FULL PAPER DOI:10.1002/ejic.201200890 Crucial Influence of the Intramolecular Hydrogen Bond on the Coordination Mode of RC(S)NHP(S)(OiPr) 2 in Homoleptic Complexes with Ni II Maria G. Babashkina,* [a] Damir A. Safin, [a] Monika Srebro, [b] Piotr Kubisiak, [b] Mariusz P. Mitoraj,* [b] Michael Bolte, [c] and Yann Garcia [a] Keywords: Coordination modes / Nickel / Thioureas / Density functional calculations / X-ray diffraction Reaction of the deprotonated N-thiophosphorylated thio- ureas RC(S)NHP(S)(OiPr) 2 [R = EtNH (HL I ), iPrNH (HL II ), Et 2 N (HL III ), 2,5-Me 2 C 6 H 3 NH (HL IV ), 4-Me 2 NC 6 H 4 NH (HL V )] with Ni II leads to complexes of the formula [NiL I–V 2 ]. The molecular structures of the complexes in the solid were elucidated by single-crystal X-ray diffraction analysis. In the complexes, the metal atom is found to be in a square-planar trans-N 2 S 2 ([NiL II,IV 2 ]) environment formed by the C=S sulfur atoms and the P–N nitrogen atoms, or in a square-planar trans-S 2 S' 2 ([NiL I,III 2 ]) environment formed by the C=S and P=S sulfur atoms of two deprotonated ligands. Reaction of deprotonated N-thiophosphorylated thiourea HL V with NiCl 2 leads to violet [Ni(L-1,3-N,S) 2 ] or dark violet [Ni(L-1,5-S,S') 2 ]· (CH 3 ) 2 C=O crystals that were isolated by recrystallization from a mixture of CH 2 Cl 2 or acetone, respectively, and n- hexane. DFT calculations confirmed that the [Ni(L I,II,IV,V - Introduction In the literature there is a number of Ni II complexes with the chalcogenated imidodiphosphinate ligands R 2 P(X)- NP(Y)R' 2 (IDP; X, Y = O, S, Se, Te) [1] and acylthioamides RC(S)NC(X)R' (AA; X = O, S) or aroylthioureas R 2 NC(S)- NC(X)R' (ATU; X = O, S). [2] These complexes are of great interest owing to their structural versatility (square-planar, octahedral, tetrahedral). However, the chelate backbones of the IDP , AA and ATU ligands are coordinated towards the Ni II cation through the donor X and Y atoms. [a] Institute of Condensed Matter and Nanosciences, MOST – Inorganic Chemistry, Université Catholique de Louvain, Place L. Pasteur 1, 1348 Louvain-la-Neuve, Belgium E-mail: maria.babashkina@ksu.ru Homepage: www.uclouvain.be/262038.html [b] Department of Theoretical Chemistry, Faculty of Chemistry, Jagiellonian University, R. Ingardena 3, 30-060 Kracow, Poland E-mail: mitoraj@chemia.uj.edu.pl [c] Institut für Anorganische Chemie, J.-W.-Goethe-Universität, 60438 Frankfurt/Main, Germany Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/ejic.201200890. Eur. J. Inorg. Chem. 2013, 545–555 © 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 545 N,S) 2 ] conformers are more stable (by 5–7 kcal/mol) than [Ni- (L I,II,IV,V -S,S') 2 ], whereas [Ni(L III -N,S) 2 ] is less stable (by 7– 9 kcal/mol) than [Ni(L III -S,S') 2 ]. The main reason for higher stability of the 1,3-N,S versus 1,5-S,S' isomers is the forma- tion of intramolecular N–H···S=P hydrogen bonds. The same hydrogen bonds are impossible in complex [NiL III 2 ]. In solu- tion, complex [NiL III 2 ] has revealed an exclusively 1,5-S,S' coordination, whereas compounds [NiL I,II,IV,V 2 ] reveal at le- ast two isomers in the 1 H and 31 P{ 1 H} NMR spectra. The major species is assigned to the 1,3-N,S-coordinated isomer, and the minor signals are assigned to the 1,5-S,S' isomer, which was confirmed by UV/Vis spectroscopic results. The electrochemical measurements reveal reversible one-elec- tron reduction and irreversible oxidations both assigned to ligand-centred processes. Ligand-based oxidation processes agree well with TD-DFT results. The synthesis and complexation properties of N-(thio)- phosphorylated thioamides and thioureas RC(S)NHP- (X)(OR') 2 (NTT; X = O, S), which are asymmetrical ana- logues of IDPs, AAs and ATUs, have been extensively studied, [3] but there is still limited information about struc- tures of Ni II complexes with NTT . In previous contri- butions we have also studied the structures of Ni II com- plexes with NTT (X = O) ligands and demonstrated that their square-planar complexes with Ni II exhibit either a 1,3- N,S or 1,5-O,S coordination mode. It was established that intramolecular hydrogen bonds N–H···O=P are a necessary condition for the formation of 1,3-N,S isomers for R = PhNH, p-MeOC 6 H 4 NH, p-BrC 6 H 4 NH, iPrNH, tBuNH, cyclo-C 6 H 11 NH, 1-AdNH and (4'-benzo-15-crown-5)NH; [4] whereas 1,5-O,S coordination takes place when hydrogen bonding in the coordinated anionic ligands is not possible (R = Et 2 N, morpholino). [4b] Moreover, N-phosphorylated thioamides RC(S)NHP(O)(OiPr) 2 (R = p-BrC 6 H 4 , Ph [5] ) form distorted octahedral complexes with Ni II , in which two deprotonated ligands are coordinated through the sulf- ur and oxygen atoms of the C=S and P=O groups, respec- tively, and two neutral forms of the ligands are bonded through the oxygen atoms of the P=O groups. Furthermore,