DOI: 10.1002/zaac.200800100 Structural and NMR Studies of the Hexameric Copper(I) Complex with N-n-butyl-N-ethoxycarbonyl-thioureate Sue E. Boyd, Peter C. Healy*, Gregory A. Hope, and Ronald Woods Nathan, Queensland/Australia, School of Biomolecular and Physical Sciences, Griffith University Received March 18 th , 2008. Abstract. The copper sulfide mineral flotation collector, N-n-butyl- N-ethoxycarbonyl-thiourea (H 2 bectu), and the 1:1 hexameric cop- per(I) thioureate complex, [Cu(Hbectu)] 6 , have been characterized by single crystal X-ray diffraction. H 2 bectu crystallizes in the tri- clinic space group P1 ¯ with a  5.2754(4), b  9.0042(7), c  12.6030(9) A ˚ , α  80.528(6), β  90.173(6), γ  76.472(7)°. An intramolecular N-H···O hydrogen bond between the thioamide pro- ton and carbonyl oxygen forms a planar six-membered ring in the central core of the molecule with CO, CS and C-N bond lengths in accord with those reported for other N-alkyl/aryl-N- acyl-thiourea compounds. [Cu(Hbectu)] 6 crystallizes in the mono- clinic space group C2/c with a  23.269(5), b  13.243(4), c  Introduction Organic sulfur compounds, such as dithiocarbonates, dithiophosphates, thionocarbamates and thiazoles, are used extensively in mineral extraction to hydrophobize metal sul- fides in order to separate and recover them from mineral ores by froth flotation [1]. These compounds form by coor- dination of sulfur, nitrogen, phosphorus or oxygen donor atoms to metal atoms on the mineral surface while pre- senting the organic substituent groups to the solution phase. Acyl thiourea compounds (scheme I) have also been found to be an important ligand system in flotation chemis- try for the selective complexation of soft and borderline me- tal cations [2, 3] and Cytec Industries have introduced one of these, N-n-butyl-N-ethoxycarbonyl-thiourea (H 2 bectu), under the trade name Aero 5500 for the recovery of copper from copper sulfide minerals [46]. Scheme 1 * Prof. Peter C. Healy School of Biomolecular and Physical Sciences, Griffith University Queensland 4111 Australia Tel: (617 3735 7442FAX(617) 3735 7656 email: P.Healy@griffith.edu.au Z. Anorg. Allg. Chem. 2008, 634, 15371541 © 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1537 23.037(7) A ˚ , β  91.81(2)° as discrete hexameric clusters disposed about a crystallographic centre of symmetry with a Cu 6 S 6 core con- sisting of two Cu 3 S 3 chair-shaped rings linked by coordination of the deprotonated amide nitrogen atom to a copper atom in the adjacent ring. The six ligands assemble as a paddlewheel structure with the ethoxy and n-butyl substituents packing in an alternating head to tail arrangement. Temperature dependent solution 1 H NMR spectroscopic studies show that the hexameric structure of the complex is maintained in solution. Keywords: Copper; Crystal structures; Acylthiourea; NMR spec- troscopy Early work on the use of H 2 bectu as a copper collector postulated formation of a coordination complex with the copper atoms coordinated by the sulfur and carbonyl oxy- gen atoms of the ligand [5, 6]. However, surface enhanced Raman spectro-electrochemical, NMR and preliminary X- ray crystallographic studies [4] showed that the copper atoms were coordinated by sulphur and deprotonated HNCO amide nitrogen atoms to form a 1:1 hexameric cop- per(I) thioureate complex, [Cu(Hbectu)] 6 . In this present study, we report and discuss the single crystal X-ray struc- ture results for H 2 bectu and [Cu(Hbectu)] 6 and related com- pounds; together with further spectroscopic characteriz- ation of the structure of [Cu(Hbectu)] 6 in solution by tem- perature dependent 1 H NMR spectroscopy. The results highlight the stability of this complex cluster in both solid and solution states. Experimental Section Synthesis of [(Cu(Hbectu)] 6 An excess of H 2 bectu dissolved in a 70:30 aqueous ethanol solution was added to a solution of cupric sulphate in 70:30 aqueous etha- nol. Ascorbic acid was then added to the solution to yield [(Cu(Hbectu)] 6 as a microcrystalline precipitate which was filtered and washed with water. Dissolution of the complex in a saturated chloroform-ethanol solution followed by slow solvent evaporation at room temperature yielded small colourless crystals of the com- plex suitable for X-ray diffraction studies. mp 158  165 °C (dec.). Anal. Calc. for C 48 H 90 Cu 6 N 12 O 12 S 6 : C 36.01, H 5.67 %. Found: C 35.45, H 5.54 %.