A New 3D Coordination Polymer Based on Pentanuclear Cd(II) Rod-Shaped Secondary Building Unit: Synthesis, Crystal Structure and Luminescent Property
Hua-Rui Wang
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Jian-Ge Wang
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H.-R. Wang (&) J.-G. Wang College of Chemistry and Chemical Engineering, Luoyang Normal University
, Luoyang 471022, People
A new coordination polymer [Cd2.5(l3OH)(L)2(bipy)]n (1). (L = 1,2-naphthalene dicarboxylate, bipy = 4,40-bipyridine), was obtained under hydrothermal condition. The structure of 1 has been determined by single-crystal X-ray diffraction analysis and further characterized by elemental analysis and IR spectrum. Singlecrystal X-ray diffraction analyses reveal that complex 1 crystallizes in triclinic system, P space group. Complex 1 possesses a 3D pcu net based on a pentanuclear Cd(II) cluster. Each pentanuclear Cd(II) cluster links with neighboring ones and generates a rod-shaped secondary building unit, which is further extended by bipy ligands to forms a three-dimensional network. Furthermore, the luminescent properties of this complex and the free ligand have been investigated. Complex 1 can be excited directly and emit strong soild-state fluorescence at room temperature, which may make them excellent candidates for fluorescent materials. During the past two decades, metal-organic frameworks (MOFs), as an important class of crystalline solid materials, have received tremendous attention because of their potential in various applications, such as gas adsorption
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and separation, catalysis, drug delivery, electrochemistry,
molecular recognition, sensing, and detection [113]. The
major task of the synthesis for such MOFs is to choose
appropriate metal-connecting nodes and organic bridging
ligands to control the formation of these complexes with
required structures and properties. Among this topic realm,
as an attractive subarea, homometallic cluster chemistry
has been a small but growing family in recent years. In this
case, homometallic cluster as secondary building units
(SBUs) have been proved as an effective and powerful
synthetic strategy in constructing new MOFs [14].
Depending on their architecture, MOFs based on
polynuclear metallic units offer potential for unique properties,
such as luminescence, magnetism and catalysis [15].
When the coordination number and geometry of metal
centers are relatively fixed, organic ligands acting as
bridging linkers to connect metal centers play the essential
role [16]. From the point of view of organic ligand design,
it is desirable to synthesize bulky ligands that have the
coordinating atoms pointing on one side of the molecule,
this favoring isolation of diverse discrete (dinuclear,
tetranuclear, pentanuclear, or hexanuclear) and infinite (1D,
2D, or 3D) structures [17]. Following this strategy, the
aromatic chelate ligand phthalic acid has been used as a
good ligand for the construction of coordination polymers
with polynuclear clusters due to the ability to bind more
metals and isolate discrete metal cluster. For example, one
decanuclear manganese [18] and three uranyl [19]
compounds have been reported by G. Christou, in the presence
of phthalate. To investigate the influence of bulky aromatic
skeletons of such ligands on structures and properties of
their coordination complexes, the naphthalene-based
dicarboxyl ligand 1,2-naphthalene dicarboxylic acid (H2L),
an expansion of phthalic acid, was chosen as the organic
ligand in our recently work. To date, coordination
Table 1 Crystallographic data and structure refinement parameters
for complex 1
polymers constructed from the L ligand have rarely been
synthesized. Also, the introduction of naphthalene based
ligands into coordination polymers might lead to
interesting luminescence properties of the final product. In this
paper, we report the syntheses and characterizations of one
coordination polymers [Cd2.5(l3-OH)(L)2(bipy)]n (1) based
on 1,2-naphthalene dicarboxylic acid and 4,40-bipyridine.
To our interest, this complex consists of pentanuclear
Cd(II) rod-shaped SBUs and exhibits interesting
luminescent properties.
2 Experimental Section
2.1 General Procedures
All chemicals and reagents were used as received from
commercial sources without further purification. All
reactions were carried out under hydrothermal conditions.
Elemental analyses (C, H, N) were determined with a
Elementar Vario EL III elemental analyzer; IR spectra
were recorded as KBr pellets on a Bruker EQUINOX55
spectrophotometer in the 4000400 cm-1 region.
Fluorescence spectra were performed on a Hitachi F-4500
fluorescence spectrophotometer at room temperature. The
X-ray powder diffraction pattern was recorded with a
Pigaku D/Max 3III diffractometer.
2.2 Synthesis of Complex
[Cd2.5(l3-OH)(L)2(bipy)]n (1)
A mixture of H2L (10.8 mg, 0.05 mmol), Cd(OAc)2 2H2O
(26.6 mg, 0.1 mmol), bipy (15.6 mg, 0.1 mmol) and KOH
(5.6 mg, 0.1 mmol) were added to water (12 mL) in a
25 mL Teflon-lined stainless steel vessel. The mixture was
heated at 180 C for 4 days. After the reactive mixture was
slowly cooled to room temperature, colorless block crystals
of 1 were obtained (yield: 50 %, based on Cd). Anal. C (...truncated)