Diaquadi-μ-formato-bis{μ-2,2′-[propane-1,3-diylbis(nitrilomethanylylidene)]diphenolato}cadmium(II)dinickel(II) dihydrate

In the centrosymmetric title compound, [CdNi2(C17H16N2O2)2(HCOO)2(H2O)2]·2H2O, The NiII cation is chelated by a 2,2′-[propane-1,3-diylbis(nitrilomethanylylidene)]diphenolate (salpn) anion, and further coordinated by a formate anion and a water molecule in a distorted NiN2O4 octahedral geometry. The CdII cation, located on an inversion center, is coordinated by four deprotonated hydroxy groups from two salpn anions and two carboxylate O atoms from formate anions in a distorted octahedral geometry. Both formate and salpn anions bridge the Cd and Ni cations, forming a trinuclear complex. Within the salpn anion, the benzene rings are twisted to each other at a dihedral angle of 61.46 (18)°. Intermolecular O—H⋯O hydrogen bonding is present in the crystal structure. The lattice water molecule is disorder over two positions with an occupancy ratio of 0.75:0.25.


Jian-Feng Zhang, Bo Wan, Wen Liu and Qian Shi Comment
The molecular design and synthesis of Ni(II) complexes with the salen type Schiff-base ligands have attracted much attention in the past few years (Niederhoffer et al., 1984;Tisato et al., 1994;Yamada, 1999). Hererin we reported the structure of the title complex containing the Schiff base compound, N,N′-bis(salicylidene)-1,3-propanediaminato (salpn).
In the compound, the formate anion may be generated from the decomposition of DMF solvents in solvothermal conditions, it has been reported by Wang et al. (2004) and by Zhang et al. (2007) previously.
In the title compound, the Cd(II) ion is situated on an inversion centre and two terminal Ni(II) ions are located on the symmetrical sides, forming a linear Ni-Cd-Ni trinuclear complex (Fig. 1). The Cd(II) ion has a distorted octahedral

Refinement
All H atoms were positioned geometrically with C-H = 0.93 (aromatic), 0.97 Å (methylene) and O-H = 0.85 Å, and allowed to ride in their parent atoms with U iso (H) = 1.2U eq (C) or 1.5U eq (O). The lattice water molecule is disorder over two sites, occupancies were fixed as 0.75 and 0.25 for two components.

Figure 1
The molecular structure of the title compound showing displacement ellipsoids at 30% probability level [symmetry code:

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.