Homogeneous oxidation of alcohol and alkene with copper (II) complex in water

Article abstract of DOI:10.1007/s12039-018-1439-y

Abstract: A new water-soluble copper(II) complex bearing 4-bromobenzoate/2,2’-dipyridylamine ligands was successfully synthesized and characterized by using single crystal X-ray diffraction and spectroscopic techniques. The catalytic activity of the compo

Full text of DOI:10.1007/s12039-018-1439-y

J. Chem. Sci. (2018) 130:33
© Indian Academy of Sciences
https://doi.org/10.1007/s12039-018-1439-y
REGULAR ARTICLE
Homogeneous oxidation of alcohol and alkene with copper (II)
complex in water
HAKAN ÜNVER∗ and IBRAHIM KANI
Department of Chemistry, Faculty of Science, Anadolu University, 26210 Eskisehir, Turkey
E-mail: hakanunver@anadolu.edu.tr
MS received 16 January 2018; revised 14 February 2018; accepted 20 February 2018
Abstract. A new water-soluble copper(II) complex bearing 4-bromobenzoate/2,2’-dipyridylamine ligands
was successfully synthesized and characterized by using single crystal X-ray diffraction and spectroscopic
techniques. The catalytic activity of the compound was investigated as a homogeneous catalyst in the oxidation
of several alcohols (benzyl alcohol, cinnamyl alcohol, 1-phenylethanol, cyclohexanol, 1-heptanol) and alkenes
(styrene, ethylbenzene, cyclohexene) in aqueous medium. The copper(II) catalyst was found to be active for
the studied alcohols and alkenes. H2O2 was used as an active oxidant for alcohol oxidation, while t-BuOOH
(TBHP) was used for alkenes. The compound exhibited high selectivity toward benzaldehyde (88%) in cinnamyl
◦
alcohol oxidation under mild conditions (70 C) after 4 h. Particularly, remarkable results were obtained for
the oxidation of styrene and cyclohexene; transformation via allylic oxidation to 2-cyclohexene-1-one as one
product in 2 h (TOF = 50 h−1) and benzaldehyde in 1 h (100% conversion, TOF = 86 h−1, 100% selectivity).
The Cu(II)/TBHP (or H2O2)/H2O system proved to be an alternative for catalytic oxidations in the green
chemistry concept.
Keywords. Copper (II)complex; oxidation; alcohol; alkene.
1. Introduction
Expensive transition metal catalysts, i.e., as palla-
dium,10 platinum,11 and ruthenium12 have been reported
to be efficient catalysts for alcohol and alkene oxidations
in water. Compared to the aforementioned high-cost
metal compounds, relatively low-cost metal catalysts,
such as copper,13 iron,14 and manganese15 compounds
are a lot scarce for homogeneous catalytic oxidations in
water. In this respect, the catalytic oxidation of alcohol
and alkenes in water to the corresponding products has
always attracted interest in the past decade.13,16–22
Many copper complexes have been found to cat-
alyze for peroxidative oxidation in homogeneous and
heterogeneous catalytic systems.23–27 Some Cu–Schiff
base complexes in a heterogeneous system can lead
to a higher yield (∼90%, TOF = 18.2 h−1) of prod-
ucts in cyclohexene oxidation.28 Mizar et al., published
a study of an effective catalyst for benzyl alcohol
for benzaldehyde transformation with copper(II)-2-N-
arylpyrrolecarbaldimine catalysts under atmospheric
oxygen pressure at 80 ◦C within 2 h in water (yield : 68–
99%).29 Hu et al., synthesized and used some copper
complexes with tetradentate pyridyl-imine terminated
Chemical reaction in green solvent systems is one
of the major investigation areas of green synthesis.
The number of published environmentally friendly cat-
alytic systems in the literature is increasing over time.
There are many examples of catalytic reactions per-
formed in supercritical fluids,1 ionic liquids,2 fluorous
solvents,3 or solvent-free systems.4,5 Reactions espe-
cially applied in water solvent systems are extremely
important because they have many advantages, such as
non-toxicity, absence of hazards, low wastage in pro-
duction, economical method, and so on. Water has been
used as a solvent in many types of transition metal-
catalyzed reactions, i.e., carbonylation,6 arylation,7
hydroformylation,8 and hydrogenation.9 In synthetic
chemical production processes, such as those in the dye,
pigment, medicine, and perfume industries, selective
alcohol and alkene oxidations are important reactions
for obtaining numerous starting or intermediate chem-
icals, aldehydes, ketones, diols, and carboxylic acids.
*
For correspondence
Electronic supplementary material: The online version of this article (https://doi.org/10.1007/s12039-018-1439-y) contains
supplementary material, which is available to authorized users.

33 Page 2 of 9
J. Chem. Sci. (2018) 130:33
Schiff base ligands to investigate their aerobic alcohol using direct methods. Non-hydrogen atoms were refined
oxidation activities in aqueous media.30
anisotropically using full-matrix least squares on F2.
To the best of our knowledge, water-soluble
carboxylate-Cu(II)-catalyzed reactions of alkenes to
ketones and also the oxidation of alcohols in water are
very scarce. Recently, we published a successful appli-
2.2 Synthesis of complex, ([Cu(OOC(C6H5)Br)
(C10H9N3)](ClO4)),([aqua(4-bromobenzoato)
cation of a new copper(II)/triphenylacetic acid/bipyridyl
complex for oxidation of primary and secondary alco-
hols with H2O2 under mild conditions in pure water.31
Water-soluble copper(II) complexes with sulfonic-
functionalized arylhydrazone of β-diketone are used as
catalyst precursors for the selective peroxidative (with
TBHP) allylic oxidation of cyclohexene to cyclohex-
2-enol (Cy-ol) and cyclohex-2-enone (Cy-one) with
a total yield of ∼70% and TONs of up to 350,29
but that is lower than those (>90%) we observed
in our Cu(II)-complex. Copper(II) catalytic systems
with mixed-ligand aminoalcohol-dicarboxylate coor-
dination polymers act as homogeneous catalysts in
aqueous acetonitrile under mild conditions (50–60
◦C): the oxidation of cyclohexene through H2O2 and
in the presence of a trifluoroacetic acid promoter
results in total product yields (∼15–18% based on the
substrate).32–36 Cu-MOF, [Cu(bpy)(H2O)2(BF4)2(bpy)]
(bpy: 4,4’-bipyridine), exhibited catalytic activity and
high selectivity in the allylic oxidation of cyclohexene
with molecular oxygen under solvent-free conditions
(TON = 13–37).25 However, these catalysts show lower
selectivity than our systems. Therefore, the title Cu(II)-
complex is the best catalyst precursor for selective
allylic cyclohexene oxidation, which results in the for-
mation of ketone as a single product.
(2,2’dipyridylamine)copper(II)](perchlorate))
Neutralized solution of 4-bromobenzoic acid (100 mg, 0.49
mmol, 10 mL methanol) with sodium hydroxide (19.5 mg,
0.49 mmol) was added dropwise to the methanolic solution
of copper(II)◦perchlorate hexahydrate (10 mL, 181 mg, 0.49
mmol) at 50 C for 2 h. Then, 2,2’-dipyridylamine solution
in methanol (84 mg, 0.49 mmol, 5 mL) was reacted overnight
with a metal salt-bromobenzoate solution to obtain a cop-
per(II) complex. Dark-blue crystals were obtained from the
evaporation of the solvent after 7 days (180 mg, yield 69%,
◦
M.p.: 250 C) FT-IR (KBr; , cm−1) (s. strong; m. medium; w.
ν
ν
ν
ν
weak): 3416w N−H; 1590m C=N; 1644m COOasym; 1484m
νCOOsym
νC=N−C=C
νO−H
max
νC−O
; 1530m
; 1114m
UV–Vis
; 1088s
;
ν
ν
769m C−N; 625m
nm (CH3CN):
λ
Cu−O−Cu
244. 295. 312. Magnetic moment (μ) = 1.4 B.M. at room
temperature.
2.3 X-ray crystallography
Diffraction data for the complex collected with Bruker AXS
APEX CCD diffractometer equipped with a rotation anode
at 296 (2) K, respectively using graphite monochromated
Mo Kα radiation at λ = 0.71073 Å. The data reduction
was performed with the Bruker SMART program package.37
The structures were solved by direct methods and the non-
hydrogen atoms were located through subsequent difference
Fourier syntheses.38 Structure solution was found with the
SHELXS-97 package using the direct methods and were
refined SHELXL-9739 against F2 using first isotropic and
later anisotropic thermal parameters for all non-hydrogen
atoms. Hydrogen atoms were added to the structure model
at calculated positions. The molecular drawing was obtained
using MERCURY.40 Geometric calculations were performed
with PLATON.41
Herein, we present a new water-soluble copper(II)/
4-bromobenzoate/2,2’-dipyridylamine complex ([Cu
(OOC(C6H5)Br)(C10H9N3)](ClO4)) and its successful
application for selective oxidation of alcohols and
alkenes under mild reaction medium (70 ◦C) with H2O2
or t-BuOOH in green solvent water.
2. Experimental
2.4 General procedure for alcohol/alkene oxidation
Alcohol or alkene (9.3 × 10−4 mol) (substrate/catalyst ratio
2.1 Materials and Physical measurements
All chemicals were obtained from commercial companies (≥ = 100) copper catalyst (9.3 × 10−6 mol) and oxidant H2O2 (2
98%, Sigma-Aldrich and Merck, Germany) and used with- mL, 1.92 × 10−4 mol) or t-BuOOH (2 mL, 1.4 × 10−2 mol)
out further purification. IR spectra were recorded with Jasco were mixed in 10 mL water in a 50 mL reaction flask with a
FT/IR-300 E Spectrophotometer using KBr pellets between condenser at 70 ◦C for 24 h. Internal samples were taken from
4000 and 400 cm−1. UV spectra were recorded using a Shi- reaction media after certain time intervals for monitoring the
madzu UV-2450 spectrophotometer. Crystallographic data substrate/product(s) percentage on a GC with an HP-5 quartz
were collected with Bruker APEX II CCD using Mo-Ka capillary column (30 m × 0.32 mm × 0.25 μm) and a flame
radiation at room temperature and corrected for absorption ionization detector (FID). An unknown peak definition was
with SADABS. A complex structure solution was performed made by analyzing real GC standards.

J. Chem. Sci. (2018) 130:33
Page 3 of 9 33
N
N
O
O
-
ClO4
HN
Cu
Br
Figure 1. Molecular and ChemDraw structures of the complex 1.
Table 1. Crystal data and structure refinement for complex 1.
Empirical formula
Formula weight
Temperature
C17H13BrClCuN3O6
534.20
296(2) K
Wavelength
Crystal system, space group
Unit cell dimensions
0.71073 Å
monoclinic, P21/c
a = 7.018(3) Å alpha = 90 ◦
b = 20.472(8) Å beta = 99.25(3)degr
c = 13.619(6) Å gamma = 90 o
1931.3(13) A3
Volume
Z, Calculated density
Absorption coefficient
F(000)
4, 1.837 Mg/m3
3.379 mm−1
1060
Crystal size
0.22 × 0.18 × 0.09 mm
Theta range for data collection 1.81 to 28.97 degr
Limiting indices
Reflections collected/unique
−9 <=h<=9, -27<=k<=24, -14<=l<=18
16900/4864 [R(int) = 0.0670]
Completeness to theta = 28.97 94.7%
Absorption correction
Max. and min. transmission
Refinement method
Integration
0.7507 and 0.5235
Full-matrix least-squares on F2
4864/0/274
Data/restraints/parameters
Goodness-of-fit on F2
0.951
Final R indices [I>2sigma(I)] R1 = 0.0570, wR2 = 0.1491
R indices (all data)
Largest diff. peak and hole
R1 = 0.1076, wR2 = 0.1777
0.580 and −1.052e.A−3
3. Results and Discussion
distances, and angles relevant to the metal coordination
sphere of the compound 1 are listed in Tables 1–2.
Copper(II) has a disordered square planar geometry
and is coordinated with two nitrogen atoms (Cu–N =
1.928 (4) and 1.938 (4) Å) from a chelating dpya ligand
and two oxygen atoms (Cu–O = 1.976 (3) and 2.017
(3) Å) from the carboxylate group of the dpya ligand in
μ2 mode. The +2 charge on the copper ion is balanced
with a coordinated deprotonated dpya and perchlorate
anion as counter ion. The geometry is far removed from
the ideal square plane, principally because of the “bite”
of dpya (N1-Cu1-N2 = 95.34 (16)degr) and bba (O1-
Cu1-O2 = 65.19(14)degr). Large deviations were
3.1 Structural analysis of the complex 1
The copper(II)-complex, ([Cu(OOC(C6H5)Br)(C10H9
N3)](ClO4)), with 4-bromobenzoate (bba) and 2,2’-
dipyridylamine (dpya) ligands, was successfully syn-
thesized via the stoichiometric reaction of reactants in
ethanolic solution. Dark-blue crystals were obtained
through solvent evaporation within one week. The crys-
tals of the compound exhibited monoclinic, P21/c and
symmetry. The molecular structure of the compound 1
is presented in Figure 1. Crystallographic data, bond

33 Page 4 of 9
J. Chem. Sci. (2018) 130:33
Table 2. Selected bond lengths (Å) and angles (degr).
Bond Lengths
Bond Angles
Br(1)-C(15)
Cu(1)-N(1)
Cu(1)-N(2)
Cu(1)-O(2)
Cu(1)-O(1)
C(10)-N(2)
N(3)-C(6)
1.895(5) N(1)-Cu(1)-O(2)
1.928(4) N(2)-Cu(1)-O(2)
1.938(4) N(1)-Cu(1)-O(1)
1.976(3) N(2)-Cu(1)-O(1)
2.017(3) O(2)-Cu(1)-O(1)
1.346(6) C(11)-O(1)-Cu(1) 87.3(3)
1.355(6) N(2)-C(10)-C(9)
165.29(15)
98.38(14)
100.41(15)
161.48(15)
65.19(14)
123.4(5)
118.4(4)
N(1)-Cu(1)-N(2) 5.34(16) O(1)-C(11)-O(2)
C(11)-O(2)-Cu(1) 89.1(3)
C(6)-N(2)-Cu(1) 124.2(3)
C(10)-N(2)-Cu(1) 117.3(3)
C(5)-N(1)-Cu(1)
124.7(3)
π
π
Figure 2. Chain formation of complex via hydrogen bonding and · · · interactions along a direction.
observed from 180degr for the N1-Cu1-O2 (165.29 3094 cm−1 is attributed to the aromatic (C-H) vibration
ν
(15)degr) and N2-Cu1-O1 angle (161.48 (15)degr). of two coordinated ligands. Carboxylate group asym-
The chelate ring adopts an approximate plane conforma- metric and symmetric vibration peaks were observed at
tion, which the observed torsion angles; C5N3N1C6 and 1644 and 1484 cm−1, respectively. The neutral ligand
ν
Cu1O2C11O1 are –1.0(8)degr and 1.2(4)degr, respec- azomethine (C=N) vibration peak difference between
tively.
the coordinated and the uncoordinated form is found
Weak intermolecular hydrogen bonding interactions to be about 60 cm−1, indicating that metal center and
are observed between the perchlorate ion and dpya. Two nitrogen atom coordination occurs. Two bands encoun-
mononuclear units are linked by two N-H O hydro- tered at 625 and 769 cm−1 are related to the nitrogen
...
gen bonds between the nitrogen atom of the coordinated atoms of dipyridylamine and metal center coordina-
dpya and the oxygen atoms of the lattice perchlorate tion.
...
ion, with an N3 O6 distance of 2.898 (6) Å (N3 –
The UV-Vis spectrum of the complex shows three
H6 O6). In addition, the π...π interactions between absorption bands at 244, 295 and 312 nm in acetoni-
...
the two parallel rings of the dpya and bba ligands trile solution. The lower wavelength band is dedicated
π
π
* transitions. The
(R1=C12C13C14C15C16C17, R2=N1C1C2C3C4, and to anionic carboxylate group
→
R3=N2C6C7C8C9C10), R1 ... R2 = 4.529 Å and R1 ... other two absorption bands are related to the n →
*
π
R3 = 4.175 Å, form a chain along a direction (Figure 2). transitions of dpya ligand. Additionally, d → d transi-
tions were not observed.
Based on the magnetic measurements of the solid
Cu(II) complex at room temperature, the magnetic
3.2 Spectroscopic study
The X-ray structure of the complex is consistent with the moment value is 1.4 B.M., and it is consistent with one
infrared spectra. The band observed between 3042 and unpaired electron system.

J. Chem. Sci. (2018) 130:33
Page 5 of 9 33
Table 3. Copper complex catalyzed oxidation of primary and secondary alcohols.
Reaction conditions: alcohol (9.3 × 10−4 mol), catalyst (0.1 mol%), H2O2 (0.192 mmol), water (10 mL), T =
a
70 ◦C
b
Determined with GC analysis
3.3 Catalytic experiments
uncatalyzed oxidation of the studied alcohols and
alkenes were negligible under the applied
conditions.
The results indicated that a synthesized compound
1 has a catalytic effect on both the studied alco-
hol and alkene oxidations in water. The activity of
the Cu(II)/H2O2/H2O catalytic system is found to be
The catalytic oxidation reactions of primary/secondary
alcohol and alkene were performed in a 50 mL round-
bottom flask◦with a temperature-controlled magnetic
stirrer at 70 C. The experiments were carried out in
water and H2O2 or TBHP as the oxygen source. Com-
parison of catalytic results was presented in Tables 3–4 higher in aromatic alcohols than in aliphatic ones. In
and Figures 3–4. A blank experiment showed that the a 6 h reaction time, the total % conversions of 90,

33 Page 6 of 9
Table 4. Copper complex catalyzed oxidation of alkenes.
J. Chem. Sci. (2018) 130:33
a
Reaction conditions: alkene (9.3 × −4 mol), catalyst (0.1 mol%), TBHP (14.5 mmol), water (10 mL), T = 70 ◦C
b Determined with GC analysis
86, 71, 29, and 13 were obtained for cinnamyl alco- h reaction time, conversion increased to 84%, and the
hol, 1-phenylethanol, benzyl alcohol, cyclohexanol, and aldehyde selectivity was found to be 88% as benzalde-
1-heptanol, respectively. Benzaldehyde was detected as hyde (Entry 2). Cinnamaldehyde is a minor product
a major product of both benzyl alcohol and cinnamyl with a selectivity value of 12% after 4 h. The result
alcohol oxidations (Table 3, Entries-2, 4, 1, 3, 5).
that needs to be emphasized is cinnamaldehyde car-
In benzyl alcohol oxidation, the substrate selectively boxylation, which is converted to benzaldehyde through
converted to one product, benzaldehyde, with 71% for- the carboxylation process as the reaction proceeds. As
mation in 6 h reaction time (Entry 1). Additionally, a cyclic alcohol, cyclohexanol was poorly oxidized to
formation of the over oxidation product, benzoic acid, the corresponding ketone, and 29% cyclohexanone for-
was not observed even when the reaction was prolonged mation was obtained at 6 h reaction time (Entry 3).
to 24 h. In the oxidation of secondary alcohol phenyl The lowest conversion rate was observed in 1-heptanol
ethanol, a TOF value of 1200 was reached at the first oxidation as the primary aliphatic alcohol (13% total
minute of the catalytic oxidation with 20% acetophe- conversion, Table 3, Entry 5). Generally, aliphatic alco-
none formation. After a 6 h reaction time, acetophenone hols are less reactive than aromatic alcohols, and these
was the only product observed at 86% (Entry 4). The findings are in agreement with published results.42,43
highest TOF value was obtained in allylic-type alcohol,
In alkene oxidation reactions, hydrogen peroxide has
cinnamyl alcohol oxidation (2100 h−1 at the first minute been found to be an ineffective oxygen source. That is
of the reaction with 35% total conversion). After a 4 why TBHP was used as oxidant. The Cu(II)/TBHP/H2O

J. Chem. Sci. (2018) 130:33
Page 7 of 9 33
100
90
80
70
60
50
40
30
20
10
Cinnamyl Alcohol
1-Phenyl Ethanol
Benzyl Alcohol
Cyclohexanol
1-Heptanol
0
0
0 . 5
1
2
3
4
5
6
2 4
Time (h)
Figure 3. Comparison of alcohol oxidation with compound in water.
100
90
80
70
60
50
40
30
20
10
0
Styrene
Ethyl Benzene
Cyclohexene
0
0 . 5
1
2
3
4
5
6
2 4
Time (h)
Figure 4. Comparison of alkene oxidation with compound in water.
catalytic system shows good activities of styrene, ethyl- ∼97%) (Entry 2). Among the studied alkenes, cyclo-
benzene, and cyclohexene oxidation with reasonably hexene oxidation is the fastest catalytic reaction (in the
good selectivity (Table 4) at 70 ◦C. In styrene oxidation, first 15 min of the reaction time, 71% yield and TOF =
acetophenone (2%) and benzaldehyde (85%, selectiv- 280 h−1). In cyclohexene, the oxidation of the carbon-
ity 98%) were observed in the initial period of reaction carbon double bond does not convert to cyclohexene
with a TON value of 87. After 4 h of reaction time, oxide(epoxide)withTBHP, whereastheoxidationofthe
complete conversion of styrene to benzaldehyde was allylic C-H bond results in 2-cyclohexene-1-ol, which is
observed as the sole product. When the reaction con- further oxidized to 2-cyclohexene-1-one as one product
tinued, the over-oxidation product, benzoic acid, was within a reaction time of 2 h (TOF = 50 h−1) (Table 2,
obtained (77% after 24 h) (Entry 1). In ethylbenzene Entry 3).
oxidation, acetophenone was obtained as a major prod-
The adopted Cu(II)/TBHP(or H2O2)/H2O system
uct and changed from 62% (TOF = 64.4) to 97% (TOF = was simpler, greener, and more efficient for alcohol and
17 h−1.) within a 1–6 h reaction time (overall selectivity especially alkene oxidation under mild reaction condi-

33 Page 8 of 9
J. Chem. Sci. (2018) 130:33
tions. A clean oxidant H2O2 was used since it produces
water, and more importantly, using water as a solvent is
an important feature of a green chemical reaction.
It should be emphasized that such level of yields is
extremely good in the field of alkene (particularly cyclo-
hexene) oxidation, especially for the inertness of the
saturated hydrocarbon and mild reaction conditions.44,45
The obtained products and yields are also comparable
with or even superior to those achieved using other
related copper catalysts bearing carboxylate and N-
based ligands.32–36
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4-bromobenzoate and neutral 2,2’-dipyridylamine lig-
ands. The compound has been fully characterized using
X-ray and other spectroscopic techniques. It is found
that compound is an active catalyst for the perox-
idative oxidation of alkenes and alcohols with H2O2
and/or TBHP under mild conditions without any pro-
moter in water, a green solvent system. In particular,
high conversions for alkene oxidation, and an excellent
selectivity for 2-cyclohexe-1-one for cyclohexene oxi-
dation in water were obtained. Using a low-cost catalyst,
TBHP/H2O2, and water as solvent made our catalytic
system attractive and environmentally sustainable.
Supplementary Information (SI)
All spectroscopic measurement data (FT-IR, UV-Vis and Sin-
gle crystal x-ray structure) are given in supplementary file.
CCDC 1578707 contains the supplementary crystallographic
data for the compound 1. These data can be obtained free of
charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html,
or from the Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-
336-033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary
Information is available at www.ias.ac.in/chemsci
12. Aliende C, Manrique M P, Jalon F A, Manzano B
R, Rodriguez A M and Espino G 2012 Arene Ruthe-
nium Complexes as Versatile Catalysts in Water in
both Transfer Hydrogenation of Ketones and Oxidation
of Alcohols. Selective Deuterium Labeling of rac-1-
Phenylethanol Organometallics 31 6106
13. Wu J, Liu Y, Ma X, Liu P, Gu C and Dai B 2016 Highly
selective copper-catalyzed oxidation of benzyl alcohols
to aromatic aldehydes in water at room temperature Appl.
Organomet. Chem. 30 577
14. Monfared H H, Nather C, Winkler H and Janiak
C 2012 Highly selective and “green” alcohol oxida-
tions in water using aqueous 10% H2O2 and iron-
benzenetricarboxylate metal–organic gel Inorg. Chim.
Acta 391 75
15. Chen G, Chen L, Ma L, Kwong H K and Lau T C 2016
Photocatalytic oxidation of alkenes and alcohols in water
by a manganese(V) nitrido complex Chem. Commun. 52
9271
Acknowledgements
Authors thankfully acknowledge the Medical Plants and
Medicine Research Centre of Anadolu University, Eskis¸ehir,
Turkey for using X-ray Diffractometer.
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