Construction of copper halide-triiron selenide carbonyl complexes: synthetic, electrochemical, and theoretical studies.

A new family of CuX-, Cu(2)X(2)-, and Cu(4)X(2)-incorporated mono- or di-SeFe(3)-based carbonyl clusters were constructed and structurally characterized. When the selenium-capped triiron carbonyl cluster Et(4)N[SeFe(3)(CO)(9)] was treated with 1-3 equiv of CuX in tetrahydrofuran (THF) at low or room temperatures, CuX-incorporated SeFe(3) complexes Et(4)N[SeFe(3)(CO)(9)CuX] (X = Cl, Et(4)N[1a]; Br, Et(4)N[1b]; I, Et(4)N[1c]), Cu(2)X(2)-incorporated SeFe(3) clusters Et(4)N[SeFe(3)(CO)(9)Cu(2)X(2)] (X = Cl, Et(4)N[2a]; Br, Et(4)N[2b]), and Cu(4)X(2)-linked di-SeFe(3) clusters Et(4)N[{SeFe(3)(CO)(9)}(2)Cu(4)X(2)] (X = Cl, Et(4)N[3a]; Br, PPh(4)[3b]) were obtained, respectively, in good yields. SeFe(3)CuX complexes 1a and 1b were found to undergo cluster expansion to form SeFe(3)Cu(2)X(2) complexes 2a and 2b, respectively, upon the addition of 1 equiv of CuX (X = Cl, Br). Furthermore, complexes 2a and 2b can expand further to form Cu(4)X(2)-linked di-SeFe(3) clusters 3a and 3b, upon treatment with 1 equiv of CuX (X = Cl, Br). Et(4)N[{SeFe(3)(CO)(9)(CuCl)(2)}(2)] (Et(4)N[4a]) was produced when the reaction of Et(4)N[SeFe(3)(CO)(9)] with 2 equiv of CuCl was conducted in THF at 40 degrees C. The Cu(2)Cl(2)-linked di-SeFe(3)CuCl cluster 4a is a dimerization product derived from complex 2a. Further, it is found that complex 4a can convert to the Cu(4)Cl(2)-linked di-SeFe(3) cluster 3a upon treatment with CuCl. The nature, formation, stepwise cluster expansion, and electrochemical properties of these CuX-, Cu(2)X(2)-, and Cu(4)X(2)-incorporated mono- or di-SeFe(3)-based clusters are elucidated in detail by molecular calculations at the B3LYP level of the density functional theory in terms of the effects of selenium, iron, copper halides, and the size of the metal skeleton.