Novel boxlike dinuclear or chain polymeric silver(I) complexes with polypyridyl bridging ligands: Syntheses, crystal structures, and spectroscopic and electrochemical properties

The syntheses, characterization, crystal structures, and photophysical and electrochemical properties of two dinuclear and two polymeric Ag-I complexes with three polypyridyl ligands, 2,3-di-2-pyridylquinoxaline (L-1), 2,3-di-2-pyridyl-5,8-dimethoxyquinoxaline (L-2), and 2,3,7,8-tetrakis(2-pyridyl)pyrazino[2,3-g] quinoxaline (L-3), are described. The structures of the two boxlike dinuclear complexes with L-1 and L-2 and two chemically the same but differently crystallized one-dimensional zigzag chain coordination polymers also consisting of boxlike dinuclear subunits have been elucidated by X-ray analysis. [AgL1(CH3CN)](2)-(BF4)(2). 2CHCl(3) (1): monoclinic, C2/c; a = 28.631(2), b = 12.2259(11), c = 14.3058(12) Angstrom; beta = 99.180(2)degrees; Z = 4. [AgL2(CH3CN)(2)](2)(ClO4)(2) (2): triclinic, P (1) over bar; a = 12.3398(2), b = 13.750(2), c = 14.326(7) Angstrom; alpha = 83.494(3), beta = 74.631(3), gamma = 76.422(3)degrees; Z = 4. {[Ag2L3(NO3)(2)]. CH3CN}(infinity) (3a): monoclinic, P2(1)/c; a = 9.5836(8), b = 13.4691(12), c = 14.0423(12) Angstrom; beta = 107.753(2)degrees; Z = 4. [Ag2L3(NO3)(2)](infinity) (3b): monoclinic, P2(1)/c; a = 8.4689(6), b = 16.0447(12), c = 11.7307(8) Angstrom; beta = 102.051(1)degrees; Z = 2. The structures of the,,dinuclear complexes 1 and 2 are similar to each other, with the two intramolecular Ag-I centers of each complex being spanned by two ligands thus forming a unique boxlike cyclic dimer. In 1, each Agi center is four-coordinated by three nitrogen atoms of two L-1 ligands and a CH3CN nitrogen donor, taking a distorted tetrahedral coordination geometry. The coordination environment of Ag-I in 2 is similar to that in 1, except the formation of an additional weak coordination bond with the oxygen atom of the methoxy group of L-2. The structures of 3a,b are very similar to each other, except for the stacking patterns in the crystal lattices, and the cyclic boxlike dinuclear unit, which is similar to the structure of 1, constitutes the fundamental building block to form the one-dimensional zigzag chain structures due to the "end-on" nature of L-3. 1-3 exhibit metal-perturbed intraligand transitions in solution in 360-390 nm regions. Cyclic voltammetric studies of these complexes show the presence of reduction peak at similar to -0.5 V vs Fc(+/0). In the solid state at 77 K, they exhibit broad emission that may be assignable to originate from the metal-perturbed intraligand transitions.