Discrete water clusters in tetra-μ-cyanido-tetracyanidobis(1,4,7-triisopropyl-1,4,7-triazacyclononane)dicopper(II)dinickel(II) tetrahydrate

The title tetracyanidonickelate–copper complex, [Cu2Ni2(CN)8(C15H33N3)2]·4H2O, was synthesized by self-assembly using potassium tetracyanidonickelate(II) and dichlorido(1,4,7-triisopropyl-1,4,7-triazacyclononane)copper(II). The asymmetric unit contains half of a complex molecule and two water molecules. The entire complex has -1 symmetry and contains Ni(II) in a slightly distorted square-planar and Cu(II) in a square-pyramidal coordination environment. The crystal packing shows a discrete tetramer water cluster. Within the cluster, the four water molecules are fully coplanar and each water monomer acts both as single O—H⋯O and O—H⋯N hydrogen-bond donor and acceptor.

The asymmetric unit contains half of a complex molecule and two water molecules. The entire complex has 1 symmetry and contains Ni(II) in a slightly distorted square-planar and Cu(II) in a square-pyramidal coordination environment. The crystal packing shows a discrete tetramer water cluster. Within the cluster, the four water molecules are fully coplanar and each water monomer acts both as single O-HÁ Á ÁO and O-HÁ Á ÁN hydrogen-bond donor and acceptor.

Related literature
For properties and applications of cyanide-bridged coordination complexes, see: Zhao et al. (2009) ;Dunbar & Heintz (1997); Orendac et al. (2002). For the use of the tetracyanidonickelate anion as a bridging ligand in the construction of one-, two-and three-dimensional structures, see: Bozoglian et al. (2005); Maji et al. (2001); Dunbar & Heintz (1997); Č erná k et al. (1988,1990); Č erná k & Abboud (2000). For the influence on water aggregations of the overall structure of their surroundings, see: Long et al. (2004); Xantheas (1995). For water clusters, see: Ugalde et al. (2000); Gregory & Clary (1996). For the synthesis of the ligand, see: Hay & Norman (1979). Chen et al. (2009 Table 1 Hydrogen-bond geometry (Å , ). In recent years, much attention has been paid to assemble cyanide-bridged coordination complexes because of their promising properties and applications including electronics, magnetism and catalysis (Zhao et al., 2009;Dunbar & Heintz, 1997;Orendac et al., 2002), in which tetracyanonickelate complexes have also become the focus. On the one hand, diamagnetic [Ni(CN) 4 ] 2is an excellent model for magnetic studies which bridge paramagnetic ions, but on the other hand the tetracyanonickelate anion, as a bridging ligand, can be used to construct one-dimensional, twodimensional and three-dimensional structures (Bozoglian et al., 2005;Maji et al., 2001;Dunbar & Heintz, 1997;Černák et al., 2000;1988;. Low-dimensional cyanide-bridged complexes based on [Ni(CN) 4 ] 2form a new family of molecular magnetic materials. However, the use of macrocyclic ligands as terminal group to control the low-dimensional structure is still relatively rare. On the other hand, water clusters can play an important role in the stabilization of supramolecular systems both in solution and in the solid state, and there is clearly a need for a better understanding of how such water aggregations are influenced by the overall structure of their surroundings (Long et al., 2004;Xantheas, 1995). In the past several decades, considerable attention has been focused on theoretical and experimental studies of small water clusters to understand the structures and characteristics of liquid water and ice (Ugalde et al., 2000;Gregory et al., 1996).

Refinement
A total of 6 similarity restraints were used for the H atoms of the water molecules which were initially refined with fixed O-H distances of 0.85 Å and 1.2U eq (O). The other H atoms were placed in calculated positions and refined as riding on the parent C atoms with C-H = 0.93-0.97 Å and U iso (H) = 1.2 U eq (C).

Figure 1
The molecular structure of 1 showing 30% probability displacement ellipsoids for non-H atoms. The second half of the molecule is generated by symmetry code -x, -y -1, -z -1. Stacking diagram of 1 and hydrogen bonding in the water cluster (symmetry code A: 1 -x, 1 -y, -z).

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq