Coordination bonding in dicopper and dichromium tetrakis(μ‐acetato)‐diaqua complexes: Nature, strength, length, and topology

Abstract

Geometry optimization, energetics, electronic structure, and topology of electron density of dicopper (I) and dichromium (II) tetrakis(μ‐acetato)‐diaqua complexes are studied focusing on the metal–metal interactions. The performance of broken symmetry (BS) single‐determinant ab initio (Hartree–Fock, Møller–Plesset perturbation theory to the second and third orders, coupled clusters singles and doubles) and density functional theory (BLYP, B3LYP, B3LYP‐D3, B2PLYP, MPW2PLYP) methods is compared to multideterminant ab initio (CASSCF, NEVPT2) methods as well as to the multipole model of charge density from a single‐crystal X‐ray diffraction experiment (Herich et al., Acta Cryst. 2018, B74, 681–692). In vacuo DFT geometry optimizations (improper axial water ligand orientation) are compared against the periodic ones. The singlet state is found to be energetically preferred. J coupling of (I) becomes underestimated for all ab initio methods used, when compared to experiment. It is concluded that the strength of the direct M─M interactions correlates closely with the J coupling magnitude at a given level of theory. The double potential well character of (II) and of the dehydrated form of (II) are considered with respect to the Cr─Cr distance. The physical effective bond order of the metal–metal interaction is small (below 0.1 e) in (I) and moderate (0.4 e) in (II). The CASSCF results overestimate the electron density of the metal–metal bond critical point by 20% and 50% in (I) and (II), respectively, when compared to the multipole model. © 2019 Wiley Periodicals, Inc.

The Ruthenium Nitrosyl Moiety in Clusters: Trinuclear Linear μ-Hydroxido Magnesium(II)-Diruthenium(II), μ3-Oxido Trinuclear Diiron(III)–Ruthenium(II), and Tetranuclear μ4-Oxido Trigallium(III)-Ruthenium(II) Complexes

“…CASSCF- and NEVPT2-calculated J couplings of the neutral species of 6 (extracted for S = 5, making Δ E relative to S = 0) are −0.067 and −0.159 kJ/mol (−5.6 and −13.3 cm –1 ), respectively. The underestimation of J coupling for the CASSCF and NEVPT2 methods confirms the trends in results previously found for a dicopper­(II)-tetrakis­(μ-acetato)-diaqua complex . Results for the oxidized and reduced species of 6 can be found in the Supporting Information (section on DFT and ab initio results of [ 6 ] + and [ 6 ] − and Tables S1 and S2).…”

“…The underestimation of J coupling for the CASSCF and NEVPT2 methods confirms the trends in results previously found for a dicopper(II)-tetrakis(μ-acetato)-diaqua complex. 81 Results for the oxidized and reduced species of 6 can be found in the Supporting Information (section on DFT and ab initio results of [ 6 ] + and [ 6 ] − and Tables S1 and S2 ).…”

Spin-Adapted Externally Contracted Multireference Configuration Interaction Method Based on Selected Reference Configurations

“…Here, we choose tetrakis­(μ 2 -acetato)-diaqua-dicopper­(II) (Cu 2 (OAc) 4 (H 2 O) 2 , shown in Figure ) as an example. Its experimental S 0 –T 1 gap is less than 1 kcal/mol, − which is challenging for theoretical prediction.…”

“…The experimental geometry is taken from ref . Previous research suggests that more Cu–O interactions should be accounted for in active space to obtain more accurate results. Therefore, in addition to the 3d, 4s, and 4d atomic orbitals of the two copper centers, a sp-PHO (projected hybrid orbital , ) of each O atom in (OAc) − and a sp 2 -PHO of each O atom in H 2 O are selected to the (38e, 32o) active space by the imposed automatic selection and localization of active orbitals (iCAS) approach using the BDF package (development version) .…”

A supported Cr–Cr sextuple bond in an all-metal cluster

“…[12][13][14] As a multiple bonding prototype, the chromium dimer has been widely studied, especially since Nguyen et al synthesized the first stable Cr-Cr quintuple bonding [Cr 2 (Ar′) 2 ] complex in 2005, 14 which still holds the record of the highest bond order among the stable molecules. 7,9,[15][16][17][18][19][20][21][22][23][24][25][26][27][28] Since then, there are burgeoning research studies on the characterization and exploration of Cr-Cr and other high multiplicity metal-metal bonding structures. Notably, sextuple bonds were only considered to exist in naked Mo 2 and W 2 dimers on the theoretical shelf, [28][29][30] while the radial distribution maxima of the 3d orbitals of Cr lie in the same region as those of the inner 3s and 3p orbitals, resulting in two intrinsically weak δ overlaps and they were only suggested to be quadruple.…”