Crystal structure of di-μ-acetato-diacetatobis(μ-6,6′-dimethoxy-2,2′-{[(propane-1,3-diylbis(azanylylidene)]bis(methanylylidene)}diphenolato)tetrazinc

The tetranuclear title complex, [Zn4(C19H20N2O4)2(CH3COO)4], is formed from two dinuclear motifs related by an inversion centre. The two crystallographically independent ZnII ions in the asymmetric unit are in different coordination environments. One is square-based pyramidal with one O atom of an acetate group occupying the axial position and two N and O atoms of one bmspd [H2bmspd = N,N′-bis(3-methoxysalicylidene)propylene-1,3-diamine] Schiff base ligand forming the basal plane. The other ZnII atom is six-coordinated by four O atoms of the bmspd ligand forming the equatoral plane and two O atoms of different acetate groups located in the axial positions. As a result, the two phenolic planes of the bicompartmental Schiff base ligand are distorted slightly. However, the planes of the two Schiff base ligands are parallel. In addition, the Zn—N and Zn—O bond lengths span the reasonable ranges 2.062 (2)–2.073 (2) and 1.9261 (15)–2.4356 (16) Å, respectively. The Zn⋯Zn distances separated by phenolic O atoms are 3.2466 (4) Å while the Zn⋯Zn distances bridged by acetate groups are 5.9835 (6) Å. The tetranuclear moieties are connected by van der Waals interactions, and form a chain along c axis.

The compound is composed of two [Zn 2 (bmspd)(OAc))] + ions bridged by two acetate ions. There are two kinds of symmetry-independent zinc ions in this compound. One zinc ion (Zn1) is located in a five-coordinated environment, as shown in Figure 1. The other kind of zinc ion (Zn2) is coordinated by the O 4 cavity in bmspd ligand and two oxygen atoms of acetate ions in pseudo-octahedral geometry. The neighbouring tetranuclear molecules form a two-dimensional supramolecular network by virtue of intermolecular π-π interactions. (Figure 2)

S2. Experimental
A mixture of metal-free Schiff-base ligand H 2 bmspd (0.4 mmol 0.1368 g) and Zn(OAc) 2 ·2H 2 O (0.4 mmol 0.0878 g) in methanol (20 ml) was stirred for 30 min at room temperature. Then, a solution of Zn(OAc) 2 ·2H 2 O (0.4 mmol 0.0878 g) in methanol was added dropwise and the mixture was kept stirring for another 30 min at room temperature. Pale yellow block-shaped crystals for suitable for X-ray diffraction were obtained by slowly diffusing diethyl ether into the filtrate.
The final mass of product was 0.0966 g.

S3. Refinement
The coordinates of the difference H atoms bound to C atoms were placed using the HFIX commands in SHELXL-97, with C-H distances of 0.93-0.97 Å. All H atoms were allowed for as riding atoms with U iso (H) = 1.2U eq (C) or 1.5U eq (C). The orientation of hydrogen atoms of methyl groups of acetate was allowed to refine subject to geometric restraints.

Di-µ-acetato-diacetatobis(µ-6,6′-dimethoxy-2,2′-{[(propane-1,3diylbis(azanylylidene)]bis(methanylylidene)}diphenolato)tetrazinc
Crystal data  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.