Coordination of ScO+ and YO+ by multiple Ar, Kr, and Xe atoms in noble gas matrixes: a matrix isolation infrared spectroscopic and theoretical study

The combination of matrix isolation infrared spectroscopic and quantum chemical calculation results provide strong evidence that scandium and yttrium monoxide cations, ScO+ and YO+, coordinate multiple noble gas atoms in forming noble gas complexes. The results showed that ScO+ coordinates five Ar, Kr, or Xe atoms, and YO+ coordinates six Ar or Kr and five Xe atoms in solid noble gas matrixes. Hence, the ScO+ and YO+ cations trapped in solid noble gas matrixes should be regarded as the [ScO(Ng)5]+ (Ng = Ar, Kr, or Xe), [YO(Ng)6]+ (Ng = Ar or Kr) or [YO(Xe)5]+ complexes. Experiments with dilute krypton or xenon in argon or krypton in xenon produced new IR bands, which are due to the stepwise formation of the [ScO(Ar)(5-n)(Kr)n]+, [ScO(Kr)(5-n)(Xe)n]+ (n = 1-5), [YO(Ar)(6-n)(Kr)n]+ (n = 1-6), and [YO(Ar)(6-n)(Xe)n]+ (n = 1-4) complexes.     

Noble gas-transition metal complexes: coordination of ScO+ by multiple Ar, Kr, and Xe atoms in noble gas matrixes

The combination of matrix isolation infrared spectroscopic and density functional calculation results provides strong evidence that the transition metal monoxide cation, ScO+, coordinates five noble gas atoms in forming the [ScO(Ng)5]+ (Ng = Ar, Kr, or Xe) complexes in noble gas matrixes.     

Coordination of niobium and tantalum oxides by Ar, Xe and O2: Matrix isolation infrared spectroscopic and theoretical study of NbO2(Ng)2 (Ng = Ar, Xe) and MO4(X) (M = Nb, Ta; X = Ar, Xe, O2) in solid argon

The combination of matrix isolation infrared spectroscopic and quantum chemical calculation results indicate that the NbO₂ molecule is coordinated by two noble gas atoms in forming the NbO₂(Ng)₂ (Ng = Ar, Xe) complexes in solid noble gas matrixes. In contrast, the TaO₂ molecule is not able to form similar noble gas complex. The niobium and tantalum dioxides further react with dioxygen to form the side-on bonded superoxo-dioxide complexes MO₄ (M = Nb, Ta), which are coordinated by one argon atom in solid argon matrix. The coordinated Ar atom in MO₄(Ar) can be replaced by O₂ or Xe in forming the MO₆ and MO₄(Xe) complexes. The results indicate that the NbO₂, NbO₄ and TaO₄ molecules trapped in solid noble gas matrixes should be regarded as the NbO₂(Ng)₂ and MO₄(Ng) (Ng = Ar, Xe; M = Nb, Ta) complexes instead of “isolated” metal oxide species.     

Matrix isolation infrared spectroscopic and theoretical study of NgMO (Ng = Ar, Kr, Xe; M = Cr, Mn, Fe, Co, Ni) complexes

The matrix isolation infrared spectroscopic and quantum chemical calculation results indicate that late transition metal monoxides CrO through NiO coordinate one noble gas atom in forming the NgMO complexes (Ng = Ar, Kr, Xe; M = Cr, Mn, Fe, Co, Ni) in solid noble gas matrixes. Hence, the late transition metal monoxides previously characterized in solid noble gas matrixes should be regarded as the NgMO complexes, which were predicted to be linear. The M-Ng bond distances decrease, while the M-Ng binding energies increase from NgCrO to NgNiO. In contrast, the early transition metal monoxides, ScO, TiO, and VO, are not able to form similar noble gas atom complexes.     

Matrix isolation infrared spectroscopic and theoretical study of noble gas coordinated rhodium-dioxygen complexes

Reactions of rhodium atoms with dioxygen molecules in solid argon have been investigated using matrix isolation infrared absorption spectroscopy. The rhodium-dioxygen complexes, Rh(eta2-O2), Rh(eta2-O2)2, and Rh(eta2-O2)2(eta1-OO), are produced spontaneously on annealing. The Rh(eta2-O2) complex rearranges to the inserted RhO2 molecule under visible light irradiation. Experiments doped with xenon in argon show that the rhodium-dioxygen complexes are coordinated by one or two noble gas atoms in solid noble gas matrixes. Hence, the Rh(eta2-O2), Rh(eta2-O2)2, and Rh(eta2-O2)2(eta1-OO) molecules trapped in solid noble gas matrixes should be regarded as the Rh(eta2-O2)(Ng)2, Rh(eta2-O2)2(Ng)2, and Rh(eta2-O2)2(eta1-OO)(Ng) (Ng = Ar or Xe) complexes. The product absorptions are identified on the basis of isotopic substitution and density functional theory calculations.     

Noble gas-actinide complexes of the CUO molecule with multiple Ar,Kr, and Xe atoms in noble-gas matrices

Laser-ablated U atoms react with CO in excess argon to produce CUO, which is trapped in a triplet state in solid argon at 7 K, based on agreement between observed and relativistic density functional theory (DFT) calculated isotopic frequencies ((12)C(16)O, (13)C(16)O, (12)C(18)O). This observation contrasts a recent neon matrix investigation, which trapped CUO in a linear singlet state calculated to be about 1 kcal/mol lower in energy. Experiments with krypton and xenon give results analogous to those with argon. Similar work with dilute Kr and Xe in argon finds small frequency shifts in new four-band progressions for CUO in the same triplet states trapped in solid argon and provides evidence for four distinct CUO(Ar)(4-n)(Ng)(n) (Ng = Kr, Xe, n = 1, 2, 3, 4) complexes for each Ng. DFT calculations show that successively higher Ng complexes are responsible for the observed frequency progressions. This work provides the first evidence for noble gas-actinide complexes, and the first example of neutral complexes with four noble gas atoms bonded to one metal center.     

Insertion of noble gas atoms into cyanoacetylene: an ab initio and matrix isolation study

A computational and experimental matrix isolation study of insertion of noble gas atoms into cyanoacetylene (HCCCN) is presented. Twelve novel noble gas insertion compounds are found to be kinetically stable at the MP2 level of theory, including four molecules with argon. The first group of the computationally studied molecules belongs to noble gas hydrides (HNgCCCN and HNgCCNC), and we found their stability for Ng = Ar, Kr, and Xe. The HNgCCCN compounds with Kr and Xe have similar stability to that of previously reported HKrCN and HXeCN. The HArCCCN molecule seems to have a weaker H-Ar bond than in the previously identified HArF molecule. The HNgCCNC molecules are less stable than the HNgCCCN isomers for all noble gas atoms. The second group of the computational insertion compounds, HCCNgCN and HCCNgNC, are of a different type, and they also are kinetically stable for Ng = Ar, Kr, and Xe. Our photolysis and annealing experiments with low-temperature cyanoacetylene/Ng (Ng = Ar, Kr, and Xe) matrixes evidence the formation of two noble gas hydrides for Ng = Kr and Xe, with the strongest IR absorption bands at 1492.1 and 1624.5 cm(-1), and two additional absorption modes for each species are found. The computational spectra of HKrCCCN and HXeCCCN fit most closely the experimental data, which is the basis for our assignment. The obtained species absorb at quite similar frequencies as the known HKrCN and HXeCN molecules, which is in agreement with the theoretical predictions. No strong candidates for an Ar compound are observed in the IR absorption spectra. As an important side product of this work, the data obtained in long-term decay of KrHKr+ cations suggest a tentative assignment for the CCCN radical.     

On the noble-gas-induced intersystem crossing for the CUO molecule: experimental and theoretical investigations of CUO(Ng)n (Ng = Ar, Kr, Xe; n = 1, 2, 3, 4) complexes in solid neon

Uranium atoms excited by laser ablation react with CO in excess neon to produce the novel CUO molecule, which forms distinct Ng complexes (Ng = Ar, Kr, Xe) when the heavier noble gases are added. The CUO(Ng) complexes are identified through CO isotopic and Ng substitution on the neon matrix infrared spectra and by comparison to DFT frequency calculations. The U-C and U-O stretching frequencies of CUO(Ng) complexes are slightly red-shifted from frequencies for the (1)Sigma(+) CUO ground state, which identifies singlet ground state CUO(Ng) complexes. In solid neon the CUO molecule is also a complex CUO(Ne)(n), and the CUO(Ne)(n-1)(Ng) complexes are likewise specified. The next singlet CUO(Ne)(x)(Ng)(2) complexes in excess neon follow in like manner. However, the higher CUO(Ne)(x)(Ng)(n) complex (n = 3, 4) stretching modes approach pure argon matrix CUO(Ar)(n) values and isotopic behavior, which are characterized as triplet ground state complexes by DFT frequency calculations. This work suggests that the singlet-triplet crossing occurs with 3 Ar, 3 Kr, or 4 Xe and a balance of Ne atoms coordinated to CUO in the neon matrix host.     

Bonding of multiple noble-gas atoms to CUO in solid neon: CUO(Ng)n (Ng=Ar, Kr, Xe; n=1, 2, 3, 4) complexes and the singlet-triplet crossover point

Laser-ablated U atoms co-deposited with CO in excess neon produce the novel CUO molecule, which forms distinct Ng complexes (Ng=Ar, Kr, Xe) with the heavier noble gases. The CUO(Ng) complexes are identified through CO isotopic and Ng reagent substitution and comparison to results of DFT frequency calculations. The U[bond]C and U[bond]O stretching frequencies of CUO(Ng) complexes are slightly red-shifted from neon matrix (1)Sigma(+) CUO values, which indicates a (1)A' ground state for the CUO(Ng) complexes. The CUO(Ng)(2) complexes in excess neon are likewise singlet molecules. However, the CUO(Ng)(3) and CUO(Ng)(4) complexes exhibit very different stretching frequencies and isotopic behaviors that are similar to those of CUO(Ar)(n) in a pure argon matrix, which has a (3)A" ground state based on DFT vibrational frequency calculations. This work suggests a coordination sphere model in which CUO in solid neon is initially solvated by four or more Ne atoms. Up to four heavier Ng atoms successively displace the Ne atoms leading ultimately to CUO(Ng)(4) complexes. The major changes in the CUO stretching frequencies from CUO(Ng)(2) to CUO(Ng)(3) provides evidence for the crossover from a singlet ground state to a triplet ground state.     

Noble gas-actinide compounds: evidence for the formation of distinct CUO(Ar)(4-n)(Xe)(n) and CUO(Ar)(4-n)(Kr)(n) (n = 1, 2, 3, 4) complexes

Laser-ablated U atoms react with CO in excess argon to produce CUO, which gives rise to 852.5 and 804.3 cm-1 infrared absorptions for the triplet state CUO(Ar)n complex in solid argon at 7 K. Relativistic density functional calculations show that the CUO(Ar) complex is stable and that up to four or five argon atoms can complex to CUO. When 1-3% Xe is added to the argon/CO reagent mixture, strong absorptions appear at 848.0 and 801.3 cm-1 and dominate new four-band progressions, which increase on annealing to 35-50 K as Xe replaces Ar in the intimate coordination sphere. Analogous spectra are obtained with 1-2% Kr added. This work provides evidence for eight distinct CUO(Ng)n(Ar)4-n (Ng = Kr, Xe, n = 1, 2, 3, 4) complexes and the first characterization of neutral complexes involving four noble-gas atoms on one metal center.     

Noble‐Gas Complexes: Theoretical Investigation of Multicenter Polynuclear Species

Ab initio calculations at the MP2 level of theory disclose the conceivable existence of neutral complexes containing four or five distinct noble gases (Ng) each bound to a distinct Be‐atom. These multicenter polynuclear Ng molecules are formally obtained by replacing the H‐atoms of CH₄ and but‐2‐yne with ? NBeNg moieties, which behave as independent monovalent ‘functional groups’. Our investigated complexes include the five homotetranuclear [C(NBeNg)₄] complexes 1 – 5 (Ng=He? Xe), the five heterotetranuclear complexes [CN₄Be₄(He)(Ne)(Ar)(Kr)] ( 6 ), [CN₄Be₄(He)(Ne)(Ar)(Xe)] ( 7 ), [CN₄Be₄(He)(Ne)(Kr)(Xe)] ( 8 ), [CN₄Be₄(He)(Ar)(Kr)(Xe)] ( 9 ), and [CN₄Be₄(Ne)(Ar)(Kr)(Xe)] ( 10 ), and the heteropentanuclear complex [HC₄N₅Be₅(He)(Ne)(Ar)(Kr)(Xe)] ( 11 ). We also investigated the five model complexes [H₃CNBeNg] (Ng=He? Xe) containing a single ? NBeNg moiety. The geometries and vibrational frequencies of all these species, invariably characterized as minimum‐energy structures, were computed at the MP2(full)/6‐31G(d,p)/SDD level of theory, and their stability with respect to the loss of the various Ng‐atoms was evaluated by single‐point calculations at the MP2(full)/6‐311G(d)/SDD level of theory. The beryllium‐Ng binding energies range from ca. 17 (Ng=He) to ca. 63 (Ng=Xe) kJ/mol, and the results of natural‐bond‐orbital (NBO) and atoms‐in‐molecules (AIM) analysis reveal that the Be? Ng interaction is essentially electrostatic for helium, neon, argon, and krypton, and has probably a small covalent contribution for xenon.     

Is This a Chemical Bond? A Theoretical Study of Ng2@C60 (Ng=He,Ne, Ar,Kr, Xe)

Quantum-chemical calculations using DFT (BP86) and ab initio methods (MP2, SCS-MP2) have been carried out for the endohedral fullerenes Ng2@C60 (Ng=He-Xe). The nature of the interactions has been analyzed with charge- and energy-partitioning methods and with the topological analysis of the electron density (Atoms-in-Molecules (AIM)). The calculations predict that the equilibrium geometries of Ng2@C60 have D3d symmetry when Ng=Ne, Ar, Kr, while the energy-minimum structure of Xe2@C60 has D5d symmetry. The precession movement of He2 in He2@C60 has practically no barrier. The Ng--Ng distances in Ng2@C60 are much shorter than in free Ng2. All compounds Ng2@C60 are thermodynamically unstable towards loss of the noble gas atoms. The heavier species Ar2@C60, Kr2@C60, and Xe2@C60 are high energy compounds which are at the BSSE corrected SCS-MP2/TZVPP level in the range 96.7-305.5 kcal mol(-1) less stable than free C60+2 Ng. The AIM method reveals that there is always an Ng--Ng bond path in Ng2@C60. There are six Ng--C bond paths in (D3d) Ar2@C60, Kr2@C60, and Xe2@C60, whereas the lighter D3d homologues He2@C60 and Ne2@C60 have only three Ng--C2 paths. The calculated charge distribution and the orbital analysis clearly show that the bonding situation in Xe2@C60 significantly differs from those of the lighter homologues. The atomic partial charge of the [Xe2] moiety is +1.06, whereas the charges of the lighter dimers [Ng2] are close to zero. The a2u HOMO of (D3d) Xe2@C60 in the 1A1g state shows a large mixing of the highest lying occupied sigma* orbital of [Xe2] and the orbitals of the C60 cage. There is only a small gap between the a2u HOMO of Xe2@C60 and the eu LUMO and the a2u LUMO+1. The calculations show that there are several triplet states which are close in energy to each other and to the 1A1g state. The bonding analysis suggests that the interacting species in Xe2@C60 are the charged species Xe2q+ and C60q-, where 1相似文献   

How strong is the interaction between a noble gas atom and a noble metal atom in the insertion compounds MNgF (M=Cu and Ag, and Ng=Ar, Kr, and Xe)?

Ab initio molecular orbital calculations have been carried out to investigate the structure and the stability of noble gas insertion compounds of the type MNgF (M=Cu and Ag, and Ng=Ar, Kr, and Xe) through second order Moller-Plesset perturbation method. All the species are found to have a linear structure with a noble gas-noble metal bond, the distance of which is closer to the respective covalent bond length in comparison with the relevant van der Waals limit. The dissociation energies corresponding to the lowest energy fragmentation products, MF+Ng, have been found to be in the range of -231 to -398 kJ/mol. The respective barrier heights pertinent to the bent transition states (M-Ng-F bending mode) are quite high for the CuXeF and AgXeF species, although for the Ar and Kr containing species the same are rather low. Nevertheless the M-Ng bond length in MNgF compounds reported here is the smallest M-Ng bond ever predicted through any experimental or theoretical investigation, indicating strongest M-Ng interaction. All these species (except AgArF) are found to be metastable in their respective potential energy surface, and the dissociation energies corresponding to the M+Ng+F fragments have been calculated to be 30.1-155.3 kJ/mol. Indeed, in the present work we have demonstrated that the noble metal-noble gas interaction strength in MNgF species (with M=Cu and Ag, and Ng=Kr and Xe) is much stronger than that in NgMF systems. Bader's [Atoms in molecules-A Quantum Theory (Oxford University Press, Oxford, 1990)] topological theory of atoms in molecules (AIM) has been employed to explore the nature of interactions involved in these systems. Geometric as well as energetic considerations along with AIM results suggest a partial covalent nature of M-Ng bonds in these systems. The present results strengthen our earlier work and further support the proposition on the possibility of experimental identification of this new class of insertion compounds of noble gas atoms containing noble gas-noble metal bond.     

Are matrix isolated species really “isolated”? Infrared spectroscopic and theoretical studies of noble gas-transition metal oxide complexes

In this review, we summarize our recent results on matrix isolation infrared spectroscopic studies and theoretical investigations of noble gas-transition metal oxide complexes. The results show that some transition metal oxide species trapped in solid noble gas matrices are chemically coordinated by one or multiple noble gas atoms forming noble gas complexes and, hence, cannot be regarded as isolated species. Noble gas coordination alters the vibrational frequencies as well as the geometric and electronic structures of transition metal oxide species trapped in solid noble gas matrixes. The interactions between noble gas atoms and transition metal oxides involve ion-induced dipole interactions as well as chemical bonding interactions. Periodic trends in the bonding in these noble gas-transition metal complexes are discussed.     

Theoretical prediction of noble-gas compounds: Ng-Pd-Ng and Ng-Pt-Ng

Following our recent study on Ng-Pt-Ng (Ng=Ar,Kr,Xe) [J. Chem. Phys. 123, 204321 (2005)], the binding of noble-gas atoms with Pd atom has been investigated by the ab initio coupled cluster CCSD(T) method with counterpoise corrections, including relativistic effects. It is shown that two Ng atoms bind with Pd atom in linear geometry due to the s-d(sigma) hybridization in Pd where the second Ng atom attaches with much larger binding energy than the first. The binding energies are evaluated as 4.0, 10.2, and 21.5 kcalmol for Ar-Pd-Ar, Kr-Pd-Kr, and Xe-Pd-Xe, respectively, relative to the dissociation limit, Pd ((1)S)+2Ng. In the hybrid Ng complexes, the binding energies for XePd and Ng (=Ar,Kr) are evaluated as 4.0 and 6.9 kcalmol for XePd-Ar and XePd-Kr, respectively. The fundamental frequencies and low-lying vibrational-rotational energy levels are determined for each compound by the variational method, based on the three-dimensional near-equilibrium potential energy surface. Results of vibrational-rotational analyses for Ng-Pt-Ng (Ng=Ar,Kr,Xe) and Xe-Pt-Ng (Ng=He,Ne,Ar,Kr) compounds are also given.     

Photodissociation of formyl fluoride in rare gas matrixes

Photodissociation of formyl fluoride (HCOF) is studied in Ar, Kr, and Xe matrixes at 248 and 193 nm excitation by following spectral changes in the infrared absorption spectra. In all matrixes, the main photodissociation products are CO/HF species, including CO-HF and OC-HF complexes and thermally unstable CO/HF species (a distorted CO/HF complex or a reaction intermediate), which indicate negligible cage exit of atoms produced via the C-F and C-H bond cleavage channels. However, the observation of traces of H, F, CO, CO(2), F(2)CO, FCO, and HRg(2)(+) (Rg = Kr or Xe) in Kr and Xe matrixes would imply some importance of other reaction channels too. The analysis of the decay curves of the precursor shows that dissociation efficiency of HCOF increases as Ar < Kr < Xe, the difference being the factor of 10 between Ar and Xe. Moreover, HCOF dissociates 20-50 times faster at 193 nm compared to 248 nm. Interestingly, whereas the CO/HF species are stable with respect to photolysis in Ar, they photobleach in Kr and Xe matrixes at 248 and 193 nm, even though the first excited states of CO and HF are not energetically accessible with 193 and 248 nm photons. In krypton matrix, the photodissociation of CO/HF species at 248 nm is observed to be a single photon process. Quantum chemical calculations of electronic excitation energies of CO-HF and OC-HF complexes show that the electronic states of HF and CO mostly retain their diatomic nature in the pair. This clearly demonstrates that photodissociation of CO/HF complexes is promoted by the surrounding rare gas lattice.     

HXeCCH in Ar and Kr matrices

HXeCCH molecule is prepared in Ar and Kr matrices and characterized by IR absorption spectroscopy. The experiments show that HXeCCH can be made in another host than the polarizable Xe environment. The H-Xe stretching absorption of HXeCCH in Ar and Kr is blueshifted from the value measured in solid Xe. The maximum blueshifts are +44.9 and +32.3 cm(-1) in Ar and Kr, respectively, indicating stabilization of the H-Xe bond. HXeCCH has a doublet H-Xe stretching absorption measured in Xe, Kr, and Ar matrices with a splitting of 5.7, 13, and 14 cm(-1), respectively. Ab initio calculations for the 1:1 HXeCCHcdots, three dots, centeredNg complexes (Ng = Ar, Kr, or Xe) are used to analyze the interaction of the hosts with the embedded molecule. These calculations support the matrix-site model where the band splitting observed experimentally is caused by specific interactions of the HXeCCH molecule with noble-gas atoms in certain local morphologies. However, the 1:1 complexation is unable to explain the observed blueshifts of the H-Xe stretching band in Ar and Kr matrices compared to a Xe matrix. More sophisticated computational approach is needed to account in detail the effects of solid environment.     

Ab Initio Study on the Stability of NgnBe2N2, NgnBe3N2 and NgBeSiN2 Clusters

The global minima of Be₂N₂, Be₃N₂ and BeSiN₂ clusters are identified using a modified stochastic kick methodology. The structure, stability and bonding nature of these clusters bound to noble gas (Ng) atoms are studied at the MP2/def2‐QZVPPD level of theory. Positive Be?Ng bond dissociation energy, which gradually increases down Group 18 from He to Rn, indicates the bound nature of Ng atoms. All of the Ng‐binding processes are exothermic in nature. The Xe and Rn binding to Be₂N₂ and Be₃N₂ clusters and Ar?Rn binding to BeSiN₂ are exergonic processes at room temperature; however, for the lighter Ng atoms, lower temperatures are needed. Natural population analysis, Wiberg bond index computations, electron density analysis, and energy decomposition analysis are performed to better understand the nature of Be?Ng bonds.     

Investigating the nature of intermolecular and intramolecular bonds in noble gas containing molecules

This article presents a theoretical study on a number of selected noble gas containing systems of the general formula FNgR and NgR (Ng = He, Ne, Ar, Kr, Xe and R = CH₃, CN, CCH, BO, BNH, H, BeO, and AuF). The principal structures, bond energies, spectroscopic, and electronic properties of 28 noble gas containing molecules were investigated using density functional theory at the BMK level. Quantum theory of atoms in molecules, natural bond orbital, and several other analysis methods have been used to provide more insight into the nature of noble gas bonds. Although both F? Ng and Ng? R bonds in the investigated molecules are assigned to have partially covalent and partially electrostatic nature, the covalent character is dominant in Ng? R bonds. In the second part, the intermolecular interactions between FNgR molecules and hydrogen fluoride are overviewed with emphasis on the hydrogen bonding through the fluorine side of noble gas molecule with hydrogen of HF. The calculated interaction energies were found to decrease in magnitude going down the noble gas series. For all noble gases, the strongest hydrogen bond has been observed in the case R=CH₃. On the contrary, using R=CN in the FNgR moiety weakens the interaction strength. © 2014 Wiley Periodicals, Inc.     

A noble interaction: An assessment of noble gas binding ability of metal oxides (metal = Cu,Ag, Au)

An in silico study is performed on the structure and the stability of noble gas (Ng) bound MO complexes (M = Cu, Ag, Au). To understand the stability of these Ng bound complexes, dissociation energies, dissociation enthalpy, and dissociation free energy change are computed. The stability of NgMO is also compared with that of the experimentally detected NgMX (X= F, Cl, Br). It is found that MO has lower Ng binding ability than that of MX. All the dissociation processes producing Ng and MO are endothermic in nature and for the Kr‐Rn bound MO (M = Cu, Au), and Xe and Rn bound AgO cases, the corresponding dissociation processes are turned out to be endergonic in nature at standard state. The Wiberg bond indices of Ng? M bonds and Ng→M electron transfer gradually increase from Ar to Rn and for the same Ng they follow the order of NgAuO > NgCuO > NgAgO. Energy decomposition analysis shows that the Ng? M bonds in NgMO are partly covalent and partly electrostatic in nature. Electron density analysis further highlights the partial covalent character in Ng? M bonds. © 2016 Wiley Periodicals, Inc.