The first heterometallic Cu(II)/Cr(III) complex with an open-chain Schiff-base ligand self-assembled from copper powder, Reineckes salt, ethylendiamine and acetone

A novel supramolecular assembly [{Cu(enac)}2Cr(NCS)4(NH3)2][Cr(NCS)4(NH3)2]3 · 4(CH3)2CO (enac = 4,6,6-trimethyl-3,7-diazanon-3-ene-1,9-diamine), the first example of a Cu/Cr heterometallic compound containing a Schiff-base ligand such as enac, and an anion of Reineckes salt, Cr(NCS)4(NH3)2−, as a building block, was obtained by the self-assembly reaction of copper powder and Reineckes salt in an acetone/methanol (1:4) solution of ethylenediamine in the open air. An X-ray study shows that the complex includes a trinuclear Cu2Cr cation, constructed from two Cu(enac)2+ moieties and a trans-[Cr(NCS)4(NH3)2]− block as a two-linking bridging ligand. The metal–metal separations within the cation are Cu⋯Cr = 6.393(31) Å and Cu⋯Cu = 12.786(63) Å. The supramolecular architecture of the complex involves two types of H-bonded chains, the first chain is generated by trinuclear cations [{Cu(enac)}2Cr(NCS)4(NH3)2]2+, [Cr(NCS)4(NH3)2]− anions and (CH3)2CO molecules, while the second by crystallographically different anions of Reineckes salt and (CH3)2CO. Variable-temperature (1.8–300 K) magnetic susceptibilities show a slight change of the μB value at low temperature, indicative of weak antiferromagnetic interactions (JCuCr = −0.9 cm−1) between the paramagnetic centers.

Graphical abstractThe one-pot self-assembly reaction of copper powder and Reineckes salt in an acetone/methanol solution of ethylendiamine in the open air affords the novel heterometallic complex [{Cu(enac)}2Cr(NCS)4(NH3)2][Cr(NCS)4(NH3)2]3 · 4(CH3)2CO (enac = 4,6,6-trimethyl-3,7-diazanon-3-ene-1,9-diamine). The structural features, as well as spectroscopic and magnetic properties, are reported.Figure optionsDownload full-size imageDownload as PowerPoint slide