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The reactions of laser-ablated Ce, Sm, Eu, and Lu atoms with acetonitrile were studied by matrix infrared spectra in a neon matrix, and M←NCCH3, M-η2-(NC)-CH3, and CN-M-CH3 were identified with isotopic substitution and quantum chemical calculations. The major product is the insertion complex (CN-M-CH3), while the end-on and side-on complexes (M←NCCH3 and M-η2-(NC)-CH3) are also trapped in the matrix. The CCN antisymmetric stretching mode for Ce-η2-(NC)-CH3 was observed at 1536.9 cm-1, which is much lower than the same modes observed for other lanthanides. NBO analysis reveals that Ce exhibits a remarkable 4f-orbital contribution in bonding to N and to C, reconfirming an active 4f-orbital contribution of cerium in bonding in the side-on complex, while the 4f contributions of Sm and Eu to the M-N and M-C bonds are much lower and the 4f orbital of Lu is not involved in bonding.

The products in reactions of laser-ablated boron atoms with cyanogen in excess argon have been identified via investigation of the matrix spectra and their variation on photolysis, annealing, and isotopic substitutions. DFT calculations have been performed for the plausible products and reaction paths, providing helpful guides. B-NCCN and B-η2-(NC)-CN were observed in the original deposition spectra, but they disappear on photolysis with λ > 220 nm while more stable NCBCN, CNBCN, and CNBNC were produced. Besides these primary products, high-order products [(NC)2B-NCCN, (CN)(NC)B-NCCN, (CN)2B-NCCN, and (NC)2B-B(CN)2] were also observed, which increased in the later stage of annealing. Our calculations show that initially produced B-NCCN is interconvertible to B-η2-(NC)-CN and the more stable boron cyanide and isocyanide, consistent with the observed results. The formation of high-order products demonstrates that boron highly prefers the trivalent state in reactions with cyanogen, similar to aluminum.

Reactions of group 11 metals with cyanogen, N≡C–C≡N, in excess argon and neon have been carried out, and the products were identified via examination of the matrix spectra and their variation upon ...

Cadmium atoms from laser ablation react with cyanogen, NC=CN, in excess argon during co-deposition at 4 K, and even more on UV irradiation of the cold samples. Final annealing to 35 K increases bands at 2187.3 and 2089.2 cm-1 at the expense of weaker bands at 2194.6 and 2092.2 cm-1 through addition of another cadmium atom. Reaction products were identified by comparison with B3LYP and CCSD(T) computed frequencies and energies, through frequency differences between Zn and Cd products, and by cyanogen isotopic substitution. The CN radical, ZnNC, and CdNC were observed on sample deposition. Hg arc ultraviolet (UV) irradiation activates the insertion of Cd and Zn to form the NCCdCN, CNCdNC, NCZnCN and CNZnNC molecules. Next annealing increased the dimetal products NCCdCdCN, CNCdCdNC, NCZnZnCN, and CNZnZnNC at the expense of their single metal analogs. Laser ablated mercury amalgam also produced NCHgCN, NCHg-HgCN, CNHgNC and CNHg-HgNC. The Group12 metals form both cyanide and isocyanide products, and the argon matrix also traps the higher energy but much more intensely absorbing isocyanides. In the isocyanide case bond polarity results in very intense infrared absorptions. Group 12 metals produce shorter M-M bonds in the dimetal cyanides NCM-MCN and isocyanides CNM-MNC than in the M-M itself, and their computed M-M bond lengths compare favorably with those measured for dimetal complexes stabilized by large ring containing molecular ligands.

Reactions of laser-ablated silver atoms with tetrahalomethanes have been carried out in excess argon, and the products were identified via examination of the matrix spectra and their variation on photolysis and annealing. While production of the insertion products (CX3-AgX) was evident in all Ag reactions, different sets of product absorptions were also observed in the higher frequency region (1260-720 cm-1). They increased on photolysis but decreased on annealing, opposite to the absorptions of the insertion products. They have been assigned to weakly bound complexes of CX3 and AgX (X2CX···AgX), which were generated in halogen abstraction by the metal atom from CX4. These Cl-mediated Ag complexes are only slightly higher in energy than the insertion products due to the d10s1 electron configuration of the group 11 metal. NBO analyses reveal that the CX3 radical is coordinated to an ionic species (Ag+Cl-) via electron-rich X. The product absorptions marked "m" in the previous Au + CX4 study also most probably originated from the weakly bound product, which is more stable than the methylidene (X2C-AuX2).

The cyanogen complexes of iridium, palladium, and platinum were prepared via the reactions of noble metal atoms with cyanogen in argon matrixes, and the product structures were determined by infrared spectroscopy and density functional theory calculations. These complexes were predicted to possess linear geometries with the metal center coordinated by the nitrogen atom of cyanogen in end-on fashions. On the basis of the B3LYP calculations, doublet, singlet, and singlet spin states are most stable for [Ir(NCCN)], [Pd(NCCN)], and [Pt(NCCN)]. Bonding analysis revealed the presence of electron donation from the polarized σ orbital of cyanogen into the empty metal d

An investigation of pulsed-laser-ablated Zn, Cd and Hg metal atom reactions with HCN under excess argon during co-deposition with laser-ablated Hg atoms from a dental amalgam target also provided Hg emissions capable of photoionization of the CN photo-dissociation product. A new band at 1933.4 cm���1 in the region of the CN and CN+ gas-phase fundamental absorptions that appeared upon annealing the matrix to 20 K after sample deposition, and disappeared upon UV photolysis is assigned to (Ar)nCN+, our key finding. It is not possible to determine the n coefficient exactly, but structure calculations suggest that one, two, three or four argon atoms can solvate the CN+ cation in an argon matrix with C���N absorptions calculated (B3LYP) to be between 2317.2 and 2319.8 cm���1. Similar bands were observed in solid krypton at 1920.5, in solid xenon at 1935.4 and in solid neon at 1947.8 cm���1. H13CN reagent gave an 1892.3 absorption with shift instead, and a 12/13 isotopic frequency ratio���nearly the same as found for 13CN+ itself in the gas phase and in the argon matrix. The CN+ molecular ion serves as a useful infrared probe to examine Ng clusters. The following ion reactions are believed to occur here: the first step upon sample deposition is assisted by a focused pulsed YAG laser, and the second step occurs on sample annealing: (Ar)2++CN���Ar+CN+���(Ar)nCN+.

The reactions of laser-ablated Ce, Sm, Eu, and Lu atoms with acetonitrile were studied by matrix infrared spectra in a neon matrix, and M←NCCH

Cyanogen diluted in argon was reacted with laser ablated Zn atoms to produce the NCZnCN and NCZnZnCN cyanides and higher energy isocyanides ZnNC, CNZnNC, and CNZnZnNC, which were isolated in excess argon at 4 K. These reaction products, identified from the matrix infrared spectra of their -CN and -NC chromophore ligand stretching modes, were confirmed by 13 C and 15 N isotopic substitution and comparison with frequencies calculated by the B3LYP and CCSD(T) methods using the all electron aug-cc-pVTZ basis sets. The cyanide and isocyanide products were increased markedly by mercury arc UV photolysis, which covers the zinc atomic absorption. The above electronic structure calculations that produce appropriate ligand frequencies for these dizinc products also provide their Zn-Zn bond lengths: CCSD(T) calculations find a short 2.367 A Zn-Zn bond in the NCZnZnCN cyanide, a shorter 2.347 A Zn-Zn bond in the 37.4 kJ mol-1 higher energy isocyanide CNZnZnNC, and a longer 4.024 A bond in the dizinc van der Waals dimer. Thus, the diatomic cyanide (-CN) and isocyanide (-NC) ligands are as capable of stabilizing the Zn-Zn bond as many much larger ligands based on their measured and our calculated Zn-Zn bond lengths. This is the first example of dizinc complexes stabilized by different ligand isomers. Additional weaker bands in this region can be assigned to the analogous trizinc molecules NCZnZnZnCN and CNZnZnZnNC.

Reactions of laser-ablated Fe, Ru, and Pt atoms with acetonitrile have been carried out in excess argon, and the products identified in the matrix spectra. CH3CN→Fe and Fe-η2-(NC)-CH3 observed in the original deposition spectra converted to CH3-FeNC on uv irradiation. CH3CN→Ru, the only product detected in the Ru system, dissociated on uv irradiation, but was partly reproduced on subsequent visible irradiation and annealing. Similar behavior was found for CH3CN→Pt. The major products (CH3-FeNC, CH3CN→Ru, and CH3CN→Pt) are the most stable constituents in the previously proposed reaction path for Group 4, 5, 6, and 7 metal atoms and acetonitrile, parallel with the previous results. The Group 8 metal π-coordination products are weakly bound complexes due to limited back-donation to the π*-orbitals of CH3CN. Calculations show that the Fe insertion product has a much less bent structure than the Ru analogue, in line with its higher s-character from the first row transition-metal to the C-Fe bond, and the group 8 metal methylidenes are not agostically distorted. The Pt to N bond in CH3CN→Pt is the strongest of all the metals we have investigated owing in large part to its higher electron affinity, which prevents nitrogen lone pair density from entering the pi* orbitals of the C-N group.

The boron–transition-metal triple-bond complexes FB≡MF2 (M= Ir, Os, Re, W, Ta) were trapped in excess solid neon and argon through metal atom reactions with boron trifluoride and identified by matrix isolation infrared spectroscopy and quantum chemical calculations. The FB≡MF2 molecule features very high 11B–F stretching frequencies at 1586.6 cm–1 (Ir), 1526.6 cm–1 (Os), 1505.5 cm–1 (Re), and 1453.2 cm–1 (W), respectively. The very high strength of B≡M bonds with triple-bonding character is confirmed by EDA-NOCV calculations and the active molecular orbital and NBO analysis. The experimental observation of FB stabilization by heavy transition-metal atoms with triple bonds opens the door to design new boron–transition-metal complexes.

Laser ablation of metallic Ce and Nd reacting with cyanogen in excess argon during codeposition at 4 K forms Ce(NC)x and Nd(NC)x for x = 1-3, which are identified from their matrix infrared spectra using cyanogen substituted with 13C and 15N. The electronic structure calculations were performed for isocyano and cyano Cd and Nd compounds for up to n = 4. The frequencies were calculated at the density functional theory level with three different functionals as well as correlated molecular orbital theory (MP2) and are consistent with the experimental assignments and the corresponding 12C/13C isotopic frequency ratios for the isocyano species. The computed frequencies for the analogous cyanide complexes are significantly higher than those for the isocyano isomers, and they are not observed in the spectra. The high spin isocyano complexes are the lowest energy structures. On the basis of the natural population analysis results, the bonding in 4CeNC and 6NdNC is essentially purely ionic with the Ce/Nd in the +I-oxidation state. The bonding for disocyano (3Ce(NC)2 and 5Nd(NC)2) and triisocyano (2Ce(NC)3 and 4Nd(NC)3) complexes is still quite ionic with the lanthanide in the +II and +III formal oxidation states, respectively. For 1Ce(NC)4, the oxidation state is best described as being between +III and +IV. Formation of 5Nd(NC)4 does not really change the electron configuration on the Nd from that in 4Nd(NC)3 and the oxidation state on the Nd remains at +III. Although Nd compounds with up to 3 NC- groups have more ionic binding than do the corresponding Ce compounds, Ce(NC)4 has more ionic binding than does Nd(NC)4. The ionic nature of isocyano Ce and Nd complexes decreases as the number of isocyano groups increases. The energetics of formation of the isocyano Ce and Nd complexes using cyanogen or CN radicals are calculated to be mostly due to exothermic processes, with the exothermicity decreasing as the number of isocyano groups increases.

Mercury atoms, laser-ablated from an amalgam dental filling target, react with cyanogen in excess argon during condensation at 4 K to form two major products in the 2200 cyanide M-C-N stretching region of the IR spectrum, which were assigned to NCHgCN and NCHgHgCN from their antisymmetric C-N stretching mode absorptions at 2213.8 and 2180.1 cm-1 . Two broader bands in the isocyanide region at 2098.2 and 2089.6 cm-1 were assigned to CNHgNC and CNHgHgNC. The N-bonded isomers were computed to be 603/33 and 823/69 times more intense IR absorbers than the C-bonded isomers at the CCSD level of theory. The dissociation energy for the NCHg-HgCN molecule into two HgCN molecules was calculated to be 296 kJ mol-1 and that for CNHg-HgNC into two HgNC molecules is 304 kJ mol-1 . These simple molecules with two cyanide or two isocyanide ligands have two of the shortest and strongest known Hg-Hg single bonds as the two electronegative CN ligands withdraw antibonding electron density from the bonding region.

Tin insertion products (oxidation state 2+) were observed in reactions of laser-ablated Sn atoms with ethane, and halomethanes in excess argon, parallel to the Pb reactions. The CSnX bond angles of the observed Sn complexes are close to right angles, and natural bond orbital calculations show that Sn also utilizes mostly its p-orbitals to make chemical bonds. Bridged Sn complexes [CX2(X)–SnX] were also provided in reactions of tetrahalomethanes via photo-isomerization of the insertion products, showing that the p-orbitals of Sn are more accessible than those of Pb. These products were identified from the matrix infrared spectra on the basis of isotopic shifts and density functional theory frequencies. Considering the previously reported high-oxidation-state products of the lighter group 14 elements and the Pb products with primarily oxidation state 2+ because of the relativistic effects, the observed Sn complexes show a trend that the high-oxidation-state complexes are less favored with increasing atomic ...

Laser-ablated group 2 metal atoms exhibit different reactivities with (CN)2 in excess argon and neon during condensation at 4 K. UV irradiation (220–290 nm) is required to activate Be to produce the linear CNBeNC di-isocyanide molecule with a strong antisymmetric C–N stretching band at 2104.3 cm–1 and a C-N-Be-N-C stretching mode at 1265.7 cm–1. The di-isocyanide appears at lower frequency and exhibits more nitrogen and less carbon isotopic shift than the cyanide counterpart, which is confirmed by B3LYP isotopic frequency calculations. Two weak bands were observed for the cyanide NCBeCN, and three absorptions were found for the mixed ligand CNBeCN molecule, which would be difficult to synthesize and put into a bottle. Mg reacts with (CN)2 to form the CNMgNC counterpart at 2085.8 cm–1 on annealing to 25 K. Absorptions for the Ca(NC)2, Sr(NC)2, and Ba(NC)2 molecules at 2060.8, 2048.1, and 2045.9 cm–1 increase on sample annealing with these more reactive heavier alkaline earth metal atoms, which have calcula...

An investigation of pulsed-laser-ablated Zn, Cd and Hg metal atom reactions with HCN under excess argon during co-deposition with laser-ablated Hg atoms from a dental amalgam target also provided Hg emissions capable of photoionization of the CN photo-dissociation product. A new band at 1933.4 cm

Reactions of laser-ablated silver atoms with tetrahalomethanes have been carried out in excess argon, and the products were identified via examination of the matrix spectra and their variation on photolysis and annealing. While production of the insertion products (CX

Uranium and thorium hydrides are known as functional groups for ligand stabilized complexes and as isolated molecules under matrix isolation conditions. Here, the new molecular products of the reactions of laser-ablated U and Th atoms with HCl and with HBr, namely HUCl, HUBr and HThCl, HThBr, based on their mid and far infrared spectra in solid argon, are reported. The assignment of these species is based on the close agreement between observed and calculated vibrational frequencies. The H-U and U-35 Cl stretching modes of HUCl were observed at 1404.6 and 323.8 cm-1 , respectively. Using DCl instead to form DUCl gives absorption bands at 1003.1 and 314.7 cm-1 . The corresponding bands of HThCl are 1483.8 (H-Th) and 1058.0 (D-Th), as well as 340.3 and 335.8 cm-1 (Th-35 Cl), respectively. HUBr is observed at 1410.6 cm-1 and the BP86 computed shift from HUCl is 6.2 cm-1 in excellent agreement. The U-H stretching frequency increases from 1383.1 (HUF), 1404.6 (HUCl), 1410.6 (HUBr) to 1423.6 cm-1 (UH) as less electronic charge is removed from the U-H bond by the less electronegative substituent. These U-H stretching frequencies follow the Mayer bond orders calculated for the three HUX molecules. A similar trend is found for the Th counterparts. Additional absorptions are assigned to the H2 AnX2 molecules (An=U, Th, X=Cl, Br) formed by the exothermic reaction of a second HX molecule with the above primary products.

Strong absorptions for Cl--HCCl2 with D and 13C isotopes were observed in the spectra of CHCl3 codeposited with laser-ablated metal atoms, cations, electrons, and vacuum ultraviolet radiation, which shows that the precursor is an effective electron scavenger. The IR spectra, isotopic shifts, and DFT calculations identified the major product as Cl--HCCl2, which is characterized by a strong, broad C-H stretching mode interacting with the overtone of the H-C-Cl bending fundamental. These absorptions decreased on subsequent annealing and photolysis treatments while the ClHCl- absorptions increased, suggesting that dissociation of the chloroform anion generates the stable symmetrical hydrogen dichloride anion as does the reaction of HCl and Cl-. A new set of strong, broad absorptions in the deposition spectra that diminished on the early annealing and photolysis are assigned to the Cl-ClCCl radical isomer. Dominant spectral features in the C-H stretching region for the experiments with CH2Cl2 are assigned to the symmetric C-H and the antisymmetric Cl-H-C-H stretching bands of the methylene chloride anion Cl--HCHCl. The stronger, broader, lower frequency bands are due to the hydrogen-bonded hydrogen stretching, and the weaker, sharper, higher frequency absorptions are due to the terminal C-H bond stretching. Similar experiments with CHBr3 produced absorptions for the analogous Br--HCBr2 and BrHBr- anions.

The insertion products of laser-ablated Pb atom reactions with ethane and mono-, di-, tri-, and tetrahalomethanes in excess argon were prepared and identified from their matrix infrared spectra on the basis of DFT computed frequencies and observed isotopic shifts. Unlike the lighter elements in group 14, the heaviest member lead exists primarily in the oxidation state 2+ using 6p orbitals in reaction products due to relativistic contraction of the 6s orbital. The C–Pb–X (X = H, F, Cl) bond is close to a right angle, indicating that Pb contributes mostly p-character to the C–Pb and Pb–X bonds. The lead reaction product with ethane is CH3CH2–Pb–H. The lower energy product in the CH2FCl reaction is CH2F–PbCl, which is photoisomerized to CH2Cl–PbF. A lead methylidene (CCl2–PbCl2) was identified only in reactions with CCl4. The relatively small energy difference between the insertion and methylidene products in the tetrachloride system allows photochemical conversion from the insertion product to the unusual 3...

A series of group 3 metal isocyanide complexes were prepared via the reactions of laser ablated scandium, yttrium, and lanthanum atoms with (CN)2 in an argon matrix. The product structures were identified on the basis of their characteristic infrared absorptions from isotopically labeled (CN)2 samples as well as the calculated frequencies and isotopic frequency ratios. Group 3 metal atoms reacted with (CN)2 to form M(NC)2 (M = Sc, Y, La) when the samples were subjected to λ > 220 nm irradiation. Other products such as M(NC)3 and MNC were produced together with M(NC)2 through either the reactions of M(NC)2 and (CN)2 or the loss of one CN ligand from M(NC)2. CCSD(T)//B3LYP calculations reveal that ScNC possesses a 3Δ ground state, while 1Σ+ is most stable for YNC and LaNC. All of the M(NC)2 and M(NC)3 complexes were predicted to have doublet and singlet ground states, respectively. Group 3 metal cyanides are less stable than the isocyanides by at least 4 kcal/mol at the CCSD(T) level, and their C-N stretches are much weaker than the N-C stretches of the isocyanides. No absorption can be assigned to the M(CN) x complex, which would appear between 2100 and 2250 cm-1.

Infrared absorptions of the matrix isolated OMS, OM(η2-SO), and OM(η2-SO)(η2-O2S) (M = Ce, Th) molecules were observed following reactions of laser-ablated Ce and Th metal atoms with SO2 during condensation in excess argon and neon. Band assignments for the main vibrational modes were confirmed by appropriate 34SO2 and S18O2 isotopic shifts. B3LYP, BPW91 density functional, and CASSCF/CASPT2 calculations were performed to characterize these new reaction products and to explore the admixture of f orbitals into the bonding giving stronger M≡O triple bonds. It is very interesting that both OM(η2-SO) and OM(η2-SO)(η2-O2S) molecules show chiral structure.

Laser-ablated Al atoms react with (CN)2 in excess argon during condensation at 4 K to produce AlNC, Al(NC)2, and Al(NC)3, which were computed (B3LYP) to be 27, 16, and 28 kJ/mol lower in energy, respectively, than their cyanide counterparts. Irradiation at 220–580 nm increased absorptions for the above molecules and the very stable Al(NC)4– anion. Annealing to 30, 35, and 40 K allowed for diffusion and reaction of trapped species and produced new bands for the Al(NC)1,2,3 dimers including a rhombic ring core (C)(AlN)2(C) with C’s attached to the N’s, a (NC)2Al(II)–Al(II)(NC)2 dimer with a computed Al–Al length of 2.557 A, and the dibridged Al2(NC)6 molecule with a calculated D2h structure and rhombic ring core like Al2H6. In contrast, the Al(NC)4– anion was destroyed on annealing presumably due to neutralization by Al+. B3LYP calculations also show that aluminum chlorides form the analogous molecules and dimers. In our search for possible new products, we calculated Al(NC)4 and found it to be a stable mol...

Laser-ablated U atoms react with (CN)2 in excess argon and neon during codeposition at 4 K to form UNC, U(NC)2, and U(NC)4 as the major uranium-bearing products, which are identified from their matrix infrared spectra using cyanogen substituted with 13C and 15N and from quantum chemical calculations. The 12/13CN and C14/15N isotopic frequency ratios computed for the U(NC)1,2,4 molecules agree better with the observed values than those calculated for the U(CN)1,2,4 isomers. Multiplets using mixed isotopic cyanogens reveal the stoichiometries of these products, and the band positions and quantum chemical calculations confirm the isocyanide bonding arrangements, which are 14 and 51 kJ/mol more stable than the cyanide isomers for UNC and U(NC)2, respectively, and 62 kJ/mol for U(NC)4 in the isolated gas phase at the CCSD(T)/CBS level. The studies further demonstrate that the isocyano nitrogen is a better π donor, so it interacts with U(VI) better than carbon. Although the higher isocyanides are more stable th...

The reactions of Ge, Sn, Pb, Sb, Bi, and Te atoms with silane molecules were studied using matrix-isolation Fourier transform infrared spectroscopy and density functional theoretical (DFT) calculations. All metals generate the inserted complexes HM-SiH3, which were stabilized in an argon matrix, while H2M═SiH2 and H3M≡SiH were not observed. DFT and CCSD(T) calculations show the insertion complex HM-SiH3 is the most stable isomer with a near right angle H–M–Si moiety. However, silydene complexes H2M═SiH2 (M = C, Si) were calculated and identified as the most stable complexes with the lighter elements. The bonding difference is mainly due to relativistic effects, which is that for heavier metal atoms valence s and p orbitals have a lower tendency to form hybrid orbitals.

Mono and diisocyanide complexes of manganese and iron were prepared via the reactions of laser-ablated manganese and iron atoms with (CN)2 in an argon matrix. Product identifications were performed based on the characteristic infrared absorptions from isotopically labeled (CN)2 experiments as compared with computed values for both cyanides and isocyanides. Manganese atoms reacted with (CN)2 to produce Mn(NC)2 upon λ > 220 nm irradiation, during which MnNC was formed mainly as a result of the photoinduced decomposition of Mn(NC)2. Similar reaction products FeNC and Fe(NC)2 were formed during the reactions of Fe and (CN)2. All the product molecules together with the unobserved cyanide isomers were predicted to have linear geometries at the B3LYP level of theory. The cyanide complexes of manganese and iron were computed to be more stable than the isocyanide isomers with energy differences between 0.4 and 4 kcal/mol at the CCSD(T) level. Although manganese and iron cyanide molecules are slightly more stable a...

CH3CH2–MH and (CH2)2–MH2 were identified in the matrix IR spectra from reactions of laser-ablated group 3 metal atoms with ethane, and they were characterized via theoretical investigations. The observed products are the most stable in the proposed reaction path. Because of the small number of valence electrons, the group 3 metal high oxidation-state complexes are less stable. The C–C insertion product [(CH3)2M], which was predicted to be more stable than the observed ones, was not observed probably because of the high energy barrier and a likely slower rate for insertion into one C–C bond than one of six C–H bonds. The C–C bond of the metallacyclopropanes is the shortest among the early transition-metal analogues, and its stretching frequencies are the highest, revealing the weakest interaction between the metal dihydride and ethylidene groups. The undetected ethylidene is not agostic, parallel to the previously examined methylidene.

Group 6 metal oxide fluoride molecules in the form of OMF2 and OMF (M = Cr, Mo, W) were prepared via the reactions of laser-ablated metal atoms and OF2 in excess argon. Product identifications were performed by using infrared spectroscopy, 18OF2 samples, and electronic structure calculations. Reactions of group 6 metal atoms and OF2 resulted in the formation of ternary OCrF2, OMoF2, and OWF2 molecules with C2v symmetry in which the tetravalent metal center is coordinated by one oxygen and two fluorine atoms. Both OCrF2 and OMoF2 are computed to possess triplet ground states, and a closed shell singlet is the ground state for OWF2. Triatomic OCrF, OMoF, and OWF molecules were also observed during sample deposition. All three molecules were computed to have a bent geometry and quartet ground state. A bonding analysis showed that the OMF2 molecules have highly ionic M–F bonds. 3OCrF2 and 3OMoF2 have an M–O double bond composed of a σ bond and a π bond. 1OWF2 has an M–O triple bond consisting of a σ bond, a π...

The primary products in reactions of laser-ablated group 5 metal atoms with ethane were identified in argon matrix IR spectra and characterized via density functional theory computations. The second- and third-row transition metals Nb and Ta produced insertion, metallacyclopropane, vinyl trihydrido, and anionic ethylidyne complexes (CH3CH2–MH, (CH2)2–MH2, CH2═CH–MH3, and CH3C≡MH3–), while the first-row transition metal V yielded only the insertion and metallacyclopropane products. The energetically higher ethylidenes and neutral ethylidynes (CH3CH═MH2 and CH3C≐MH3) were not detected. The unique anionic ethylidynes are the most stable anionic species in the Nb and Ta systems. Evidently back-donation from the metal center to the C–C π* orbital is stronger than that in the group 6 metal analogue but weaker than that in the corresponding group 4 metal complex. The C–M bond for the Nb and Ta ethylidyne anions is a true triple bond.

Homoleptic thorium isocyanide complexes have been prepared via the reactions of laser-ablated thorium atoms and (CN)2 in a cryogenic matrix, and the structures of the products were characterized by infrared spectroscopy and theoretical calculations. Thorium atoms reacted with (CN)2 under UV irradiation to form the oxidative addition product Th(NC)2, which was calculated to have closed-shell singlet ground state with a bent geometry. Further reaction of Th(NC)2 and (CN)2 resulted in the formation of Th(NC)4, a molecule with a tetrahedral geometry. Minor products such as ThNC and Th(NC)3 were produced upon association reactions of CN with Th and Th(NC)2. Homoleptic thorium cyanide isomers Th(CN)x (x = 1–4) are predicted to be less stable than the corresponding isocyanides. The C–N stretches of thorium cyanides were calculated to be between 2170 and 2230 cm–1 at the B3LYP level, more than 120 cm–1 higher than the N–C stretches of isocyanides and with much weaker intensities. No experimental absorptions appea...

Reactions of laser-ablated group 6 metal atoms with ethane have been carried out, and the products identified in argon matrix IR spectra on the basis of deuterium shifts, correlation with computation results, and previous related works. Mo and W generated the insertion, metallacyclopropane, and ethylidyne complexes [CH3CH2–MH, (CH2)2–MH2, and CH3C≡MoH3], whereas Cr gave only the insertion product. The higher oxidation-state complex from ethane becomes relatively more stable in the heavier metal system, parallel to those from methane. The unobserved ethylidene CH3CH═MH2 is energetically higher than (CH2)2–MH2, and the energy barrier from CH3CH2–MH to the ethylidene is also substantially higher than that for the observed cyclic product. NBO calculations indicate that the C–M bonds of the group 6 metal ethylidenes and ethylidynes are true double and triple bonds.

The boron-transition-metal triple-bond complexes FB≡MF

Laser-ablated group 2 metal atoms exhibit different reactivities with (CN)

Our first review article in 2006 outlined the observation, photochemical properties, and theoretical investigations of a new breed of small transition-metal complexes with C-M multiple bonds generated from reactions of group 4–6 metals with methane and methyl halides. Since then, numerous small high oxidation-state complexes have been provided by reactions of laser ablated group 3–12 transition metal, group 14 silicon atoms and lanthanide and actinide atoms with small organic precursors. Periodic trends in the primary products and their molecular structures and photochemistry are apparent. While no methylidyne reaction products were detected in reactions of the elements on the left and right sides of the d-block in the periodic table, they were the sole products in reactions of Re and Os. The actinide products identified are comparable to those from early transition-metal reactions. Agostic distorted molecular structures, photo-reversible conversions, vibrational frequencies, intensities and reaction paths have been theoretically investigated. These recent results show that C–H or C–X bond insertion and subsequent H or X migration to form higher oxidation-state products are a general phenomenon in most transition-metal systems, generating small relatives of the much larger analogues stabilized by ligands in solutions.

The reactions of laser-ablated lanthanide metal atoms with hydrogen peroxide or hydrogen plus oxygen mixtures have been studied experimentally in a solid argon matrix and theoretically with the ab initio MP2 and CCSD(T) methods. The Ln(OH)3 and Ln(OH)2 molecules and Ln(OH)2+ cations are the major products, and the reactions to form those hydroxides are predicted to be highly exothermic at the CCSD(T) level. Vibronic interactions are hypothesized to contribute to the abnormalities in deuterium shifts for Ln–OH(D) stretching modes for several hydroxides, consistent with CASSCF calculations. Additional new absorptions were assigned as HLnO or LnOH and OLnOH molecules. The tetrahydroxides of Ce, Pr, and Tb have also been observed. These reactive intermediates were identified from their matrix infrared spectra by using D2O2, HD, D2, 16,18O2, and 18O2 isotopic substitution, by matching observed frequencies with values calculated by electronic structure methods, and by following the trends observed in frequencie...

Thorium atoms from laser ablation react with phosphine during condensation in excess argon to produce two new infrared absorptions at 1467.2 and 1436.6 cm–1 near weak bands for ThH and ThH2, which increase on annealing to 25 and 30 K, indicating spontaneous reactions. Analogous experiments with uranium produced two similar bands at 1473.4 and 1456.7 cm–1 above UH at 1423.8 cm–1 and another absorption at 1388.2 cm–1. Electronic structure calculations at the coupled cluster CCSD(T) for Th and density functional theory calculations for U as well as their proximity to other actinide hydride absorptions support assignments of these bands to the simplest molecules HP═ThH2, HP═UH2, and PH2–UH. Arsine gave the analogous products HAs═ThH2, HAs═UH2, and AsH2–UH. The HE═AnH2 molecules (E = P, As; An = Th, U) have strong agostic An–H(E) interactions with H–E–An angles in the range of 60–64°. The calculated agostic bond distances are 9% to 12% longer than terminal single An–H bonds, which suggests that these strong ag...

Laser ablated Ti, Zr, and Hf atoms react with phosphine during condensation in excess argon or neon at 4 K to form metal hydride insertion phosphides (H2P-MH) and metal dihydride phosphinidenes (HP═MH2) with metal phosphorus double bonds, which are characterized by their intense metal-hydride stretching frequencies. Both products are formed spontaneously on annealing the solid matrix samples, which suggests that both products are relaxed from the initial higher energy M-PH3 intermediate complex, which is not observed. B3LYP (DFT) calculations show that these phosphinidenes are strongly agostic with acute H-P═M angles in the 60° range, even smaller than those for the analogous methylidenes (carbenes) (CH2═MH2) and in contrast to the almost linear H-N═Ti subunit in the imines (H-N═TiH2). Comparison of calculated agostic and terminal bond lengths and covalent bond radii for HP═TiH2 with computed bond lengths for Al2H6 finds that these strong agostic Ti-H bonds are 18% longer than single covalent bonds, and the bridged bonds in dialane are 10% longer than the terminal Al-H single bonds, which show that these agostic bonds can also be considered as bridged bonds. The analogous arsinidenes (HAs═MH2) have 4° smaller agostic angles and almost the same metal-hydride stretching frequencies and double bond orders. Calculations with fixed H-P-Ti and H-As-Ti angles (170.0°) and Cs symmetry find that electronic energies increased by 36 and 44 kJ/mol, respectively, which provide estimates for the agostic/bridged bonding energies.

Strong absorptions for Cl

Uranium and thorium hydrides are known as functional groups for ligand stabilized complexes and as isolated molecules under matrix isolation conditions. Here, the new molecular products of the reactions of laser-ablated U and Th atoms with HCl and with HBr, namely HUCl, HUBr and HThCl, HThBr, based on their mid and far infrared spectra in solid argon, are reported. The assignment of these species is based on the close agreement between observed and calculated vibrational frequencies. The H-U and U

Cesium fluoride evaporated from a small stainless steel Knudsen cell at 495 °C was codeposited with F2 in excess argon onto a copper wedge at 15 K and examined by focused blue argon ion laser lines scattered from the matrix sample. An 892 cm−1 Raman shifted signal was observed for F2, and stronger 461 cm−1 and weaker 389 cm−1 Raman shifted signals were observed for reaction products. All of these signals decreased in intensity upon prolonged exposure to laser light, but the 389 cm−1 signal decreased more rapidly than the 461 cm−1 signal. Temperature cycling to 40 K destroyed the 389 cm−1 signal, but the 461 cm−1 band remained intense, which was the same behavior for the very intense 550 cm−1 infrared absorption in similar experiments using a different instrument. The two strong 461 and 550 cm−1 bands related by annealing behavior were assigned to the symmetric and antisymmetric (F–F–F)− stretching modes for the trifluoride anion, respectively, in the Cs+F3− ion pair species with mutual exclusion. The weaker more vulnerable 389 cm−1 signal was attributed to an unknown, less stable (i.e. more reactive) secondary reaction product (Ault and Andrews, J. Am. Chem. Soc., 1976, 98, 1591). Nevertheless, Redeker, Beckers and Riedel (RSC Adv., 2015, 5, 106568), on the basis of the detection of a very weak assigned combination band and CCSD(T) frequency calculations, reassigned the two clearly unrelated strong 550 cm−1 IR and weak 389 cm−1 Raman bands to the same stable Cs+F3− ion pair species. We can now identify the weaker 389 cm−1 Raman band for a more photosensitive and reactive carrier as the isolated F3− anion. The required Raman blue laser photo-ionization of Cs and Rb atoms in the system and the case for this new assignment are considered in the following paper. The antisymmetric stretching frequency for this isolated anion has been assigned at 510.6 cm−1 in other IR work. We again assign with confidence the two strong and related 550 cm−1 IR and 461 cm−1 Raman bands to the same stable Cs+F3− ion pair species in solid argon.

Infrared absorptions of the matrix isolated OMS, OM(η

Laser ablation of tungsten metal provides W atoms which react with phosphine and arsine during condensation in excess argon and neon, leading to major new infrared (IR) absorptions. Annealing, UV irradiation, and deuterium substitution experiments coupled with electronic structure calculations at the density functional theory level led to the assignment of the observed IR absorptions to the E≡WH3 and HE═WH2 molecules for E = P and As. The potential energy surfaces for hydrogen transfer from PH3 to the W were calculated at the coupled-cluster CCSD(T)/complete basis set level. Additional weak bands in the phosphide and arsenide W—H stretching region are assigned to the molecules with loss of H from W, E≡WH2. The electronic structure calculations show that the E≡WH3 molecules have a W—E triple bond, the HE═WH2 molecules have a W—E double bond, and the H2E—WH molecules have a W—E single bond. The formation of multiple E—W bonds leads to increasing stability for the isomers.

Reactions of laser-ablated silicon atoms with di-, tri-, and tetrahalomethanes in excess argon were investigated, and the products were identified from the matrix infrared spectra, isotopic shifts, and density functional theory energy, bond length, and frequency calculations. Dihalomethanes produce planar singlet silenes (CH2═SiX2), and tri- and tetrahalomethanes form triplet halosilyl carbenes (HC-SiX3 and XC-SiX3). The Si-bearing molecules identified are the most stable, lowest-energy product in the reaction systems. While the C-Si bond in the silene is a true double bond, the C-Si bond in the carbene is a shortened single bond enhanced by hyperconjugation of the two unpaired electrons on C to σ*(Si-X) orbitals, which contributes stabilization through a small amount of π-bonding and reduction of the HCSi or XCSi angles. The C-Si bond lengths in these carbenes (1.782 Å for HC-SiF3) are between the single-bond length in the unobserved first insertion intermediate (1.975 Å for CHF2-SiF) and the double-bond length in the silene (1.704 Å for CHF═SiF2). The silicon s(2)p(2) and titanium s(2)d(2) electron configurations produce similar primary products, but the methylidyne with Ti has a bond to carbon stronger than that of the halosilyl carbene.

Palladium atoms generated by thermal evaporation and laser ablation were reacted with and trapped in F2/Ar, F2/Ne, and neat F2 matrices. The products were characterized by electronic absorption and infrared spectroscopy, together with relativistic density functional theory calculations as well as coupled cluster calculations. Vibrational modes at 540 and 617 cm(-1) in argon matrices were assigned to molecular PdF and PdF2, and a band at 692 cm(-1) was assigned to molecular PdF4. A band at 624 cm(-1) can be assigned to either PdF3 or PdF6, with the former preferred from experimental considerations. Although calculations might support the latter assignment, our conclusion is that in these detailed experiments there is no convincing evidence for PdF6.

Reactions of laser-ablated Y and La atoms with di-, tri-, and tetrahalomethanes in excess argon were investigated and the products were identified from their infrared matrix spectra, isotopic shifts, and comparison with frequencies computed by density functional theory. These DFT calculations also show that the primary products are planar and bridged methylidenes depending on the number of halogen atoms with no trace of insertion and products, parallel to the previous Sc results. While the C–M bond in the planar configuration has a considerable amount of -character, the observed bridged Y and La methylidene structures are indicative of strong electron donation to the empty d-orbtals on the metal center. These identified products reconfirm that the electronic structures of group 3 metals (d1s2) do not allow formation of the higher oxidation-state product in reaction with halomethanes. The preference of a group 3 metal product with more M–F bonds over those with more M–Cl bonds is also investigated.

The compounds H2ThSe and H2USe were synthesized by the reaction of laser-ablated actinide metal atoms with H2Se under cryogenic conditions following the procedures used to synthesize H2AnX (An = Th, U; X = O, S). The molecules were characterized by infrared spectra in an argon matrix with the aid of deuterium substitution and electronic structure calculations at the density functional theory level. The main products, H2ThSe and H2USe, are shown to have a highly polarized actinide-selenium triple bond, as found for H2AnS on the basis of electronic structure calculations. There is an even larger back-bonding of the Se with the An than found for the corresponding sulfur compounds. These molecules are of special interest as rare examples of multiple bonding of selenium to a metal, particularly an actinide metal.

Laser-ablated Hf and Ti atoms produce M–η2-(NC)–CH3, CH3–MNC, and CH2=M(H)NC in reactions with acetonitrile, parallel to the earlier Zr results, based on isotopic substitution and frequencies computed by DFT. These products are the most stable components in the previously proposed reaction path for reactions of metal atoms with acetonitrile, in line with the observed products in other metal systems and DFT calculations. Other plausible products [CH3CN–M and CH≡M(H2)NC] are energetically too high to be generated in reactions of the group 4 metals. The group 4 metals form strong π complexes with the nitrile group as they do with acetylene and ethylene. The methylidenes are slightly more agostic due to the metal-containing conjugation system than those produced from small alkanes and methyl halides. Relativistic contraction is also evident in that the Hf bonds are shorter than the Zr bonds.