TERNARY COPPER(II) COMPLEXES WITH THE VERSATILE -METHYL-7-OXO-[1,2,4]TRIAZOLO[1,5-ALPHA]PYRIMIDINE LIGAND

The synthesis and structural characterization by X-ray crystallography , thermal, spectroscopic and magnetic methods of the ternary copper(II ) complexes [Cu(Hmtpo-N-3)(2)(H2O)(2)](NO3)(2) . 2H(2)O (1), [Cu(mtpo- N-3)(2)(eta(2)-en)(H2O)]. 1.5H(2)O (2), [Cu(mtpo-N-3)(eta(2)-mtpo-N-1, O-7)(eta(2)-tn)]. 2H(2)O (3), [Cu(mtpo-N-3)(2)(py)(2)(H2O)(2)] (4), [C u(mtpo-N-3)(2)(eta(2)-bpy)(H2O)]. 2H(2)O (5), and [Cu(mtpo-N-3)(2)(eta (2)-phen)(H2O)(2)] (6) is reported (Hmtpo = -5-methyl-7-oxo[1,2,4]tria zolo[1,5-a]pyrimidine,en = 1,2-ethylenediamine, tn = 1,3-propanodiamin e, py = pyridine, bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline). Crystals of 1 are monoclinic, space group C2/c, with unit cell dimensi ons a = 19.473(2), b = 8.603(3) c = 15.198(3) Angstrom, beta = 122.230 (6)degrees, V = 2153.7(8) Angstrom(3), Z = 4. The structure was refine d to final R = 0.042 for 1659 reflections with I greater than or equal to 3.0 sigma(I). Crystals of 2 are monoclinic, P2(1)/n with a = 13.02 9(4), b = 11.388(2), c = 13.518(4) Angstrom, beta = 101.52(3)degrees, V = 1965(1) Angstrom(3), Z = 4, and R = 0.038 for 2707 reflections. Cr ystals of 3 are triclinic, P (1) over bar, with a = 10.241(2), b = 12. 271(2), c = 9.296(1) Angstrom, alpha = 107.69(1)degrees, beta = 113.95 (1)degrees, gamma = 84.42(1)degrees, V = 1016.7(3) Angstrom(3), Z = 2, and R = 0.036 for 3554 reflections. Crystals of 4 are monoclinic, P2( 1)/c, with a = 8.561(1), b = 10.645(1), c = 13.8882(7) Angstrom, beta = 103.530(7)degrees, V = 1230.6(2) Angstrom(3), Z = 2, and R = 0.056 f or 1837 reflections. Crystals of 5 are triclinic, P (1) over bar, with a = 13.236(6), b = 14.395(5), c = 9.033(2) Angstrom, alpha = 95.14(3) degrees, beta = 106.27(2)degrees, gamma = 68.31(3)degrees, V = 1534(1) Angstrom(3), Z = 2, and R = 0.075 for 3252 reflections. Crystals of 6 are monoclinic, C2/c, with a = 11.439(1), b = 11.791(1), c = 19.718(3 ) Angstrom, beta = 106.20(1)degrees, V = 2553.9(5) Angstrom(3), Z = 4, and R = 0.048 for 2057 reflections. The X-ray crystal structures show that Hmtpo, both in its neutral and monoanionic forms, binds the cent ral atom preferentially through N3, nevertheless, compound 3 presents an unusual N1, O7 chelate, which is analogous to the rare B-oxo-purine s N7, O6 chelate. Further, the Cu(II) polyhedron in this set of comple xes follows a trend to higher coordination numbers with increasing pi- acid character of the auxiliary ligands. Finally, the coordination pot ential of the Hmtpo ligand is discussed on the basis of molecular orbi tal semi-empirical PM3 calculations, performed for the neutral and mon oanionic forms of Hmtpo. (C) 1998 Elsevier Science S.A. All rights res erved.