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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
Gloeckle,Huebler,Kuemmerer,Denninger,Kaim
, p. 2263 - 2269 (2001)
The complexes {(μ-bmtz·-)[Cu(PPh3)2] 2}(BF4) (1) and {(μH2bmtz)[Cu (PPh3)2]2}(BF4)2 (2) (bmtz = 3,6-bis(2′-pyrimidyl)-1,2,4,5-tetrazine and H2bmtz = 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: C84H70BCl4 Cu2F4N8P4; monoclinic, C2/c; a = 26.215(7) A, b = 22.122(6) A, c = 18.114(5) A, β = 133.51(1)°; Z = 4. 2·CH2Cl2: C83H70B2 Cl2Cu2F8N8P4; triclinic, P1; a = 10.948(2) A, b = 12.067(2) A, c = 30.287(6) A, α = 93.82(3)°, β = 94.46(3)°, γ = 101.60(3)°; Z = 2. Bmtz itself was also structurally characterized (C10H6N8; monoclinic, P21/c; a = 3.8234(8) A, b = 10.147(2) A, c = 13.195(3) A, β = 94.92(3)°; 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 H2bmtz 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.
