Spontaneous transformation of the thermally stable [HS](-)-bound {Fe(NO)2}(9) dinitrosyl iron complex (DNIC) [(HS)2Fe(NO)2](-) (1) into [(NO)2Fe(μ-S)]2(2-) (Roussin's red salt (RRS)) along with release of H2S, probed by NBD-SCN (NBD = nitrobenzofurazan), was observed when DNIC 1 was dissolved in water at ambient temperature. The reversible transformation of RRS into DNIC 1 (RRS → DNIC 1) in the presence of H2S was demonstrated. In contrast, the thermally unstable hydrosulfide-containing mononitrosyl iron complex (MNIC) [(HS)3Fe(III)(NO)](-) (3) and [Fe(III)(SH)4](-) (5) in THF/DMF spontaneously dimerized into the first structurally characterized Fe(III)-hydrosulfide complexes [(NO)(SH)Fe(μ-S)]2(2-) (4) with two {Fe(NO)}(7) motifs antiferromagnetically coupled and [(SH)2Fe(μ-S)]2(2-) (6) resulting from two Fe(III) (S = 5/2) centers antiferromagnetically coupled to yield an S = 0 ground state with thermal occupancy of higher spin states, respectively. That is, the greater the number of NO ligands bound to [2Fe2S], the larger the antiferromagnetic coupling constant. On the basis of DFT computation and the experimental (and calculated) reduction potential (E1/2) of complexes 1, 3, and 5, the NO-coordinate ligand(s) of complexes 1 and 3 serves as the stronger electron-donating ligand, compared to thiolate, to reduce the effective nuclear charge (Zeff) of the iron center and prevent DNIC 1 from dimerization in an organic solvent (MeCN).

Five new three-dimensional transition metal coordination polymers (CPs) with dia and different aromatic carboxylates, [Cd(oba)(dia)0.5] (1), [Cd(Hbtc)(dia)]·3H2O (2), and [M3(2-stp)2(dia)6(H2O)2] (3a, M = Cd; 3b, M = Co; 3c, M = Ni) were synthesized under hydrothermal condition (dia = 9,10-di(1H-imidazol-1-yl)anthracene; oba = 4,4′-oxybis(benzoate); btc = benzene-1,3,5-tricarboxylate; 2-stp = 2-sulfoterephthalate). Compounds 3a–c are isostructural. The coordination geometries at cadmium in 1, 2, and 3a are capped trigonal prism, pentagonal bipyramid, and octahedron, respectively. This diversity in coordination geometry is in sharp contrast to 3c and previously reported nickel complexes of a similar ligand set. The difference in metal-containing node geometries and carboxylate structures results in diverse network connectivity, including a tcs topology for 1, an unprecedented binodal topology of (42.63.85)(42.6) for 2, and a rare trinodal topology of (4.64.8)2(43.63)2(44.610.8) for 3. Based on secondary building units, the networks in 2 and 3 can be, alternatively, described as rob and pcu (or ilc) nets, respectively. This work shows the effect of the specific ion and the rich potential of using bulky bis(imidazole) and aromatic carboxylate as ligands in the construction of CPs with unusual topologies.

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