Synthesis, Crystal Structures, and Spectroscopic Characterization of Two Pairs of Racemic Isomers of [{Co₂(aet)₂}{Co(aet)₃}₂]⁴⁺(aet = 2-Aminoethanethiolate):  A Novel S-Bridged Tetranuclear Cobalt(III) Complex Formed by Ligand Transfer from Nickel(II) to Cobalt(III)

Abstract

A novel S-bridged tetracobalt(III) complex, [{Co 2 (aet) 2 }{Co(aet) 3 } 2 ] 4+ (1), was prepared by reacting [Ni(aet) 2 ] (aet ) 2-aminoethanethiolate) with [CoCl(NH 3 ) 5 ] 2+ or [CoCl 2 (en) 2 ] + (en ) ethylenediamine) in water. 1 formed two pairs of racemic isomers, 1a and 1b, which were separated by fractional crystallization and/or cation-exchange column chromatography. The crystal structures of 1a and 1b were determined by X-ray crystallography. 1a(NO 3 ) 4 ‚2H 2 O, empirical formula C 16 H 52 N 12 O 14 S 8 Co 4 , crystallizes in the triclinic space group P1 h with a ) 13.585(3) Å, b ) 15.132(3) Å, c ) 10.699(2) Å, R ) 101.46(1)°, β ) 104.78(1)°, γ ) 95.89(1)°, and Z ) 2. 1b(NO 3 ) 4 ‚2H 2 O crystallizes in the monoclinic space group Cc with a ) 26.633(6) Å, b ) 10.204(1) Å, c ) 15.907( 4) Å, β ) 110.33(1)°, and Z ) 4. Each of 1a and 1b contains four cobalt atoms which are linked by one double and two triple sulfur bridges in a boat-type metal array. The two outer cobalt atoms have a fac-Co(N) 3 -(S) 3 chromophore, while the two inner cobalt atoms have a Co(N)(S) 5 chromophore. The isomers possible for 1 are discriminated by a combination of the ∆ or Λ configuration for the outer cobalt centers and the C or A configuration for the inner cobalt centers, and X-ray analyses indicated that 1a and 1b have the ∆AA∆/ΛCCΛ and ∆CC∆/ΛAAΛ configurations, respectively. Each of 1a and 1b was optically resolved, and their electronic absorption, circular dichroism (CD), and NMR spectral properties are also reported. The additivity on CD was considered to assign the absolute configuration for the optically resolved isomers of 1a and 1b.

Molecular assembly of two [Co(ii)4] linear arrays

“…À counterions, located within the crystal lattice, helping to connect the cations to each other through a network of hydrogen bonds.w This molecule joins a small group of structurally characterized tetranuclear complexes of Co(II) with a chain-like topology. 5,9,[11][12][13] The structure of 2 corroborates the hypothesis that the [Co 4 L 2 ] 4+ unit is a robust moiety and remains intact after substitution of MeOH ligands by H 2 O. In fact, it was inferred previously that the all methanol derivative 1 replaces completely its MeOH ligands by water upon exposure to air, while maintaining the molecular backbone.…”

Designed Topology and Site‐Selective Metal Composition in Tetranuclear [MM′⋅⋅⋅M′M] Linear Complexes

“…The numerous aromatic rings present in 2 help the packing of its molecules through van der Waals and p-stacking interactions; along the a axis, chains of complexes are connected through bonds between aromatic moieties of the L 4À ligands, whereas in the a direction the molecules pack with the help of p-p interactions between pyridine ligands. Although almost two hundred [Co 4 ] clusters have been reported, we have only found three examples consisting of linear strings of four cobalt ions, [31][32][33] thus confirming the rarity of discrete linear clusters in coordination chemistry.…”

A Molecular Chain of Four CoII Ions Stabilized by a Tris-Pyridyl/Bis-?-Diketonate Ligand

“…Surprisingly, there are very few examples with a linear topology, [28][29][30] which shows that such an arrangement is difficult to achieve.…”