Polyhalide anions in crystals .2. I-3(-) asymmetry and N-H...I bonding: Triiodides of the Me(2)NH(2)(+),Ph(2)I(+), tropanium, N,N,N',N'-Me(4)-1,2-ethanediammonium, N,N,N',N'-Me(4)-1,3-propanediammonium, N-Me-piperazinium(2+), and N,N'-Me(2)-piperazinium(2+) cations, and Me(2)NH(2)I

Crystal-structure determinations are reported for Me(2)NH(2)I(3), (Ph(2)I)I-3, tropanium . I-3, [Me(2)HN(CH2)(2)NHMe(2)](I-3)(2), [Me(2)HN(CH2)(3)NHMe(2)](I-3)(2), (N-Me-piperazinium) (I-3)(2) . H2O, (N,N'-Me(2)-piperazinium)(I-3)(2), and Me(2)NH(2)I. The features of these and relevant literature structures are used toll) classify triiodide structures by their ion-packing types; (2) analyze the relationship between the two I-I bond lengths d and d* in the I-3(-) anion; and (3) examine the effect of N-H(N)...I hydrogen bonding on the symmetry of the I,- anion. It is found that the d,d* relationship can be represented to a high degree of correlation by the power function d* - d(0) = K(d - d(0))(-c) (d* greater than or equal to d, d(0) = d(I-I) in I-2(g)) based on the 3c4e model of the anion. An empirical correlation is shown to exist between the H(N)...I and N...I distances both for unbranched and branched N-H(N)...I bonds. Comparison of the degree of asymmetry of I-3(-) in two samples, one containing H-bonded I-3(-) anions, the other with H-bonding absent, leads to the conclusion that while H-bonding is a factor affecting I-3(-) symmetry, it is not a preferential factor. The four 1:2 title triiodides have structures of, or related to, the CdI2 type, in which the anions form infinite pseudo-hexagonal channels. The positioning of the divalent cations on the axes of these channels gives rise to an interesting ''vernier'' effect governed by the cation length and H-bonding ability. Bonding in centrosymmetric I-4 rings in (Ph(2)I)I-3 and (Ph(2)I)I is examined.