Preparation, spectra and crystal structure of a novel NiII complex with a new oxime-functionalized diazamesocyclic ligand

Article abstract of DOI:10.1016/j.molstruc.2003.09.016

A four-coordinated monomeric Ni^II complex with a new tetradentate diazamesocyclic ligand funtionalized by oxime donor pendants, [Ni(HL)]ClO₄ (1), where H₂L = N,N′- bis(acetophenoneoxime)-1,5-diazacyclooctane, has been synthesized and characterized by elemental analyses, IR, UV-vis and X-ray diffraction techniques. The crystal structure of complex 1 reveals that the Ni^II center has a NiN₄ distorted planar environment and the 1,5-diazacyclooctane ring takes the unusual boat-boat configuration. The oxime groups exhibit the only N-binding mode with Ni^II ion. A striking structural feature of complex 1 residues in the formation of a two-dimensional (2D) hydrogen-bonding supramolecular architecture with (6,3) topology through intermolecular C-H?O interactions, in which both ClO₄ ^- counter anions and the coordination cations act as 3-connected nodes. The spectral properties of the title complex have been further analyzed in detail.

Full text of DOI:10.1016/j.molstruc.2003.09.016

Journal of Molecular Structure 687 (2004) 119–124
www.elsevier.com/locate/molstruc
Preparation, spectra and crystal structure of a novel NiII complex
with a new oxime-functionalized diazamesocyclic ligand
Xiao-Jun Zhaoa,b, Miao Dub, Ying Wangb, Xian-He Bua,
*
aDepartment of Chemistry, Nankai University, Tianjin 300071, China
bCollege of Chemistry and Life Science, Tianjin Normal University, Tianjin 300074, China
Received 2 August 2003; revised 13 September 2003; accepted 25 September 2003
Abstract
A four-coordinated monomeric NiII complex with a new tetradentate diazamesocyclic ligand funtionalized by oxime donor pendants,
[Ni(HL)]ClO4 (1), where H2L ¼ N,N0-bis(acetophenoneoxime)-1,5-diazacyclooctane, has been synthesized and characterized by elemental
analyses, IR, UV–vis and X-ray diffraction techniques. The crystal structure of complex 1 reveals that the NiII center has a NiN4 distorted
planar environment and the 1,5-diazacyclooctane ring takes the unusual boat–boat configuration. The oxime groups exhibit the only N-
binding mode with NiII ion. A striking structural feature of complex 1 residues in the formation of a two-dimensional (2D) hydrogen-bonding
supramolecular architecture with (6,3) topology through intermolecular C–H· · ·O interactions, in which both ClO24 counter anions and the
coordination cations act as 3-connected nodes. The spectral properties of the title complex have been further analyzed in detail.
q 2003 Elsevier B.V. All rights reserved.
Keywords: NiII complex; Crystal structure; 1,5-Diazacyclooctane; Hydrogen-bonding; IR and electronic spectra
1. Introduction
Recently, a series unique polynuclear metal complexes
with an oxime-functionalized tacn (referring to 1,4,7-
triazacyclononane) ligand were reported by Chaudhuri
et al. [24]. Oximes have played a notable role in the
development of transition metal coordination chemistry
because of their rich chemistry and variety of bonding
modes: only N-, only O-, or both N- and O-binding sites
[25], and the deprotonated oxime groups have been
demonstrated to stabilize high oxidation states at the metal
sites, such as NiIII or CuIII [26]. Combining all aspects stated
above, thus, we anticipated that the incorporation of the
oxime groups on the backbone of DACO would lead to
novel complexes when treated with the metal ions. In this
paper, we will report the synthesis, characterization, spectra
and crystal structure of a mononuclear NiII complex,
[Ni(HL)]ClO4 (1), with a new tetradentate DACO ligand
funtionalized by oxime donor pendants (see Chart 1).
Macrocyclic polyamines functionalized by pendant arms
and their metal complexes have attracted much attention
during the past two decades, as they provide a useful control
over the ligand environment around the transition metal
ions, which have found applications in different areas
ranging from analytical chemistry to biochemistry and
medicine [1–5]. 1,5-Diazacyclooctane (DACO), one of the
most typical examples of the diazamesocyclic ligands,
offers unique conformational requirements and potential for
further functionalization [6], which is now well-established
as a transition metal coordinating ligand and used for the
synthesis of unusual polymeric metal systems, as well as for
the preparation of models of metal-containing proteins due
to their ability to form stable complexes with metal ions [7,
8]. Until now, many examples of DACO derivatives with
pendent arms such as carboxyl, phenol, pyridine, imidazole
and thiol, etc. and their metal complexes have been reported
by us and others [7–23].
2. Experimental
2.1. Materials and general methods
*
Corresponding author. Tel.: þ86-22-23502809; fax: þ86-22-
The ligand H2L·2HCl was prepared by the reaction of
2 equiv. of 4-chloroacetophenoneoxime with DACO in
23502458.
E-mail address: buxh@nankai.edu.cn (X.-H. Bu).
0022-2860/$ - see front matter q 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2003.09.016

120
X.-J. Zhao et al. / Journal of Molecular Structure 687 (2004) 119–124
(730 mg, 5.6 mmol) and the suspension was stirred for 1 h.
The suspension was then filtered and to the filtrate was
added Ni(ClO4)2·6H2O (36.6 mg, 0.1 mmol), resulting in a
clear light-green solution. The pH value of this solution was
adjusted to ca. 6–7 by further adding several drops of
triethylamine with stirring, and the solution turns yellow.
The stirring was continued for 1 h under reflux, and then the
resultant solution was filtered after cooling to room
temperature. Vapor diffusion of diethyl ether to this filtrate
yielded X-ray quality yellow block crystals in ca. 80% yield.
Found: C, 49.2; H, 5.1; N, 10.4. Calc. for C22H27N4ClO6Ni:
C, 49.5; H, 5.1; N, 10.2%. FT-IR (KBr pellet, cm21): 3424s
(br), 2929w, 1624m, 1592w, 1577w, 1552w, 1496m,
1459m, 1446s, 1379w, 1321w, 1286w, 1226w, 1193w,
1156m, 1125vs, 1108vs, 1091vs, 1032m, 989s, 932s, 920s,
863s, 835s, 813s, 772s, 689s, 623s, 573m. lmax (nm) (1
(dm3 mol21 cm21)) (MeOH): 438 (287) and 315 (9500).
Caution. Although no problems were encountered in this
study, transition metal perchlorate complexes are poten-
tially explosive and should be handled with proper
precautions.
Chart 1.
presence of sodium bicarbonate according to the very
similar literature procedure [24]. All reagents for synthesis
and analysis were obtained commercially with analytical
grade and used as received. 1H NMR spectrum was recorded
on a Bruker AC-P 200 spectrometer (300 MHz) at 298 K
with tetramethylsilane as the internal reference. FT-IR
spectra (KBr pellets) were taken on a FT-IR 170SX
(Nicolet) spectrometer and electronic spectra with a Hitachi
UV-3010 spectrophotometer. Carbon, hydrogen and nitro-
gen analyses were performed on a Perkin–Elmer 240C
analyzer.
2.4. Crystallographic data collection and structure
determination
2.2. Synthesis of the ligand
A solution of DACO·2HBr (2.76 g, 10 mmol) and LiOH
(0.84 g, 20 mmol) in anhydrous ethanol (40 ml) was stirred
severely for ca. 4 h and filtered at room temperature. Then,
4-chloroacetophenoneoxime (3.4 g, 20 mmol) was added
to the filtrate with stirring. After addition of NaHCO3
(1.68 g, 20 mmol), the mixture was stirred under ice-cooling
for 1 h (to keep the pH value of the mixture at 8–9 during
this period), and then at room temperature for an additional
2 days. The precipitated white solid was filtered off and
washed once with cold ethanol. The white solid was
suspended in methanol (100 ml) and stirred at ambient
temperature for 20 min and then filtered off. This process of
suspension and stirring in methanol was repeated altogether
four times. The solid was discarded and the combined
filtrate (,400 ml) was evaporated under reduced pressure
to yield the light-yellow pure ligand in its hydrochloride
form in 52% yield. Found: C, 58.1; H, 6.5; N, 12.4. Calc. for
Single-crystal X-ray diffraction study of complex 1 were
performed on a BRUKER SMART 1000 CCD diffract-
ometer equipped with a graphite crystal monochromator
situated in the incident beam for data collection. The
determination of unit cell parameters and data collections
˚
were performed with Mo Ka radiation (l ¼ 0.71073 A) by
4 scan mode in the range of 2:20 , u , 25:038 at
293(2) K. All data were corrected by semi-empirical
method using SADABS program. The program SAINT [27]
was used for integration of the diffraction profiles.
The structure was solved by direct methods using SHELXS
program of the SHELXL-97 package and refined with SHELXL
[28]. NiII center was located from the E-map and other non-
hydrogen atoms were located in successive difference
Fourier syntheses. The final refinement was performed by
full matrix least-squares methods with anisotropic thermal
parameters for non-hydrogen atoms on F2: The hydrogen
atoms of the ligand were placed in the geometrically
calculated positions (the hydrogen atom of the protonated
oxime group was first found in a difference electron density
map, and then placed in the calculated site) and included in
the final refinement in the riding model approximation with
displacement parameters derived from the parent atoms to
which they were bonded. The refinement converged to final
1
C22H28N4O2·2HCl: C, 58.3; H, 6.7; N, 12.4%. H NMR
(CD3OD): d 1.89–1.92 (m, 4H), 3.00 (t, J ¼ 5:6 Hz; 8H),
3.74 (s, 4H), 7.36–7.45 (m, 6H), 7.54–7.57 (m, 4H). IR
(KBr pellet, cm21): 3431s (br), 3187vs, 3055m, 2959w,
2933w, 2919w, 2812m, 1961vw, 1897vw, 1818vw, 1649m,
1601w, 1577w, 1494s, 1464vs, 1443s, 1415s, 1388m,
1290s, 1264m, 1192m, 1147m, 1104m, 1062m, 1042m,
1024m, 985vs, 926m, 876w, 849m, 801w, 767s, 733w,
699vs, 676s, 590m, 578m.
R ¼ 0.0549, wR ¼ 0.0801, S ¼ 0.988, ðD=sÞmax
¼
ðD=sÞmin ¼ 0:000: The ratio of minimum to maximum
apparent transmission is 0.7794. Molecular graphics were
drawn with the program package XP. Further crystal-
lographic data and experimental details for structural
analyses of the title complex are summarized in Table 1,
2.3. Synthesis of the title complex 1
[Ni(HL)]ClO4 (1). To methanol (20 ml) were added the
oxime ligand H2L·2HCl (45.3 mg, 0.1 mmol) and NaClO4

X.-J. Zhao et al. / Journal of Molecular Structure 687 (2004) 119–124
121
Table 1
five-membered chelate rings [N(1)–C(7)–C(8)–N(3)–
Ni(1) and N(2)–C(5)–C(6)–N(4)–Ni(1)].
The Ni–N bond distances lie in the range of 1.891(4)–
Crystallographic data and structure refinement summary for complex 1
Formula
C22H27N4O6ClNi
˚
1.929(4) A, all being normal Ni–N coordination bonds.
Mr
537.64
Crystal size (mm3)
Crystal system
Space group
˚
a (A)
˚
b (A)
0.20 £ 0.16 £ 0.12
However, the bond lengths of Ni–NDACO are longer than
those of Ni–Noxime (see Table 2), indicating weaker
coordination of the DACO rings compared with the oxime
pendants, which is also observed in other related coordi-
nation complexes with heterocycle-functionalized DACO
derivatives [12,13]. It has been well demonstrated that
DACO ring normally exhibits a boat–chair configuration in
the metal complexes and the central methylene C–H group
of the chair form in DACO ring could effectively block one
axial coordination position to give special five-coordination
metal complexes [7,9–15]. However, in the crystal structure
of complex 1, the DACO ring adopts an unusual boat–boat
configuration and gives rise with the NiII center to two five-
membered chelate rings, which enhance the coordination
ability to the NiII ion. Furthermore, in the case reported here,
although the two axis positions of NiII center are completely
open, but no ligand (such as water or chloride) is in the
position to interact with the NiII center, resulting in the final
square–planar coordination geometry. It appears that the
formation of the four-coordinated NiII complex is mainly a
result of the ligand field stabilization effects of the d8 system
and is not due to the steric blocking of the axial position,
which was also found in other NiII complex of DACO [29].
In addition, the NDACO· · ·NDACO non-bonding distance
Orthorhombic
Pbca
10.030(3)
18.553(6)
˚
c (A)
24.549(7)
3
V (A )
˚
4568(2)
Z
8
Dcalc (g cm23
)
1.563
m (mm21
F(000)
)
1.014
2240
Range of h, k, l
210/11, 213/22, 229/19
17,590
Total reflections
Independent reflections
Parameters
3935
307
R indices ðI . 2sðIÞÞ
0.0549, 0.0801
0.988
Goodness-of-fit on F2
23
)
˚
Max. res. peak and hole (e A
0.438 and 20.302
and selected bond lengths and angles with their estimated
standard deviations in Table 2.
3. Results and discussion
3.1. Description of the crystal structure of 1
˚
(2.746(5) A for 1) is much shorter than that of the
˚
pendant· · ·Npendant (2.855(4) A). Consequently, the bite
N
The structure of complex 1 consists of a discrete
[Ni(HL)]þ cation and a perchlorate counter anion. The
ORTEP view of the coordination cation in complex 1 with
atom labeling is shown in Fig. 1a. The coordination
geometry around the NiII center could be described as a
distorted square plane generated by N(1)–N(2)–N(3)–
N(4): two nitrogen of the oxime pendant groups and the
other two nitrogen donors of the DACO ring are in the cis
positions in the coordination plane, and the NiII ion is
deviated from the mean coordination plane by approxi-
angle of NDACO–Ni–NDACO is significantly smaller than
the angle of Npendant–Ni–Npendant due to the sterochemical
requirement.
Although the oxime groups have three possible bonding
modes with the metal centers as stated in Section 1, only the
N-binding site was observed in complex 1 discussed here. In
1, one of the two oxime pendants is protonated, forming a
single directed intramolecular O(1)–H(1)· · ·O(2) inter-
action with the other deprotonated oxime group. Meantime,
two hydrogen atoms [H(14) and H(22)] from the phenyl ring
take active part in the formation of two intramolecular C–
H· · ·O weak interactions with the adjacent oxime oxygen
donors (see Fig. 1a), which further stabilize the discrete
˚
mately 0.13 A. The dihedral angle of the two phenyl planes
of the pendants is 130.5(4)8. In this complex, the ligand
adopts the unusual boat–boat configuration, which is also
observed in a NiII complex with a carboxylic-functionalized
DACO ligand [16], and gives rise with the NiII center to two
˚
structure unit in 1. In addition, the N–O (average: 1.344 A)
˚
and CyN (average: 1.287 A) bond lengths and C–N–O
bond angles (average: 119.28) of the oxime ligands are
comparable to those reported in Ref. [25]. It should be noted
that this report represents the first example of the
incorporation of the oxime groups on the backbone of
DACO, and consequently, may open new perspectives of
the coordination chemistry of diazamesocyclic system.
Analysis of the crystal packing of complex 1 shows that a
notable feature of this structure resides in the formation of a
novel two-dimensional (2D) hydrogen-bonding supramole-
cular networks through intermolecular C–H· · ·O inter-
actions. As shown in Fig. 1b, in the structure of 1, both
Table 2
˚
Selected bond lengths (A) and angles (deg) for complex 1
Bond lengths
Ni(1)–N(4)
Ni(1)–N(2)
N(3)–O(1)
1.891(4)
1.916(4)
1.336(4)
Ni(1)–N(3)
Ni(1)–N(1)
N(4)–O(2)
1.889(4)
1.929(4)
1.351(4)
Bond angles
N(4)–Ni(1)–N(3)
N(3)–Ni(1)–N(2)
N(3)–Ni(1)–N(1)
98.1(2)
171.6(2)
84.8(2)
N(4)–Ni(1)–N(2)
N(4)–Ni(1)–N(1)
N(2)–Ni(1)–N(1)
84.9(2)
171.3(2)
91.2(2)

122
X.-J. Zhao et al. / Journal of Molecular Structure 687 (2004) 119–124
Fig. 1. (a) ORTEP structure of the [Ni(HL)]þ cation in 1. (b) View of the 2D hydrogen-bonding network in 1 along ac plane.
the coordination cation [Ni(HL)]þ and the perchlorate anion
could be considered as the 3-connected nodes, which are
extended into a 2D sheet with (6,3) topology [30] along
crystallographic [101] place through three intermolecular
C–H· · ·O weak interactions. All the hydrogen bond
geometries are listed in Table 3. For the intermolecular
C–H· · ·O interactions stated above, the C· · ·O separations
Table 3
Hydrogen-bonding geometry (A, deg) for complex 1
˚
D–H· · ·A
D–H
H· · ·A
D· · ·A
D–H· · ·A
O(1)–H(1)–O(2)
0.849
0.930
0.930
0.970
0.970
0.930
1.641
2.295
2.335
2.561
2.538
2.407
2.426(4)
2.830(6)
2.883(6)
3.443(7)
3.416(7)
3.303(7)
152.52
116.13
117.31
151.28
150.44
161.81
C(14)–H(14)–O(1)
C(22)–H(22)–O(2)
C(1)–H(1A)–O(4)i
C(3)–H(3A)–O(6)ii
C(20)–H(20)–O(3)iii
˚
are in the 3.303(7)–3.443(7) A range with H· · ·O distances
˚
in the 2.407–2.561 A region, respectively, and the smallest
bond angle is 150.448, falling into the normal range
of interaction of type C–H· · ·O defined by Desiraju [31].
It is noteworthy that the crystal structure of 1 clearly
Symmetry codes: (i) 21=2 þ x; 1=2 2 y; 1 2 z; (ii) 1=2 þ x; 1=2 2 y;
1 2 z; (iii) 1=2 þ x; y; 1=2 2 z:

X.-J. Zhao et al. / Journal of Molecular Structure 687 (2004) 119–124
123
ture. The board band centered at ca. 438 nm can be assigned
to the d–d transition of the metal center, which is the
characteristic absorption of the square–planar NiII ion
having NiN4 coordination environment [13] and consistent
with its solid structure. In addition, the very strong bands
observed at 315 and 200–260 nm of the solution spectra of
1 are p ! p p transitions of the ligand.
4. Supplementary materials
Crystallographic data for the crystal structure reported in
this paper have been deposited with the Cambridge
Crystallographic Data Center (CCDC No. 213770). This
material can be obtained free of charge via www.ccdc.cam.
ac.uk/conts/retrieving.html (or from the CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK; fax: þ44-1223-336033; e-
mail: deposit@ccdc.cam.ac.uk).
Scheme 1. View of the 2D (6,3) topological network through hydrogen-
bonding interactions in 1.
demonstrates that the nature of the counter anion (donor
ability and bridging fashion) plays a critical role in
construction of the final hydrogen-bonding supramolecular
network with (6,3) topology (see Scheme 1).
Acknowledgements
This work was financially supported by the Natural
Science Foundation of Tianjin Education Commission (No.
20020901), Outstanding Youth Foundation of NSFC (No.
20225101) and the Starting Funding of Tianjin Normal
University.
3.2. Preparation and spectral characterization of complex 1
The title complex 1, prepared in methanol from the
respective metal salt and free base form of the ligand H2L
(since the corresponding ligand is the HCl salt, it must be
neutralized with triethylamine prior to complexation), was
isolated as perchlorate salt. It is interesting that the
perchlorate anion in the final product 1 may come from
the excess NaClO4 but not Ni(ClO4)2, because we have
isolated the same substances (confirmed by IR, elementary
analyses and X-ray diffraction) when using NiSO4,
Ni(NO3)2 or NiCl2 instead of Ni(ClO4)2 during the
preparation procedure of 1. Although the ligand has two
potentially dissociable protons present as OH groups in the
oxime part of the ligand, only one of them was deprotonated
in the resultant complex to yield a mononuclear complex,
which is determined by the nature of the metal ion as stated
in Ref. [24].
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