Syntheses, crystal structures and magnetic properties of copper(II) polynuclear and dinuclear compounds with 2,3-bis(2-pyridyl)pyrazine (dpp) and pseudohalide as ligands

The preparation, crystal structures and magnetic properties of four heteroleptic copper(II) complexes with 2,3-bis(2-pyridyl)pyrazine (dpp) and azide, cyanate or thiocyanate as ligands are reported, [Cu(dpp)(N-3)(2)](n) (1), [Cu(dpp)(NCO)(2)](n) (2), [Cu(dpp)(NCS)(2)](2) (3) and [Cu(H2O)(dpp)(NCS)(2)](2). 2H(2)O (4). Compounds 1 and 2 are isomorphous, triclinic, space group P (1) over bar, and consist of mononuclear building blocks featuring copper atoms with close to square planar coordination geometries. The mononuclear units are, however, associated into chains through weak axial Cu-N bonds formed by end-on asymmetrically bridging azido/cyanato groups and by pyridyl nitrogen atoms. Taking these contacts into account, copper may be described as elongated octahedral. Compound 3 is monoclinic, space group P2(1)/c. The mononuclear building blocks are similar to those in 1 and 2, but in this case the association between these units is such as to form dinuclear molecules through end-to-end bridging thiocyanate with weak axial Cu-S bonds, yielding a square pyramidal environment of copper, Compound 4 is triclinic, space group P (1) over bar, and features a mononuclear unit which contains an apically coordinated water molecule. This leads to a significantly weaker intermolecular (CuS)-S-... contact as compared to that found in 3, but an association into dinuclear units is structurally and magnetically evident. The shortest Cu . . . Cu separations occur across the azido, cyanato or thiocyanato bridges, respectively, which are coordinated equatorially to one unit and axially to the neighbouring unit; 3.568(1) (1), 3.547(1) (2), 5.432(1) (3) and 5.371(1) Angstrom (4). Variable temperature magnetic susceptibility measurements on compounds 1, 2 and 4 reveal weak antiferromagnetic coupling across the azido, cyanato and thiocyanato bridges, respectively (J-values of - 2.3(1) (1), - 1.0(1) (2) and - 1.0(1) (4) cm(-1)). (C) 2001 Elsevier Science B.V. All rights reserved.