Characterization of Zn^q+–imidazole (q = 0, 1, 2) organometallic complexes: DFT methods vs. standard and explicitly correlated post-Hartree–Fock methods

Abstract

In the present work, we investigate the bonding, structures, stability and spectra of the Zn(q+)Im (where q = 0, 1, and 2) complexes, which are zeolitic imidazolate frameworks (ZIFs) and Zn-enzyme sub-units. Through a benchmark work, we used density functional theory (DFT) with dispersion correction and standard and explicitly correlated ab initio methods. For neutral Zn(0)Im, we found two stable weakly bound forms: (i) a stacked ferrocene-like complex and (ii) a planar σ-type complex. This is the first report of the Zn(0) organic compound with a stacked ferrocene-like structure. The most stable isomers of the ionic species consist of σ-type bonded complexes. The role of various types of covalent and noncovalent interactions within these complexes is discussed after performing vibrational, NBO, charge and orbital analyses. For neutral species, van der Waals (vdWs) and charge transfer through covalent as well as noncovalent interactions are in action; whereas the bonding is dominated by charge transfer from Zn to Im within the ionic species. These findings are important to understand, at the microscopic level, the structure and the bonding within the ZIFs and the Zn-enzymes. Moreover, we establish the ability and reliability of M05-2X and PBE0 functionals for the simultaneous correct description of covalent and noncovalent interactions since this DFT leads to a close agreement with post-Hartree-Fock methods. The newly launched M11 functional is also suited for the description of noncovalent interactions. Therefore, M05-2X and PBE0 functionals are recommended for studying the larger complexes formed by Zn and Im, such as the ZIFs and Zn-enzymes.

Ab Initio and DFT Studies on CO2 Interacting with Znq+–Imidazole (q=0, 1, 2) Complexes: Prediction of Charge Transfer through σ‐ or π‐Type Models

“…Slight deviations between the other DFTs with MP2 and M05‐2X+D3 data are apparent, which are due to the omission of a D3 correction, as discussed in Ref. .…”

“…At the M05‐2X+D3/6‐311++G(d,p) level of theory, the distance between Zn and the center of the Im cycle ( R Zn−π ) was computed at approximately 3.3–3.4 Å. This distance is longer than that of isolated [Zn 0 Im] MII complex (≈2.755 Å) because of the weakening of this bond upon clustering. For CO 2 –[Zn 0 Im] distances, we found similar trends as described above for CO 2 @[Zn 0 Im] MI.…”

“…We characterized three stable forms of CO 2 @Im clusters: a global minimum with a strong electron‐donor–acceptor (EDA) complex (denoted CO 2 @Im a ), a π‐stacked structure (CO 2 @Im b ) and a σ‐type H‐bonded complex (CO 2 @Im c ) . For neutral [Zn 0 Im], two modes of interaction between Zn 0 and Im were found: model I (MI), dominated by partial covalent character between Zn and N, in which Zn 0 is attached to the non‐protonated nitrogen atom of Im, and model II (MII) corresponding to the π‐stacking interaction between Im and Zn 0 . For [Zn + Im] and [Zn 2+ Im], only covalent σ‐type coplanar structures were identified …”

“…For neutral [Zn 0 Im], two modes of interaction between Zn 0 and Im were found: model I (MI), dominated by partial covalent character between Zn and N, in which Zn 0 is attached to the non‐protonated nitrogen atom of Im, and model II (MII) corresponding to the π‐stacking interaction between Im and Zn 0 . For [Zn + Im] and [Zn 2+ Im], only covalent σ‐type coplanar structures were identified …”

“…These methods provide reliable properties for such complexes, as we established recently for Zn q + –Im complexes (see Ref. for more details). The present computations have been performed using MOLPRO (version 2012.1) and Gaussian 09 (G09‐D.01) packages.…”