Extended polymorphism in copper(II) imidazolate polymers: A spectroscopic and XRPD structural study

Copper(H) bisimidazolate affords five different polymorphs; of these, one w as structurally characterized 40 years ago by standard single-crystal X-ray diffraction (Jarvis, J. A. J.; Wells, A. F. Acta Crystallogr. 1960, 13, 10 27), while the remaining four, selectively prepared as pure polycrystalline phases, have been now studied by X-ray powder diffraction (XRPD) methods. Of the four new (blue, green, olive-green, and pink) phases, three were sol ved by the ab initio XRPD technique and refined by the Rietveld method, and the fourth phase (pink) could not be structurally characterized. Crystal d ata for [Cu(imidazolate)(2)](n): blue phase, a = 27.559(3) Angstrom, c = 5. 3870(9) Angstrom, trigonal, R (3) over bar, Z = 54; green phase, a = 21.139 (1) Angstrom, b = 19.080(1) Angstrom, c = 9.2842(8) Angstrom, orthorhombic, Ccca, Z = 20; olive-green phase, a = 11.7556(8) Angstrom, b 23.422(2) Angs trom, c = 9.0727(9) Angstrom, beta = 104.993(5)degrees, monoclinic, C2/c, Z = 12. All polymorphs contain four-coordinate CuN4 chromophores and (N,N')- exobidentate imidazolate ligands, but show different spectroscopic and stru ctural properties, the latter ranging from 2D to different 3D networks of t he PtS, sodalite, and moganite archetypes. The intermediacy of the [Cu(imid azole)(2)CO3].H2O species in the synthesis of the blue polymorph has been c onfirmed by spectroscopic and thermal analyses. FTIR, Raman, and electronic spectra were correlated with the structural features revealed in the prese nt work, and used to gain insight into the coordination geometry of copper( II) ions of the pink polymorph. In addition, the correct Raman spectrum for copper(II) bisimidazolate, common for all polymorphs, has been definitely determined.