Inorganic Chemistry, Vol.42, No.22, 7026-7036, 2003
A solid-state spectral effect in eclipsed tetracyanonickelates: X-ray crystal structure, polarized specular reflectance spectroscopy, and ZINDO modeling of Sr[Ni(CN)(4)]center dot 5H(2)O, Rb-2[Ni(CN)(4)]center dot H2O, and Na-2[Ni(CN)(4)]center dot 3H(2)O
Crystal structures of three Ni(CN)(4)(2-) salts all with eclipsed ligands and varying axial stacking arrangements are presented. The absorption spectra of all three salts show a slight red shift in the x,y-polarizations and a large red shift in their z-polarizations upon crystallization from solution. Semiempirical ZINDO calculations provide a good model of the solid state, even with only a three-molecule segment, allowing reproduction of the red-shifting and intensity increase upon crystallization found experimentally. The modified nickel P,,p bonding parameter of -5 found appropriate for Ni coordination in our previous studies of single Ni(CN)(4)(2-) planes and a helically stacked Cs-2[Ni(CN)(4)].H2O crystal was changed to -3 for the more parallel-stacked Ni(CN)(4)(2-) planes in this case, while beta(d) was retained at -41. Crystal data are as follows: Na-2[Ni(CN)(4)].3H(2)O, triclinic space group P (1) over bar, a = 7,2980(10) Angstrom, b = 8.8620(10) Angstrom, c = 15.132(2) Angstrom, alpha = 89.311(5)degrees, beta = 87.326(5)degrees, gamma = 83.772(6)degrees, V = 971.8(2) Angstrom(3), T = 100 K, Z = 4, R = 0.024, R-w = 0.064; Sr[Ni(CN)(4)].5H(2)O, monoclinic space group C2/m, a 10.356(2) Angstrom, b = 15.272(3) Angstrom, c = 7.1331(10) Angstrom, beta = 98.548(12)degrees, V = 1115.6(3) Angstrom(3), T = 100 K, Z = 4, R = 0. 024, R-w = 0.059; Rb-2[Ni(CN)(4)].1.05H(2)O, triclinic space group P (1) over bar, a = 8.6020(10) Angstrom, b = 9.6930(10) Angstrom, c = 12.006(2) Angstrom, alpha = 92.621(6)degrees, beta = 94.263(6)degrees, gamma = 111.795(10)degrees, V = 924.0(2) Angstrom(3), T = 100 K, Z = 4, R = 0.034, R-w = 0.067.