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, C(27)H(16)ClN(6)O(3)Re.MeOH: monoclinic, P2(1)/n, a = 9.2217(7), b = 10.7628(8), c = 26.932(2) A, beta= 94.130(1) degrees , V = 2666.1(3) A(3), Z = 4. 2, C(27)H(16)BrN(6)O(3)Re: monoclinic, P2(1)/n, a = 9.2931(6), b = 10.2387(7), c = 27.993(2) A, beta = 94.615(1) degrees , V = 2654.8(3) A(3),Z = 4. 1', C(27)H(16)ClN(6)O(3)Re.2H(2)O: monoclinic, C(2)/c, a = 18.584(4), b = 21.693(5), c = 15.392(4) A, beta = 122.328(3) degrees , V = 5243(2) A(3), Z = 8. 3, C(30)H(16)Br(2)N(6)O(6)Re(2): triclinic, P1, a = 7.4668(6), b = 11.4902(10), c = 19.3736(16) A, alpha = 73.659(2), beta = 85.183(2), gamma = 77.097(1) degrees , V = 1554.3(2) A(3), Z = 2. 4, C(33)H(16)Cl(3)N(6)O(9)Re(3).1/2C(6)H(6): orthorhombic, Pbca, a = 18.828(1), b = 16.715(1), c = 25.366(2) A, V = 7983.2(10) A(3), Z = 8.