Comparative study of two new grid complexes: Synthesis, X-ray structure characterization, thermogravimetric, and spectroscopic properties

Article abstract of DOI:10.1080/00958972.2011.639873

The synthesis and characterization of two new grid complexes, [Ni ₄(L)₄(DMF)₄]·2H₂O (1) and [Mn₄(L)₄(DMF)₄] (2) (where L is the anion of 3,5-dichlorosalicylaldehyde pyridine-2-formyl hydrazone), were investigated. X-ray crystal structure analysis reveals that the metal centers in both complexes exhibit slightly distorted square-bipyramidal coordination geometry. The dominating interaction of two adjacent grids for 1 and 2 is Cl...H hydrogen bonds. The halogen-hydrogen bond is a key factor to stabilize the crystal structure of chloro-substituted grid compounds. Thermogravimetric curves of 1 and 2 exhibit distinct weight loss stages at different temperatures and reflect the thermal stability of the complexes. Both UV-visible and fluorescence spectra of 1 and 2 indicate they have a stronger conjugated system and the same significant quenching ability compared with H₂L. The ESI-MS spectra of 1 and 2 prove that the tetranuclear grids decompose in methanol/water solution.

Full text of DOI:10.1080/00958972.2011.639873

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Comparative study of two new grid
complexes: synthesis, X-ray structure
characterization, thermogravimetric,
and spectroscopic properties
Yuan Wang a b , Zheng Liu a a , Yongliao Wang c , Jiongyang Gao a
Yanhong Li d e
&
a College of Chemical and Biological Engineering, Guilin University
of Technology , Guilin 541004 , PR China
b Center for Structural and Molecular Biology, Institute of
Biophysics, Chinese Academy of Sciences , Beijing 100101 , PR
China
c College of Environmental Science and Engineering, South China
University of Technology , Guangzhou 510006 , PR China
d Guangxi Key Laboratory of Environmental Engineering,
Protection and Assessment, Guilin University of Technology ,
Guilin 541004 , PR China
e College of Environmental Science and Engineering, Guilin
University of Technology , Guilin 541004 , PR China
Published online: 05 Dec 2011.
To cite this article: Yuan Wang , Zheng Liu , Yongliao Wang , Jiongyang Gao & Yanhong Li (2011)
Comparative study of two new grid complexes: synthesis, X-ray structure characterization,
thermogravimetric, and spectroscopic properties, Journal of Coordination Chemistry, 64:24,
4357-4372, DOI: 10.1080/00958972.2011.639873
To link to this article: http://dx.doi.org/10.1080/00958972.2011.639873
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Journal of Coordination Chemistry
Vol. 64, No. 24, 20 December 2011, 4357–4372
Comparative study of two new grid complexes: synthesis,
X-ray structure characterization, thermogravimetric,
and spectroscopic properties
YUAN WANGyz, ZHENG LIU*y, YONGLIAO WANGx,
JIONGYANG GAOy and YANHONG LI{?
yCollege of Chemical and Biological Engineering, Guilin University of Technology,
Guilin 541004, PR China
zCenter for Structural and Molecular Biology, Institute of Biophysics, Chinese
Academy of Sciences, Beijing 100101, PR China
xCollege of Environmental Science and Engineering, South China University of
Technology, Guangzhou 510006, PR China
{Guangxi Key Laboratory of Environmental Engineering, Protection and Assessment,
Guilin University of Technology, Guilin 541004, PR China
?College of Environmental Science and Engineering, Guilin University of
Technology, Guilin 541004, PR China
(Received 15 June 2011; in final form 24 October 2011)
The synthesis and characterization of two new grid complexes, [Ni4(L)4(DMF)4] ꢀ 2H2O (1) and
[Mn4(L)4(DMF)4] (2) (where L is the anion of 3,5-dichlorosalicylaldehyde pyridine-2-formyl
hydrazone), were investigated. X-ray crystal structure analysis reveals that the metal centers in
both complexes exhibit slightly distorted square-bipyramidal coordination geometry. The
dominating interaction of two adjacent grids for 1 and 2 is Cl ꢀ ꢀ ꢀ H hydrogen bonds. The
halogen–hydrogen bond is a key factor to stabilize the crystal structure of chloro-substituted
grid compounds. Thermogravimetric curves of 1 and 2 exhibit distinct weight loss stages at
different temperatures and reflect the thermal stability of the complexes. Both UV-visible and
fluorescence spectra of 1 and 2 indicate they have a stronger conjugated system and the same
significant quenching ability compared with H2L. The ESI-MS spectra of 1 and 2 prove that the
tetranuclear grids decompose in methanol/water solution.
Keywords: Grid complexes; Halogen-substituted; Fluorescence; Properties
1. Introduction
With progress of supramolecular coordination chemistry, a series of self-assembled
compounds known as grid-like architectures were synthesized. These compounds
contain 2-D arrays of metal ions which connect to a set of ligands in a perpendicular
arrangement to generate a multiple linear and rigid network. These grid-type
compounds can be synthesized with high yield and are thermodynamically stable and
their intriguing magnetic and electronic properties make them valuable in application of
*Corresponding author. Email: lisa4.6@163.com
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2011 Taylor & Francis
http://dx.doi.org/10.1080/00958972.2011.639873

4358
Y. Wang et al.
information storage and processing technology [1–3]. Among the most widely studied
ligands are poap (N3-(2-pyridoyl)-2-pyridinecarboxamidrazone) [4–8], pahap (picolina-
mide azine) [6, 8], Hpop (2-(hydroxyimino)-N0[1-(2-pyridyl)ethylidene]propanohydra-
zone) [9–11], and their transition metal complexes. Grid-like complexes of poap as well
as other N-heterocyclic derivatives [12, 13] have been studied, but there have been no
reports of complexes of 2-hydroxybenzaldehyde hydrazone molecular skeletons. From
the standpoint of structure, the role of halogen in the grid complex crystals is unknown.
The only record of fluorescence properties of grids was reported by Cao et al. [13]. In all
open-shell transition metal grids of derivatives from condensation of carbohydrazides
and 2-phenylpyrimidine-4,6-dicarbaldehyde, only Zn2þ grids have quenching phenom-
ena [13]. However, an important bioelement, Mn2þ, as reflected in Irving–Williams
sequence, has not had fluorescence reported due to oxidation complexity and relatively
low stability of its complexes.
In this contribution, based on the fact that hydrazine can form mononuclear,
dinuclear [8], tetranuclear or even multinuclear [7] coordination features, we synthesized
chloro-substituted 2-hydroxybenzaldehyde acylhydrazone H2L (scheme 1) and two new
grid-like complexes, which in combination with the salicyl groups may enhance their
anti-inflammatory activity [14]. Comparison of X-ray crystal structures, thermogravi-
metric (TG) analysis, electronic spectroscopic studies and fluorescence properties of the
two complexes are reported. In particular, we discuss the characteristics of halogen–
hydrogen bonds between adjacent lattices and the differences between solvent with axial
coordination in two grids by TG curves. To the best of our knowledge, this report is the
first to study the TG properties of grids and fluorescence for Ni2þ, Mn2þ lattice
complexes.
2. Experimental
2.1. Materials
All reagents and solvents were purchased from commercial sources and used as
received.
2.2. Methods
Solution 1H (500 MHz) nuclear magnetic resonance (NMR) spectra were recorded with
a Bruker Ultrashield Avance DRX-500 instrument using residual solvent proton
Scheme 1. Schematic drawing of ligand H2L.

Two grid complexes
4359
1
resonances as internal reference for the H NMR. Elemental analysis for C, H, and N
was performed on a Vario EL elemental analyzer. IR spectra were recorded on a
Shimadzu FTIR-8400 using KBr pellets. Thermal stability analyses were performed on
a Netzsch STA-449 instrument in N2 with a heating rate of 10ꢁC min–1. UV-Vis spectra
were obtained in anhydrous DMF with a Shimadzu UV-2450 Spectrophotometer.
Luminescence measurements were carried out on a Perkin Elmer LS-45/55 Fluorescence
Spectrophotometer. High-resolution mass spectra were obtained on an Agilent 6100
Single Quadropole system equipped with an Agilent 1200 LC module (Agilent, Santa
Clara, USA), and with an electrospray ionization source. The mass spectrometer was
operated in the positive ion mode. Single-crystal samples of 1 and 2 were washed with
acetonitrile and methanol, respectively, dried under vacuum and then ground by agate
mortar for 1 h.
2.3. X-ray structure determination
X-ray diffraction data for single crystals of 1 and 2 (1, 0.32 ꢂ 0.16 ꢂ 0.13 mm; 2,
0.17 ꢂ 0.15 ꢂ 0.08 mm) were collected at 293(2) K on a Bruker Smart CCD system
˚
equipped with monochromated Mo-Ka radiation (ꢀ ¼ 0.71073 A) using the !–ꢁ scan
technique. Data integration and empirical absorption corrections were performed by
SAINT programs [15]. The structures were solved by direct methods using SHELXS-97
[16] and refined by full-matrix least-squares on F2 using SHELXL-97 [17]. All atoms
except hydrogen were refined anisotropically.
2.4. Synthesis of the ligand H2L
H2L was obtained from the hydrazide reaction of pyridine-2-carboxylic acid methyl
ester and hydrazine followed by condensation of 3,5-dichlorosalicylaldehyde and
2-picoloylhydrazine, prepared according to published procedures [18, 19]. The
compound was recrystallized from boiling ethanol by cooling on ice (yield: 87%).
Anal. Found: C, 50.17; H, 2.98; N, 13.55. Calcd for C13H9N3O2Cl2 (%): C, 50.22; H,
1
2.92; N, 13.51. H NMR (500 MHz, DMSO-d6) (ppm): ꢂ ¼ 12.89(s, 1H, OH), 12.57(s,
9
7
1H, NH), 8.09–8.06(m, 1H, CH), 8.80(s, 1H, 12CH), 8.15(d, 1H, J ¼ 7.75Hz, 13CH),
8.74(d, 1H, J ¼ 4.05Hz, 14CH), 7.71–7.69(m, 1H, 15CH), 7.57(d, 1H, J ¼ 2.15Hz, CH),
4
7.63(d, 1H, J ¼ 2.2Hz, CH). IR(KBr pellet, cm–1): 1592(s), 3068(m), 3264(s), 1676(s),
6
1513(s), 1454(s), 1439(s), 1184(m), 1222(m), 1272(m), 1000(m), 736(m).
2.5. Synthesis of [Ni4(L)4(DMF)4] ꢀ 2H2O (1)
An anhydrous methanol solution (10 mL) of Ni(NO3)2 ꢀ 6H2O (0.5 mmol, 0.145 g) was
slowly added to a stirred slurry of H2L (0.5 mmol, 0.155 g) in methanol (15 mL) at 65ꢁC
gave a grass green solution; 45 min later, with 6 drops of concentrated ammonia, the pH
of the solution was adjusted to between 7 and 8. Copious precipitation of brown solid
occurred immediately. The solution was equilibrated for 1.5 h and then filtered. The
residue was dissolved in DMF (20 mL) and the solution was filtered to remove a small
amount of gelatinous material. The solution was mixed with same volume of anhydrous
acetonitrile. Brown stripe single crystal was formed several days later by slow

4360
Y. Wang et al.
evaporation at room temperature (yield: 73%). Anal. Found: C, 42.72; H, 3.14;
N, 12.65. Calcd for C64H60Cl8N16Ni4O14 (%): C, 42.81; H, 3.37; N, 12.48. IR(KBr
pellet, cm–1): 1606(s), 1651(s), 2925(w), 3054(w), 1159(m), 1537(s), 1479(s), 1444(s),
3646(w), 3585(w), 1594(m), 1209(m), 752(m).
2.6. Synthesis of [Mn4(L)4(DMF)4] (2)
A distilled water solution (10 mL) of MnCl2 ꢀ 4H2O (0.5 mmol, 0.099 g) was slowly
added to a stirred slurry of H2L (0.5 mmol, 0.155 g) in anhydrous methanol (15 mL) at
65ꢁC and gave a turbid yellow solution; 45 min later, with 8 drops of triethylamine, the
pH of the solution was adjusted to between 7 and 8. After 1.5 h, red-brown precipitate
appeared and the solution was filtered. The residue was dissolved in DMF (40 mL),
filtered to remove a small amount of gelatinous material and the solution was mixed
with same volume of anhydrous methanol. Red block single crystals were formed
several days later by slow evaporation at room temperature (yield: 68%). Anal. Found:
C, 44.14; H, 3.29; N, 12.78. Calcd for C64H56Cl8N16Mn4O12 (%): C, 44.06; H, 3.24;
N, 12.85. IR(KBr pellet, cm–1): 1601(s), 3401(s), 1653(s), 2929(w), 3072(w), 1156(m),
1535(s), 1475(s), 1452(s), 1581(s), 1207(m), 755(m).
Details of the crystal parameters, data collection, and refinements for 1 and 2 are
summarized in table 1. Selected bond lengths and angles for 1 and 2 are listed in table 2.
3. Results and discussion
3.1. X-ray crystallography
3.1.1. [Ni4(L)4(DMF)4] E 2H2O (1). The results of crystal structure analysis reveal that
1 is a centrosymmetric configuration. From bond lengths (table 2) and figure 1, each
Ni2þ is coordinated by two mutually perpendicular enol-type L2– (scheme 2) and one
solvent DMF to form repeating units, while two water molecules dissociate from the
lattice. The molecule is electroneutral. Ni1 and Ni1A have the same slightly distorted
tetragonal-bipyramid coordination mode, each six-coordinate by three nitrogen atoms,
two oxygen atoms from L, and one oxygen atom from DMF. Similarly, Ni2 (Ni2A) is
coordinated by two nitrogen atoms, three oxygen atoms from L, and one oxygen atom
from DMF. These atoms around each metal form two five-membered rings and one six-
membered ring. The acyl oxygen atoms and hydrazide (–N–N–) are bridge. Bridge angle
Ni1–O3–Ni2A (Ni1A–O3A–Ni2) is 140.682(6)ꢁ, close to 139.08(10)ꢁ reported by
Matthews et al. [5]. Torsion angle Ni1–N2–N3–Ni2 (Ni1A–N2A–N3A–Ni2A) is
159.221(8)ꢁ. For Ni1, the equatorial plane is defined by O3, N6, O4, N2, and the apical
positions are occupied by N1, O5, while Ni1 deviates from the tetragonal plane by
˚
0.0232 A toward O5. For Ni2, the equatorial plane is defined by O1, N3, O2, N4A and
the apical positions are occupied by O3A, O6, while Ni2 deviates from the tetragonal
˚
plane by 0.0045 A toward O3A.
As shown in figure 1, four nickels are arranged in an approximate rectangle. Each
nickel is in the least-squares plane, indicating the complex is a highly symmetrical, in
˚
˚
which the shorter edge (Ni1(Ni1A) ꢀ ꢀ ꢀ Ni2A(Ni2)) length (3.9015(4) A) is close to 3.91 A

Two grid complexes
Table 1. Crystallographic data for 1 and 2.
4361
Complex
Formula
Formula weight
Crystal system
Space group
1
2
C
1795.72
64H60CL8N16N14O14
C64H56CL8N16Mn4O12
1744.62
Triclinic
Triclinic
ꢀ
ꢀ
P1
P1
ꢁ
˚
Unit cell dimensions (A,
)
a
b
c
ꢄ
ꢅ
ꢆ
12.3311(13)
12.7538(15)
13.4979(18)
70.8120(10)
66.5230(10)
88.552(2)
1825.2(4), 1
1.634
1.383
0.0894
0.0909
0.2399
1.007
12.6472(12)
12.6975(13)
13.6241(15)
102.8770(10)
94.6730(10)
119.686(2)
1804.7(3), 4
1.605
1.052
0.0558
0.0683
0.1796
1.028
3
˚
Volume (A ), z
Calculated density (g cmꢃ3
)
ꢇ (mmꢃ1
Rint
)
R1(I 4 2ꢈ(I))a
wR2 (all data)b
Goodness-of-fit on F 2
P
P
P
P
b
aR1 ¼ ||Fo|–|Fc||/ |Fo|, wR2 ¼ [ w(Fo2 ꢃ Fc2)2/ w(Fo2)2]1/2
.
ꢁ
˚
Table 2. Selected bond lengths (A) and angles ( ) for 1 and 2.
1
Ni1–N1
Ni1–N2
Ni1–N6
Ni1–O3
Ni1–O4
Ni1–O5
N1–Ni1–O5
N2–Ni1–O3
O3–Ni1–O6
N6–Ni1–O4
2.051(9)
2.060(8)
1.973(8)
2.055(7)
1.996(8)
2.225(8)
175.2(3)
98.3(3)
Ni2–N3
1.987(8)
2.020(8)
2.051(7)
1.991(7)
2.088(7)
2.142(9)
92.3(3)
167.9(3)
78.9(3)
90.4(3)
C1–N2
N2–N3
N3–C7
C14–N5
N5–N6
N6–C20
O2–M2–N4A
N4A–Ni2–O1
1.310(13)
1.391(10)
1.278(12)
1.281(12)
1.396(11)
1.294(13)
96.4(3)
Ni2–N4A
Ni2–O1
Ni2–O2
Ni2–O3A
Ni2–O6
O4–Ni1–N2
O3A–Ni2–O6
O1–Ni2–N3
N3–Ni2–O2
94.4(3)
79.8(3)
89.8(3)
2
Mn1–O1
Mn1–O2
Mn1–O4
Mn1–O5
Mn1–N1
Mn1–N6
O4–Mn1–O5
O1–Mn1–N1
Nl–Mn1–O2
O2–Mn1–N6
2.047(5)
2.157(5)
2.173(5)
2.229(5)
2.250(5)
2.254(5)
156.97(18)
82.03(19)
71.81(19)
84.14(19)
Mn2A–O3A
Mn2A–O4A
Mn2A–O6A
Mn2A–N2
Mn2A–N3A
Mn2A–N4A
N6–Mn1–O1
O3A–Mn2A–O4A
N2–Mn2A–N3A
N3A–Mn2A–O6A
2.085(5)
2.189(5)
2.262(5)
2.205(5)
2.241(6)
2.238(6)
122.23(19)
146.1(2)
73.6(2)
C1–N1
N1–N2
N2–C8
C14–M4
N4–N5
N5–C21
O6A–Mn2A–N4A
N4A–Mn2A–N2
1.262(8)
1.385(7)
1.314(8)
1.268(9)
1.393(7)
1.284(8)
84.4(2)
121.2(2)
83.6(2)
in previous study [5]. The shorter edge distance is less than the sum of Ni ꢀ ꢀ ꢀ Ni van der
˚
Waals radii (4.00 A), showing weak interactions between the short side of the metal ions
may exist.
Complex 1 comprises two sets of ꢃ–ꢃ stacking phenomena (figure 2), each ꢃ–ꢃ stack
includes a benzene ring (C8, C9, C10, C11, C12, C13) of acylhydrazone and another

4362
Y. Wang et al.
Figure 1. Diamond drawing of [Ni4(L)4(DMF)4] ꢀ 2H2O. Hydrogen atoms were omitted for clarity.
Scheme 2. Schematic drawing of tautomeric form for L2–
.
pyridine ring (N1, C2, C3, C4, C5, C6). The dihedral angle of two ring planes is 4.4ꢁ,
which indicates an almost exactly face to face overlap. The center distance is
˚
Cg1 ꢀ ꢀ ꢀ Cg2 3.5548(3) A (table 3). The interactions of a pair of longer edges of
contiguous grid (namely the interactions between chlorides of one grid and the adjacent
˚
grid DMF methyl H) is 2.9733(3) A (H29B ꢀ ꢀ ꢀ Cl2). The shorter sides of the adjacent
˚
lattice have four pairs of interactions (figure 3), and they are H6ꢀ ꢀ ꢀN5 3.0804(3) A,
˚
˚
˚
H20 ꢀ ꢀ ꢀ Cl1 3.0216(4) A, H26 ꢀ ꢀ ꢀ Cl1 3.0169(3) A, and H26 ꢀ ꢀ ꢀ Cg3 3.0089(3) A (Cg3:
N4, C15, C16, C17, C18, C19). As the essential molecular features, centrosymmetric
aryl C–H ꢀ ꢀ ꢀ N dimer was simple and general in a diquinoline derivative reported by
Marjo et al. [20]. A subsequent statistical analysis, using the Cambridge Structural

Two grid complexes
4363
Figure 2. View of the interactions between longer edges of two adjacent grids for 1 depicted as broken
green lines.
Table 3. Hydrogen-bond data (A and ꢁ) for 1 and 2.
˚
D–H ꢀ ꢀ ꢀ A
d(D–H)
d(H ꢀ ꢀ ꢀ A)
d(D ꢀ ꢀ ꢀ A)
ffDHA
1
C6–H6 ꢀ ꢀ ꢀ N5a
C20–H20 ꢀ ꢀ ꢀ Cl1b
C26–H26 ꢀ ꢀ ꢀ Cl1b
C26–H26 ꢀ ꢀ ꢀ Cg3c
C29–H29B ꢀ ꢀ ꢀ C12d
Cg1 ꢀ ꢀ ꢀ Cg2c
0.9300(1)
0.9300(1)
0.9300(1)
0.9300(1)
0.9600(1)
–
3.0804(3)
3.0216(4)
3.0169(3)
3.0089(3)
2.9733(3)
3.5548(3)
3.9819(4)
3.4256(4)
3.4322(3)
3.3467(3)
3.7229(3)
–
163.780(12)
108.032(10)
108.857(10)
103.243(9)
135.871(10)
–
2
Cl1–H11 ꢀ ꢀ ꢀ C12e
0.9300(1)
–
2.7847(2)
3.4789(3)
3.7052(3)
–
170.565(11)
–
Cg4 ꢀ ꢀ ꢀ Cg5c
Symmetry codes: a: 1 – x, –y, 1 – z; b: x, y – 1, z; c: x, y, z; d: 1 – x, 1 – y, –z; e: 2 – x, 4 – y, 2 – z. Cg1¼C2,
C3, C4, C5, C6, N1; Cg2¼C8, C9, C10, C11, C12, C13; Cg3¼C15, C16, C17, C18, C19, N4;
Cg4¼C2, C3, C4, C5, C6, C7; Cg5¼C9, C10, C11, C12, C13, N3.
Database (CSD), of C–H ꢀ ꢀ ꢀ N interactions show that they exist in the reported
˚
˚
structures with Hꢀ ꢀ ꢀN distances shorter than 2.45 A (van der Waals sum 2.75 A) and
with a mean C–H ꢀ ꢀ ꢀ N angle of 120 ꢄ ꢄ ꢄ 180ꢁ [21]. Thallapally and Nangia defined a
˚
C–H ꢀ ꢀ ꢀ Cl contact as either short, medium, or long using the criteria 52.6 A, 2.6–3.0
˚
˚
A, and 43.0 A, respectively [22]. On closer inspection of these four pairs of
˚
interactions, the pair of H ꢀ ꢀ ꢀ N interactions (H ꢀ ꢀ ꢀ N 3.0804(3) A, ffC–H ꢀ ꢀ ꢀ N is
ꢁ
˚
163.78 ) are weak. The two pairs of H ꢀ ꢀ ꢀ Cl bonds (H20ꢀ ꢀ ꢀCl1 3.0216(4) A, H26 ꢀ ꢀ ꢀ Cl1
˚
3.0169(3) A) belong to a relatively stronger interaction and the C–H ꢀ ꢀ ꢀ ꢃ interactions
provide an extra source of stability.
Thus, while strong halogen–hydrogen bonds play
a central role between
the two grids, the combined influence of weak interactions is also evident in the
structures.

4364
Y. Wang et al.
Figure 3. View of the interactions between shorter edges of two adjacent grids for 1 depicted as broken
green lines.
Figure 4. Diamond drawing of [Mn4(L)4(DMF)4]. Hydrogen atoms were omitted for clarity.
3.1.2. [Mn4(L)4(DMF)4] (2). Complex 2 has the same crystal system and space group
compared with complex 1, but their cell parameters have notable differences. Similar
to 1, H2L in 2 with doubly deprotonated enol-type structure L2– coordinates to Mn
(figure 4). O1, N1, O2, and N6 around Mn1 form the equatorial plane, while DMF and
an oxo bridge are in the axial positions; Mn1 deviates from the best-fit plane by

Two grid complexes
4365
Figure 5. View of the interactions between shorter edges of two adjacent grids for 2 depicted as broken
green lines.
2þ
˚
0.0072 A toward O4. Different from Ni of 1 and Mn1 (Mn1A) of 2, DMF is not in
˚
apical positions around Mn2 (Mn2A), which deviates 0.0213 A from the equatorial
˚
plane (N2, N3A, N4A, O6A). The average axial length of 2.169(5) A in 2 is 0.245 A,
˚
˚
which is longer than the average Mn–O/N distance of 1.924 A in the equatorial plane
[23] from Jahn–Teller effects. The Jahn–Teller projections of Mn1 (Mn1A) and Mn2
(Mn2A) within 2 are not mutually collinear because of the presence of two symmetry-
independent species. Bridge angle Mn1–O4–Mn2 (Mn1A–O4A–Mn2A) 128.053(7)ꢁ is
close to 119.7–128.8ꢁ in Mn16 grid prepared by Dey et al. [24]. Torsion angle Mn1–N1–
N2–Mn2A (Mn1A–N1A–N2A–Mn2A) is 165.374(8)ꢁ. Different structures of the two
grids were determined by free rotation of mono-coordinated hydrazide N4–N5(N4A–
˚
N5A) in 2 and N5–N6 (N5A–N6A) in 1 [25]. The distance H1ꢀ ꢀ ꢀMn2 (2.8658(3) A) and
angle C1–H1–Mn2 (121.515(10)ꢁ) indicate a pair of weak Hꢀ ꢀ ꢀM interactions in the
grids [26]. Of note is the fact that all of the coordination bond lengths of 2 are shorter
than those of 1, and more uneven distribution of coordination bond angles of 2
compared to 1 (table 2), suggesting that L anion better matches with Ni2þ
.
Four manganese ions are arranged in an approximate rectangle, while each
manganese is on their least-squares plane, in which the shorter edge (Mn1
˚
(Mn1A) ꢀ ꢀ ꢀ Mn2A(Mn2)) length (3.9216(3) A) and the longer edge (Mn1(Mn1A) ꢀ ꢀ ꢀ
˚
Mn2(Mn2A)) length (5.2674(4) A) approach to 3.930 A and 5.290 A, respectively,
˚
˚
reported by Thompson et al. [27]. The length of the shorter edge is less than the sum of
˚
Mnꢀ ꢀ ꢀMn van der Waals radii (4.10 A), showing that weak interactions between the
short side of the metal ions might exist.
As in 1, there are also ꢃ–ꢃ stacking interactions in 2, including a benzene ring and a
pyridine ring. In figure 5, the dihedral angle of two ring planes (C2, C3, C4, C5, C6, C7;
N3, C9, C10, C11, C12, C13) is 3ꢁ, almost exactly face to face overlap. The center
˚
distance Cg4 ꢀ ꢀ ꢀ Cg5 is 3.4789(3) A, highlighting the importance of ꢃ stacking forces by
‘‘seizing’’ a molecule in proximity to a metal ion site. Maximization of stabilizing ꢃ–ꢃ
contacts between ligands, the rigid conjugated structure of enol-type (–C¼N–N¼CO–)
and balance of the coordination algorithms of the metals lead to all ligands in 1 and 2

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Y. Wang et al.
adopting a fairly flat overall conformation. In the packing of the Mn4 grid, the
interactions which belong to moderate hydrogen bonds of the adjacent shorter side
˚
(H11 ꢀ ꢀ ꢀ Cl2 2.7847(2) A) are the only directional stabilization of the connection
between lattices.
Compounds 1 and 2 are not same as a consequence of the coordination ability
of metal combined with the different bridge angles (M–O–M) and torsion angles
(M–N–N–M). However, there are several structural similarities between 1 and 2; most
important, chlorides as substituent groups have some influence in promoting stacking
of 1 and 2, which is a driving force for intermolecular recognition.
3.2. TG analysis
The TG analysis of 1 exhibits three continuous weight loss stages: first releasing all
lattice water molecules below 82ꢁC, then on heating from 82ꢁC to 396ꢁC release of
coordination DMF (Found 15.87, Calcd 16.61%), the ligand decomposes completely at
361ꢁC (figure 6). Simultaneously in one temperature range 1 loses its four DMF
molecules (figure 7), indicating that their chemical environments are identical.
However, 2 only releases two DMF molecules below 355ꢁC (Found 8.61, Calcd
8.37%) (figure 8) and there is no clear mass loss plateau of the other two-coordinated
DMF. The fact that the four-coordinated DMF molecules dissociate at different
temperatures indicates strength difference of the interaction between DMF and
[Mn4(L)4]. Qin et al. found similar TG phenomena for [Ba(DMF)2(H2O)]2
[Mo8O26] ꢀ 2DMF also releasing coordinated DMF step by step [28].
Figure 6. TG chart of the ligand H2L.

Two grid complexes
4367
Figure 7. TG chart of 1.
Figure 8. TG chart of 2.

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Y. Wang et al.
Figure 9. Distribution of DMF in 1 and 2.

Two grid complexes
4369
Although coordination of 1 and 2 are similar, the arrangement of four coordinated
DMF molecules is completely different, which is the major reason for different DMF
mass loss curves (figure 9). L2– coordinated to Ni2þ ions are a better fit and can form a
more symmetrical molecule than Mn2þ ions. The final mass loss percentage compo-
sition of 1 and 2 at 900ꢁC are 27.00% and 33.97%, respectively. Neither reaches
constant weight and decomposition is still going on.
3.3. UV-Vis and luminescence
The solution UV-Vis spectrum of H2L (figure 10) has maxima responses at 409 nm
(" ¼ 175), 338 nm (" ¼ 1105), 309 nm (" ¼ 2025), 296 nm (" ¼ 2068), and 263 nm
(" ¼ 1138). The absorption spectra of complexes show three bands, 1 at 426 nm
3
(" ¼ 5650) and 2 at 421 nm (" ¼ 6320) (Band 1 are assigned to T1g 3A2g transitions
for an octahedral environment [29]). Band 1 is expected to be sensitive to the nature of
the axial ligand DMF [30, 31]. Band 2 of 1 and 2 display two clear absorptions at 334
nm (" ¼ 3340) and 329 nm (" ¼ 6210), respectively, attributed to metal-ligand charge
transfer. They exhibit blue-shift compared with the free ligand absorption at 338 nm.
The molar absorption coefficient of 2 at 329 nm is nearly twice as much as 1 at 334 nm,
showing that reductive capacity of Mn ions are stronger than Ni ions. Compared with
the ligand, complexes have high-intensity absorption above 300 nm, suggesting large
conjugated system. The third band, 1 at 267 nm (" ¼ 6450) and 2 at 266 nm (" ¼ 5280),
both have strong absorption due to the n–ꢃ* transition in the ligands. Despite the UV
spectra shape of 1 and 2 being similar, the maximum absorption of 1 is at 267 nm, while
Figure 10. Room temperature UV spectra of H2L (line 1, 4 ꢂ 10–5 mol L–1), 1 (line 2, 1 ꢂ 10–5 mol L–1) and 2
(line 3, 1 ꢂ 10–5 mol L–1) in DMF.

4370
Y. Wang et al.
Figure 11. Room temperature fluorescence emission spectra of H2L (line 1, 4 ꢂ 10–5 mol L–1), 1 (line 2,
1 ꢂ 10–5 mol L–1) and 2 (line 3, 1 ꢂ 10–5 mol L–1) in DMF.
that of 2 is at 421 nm. ESI-MS spectra prove that neither 1 nor 2 exists with tetranuclear
grid coordination in methanol/water (Vmethanol : Vwater ¼ 80 : 20) solution (for solubility
plus ESI compatibility), which is different from [Cu2Mn2(pop)4(OAc)4] ꢀ 7H2O reported
by Moroz et al. [9]. The difference is mainly due to the axial DMF molecules in grids
replaced by more polar water, which leads to tetranuclear lattice transforming into
mono- or di-nuclear complexes.
At room temperature, the comparison of fluorescence emission spectra for H2L, 1
and 2 is given in figure 11. Fluorescence data were collected in DMF with fluorophore
concentrations of 1 ꢂ 10–5 mol Lꢃ1. Around 540 nm is a fluorescence peak which is
generated by the ligand structure itself, and the fluorescence peak position of 1 is
consistent with 2. A comparison of the three spectra (figure 11) reveals significant
quenching of the emission intensity of 1 and 2. Because of the conjugated enol-type
hydrazone in complexes, each metal is connected with a pyridine ring and benzene ring.
After formation of complexes, the overall grids become larger conjugated clusters.
Raising the conjugated degree of ꢃ electrons enhances the delocalization of ꢃ electrons,
reducing the energy barrier required by system transition and the conjugated system.
Increasing the rigidity of plane weakens the vibration of molecules so that the excited
energy of molecules cannot be easily released by thermal energy.
4. Conclusions
Halogen–hydrogen interactions are the least studied variety of weak hydrogen bonds
and in this work we have an experimental approach to the nature of these interactions

Two grid complexes
4371
in grid complexes. Herein, we designed and prepared two grid complexes,
[Ni4(L)4(DMF)4] ꢀ 2H2O (1) and [Mn4(L)4(DMF)4] (2), with H2L (3,5-dichlorosalicy-
laldehyde pyridine-2-formyl hydrazone). X-ray crystal structures reveal that they have
very similar configuration. In 1 and 2, intermolecular C–H ꢀ ꢀ ꢀ Cl hydrogen-bonding
interactions result in a 2-D network and a 3-D supramolecular assembly, respectively.
Chlorides as substituent groups have some influences on promoting the stacking of
complexes, which is a driving force for intermolecular recognition.
The properties of two grids are compared herein. Neither 1 nor 2 exists with
tetranuclear grid coordination in methanol/water solution. Their UV-Vis spectra and
fluorescence emission spectra at room temperature have a similar pattern, which leads
to significant quenching of the emission intensity compared to H2L. Their distinctly
different TG analyses suggest that the coordinated DMF in 1 and 2 possess different
chemical environments. Clearly, L combining with Ni2þ is more symmetrical than that
of 2, which is consistent with the difference of their crystal structure.
Supplementary material
Crystallographic data (excluding structure factors) for the structures reported in this
article have been deposited with the Cambridge Crystallographic Data Center as
Supplementary Publication Nos CCDC-724385 (1) and CCDC-724386 (2). Copies of
the data can be obtained free of charge on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK, Fax: þ44 1233 336 033; E-mail: deposit@ccdc.cam.ac.uk.
Acknowledgments
The authors thank the Key Laboratory of Environmental Engineering, Protection, and
Assessment of Guangxi, the National Water Pollution Control and Management of
China (No. 2008ZX07317-02), and the Program to Sponsor Teams for Innovation in
the Construction of Talent Highlands in Guangxi Institutions of Higher Learning
(GuiKeRen 2007-71) for the financial support.
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