–60
57
of 2.005(6) Å of the Ga(II) complex, 3 [7]. Finally, the Ga–Cl average
bond length of 2.2410(11) Å is comparable to Ga–Cl bond lengths
lengths of 2.247(3) Å and 2.390(3) Å [30]. Another seven-coordi-
nate carboxylate with a terpyridine and two azide ligands had a
slightly less asymmetric carboxylate with In–O bond lengths of
2.274(2) Å and 2.354(2) Å [4]. A similar degree of asymmetry is ob-
served for a series of trinuclear and tetranuclear metal cluster
butyrates containing In, and Co or Ni atoms [31].
determined for compounds
3 (2.195(2) Å) and 4 (cation –
2.320(2) Å; anion – 2.157(3) Å) [7], 5 (anion – 2.126(12) Å) [9],
and 2.2827(16) Å averaged for [GaCl2(c-pic)2(S2CNR2)] (R = Me
[8], Et [7]).
The N1–Ga–N2 angle is 171.04(12)°; as expected the picoline
rings tilt towards the chelated benzoate. The three aromatic rings
are roughly parallel; giving the complex a semi-paddlewheel
appearance, more typically associated with bridging carboxylate
structures [9,28]. The narrow angle of the benzoate results in a lar-
ger Cl2–Ga–Cl1 angle of 104.96(4)°. The O2–C1–O1 angle of
117.6(4)° is slightly smaller than the 120° expected for an sp2
hybridized RCOꢁ2 moiety; this is likely due to the steric hindrance
of the chelated benzoate bonding to a Ga(III) center. For the less-
constrained six bridging benzoates in complex 5, the COꢁ2 angle
ranged from 123° to 128° [9]. In CH3Ga(OAc)2, the average bridging
COꢁ2 bonding angle was 120.3(3)°; the mono-dentate acetate had a
122.0(5)° COꢁ2 bonding angle [19]; and the mono-dentate acetate
of (Ga(OAc)(tpp) had a 122.9(5)° COꢁ2 bonding angle [22]. The other
chelating carboxylates [19,21] had more narrow O–C–O angles of
approximately 118°, expected for the wider O–Ga–O chelate.
An unsymmetrical acetate is found in a (TPP)In(O2CCH3)
(TPP = tetraphenylporphinato) complex with In–O bond lengths
of 2.215(4) Å and 2.322(4) Å [33]. A pair of related tetra-arylpor-
phyrinato indium carboxylates (TRP)In(O2CCH3) (R = py, 4-pyridyl;
mp, 4-methoxyphenyl) resulted in nearly symmetrical (R = py,
In–O range from 2.24(1) to 2.34(1) Å) and unsymmetrical (R =
mp, In–O = 2.185(6) Å and 2.412(6) Å) carboxylates [34]. An asym-
metrically-bound acetate is also found in an (OEP)In(O2CCH3)
(OEP = octaethylporphyrinato) complex with In–O bond lengths
of 2.60(2) Å and 2.14(1) Å [35]. Two related ylide-containing halide
compounds had In–O coordination that varied from slightly
(<0.1 Å) to moderately asymmetric (>0.25 Å) [29]. Finally, the most
asymmetric bidentate chelate is found in a dimeric
neutral seven-coordinate complex [L2In2(CH3CO2)4(
(L = 1,4,7-triazacyclononane) with each In(III) bound to a mono-
dentate and chelating acetate group; significantly different average
In–O bond lengths in the chelating groups of 2.142(5) Å and
2.863(7) Å [36] are present.
l
-oxo bridged
l
-O)]ꢀ2NaClO4
3.3. Structural features of compound 2
The In–Cl bond length in 2 is 2.4132(15) Å and similar to the re-
lated octahedral chloro–benzoato compound, 2.391(2) Å [32]. It is
also comparable to the cis-In–Cl bond length in mer-InCl3(4-Etpy)3
of 2.41 Å but shorter than the trans-In–Cl bond length of 2.46 Å
[38]. The cis-(2.471(1) Å) and trans-(2.476(2) Å) In–Cl bond lengths
in mer-InCl3(py)3ꢀpy [39] are practically equal within experimental
error. The ylide compound with chloride ligands has an In–Cl bond
length that ranges from 2.26(1) to 2.49(1) Å [29].
The In–N bond lengths are unremarkable but slightly unsym-
metrical; there is a slight lengthening of the In–N bond trans to
the Cl (2.312(4) Å versus 2.286(4) Å in the plane). The two In–N
bond lengths for the trans pyridines in the related octahedral com-
pound are (2.250(5) and 2.300(6) Å [32]. This is typically not ob-
served in the family of mer-InX3(Rpy)3 (R = H, X = I, Br; R = Et;
X = Cl; R = Me, and X = I) complexes where the average In–N bond
length is 2.31 Å [38–41]. There is some asymmetry in mer-In-
Cl3(py)3ꢀpy where there is a some lengthening of the In–N bond
trans to a Cl (2.377(21) Å) versus 2.302(7) Å (for trans pyridines).
The In–N bond lengths were similar for the two seven-coordinate
compounds with terpyridine (2.292(2)–2.341(2) Å) and azide
(2.203(3) Å) ligands [4] and the triazacyclononane chelate
(2.271(5)–2.324(5) Å) [36]. The tetradentate bis(aminoethanethiol)
octahedral compound (2.298(3) and 2.367(3) Å) was also similar
[30]. The In–N bond lengths for the porphyrin compounds were
shorter and ranged from 2.16 to 2.18 Å [33–35].
As has been noted previously, bidentate chelating In (III) car-
boxylate bonding has not frequently been observed [17,18]. Com-
pound 2 (shown in Fig. 2) had In–O bond distances ranging from
2.212(3) Å to 2.417(4) Å with one symmetrical benzoate, like com-
plex 1, with an average In–O distance of 2.283(4) Å, the other
unsymmetrical with a 0.205 Å
DIn–O bond length. A review of
In–O bond lengths in chelating In carboxylates exhibits a range
from 2.142(5) to 2.875(8) Å from (nearly) symmetrical to asym-
metrical [4,10,29–36]. In our previously reported eight-coordinate
In benzoate complex, one benzoate was symmetrical with an In–O
bond distance of 2.286(5) Å, and the other two were asymmetrical
with distances of 2.225(6) Å and 2.413(5) Å [10]. Asymmetrical
bonding of chelating-carboxylate groups to an In(III) center has
been observed for other eight-coordinate carboxylates: In(O2C-
Me)3L (L = phen,
DIn–O = 0.157(7) Å and 0.198(7) Å; L = bipy,
D
In–O = 0.172(6) Å) [37]. A related but simpler, cis-dichloro chelat-
ing–benzoato octahedral complex with two trans pyridine ligands
had similar, nearly symmetrical In–O bond lengths of 2.246(4) Å
and 2.280(4) Å [32]. Another octahedral benzoate compound with
a tetradentate N2S2 bis(aminoethanethiol) chelate had a signifi-
cantly more asymmetric benzoate coordination with In–O bond
The Cl(2)–In(1)–N(1) bond angle is 174.91(10)°, the apical Cl
atom is inclined away from the other five coordinated atoms in
the InO4N plane at angles from 93.44(11)° (N(2)–In(1)–Cl(2)) to
97.07(11)° (O(3)–In(1)–Cl(2)). The two In–N bonds are nearly per-
pendicular forming a (N(2)–In(1)–N(1) angle of 90.28(15)°. The
four In–O bonds are bent towards the apical N(1) forming
O–In(1)–N(1) angles that vary from an average of 81.42(14)° for
In–O(1) and In–O(2) to 86.83(14)° for In–O(3). Steric factors can
be invoked to explain this structural feature. As with the gallium
complex above, the two chelating benzoates and the apical picoline
are roughly parallel and form a semi-paddlewheel structure.
The benzoate chelates contain smaller angles of 56.99(12)° and
55.57(13)° for (O(1)–In(1)–O(2)) and (O(3)–In(1)–O(4)), respec-
tively, in the indium complex (2) than the gallium complexes (1)
and [19–21]. The individual nearest-neighbor atoms in the InO4N
plane form five angles that add up to approximately 359°; the
non-chelated atoms form average angles of 82°. The larger size of
Fig. 2. ORTEP diagram and atomic labeling scheme of first coordination sphere of
[InCl(O2CPh)2(4-Mepy)2]ꢀ(4-Mepy) (2) (hydrogen atoms and the co-crystallized
picoline not shown for clarity).

58
S.A. Duraj et al. / Inorganica Chimica Acta 365 (2011) 54–60
the In(III) center results in less steric strain for the chelates and a
nearly symmetrical RCOꢁ2 average bond angle of 119.9(5)°. The clo-
sely-related eight-coordinate tris-benzoato bis-picoline indium (III)
complex had quite similar O–In–O angles of 56.5(3)° and 55.9(2)°
[10]. The eight-coordinate complex also had a nearly symmetrical
RCOꢁ2 average bond angle of 119.5(8)°. The octahedral benzoato
complex, isostructural with compound 1, had a similar RCOꢁ2 angle
(118.9(6)°), with a wider O–In–O angle of 57.5(1)° [32], similar to
the larger of the two angles of compound 2, but significantly less
than the O–Ga–O angle of 62.83(10)° of 1. With a few exceptions,
the O–In–O benzoate angle ranged from a low of 55.57(13) to
56.99(12) for many of the six, seven, or eight-coordinate carboxyl-
ates. The six-coordinate porphyrin acetate compounds had slightly
smaller average O–In–O (54.6(3)°) and RCOꢁ2 (118.5(4)°) angles
similar fashion without undue steric hindrance. Two other macro-
cycle-stabilized structures of seven-coordinate In(III) to note are
two related pentagonal bipyramid complexes, [InCl3(L0)(MeOH)]
and [InCl(g2-C2O4)(L0)(OH2)] (L0 = 2,6-bis(acetyloxime)-pyridine)
[42,43]. A final observation to make is that compounds 1 and 2
adopt a roughly pentagonal bipyramidal structure. Compound 1,
and the isostructural In complex [32], can be described as semi-
paddlewheel with three roughly parallel aromatic rings. The
semi-paddlewheel motif of compound 2 has a more propeller-like
appearance with a bowl-shaped triple aromatic-ring coordination
plane.
3.4. Comparison of compounds 1 and 2 with similar molecular
complexes of other metals
[33,34]. The dimeric
l-oxo bridged neutral seven-coordinate com-
plex [L2In2(CH3CO2)4(
l
-O)]ꢀ2NaClO4 (L = 1,4,7-triazacyclononane)
It is interesting to include a survey of other related chelating-
carboxylate complexes of other metals similar in size to In(III)
ions. Table 3 includes compounds 1 and 2, other related indium
and gallium structures, and other related structures of mostly
main group complexes with higher coordination numbers and
similar ionic radii (0.8–0.92 Å) to In(III) complexes. A key feature
of nearly every compound in Table 3 is complexation with aro-
matic rings for electronic and steric stability. These chelating
compounds rely on a variety of motifs for supporting the chelat-
ing structure: macrocyclic and/or multi-dentate ligands [4,10,19–
21,26,30,33–37], carboxylates with unsaturated bonds or pendant
groups for structural or electronic stabilization [4,26,27,29,44,45],
with asymmetric chelating acetate groups had a significantly con-
strained O–In–O bond angle of 48.9(2)°. The smaller O–In–O angle
with the porphyrin-containing structures is expected as the macro-
cycles impose steric strain. The ylide compounds [29] and the mul-
ti-nuclear cluster compounds [31] had larger bond angles ranging
from around 57° to 59°.
As noted above and compiled in Table 3, there are nearly 15
chelated In(III) carboxylate or related molecular structures that
are five [29] six [29–36], seven (2 and [4,31,36]), and eight
[10,37] coordinate. Many of these chelating-carboxylate structures
consist of a macrocyclic or large heterocyclic chelating ligand
[4,30,33–36] or multi-nuclear cluster structure [31]. It is reason-
able to assert that the aromatic benzoato chelate and pyridine-like
ligands [10,32], electron-withdrawing halide ligands (2, [29,32])
and solvent of crystallization (2, [10] stabilize the structures in a
or electronic-withdrawing ligands such as halides and CF3COꢁ (1,
2
2, [29,32,37,38,46]). Interestingly, several structures contained
multiple modes of coordination to identical carboxylate groups
[27,31].
Table 3
Selected bond distances (Å) and angles (°) for molecular complexes with chelating carboxylates of Ga, In and other metals with similar ionic radii.
Compound
CN
4
dM–O (Å)
O–M–O (°)
O–C–O (°)
Reference
[26]
[Ag(O2CR)(P(C6H5)3)2]
2.401(3)–2.495(2)
52.61(7)–53.86(6)
122.6(2)–126.4(3)
R = CH2CN, (CH2)2CH@CH2, or C(Me)@C(H)Me
[{Ga((Me3Si)2CH)2}2(ndc)]ꢀ2MeC5H9
H2ndc = 1,6-naphthalenedicarboxylic acid
4
2.042(2), 2.056(2)
64.53(8)
118.0(3)
[19]
[InCl3(g
2-O2CC{P(C6H5)3}2]
2-O2CC{P(C6H5)3}2+][Iꢁ]
5
6
6
2.181(6), 2.304(6)
2.168(5)–2.437(5)
2.048(3), 2.127(3)
58.7(2)
57.0(2), 58.6(2)
62.3(1)
118.6(8)
117.9(7), 120.1(7)
[29]
[29]
[20]
[InI2(g
[H2B(pz)2]2Ga(O2CCH3)
pz = {N2(CH)3}
[Ga(hbo)2(O2CCH3)]
6
2.117(2)
61.1(1)
118.2(4)
[21]
Hhbo = 2-(20-hydroxyphenyl)-2-benzoxazole
[GaCl2(O2CPh)(4-Mepy)2]ꢀ4-Mepy
[In (BAT-TM)(O2CC6H5)]
6
6
2.099(2), 2.102(3)
2.247(3), 2.390(3)
62.83(10)
56.3(1)
117.6(4)
120.7(4)
This work
[30]
BAT-TM = N2S2 tetradentate ligand
[In2M2(OH)2(O2CtBu)8L2]a
(M,L = Co, MeCN; M,L = Ni, MeCN/HO2CtBu)
[InCl2(O2CPh)(py)2]
6
2.2091(13)–2.275(8)
56.9(3)–59.1(3)
117.1(10)–120.6(10)
[31]
6
6
2.246(4), 2.280(4)
2.215(4), 2.322(4)
57.5(1)
54.4(2)
118.9(6)
118.5(4)
[32]
[33]
[In(TPP)(O2CCH3)]
TPP = tetraphenylporphyrin
[In(TRP)(O2CCH3)]
6
2.185(6)–2.412(6)
54.4(4), 55.0(2)
115(2)–121.1(7)
[34]
R = 4-pyridyl or 4-methoxyphenyl
[InCl(O2CPh)2(4-Mepy)2]ꢀ(4-Mepy)
7
7
2.212(3)–2.417(4)
2.142(5)–2.875(8)
55.57(13), 56.99(12)
48.9(2)
119.6(5), 120.2(5)
This work
[36]
[L2In2(O2CCH3)4(
l-O)]ꢀ2NaClO4
L = 1,4,7-triazacyclononane
[In2Ni(OH)(O2CtBu)7(HO2CtBu)x]a
(x = 1,2)
[(terpy)In(N3)2(O2C(CH2)2CH2OH)]
terpy = terpyridine
7
7
2.208(6)–2.249(6)
2.274(2), 2.354(2)
58.4(2), 58.5(2)
56.31(7)
118.6(8), 119.0(8)
120.2(2)
[31]
[4]
[SbCl(C6H5)2(O2C(2-Me)C6H4)2]
[Cd(O2C(3,4-OH)C6H3)2(H2O)3]
[MoBr(O2CCF3)(CO)2(P(C6H5)3)2]
[Bi(O2C(2-EtO)C6H4)3]2
7
7
7
8
8
8
2.213(3)–2.296(3)
2.304(4)–2.513(4)
2.304(9), 2.320(9)
2.207(1), 2.532(1)
2.225(6)–2.413(5)
2.221(3)–2.422(6)
57.46(11), 57.58(11)
54.0(1), 54.3(1)
56.5(3)
55.06(4)
55.9(2), 56.5(3)
54.4(2)–56.5(3)
118.8(6), 120.5(7)
117.3(4), 117.6(4),
126.0(1)
120.2(2)
119(1), 120.0(7)
[44]
[45]
[46]
[27]
[10]
[37]
[In(O2CPh)3(4-Mepy)2]ꢀ4H2O
[In(O2CCH3)3L]
L = 2,20-bipy or 1,10-phen
a
Data for In coordination environment only.

S.A. Duraj et al. / Inorganica Chimica Acta 365 (2011) 54–60
59
The structure most similar to compound 1 is the analogous six-
coordinate In benzoate complex [32]. However, due to the larger
size of the In(III) ion, this structure does not contain as much strain
around the chelating benzoate. The seven-coordinate Sb(V) orga-
nometallic compound is most similar in structure to 2 [44]. The
other structurally-characterized seven-coordinate In(III) carboxyl-
ate environments are sterically constrained by tri-dentate chelat-
ing ligands [4,36] or a multi-nuclear cluster environment [31].
Apparently, electron-withdrawing chloride ligand(s) and the
inherent stability of the semi-paddlewheel structure of the aro-
matic rings enables the use of simpler ligands via a straightforward
synthesis used to produce compounds 1 and 2 and the related octa-
hedral indium complex [27].
benzoates from this study (compound 2) and Ref. [10], respectively.
Table 4 includes five basic types of In polymer constructs: seven-
coordinate In polymers from di- [47–49], tri- [50–53] and tetracarb-
oxylates [54,55] and eight-coordinate In polymers from di- [56–59]
and tricarboxylates [60,61], several of which are chiral [51,58,59].
The most notable observation to make when viewing the rele-
vant bond distances and angles of the polymer materials as com-
pared to the respective molecular species is the striking
similarity of the In coordination environments; this is expected
due to a lack of steric strain around In atoms from the flexible poly-
mer coordination environment, it is this flexibility that gives rise to
a variety of intriguing 2D and 3D structural features. The In–O
bond distances and O–In–O and O–C–O carboxylate angles of the
polymer materials are quite similar to the molecular benzoates.
3.5. Comparison of molecular indium benzoates with indium
coordination polymers
4. Conclusion
While a slight departure from the major thrust of this paper, it is
useful to include a brief survey of recently reported chelating-
carboxylate indium coordination polymers [47–61], part of a
recent wave of a literature describing intriguing new hybrid
organic–inorganic materials with many potential applications.
Table 4 includes numerous examples of indium carboxylate poly-
mer framework materials and seven- and eight-coordinate indium
In summary, we have prepared two new simple chelating
benzoate complexes of gallium and indium by straightforward
oxidation of the Ga(II) and In(I) chlorides by benzoyl peroxide in
4-methylpyridine at room temperature. The six-coordinate gallium
complex, which also includes two chloride and two c-picoline li-
gands, is the first example of a structurally-characterized chelating
gallium benzoate. It is isostructural with a previously characterized
Table 4
Selected bond distances (Å) and angles (°) for indium coordination polymers and molecular benzoates.
Compound
CN
dM–O (Å)
O–M–O (°)
O–C–O (°)
Reference
[InCl(O2CPh)2(4-Mepy)2]ꢀ(4-Mepy)
[In(OH)(ndc)2(H2O)]n
7
7
2.212(3)–2.417(4)
2.247(2)–2.3458(18)
55.57 (13), 56.99(12)
56.39(12), 58.00(8)
119.6(5), 120.2(5)
119.1(2), 119.5(3)
This work
[47]
H2ndc = 2,6- or 2,7-naphthalenedicarboxylic acid
[In2OH)2(pdc)2(H2O)]n
H2pdc = 3,5-pyridinedicarboxylic acid
[In(OH)(tca)(H2O)]n
7
7
7
2.255(2), 2.311(2)
2.209(2)–2.391(2)
2.208(4)–2.360(5)
57.53(5)
121.36(18)
[48]
[49]
[50]
56.86(7), 57.53(7)
54.4(4), 55.0(2)
119.8(2), 120.2(2)
120.1(6), 120.3(6)
H2tca = thiophene-2,5-dicarboxylic acid
{[Hbipy+][In(Hbtc)2(bipy)ꢁ]ꢀ0.5H2O}n
H3btc = benzenetricarboxylic acid
bipy = 4,40-bipyridine
{[Hpy+]2[In2(btc)2(
l
-OH)22ꢁ]}n
7
7
2.140(11)–2.569(10)
2.170(4)–2.434(4)
54.8(3)–57.1(4)
119.5(13)–124.1(14)
119.4(5), 120.4(5)
[51]
[52]
H3btc = benzenetricarboxylic acid
py = pyridine
{[In2(btc)2(bipy)2]ꢀ4H2O}n
H3btc = benzenetricarboxylic acid
bipy = 2,20-bipyridine
56.06(13), 56.38(12)
{[In2(btc)2(H2O)2]ꢀ2H2O}n
H3btc = benzenetricarboxylic acid
[In2(btec)(bipy)2Cl2]n
7
7
2.575(2), 2.580(2)
2.176(8)–2.551(9)
56.75(11), 58.10(11)
54.7(2)–57.5(2)
119.4(4), 119.8(4)
118.8(7)–122.3(11)
[53]
[54,55]
H4btec = benzenetetracarboxylic acid
bipy = 2,20-bipyridine
[In(O2CPh)3(4-Mepy)2]ꢀ4H2O
{[H+][In(bdc)2ꢁ]}n
8
8
2.225(6)–2.413(5)
2.267(7), 2.283(7)
55.9(2), 56.5(3)
57.7(3)
119(1), 120.0(7)
120.8(9)
[10]
[56]
H2bdc = benzenedicarboxylic acid
È
É
[ ½MðH2OÞ63þꢃ½In3ð
l
2-pdcÞ63ꢁꢃ ꢀ 15H2O
8
2.236(4)–2.446(6)
54.9(2)–55.4(3)
120.3(5)–123.4(8)
[57]
n
H2pdc = 2,3-pyrazinedicarboxylic acid
M = In, Cr0.7In0.3, or Fe0.3In0.7
{[(Htmdp)+][InðpdcÞ2ꢁ]ꢀ(EtOH)(H2O)2}n
tmdp = 4,40-trimethylenedipiperidine
H2pdc = 2,5-pyridinedicarboxylic acid
{½NR4þꢃ½InðDL-camÞ2ꢁꢃꢀ(H2O)2}n
8
8
8
8
8
2.205(5), 2.588(5)
2.188(7)–2.407(8)
2.163(3)–2.481(3)
2.204(3)–2.551(4)
2.155(5)–2.409(5)
54.29(17)
122.5(7)
[58]
[59]
[60]
[61]
[62]
55.4(3)–57.3(3)
54.7(4)–58.2(4)
53.50(11)–57.22(10)
56.36(18)
119.0(10)–120.7(9)
117(2)–124.8(16)
120.1(4), 120.5(4)
120.3(6)
R = CH3; D- and L-camphorate
þ
NR4 = choline; D-camphorate
{{½NR4þꢃ½InðDL-camÞ2ꢁꢃꢀ(H2O)2}n
R = n-propyl; D- or DL-camphorate
NR4 = imidizolium; D-camphorate
[In(btc)1.5(bipy)]n
a
þ
H3btc = 1,4-benzenetricarboxylic acid
bipy = 2,20-bipyridine
{[H2tmdp2+]3[In6ðbtcÞ86ꢁ]ꢀ40H2O}n
tmdp = 4,40-trimethylene dipiperidine
H3btc = benzenetricarboxylic acid
a
Table entry also includes three more related structures (total of six) from same publication.

60
S.A. Duraj et al. / Inorganica Chimica Acta 365 (2011) 54–60
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bis-benzoate also includes one chloride and two -picoline ligands
c
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structural analogue to a seven-coordinate Sb(V) organometallic
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a
sabbatical at Case Western Reserve University. A.F. Hepp
acknowledges support from the NASA Glenn Research Center’s
Internal Research and Development Fund. S.A. Duraj, R.A. Wol-
oszynek, and J.D. Protasiewicz acknowledge support from the
Department of Chemistry, Case Western Reserve University. M.
Dequeant and T. Ren acknowledge support from the Department
of Chemistry at University of Miami Coral Gables, FL where the
structural data were collected and solved.
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CCDC 753437 and 753438 contains the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.ica.2010.08.026.
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