Tetraaquabis(1,10-phenanthroline)bis[μ2-1H-pyrazole-3,5-dicarboxylato(3−)]tricopper(II) dihydrate

The title compound, [Cu3(C5HN2O4)2(C12H8N2)2(H2O)4]·2H2O, is a trinuclear copper(II) complex in which two centrosymmetrically related pyrazole-3,5-dicarboxylate(3−) and 1,10-phenanthroline ligands bind three CuII atoms, with one CuII atom located on a center of symmetry. In each complex, there are four coordinated water molecules and two solvent water molecules, which participate in extensive hydrogen-bond patterns. These interactions, as well as π–π interactions between neighbouring 1,10-phenanthroline ligands [shortest atom-to-atom distance = 3.363 (3) Å], extend the crystal structure into a three-dimensional supramolecular network.


Related literature
For the potential applications of novel coordination architectures as new classes of materials, see: Kitagawa et al. (2004). The potential coordination sites of 3,5-pyrazoledicarboxylate are highly accessible to metal ions, see: Li (2005). However, divalent copper ions have rarely been coordinated with 3,5pyrazoledicarboxylic acid at ambient temperature, see: King et al. (2003).

Comment
The design and synthesis of novel coordination architectures has attracted wide attention because of their intriguing network topologies and potential applications as new classes of materials (Kitagawa et al., 2004). 3,5-pyrazoledicarboxylate has several potential coordination sites: both nitrogen atoms of the pyrazole ring and the four carboxylate oxygen atoms, which are highly accessible to metal ions (Li, 2005). However, divalent copper ions have rarely been coordinated with 3,5pyrazoledicarboxylic acid under ambient temperatures (King et al., 2003). In this study, we chose 3,5-pyrazoledicarboxylic acid and 1,10-phenanthroline as mixed ligands to obtain blue crystals of the title compound (I), which as shown in Fig. 1 is a copper(II) trimer.
The central copper atom, Cu(1), lies on a crystallographic inversion center, and has a six-coordinate octahedral geometry, in the which two oxygen atoms and two nitrogen atoms from two 3,5-pyrazoledicarboxylate ligands occupy the equatorial plane. The axial coordination sites are occupied by two water molecules. The Cu(1)-N/O bond distances span a very large range from 1.974 (5) to 2.595 (5) Å. The other two symmetry-related copper atoms, Cu(2), have pentacoordinate square-pyramidal geometry: a pyrazole nitrogen N(2) and a carboxylate oxygen O(3) from one 3,5-pyrazoledicarboxylato ligand occupy two coordination sites, two nitrogen atoms from one 1,10-phenanthroline chelate the Cu(2) atoms, while the remaining position is occupied by a water molecule. The Cu(2)-N/O bond distances range from 1.979 (6) to 2.171 (5) Å.
The 3,5-pyrazoledicarboxylate ligand is nearly planar, with greatest deviation from the mean plane defined by the pyrazole ring by the carboxylate groups with values ranging from 0.0015 (1) to 0.0937 (1) Å. It can be seen that the ligand bite angles at the two different copper centers Cu(1) and Cu(2) are similar, 80.9 (3)° and 82.5 (4)°, respectively. This implies that the 3,5-pyrazoledicarboxylate ligand is a fairly rigid ligand and retains its integrity on metal chelation.
In the asymmetric unit, there is one lattice water molecule, O(7), and because each trimer contains four coordinated water molecules and carboxylate oxygen atoms, a complex network of hydrogen-bonding interactions is formed. Each 3,5-pyrazoledicarboxylato contains four hydrogen bond acceptors, while each coordinated water molecule acts as both a two hydrogen bond donor and a hydrogen bond acceptor, and the lattice water molecule is only a two hydrogen bond donor. In the crystal structure, π-π interactions also exist between neighbouring 1,10-phenanthroline ligands, with the nearest atom-to-atom distance between neighbouring 1,10-phenanthroline ligands being 3.363 (3) Å. The strong hydrogen bonding interactions as well as π-π interactions extend the crystal structure into a three-dimensional supramolecular network (Fig. 2).

Experimental
The title complex was prepared by the addition of Cu(BF 4 ) 2 (20 mmol), 1,10-phenanthroline (30 mmol) and 3,5-pyrazoledicarboxylic acid (30 mmol) to 40 ml water. The mixture was stirred for 1 h, a blue precipitate was obtained. A minimum amount of ammonia (14 M) was added to give a blue solution. Suitable crystals were obtained after standing at room temperature for several days (yield 42% based on Cu). supplementary materials sup-2 Refinement H atoms were placed geometrically and refined with fixed individual displacement parameters [U iso (H) = 1.2U eq (C,N)], using a riding model, with a C-H distance of 0.93 Å. The H atoms bonded to O atoms of water molecules were located in a difference Fourier map and refined with fixed individual displacement parameters U iso (H) = 1.2U eq (O). Fig. 1. A view of (I), with the atom-labeling scheme and 30% probability displacement ellipsoids. [Symmetry code: (A) 1 -x, 1 -y, 1 -z.] For clarity the lattice water molecules have been omitted.