Structural and Optical Properties of Metal-Nitrosyl Complexes

Therapeutic and Diagnostic Agents based on Bioactive Endogenous and Exogenous Coordination Compounds

Metal-based coordination compounds have very special place in bioinorganic chemistry because of their different structural arrangements and significant application in medicine. Rapid progress in this field increasingly enables the targeted design and synthesis of metal-based pharmaceutical agents that fulfill valuable roles as diagnostic or therapeutic agents. Various coordination compounds have important biological functions, both those initially present in the body (endogenous) and those entering the organisms from the external environment (exogenous): vitamins, drugs, toxic substances, etc. In the therapeutic and diagnostic practice, both the essential for all living organisms and the trace metals are used in metal-containing coordination compounds. In the current review, the most important functional biologically active compounds were classified group by group according to the position of the elements in the periodic table.

Simulations of the Aqueous "Brown-Ring" Complex Reveal Fluctuations in Electronic Character

Ab initio molecular dynamics (AIMD) simulations of the aqueous [Fe(H2O)5(NO)]2+ "brown-ring" complex in different spin states, in combination with multiconfigurational quantum chemical calculations, show a structural dependence on the electronic character of the complex. Sampling in the quartet and sextet ground states show that the multiplicity is correlated with the Fe-N distance. This provides a motivation for a rigid Fe-N scan in the isolated "brown-ring" complex to investigate how the multiconfigurational wave function and the electron density change around the FeNO moiety. Our results show that subtle changes in the Fe-N distance produce a large response in the electronic configurations underlying the quartet wave function. However, while changes in spin density and potential energy are pronounced, variations in charge are negligible. These trends within the FeNO moiety are preserved in structural sampling of the AIMD simulations, despite distortions present in other degrees of freedom in the bulk solution.

Projection-Based Density Matrix Renormalization Group in Density Functional Theory Embedding

The density matrix renormalization group (DMRG) method has already proved itself as a very efficient and accurate computational method, which can treat large active spaces and capture the major part of strong correlation. Its application on larger molecules is, however, limited by its own computational scaling as well as demands of methods for treatment of the missing dynamical electron correlation. In this work, we present the first step in the direction of combining DMRG with density functional theory (DFT), one of the most employed quantum chemical methods with favorable scaling, by means of the projection-based wave function (WF)-in-DFT embedding. On two proof-of-concept but important molecular examples, we demonstrate that the developed DMRG-in-DFT approach provides a very accurate description of molecules with a strongly correlated fragment.

Vector Correlations in the 225 nm Photodissociation of Co(CO)3NO

Metal nitrosyls are fascinating compounds because they undergo significant geometry changes in the excited state. The volatile compound, Co(CO)₃NO, is a model for understanding the excited-state behavior. In this experiment, Co(CO)₃NO was photodissociated in a DC-sliced velocity mapping ion imaging apparatus with 1 + 1' resonance-enhanced multiphoton ionization (REMPI) detection of the nascent NO. Ion images were collected for different linear polarization of the dissociation and probe lasers to determine the vector correlations in the photodissociation. The fastest NO products arise from an excitation parallel to the dissociating Co-NO bond. The Co-NO bond bends in the excited state, producing an NO photoproduct with angular momentum that is also aligned in the laboratory frame. The μ-v-J vector correlations were measured and are consistent with the orientation μ||v⊥J caused by an excited-state Co-NO bend prior to dissociation. Slower NO photoproducts emerge with smaller vector correlations stemming from fragmentation, parent or fragment rotation, or intersystem crossing.

Characteristic vibrational frequencies of osmium(ii) nitrosyl complexes probed by Raman spectroscopy and DFT calculations

Raman spectroscopy at variable temperature provides experimental frequencies for osmium(ii) nitrosyl complexes. Vibrational transitions are assigned using DFT calculations.

A Density Matrix Renormalization Group Study of the Low-Lying Excited States of a Molybdenum Carbonyl-Nitrosyl Complex

A density matrix renormalization group-self consistent field (DMRG-SCF) study has been carried out to calculate the low-lying excited states of CpMo(CO)₂ NO, a molybdenum complex containing NO and CO ligands. In order to automatically select an appropriate active space, a novel procedure employing the maximum single-orbital entropy for several states has been introduced and shown to be efficient and easy-to-implement when several electronic states are simultaneously considered. The analysis of the resulting natural transition orbitals and charge-transfer numbers shows that the lowest five excited electronic states are excitation into metal-NO antibonding orbitals, which offer the possibility for nitric oxide (NO) photorelease after excitation with visible light. Higher excited states are metal-centered excitations with contributions of metal-CO antibonding orbitals, which may serve as a gateway for carbon monoxide (CO) delivery. Time-dependent density functional theory calculations done for comparison, show that the state characters agree remarkably well with those from DMRG-SCF, while excitation energies are 0.4-1.0 eV red-shifted with respect to the DMRG-SCF ones.