Dicopper(I) complexes with reduced states of 3,6-bis(2'-pyrimidyl)-1,2,4,5-tetrazine: crystal structures and spectroscopic properties of the free ligand, a radical species, and a complex of the 1,4-dihydro form.
The complexes [(mu-bmtz(*-))[Cu(PPh(3))(2)](2)](BF(4)) (1) and [(mu-H(2)bmtz)[Cu(PPh(3))(2)](2)](BF(4))(2) (2) (bmtz = 3,6-bis(2'-pyrimidyl)-1,2,4,5-tetrazine and H(2)bmtz = 1,4-dihydro-3,6-bis(2'-pyrimidyl)-1,2,4,5-tetrazine) were obtained as stable materials that could be crystallized for structure determination. 1.2 CH(2)Cl(2): C(84)H(70)BCl(4)Cu(2)F(4)N(8)P(4); monoclinic, C2/c; a = 26.215(7) A, b = 22.122(6) A, c = 18.114(5) A, beta = 133.51(1) degrees; Z = 4. 2.CH(2)Cl(2): C(83)H(70)B(2)Cl(2)Cu(2)F(8)N(8)P(4); triclinic, P1; a = 10.948(2) A, b = 12.067(2) A, c = 30.287(6) A, alpha = 93.82(3) degrees, beta = 94.46(3) degrees, gamma = 101.60(3) degrees; Z = 2. Bmtz itself was also structurally characterized (C(10)H(6)N(8); monoclinic, P2(1)/c; a = 3.8234(8) A, b = 10.147(2) A, c = 13.195(3) A, beta = 94.92(3) degrees; Z = 2). Whereas the radical complex ion contains a planar tetrazine ring in the center, the 1,4-dihydrotetrazine heterocycle in the corresponding complex of H(2)bmtz is considerably folded. Both systems exhibit slight twists between the tetrazine and the pyrimidine rings. The intra-tetrazine distances are characteristically affected by the electron transfer, as is also evident from a comparison with the new structure of free bmtz; the bonding to copper(I) changes accordingly. Spectroscopy including X- and W-band EPR of the radical species confirms that the electron addition is mainly to the tetrazine ring.