Tungsten Hydride Phosphorus- and Arsenic-Bearing Molecules with

Article Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

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Tungsten Hydride Phosphorus- and Arsenic-Bearing Molecules with Double and Triple W−P and W−As Bonds Lester Andrews,*,† Han-Gook Cho,†,‡ Zongtang Fang,§ Monica Vasiliu,§ and David A. Dixon*,§ †

Department of Chemistry, University of Virginia, P.O. Box 400319, Charlottesville, Virginia 22904-4319, United States Department of Chemistry, Incheon National University, 119 Academy-ro, Yeonsu-gu, Incheon 406-772, South Korea § Department of Chemistry and Biochemistry, The University of Alabama, Shelby Hall, Tuscaloosa, Alabama 35487-0366, United States ‡

S Supporting Information *

ABSTRACT: 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.

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WH3.16 The reaction of W with H2 in excess neon gave five hydrides, WHn, with n = 1, 2, 3, 4, and 6.17 Stable uranium(IV)-terminal parent phosphide and phosphinidene complexes and their arsine counterparts have recently been synthesized.18,19 Complexes of yttrium with arsenide and arsinidene ligands have also been reported.20 The reactivity of terminal electrophilic phosphinidene complexes of molybdenum and tungsten has been investigated.21 Terminal parent phosphanide and phosphinidene complexes of zirconium(IV) have been prepared recently.22 Tungsten phosphinidene and arsinidene complexes react to form four-membered heterocycles.23 The reactivity of a phosphanylphosphinidene complex of tungsten(VI) with phosphines has also been investigated.24 We report here the simplest H2EWH, HEWH2, EWH3, and EWH2 molecules prepared from the reaction of laserablated W atoms with PH3 and with AsH3 in excess argon and neon. These investigations indicate what is physically stable using the simplest hydrogen ligand for tungsten pnictogens, and thus provide directions for synthetic chemists to synthesize molecules with larger ligands that can be stabilized at higher temperatures and in macroscopic quantities.

INTRODUCTION Small molecules containing carbonmetal double and triple bonds have been investigated using matrix isolation spectroscopy through reactions of laser-ablated metal atoms with methane and halomethanes coupled with electronic structure calculations.1−3 Reactions of early transition metal atoms with ammonia gave insertion products H2NMH, which rearranged to HNMH2 imines.4,5 Similar reactions were observed with thorium and uranium atoms.6,7 Earlier multiconfiguration self-consistent field (MCSCF) calculations predicted triple bond character for the HNTiH2 imine and a triangular strongly agostic HPTi structure for the phosphine reaction product phosphinidene.8 These group 4 metal atom phosphinidene and arsinidene molecules were investigated by matrix infrared (IR) spectra and density functional theory (DFT) calculations with the B3LYP exchange-correlation functional.9 Terminal Mo and W nitrides, phosphides, and arsenides have been prepared from laserablated metal atom reactions with NH3, NF3, PF3, AsF3, and PCl3.10−12 Similar reactions with uranium atoms led to the formation of EUF3 molecules for all three trifluorides (E = N, P, As), and the arsenide triple bond was computed to be weaker than phosphide and nitride triple bonds.13,14 However, uranium reactions with phosphine and arsine gave only the single- and double-bonded product species, as did those with thorium.15 Methane as a reagent gave three analogous products for the tungsten reaction: CH3WH, CH2WH2, and HC © XXXX American Chemical Society

Received: February 6, 2018

A

DOI: 10.1021/acs.inorgchem.8b00348 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

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lations were used to determine the vibrational zero-point energies (ZPEs) for the term ΔEZPE. For W, we calculated the TAE to the first excited state (7S3), which has no spin−orbit correction, and then used the experimental correction of 8.44 kcal/mol to get the TAE with respect to the ground state (5D0) of W.54 There are no additional atomic spin−orbit corrections. Heats of formation at 0 K were calculated by combining our computed ∑D0 values with the known enthalpies of formation at 0 K for the elements: ΔHf,0K(H) = 51.63 kcal/mol, ΔHf,0K(N) = 112.53 kcal/mol, ΔHf,0K(P) = 75.42 ± 0.24 kcal/mol, and ΔHf,0K(W) = 203.1 ± 1.5 kcal/mol.55 We used a value of ΔHf,0K(As) = 68.87 ± 0.8 kcal/ mol from our recent high-level computational work.56 Heats of formation at 298 K were calculated by following the procedures outlined by Curtiss et al.57 using the thermal corrections for the atoms. The CCSD(T) calculations were performed with the MOLPRO 2015.1 program package.58,59 All of the calculations were performed using local resources at The University of Alabama.

EXPERIMENTAL AND COMPUTATIONAL METHODOLOGIES

Experimental Section. Laser-ablated W atoms were reacted with phosphine (Matheson, condensed at 77 K and evacuated to remove volatile impurities) in excess argon or neon during condensation on a 4 K CsI window cooled by a closed-cycle refrigerator (Sumitomo).1,9−11,15 Arsine (Matheson, 10% in hydrogen, condensed at 77 K to remove H2) was reacted in the same manner. Deuterium-exchanged phosphine was prepared by condensing PH3 on D2O several times in a D2O-exchanged stainless steel vacuum line, which resulted in stronger PD3, PHD2, and PH2D absorptions as compared to residual PH3. These samples were approximately 80% deuterium-enriched.9 Reagent gas mixtures ranged from 0.5% to 2% in argon or neon (Spectra Gases). Caution: These reagents are highly toxic! Our vacuum system pump was vented through a garden hose into a laboratory f ume hood exhausted through the roof. The Nd:YAG laser fundamental (Continuum Minilite II, 1064 nm, 10 Hz repetition rate, 10 ns pulse width) was focused using 5−10 mJ/pulse onto a rotating tungsten metal disc sawed from a 1 cm diameter rod (Johnson Matthey). IR spectra were recorded at 0.5 cm−1 resolution using a Nicolet iS50 spectrometer with a liquid nitrogen cooled HgCdTe range A detector after sample deposition. Next, samples were annealed (warmed and re-cooled) using resistance heat (temperature measured by gold/cobalt vs chromel thermocouple), and selected samples were irradiated for 10 min periods by a mercury arc street lamp, 175 W, output range 220−580 nm, with the globe removed.1,11 Computational Details. The initial structures and vibrational frequencies of the molecules were optimized at the DFT level using the B3LYP hybrid exchange-correlation functional.25,26 The basis set was composed of the aug-cc-pVDZ basis set for H and N,27,28 the augcc-pV(D+d)Z for P including tight d functions,29,30 and the aug-ccpVDZ-PP basis sets for the As31,32 and W33 with the accompanying pseudopotential (abbreviated as aD).34 The calculations were performed using Gaussian09.35 Atomic orbital occupancies were calculated using NBO636,37 for the natural bond orbital (NBO)38−41 population analysis at the DFT level. Wiberg bond orders were also calculated from the NBO results.42 The DFT geometries were used for the coupled-cluster R/UCCSD(T)43−49 level calculations with the above combination of aug-cc-pVnZ, aug-cc-pV(n + d)Z, and aug-ccpVnZ-PP basis sets, for n = D, T, and Q. Only the valence electrons were correlated. In the R/UCCSD(T) approach, a restricted openshell Hartree−Fock (ROHF) calculation was initially performed, and the spin constraint was then relaxed in the coupled-cluster calculation. The CCSD(T) energies were extrapolated to the complete basis set (CBS) limit by fitting to a mixed Gaussian/exponential (eq 1):50

E(n) = ECBS + A exp[− (n − 1)] + B exp[− (n − 1)2 ]

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RESULTS AND DISCUSSION Matrix IR spectra and frequency, structure, and energy calculations are reported for the products of tungsten metal atom reactions with phosphine and arsine in argon and neon matrixes. Argon Matrix Spectra. Figure 1 compares the argon matrix IR spectra of the products form the reaction of W atoms

(1)

where n = 2, 3, and 4 (D, T, and Q). Values obtained from this procedure will be denoted as CBS. Total atomization energies (TAEs or ∑D0) at 0 K were calculated from the following expression (eq 2) using the Feller−Peterson− Dixon (FPD) approach,51−53 with Δ referring to the difference between the molecule (reactant) and the atomic products for each energy component:

∑ D0 = ΔECBS + ΔErel + ΔEcv + ΔEZPE

Figure 1. Infrared spectra of the major reaction products from laserablated W atoms and PH3 or with AsH3 in argon: (a) after deposition of W and 1% PH3 in Ar for 50 min, (b) after annealing to 20 K, (c) after annealing to 25 K, (d) after >220 nm irradiation for 10 min, (e) after annealing to 37 K, (f) after deposition of W with 1% AsH3 in Ar for 50 min, (g) after annealing to 25 K, and (h) after annealing to 30 K.

(2)

Additional corrections to the CCSD(T)/CBS energy (ΔECBS) are necessary to reach chemical accuracy (±1 kcal/mol). Scalar relativistic corrections for light elements together with corrections for the PP approximation, ΔErel, were obtained using the second-order Douglas− Kroll−Hess (DKH) Hamiltonian at the CCSD(T)/aug-cc-pwCVTZDK level of theory (denoted as wCVTZ-DK): ΔErel = ΔEawCVTZ‐DK − ΔEawCVTZ‐PP

with PH3 and AsH3. The small shifts between the strong P- and As-bearing product absorptions can be deduced from the frequencies listed in Table 1. The major products for the phosphine reaction are labeled pt (for phosphide trihydride), and the two strongest bands at 1903.7 and 1910.0 cm−1 are associated by their common behavior of increasing on

(3)

where ΔEawCVTZ‑DK and ΔEawCVTZ‑PP are the valence electronic energy differences calculated at the CCSD(T)-DK/awCVTZ-DK and CCSD(T)/awCVTZ-PP levels, respectively. The core−valence corrections, ΔEcv, were obtained at the CCSD(T)/awCVTZ-PP level. The unscaled vibrational frequencies from the CCSD(T)/aVnZ calcuB


Article

Inorganic Chemistry

Table 1. Infrared Absorption Frequencies (cm−1) Observed for Tungsten Reaction Products with PH3 and AsH3 Compared with Methane and Hydrogen Reaction Products

a

molecule

WH str

WH str

NWH3 PWH3 PWH2 AsWH3 AsWH2 HCWH3 WH3 HPWH2 HAsWH2 CH2WH2 H2PWH H2AsWH CH3WH

1924.1 1910.0 1907.7 1907.4 1906.1 1907.5 1878.6 1865.1 1861.8 1864.5 1837.4 1835.7 1822.2d

1917.0 1903.7b 1905.4 1901.0b 1904.1 1896.3

PWH3 PWH2 AsWH3 WH3

1927.0 1925.2 1924.5 1895.3

1922.2 1923.0 1919.6

1816.1 1813.5 1817.2

molecule

WD str

Argon Matrix NWD3 1377.0 PWD3 1365.6

WD str

H/D ratio

H/D ratio

1377.0 1367.7

1.3973 1.3987

1.3922a 1.3919

1.3997c 1.3975d

DCWD3 WD3 DPWD2

1362.8 1344.3

CD2WD2

1336.2

1303.1

1.3954

1.3945

Neon Matrix PWD3 1377.3

1380.3

1.3991

1.3926

1298.6

WD3

1.3985

1.3925c

1361.1 −1

b

c

d

Ref 10. Weaker bands observed in Figure 1 for pt and at are 833.2 and 833.9 cm , respectively. Ref 16. Ref 17.

annealing (Figure 1b,c), decreasing on UV irradiation (Figure 1d), and increasing again on final annealing (Figure 1e). The corresponding product bands for the arsine reaction at 1901.0 and 1907.4 cm−1 labeled at (for arsenide trihydride) also increase on annealing (Figure 1f−h), and they are 2.7 and 2.6 cm−1 lower than their phosphine counterparts. These bands decrease markedly on irradiation. The next pair of bands for the phosphine reaction products at 1816.1 and 1865.1 cm−1 (Figure 1f−h) are labeled wp for tungsten phosphinidene); they increase and then decrease slightly on annealing cycles. The arsine reaction product counterparts at 1813.5 and 1861.5 cm−1 labeled wa (for tungsten arsinidene) are slightly stronger. The sharp weaker bands labeled i (for insertion product) increase slightly on annealing, and the phosphine counterpart, 1837.4 cm−1, is 1.7 cm−1 higher than the arsine analogue, 1835.7 cm−1. Figure 2 illustrates the spectra from 80% deuterium-enriched phosphine. The strongest two bands are 1367.7 and 1365.6 cm−1, and their intensities are reversed from the hydrogen counterparts, where the stronger band has the lower frequency. Thus, when we calculate isotopic H/D frequency ratios we use the stronger pair and the weaker pair, i.e., 1903.7/1367.7 = 1.3919 and 1910.0/1365.6 = 1.3987. These ratios are appropriate for WH/WD stretching modes, and they may be compared with those for tungsten trihydride17 WH3/ WD3 = 1878.6/1344.3 = 1.3985. The strongest product band with phosphine, 1903.7 cm−1, is 25.1 cm−1 or 1.3% higher than the antisymmetric stretching frequency for WH3 itself. Annealing brings in other bands at 1365.6 and 1360.9 cm−1, and broad bands in the upper region give way to sharper features at 1907.5, 1905.3, 1903.5, and 1889.5 cm−1. Neon Matrix Spectra. The neon matrix spectra in Figure 3 mimic the two higher frequency bands in Figure 1. The phosphine counterparts at 1922.2 and 1927.0 cm−1 are 18.5 and 17.0 cm−1 higher than the argon matrix frequencies, and 2.5 and 2.6 cm−1 higher than the arsine values in Ne. Annealing to 8 K increased both products, and annealing to 10 K increased

Figure 2. Infrared spectra of the major reaction products of laserablated W atoms and PH3 exchanged with D2O and diluted in argon: (a) after deposition of W and 2% PH3/PH2D/PHD2/PD3 with 80% D in Ar for 50 min, (b) after annealing to 20 K, (c) after annealing to 30 K, (d) after annealing to 35 K, and (e) after annealing to 41 K.

the phosphine product another 10%; irradiation with the mercury arc lamp decreased these bands by 10% (Figure 3d. Similar irradiation of the arsine sample decreased the absorptions markedly (not shown). Figure 4 shows spectra from reactions with the deuteriumenriched sample. As observed with the argon matrix, the two strongest bands reversed intensity with the higher 1380.0 cm−1 band stronger than the lower band at 1377.3 cm−1, and the WH/WD stretching mode ratios are 1.3991 and 1.3926, again in excellent agreement with the ratios computed from the argon matrix values. The upper region revealed a structured C


Article

Inorganic Chemistry

Figure 4. Infrared spectra of the major reaction products of laserablated W atoms and PH3 exchanged with D2O and diluted in neon: (a) after deposition of W and 2% PH3/PH2D/PHD2/PD3 with 80% D in Ne for 50 min, (b) after annealing to 8 K, (c) after annealing to 10 K, (d) after >220 nm irradiation for 10 min, (e) after a second annealing to 10 K, and (f) after annealing to 12 K.

stretching frequencies. Fortunately, the WH stretching frequencies are intense modes, and this facilitates their observation. The WH frequencies are predicted to decrease with fewer hydrogen atoms on the W just as found for the pure hydrides WHn (n = 1−6).17 The strongest product bands in solid argon are the two strong pt bands at 1903.7 and 1910.0 cm−1, which are 71.6 and 74.9 cm−1 (3.8 and 3.9%) lower than the calculated harmonic frequencies for the e and a1 modes, respectively, of PWH3 in C3v symmetry. Most of this discrepancy is due to anharmonicity in the WH bond, and some is due to the matrix. The Ne matrix frequencies at 1922.2 and 1927.0 cm−1 are 18.5 and 17.0 cm−1 higher and closer to the presumed gas-phase frequencies. The computed harmonic frequency ratio 1975.3/1403.5 = 1.4074 for the H/D substitution is higher than the observed anharmonic frequency ratio discussed below. This level of agreement is consistent with what is expected for the B3LYP exchange-correlation functional.1 The calculated WH stretching mode separation is 0.50% of the e mode, and the observed mode separation is 0.33%. The strongest band in the deuterium-enriched phosphine experiments is 1367.7 cm−1, which defines a 1903.7/1367.7 = 1.3919 ratio for the antisymmetric stretching modes (Figure 2). This ratio may be compared to the 1.3997 ratio observed for the analogous mode of HCWH3.1 The two WH stretching modes for the latter molecule are 1896.3 and 1907.5 cm−1, just 7.4 and 2.5 cm−1 lower than observed here for PWH3 (Table 1). The symmetric counterpart is computed to lie higher, at 1984.9 cm−1, and to have 46% of the intensity of the e mode. This a1 mode is observed at 1910.0 cm−1 (the computed value is 3.9% too high) and has 40% of the intensity of the e mode at 1903.7 cm−1, in agreement with the computed intensity ratio. The antisymmetric WH stretching mode for PWH3 is just

Figure 3. Infrared spectra of the major reaction products of laserablated W atoms and PH3 or with AsH3 in neon: (a) after deposition of W with 1% PH3 in Ne for 50 min, (b) after annealing to 8 K, (c) after annealing to 10 K, and (d) after >220 nm irradiation for 10 min, (e) after deposition of 1% AsH3 in Ne for 50 min, and (f) after annealing to 8 K.

feature which produced the major component on annealing at 1923.3 cm−1. Note that this band falls between the two major bands using PH3. Shoulder absorptions were observed at 1921.2 and 1925 cm−1 in the upper region and at 1376.4 cm−1 in the lower region. Annealing the Ne matrix must be done carefully to avoid Ne evaporation and a runaway rising temperature. Annealing to 8 and 10 K increased both product bands, 220−580 nm irradiation reduced the absorptions, and another 10 and 12 K annealing increased the product bands. The bands in the upper region labeled pt are due to mixed H, D isotopic terminal phosphides. Calculated Product Frequencies. The energies relative to the most stable structure for the products of the reaction of W with PH3 and AsH3 were calculated at the CCSD(T)/CBS level (Table 2). The terminal tungsten trihydride phosphide P WH3 is clearly the most stable reaction product, labeled pt in the figures. Frequencies for the products from the reaction of W and PH3 and AsH3 computed at the B3LYP level are given in Table 3. The ammonia product frequencies are shown in Table S1. Table 4 compares frequencies for the three deuterium substituted phosphides. Tungsten Trihydride Phosphide Assignment. The harmonic B3LYP frequencies (Table 3) predict that the trihydride phosphide PWH3 has moderately intense WH D


Article

Inorganic Chemistry Table 2. Relative Energies (ΔH(0 K), kcal/mol) at Different Computational Levels EWH3

HEWH2

1

level

3

A1/C3v

H2EWH

H2EWH

5

A″/Cs

3

A′/Cs

A″/Cs

WEH3

WEH3

7

5

A1/C3v

5

W + EH3

A1/C3v

E=N CCSD(T)/aD CCSD(T)/CBS B3LYP/aD

0.0 0.0 0.0

14.0 13.5 11.3

32.2 33.7 29.8

CCSD(T)/aD CCSD(T)/CBS B3LYP/aD

0.0 0.0 0.0

23.0 24.6 21.1

38.4 42.0 35.6


0.0 0.0 0.0

23.4 25.4 22.0

43.8 48.2 41.4

44.4 43.4 38.0

66.1 72.8 72.5

68.1 73.7 81.9

63.8 71.3 69.1

59.5 58.5 54.5

63.4 70.1 67.3

65.4 68.7 68.4

62.2 72.2 67.7

69.7 72.2 59.0

72.9 81.4 80.6

76.1 81.6 78.1

68.9 79.8 74.5

E=P

E = As

Table 3. Calculated Frequencies (ν, cm−1) and IR Intensities (I, km/mol) for E = P and As EWH3 ν

I

3

5

HEWH2

H2EWH

ν

ν

I

7

H2EWH

I

5

WEH3

WEH3

ν

I

ν

I

ν

I

170.5 296.7 341.8 416.6 556.1 1098.3 1920.7 2325.0 2416.2

17 11 103 2 115 107 130 95 45

179.0 190.6e 995.2 1096.8e 2351.7 2360.0e

0 10 220 2 266 31

264.5 391.1e 999.5 1075.5e 2370.6e 2381

21 4 80 6 24 121

176.7 204.1 301.9 452.6 524.6 968.3 1933.0 2114.4 2129.7

19 3 10 4 38 23 143 64 51

94.8 115.4e 910.3 990.1e 2110.9 2133.0e

1 8 211 4 543 92

154.1 288.7e 899.7 974.6e 2145.0 2153.0e

3 8 68 6 272 85

E=P 571.8 584.2e 654.8 851.6e 1975.3e 1984.9

0 50 39 57 258 118

136.4 381.9 445.8 459.0 752.3 888.9 1878.1 1939.3 2073.3

37 14 13 0 3 50 257 121 2

247.5 293.4 322.4 493.0 530.6 1069.3 1907.5 2347.5 2360.6

26 34 12 0 31 29 175 33 23

383.5 560.1e 620.0 852.4e 1973.5e 1983.3

0 50 39 57 258 118

45.0 296.7 357.3 445.9 733.3 886.6 1808.2 1874.5 1943.0

24 3 24 5 18 70 20 254 118

201.5 215.8 325.0 459.5 509.0 968.0 1919.8 2118.0 2134.4

1 22 16 0 46 22 153 70 58

E = As

Table 4. Calculated Frequencies (ν, cm−1) and IR Intensities (I, km/mol) for PWHxD3‑x PWD3

PWHD2

mode for PWD3 as the 1910.0/1365.6 = 1.3987 ratio is almost the same as observed for the e mode. The broad band at 1890 cm−1 with substructure is most likely due to the adjacent PWH3 absorption perturbed by the reagent phosphine in the same matrix cage. A weaker band at 833.2 cm−1 in the argon phosphine experiments tracks with the strong bands at 1903.7 and 1910.0 cm−1, having the common behavior of increasing on annealing and decreasing on irradiation. The 833.2 cm−1 band has 14% of the 1903.7 cm−1 band’s intensity. The calculated degenerate antisymmetric HWP bending mode is 851.6 cm−1 with 16% of the IR intensity of the strongest e stretching mode, in support of this assignment. Additional weak bands were observed in the deuteriumenriched phosphine experiments at 1360.9, 1365.0, 1889.5, 1903.5, 1905.3, and 1907.5 cm−1. Our frequency calculations in Table 4 for deuterated phosphide molecules suggest that the WD modes for PWD2H and PWH2D would be covered

PWH2D

ν

I

ν

I

ν

I

421.6e 447.1 596.5 604.1e 1403.5e 1404.2

24 11 13 28 180 61

425.8 437.1 552.8 598.0 655.5 767.9 1403.9 1403.9 1978.5

14 11 2 14 41 16 72 90 157

432.6 569.2 573.1 638.4 715.7 844.0 1404.3 1975.0 1981.7

14 15 3 35 34 22 82 177 138

25.1 cm−1 or 1.3% higher than this mode for WH3.17 The second strongest band in the deuterium-enriched phosphine experiments is 1365.6 cm−1, and this can be assigned to the a1 E


Article

Inorganic Chemistry

Initial Insertion Products. The two weak sharp bands labeled i in Figure 1 at 1837.4 and 1835.7 cm−1 for the P and As products, respectively, are assigned to the strong WH stretching modes for the H 2 PWH and H 2 AsWH phosphanyl and arsinanyl tungsten hydrides, which are just above the corresponding frequency16 for CH3WH in argon at 1822.2 cm−1. Our calculations predict these two metal monohydrides to have frequencies intermediate between the two modes for the doubly bonded dihydrido products. These initial insertion products H2EWH are predicted to be 42 and 48 kcal/mol less stable than EWH3 at the CCSD(T)/CBS level for E = P and As, respectively. Tungsten Dihydride Phosphide Assignment. The above discussion demonstrates that the saturated phosphide and higher multiplicity tungsten-bearing molecules have WH stretching modes in distinctly different regions: the former are computed to be 50−100 cm−1 higher than the latter, and our observations are in good agreement. This point is underscored by noting that the computed WH stretching frequencies (Table 5) for 2PWH2 fall between the e and a1 stretching

by the strong PWD3 absorptions. However, the weak 1365.0 cm−1 peak could be due to either of these molecules. The strongest of the higher peaks at 1905.3 cm−1 is most likely due to PWHD2, which is computed to be 3.0 cm−1 higher than the (e) mode for PWH3. . Finally, the 1903.5 and 1907.5 cm−1 bands are good candidates for PWH2D, which is expected in this region, but we cannot be certain of this as the 1903.5 cm−1 band could also be due to PWH3 as they share common computed frequency bands. Tungsten Trihydride Arsenide Assignment. Table 1 lists the 1901.0 and 1907.4 cm−1 argon matrix bands, which are 2.7 and 2.6 cm−1 below the bands assigned above to PWH3. Our B3LYP calculations predict that the e and a1 WH stretching modes for AsWH3 will be 1.6 and 1.8 cm−1 below the corresponding modes for PWH3, so these bands can readily be assigned to AsWH3. Our Ne matrix bands for AsWH3 are 2.6 and 2.5 cm−1 lower than the Ne matrix bands for PWH3, again in agreement with the predicted values. The e and a1 WH stretching mode separations are 6.4 cm−1 for AsWH 3 , which can be compared with the 6.3 cm −1 separation for PWH3 and the 7.1 cm−1 mode difference10 for NWH3. Note that the NWH3 bands10 are substantially higher, 13.3 and 14.1 cm−1, than the PWH3 bands. The broad band at 1889 cm−1 with substructure is most likely due to the adjacent AsWH3 absorption perturbed by the reagent arsine. The weak band at 833.9 cm−1 labeled at also tracks with the two stronger bands for the AsWH3 molecule, and unlike the WH stretching modes, which exhibit small red shifts from the PWH3 values, this HWAs bending mode exhibits a 0.7 cm−1 blue shift from the 833.2 cm−1 value observed for the corresponding HWP mode. In addition the calculated value of 852.4 cm−1 for AsWH3 is 0.8 cm−1 higher than 851.6 cm−1computed for PWH3 (Table 3). This excellent blue shift agreement helps to confirm the vibrational assignments for both AsWH3 and PWH3. Tungsten Dihydride Phosphinidene Assignment. The 1816.1 and 1865.1 cm−1 bands labeled wp in Figure 1 are assigned to the tungsten dihydride phosphinidene HPWH2 based on agreement with our B3LYP calculations, which predict two WH stretching modes at 1878.1 and 1939.3 cm−1 for this molecule. These are the two strongest IR absorptions and 3.4 and 4.0% higher than the observed bands, which is the same order of error due to missing anharmonic corrections as observed for the phosphide. A weak band in the PD3 experiment is observed at 1298.6 cm−1(not shown) giving a 1816.1/1298.6 = 1.3985 H/D isotopic frequency ratio, which is also close to the frequency ratios for the phosphide. HPWH2 is predicted to be 24.6 kcal/mol less stable than PWH3 at the CCSD(T)/CBS level. Tungsten Dihydride Arsinidene Assignment. The similar 1813.5 and 1861.8 cm−1 bands labeled wa in Figure 1 are assigned to the tungsten dihydride arsinidene HAsWH2, also based on comparison with the B3LYP frequency calculations. The observed WH stretching bands for the arsinidene are 2.6 and 3.3 cm−1 lower than those for the phosphinidene. The analogous modes for the methylidene16 CH2WH2 are near the bands for the HP and AsP derivatives but not as close as the latter derivatives are to each other. HAsWH2 is predicted to be 25.4 kcal/mol less stable than AsWH3 at the CCSD(T)/CBS level, which is within one kcal/ mol of the energy difference between the corresponding phosphorus compounds.

Table 5. Calculated Frequencies (ν, cm−1) and IR Intensities (I, km/mol) for Compounds with Two H Atoms for E = P and As 2

4

EWH2

HEWH (trans)

ν

I

ν

557.4 601.1 607.8 738.9 1976.5 1982.7

0 50 46 54 175 105

428.2 439.1 444.0 760.0 1877.4 2004.0

364.8 577.0 584.9 727.6 1975.5 1982.4

0 53 39 54 170 115

288.2 400.4 427.8 757.9 1710.2 1870.9

4

HEWH (cis)

EWH2

I

ν

I

E=P 3 287.5 9 302.0 62 410.7 34 542.8 225 1928.2 25 2301.3

11 26 5 53 152 20

301.3 475.0 509.9 1066.6 2307.6 2319.7

1 3 0 17 41 35

E = As 0 255.7 16 267.4 56 281.6 71 510.0 28 1933.3 253 2103.9

0 17 1 55 147 52

200.8 441.6 464.3 963.1 2093.1 2108.3

0 13 0 14 79 74

I

ν

6

modes for PWH3. Given these values, we examined expanded-scale spectra (Figure 5) between the strong 1903.7 and 1910.0 cm−1 absorptions for PWH3 and found two sharp weak bands at 1905.4 and 1907.7 cm−1. These bands increase on annealing with the stronger PWH3 absorptions, where the lower band is not resolved from the broadened 1903.7 cm−1 absorption; however, they increase slightly on UV irradiation at the expense of the decreasing stronger bands, as illustrated in Figure 5d with resolution of the weaker 1905.4 cm−1 band from the stronger 1903.7 cm−1 absorption. The neon matrix spectra are not quite as clear, but the final UV irradiation scan shows the growth of two broad new features at 1923.0 and 1925.2 cm −1 between the stronger 1922.2 and 1927.0 cm −1 absorptions (Figure 3). These Ar-to-Ne matrix shifts of 17.6 and 17.5 cm−1 are within one wavenumber of the matrix shifts observed for PWH3. We therefore assign the bands at 1905.4 and 1907.7 cm−1 to the symmetric and antisymmetric WH stretching modes for PWH2. The relative energies for the various isomers with two H atoms are given in Table 6. The 2EWH2 isomer is the most F


Article

Inorganic Chemistry

1973.5 and 1983.3 cm−1, which are in line with our observations. These new bands also follow the trihydride relationship and fall slightly (1.3 and 1.6 cm−1) lower than the phosphide counterpart. The two weak bands at 1904.1 and 1906.1 cm−1 are assigned to the symmetric and antisymmetric WH stretching modes for AsWH2. The two bands 1889.5 and 1360.9 cm−1 not marked in Figure 2 exhibit a 1.3884 ratio, so they could be H and D counterparts of a minor product. A tentative possibility is H PWH with computed frequencies given for the two isomers in Table 5. Heats of Formation and Bond Dissociation Energies (BDEs). The components for predicting the heats of formation of EWH3 and EWH2 at the Feller−Peterson−Dixon (FPD) level are given in Table 7. The core−valence corrections increase from E = N to E = As. Scalar relativistic corrections are comparable to or larger than the core−valence corrections, and neither can be neglected for chemical accuracy. The calculated heats of formation and BDEs at 0 K are given in Table 8. The heats of formation of the less stable isomers are calculated from the values derived from Table 7 and the various relative energies given above in Tables 2 and 6. Not surprisingly, the NW bond in 1NWH3 is quite strong, with a BDE of 160 kcal/mol. The PW BDE in 1PWH3 is substantially smaller, 113 kcal/mol, and the AsW in 1AsWH3 is even lower, 99 kcal/mol. The WH BDEs are comparable for 1NWH3 and 1PWH3, whereas that for 1AsWH3 is larger, consistent with a lower stability for 2AsWH2. For the higher energy isomers, the WH BDEs are larger than the EH BDEs. The values do not show any periodic trends, and the values for E = As are always the largest ones, consistent with the product radicals containing As being less stable. Reactions in the Laser Ablation Matrix Isolation Experiments. Reactions occur on sample deposition with energetic W atoms under irradiation by light in the laser ablation plume from the focal point of the pulsed 1064 nm laser. (See ref 1 for a real-time photograph of this process.) Reactions also occur during annealing through diffusion and association of reagents in the cold matrix. Ultraviolet irradiation of the cold matrix sample can also initiate photochemistry. Reactions during the deposition phase are characterized by the first IR spectrum recorded after deposition of W metal atoms into the Ar or Ne matrix gas containing the PH3 or AsH3 reagent molecules. Reactions proceed during annealing (temperature cycling) as shown by increases of the strong pt and at and weaker pd and ad absorptions in Figures 1and 5. These processes are summarized in Figure 6 with energies at the CCSD(T)/CBS level and geometries obtained at the B3LYP level. The transition states have a single imaginary frequency, and the paths between reactants and products of the same spin were confirmed by intrinsic reaction coordinate calculations60,61 at the B3LYP level. In the first step, W(5D) inserts into the PH bond to form the WH product 5 H2PWH with no change in spin. A pre-complex in a shallow well may form, but the barrier to transfer H is above the reactant asymptote so a direct insertion is most likely. We only predict the pre-complex to be bound for E = P; for E = N and As, the pre-complexes are predicted to be minima but slightly above the reactant asymptote. The initial insertion step is followed by H transfer from P to W. In order for this step to be exothermic, the spin has to change from a quintet to a triplet. Searching for such spin crossing transition states is beyond the current scope of this work. Once the 3HPWH2 is formed, a

Figure 5. Expanded wavenumber scale infrared spectra of the phosphide and arsenide reaction products from laser-ablated W atoms and PH3 or with AsH3 in argon taken from Figure 1.

Table 6. Relative Energies (ΔH(0 K), kcal/mol) for Compounds with Two H Atoms at Different Computational Levels for E = N, P, and As EWH2 level

2

A′/Cs

HEWH (trans) 4

A″/Cs

HEWH (cis) 4

A″/Cs

H2EW 6

A′/Cs


0.0 0.0 0.0

E=N 19.0 19.5 17.7


0.0 0.0 0.0

E=P 16.4 18.9 16.3

22.8 22.5 20.6

29.1 34.3 30.4


0.0 0.0 0.0

E = As 16.2 18.8 16.8

24.3 26.7 22.5

33.1 37.5 35.0

12.8 13.6 12.2

32.7 35.6 33.9

stable in all cases. The next most stable isomer is 4HEWH. For E = N, the cis conformer is more stable than the trans. The trans conformer is more stable than the cis for the E = P and As. Tungsten Dihydride Arsenide Assignment. Two weaker bands appear at 1904.1 and 1906.1 cm−1 on annealing between the two strong absorptions for AsWH3 at 1901.0 and 1907.4 cm−1 in Figure 5f−h. Calculations predict the bands for AsWH2 at 1975.5 and 1982.4 cm−1 and for AsWH3 at G


Article

Inorganic Chemistry Table 7. Components of FPD Total Atomization Energies in kcal/mol molecule

ΔECBS

ΔEZPE

ΔEcv

ΔErel

∑D0

ΔHf,0K

ΔHf,298K

1

371.35 322.13 306.07 292.74 243.29 214.79 206.56

−15.54 −14.34 −13.95 −10.2 −9.2 −8.9 −10.9

0.16 0.88 2.12 0.39 1.00 1.68 0.48

1.12 1.77 1.69 1.01 1.64 1.57 0.91

348.65 302.00 287.49 275.45 228.24 200.72 188.61

121.9 131.4 139.4 143.4 153.5 174.5 169.4

119.3 128.8 137.1 141.8 151.8 173.1 167.9

NWH3 1 PWH3 1 AsWH3 2 NWH2 2 PWH2 2 AsWH2 4 WH3

Table 8. Heats of Formation and BDEs in kcal/mol BDE molecule

ΔHf,0K

ΔHf,298K

WE

WH

EH

NWH3 1 PWH3 1 AsWH3 3 HNWH2 3 HPWH2 3 HAsWH2 5 H2NWH 5 H2PWH 5 H2AsWH 2 NWH2 2 PWH2 2 AsWH2 4 HNWH cis 4 HPWH cis 4 HAsWH cis 4 HNWH trans 4 HPWH trans 4 HAsWH trans 6 H2NW 6 H2PW 6 H2AsW 4 WH3

121.9 131.4 139.4 135.4 156.0 164.8 155.6 173.4 187.6 143.4 153.5 174.5 157.0 176.0 201.2 162.9 172.4 193.3 179.0 187.8 212.0 169.4

119.3 128.8 137.1 133.3 153.9 163.1 153.4 171.4 185.9 141.8 151.8 173.1 155.6 177.8 200.3 161.6 170.9 192.1 177.7 185.9 210.8 167.9

160.0 113.4 98.9

73.2 73.8 86.8 73.2 (cis) 68.0 (trans) 80.1 (trans) 75.0 66.0 76.0

59.6 49.1 61.3 52.2 (cis) 50.6 (trans) 57.3 (trans)

1

the PH3 group to the W to complete a valency of 6 electron pairs, the spin is reduced as the excess electrons on the W pair up with the electron on H to form WH bonds. In the sense of a formal oxidation state approach, the most stable product has the W in the +VI oxidation state. The introduction of UV radiation into the sample decreases the pt absorptions (see Figure 1d) and the at bands (not shown), but increases the pd peaks (see Figure 5d). The photolysis leads to breaking a WH bond converting some 1 PWH3 into 2PWH2. The WH BDE for this process is 74 kcal/mol (3.20 eV) so there is more than sufficient energy in the UV photons for this to occur. Structures and Bonding. The B3LYP/aD optimized structures are shown in Figure 7. The structures for E = N differ from those for E= P and As when there is one H on the E. These are clear agostic interactions in 3HPWH2 and 3HAsWH2. There are also agostic interactions in HEWH for E = P and As, but not for E = N. These agostic interactions are similar to what is found for the corresponding Group 4, thorium and uranium molecules with similar structures.9,15 The WH2 moieties in HEWH2 are planar. The E center in the H2EWH molecules is nonplanar and becomes increasingly pyramidal as E increases in atomic number, with the sum of the angles at E being 355.3°,

Figure 6. CCSD(T)/CBS energies + ZPE at 0 K (ΔH(0K)) of the products and corresponding transition states with the same spin relative to the reactants [W(5D) + PH3]. Values in red are reaction energy barriers.

second H transfer to W can occur to form 1PWH3, and again the spin changes from a triplet to a singlet for the process to be exothermic. Note that as more H atoms are transferred from H


Article

Inorganic Chemistry

Figure 7. Calculated B3LYP/aD geometry parameters (EW bond distances in angstroms and bond angles in degrees). The W is dark blue, the N is gray, the P is orange, the As is purple, and the H is white.

300.7°, and 284.9° in the order N, P, As. The corresponding sum of the bond angles in the EH3 hydrides are 320.1°, 279.9°, and 275.1° for E = N, P, and As, respectively, at the same level of theory. This is due to diminished s-p hybridization in the heavier pnictogens. The bond lengths increase as hydrogens are transferred from W to E consistent with an effective triple bond in EWH3, a double bond in HEWH2, and a single bond in H2EWH as discussed below in the population analysis. Removal of an H from W does not change the WE bond distance by more than 0.02 Å; in most cases, the change is much smaller than this. The molecular orbitals (Figure 8) for the compounds show that there is a triple bond between the E and W. For E = N, the HOMO is the σ bond, and the two degenerate π bonds are more stable by 0.3 eV. For E = P and As, the HOMO is the degenerate π orbitals, and the HOMO−2 is the σ orbital. The HOMO is 0.4 eV less stable than the HOMO−2 for P and 0.5 eV less for As. The σ orbitals are all quite similar, and the π orbitals are as well. The NBO analysis of the WE orbitals is given in Table 9. The WN σ and π bonds are polarized toward the N, with about 60% on the N and 40% on the W. The N is approximately sp3 hybridized for this orbital, whereas the W portion has 80% d character and 20% s character. The π bonds are ∼100% d on W and 100% p on N. The N lone pair is slightly delocalized onto the W. In contrast, the bonding for E = P and E = As is quite similar to the σ orbital, having equal contributions from the P or As and W and the π orbitals polarized toward the W. The P or As contribution to the σ orbital is dominated by p character, with about 85% p. The W has about 30% s and 70% d for the σ orbital. The π orbital is almost pure d on the W and pure p on the P or As. The total Wiberg bond orders (Table 10) clearly show that the WE bond in EWH3 should be considered as a triple bond with total bond orders at W of 5.8−5.9. The E has a bond order slightly greater than 3 consistent with the bond orders at W. The WH bonds are clearly single bonds. Removal of H to

Figure 8. HOMO to HOMO−2 orbitals and their energies in eV for EWH3 with E = N (blue), P (orange), and As (purple), respectively, top to bottom.

form 2EWH2 leads to a decrease in the bond order of 1 on the W as expected for loss of a WH bond. Transfer of a H to E results in a bond order decrease of ∼2 on W with the bond order loss larger for E = N than for E = P or As. This is consistent with loss of a WH bond and formation of an E H bond which removes an electron from the E so that it can no longer participate in the WE bond. Thus, the bond order is I


Article

Inorganic Chemistry

of a second H to the E to from 5H2EWH gives a bond order near 2 on W due to a WH bond and an EW single bond. The bond order at W is again smaller for N than for P or As. The changes in the spin states are also consistent with the changes in the bond orders at W. The NPA analysis shows that the W is quite positive for E = N with polar WH and WN bonds, with both the H and N carrying the negative charge. For E = P, the W is slightly negative, so the WP bond is polarized in the opposite direction. The WH bonds are essentially nonpolar. Essentially the same results are also found for E = As.

Table 9. NBO Bond Analysis for EWH3 with E = N, P, and Asa bond

%W

%W(6s)

WE σ WE π E lp

40 43 6

19


51 55

30


9

51 56

31

%W(5d)

%E

%E(ns)

%E(np)

60 57 94

26

74 100 26

49 45 100

18

E=N 81 98 88 E=P 68 95

E = As 67 95

49 44 100

74

83

15 86

82 100 17

■

CONCLUSIONS

Laser ablation of tungsten metal provides atoms to react with phosphine during condensation in excess argon and produces major new infrared absorptions at 1903.7 and 1910.0 cm−1 that increase together on annealing and decrease together on UV irradiation. These bands shifted to 1922.2 and 1927.0 cm−1 when the reaction was done in condensing neon. Deuterium counterparts were observed at 1367.7, 1365.2 and at 1380.3, 1377.3 cm−1, which define H/D frequency ratios of 1.3987, 1.3991 and 1.3926, 1.3991 for these WH stretching frequencies. New bands at 1816.1 and 1865.1 cm−1 behave similarly on photolysis and annealing. Similar experiments with arsine gave product absorptions a few inverse centimeters lower. Additional weak bands in this phosphide and arsenide WH stretching region are assigned to PWH2 and P WH2.

85 100 14

a

%W and %E are the percentages of the orbital on W and E, respectively. %W(6s) and %W(5d) are the percentages on W in the 6s and 5d orbitals, respectively. %E(ns) and %E(np) are the percentages on E for the ns and np orbitals, respectively, with n = 2 for N, n = 3 for P, and n = 4 for As. σ is the σ orbital between E and W. π is the π orbital between E and W. These are doubly degenerate. lp is the lone pair on E.

∼4 with two WH bonds and a W = E double bond. The E has a bond order near 3 consistent with this result, an EH bond and the WE double bond. The increase for E = P and As is due to the agostic EH interaction with the W. Transfer

Table 10. Wiberg Bond Orders (WBO) and Natural Population Analysis (NPA) from NBO Analysis with E = N, P, and As 1

EWH3

W WBO N WBO H WBO W NPA N NPA H NPA

W WBO P WBO H WBO W NPA P NPA H NPA

W WBO As WBO H WBO W NPA As NPA H NPA

5.91 3.15 0.99(3) 0.64 −0.34 −0.10

5.85 3.11 0.99(3) −0.06 0.28 −0.07(3)

5.82 3.08 0.99(3) −0.09 0.33 −0.08(3)

3

HEWH2

5

H2EWH

3.87 3.08 0.84 (N) 0.91, 0.96 (W) 0.95 −0.85 0.41 (N) −0.30, −0.21 (W)

E=N 1.79 2.63 0.83(2) (N) 0.88 (W) 0.76 −1.22 0.39(2) (N) −0.33 (W)

4.07 2.96 1.02 (P) 0.96, 0.98 (W) 0.35 0.03 −0.02 (P) −0.22, −0.14 (W)

E=P 1.98 3.03 0.99(2) (P) 0.93 (W) 0.52 −0.26 0.01(2) (P) −0.27 (W)

4.06 2.87 1.01 (As) 0.95, 0.99 (W) 0.30 0.12 −0.06 (As) −0.23, −0.13 (W)

E = As 1.95 2.98 0.99(2) (As) 0.93 (W) 0.49 −0.18 −0.02(2) (As) −0.26 (W) J

2

EWH2

4.89 3.08 0.98(2) 0.93 −0.50 −0.21(2)

4.87 3.07 0.99(2) 0.32 0.04 −0.18

4.83 3.01 0.99(2) 0.28 0.09 −0.18(2)

4

HEWH (trans) 2.93 2.89 0.84 0.91 0.92 −0.98 0.39 −0.33

3.01 2.89 0.98 0.93 0.54 −0.13 −0.09 −0.31

2.98 2.80 0.97 0.93 0.51 −0.04 −0.14 −0.33

(N) (W)

(N) (W)

(P) (W)

(P) (W)

(As) (W)

(As) (W)

4

HEWH (cis) 2.83 2.94 0.84 0.86 1.01 −0.96 0.39 −0.44

2.90 2.94 0.99 0.95 0.52 −0.26 −0.01 −0.26

2.83 2.83 0.99 0.95 0.49 −0.19 −0.04 −0.25

(N) (W)

(N) (W)

(P) (W)

(P) (W)

(As) (W)

(As) (W)


Article

Inorganic Chemistry

BES Catalysis Center Program by a subcontract from Pacific Northwest National Laboratory (KC0301050-47319). D.A.D. also thanks the Robert Ramsay Chair Fund of The University of Alabama for support.

DFT electronic structure calculations support these frequency assignments. The most stable products are predicted to be the phosphide and arsenide (EWH3) molecules, 72 and 80 kcal/mol lower in energy than the corresponding reagents, W and EH3. The corresponding phosphinidene and arsenidine (HEWH2) generated by hydrogen transfer from the W to the E from the minimum energy structure are predicted to be 25 kcal/mol above the respective ground state and 48 and 54 kcal/mol below the reactant asymptote, respectively. The compounds with a single WE bond generated by an additional H transfer from W to E are predicted to be 42 and 48 kcal/mol above the ground state and 30 and 32 kcal/ mol below the reactants asymptote for E = P and As, respectively. Starting from the reactants, the single bond, double bond, and triple bond structures are generated by successive H atom transfers from the PHx group to the WHy. The first H atom transfer does not involve a spin change as the W is a quintet as is H2PWH, the next H atom transfer is accompanied by a spin change from a quintet to a triplet, and the final H atom transfer is accompanied by a spin change from a triplet to a singlet. As the formal oxidation state on the W changes from 0 to + VI with the H atom transfers, the spin also decreases. A number of different approaches for the analysis of the bonding show that the bonding in 1EWH3 is best described by three WH single bonds and an EW triple bond. The bonding in 3HEWH2 is best described by two WH single bonds, an EH single bond, and an EW double bond. The bonding in 1H2EWH is best described by a WH single bond, two EH single bonds, and an EW single bond. The EW triple bond for E = N is quite strong, 160 kcal/mol, and the BDE for the triple bond decreases to 113 kcal/mol for E = P and to 99 kcal/mol for E = As. The NW triple bond is slightly stronger than the estimated value for the WO double bond energy of 153 kcal/mol (from the atomization energy of WO3).62 This energy comparison is consistent with the interpretation of the bonding in these systems.

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(1) Andrews, L.; Cho, H.-G. Matrix Preparation and Spectroscopic and Theoretical Investigations of Simple Methylidene and Methylidyne Complexes of Group 4−6 Transition Metals. Organometallics 2006, 25, 4040−4053. (2) von Frantzius, G.; Streubel, R.; Brandhorst, K.; Grunenberg, J. How Strong Is an Agostic Bond? Direct Assessment of Agostic Interactions Using the Generalized Compliance Matrix. Organometallics 2006, 25, 118−121. (3) Cho, H.-G.; Andrews, L. Matrix Preparation and Spectroscopic and Theoretical Investigation of Small High Oxidation-State Complexes of Group 3−12 and 14, Lanthanide and Actinide Metal Atoms. Coord. Chem. Rev. 2017, 335, 76−102. (4) Chen, M.; Lu, H.; Dong, J.; Miao, L.; Zhou, M.-F. Reactions of Atomic Silicon and Germanium with Ammonia: A Matrix-Isolation FTIR and Theoretical Study. J. Phys. Chem. A 2002, 106, 11456− 11464. (5) Zhou, M.-F.; Chen, M.; Zhang, L.; Lu, H. Reactions of Zirconium and Hafnium Atoms with Ammonia. Matrix Infrared Spectra and Density Functional Calculations of the MNH3 and H2MNH (M = Zr and Hf). J. Phys. Chem. A 2002, 106, 9017−9023. (6) Wang, X.-F.; Andrews, L.; Marsden, C. J. Infrared Spectrum and Structure of Thorimine, [HN = ThH2]. Chem. - Eur. J. 2007, 13, 5601−5606. (7) Wang, X.-F.; Andrews, L.; Marsden, C. J. Reactions of Uranium Atoms with Ammonia: Infrared Spectra and Quasi-Relativistic Calculations of the U: NH3, H2N-UH, and HN = UH2 Complexes. Chem. - Eur. J. 2008, 14, 9192−9201. (8) Chung, G.; Gordon, M. S. MCSCF Study of Multiple Bonding between Ti and the Main-Group Elements C, Si, N, and P. Organometallics 2003, 22, 42−46. (9) Andrews, L.; Cho, H.-G. Matrix Infrared Spectra and Quantum Chemical Calculations of Ti, Zr, and Hf Dihydride Phosphinidene and Arsinidene Molecules. Inorg. Chem. 2016, 55, 8786−8793. (10) Wang, X.-F.; Andrews, L. Infrared Spectra, Structure and Bonding of the Group 6 M: NH3,H2N-MH, and N≡MH3 Reaction Products in Solid Argon. Organometallics 2008, 27, 4885−4891. (11) Wang, X.-F.; Andrews, L.; Lindh, R.; Veryazov, V.; Roos, B. O. A Combined Theoretical and Experimental Study of Simple Terminal Group 6 Nitride and Phosphide N≡MX3 and P≡MX3 Molecules. J. Phys. Chem. A 2008, 112, 8030−8037. (12) Wang, X.; Andrews, L.; Knitter, M.; Malmqvist, P.-Å.; Roos, B. O. An Experimental and Theoretical Investigation of Simple Terminal Group 6 Arsenide As≡MF3 Molecules. J. Phys. Chem. A 2009, 113, 6064−6069. (13) Andrews, L.; Wang, X.; Lindh, R.; Roos, B. O.; Marsden, C. J. Simple N≡UF3 and P≡UF3 Molecules with Triple Bonds to Uranium. Angew. Chem., Int. Ed. 2008, 47, 5366−5370. (14) Andrews, L.; Wang, X.; Roos, B. O. The As≡UF3 Molecule with a Weak Triple Bond to Uranium. Inorg. Chem. 2009, 48, 6594−6598. (15) Andrews, L.; Cho, H.-G.; Thanthiriwatte, K. S.; Dixon, D. A. Thorium and Uranium Hydride Phosphorus and Arsenic Bearing Molecules with Single and Double Actinide-Pnictogen and Bridged Agostic Hydrogen Bonds. Inorg. Chem. 2017, 56, 2949−2957. (16) Cho, H.-G.; Andrews, L.; Marsden, C. Infrared Spectra of CH3− CrH, CH3−WH, CH2=WH2, and CH≡WH3 Formed by Activation of CH4 with Cr and W Atoms. Inorg. Chem. 2005, 44, 7634−7643. (17) Wang, X.-F.; Andrews, L. Neon Matrix Infrared Spectra and DFT Calculations of Tungsten Hydrides WHx (x = 1−4,6). J. Phys. Chem. A 2002, 106, 6720−6729. (18) Gardner, B. M.; Balazs, G.; Scheer, M.; Tuna, F.; McInnes, E. J. L.; McMaster, J.; Lewis, W.; Blake, A. J.; Liddle, S. T. Triamidoamine−

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.8b00348. Complete refs 35 and 59; tables of optimized geometries and energies (PDF)

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REFERENCES

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Lester Andrews: 0000-0001-6306-0340 Han-Gook Cho: 0000-0003-0579-376X David A. Dixon: 0000-0002-9492-0056 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Chemical Sciences, Geosciences and Biosciences Division, Office of Basic Energy Sciences, U.S. Department of Energy (DOE) under the DOE K


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