MP2-Based Correction Scheme to Approach the Limit of a Complete Pair Natural Orbitals Space in DLPNO-CCSD(T) Calculations.

The domain-based local pair natural orbital (PNO) coupled-cluster DLPNO-CCSD(T) method has been proven to provide accurate single-point energies at a fraction of the cost of canonical CCSD(T) calculations. However, the desired "chemical accuracy" can only be obtained with a large PNO space and extended basis set. We present a simple yet accurate and efficient correction scheme based on a perturbative approach. Here, in addition to DLPNO-CCSD(T) energy, one calculates DLPNO-MP2 correlation energy with the same settings as in the preceding coupled-cluster calculation. In the next step, the canonical MP2 correlation energy is obtained in the same orbital basis. This can be efficiently performed for essentially all molecule sizes accessible with the DLPNO-CCSD(T) method. By taking the difference between the canonical MP2 and DLPNO-MP2 energies, we obtain a correction term that can be added to the DLPNO-CCSD(T) correlation energy. This way, one can obtain the total correlation energy close to the limit of the complete PNO space (cPNO). The presented approach allows us to significantly increase the accuracy of the DLPNO-CCSD(T) method for both closed- and open-shell systems. The latter are known to be especially challenging for locally correlated methods. Unlike the previously developed PNO extrapolation procedure by Altun, Neese, and Bistoni ( J. Chem. Theory Comput. 2020, 16, 6142-6149), this strategy allows us to get the DLPNO-CCSD(T) correlation energy at the cPNO limit in a cost-efficient way, resulting in a minimal overall increase in calculation time as compared to the uncorrected method.

Expanding manganese(IV) aqueous chemistry: unusually stable water-soluble hexahydrazide clathrochelate complexes.

Mn cage complexes are rare, and the ones successfully isolated in the solid state are not stable in water and organic solvents. Herein, we present the first report of mononuclear Mn clathrochelates, in which the encapsulated metal exists in the oxidation state +4. The complexes are extremely stable in the crystalline state and in solutions and show rich redox chemistry.

Crystal structure of bis-[(S)-2-(2-hy-droxy-benzyl-amino)-4-methyl-penta-noato-κ2 N,O 1](1,10-phenanthroline-κ2 N,N')cadmium dihydrate.

The asymmetric unit of the mononuclear mixed-ligand title complex, [Cd(C13H18NO3)2(C12H8N2)]·2H2O, contains two crystallographically independent mol-ecules that differ insignificantly in their geometrical parameters. In both, the CdII cation lies on a twofold rotation axis and is coordinated in a distorted octa-hedral fashion to two monodeprotonated residues of the l-leucine-derived ligand (S)-2-(2-hy-droxy-benzyl-amino)-4-methyl-penta-noic acid (L), as well as to a 1,10-phenanthroline ligand in a κ2 N,N' mode. The former coordinate in an N,O-chelating mode, exhibiting a trans-N,N' mutual disposition. The phenolic oxygen donor groups remain protonated and do not coordinate to the cation but take part in intra- and inter-molecular hydrogen bonds. In the crystal, O-H⋯O hydrogen bonding results in the formation of a three-dimensional network structure. The contribution to the electron density of two disordered water mol-ecules was removed with the SQUEEZE procedure in PLATON [Spek (2015 ▸). Acta Cryst. C71, 9-18]. The studied crystal was refined as a two-component inversion twin. The title complex was also characterized by IR and 1H NMR spectroscopic methods.

Structural characterization and DFT study of bis-{(S)-2-[(2-hy-droxy-benz-yl)amino]-3-(4-hy-droxy-phen-yl)propano-ato-κ2N,O}(1,10-phenanthroline-κ2N,N')cadmium(II) tetra-hydrate.

In the title compound, [Cd(C16H16O3)2(C12H8N2)]·4H2O, the Cd ion lies on a twofold rotation axis and is chelated by two monodeprotonated residues of the l-tyrosine-derived ligand (S)-2-[(2-hy-droxy-benz-yl)amino]-3-(4-hy-droxy-phen-yl)propanoic acid (L) in a κ2N,O amino acid chelating mode, exhibiting an (N,N')-trans disposition, and by 1,10-phenanthroline in a κ2N,N' mode. The latter ligand is also located about the twofold rotation axis that bisects the central six-members ring. The phenolic groups remain protonated and non-coordinating and take part as acceptors in the intra-molecular hydrogen bonds with the amino groups of the acido ligands. The Cd ion is six-coordinated in a distorted octa-hedral environment. In the crystal, O-H⋯O hydrogen bonds result in the formation of three-dimensional network structures. The title complex has also been characterized by IR and 1H NMR spectroscopy and DFT studies. The crystal studied was refined as an inversion twin.