Synthesis, vibrational spectra and X-ray structures of copper(I) thiourea complexes

Complex formation of thiourea with copper takes place as an intermediate step in the preparation of copper sulfide thin films by spray pyrolysis starting from aqueous solutions of copper(II) chloride and thiourea. The stoichiometry of the complex and that of the resulting thin film primarily depends on the molecular ratio of the starting materials. For comparison, the structures of all copper(I) thiourea complexes found in the Cambridge Structural Database are classified in this paper. In addition, syntheses, structural (single crystal XRD also at low temperature 193 K) and spectroscopic studies (FTIR and Raman) of six copper–thiourea complexes are now reported. The copper to thiourea stoichiometric ratio is 1:3 in four of these complexes, but their structures are basically different as dimerization or polymer formation takes place depending on whether the water of crystallisation is present or absent. The structure of bis(μ-thiourea)tetrakis(thiourea)dicopper(I) dichloride dihydrate, [Cu2(tu)6]Cl2 · 2H2O (1) was determined at room and also at low temperature. Bis(μ-thiourea)tetrakis(thiourea)dicopper(I) dibromide dihydrate, [Cu2(tu)6]Br2 · 2H2O (2) is isomorphous with 1, like the anhydrous compounds chlorotris(thiourea)copper(I), [Cu(tu)3]Cl (3) and bromotris(thiourea)copper(I), [Cu(tu)3]Br (4) are isomorphous. In the third isomorphous pair of complexes the copper to thiourea stoichiometric ratio is 1:1, viz. chloro(thiourea)copper(I) hemihydrate, [Cu(tu)]Cl · 0.5H2O (5) and bromo(thiourea)copper(I) hemihydrate, [Cu(tu)]Br · 0.5H2O (6). During the preparation of chloro(thiourea)copper(I) hemihydrate (5) a reaction by product α,α′-dithiobisformamidinium dichloride, [SC(NH2)2]2Cl2 (7) was identified and structurally characterized which made it possible to suggest a reaction path leading to complex formation.