Synthesis, structural isomerism, and magnetism of extended framework compounds of type [Cu(dca)2(pyz)]n, where dca = dicyanamide (N(CN)2-) and pyz = pyrazine

Two structural isomers of the dicyanamide (dca, N(CN)(2)(-)) complex [Cu(dca)(2)(pyz)](n) (pyz = pyrazine) were prepared from aqueous solution and crystals were grown by slow diffusion and gel techniques. Crystal data: alpha-[Cu(dca)(2)(pyz)](n), CuC8H4N8, monoclinic, Pn, Z = 16, a = 24.2549(7) Angstrom, b = 6.8571(2) Angstrom, c = 24.6445(7) Angstrom, beta = 91.023(2)degrees, V = 4098.2(2) Angstrom(3), R(F)= 0.0466 (F > 4 sigma(F)), R-w(F-2)= 0.0939 (all data); beta-[Cu(dca)(2)(pyz)](n), CuC8H4N8, monoclinic, C2/m, Z = 2, a = 9,7659(8) Angstrom, b = 6.8787(7) Angstrom, c = 7.3870(5) Angstrom, beta = 95.254(7)degrees, V = 494.15(6) Angstrom(3), R(F)= 0.038, R-w(F)= 0.074 (I > 3 sigma(I)). The alpha-isomer consists of two interpenetrating alpha-Po related networks, while the beta-isomer contains sheets composed of Cu(dca), chains linked by bridging pyz ligands. Despite the differences in their network structures, the magnetic properties of these structural isomers are essentially the same. Weak antiferromagnetic coupling of the S = 1/2 centers leads to a maximum in susceptibility at 3.5 K, One of the aims of this work is to prepare long-range ordered materials but no magnetic order is observed in the present compounds. The antiferromagnetic coupling is a little stronger than that in the parent Cu(dca), but of similar strength to that in chain compounds of type [Cu(dca)(2) (imidazole)(2)](n). Thus, the pyz linkers enhance the coupling to only a small degree. The networks in the a-isomer behave independently and identically from the magnetic point of view. (C) 1999 Academic Press.