Synthesis and Characterization of the Five-Coordinate Sixteen-Electron Manganese(I) Complex [Mn(CO)3(S-C6H4-NH)]-

Full text of DOI:10.1021/ic9809153

6396
Inorg. Chem. 1998, 37, 6396-6398
Scheme 1
Synthesis and Characterization of the
Five-Coordinate Sixteen-Electron Manganese(I)
Complex [Mn(CO)3(S-C6H4-NH)]-
Wen-Feng Liaw,*,† Chien-Ming Lee,†
Gene-Hsiang Lee,‡ and Shie-Ming Peng‡
Department of Chemistry, National Changhua University of
Education, Changhua 50058, Taiwan, and Instrumentation
Center and Department of Chemistry, National Taiwan
University, Taipei 10074, Taiwan
ReceiVed July 31, 1998
Introduction
The NH‚‚‚S hydrogen bond which arguably plays a major
role in determining the redox potential and the electronic
structure of biologically important metalloproteins and metal-
loenzymes (e.g., iron-sulfur proteins, ferredoxins, and rubre-
doxins)1 has been observed in biomimetic structural model
complexes.2
Recent work in this laboratory has shown that the anionic
metal carbonyl fragments ([Mn(CO)5]- and [PhEFe(CO)4]- (E
) Se, Te)) activate the E-E bond of diorganyl dichalcogenides
to yield cis-[Mn(CO)4(ER)2]- and fac-[Fe(CO)3(EPh)3]- com-
plexes which are useful in the syntheses of (CO)4Mn(µ-ER)2Co-
(CO)(µ-ER)3Mn(CO)3 with a unique terminal CoIII-CO bond,3
[(CO)3M(µ-SePh)3M′(µ-SePh)3M(CO)3]-/0 (M ) Mn, M′ ) Co;
M ) Fe, M′ ) Ni, Zn, Cd, Fe) with homoleptic hexaseleno-
latometal core,4 and distorted square planar [Ni(CO)(SPh)n-
(SePh)3-n]- (n ) 0, 1, 2),5 the biomimetic nickel-site structure
of [NiFeSe] hydrogenases and CO dehydrogenase. In this paper
we combine the dichalcogen synthetic technology with the
potential for intramolecular H-bonding to synthesize five-
coordinate sixteen-electron Mn(I) complex [Mn(CO)3(S-C6H4-
NH)]- stabilized by S,N π-donation of bidentate [S-C6H4-
NH]2- ligand. To our knowledge, a few examples of transition-
metal carbonyl complexes containing five-coordinate sixteen-
electron metal core (d6) have been reported,6,7 e.g. [Mn(CO)3-
(DBCat)]- prepared by oxidative substitution of two CO ligands
of [Mn(CO)5]- by 3,5-di-tert-butyl-1,2-benzoquinone,6a and
[W(CO)3(NHC6H4NH)]2- prepared from W(CO)5(THF) and 2
equiv of monodeprotonated ligands [NHC6H4NH2]- by inter-
molecular deprotonation.7c
(1) (a) Backes, G.; Mino, Y.; Loehr, T. M.; Meyer, T. E.; Cusanovich,
M. A.; Sweeney, W. V.; Adman, E. T.; Sanders-Loehr, J. J. Am. Chem.
Soc. 1991, 113, 2055. (b) Fan, C.; Kennedy, M. C.; Beinert, H.;
Hoffman, B. M. J. Am. Chem. Soc. 1992, 114, 374. (c) Watenpaugh,
K. D.; Sieker, L. C.; Jensen, L. H. J. Mol. Biol. 1979, 131, 509. (d)
Kru¨ger, H.-J.; Peng, G.; Holm, R. H. Inorg. Chem. 1991, 30, 734. (e)
Hill, C. L.; Renaud, J.; Holm, R. H.; Mortenson, L. E. J. Am. Chem.
Soc. 1977, 99, 2549.
(2) (a) Ueyama, N.; Okamura, T.; Nakamura, A. J. Am. Chem. Soc. 1992,
114, 8129. (b) Ueyama, N.; Terakawa, T.; Nakata, M.; Nakamura, A.
J. Am. Chem. Soc. 1983, 105, 7098. (c) Walters, M. A.; Dewan, J. C.;
Min, C.; Pinto, S. Inorg. Chem. 1991, 30, 2656. (d) Sellmann, D.;
Soglowek, W.; Knoch, F.; Moll, M. Angew. Chem., Int. Ed. Engl.
1989, 28, 1271. (e) Okamura, T.-A.; Ueyama, N.; Nakamura, A.;
Ainscough, E. W.; Brodie, A. M.; Waters, J. M. J. Chem. Soc., Chem.
Commun. 1993, 1658. (f) Ueyama, N.; Nishikawa, N.; Yamada, Y.;
Okamura, T.; Oka, S.; Sakurai, H.; Nakamura, A. Inorg. Chem. 1998,
37, 2415.
(3) (a) Liaw, W.-F.; Ou, D.-S.; Li, Y.-S.; Lee, W.-Z.; Chuang, C.-Y.;
Lee, Y.-P.; Lee, G.-H.; Peng, S.-M. Inorg. Chem. 1995, 34, 3747. (b)
Liaw, W.-F.; Chuang, C.-Y.; Lee, W.-Z.; Lee, C.-K.; Lee, G.-H.; Peng,
S.-M. Inorg. Chem. 1996, 35, 2530.
(4) (a) Liaw, W.-F.; Lee, W.-Z.; Wang, C.-Y,; Lee, G.-H.; Peng, S.-M.
Inorg. Chem. 1997, 36, 1253. (b) Liaw, W.-F.; Chen, C.-H.; Lee, C.-
M.; Lin, G.-Y.; Ching, C.-Y.; Lee, G.-H.; Peng, S.-M. J. Chem. Soc.,
Dalton Trans. 1998, 353. (c) Liaw, W.-F.; Chiang, M.-H.; Liu, C.-J.;
Harn, P.-J.; Liu, L.-K. Inorg. Chem. 1993, 32, 1536. (d) Liaw, W.-F.;
Lai, C.-H.; Lee, C.-K.; Lee, G.-H.; Peng, S.-M. J. Chem. Soc., Dalton
Trans. 1993, 2421. (e) Liaw, W.-F.; Ou, D.-S.; Horng, Y.-C.; Lai,
C.-H.; Lee, G.-H.; Peng, S.-M. Inorg. Chem. 1994, 33, 2495.
(5) Liaw, W.-F.; Horng, Y.-C.; Ou, D.-S.; Ching, C.-Y.; Lee, G.-H.; Peng,
S.-M. J. Am. Chem. Soc. 1997, 119, 9299.
Results and Discussion
When a THF solution of 2-aminophenyl disulfide (0.1 mmol,
0.025 g) and [PPN][Mn(CO)5] (0.1 mmol, 0.073 g) is stirred
under N2, a rapid reaction ensues over the course of 5 min at
ambient temperature to give, by what may be described as an
oxidative addition/decarbonylation reaction, a thermally un-
stable, monodentate (S-bonded) cis-[Mn(CO)4(S-C6H4NH2)2]-
(1) (Scheme 1a), since the IR spectra match those of complex
cis-[Mn(CO)4(SPh)2]- previously established (by IR and X-ray
diffraction).3,8 As illustrated in Scheme 1b,c, the dark red, five-
coordinate, S,N-chelate [Mn(CO)3(S-C6H4-NH)]- (3) with
(6) (a) Hartl, F.; Vlcek, A., Jr.; deLearie, L. A.; Pierpont, C. G. Inorg.
Chem. 1990, 29, 1073. (b) Jaitner, P.; Huber, W.; Huttner, G.;
Scheidsteger, O. J. Organomet. Chem. 1983, 259, C1.
(7) (a) Darensbourg, D. J.; Klausmeyer, K. K.; Mueller, B. L.; Reibenspies,
J. H. Angew. Chem., Int. Ed. Engl. 1992, 31, 1503. (b) Darensbourg,
D. J.; Draper, J. D.; Reibenspies, J. H. Inorg. Chem. 1997, 36, 3648.
(c) Darensbourg, D. J.; Klausmeyer, K. K.; Reibenspies, J. H. Inorg.
Chem. 1996, 35, 1535. (d) Darensbourg, D. J.; Klausmeyer, K. K.;
Reibenspies, J. H. Inorg. Chem. 1996, 35, 1529. (e) Sellmann, D.;
Schwarz, J. J. Organomet. Chem. 1983, 241, 343. (f) Sellmann, D.;
Ludwig, W.; Huttner, G.; Zsolnai, L. J. Organomet. Chem. 1985, 294,
199. (g) Darensbourg, D. J.; Klausmeyer, K. K.; Reibenspies, J. H.
Inorg. Chem. 1996, 35, 5. 1529.
(8) Liaw, W.-F.; Ching, C.-Y.; Lee, C.-K.; Lee, G.-H.; Peng, S.-M. J.
Chin. Chem. Soc. (Taipei) 1996, 43, 427.
10.1021/ic9809153 CCC: $15.00 © 1998 American Chemical Society
Published on Web 11/07/1998

Notes
Inorganic Chemistry, Vol. 37, No. 24, 1998 6397
sixteen-electron Mn(I) core was finally isolated as a semisolid
from THF-diethyl ether (0.056 g, 73%) after stirring the
solution overnight in THF at room temperature. A reasonable
reaction sequence accounting for the formation of complex 3
is shown in Scheme 1b,c. The dissociation of a carbonyl ligand
resulting from chelate formation of one terminal thiolate ligand
MnI-S-C6H4-NH2 of complex 1 yielded the intermediate fac-
[Mn(CO)3(S-C6H4NH2)(S-C6H4-NH2)]- (2) with one anionic
[S-C6H4NH2] ligand bound to the MnI metal in a monodentate
(S-bonded) manner and the second anionic [S-C6H4-NH2] ligand
bound to the MnI metal in a bidentate manner (S,N-bonded),
forming a five-membered chelate ring.9 The intramolecular
N-H‚‚‚S interaction (cis arrangement of thiolate and NH2 group
in intermediate 2)2c,f,7b and the subsequent elimination of
2-aminothiophenol (the coordination of N atom presumably
increases the acidity of amine protons to accelerate the depro-
tonation of NH2)7b,c,10 yielded the five-coordinate complex 3.
The IR spectrum of complex 3 shows two strong CO stretching
bands, which supports a facial orientation of three CO ligands.
Figure 1. ORTEP drawing and labeling scheme of [Mn(CO)3(S-C6H4-
NH)]- with thermal ellipsoids drawn at the 50% probability level.
The reversibility of CO ligand-binding demonstrates the com-
plexes 4 and 5 are chemically interconvertible.
The molecular structure of complex 3 is depicted in Figure
1. Manganese is best described as existing in a distorted
tetragonal pyramidal coordination environment with the C(1)O-
(1) ligand occupying the apex. The MnI-S distance 2.268(1)
Å in the title complex is significantly shorter than the reported
MnI-SPh bond 2.398(1) Å in the cis-[Mn(CO)4(SPh)2]-,8
1
The H and 13C NMR spectra show the expected signals for
the S,N chelate [S-C6H4-NH]2- ligand in a diamagnetic d6
Mn(I) species. Oxidation chemistry was also successful in the
synthesis of complex 3. Upon contact with dry O2, the color
of reaction mixture immediately turns from orange to dark red
MnII-SPh bond 2.442(3) Å in the [Mn(SPh)4]2- 11 The MnI-N
.
bond distance is 1.889(3) Å, which is also significantly shorter
than that in [Mn0(CO)3(TMPO)] (TMPO ) 2,2,6,6-tetrameth-
ylpiperidinyl-1-oxo) (1.981(3) Å),6b and in [MnIII(edt)2(ImH)]-
(edt ) ethane-1,2-dithiolate) (2.224(7) Å).12 This shortening
of Mn-S and Mn-N bonds in complex 3 may be attributed to
the significantly π-donating ability of the bidentate [S-C6H4-
NH]2- ligand.7,13
1
in THF/CH3CN. The IR and H NMR spectra indicated the
formation of complex 3 accompanied by byproducts, H2O and
1
2-aminophenyl disulfide identified by H NMR (Scheme 1c′).
In this oxidative reaction, the Mn(I) was not observed to undergo
oxidation, and consequently, the oxidation process is best
assigned to the terminal thiolate ligand to yield 2-aminophenyl
disulfide via radical ([S-C6H4-NH2]•) recombination, and the
concomitant deprotonation of amine proton of intermediate 2
leads to formation of water.10
Experimental Section
Manipulations, reactions, and transfers of samples were conducted
under nitrogen according to standard Schlenk techniques or in a
glovebox (Ar gas). Solvents were distilled under nitrogen from
appropriate drying agents (ethyl ether from CaH2; acetonitrile from
CaH2/P2O5; hexane and tetrahydrofuran (THF) from Na/benzophenone;
ethyl alcohol from CaH2) and stored in dried, N2-filled flasks over 4 Å
molecular sieves. A nitrogen purge was used on these solvents before
use and transfers to reaction vessels were via stainless steel cannula
under N2 at a positive pressure. The reagents dimanganese decacar-
bonyl, 2-aminophenyl disulfide, thiophene-2-thiol, bis(triphenylphos-
phoranylidene)ammonium chloride (Aldrich) were used as received.
Infrared spectra were recorded on a spectrometer (Bio-Rad FTS-185)
with sealed solution cells (0.1 mm) and KBr windows. In NMR spectra
To further add credibility to the proposed mechanism, a
straightforward protonation of complex 3 was conducted. As
illustrated in Scheme 1d, the dropwise addition of the excess
thiophene-2-thiol to complex 3 in THF under N2 at ambient
temperature led to the formation of an orange yellow solution
immediately. The bands at 1973 vs and 1870 s cm-1 dis-
appeared, with concomitant formation of a spectrum (νCO
(THF): 1991 vs, 1891 s, 1879 s cm-1) similar to that observed
for intermediate 2, i.e., formation of six-coordinate fac-[Mn-
(CO)3(S-C4H3S)(S-C6H4-NH2)]- (4) (1H NMR (C4D8O): δ 5.53
(br), 4.89 (br) ppm (NH2)). Attempts to isolate this moderately
stable anion 4 was unsuccessful. In common with intermediate
2, complex 4 is very sensitive, converting to complex 3, H2O
1
(recorded on a Bruker AC 200 spectrometer), chemical shifts of H
and 13C are relative to tetramethylsilane. UV-visible spectra were
recorded on a GBC 918 spectrophotometer. Analyses of carbon,
hydrogen, and nitrogen were obtained with a CHN analyzer (Heraeus).
Preparation of [PPN][Mn(CO)3(S-C6H4-NH)] (3). [PPN][Mn-
(CO)5] (0.1 mmol, 0.073 g) and 2-aminophenyl disulfide (0.1 mmol,
0.025 g) dissolved in 5 mL of THF were stirred under nitrogen at
ambient temperature. A vigorous reaction occurred immediately with
evolution of CO gas. IR spectrum, νCO (THF) 2050 w, 1965 vs, 1951
m, 1913 m cm-1, indicated the formation of anionic cis-[Mn(CO)4(S-
C6H4NH2)2]. The reaction mixture was stirred overnight at room
temperature, and the yellow solution completely converted into a dark
red solution. Alternatively, upon contact with dry O2, the color of
1
and di(2-thienyl) disulfide characterized by H NMR, within
seconds on exposure to O2 (Scheme 1d′). Additionally, the ring-
opened complex cis-[Mn(CO)4(S-C4H3S)(S-C6H4NH2)]- (5)
(νCO (THF): 2055 m, 1981 vs, 1959 s, 1916 s cm-1) was
obtained upon exposing complex 4 to CO atmosphere in THF
at room temperature (Scheme 1e). Apparently, protonation of
the amide site of complex 3 labilizes the chelating ligand
[S-C6H4-NH2]- and results in the formation of complex 5. The
complete conversion of complex 5 to 4 was observed when
removing CO atmosphere under vacuum in THF (Scheme 1e′).
(11) Swenson, D.; Baenziger, N. C.; Coucouvanis, D. J. Am. Chem. Soc.
1978, 100, 1932.
(9) Liaw, W.-F.; Chen, C.-H.; Lee, G.-H.; Peng, S.-M. Organometallics
1998, 17, 2370.
(12) Seela, J. L.; Knapp, M. J.; Kolack, K. S.; Chang, H.-R.; Huffman, J.
C.; Hendrickson, D. N.; Christou, G. Inorg. Chem. 1998, 37, 516.
(13) (a) Ashby, M. T. Comments Inorg. Chem. 1990, 10, 297. (b) Penfield,
K. W.; Gay, R. R.; Himmelwright, R. S.; Eickman, N. C.; Norris, V.
A.; Freeman, H. C.; Solomon, E. I. J. Am. Chem. Soc. 1981, 103,
4382. (c) Sellmann, D.; Geck, M.; Knoch, F.; Ritter, G.; Dengler, J.
J. Am. Chem. Soc. 1991, 113, 3819. (d) Hartl, F.; Stufkens, D. J.;
Vlcek, A., Jr. Inorg. Chem. 1992, 31, 1687.
(10) (a) Okamura, T.; Takamizawa, S.; Ueyama, N.; Nakamura, A. Inorg.
Chem. 1998, 37, 18. (b) Sellmann, D.; Emig, S.; Heinemann, F. W.;
Knoch, F. Angew. Chem., Int. Ed. Engl. 1997, 36, 1201. (c) Sellmann,
D.; Emig, S.; Heinemann, F. W. Angew. Chem., Int. Ed. Engl. 1997,
36, 1734. (d) Crociani, L.; Tisato, F.; Refosco, F.; Bandoli, G.; Corain,
B.; Venanzi, L. M. J. Am. Chem. Soc. 1998, 120, 2973.

6398 Inorganic Chemistry, Vol. 37, No. 24, 1998
Notes
Table 1. Crystallographic Data of Complex
Table 2. Selected Bond Distances (Å) and Angles (deg) for
[Mn(CO)3(S-C6H4-NH)]-
[Mn(CO)3(S-C6H4-NH)]-
empirical formula
fw
cryst syst
space group
λ, Å (Mo KR)
a, Å
C45H35O3N2P2SMn
800.74
triclinic
P1h
0.7107
9.925(3)
14.251(2)
14.202(3)
89.84(1)
88.89(2)
81.60(2)
1986.8(7)
2
1.280
5.494
25
0.041
0.039
1.68
Mn-S(1)
Mn-C(1)
Mn-C(3)
N(1)-C(9)
C(2)-O(2)
2.268(1)
1.753(4)
1.776(4)
1.375(5)
1.167(5)
Mn-N(1)
Mn-C(2)
S(1)-C(4)
C(1)-O(1)
C(3)-O(3)
1.889(3)
1.761(4)
1.714(4)
1.153(5)
1.156(5)
S(1)-Mn-N(1)
S(1)-Mn-C(2)
N(1)-Mn-C(1)
N(1)-Mn-C(3)
C(1)-Mn-C(3)
Mn-S(1)-C(4)
83.42(9)
88.55(13)
120.34(16)
90.84(17)
91.36(20)
100.16(13)
S(1)-Mn-C(1)
S(1)-Mn-C(3)
N(1)-Mn-C(2)
C(1)-Mn-C(2)
C(2)-Mn-C(3)
Mn-N(1)-C(9)
97.37(15)
171.13(15)
147.98(16)
91.37(19)
92.83(19)
124.19(24)
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
Z
d
temperature. The IR spectrum (νCO (THF) 2055 m, 1981 vs, 1959 s,
1916 s cm-1) indicated the formation of the ring-opened complex cis-
[Mn(CO)4(S-C4H3S)(S-C6H4NH2)]-. The complete conversion of cis-
[Mn(CO)4(S-C4H3S)(S-C6H4NH2)]- to fac-[Mn(CO)3(S-C4H3S)(S-C6H4-
NH2)]- was observed when removing CO atmosphere under vacuum
in THF. Oxidation of complex fac-[Mn(CO)3(S-C4H3S)(S-C6H4-NH2)]-
by adding dry O2 leads to formation of [Mn(CO)3(S-C6H4-NH)]-
accompanied by byproducts H2O and di(2-thienyl) disulfide identified
calcd, g cm-3
µ, cm-1
T, °C
Ra
b
Rw
GOFc
a R ) ∑|(Fo - Fc)|/∑Fo. b Rw ) [∑w(Fo - Fc)2/∑wFo ]1/2
.
c GOF )
2
[∑[w(Fo - Fc)2/(M - N)]1/2 where M ) number of reflections and N
) number of parameters.
1
by H NMR.
Crystallography. Crystallographic data for the structure of complex
[PPN][Mn(CO)3(S-C6H4-NH)] are collected in Table 1. Bond distances
and angles are collected in Table 2. Crystals of [PPN][Mn(CO)3(S-
C6H4-NH)] used for the X-ray diffraction structural determination were
obtained from vapor diffusion of diethyl ether into concentrated THF
solution at -15 °C under nitrogen atmosphere. The dark red crystal
used for the study had approximate dimensions of 0.60 × 0.50 × 0.20
mm. The crystal was mounted on a glass fiber and quickly coated in
epoxy resin at 25 °C. The unit-cell parameters were obtained from 25
reflections with 2θ between 16.40° and 23.22° for product [PPN][Mn-
(CO)3(S-C6H4-NH)]. Diffraction measurements were carried out on a
Nonius CAD 4 diffractometer with graphite-monochromated Mo KR
radiation, λ ) 0.7107 Å, employing the θ/2θ scan mode.14 A æ scan
absorption correction was made. Structural determinations were made
using the NRCC-SDP-VAX package of programs.15
reaction mixture immediately turns from yellow to dark red. After
the reaction was completed, diethyl ether was slowly added to
precipitate a dark red semisolid. The mother liquor was removed via
cannula, and the semisolid was dried under vacuum. The product [PPN]-
[Mn(CO)3(S-C6H4-NH)], suitable for X-ray crystallography, was re-
crystallized from vapor diffusion of diethyl ether into concentrated THF
solution at -15 °C. The yield was 0.056 g (73%). IR (THF): 1973
vs, 1870 s (CO) cm-1; 3339 br cm-1 (N-H). 1H NMR (C4D8O): δ
8.98 (br) ppm (N-H), 6.90 (d), 6.60 (t), 6.43 (t) ppm (SC6H4). 13C
NMR (C4D8O): δ 115.04 (s), 115.43 (s), 119.79 (s), 128.65 (s), 133.12
(s), 133.23 (s) ppm (S-C6H4-NH). Absorption spectrum (THF) [λmax
,
nm (ꢀ, M-1 cm-1)]: 499 (6639), 403 (9745), 304 (10 400). Anal. Calcd
for C45H35O3N2P2SMn: C, 67.50; H, 4.41; N, 3.50. Found: C, 67.28;
H, 4.64; N, 3.68.
Acknowledgment. We thank the National Science Council
(Taiwan) for support of this work. The authors thank Professor
Marcetta Y. Darensbourg for helpful suggestions.
Reaction of [PPN][Mn(CO)3(S-C6H4-NH)] and Thiophene-2-thiol.
A portion (10 µL, 0.11 mmol) of thiophene-2-thiol was added dropwise
by syringe into [PPN][Mn(CO)3(S-C6H4-NH)] (0.08 g, 0.1 mmol) in
THF under N2 at ambient temperature. A vigorous reaction occurred
immediately, with the color of reaction mixture turning from dark red
to orange yellow, and was monitored with FTIR. The IR spectrum,
νCO (THF) 1991 vs, 1891 s, 1879 s cm-1, having the same pattern as,
but differing slightly in position from that of, fac-[Mn(CO)3(S-C6H4-
Supporting Information Available: An X-ray crystallographic file,
in CIF format, for the structure determination of [PPN][Mn(CO)3(S-
C6H4-NH)] is available on the Internet only. Access information is
given on any current masthead page.
IC9809153
NH2)(S-C6H4-NH2)]- (IR, νCO (THF): 1989 vs, 1887 s, 1883 s cm-1
)
obtained from reaction of HSC6H4NH2 and [Mn(CO)3(S-C6H4-NH)],
indicated the formation of fac-[Mn(CO)3(S-C4H3S)(S-C6H4-NH2)]- (1H
NMR (C4D8O): δ 5.53 (br), 4.89 (br) ppm (NH2)). Attempts to isolate
this moderately stable fac-[Mn(CO)3(S-C4H3S)(S-C6H4-NH2)]- were
unsuccessful. The orange yellow fac-[Mn(CO)3(S-C4H3S)(S-C6H4-
NH2)]- solution was stirred under CO atmosphere for 5 min at room
(14) North, A. C. T.; Philips, D. C.; Mathews, F. S. Acta Crystallogr. 1968,
A24, 351.
(15) (a) Gabe, E. J.; LePage, Y.; Chrarland, J. P.; Lee, F. L.; White, P. S.
J. Appl. Crystallogr. 1989, 22, 384. (b) Atomic scattering factors were
obtained from: International Tables for X-ray Crystallography;
Kynoch Press: Birmingham, England, 1974; Vol. IV.