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 heterol eptic 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 grou p P (1) over bar, and consist of mononuclear building blocks featuring copp er atoms with close to square planar coordination geometries. The mononucle ar units are, however, associated into chains through weak axial Cu-N bonds formed by end-on asymmetrically bridging azido/cyanato groups and by pyrid yl nitrogen atoms. Taking these contacts into account, copper may be descri bed 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 th is case the association between these units is such as to form dinuclear mo lecules 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 contain s an apically coordinated water molecule. This leads to a significantly wea ker intermolecular (CuS)-S-... contact as compared to that found in 3, but an association into dinuclear units is structurally and magnetically eviden t. The shortest Cu . . . Cu separations occur across the azido, cyanato or thiocyanato bridges, respectively, which are coordinated equatorially to on e 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 suscept ibility 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 El sevier Science B.V. All rights reserved.