HYDROTHERMAL SYNTHESIS AND CHARACTERIZATION OF A BINUCLEAR COMPLEX AND A COORDINATION POLYMER OF COPPER(II).

Two new copper complexes [(bipy)(pydc)Cu(µ-OCO-pydc)Cu(bipy)(H2O)].3.5H2O (1) and {[(µ 2-
C2O4)(2,2'-bipy)Cu].2H2O}n (2) (pydcH2 = pyridine-2,6-dicarboxylilic acid, bipy = 2,2'-bipyridine) have been hydrothermally synthesized. Both complexes were characterized by IR spectroscopy, elemental analysis and single crystal X-ray diffraction studies. Complex 1 consists of two independent neutral molecules. In every moiety, metal ion center is in a distorted octahedral geometry. Coordination polymer (2) has been prepared from the reaction of bis-(cyclohexanone)-oxal-dihydrazone,2,2'-bipyridine and Cu(NO3)2 in basic solution and under hydrothermal condition. The results showed that the bis-(cyclohexanone)-oxal-dihydrazone was converted to oxalate ion under heating and basic pH. Each metal ion center in 2 is in a distorted octahedral geometry and is coordinated by four oxygen atoms of two bridged oxalate ions and two nitrogen atoms of 2,2'-bipyridine molecules. In the crystal structure of 2, some H-bonds and π-π interaction cause formation of a 3D network.
Hydrothermal synthesis refers to the synthesis by chemical reaction of substances in a sealed
heated solution above ambient temperature and pressure. This technique provides a powerful
tool for the construction of materials containing unique structures and special properties [1].
This method with an aqueous solvent as a reaction medium is environmentally friendly since the
reactions are carried out in a closed system [2, 3]. Hydrothermal synthesis has been successful
for the preparation of some solids such as microporous crystals [4], super ionic conductors [5],
chemical sensors [6], complex oxide ceramics and fluorides [7, 8], materials including
nanometer particles [2, 9] and transition metal complexes [10-13]. The molecular structures of
complexes obtained by this method are unexpected compared to those obtained by the common
solution methods [13, 14]. Polycarboxylate ligands have attracted interest as a potential bridging ligand with a variety of connection modes with transition metal centers and abundant structural motifs [13, 15-18]. Recently, we reported hydrothermal synthesis of binuclear Co(II) complex [19] and a new complex of La III -ion with bridged benzene-1,2,4,5-tetracarboxylate ligand [20]. In continuation of our research on synthesis of transition metals complexes containing polycarboxylate ligands [21, 22], in the present work, herein we report the syntheses and crystal structures of two new complexes of Cu(II) with bridged carboxylate groups, [(bipy)(pydc)Cu(µ-OCOpydc)Cu(bipy)(H2O)].3.5H2O (1) and {[(µ 2 -C2O4 ) (2,2'-bipy) Cu].2H2O}n (2).

All the purchased chemicals were of reagent grade and used without further purification. IR
spectra were recorded using FTIR Spectra Bruker Tensor 27 spectrometer (Germany) (KBr
pellets, nujol mulls, 4000-400 cm -1 ). Elemental analyses were performed using a Costech ECS 4010 CHNS-O analyzer (Italy).

Preparation of [(bipy)(pydc)Cu(µ-OCO-pydc)Cu(bipy)(H2O)].3.5H2O (1)
Pyridine-2,6-dicarboxylic acid (0.167 g, 1 mmol) was dissolved in methanol (5 mL) and a
solution of NaOH (0.04 g, 1 mmol) in deionized water (15 mL) was added and stirred for 30
min at room temperature. Then an aqueous solution of Cu(NO3)2.3H2O (0.241 g, 1 mmol) and
2,2'-bipyridine (0.156 g, 1 mmol) was added above-mentioned solution. Reaction mixture was
placed in a Parr-Teflon lined stainless steel vessel. It was sealed and heated to 110 °C for 24 h.
The reaction mixture was gradually cooled by slow cooling to room temperature. The mother
liquid was kept at 4 °C until the blue crystals of 1 suitable for X-ray diffraction were obtained.
IR (KBr) (ν, cm-1): 3454 (O–H, water), 3030 (C–H, Ar), 1662 and 1630 (C=O, carboxylate),
1381 (C=O, carboxylate), 775–771 (2,2'-bipyridine). Anal. calcd. for C34H31Cu2N6O12.5: C,
47.93, H, 3.64, N, 9.87. Found: C, 47.88, H, 3.59, N, 9.82.

Preparation of {[(µ 2-C2O4)(2,2'-bipy)Cu] .2H2O}n (2)
bis(1,5-Cyclohexanone) oxal dihydrazone (0.139 g, 0.5 mmol) was dissolved in mixture of
water/ethanol (1:1, 25 mL). Then NaOH (0.01 g, 0.25 mmol) was added and stirred for 30 min
at room temperature. In next stage, Cu(NO3)2
.3H2O (0.12 g, 0.5 mmol) and 2,2'-bipyridine
(0.04 g) were added. Reaction mixture was placed in a Parr-Teflon lined stainless steel vessel. It
was sealed and heated to 120 °C for 17 h, then cooled by slow cooling to room temperature. The
resultant solution was kept at 4 °C. Blue crystals of 2 were obtained after two weeks. IR (KBr)
(ν, cm-1): 3422 (O–H, water), 3066 (C–H, Ar), 1658, 1310–1298 and 830 (bridging oxalate), 730–724 (2,2'-bipyridine). Anal. calcd. for C12H12Cu N2O6: C, 41.89, H, 3.49, N, 8.14. Found: C, 41.80, H, 3.41, N, 8.09.

In order to see the full paper: http://www.ajol.info/index.php/bcse/article/viewFile/60687/48915