Crystal structural diversity of sulfur-bridged cysteinato dimolybdenum(V) complexes: The influence of counter metal cations

Eight new crystal structures of sulfur-bridged dinuclear molybdenum(V) complexes with l-cysteine ligands, [Mo2(μ-S)2O2(cys)2]2− (1), were determined by changing the counter cations (K+, Ca2+, Sr2+, Mn2+, Ni2+, Cd2+, and Pb2+, where Mn2+ gave two kinds of crystal structures): K2[Mo2O2S2 (cys)2]·5H2O (1-K), Ca[Mo2O2S2 (cys)2]·8H2O (1-Ca), Sr[Mo2O2S2(cys)2]·6H2O (1-Sr), Mn[Mo2O2S2(cys)2]·12H2O (1-MnA), Mn[Mo2O2S2(cys)2]·7H2O (1-MnB), Ni[Mo2O2S2 (cys)2]·14H2O (1-Ni), Cd[Mo2O2S2(cys)2]·2H2O (1-Cd), and Pb[Mo2O2S2(cys)2]·2H2O (1-Pb). The eight crystal structures and two with other counter cations (Na2[Mo2O2S2(cys)2]·4H2O (1-Na) and Zn[Mo2(μ-S)2O2(cys)2]·2H2O (1-Zn)) so far reported were compared. The structures vary considerably by changing the counter cations, while few remarkable differences were observed with regard to the dimensions in the complex anion 1. There are four kinds of linkages: (1) one-dimensional zigzag chains appear in 1-Na, 1-Zn, 1-Cd, and 1-Pb; (2) a two-dimensional linkage appears in 1-K; (3) the cation and anion are directly linked, but they are separated from other cation–anion groups in 1-MnA; (4) the cation and anion are separated in 1-Ca, 1-Ni, 1-Sr, and 1-MnB. A good relationship exists between the coordination modes of metal cations and solubility of the corresponding metal sulfides. The coordination modes of metals are divided into two groups: Group 1: metal ions (Na+, K+, Sr2+, Ca2+, Mn2+(two kinds of crystals), and Ni2+) whose sulfides have large or medium solubility in water bind to oxygen (the carbonyl oxygen of cysteine, the terminal oxygen of Mo = O, and/or water); Group 2: metal ions (Zn2+, Cd2+, and Pb2+) whose sulfides have small solubility bind to cysteine sulfur. The HSAB principle explains the relationship.

The crystal structures of sulfur-bridged cysteinato dinuclear molybdenum (V) complexes depend on the counter metal cations, and the dependence is explained by the HSAB principle.Figure optionsDownload as PowerPoint slideHighlights
► Ten crystal structures of sulfur-bridged cysteinato dinuclear molybdenum(V) complex.
► The structures vary considerably by changing the counter metal cations.
► Metal ions whose sulfides have large solubility in water bind to cysteine oxygen.
► Metal ions whose sulfides have small solubility bind to cysteine sulfur.
► The HSAB principle explains the relationship.