One-dimensional cobalt and zinc complexes involving in situ reaction of ethylenediamine and acetonitrile to form imidazoline ligand

Article abstract of DOI:10.1016/j.inoche.2005.10.007

The solvothermal treatment of cobalt nitrate (or zinc acetate), ethylenediamine and dicarboxylate in acetonitrile produced two one-dimensional coordination polymers [Co(mimz)₂(ox)]_n (1) and [Zn(mimz)₂(ip)]_n (2)

Full text of DOI:10.1016/j.inoche.2005.10.007

Inorganic Chemistry Communications 9 (2006) 57–59
www.elsevier.com/locate/inoche
One-dimensional cobalt and zinc complexes involving in situ reaction
of ethylenediamine and acetonitrile to form imidazoline ligand
*
Zheng-Ming Hao, Xian-Ming Zhang
School of Chemistry and Material Science, Shanxi Normal University, Gongyuan Street 1, Linfen, Shanxi 041004, China
Received 3 August 2005; accepted 9 October 2005
Available online 11 November 2005
Abstract
The solvothermal treatment of cobalt nitrate (or zinc acetate), ethylenediamine and dicarboxylate in acetonitrile produced two one-
dimensional coordination polymers [Co(mimz)2(ox)]n (1) and [Zn(mimz)2(ip)]n (2) (mimz = 2-methylimidazoline, ox = oxalate, ip = iso-
phthalate) which ligand involving in situ formation of imidazoline ligand by cycloaddition reaction of ethylenediamine and acetonitrile.
Ó 2005 Elsevier B.V. All rights reserved.
Keywords: Imidazoline; Ligand reaction
The imidazole ring and its derivatives are very useful
models to understand the coordination properties and the
reaction mechanisms of the biologically important systems
where these molecules are involved [1]. The role of the imid-
azole ring as metal binding site in metalloproteins is well
known, and then studies of new synthesis route for these
complexes are of interest [2–6]. Imidazoline, one cyclic ami-
dine or derivative of imidazole, has attracted some attention
in the field, and its formation traditionally depends on the
transformation of organonitriles such as addition of nucle-
ophiles [7] to the C„N triple bond. One of the main prob-
lems in nucleophilic addition reactions is the insufficient
electrophilic activation even in the presence of very strong
electron-accepting groups R at RC„N (R = Cl). These dif-
ficulties, however, can be overcome with the use of metal
ions [8,9], in some cases even metal ions of low valence func-
tioning strong activators toward nucleophilic attack. This
activation can result in enhancement of the rate of the addi-
tion commonly in the range from 106 to 1010 [10,11]. The
lanthanide(III) and Pt(II) catalytic nucleophilic additions
of diamines to organonitriles have been reported [12–14],
which provides an alternative synthetic route for cyclic ami-
dines. The catalytic nucleophilic additions of diamines to
organonitriles to form cyclic amidines by first-row transi-
tion metal ions such as Co(II) and Zn(II) ions have not been
documented so far. It is worth noting that the above men-
tioned synthetic route for cyclic amidines are based on tra-
ditional organic methods, e.g., refluxing [12–14].
On the other hand, in situ ligand synthesis is of great
interest in coordination chemistry and organic chemistry
due to effectiveness, simplicity and environmental friendli-
ness. Hydro(solvo)thermal method has been demonstrated
to be a very promising technique to prepare complexes with
novel structures and special properties, especially in grow-
ing crystals of complexes involving in situ ligand synthesis
because of its relatively critical reaction conditions [15].
Based on these considerations, we tried to develop M2+
(M = Co, Zn) complexes of 2-methylimidazoline by solvo-
thermal nucleophilic cyclic addition of ethylenediamine
(en) and acetonitrile. We report herein two new complexes
namely [Co(mimz)2(ox)]n (1) and [Zn(mimz)2(ip)]n (2)
(mimz = 2-methylimidazoline, ox = oxalate, ip = isophth-
alate) which show one-dimensional structures formed by
bridging of [M(mimz)2]2+ (M = Co, Zn) fragments via
dicarboxylates.
*
Reaction of cobalt nitrate, oxalic acid, en, and acento-
nitrile in molar ratio of 2:2:1:435 in a 15 ml Teflon-lined
Corresponding author. Tel./fax: +86 357 2051402.
E-mail address: zhangxm@dns.sxtu.edu.cn (X.-M. Zhang).
1387-7003/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2005.10.007

58
Z.-M. Hao, X.-M. Zhang / Inorganic Chemistry Communications 9 (2006) 57–59
stainless container at 150 °C for 72 h resulted in red block-
like crystals (45% yield based on en). Reaction of zinc ace-
tate, isophthalic acid, en, and acentonitrile in molar of
1:2:1:435 in a 15 ml Teflon-lined stainless container at
150 °C for 72 h resulted in colourless block-like crystals
(25% yield based on en). The pure complexes 1 and 2 were
obtained by mechanically picking single crystals with the
help of microscopy. IR and Elemental analysis confirmed
the formulas of 1 and 2.
than that 97.5(2)° in [Co(im)2(ox)], and three trans-L–
Co–L angles (164.42(15)°, 175.34(14)° and 175.34(14)°),
which are larger than those [163.51(15)°, 171.1(5)° and
169.2(5)°] in [Co(im)2(ox)]. The structure of 1 is one-
dimensional zig-zag polymeric structure formed by
[Co(mimz)2]2+ fragments bridged by oxalate in bis-chelate
mode. In contrast, the Zn(II) ion in 2 is tetrahedrally coor-
dinated to two oxygen atoms from two isophthalates with
˚
Zn–O bond lengths of 2.016(3) and 2.021(3) A, and two
As expected, X-ray crystallography reveals that ligand
2-methylimidazoline was in situ formed in 1 and 2. Com-
pound 1 has a one-dimensional structure similar to that
of [Co(im)2(ox)] (im = imidazole) [16]. As shown in
Fig. 1, the Co(II) ion in 1 is octahedrally coordinated to
four oxygen atoms from two oxalates and two nitrogen
atoms from two 2-methylimidazolines. The Co–O bond
nitrogen atoms from two imidazoline groups with Zn–N
bond lengths of 1.992(4) and 2.005(6) A. The N–Zn–N
˚
and O–Zn–O bond angles are 117.5(2)° and 94.74(14)°,
respectively. The N–Zn–O bond angles are in the range
of 105.77(2)–119.21(16)° [av. N–Zn–O 110.35°]. 2 shows
also one-dimensional structure consisting of [Zn(mimz)2]2+
fragments and dicarboxylates. However, different from the
coordination mode of oxalate, isophthalate in 2 is coordi-
nated in bis-monodentate mode. Besides, we attempted to
prepare the other first-row transition metal complexes of
mimz but we did not get single crystals under the similar
synthetic conditions. (see Fig. 2).
˚
lengths [2.119(3) and 2.137(3) A] are close to those [av.
˚
2.120(3) A] in [Co(im)2(ox)] , and the Co–N bond lengths
˚
˚
[2.094(4) A] are close to those [2.112(2) and 2.031(1) A] in
[Co(im)2(ox)]. Two mimz ligands are located in cis- posi-
tions with N(1a)–Co(1)–N(1) 89.2(2)°, which is smaller
The formation of imidazoline by lanthanide(III) cata-
lytic nucleophilic additions of diamines to organonitriles
has been reported, and authors suggested that the Ln3+
ions activate the nitriles through a predominantly electro-
static, ion–dipole interaction [12]. For Co(II) and Zn(II)
ions which have lower charge, it seems that there is less
possibility to activate the nitriles through electrostatic
ion–dipole interaction. Considering that the acetonitrile
could function as weak N-donor ligand to electrophilically
activate the carbon atom, 2-methylimidazolines in 1 and 2
are presumably formed by nucleophilic attack of free ethy-
lenediamine on the electrophilically activated carbon atom
a
a
b
b
Fig. 1. Perspective view of coordination environment of Co(II) (a) and
zig-zag chain (b) in 1. For clarity, the hydrogen atoms of imidazoline are
omitted in (b).
Fig. 2. Perspective view of coordination environment of Zn(II) (a) and
chain-like structure of
2 (b). For clarity, the hydrogen atoms of
imidazoline are omitted in (b).

Z.-M. Hao, X.-M. Zhang / Inorganic Chemistry Communications 9 (2006) 57–59
59
˚
of the acetonitrile. We tried to isolate 2-methylimidazoline
using catalytic amounts of metal ions but failed. Thus for-
mation of insoluble solids 1 and 2 is less partly responsible
for nucleophilic addition of diamine to organonitrile. The
possible intermediate amidine undergoes rapid intramolec-
ular ring closure.
To sum up, two one-dimensional coordination polymers
of 2-methylimidazoline have been prepared by solvother-
mal reaction involving in situ nucleophilic cycloaddition
reaction of ethylenediamine and acetonitrile to form
2-methylimidazoline. The ligand reaction described here,
although not unprecedented, might open up new horizons
for the preparation of unusual types of cyclic amidine
ligands by use of first-row transition metal ions as catalysts
[17].
k = 0.71073 A). The structure was solved with the direct
methods and refined with full-matrix least-squares tech-
nique (SHELX-97) [18]. All non-hydrogen atoms were
refined anisotropically and all hydrogen atoms were were
geometrically placed and refined isotropically. For 1 the
final R1 value is 0.0624 for 87 parameters and 1387 unique
reflections and the final wR2 is 0.1154 for all 2418 reflec-
tions, and the final R1 value is 0.0494 for 226 parameters
and 3418 unique reflections and the final wR2 is 0.1194
for all 4511 reflections for 2.
Acknowledgements
This work was financially supported by NNSFC
(20401011), A Foundation for the Author of National
Excellent Doctoral Dissertation of PR China (200422)
and Youth Foundation of Shanxi (20041009).
Supplementary data
Additional material comprising atomic coordinates,
thermal parameters, and the full bond lengths and bond
angles have been deposited with the Cambridge Crystallo-
graphic Data Center (CCDC 278644 and 278645).
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Anal. Calc. for 1 C10H16CoN4O4: C, 38.11; H, 5.12; N,
17.78; O, 20.30. Found: C, 38.09; H, 5.13; N, 17.76; O,
20.32. IR (KBr,cmÀ1): 3147s, 2423w, 1633s, 1397s,
1321m, 1286m, 1161m, 1072, 965m, 858m, 805w, 707w,
546m. Anal. Calc. for 2 C16H20N4O4Zn: C, 48.32; H,
5.07; N, 14.09; O, 16.09. Found: C, 48.35; H, 5.10; N,
14.10; O, 16.05. IR (KBr, cmÀ1): 3413m, 3112s, 1700m,
1599m, 1414s, 1179m, 1027m, 977w, 948w, 860w, 523m.
Crystal data for 1 C10H16CoN4O4: monoclinic, space
˚
group C2/c, Mr = 315.20, a = 11.6634(16) A, b =
˚
˚
12.2495(16) A,
c = 9.3138
(13) A,
a = 90°,
b =
3
˚
95.387(3)°,c = 90°, V = 1324.8(3) A , Z = 4, Dc = 1.580
g cmÀ3, F(000) = 652, l = 1.311 mmÀ1, Tmax = 0.9494,
Tmin = 0.7794, S = 0.950, Dqmax/Dqmin (e AÀ3) = 0.376/
À0.357. Crystal data for 2 C16H20ZnN4O4: monoclinic,
˚
space group P21, Mr = 397.73 a = 10.0973 (15) A,
˚
˚
b = 7.9349(11) A,
c = 11.8244(18) A,
a = 90°,
b =
3
˚
115.098(2)°, c = 90°, V = 857.9(2) A , Z = 2, Dc = 1.540 g
cmÀ3, F(000) = 412, l = 1.460 mmÀ1, Tmax = 0.9047,
Tmin = 0.8107, S = 1.063, Dqmax/Dqmin (e AÀ3) = 0.641/
À0.498. Diffraction intensities were collected at 293 K on
a
Bruker Apex CCD diffractometer (Mo Ka,