Bonding modes of nitrite and nitrate in palladium(II) and platinum(II) complexes Tae Hwan Noh • Sung Min Kim • Kyung Hwan Park • Ok-Sang Jung Received: 27 March 2012 / Accepted: 9 May 2012 / Published online: 3 June 2012 Ó Springer Science+Business Media B.V. 2012 Abstract The crystal structures of the well-known com- plexes, [(Me 4 en)M(II)X 2 ] (Me 4 en = N,N,N 0 ,N 0 -tetra- methylethylenediamine; M(II) = Pd(II) or Pt(II); X - = NO 2 - or NO 3 - ) have been determined. For [(Me 4 en)- Pd(NO 2 ) 2 ] and [(Me 4 en)Pt(NO 2 ) 2 ], the nitrite anion acts as a monodentate N-donor ligand in the solid state. In con- trast, for [(Me 4 en)Pd(ONO 2 )(O 2 NO)], the two nitrate anions act as a monodentate O-donor (ONO 2 ) and a bidentate O,O 0 -donor (O 2 NO). Recrystallization of [(Me 4 en)Pt(NO 3 ) 2 ] from Me 2 SO yields the Me 2 SO adduct with a monodentate O-donor nitrate and a counteranionic nitrate, [(Me 4 en)Pt(ONO 2 )(S-Me 2 SO)](NO 3 ). The solution behavior of these complexes, including the equilib- rium between coordinated and free Me 2 SO, has been investigated. Introduction An increasing effort has been directed toward the design and synthesis of metal complexes via intermediates involving (counter)anions in order to modulate the struc- tural and physical properties of molecular materials by means of chemical triggers [1–5]. The labile bonding modes of anions have often been used to induce useful properties in the resulting complexes. Platinum(II) and palladium(II) species can be obtained in this way, with useful properties as catalysts, antitumor drugs, ring- expansion reactions, hydrogelators, interesting morpholo- gies, and induction of the ‘‘magic ring’’ phenomenon by means of labile Pd–N bonds [5–10]. Thus, the anions in such complexes play crucial roles in the synthesis of task- specific metal complexes because they have many variable features such as charge, size, geometry, solvent effects, pH dependence, template assembly, and ion-pair recognition [11–14]. However, direct comparison of nitrite and nitrate anions as a rational strategy remains relatively unexplored. In an effort to expand the role of these anions in molecular construction, this article reports the synthesis, coordination mode, and related properties of well-known complexes, namely [(Me 4 en)M(II)X 2 ] (Me 4 en = N,N,N 0 ,N 0 -tetra- methylethylenediamine; M(II) = Pd(II) or Pt(II); X - = NO 2 - or NO 3 - ). The nitrite and nitrate anions in these complexes are common species that are associated with environmental pollution, disease pathways, and biological processes [1, 14, 15]. In particular, these two anions are significant in which NO 2 - and NO 3 - complexes are gen- erally more soluble than their BF 4 - , ClO 4 - , and PF 6 - analogs in polar solvents [16]. Dimethyl sulfoxide is a strong aprotic coordinating solvent for various classes of compounds. In metal complexes of Me 2 SO, the sulfur donor coordinates with soft metal centers, while the oxygen donor prefers hard metal centers [17]. Experimental Materials and measurements Potassium tetrachloropalladate(II), potassium tetrachloro- platinate(II), N,N,N 0 ,N 0 -tetramethylethylenediamine (Me 4 en), Electronic supplementary material The online version of this article (doi:10.1007/s11243-012-9619-y) contains supplementary material, which is available to authorized users. T. H. Noh  S. M. Kim  K. H. Park  O.-S. Jung (&) Department of Chemistry and Research Institute of Functional Materials Chemistry, Pusan National University, Pusan 609-735, Korea e-mail: oksjung@pusan.ac.kr 123 Transition Met Chem (2012) 37:535–540 DOI 10.1007/s11243-012-9619-y