Bis{μ-2-[(pyridin-2-yl)iminomethyl]phenolato}bis[(2-formylphenolato)copper(II)]

The asymmetric unit of the title compound, [Cu2(C12H9N2O)2(C7H5O2)2], contains two independent (2-formylphenolato){2-[(pyridin-2-yl)iminomethyl]phenolato}copper(II) molecules that form pseudocentrosymmetric dimers via interactions between the Cu and pyridyl N atoms of independent monomers. The square-planar geometry of the Cu atoms in the monomer thus becomes square-based pyramidal in the dimer. The crystal studied was an inversion twin, with unequal populations of 0.353 (17) and 0.647 (17).


Experimental
Crystal data [Cu 2 (C 12  Intermolecular contacts are present between the copper(II) atoms and pyridyl nitrogen atoms (2.482 (4)Å and 2.469 (4) Å) with angles between the Cu-N contact and the plane of the pyridyl group observed to be 157.1 (5)° and 150.4 (5)°.
These contacts appear to be the predominant cause of dimer formation since there is no evidence for any other significant intermolecular interactions. The bonding between the salicylaldehyde ligand and the copper atom can be compared to the two known polymorphs of homoleptic bissalicylaldehydatocopper(II), one described with the symmetry of P2 1 /n (McKinnon et al., 1964), and the other as P2 1 /c (Hall et al., 1965). The Cu-O bonds Cu1-O2 and Cu2-O5 in the title compound are observed to be 1.917 (3)Å and 1.918 (3)Å respectively, which is longer than the values of the equivalent bonds in the two polymorphs of bissalicylaldehydatocopper(II) where Cu-O1 is 1.86Å in the P2 1 /n polymorph and 1.90Å in the P2 1 /c polymorph. The Cu-O bonds Cu1-O3 and Cu2-O6 in the title compound are observed to be 2.022 (3)Å and 2.019 (3)Å respectively, also longer than the values of the equivalent bonds in the two polymorphs of bissalicylaldehydatocopper (II) where Cu-O2 is 1.98Å in the P2 1 /n polymorph and 1.94Å in the P2 1 /c polymorph. Additionally, the ligand bite-angles O2-Cu1-O3 and O5-Cu2-O6 are observed to be 91.05 (14)° and 90.89 (14)° respectively, lower than the equivalent angle O1-Cu-O2 in both of the known polymorphs of bissalicylaldehydatocopper(II), which are observed to be 94.8° in the P2 1 /n polymorph and 95° in the P2 1 /c polymorph. Bond distances from the copper atom to the 2-pyridylsalicylaldimine ligand are observed to be smaller than observed in a (2-pyridylsalicylaldimine)copper(I) tetramer (Drummond et al., 1972).
In the title compound the bond lengths Cu1-O1 and Cu2-O4 are observed to be 1.916 (4)Å and 1.914 (3)Å respectively, shorter than the equivalent bond length Cu1-O1 in the (2-pyridylsalicylaldimine) copper(I) tetramer which is observed to be 1.965 (6) Å. The Cu1-N1 and Cu2-N3 bond lengths in the title compound, which are observed to be 2.022 (4)Å and 2.022 (4)Å respectively, can be compared to the equivalent bond length Cu1-N1 in the (2-pyridylsalicylaldimine) copper(I) tetramer, which is observed to be 1.975 (8) Å, shorter than those observed in the title compound. These differences can be attributed to the lower oxidation state of copper in the (2-pyridylsalicylaldimine) copper(I) tetramer compared to that in the title compound.

Experimental
A suspension of bis(2-pyridylsalicylaldimine)copper(II) (1 mg, 0.0022 mmol) in methanol (ca. 3 ml) was heated to ca. 323 K until fully dissolved. The solution was then allowed to cool to room temperature. Crystals suitable for single-crystal X-ray crystallography were grown via slow evaporation of methanol over seven days.
supplementary materials sup-2 Figures Fig. 1. The structure of the asymmetric unit of the title compound with displacement ellipsoids drawn at the 50% probability level.