Tetramers Cu4(μ4-O)(η-X)6(L4): Analysis of structural data

This review summarizes structural parameters for forty five Cu4(μ4-O)(η-X)6(L4) tetramers. There are four types of structurally equal core units, CuCl3ON, CuCl3OO, CuCl3OCl and CuBr3ON. There are also tetramers which contain structurally unequal core units: CuCl3ON (x2) and CuCl2BrON (x2); CuCl3ON (x1), CuCl2BrON (x2) and CuCl3OCl (x1). There is a tendency for an elongated Cu⋯Cu separation as well as Cu–L bond distances with increase of the covalent radius of the coordinating atom(s). Tetrahedral distortion around oxygen atom (OCu4) increases in the order: 1.67° (CuCl3OCl) < 2.10° (CuCl3ON) < 2.11° (CuCl3OO′) < 2.27° (CuBr3ON). The mean Cu–Cl–Cu bridge angle of 80.5° is about 4.0° more open than that of a Cu–Br–Cu (76.5°). The cluster Cu16O4Br7Cl17(4-Mepy)16 (4-Mepy = 4-methylpyridine) contains four crystallographically independent tetramers: Cu4OBrCl5(4-Mepy)4 (1), Cu4OBrCl5(4-Mepy)4 (2) Cu4OBr2Cl4(4-Mepy)4 (3) and Cu4OBr3Cl3(4-Mepy)4 (4), which is a unique example of stereoisomerism. There are other examples which exist in two isomeric forms. Another contains two or even four crystallographically independent tetramers within the same crystal, differing mostly by degree of distortion and is an examples of distortion isomerism. Pairs of Cu4OCl6(n-Meim)4 (n-Meim = n-methylimidazole) (n = 1 or 2) are examples of ligand isomerism.

Research highlights▶ Analysis of structural data of Cu4O(X)6(EL)4 (X = Cl, Br; E = O or N). ▶ Classification of the chromophores Cu4X3OE. ▶ Stereoisomers in the tetramers. ▶ Correloations between the Cu–L bond distances, L–Cu–L and Cu–O–Cu bond angles.