Cation-anion pair, chains structure

The structure of the compound consists of two residues, one cationic (PYS-PYSH)+, containing the S-S bond linking the two 2-mercapto-pyridine molecules one of which is protonated and Ij as a counter anion. In the crystal lattice there are four symmetry-independent cation-anion pairs. There are only a few crystal structures reported in the literature containing open chain stable cations of DS-SD dimers, such as the monocationic [(C HgN S-SNjC Hj) ) ) [15]. The two I-I bond distances of the Ij" in the four components of complex (26) are 2.887(4) and 2.944(3) A in component a, 2.874(4) and 2.957(3) A in b, 2.968(3) and 2.862(3) A in c and 2.855(4) and 2.927(3) A in d, respectively, indicating a slight asymmetry of I3 in this complex (covalent hnear asymmetric). 

Alkali metal anions are large and highly polarizable. With two electrons sharing the outer s-orbital, expansion occurs to yield radii of about 2.8,3.1. 3.2, and 3.5A for Na. K. Rb, and Cs, respectively.Crystal structure determination permitted the identification of a variety of structural motifs. In addition to isolated anions, various structures include contact ion pairs between and M. dimers of the anions. (M )2, and anionic chains. (M )n. - Although one might think that coulomb repulsion would prevent dimerization of M. a theoretical study showed that such dimers can be stabilized by adjacent cations. Dimers and chains presumably form by partial hybridization of the diffuse s-orbital with empty p-or J-orbitals. 

Another ionic liquid, containing a nonyl-rather than a butyl-side chain, is shown in Figure 4.2-2. There is little difference between the basic structures of these two ion-pairs (Figures 4.2-1 and 4.2-2) with respect to the non-bonded interactions (hydrogen bonds) occurring between the F atoms on the anion and the C-H moieties on the imidazolium cation. 

In case of [M(edt)2] based salts, the size of the small anion is similar to the size of the CsMes ligand of the cation and only type I structural motives (D+ A D+ A-chains) were observed. For the intermediate size anionic complexes, [M(tdx)2], [M(mnt)2] and [Ni(a-tpdt)2], the most common structural motive obtained in salts based on those anions is also of type I. For the larger anionic complexes, [M(bdx)2] and [M(dmix)2], types III and IV chain arrangements were observed. In both cases anion molecules (type IV) or face-to-face pair of anions (type III) alternate with side-by-side pairs of cations. The complexes [M(mnt)2] and [M(dmix)2] (M = Ni, Pd and Pt) frequently present dimerization in the solid state [19], and they are the only anions where the chain arrangements present face-to-face pairs of anions (structural motives II and III). The variety of structural... 

The crystal structure of [Fe(Cp )2][Ni(dmio)2]MeCN consists of layers composed of parallel "D+D+A D+D+A chains (type IVa), where side-by-side pairs of cations alternate with an anion, with a net charge (+) per repeat unit (D+D+A )... 

The crystal structure of [Fe(Cp)2]2[Ni(mnt)2]2[Fe(Cp)2] is composed by segregated stacks of pairs of cations, [Fe(Cp)2]+, and zig-zag dimerized anions stacks, with a neutral [Fe(Cp)2] molecule laying beside each anionic dimer [65]. In the case of [Co(Cp)2][Ni(dmit)2], the crystal structure consists of layers composed by two types of chains formed by the [Ni(dmit)2] anions, through short S—S contacts. Cation pairs are located between the anionic stacks [68], In the crystal structure of [Co(Cp)2][Ni(dmit)2]3 2MeCN, the partially oxidized anions form... 

The extended structure of [Mn(ebbg)(OH2)] [N03]3 [50,51], is difficult to ascertain, owing to the five co-ordinate Mn(III) geometry and the non co-planarity of the cations and anions. Approximate sheet architectures can be discerned in planes parallel to (-1 3 1) and (1 -2 -2). The latter is shown in Fig. 25. In this view, the cations form dimeric pairs, which are linked through N03 anions and coordinated H20 molecules to form chains aligned in the [0 1 -1] direction. The... 

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