Synthesis, characterization and crystal structures of mono-, di- and trinuclear rhenium(I) tricarbonyl complexes with 2,3,5,6-tetra(2-pyridyl)pyrazine

A series of rhenium(I) tricarbonyl complexes with the ligand 2,3,5,6-tetra(2-pyridyl)pyrazine (tppz) were synthesized and characterized crystallographically. Two different coordination modes were found when tppz functions as a monobidentate ligand. Rhenium(I) may be bound to tppz through pyrazine and pyridyl nitrogens completing a 5-membered coordination ring when the reaction was carried out in toluene. However, the same reaction in methanol produced a yellow complex in which rhenium(I) was bound to tppz through two adjacent pyridyl nitrogens with a 7-membered coordination ring. In the presence of an excess amount of [ReBr(CO)(5)], the dinuclear complex [{ReBr(CO)(3)}(2)(mu -tppz)] (3) was isolated, while the trinuclear complex [{ReCl(CO)(3)}(3)-(mu -tppz)] (4) was obtained in the case of [ReCl(CO)(5)]. Crystal data for 1, C27H16ClN6O3Re . MeOH: monoclinic, P2(1)/n, a = 9.2217(7), b = 10.7628(8), c = 26.932(2) Angstrom, beta = 94.130(1)degrees, V = 2666.1(3) Angstrom (3), Z = 4. 2, C27H16BrN6O3Re: monoclinic, P2(1)/n, a = 9.2931(6), b = 10.2387(7), c = 27.993(2) Angstrom, beta = 94.615(1)0, V = 2654.8(3) Angstrom (3), Z = 4. 1', C27H16ClN6O3Re . 2H(2)O: monoclinic, C-2/c, a = 18.584(4), b = 21.693(5), c = 15.392(4) Angstrom, beta = 122.328(3)degrees, V = 5243(2) Angstrom (3), Z = 8. 3, C30H16Br2N6O6Re2: triclinic, PT, a = 7.4668(6), b = 11.4902(10), c = 19.3736(16) Angstrom, alpha = 73.659(2), beta = 85.183(2), gamma = 77.097(1)degrees, V = 1554.3(2) Angstrom (3), Z = 2. 4, C33H16Cl3N6O9Re3.1/2C(6)H(6): orthorhombic, Pbca, a = 18.828(1), b = 16.715(1), c = 25.366(2) Angstrom, V = 7983.2(10) Angstrom (3), Z = 8. (C) 2001 Elsevier Science B.V. All rights reserved.