Binuclear Homoleptic Copper Carbonyls Cu₂(CO)_x (x = 1−6):  Remarkable Structures Contrasting Metal−Metal Multiple Bonding with Low-Dimensional Copper Bonding Manifolds

Abstract

Binuclear homoleptic copper carbonyls Cu(2)(CO)(x) (x = 1-6) have been studied using four different density functional theory methods (DFT) in conjunction with a basis set of extended double-zeta plus polarization quality, labeled as DZP. For each homoleptic binuclear copper carbonyl compound, several stationary point structures are presented, and these structures are characterized in terms of their geometries, thermochemistry, and vibrational frequencies. The optimal unsaturated Cu(2)(CO)(x) (x = 1-6) structures are generated by joining 18-electron tetrahedral, 16-electron trigonal, 14-electron linear copper carbonyl building blocks, and/or bare copper atoms with copper-copper single bonds rather than by joining 18-electron copper carbonyl units with multiple copper-copper bonds. For Cu(2)(CO)(6) the eclipsed and staggered ethane-like structure are virtually degenerate and lie significantly lower in energy than other possible structures. The eclipsed Cu-Cu single bond distance is predicted to be 2.61 A, while that for the staggered structure is 2.65 A. The lowest energy structure for Cu(2)(CO)(5) is the eclipsed ethyl radical-like structure, with r(e)(Cu-Cu) = 2.51 A. The staggered ethyl radical-like structure lies only 0.1 kcal/mol higher in energy, with a Cu-Cu distance shorter by only approximately 0.001 A. For Cu(2)(CO)(4) a methylcarbene-like structure is predicted to lie lowest, with Cu-Cu distance 2.40 A. However, twisted and planar ethylene-like structure lie only 3-5 kcal/mol higher. For Cu(2)(CO)(3) a surprising methylcarbyne-like structure with r(e)(Cu-Cu) = 2.38 A is predicted to lie lowest with all four DFT methods. However, a classical vinyl radical-like lies only 2-4 kcal/mol higher. For Cu(2)(CO)(2) theory predicts a vinylidene-like structure with r(e)(Cu-Cu) = 2.34 A to be essentially degenerate with cis and trans bent acetylene structures with copper-copper distances 2.33 A. Finally, and consistent with earlier theoretical studies, the linear end on Cu-Cu-CO structure with r(e)(Cu-Cu) = 2.27 A is the predicted global minimum for Cu(2)(CO).

Metal–Metal (MM) Bond Distances and Bond Orders in Binuclear Metal Complexes of the First Row Transition Metals Titanium Through Zinc

“…Experimental evidence for Cu 2 (CO) 6 was found (Ozin) by condensation of Cu atoms with CO using matrix isolation IR and UV–visible methods and confirmed by low temperature studies (Kasai and Jones) and spectroscopic studies (Mile and Howard , ) in inert matrices at 77 K. By the 18-electron rule, Cu 2 (CO) 6 should have a Cu–Cu single bond. The above-noted BP86 study did not propose an MM fBO for any of the species studied in the series and avoided precise descriptions of MM multiple bonds for all of the unsaturated cases. The filled d 10 shell of a Cu(0) atom could lead to difficulties in the formation of Cu–Cu multiple bonds.…”

“…Cu−Cu Bond Lengths in Homoleptic Binuclear Copper Carbonyls542 Systematic theoretical studies on a series of homoleptic dicopper carbonyls Cu 2 (CO) n (n = 6, 5, 4, 3, 2, and 1) 542 used four functionals. The BP86 predictions are presented in Table36.…”

Structure and Magnetic Properties of a 2D Paddle‐wheel Dinuclear[Cu2] Cluster‐based Polymer with 1,1‐Cyclohexanediacetate Ligand

“…Each Cu II ion is six‐coordinate and displays a octahedral arrangement. Two symmetry‐related Cu II ions are held together by four bidentate carboxylate groups in syn ‐ syn μ 2 ‐η 1 :η 1 coordination mode and result in a paddle‐wheel dinuclear [Cu 2 ] cluster with the Cu ··· Cu distances of 2.57(1) Å, which is strictly consistent with the existence of a Cu–Cu single bond , . The four syn ‐ syn carboxylate groups come from four CHDA 2– ligands (Figure b), from which the oxygen atoms define an equatorial coordinated plane of two centro‐symmetric Cu II ions with Cu–O distances ranging from 1.9421(15) to 2.0032(14) Å.…”

Photoelectron Velocity Map Imaging Spectroscopy of Lead Tetracarbonyl–Iron Anion PbFe(CO)4–

“…In order to interpret the electronic and geometrical structures of PbFe­(CO) 4 0/–1 , theoretical computations are carried out in the Gaussian 09 suite of programs . Density functional calculation, with electron correlation effects included, appears to be a practical and effective tool to study TM carbonyls. − The B3LYP hybrid functional, which consists of the Becke’s three-parameter exchange functional (B3) and Lee–Yang–Parr correlation functional (LYP), − appears to perform well for the TM carbonyls clusters and thus is chosen to elucidate the electronic and geometrical structures of PbFe­(CO) 4 0/–1 . Global minima searches are carried out using the Stuttgart relativistic small core basis set and efficient core potential for the heavy elements and 6-311+G­(d) basis sets for C and O.…”