A unique chain of trinuclear Cu(II) units containing both neutral and anionic N-(pyrimidin-2-yl) acetamide (Haapm, resp. aapm) as a ligand and dicyanamide (dca): Synthesis, characterization, X-ray structure and magnetism of [Cu 3(μ-aapm) 2(μ-dca) 2(Haapm) 2](CF 3SO 3) 2

Abstract

The synthesis, crystal structure, as well as the electronic and magnetic properties, of a new trinuclear-based Cu(II) compound [Cu 3(μ-aapm) 2(μ-dca) 2(Haapm) 2](CF 3SO 3) 2, containing the ligands N-(pyridin-2yl)acetamide (Haapm) and dicyanamide (dca) is reported. The central Cu1 atom has a distorted elongated octahedral coordination with the basal plane comprised of two nitrogens from two different tetrachelating dehydronated aapm ligands and two nitrogen atoms of two dca anions (Cu–N distances 2.016(2) and 1.988(3) Å). The apical positions are occupied by two nitrogen atoms of the two different tetrachelating aapm ligands (Cu–N distance 2.539(3) Å), with a trans angle of 180°. Also the N–Cu–N angle is extremely small (58.25(9)°), due to the four-membered chelate ring. The outer Cu2 ions have also a distorted octahedral geometry with the basal plane formed of two nitrogens and two oxygen atoms from a tetrachelating dehydronated aapm ligand (which is bridging between Cu1 and Cu2) and from a Haapm ligand (Cu–N/O distances vary from 1.95.4(2) and 2.022(2) Å), with basal angles of 177.29(9)° and 171.12(8)°. The apical positions are occupied by an oxygen atom of a triflate anion (Cu–O distance 2.534(3) Å) and a nitrogen atom of a neighbouring dca anion (Cu–N distance 2.314(3) Å), with an angle of 171.92(8)°. The Cu–Cu distance within the trinuclear unit is 5.23 Å. The dca anions are connected in an end-to-end fashion to a neighbouring Cu(II) ion (Cu–Cu distance 8.54 Å), forming in this way a chain of trinuclear units bridged by two dca anions. The EPR as a powdered solid revealed a weak S = 1 triplet spectrum at RT. The magnetic susceptibility measurements, measured from 5 to 200 K, revealed a weak ferromagnetic interaction between the Cu(II) ions.