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The synthesis and structural characterization by X-ray crystallography, thermal, spectroscopic and magnetic methods of the ternary copper(II) complexes [Cu(Hmtpo-N3)2(H2O)2](NO3)2·2H2O (1), [Cu(mtpo-N3)2(η2-en)(H2O)]·1.5H2O (2), [Cu(mtpo-N3)(η2-mtpo-N1,O7)(η2-tn)]·2H2O (3),
[Cu(mtpo-N3)2(py)2(H2O)2] (4), [Cu(mtpo-N3)2(η2-bpy)(H2O)]·2H2O (5), and [Cu(mtpo-N3)2(η2-phen)(H2O)2] (6) is reported (Hmtpo= 4,7-dihydro-5-methyl-7-oxo[1,2,4]triazolo[1,5-a]pyrimidine,
en= 1,2-ethylenediamine, tn= 1,3-propanodiamine, py= pyridine, bpy= 2,2'-bipyridine,
phen= 1,10-phenanthroline). Crystals of 1 are monoclinic, space group C2/c, with unit cell dimensions a = 19.473(2), b = 8.603(3) c = 15.198(3) Angstrom, β= 122.230(6)degrees, V = 2153.7(8) Angstrom3, Z = 4. The structure was refined to final R = 0.042 for 1659 reflections with I>3.0 σ(1). Crystals of 2 are monoclinic, P21/n with a = 13.029(4), b = 11.388(2), c = 13.518(4) Angstrom, β= 101.52(3)degrees, V = 1965(1) Angstrom3, Z = 4, and R = 0.038 for 2707 reflections. Crystals of 3 are triclinic, P1 over bar, with a = 10.241(2), b = 12.271(2), c = 9.296(1) Angstrom, α= 107.69(1)degrees, β= 113.95(1)degrees, γ= 84.42(1)degrees, V = 1016.7(3) Angstrom3, Z = 2, and R = 0.036 for 3554 reflections. Crystals of 4 are monoclinic, P21/c, with a = 8.561(1), b = 10.645(1), c = 13.8882(7) Angstrom, β= 103.530(7)degrees, V = 1230.6(2) Angstrom3, Z = 2, and R = 0.056 for 1837 reflections. Crystals of 5 are triclinic, P1 over bar, with a = 13.236(6), b = 14.395(5), c = 9.033(2) Angstrom, α= 95.14(3)degrees, β= 106.27(2)degrees, γ= 68.31(3)degrees, V = 1534(1) Angstrom3, 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, β= 106.20(1)degrees, V = 2553.9(5) Angstrom3, 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 central atom preferentially through N3, nevertheless, compound 3 presents an unusual N1, O7 chelate, which is analogous to the rare 6-oxo-purines N7, O6 chelate. Further, the Cu(II) polyhedron in this set of complexes follows a trend to higher coordination numbers with increasing π-acid character of the auxiliary ligands. Finally, the coordination potential of the Hmtpo ligand is discussed on the basis of molecular orbital semi-empirical PM3 calculations, performed for the neutral and monoanionic forms of Hmtpo.
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