Spectroscopic Characterization of Highly Excited Neutral Chromium Tricarbonyl.

Spectroscopic characterization of highly excited neutral transition-metal complexes is important for understanding the multifaceted reaction mechanisms between metals and ligands. In this work, the reactions of neutral chromium atoms with carbon monoxide were probed by size-specific infrared spectroscopy. Interestingly, Cr(CO)3 was found to have an unprecedented 7A2″ septet excited state rather than the singlet ground state. A combination of experiment and theory shows that the gas-phase formation of this highly excited Cr(CO)3 is facile both thermodynamically and kinetically. Electronic structure and bonding analyses indicate that the valence electrons of Cr atoms in the septet Cr(CO)3 are in a relatively stable configuration, which facilitate the highly excited structure and the planar geometric shape (D3h symmetry). The observed septet Cr(CO)3 affords a paradigm for exploring the structure, properties, and formation mechanism of a large variety of excited neutral compounds.

Spectroscopic characterization of carbon monoxide activation by neutral chromium carbides.

Spectroscopic characterization of carbon monoxide activation by neutral metal carbides is of essential importance for understanding the structure-reactivity relationships of catalytic sites, but has been proven to be very challenging owing to the difficulty in size selection. Here, we report a size-specific infrared-vacuum ultraviolet spectroscopic study of the reactions between carbon monoxide with neutral chromium carbides. Quantum chemical calculations were carried out to identify the low-lying structures and to interpret the experimental features. The results reveal that the most stable structure of CrC3(CO)2 consists of a CCO ketenylidene unit and that of CrC4(CO)2 has a semi-bridging CO with a very low CO stretching vibrational frequency at 1821 cm-1. The electron structure analyses show that this semi-bridging CO is highly activated through the delocalized Cr-C-C three-center two-electron (3c-2e) interaction between the antibonding orbitals of CO and the metal carbide skeleton. The formation of these metal carbide carbonyls is found to be both thermodynamically exothermic and kinetically facile in the gas phase. The present findings have important implications for the mechanical understanding of the catalytic processes with isolated metal atoms/clusters dispersed on supports.

Recent Development of Pyrimidine-Containing Antimicrobial Agents.

Multidrug-resistant bacterial infections have become an important cause of clinical death in the twenty-first century. Much effort has been made to overcome this challenge. The discovery of novel antimicrobial compounds, as well as the rational use of antibacterial drugs with different structure types and mechanisms, is helping to deal with bacterial resistance. Currently, pyrimidine-containing agents are the major areas of new antibacterial drug discovery. Given their good activities and diverse mechanisms of action, many pyrimidine-containing heterocyclic compounds have become the focus of interest for many scientists. In addition, pyrimidine structure is an important part of many endogenous substances, which is an advantage that allows pyrimidine derivatives to interact with genetic materials, enzymes and other biopolymeric substances in the cell. Scientists have focused on the discovery and structural optimization of pyrimidine derivatives, which has resulted in the discovery of many novel pyrimidine derivatives with intriguing profiles. Herein we summarize the therapeutic potentials of pyrimidine compounds that are promising for antimicrobial applications over the last decade. In particular, the relationships between the structures of modified pyrimidines and their antimicrobial activity are systematically discussed.

A Polyoxochromate Templated 56-Nuclei Silver Nanocluster.

Most of polyoxometallates (POMs) templated silver nanoclusters recorded so far are polyoxomolybdates and polyoxotungstates; however, as congeneric polyoxochromates, they are rarely observed in silver nanoclusters. Herein, a high-nuclearity polyoxochromate, (CrIII4CrVI8O36)12-, is uncovered in a novel silver nanocluster (SD/Ag56a) as an anion template. The mixed-valent (CrIII4CrVI8O36)12- consists of four edge-sharing CrIIIO6 octahedra and eight CrVIO4 tetrahedra, which are fused together by sharing one or two vertexes. The (CrIII4CrVI8O36)12- is the by far highest nuclearity polyoxochromate and is trapped by outer Ag56 bracelet-like shell coprotected by quaternary ligands including iPrS-, NapCOO- (2-naphthalenecarboxylate), CF3COO-, and CH3CN. The antiferromagnetic property and solution behavior of SD/Ag56a are discussed in detail.