Structural effects of the chelating rings in trans-[Ni{Ph 2 P(Se)NPPh 2 -Se,P} 2 ] and trans-[Ni{Ph 2 P(Se)NPPh 2 -Se,P}{Ph 2 P(Se)N(H)PPh 2 -Se,P}]ClCH 2 Cl 2 H 2 O complexes Nikolaos Levesanos a , Ioannis Stamatopoulos a , Catherine P. Raptopoulou b , Vassilis Psycharis b , Panayotis Kyritsis a, * a Inorganic Chemistry Laboratory, Department of Chemistry, National and Kapodistrian University of Athens, Panepistimiopolis, GR 157 71 Athens, Greece b Institute of Materials Science, NCSR ‘‘Demokritos”, GR 153 10 Aghia Paraskevi Attikis, Greece article info Article history: Available online 12 May 2009 This article is dedicated to Dr. Aris Terzis, on the occasion of his retirement, for his invaluable contribution to the advancement of inorganic chemistry in Greece through X-ray crystallography. Keywords: Nickel complex (Se,P)-ligand Chelating ring NMR spectroscopy X-ray crystallography abstract The reaction of the monooxidised imidodiphosphinate ligand Ph 2 P(Se)NHPPh 2 with NiCl 2 6H 2 O in the presence of t BuOK afforded [Ni{Ph 2 P(Se)NPPh 2 -Se,P} 2 ](1), which was characterized by UV–Vis, IR and NMR spectroscopies. X-ray crystallographic studies on a single crystal of 1 revealed the trans Ni(Se,P) 2 arrangement in the solid state, showing a bis-chelating type of coordination. The diamagnetic 31 P NMR peaks of 1 in CDCl 3 were interpreted as ‘‘deceptive” triplets, due to the conservation of the square–planar trans-isomer of 1 in solution. The structure of 1 exhibits a center of symmetry, with the two five-mem- bered Ni–Se–P–N–P rings being equivalent. The higher electronegativity of Se compared to P is consid- ered as the likely cause of the P–N bond length differences observed in the chelating rings of 1. During the reaction between NiCl 2 6H 2 O and the ligand Ph 2 P(Se)N{(S)-CH(CH 3 )Ph}PPh 2 , single crystals were obtained, the analysis of which by X-ray crystallography showed the formation of trans-[Ni{Ph 2 P (Se)NPPh 2 -Se,P}{Ph 2 P(Se)N(H)PPh 2 -Se,P}]ClCH 2 Cl 2 H 2 O(2). Complex 2 contains one Ni–Se–P–N(H)–P and one Ni–Se–P–N–P ring. Structural comparison between 1 and 2 makes possible to establish structural effects due to the protonation/deprotonation of the rings at their N atom. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction The coordination chemistry of bis-chalcogenated imi- dodiphosphinate type of ligands, R 2 P(E)N(H)P(E 0 )PR 0 2 (E,E 0 = O, S, Se) has been extensively explored in the course of the last 30 years [1–5]. More recently, Chivers and coworkers have pioneered the use of the Te-containing ligand [6–8]. On the other hand, the reac- tivity of the corresponding monooxidised ligands, R 2 P(E)N(H)PPR 0 2 , has been studied in a comparatively limited number of cases [2]. The coordination modes of both types of ligands have been re- viewed [2,9] and shown to predominately include the formation of six- and five-membered rings, via coordination to the metal ion of the (E,E 0 ) and (E,P) atoms, respectively. Focusing on the latter type of coordination compounds, it has been established that the chelating ligand might be either protonated, M–E–P–N(H)–P, or unprotonated, M–E–P–N–P, at their N atom. Representative cases of structurally characterized mononuclear complexes with coordinated chelating systems (E,P), E = O, S, Se, containing the two types of five-membered rings, are the complexes cis- [Pt{Ph 2 P(O)N(H)PPh 2 -O,P} 2 ](BF 4 ) 2 and cis-[Pt{Ph 2 P(O)NPPh 2 -O,P} 2 ] [10], trans-[Hg{Ph 2 P(O)NPPh 2 -O,P} 2 ] [11], [ReCl 3 (H 2 O){Ph 2 - P(O)NHPPh 2 -O,P}] [12], [Rh(cod){Ph 2 P(O)NHPPh 2 -O,P}]BF 4 [13], [Rh(CO)(PPh 3 ){Ph 2 P(O)NPPh 2 -O,P}] [14], [PdCl(CH 3 ){Ph 2 P(O)- NHPPh 2 -O,P}] [15], [Pd(C,N){Ph 2 P(O)NHPPh 2 -O,P}]BF 4 [16], [OsCl(g 6 -cym){Ph 2 P(O)NHPPh 2 -O,P}]BF 4 [17], [(C 3 H 5 )Pd{Ph 2 P(O)- NHPPh 2 -O,P}]BF 4 [18], [(g 5 -C 5 Me 5 )MCl{Ph 2 P(S)NHPPh 2 -S,P}]BF 4 , M = Rh, Ir [19], [ReO(OEt){Ph 2 P(Se)NPPh 2 -Se,P} 2 ] [20], [Ag{Ph 2 P- (Se)N(H)PPh 2 -Se,P} 2 ]Br [21], [Ru(@CHPh){Ph 2 P(Se)NPPh 2 -Se,P} 2 ] [22], trans-[Pt{Ph 2 P(Se)N(H)PPh 2 -Se,P} 2 ]Cl 2 and cis-[Pt{Ph 2 P- (Se)NPPh 2 -Se,P} 2 ] [23], [Ru(Cl)(NO){Ph 2 P(Se)NP(Se)Ph 2 -Se,Se}- {Ph 2 P(Se)NPPh 2 -Se,P}] [24], [(g 5 -C 5 Me 5 )RhCl{Ph 2 P(Se)NPPh 2 Se,P}] [25] and [Pd{Ph 2 P(Se)NPPh 2 }- Se, P}{Ph 2 P(Se)NP(Se)Ph 2 -Se,Se}] [26]. The interest in this type of systems stems from their potential to act as catalysts, or to establish previously unobserved coordination spheres. For instance, recent studies have explored the catalytic activity of [Rh(CO)(PPh 3 ){Ph 2 P(O)NPPh 2 -O,P}] in the hydroformyla- tion of styrene [14], while the structural characterization of the [Ga(l-Te){ i Pr 2 P(Te)NP i Pr 2 -Te,P}] 2 [27] and [M{Ph 2 P(Te)NPPh 2 - Te,P} 2 ] complexes, M = Zn, Cd, Hg [28], has been described. In this work, the coordination of Ph 2 P(Se)N(H)PPPh 2 to Ni(II) has been studied. Under the appropriate conditions, the synthetic procedure afforded trans-[Ni{Ph 2 P(Se)NPPh 2 -Se,P} 2 ] (1), which 0277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2009.05.006 * Corresponding author. Tel.: +30 210 7274268; fax: +30 210 7274782. E-mail address: Kyritsis@chem.uoa.gr (P. Kyritsis). Polyhedron 28 (2009) 3305–3309 Contents lists available at ScienceDirect Polyhedron journal homepage: www.elsevier.com/locate/poly