Studies of Reactions of Atomic and Dlatomlc Cr, Mn, Fe, Co, Ni, Cu

J. Phys. Chem. 1985,89, 3541-3547

3541

Studies of Reactions of Atomic and Dlatomlc Cr, Mn, Fe, Co, Ni, Cu, and Zn with Molecular Water at 15 K J. W. Kauffman, R. H. Hauge,* and J. L. Margrave Department of Chemistry and Rice Quantum Institute, Rice University, Houston, Texas 77251 (Received: January 31, 1985) Chromium, manganese, iron, cobalt, nickel, copper, and zinc metal atoms were cocondensed with H 2 0 in an argon matrix at 15 K. The metal atoms, except for nickel, formed an adduct with water. This resulted in a decrease of the water u2 bending mode frequency. The negative shifts were 13.1, 16.5, 30.5, 29.0, 20.5, 0, and 5.6 cm-I, respectively. Atomic nickel did not react with water, or at least caused no shift in the bending frequency of water. This behavior of Ni is unique among the first row transition metals in not forming either an adduct or an insertion product. Metal dimer-water adducts were formed at higher metal concentrations and caused negative water bending mode shifts of 25.5, 19.2, 16.9, 10.9, and 8.3 cm-' for chromium, manganese, iron, copper, and zinc. A higher manganese cluster-water adduct was observed with a negative u2 shift of 23.6 cm-I. Except for zinc, photolysis of the observed metal atom adducts caused the metal atom to insert into an OH bond of water to form the HMOH molecule. The HMOH molecule is found to be nonlinear in all cases. The copper and zinc adducts rearranged with photolysis during deposition to form the CuOH and ZnOH species. Other identified products are HMn20H,HMnOMnH, HFeOFeH, Fe(OH)*, HFe20H, and H.$r(OH),. A discussion of bonding trends in water-metal atom adducts and the hydroxy-metal hydrides is presented. Infrared frequencies and proposed assignments are given. Introduction

Previous work with both regular and transition metals has shown that metal atoms formed adducts with water on cocondensation.' Adduct formation was indicated by the appearance of an infrared peak shifted down from the u2 bending mode of matrix isolated water. This peak was assigned to the v2 bending mode of a perturbed water molecule in the adduct. Photolysis of the matrix resulted in the disappearance of this adduct peak with the formation of oxidative insertion products.14 Atomic zinc insertion into the carbon iodine bond of CFJ at low temperatures has also been reported by Klabunde et al.5 The present matrix isolation studies provide new information on first row transition-metal atom interactions with molecular water. Evidence suggesting the reaction of metal dimers and metal clusters with water molecules is also presented. Estimated heats of reaction are given in Table I. Estimates of bond energies were made from comparisons with known metal fluoride, chloride, and hydride bond energie~.~.'Experience has shown that if a reaction is endothermic it will be more difficult but not necessarily impossible to form those reaction products in a matrix with photolysis. Products which result from exothermic reactions can usually be formed in high yields. Finally, since water is an ever present reactant in all matrix cryochemistry, it is hoped that these results will help future researchers distinguish between metal-water chemistry and that of other reactants. Experimental Section

Chromium, manganese, iron, cobalt, and copper metals were vaporized from an aluminum oxide crucible heated by a tantalum furnace. A resistively heated nickel filament 0.25-in. wide and 0.001-in. thick was used as the source of Ni atoms to avoid possible contamination from a crucible container. Zinc was vaporized from a stainless steel crucible. The chromium, manganese, iron, cobalt, (1) Hauge, R. H.; Meier, P. F.; Margrave, J. L. Ber. Bunsenges. Phys. Chem. 1978,82,102;J . Am. Chem. Soc. 1978,100,2108. (b) Hauge, R. H.; Kauffman, J. W.; Fredin, L.; Margrave, J. L. ACS Symp. Ser. No. 179, J. L. Gole and W. C. Stwalley, Ed. (1982). pp. 355-362 and 363-376. (2) Ismail, Z. K.; Hauge, R. H.; Fredin, L.; Kauffman, J. W.; Margrave, J. L. J. Chem. Phys. 1982, 77, 1617. (3) (a) Kauffman, J. W.; Hauge, R. H.; Margrave, J. L. J . Phys. Chem., following article in this issue. (b) Hauge, R. H.; Kauffman, J. W.; Margrave, J. L. High Temp. Sci. 1984, 18, 97. (4) Hauge, R. H.; Kauffman, J. W.; Margrave, J. L. J . Am. Chem. SOC. 1980, 102, 6005. ( 5 ) Klabunde, K. J.; Key, M. S.; Low, J. Y. E. J . Am. Chem. SOC.1972, 94, 999. (6) Jackson, D. D. "Thermodynamics of the Gaseous Hydroxides"; Lawrence Livermore Laboratory: Livermore, CA, 1971; UCRL-51137. (7) Gaydon, A. G. "Dissociation Energies and Spectra of Diatomic Molecules"; Chapman and Hall: London, 1968.

0022-3654/85/2089-3541$01.50/0

TABLE I: Estimated Heats for M + Water Reactions" reaction AiT Cr + H,O HCrOH -92 Cr + 2H20 HCr(OH)2 + H -25 Cr + H20 CrO + H2 +63 -105 Mn + H 2 0 HMnOH +88 Mn + H 2 0 MnO + H2 2Mn + H 2 0 HMnOMnH -293 Fe + H 2 0 HFeOH -1 17 2Fe + H 2 0 HFeOFeH -318 Fe + 2H20 Fe(OH2)+ H2 -247 CO+ H20 HCOOH -9 2 Ni + H 2 0 HNiOH -88 CU + H20 HCUOH -13 CU+ H20 CUOH + H +167 CU+ H20 CUO+ H2 +146 Zn + H20 HZnOH -2 1 Zn + H20 ZnOH + H +188 Zn + H 2 0 ZnO + H2 +205 "One can assume AG, N Mrat low temperatures, since TAS,N 0. The values for the reactions other than those leading to the monoxides are estimated to be accurate only to 180 kJ. This is primarily due to lack of information on metal-hydride bond strengths. The monoxide heats of reaction are derived from experimental values.

-----

--

nickel, copper, and zinc metals were heated over temperature ranges of 1200-1465, 837-1025, 1230-1460, 1450-1470, 1300-1420, 1200-1380, and 295-365 OC, respectively. Matheson argon gas (+99.99%) was used as the matrix material and was further purified by passing it through a liquid nitrogen trap. In addition to H2160,isotopically substituted water H2I80 (75%) and D 2 0 (99.8%) were used to assign vibrational bands and identify reaction products. The water concentration was varied over a water:argon range of 6-13:1000 as determined with a cooled quartz crystal microbalance. The metal, water, and argon gases were cocondensed on a copper block cooled to 15 K, for either 1 or 2 h. The matrix isolation apparatus was interfaced to a Beckman IR-9 spectrometer and spectra obtained by reflecting the spectrometer beam off the polished copper block surfaces. The matrix was typically photolyzed with a 100-W mediumpressure mercury lamp and long-pass Corning filters for 15 min, except in experiments involving photolysis during cocondensation. A description of the matrix isolation apparatus can be found in ref 8. (8) (a) Ismail, Z. K. Ph.D. Thesis, Rice University, 1972. (b) Kauffman,

J. W. Ph.D. Thesis, Rice University, 1981. (9) (a) Thompson, K. R.; Easley, W. C.; Knight, L. B. J . Phys. Chem. 1973, 77, 49. (b) Huber, K. P.; Herzberg, G. "Constants of Diatomic Molecules"; Van Nostrand Reinhold New York, 1979.

0 1985 American Chemical Society

3542

Kauffman et al.

The Journal of Physical Chemistry, Vol. 89, No. 16. 1985

a M + HL60 (ARGON MATRIX)

1620

I

1580

1

ARGON MATRIX

~

I

I

I

I

1580

1540

I

1540 1620

/

cm-1

+ H2I60in argon matrices, showing metal concentration dependence of adduct bands. The matrices contain a medium water concentration. (A) Matrices with a low metal concentration, (B) matrices with a medium metal concentration, and (C) matrices with a high metal concentration. Figure 1. Expanded infrared spectra for Cr and Mn

I

I

I

I

I

I

I

I

I

I

1630

I

I

1590

I

I

1550

cm-1 Figure 3. Expanded infrared spectra showing the a and b adduct bands for the water bending mode region in an argon matrix containing (A) Cu + H2I60and (B) Zn + H2I60.

TABLE II: Measured Frequencies (cm-') and (Av,) for the Water (vj) Bending Mode in Cr, Mn, Fe, Co, Cu, and Zn Water Adducts H,160 A Y ~ H2I80 A u ~ D20 A Y ~ HDO A Y ~ water 1593.3 1586.9 1176.7 1402.6 Cr, 1580.2 13.1 1573.9 13.0 Cr2 Mnl Mn2

1567.8 1576.8 1574.1 Mn,' 1569.7 Fe, 1562.8 Fez 1576.4 Co, 1564.3 Cu, 1572.8 C U ~ 1582.4 Znl 1587.7 Zn2 1585.0

25.5 16.5 19.2 23.6 30.5 16.9 29.0 20.5 10.9 5.6 8.3

1561.6 1570.2 1567.2 1562.7 155.1 1569.9 1557.3 1567.3

25.3 16.7 19.7 24.2 31.8 17.0 29.6 19.6

1582.0

4.9

1166.1

10.6

1389.0 13.6

1158.1 18.6 1168.8 7.9 1159.9 16.8 1380.9 21.7 1165.4 11.3 1387.7 14.9 1173.8 29.9

1398.2

4.4

'x 1 3 .

Fe + H 2 0 ARGON MATRIX ( photolysis) I 1670

I

I 1630

1

I

I590

I

I

I

1550

cm-1 Figure 2. Expanded infrared argon matrix spectra of iron-water adduct (B) H2I60 + low iron concentration, (C) H2I60+ bands: (A) H2I60, medium iron concentration, (D) photolysis of matrix C with 620-580-nm light, and (E) photolysis of matrix C with 580-340-nm light.

Results M-OH,. Atomic chromium, manganese, iron, copper, and zinc reacted with water on cocondensation producing the a and b adduct peaks shown in Figures 1-3. The a peak first appeared at low metal concentrations. The a peak is assigned to the metal atom-water molecule adduct because it appears at the lowest metal

concentration. The b peak is assigned to the metal dimer-water molecule adduct since it is the first to grow in with increasing metal concentration after the a peak. In the manganese experiment a third adduct peak labeled c was observed at the highest metal concentrations and is believed to be a triatomic or larger metal cluster. A metal dimer adduct was not observed for cobalt; however, only low metal concentrations were studied. Atomic nickel did not react with water to form an observable adduct. The a, b, and c adduct peaks have been assigned to the water u2 bending mode of perturbed water in the various metal-water adducts and are listed in Table 11. HMOH. Photolysis of the chromium-argon matrix with light in the region 520-580 nm and the manganese, iron, cobalt, and copperargon matrices with light in the region 300-340 nm caused the a adduct peak to disappear. The d peaks appeared and increased as the a peak decreased. This is shown for chromium, manganese, and iron in Figures 4-6, and is similar for cobalt and copper. As shown in Figure 7 for iron the highest frequency d peaks in each case undergo a larger deuterium shift and a negligible oxygen-18 shift indicating that the vibration is due to a M-H stretching mode. The 600-700-cm-' d peaks exhibited both a significant oxygen- 18 and deuterium dependence and are thus assigned to an M-OH stretching mode. Under high resolution the copper d peak at 614 cm-I is found to be a doublet at 615.6 and 613.5 cm-I with relative intensities that reflect the 63Cuand 65Cu isotopic distribution for a single metal atom. The 433.8-cm-' chromium and the 457.6-cm-' iron d peaks are believed to be due to a hydrogen motion since they did not significantly shift on oxygen-18 substitution. They were not observed in the D20experiment because of the 400-cm-' lower limit of the

Reactions of Cr, I

I

The Journal of Physical Chemistry, Vol. 89, No. 16, 1985 3543

Mn,Fe, Co, Ni, Cu, and Zn I

1

I

I

I

+

I

I

i A

TABLE III: Observed and Calculated Frequencies (cm-') for M Water Reaction Products M-H M-0 stretch HMO OT MoH stretch (obsd) obsd calcd bend (obsd) HCrOH,d HZL60 1639.9 674.1 433.8 H21s0 1639.9 648.8 646.6 433.9 D2O 1184.5 654.0 658.2

H2160 H2"0 D20

1663.4 1663.4 1197.1

H2I60 HZ1'O D20

1731.9 1731.3 1245.3

HZL60 H2l80 DZO

1790.4 1789.9 1291.2

H M n O H ,d 648.1 624.6 621.3 628.5 633.8

HFeOH,d

h. ----- ' :

f d

d

B

Cr+

1

I

1

H2160 H2lS0 DzO

1

I

I

1075

825

575

I

1325

obsd 1910.8 1911.8 1380.8

Figure 4. Infrared spectra of Cr-+ H2I60 in argon matrices: (A) immediately after deposition and (B) after photolysis of matrix A with 620-520-nm light. I

I

I

I

CuOH, e

M-0 stretch 63cu-0

I

I

MQH H2160 H2l80 D20

bend 727.7 725.1 533.6

H2I60 H2l80

D20

AFTER PHOTOLYSIS

Mn+ H F O (ARGON MATRIX) I

1

I

I

I

1550

1300

lo50

830

550

cm-l Figure 5. Infrared spectra of M n + H20: (A) immediately after deposition and (B) after photolysis of matrix A with 300-340-nm light.

spectrometer. These peaks may be assigned to either a H-M-O or M-0-H bending mode. However, for copper, the 668.5tm-1 peak is best assigned to a M-O-H bending mode by analogy to

calcd

605.9 617.6

65CU-0,

obsd 630.6 603.8

M-O stretch

BEFORE PHOTOLYSIS

d l

obsd 632.7 605.9 635.1

ZnOH, e

A

a

65cu-o MOH bend, obsd calcd obsd 613.5 668.5 587.7 586.9 666.2 612.0 598.9 496.0

obsd 615.6 589.5 613.8

TABLE I V Observed and Calculated Frequencies (em-') for CuOH and ZnOH

"1

I

457.6 455.0

H C o O H ,d 667.4 645.7 639.6 641.9 651.6

M-H stretch, 63Cu-0,

~~'60

(ARGON MATRIX)

1575

653.9 665.9

HCuOH,d M-O stretch

f

d

682.4 654.6 660.5

obsd 649.6 621.4 648.1

%?h calcd

622.0 634.1

66Zn, obsd 648.2 619.3 646.3

%n, obsd 646.6 618.0 645.3

CuOH (see later discussion). The d peaks have been assigned to the H M O H species and are listed in Table 111. MOH. The copper e peaks appeared at the same time the d peaks grew in, but were strongest in experiments where the matrix was photolyzed during deposition. The 63 1-cm-' peak exhibits copper isotopic shifts similar to the 614-cm-l d peak, Le., a doublet at 632.7 and 630.6 cm-l. This indicates the e product also contains only one copper atom. The similarity of the e product peaks and their isotopic shifts to the analogous d product peaks and the absence of a M-H stretching mode suggest that the e species should be assigned to the molecule CuOH. Photolysis of the zinc-containing matrix after cocondensation did not cause the zinc adduct to react. Instead, it was necessary to photolyze with light in the region 250-300 nm during cocondensation to induce reaction. Reaction of the adduct is evidenced by the absence of the adduct peak and presence of the e peak at 648 cm-'. This peak was split into a triplet under higher resolution. The splitting is that which is expected for the 64Zn,&Zn, and @Zn atomic metal isotopic distribution. The 648-cm-I peak underwent a 28-cm-' oxygen-1 8 shift and a small deuterium shift as expected for the M-OH stretching mode. The absence of an H-M stretching mode suggests the e species should be assigned to

Kauffman et al.

3544 The Journal of Physical Chemistry, Vol. 89, No. 16, 1985 I

I

$7 d

d

A

I

9

U

d

I d

1750

1500 1225

U

750

IO00 I100

ARGON M A T R I X

U 500

cm-1

1

Figure 7. Infrared argon matrix spectra of iron-water photolysis products: (A) H2I60+ Fe, (B) H2I80 Fe, and (C) D,O + Fe.

+

I700

I450 IO00

750

500

cm-' Figure 6. Compressed infrared argon matrix spectra of iron-water photolysis products: (A) H2I60 + medium iron concentrations, (B) photolysis of matrix A with 620-580-nm light, (C) photolysis of matrix B with 580-340-nm light, and (D) photolysis with 580-340-nm light during deposition with water and metal concentrations similar to those for matrix A.

% 37

B

725.5

ZnOH. The e peaks are listed in Table IV. H,Cr(OH),. The chromium f product peaks listed in Table V grew in on photolysis with light in the region 580-620 nm (Figure 8). The product appeared a t high water and low metal concentrations so the f species is thought to result from reaction of one metal atom with at least two water molecules. The 1601.8-cm-I peak was assigned to a Cr-H, stretching mode by analogy to the HCrOH molecule. The 735.7-cm-l peak was split into a triplet in the mixed H2160/H2180 experiment (see Figure 5 ) . A single peak was observed in the D20experiments a t 721 cm-'. In light of the splitting in the mixed oxygen-18 study these peaks are assigned to a stretching mode of a HO-Cr-OH group. The f product peaks are thus assigned to a H,Cr(OH), molecule. It is most likely that x is 1 since 3+ is a common oxidation state of chromium. Fe(Om2. The k peak a t 737 cm-I, Table V, Figure 10, is favored by photolysis during deposition and by higher water concentrations. It splits into a triplet when mixtures of H2160 and H2l80or D 2 0 are used (Figure 10). This splitting and their relative intensities indicate that this species contains two hydroxyl groups. The absence of an iron-hydrogen mode suggests these features can be assigned to the Fe(OH), species. The known

7125

C r + WATER (ARGON MATRIX)

Figure 8. Expanded infrared spectra of the f product HO-Cr-OH stretching mode in an argon matrix: (A) H2I60,(B) H2160/H2180,and (C) D2O.

absorption of 782 cm-l for the isoelectronic FeF2species further supports the above assignment. The frequencies are listed in Table V. The calculated values were obtained by treating the OH group as a single mass and assuming a linear OFeO bond angle. HMOMH. The g peaks listed in Table V also grew with the H M O H peaks upon photolysis with light in the region 300-340 nm for manganese- and iron-containing matrices. Formation of

Reactions of Cr, Mn, Fe, Co, Ni, Cu, and Zn I

The Journal of Physical Chemistry, Vol. 89, No. 16, 1985 3545 TABLE V Observed Frequencies ( c d ) for Cr, Mn, and Fe Species

HCr(OH)2, f M-H stretch HO-Cr-OH stretch H2I60 H2180 D20

1601.8

735.7 735.7, 725.5, 712.5 721

HMnOMnH, g M-H stretch H2I60 H2180 D20

1648.7," 1643.2,' 1637.7 1648.9," 1644.2," 1638.3 1174.5

HFeOFeH, g M-H stretch H2160 H2I80 D20

1724.0,' 1708.2 1722.7," 1711.2,' 1707.5 1239.2,' 1231.8," 1228.7

HMn20H, h M-H stretch H2160

1562.0, 1556.4

M-0-M stretch 874.5," 872.3," 870.4 831.8,' 830.5," 828.3' 870.3

M-O stretch 914.5,'911.8 869.0," 865.7 914.3," 911.7

M-0 stretch 640.1

HFe20H, hb

M n + WATER (ARGON MATRIX)

M-H stretch, obsd

L

H2I60 H2I80 D20

Figure 9. Expanded infrared spectra of the g product Mn-O-Mn stretching mode absorption in an argon matrix: (A) H2I60, (B)

H260/H2180,and (C)D20.

1713.1 1711.2 1215.8

M-o stretch obsd calcd 649.9 626.8 630.4

620.1 634.3

MMO bend or M-MO stretch, obsd 522.4 516.9 521.7

Fe(OH)2,kc 0-Fe-0 stretch obsd calcd H ~ ~ ~ o / H ~ ~ ~735.5 o H2160/H2180 726.9 H2180/H2'80 714.4 7 12.9 H2160/D20 731.1 D2O/D20 721.7 724.6

.

'Decreased with matrix annealing.

Fe +WATER (ARGON MATRIX)

-cm-1-

Figure 10. Expanded infrared argon matrix spectra of Fe(OH)2 k species: (A) H2160+ Fe, (B) H2160/H2180 + Fe, and (C) H2I60/D20

+ Fe.

the g species was favored a t medium metal concentrations and was greatly enhanced in experiments with photolysis during deposition. For manganese, the 1640- and 870-cm-' peaks showed exactly the same annealing behavior, maintained the same relative intensities, and appeared at the same time. They are thus assigned to the same species. The 1640-cm-' peaks underwent a large, 460 cm-l, deuterium shift and are thus assigned to an H-M stretching mode. The 870-cm-I peaks underwent an appreciable oxygen-18 shift, but no apparent deuterium shift (see Figure 6). Thus the 870-cm-' peaks can be assigned to a Mn-O stretching mode. It cannot be assigned to a Mn-OH stretching mode because it has a much higher frequency than the M-OH stretching mode of H M n O H and because it lacks a deuterium shift. Also, assignment to diatomic MnO is not possible since it is known to absorb at 822 cm-I in an argon matrix and at 830 cm-' in the gas phase.' In addition, the oxygen-18 shift is larger than can be accounted for by assignment to a terminal Mn,O group since its predicted isotopic shift should be less than that for MnO, i.e., 140 cm-I. Both anharmonic effects and mixing of the Mn-O and Mn-Mn stretching modes will cause the true oxygen-18 shift for a terminal Mn,O bond to be