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( PPh3)(2)](2)}(BF4)(1) and {(mu -H(2)mtz)[Cu( PPh3)(2)](2)}(BF4)(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 CH2Cl2: C84H70BCl4Cu2F4N8P4; monoclinic, C2/c; a = 26.215(7) Angstrom, b = 22.122(6) Angstrom, c = 18.114(5) Angstrom, beta = 133.51(1)degrees: Z = 4.2 2 . CH2Cl2 C83H70B2Cl2Cu2F8N8P4; triclinic, P (1) over bar; a = 10.948(2) Angstrom, b = 12.067(2) Angstrom, c = 30.287(6) Angstrom, alpha = 93.82(3)degrees, beta = 94.46(3)degrees, gamma = 101.60(3)degrees; Z = 2. Bmtz itself was also structurally characterized (C10H6N8; monoclinic, P2(1)/c; 3.8234(8) Angstrom, b = 10.147(2) Angstrom, c = 13.195(3) Angstrom, 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(l) changes accordingly. Spectroscopy including X- and W-band EPR of the radical species confirms that the electron addition is mainly to the tetrazine ring.