Copper(II) acetate mediated conversion of ortho aminomethyl substituted isoquinolines to bis(isoquinolylcarbonyl)amides

Article abstract of DOI:10.1016/j.poly.2011.10.038

An ethanolic solution of ortho aminomethyl substituted isoquinolines, on stirring in air with half equivalent of [Cu(OAc)₂(H₂O)], afforded [Cu(1-L)(OAc)] (1) and [Cu(3-L)(OAc)] (2) {1-L = bis(1- isoquinolylcarbonyl)amide ion and 3-L = bis(3-isoquinolylcarbonyl)amide ion}. This reaction involves the oxidation of a methylene group and the formation of a bond between nitrogen and carbon in N-C(O) through coupling. The free ligands can be isolated as crystalline solids from compounds 1-2, by extrusion of the Cu²⁺ ion using EDTA^2-. The molecular structure of 1·2.5H₂O has been established and the copper(II) center has a pseudo square-planar N₃O environment. A packing diagram shows the existence of a centrosymmetric dimer in which two copper centers are intermolecularly linked by the O2 atom of the amide function, leading to a Cu₂O₂ unit.

Full text of DOI:10.1016/j.poly.2011.10.038

Polyhedron 33 (2012) 9–12
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
Copper(II) acetate mediated conversion of ortho aminomethyl substituted
isoquinolines to bis(isoquinolylcarbonyl)amides
⇑
Rojalin Sahu, Vijendra Kumar Fulwa, Himanshu Sekhar Jena, Vadivelu Manivannan
Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781 039, India
a r t i c l e i n f o
a b s t r a c t
Article history:
An ethanolic solution of ortho aminomethyl substituted isoquinolines, on stirring in air with half equiv-
alent of [Cu(OAc)2(H2O)], afforded [Cu(1-L)(OAc)] (1) and [Cu(3-L)(OAc)] (2) {1-L = bis(1-isoquinolylcar-
bonyl)amide ion and 3-L = bis(3-isoquinolylcarbonyl)amide ion}. This reaction involves the oxidation of a
methylene group and the formation of a bond between nitrogen and carbon in N–C(@O) through cou-
pling. The free ligands can be isolated as crystalline solids from compounds 1–2, by extrusion of the
Cu2+ ion using EDTA2ꢀ. The molecular structure of 1ꢁ2.5H2O has been established and the copper(II)
center has a pseudo square-planar N3O environment. A packing diagram shows the existence of a centro-
symmetric dimer in which two copper centers are intermolecularly linked by the O2 atom of the amide
function, leading to a Cu2O2 unit.
Received 8 September 2011
Accepted 30 October 2011
Available online 22 November 2011
Keywords:
Oxidation
N–C coupling
Bis(carbonyl)amide
Isoquinoline
Copper(II)
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
Setup for room temperature magnetic data, were used for perform-
ing the relevant measurements.
The oxidation of alkyl and aromatic substrates is an important
quest for synthetic chemists. With this aspect in mind, the role of
copper containing enzymes and their model complexes have been
reviewed [1]. Reports pertaining to the oxidation of a –CH2– group
linked to a 2-pyridyl and an amide or imine function by a suitable
metal ion are rare [2,3]. A methylene group flanked by 2-pyridyl
and an amine has been deprotonated on coordination to a Rh(-I, I)
dimer and an Ir(I) center [4,5]. Very recently we have demonstrated
the unprecedented formation of bis(carbonyl)amides from 2-ami-
nomethyl substituted pyridine and quinoline, using copper(II) ace-
tate [6]. This has prompted us to scrutinize the general applicability
of this novel method to other substrates and herein we report the
ready conversion of ortho aminomethyl substituted isoquinolines
to their bis(isoquinolylcarbonyl)amides.
X-ray crystallographic data were collected using a Bruker SMART
APEX-CCD diffractometer with MoK radiation (k = 0.71073 Å). The
a
intensity data were corrected for Lorentz and polarization effects
and empirical absorption corrections were applied using the SAINT
program [7,8]. The structure of 1ꢁ2.5H2O was solved by direct
methods using SHELXS-97 [9]. Non-hydrogen atoms located from
the difference Fourier maps were refined anisotropically by full-
matrix least-squares on F2, using SHELXL-97 [9]. All hydrogen atoms
were included in calculated positions (except for the water of crys-
tallization for which the hydrogen atoms could neither be added
at calculated positions nor located from FMAP) and were refined iso-
tropically using a riding model. The thermal displacement parame-
ters of O9 and O10 are smeared and could not be improved with least
squares refinement procedures.
2.2. General Procedures
2. Experimental
Isoquinoline, 3-cyanoisoquinoline, m-chloroperbenzoic acid
(MCPBA), dimethylcarbamyl chloride, (Aldrich, USA), trim-
ethylsilylcyanide (Spectrochem), Cu(OAc)2ꢁH2O (Merck India Ltd.)
were used as received without further purification. Dichlorometh-
ane and chloroform were dried by standard methods.
2.1. Instrumentation and materials
A
Perkin–Elmer Spectrum One FT-IR spectrometer (4000–
250 cmꢀ1), Perkin–Elmer Lambda 25 UV–Vis spectrometer, Varian
Mercury plus 400 MHz NMR spectrometer, Perkin–Elmer Series II
CHNS/O Analyzer 2400, JEOL JES FA-200 X-band EPR spectrometer,
waters Q-TOF premier mass spectrometer and a Lakshore VSM
2.3. Syntheses
2.3.1. Isoquinoline-N-oxide
⇑
IR (KBr, cmꢀ1): 1645(s), 1603(s), 1573(s), 1499(s), 1456(s),
1424(m), 1383(m), 1332(s), 1302(s), 1275(s), 1255(s), 1206(s),
Corresponding author. Tel.: +91 361 258 2306; fax: +91 361 258 2349.
E-mail address: mani@iitg.ernet.in (V. Manivannan).
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.10.038

10
R. Sahu et al. / Polyhedron 33 (2012) 9–12
1171(vs), 1127(s), 981(w), 912(m), 868(m), 820(s), 748(s), 736(s),
629(m), 534(m), 494(m), 471(m). 400 MHz 1H NMR (d (J, Hz),
CDCl3): 7.614–7.633 (2H, m), 7.696 (1H, d, 6.8), 7.755 (1H, d, 7.2),
7.812 (1H, d, 8.8), 8.167 (1H, d, 8.4), 8.812 (1H, s).
C, 58.78; H, 3.34; N, 9.30%. ESI-MS: m/z Calc. for [63Cu(3-L)]+
389.0226. Found 389.0223.
2.3.7. Bis(1-isoquinolylcarbonyl)amide (1-LH)
Complex 1 (1.0 g, 2.02 mmol) and Na2EDTA (1.50 g, 4.04 mmol)
were dissolved in H2O (50 mL) and stirred vigorously with 50 mL
of CHCl3 for 2 h. The CHCl3 layer was separated, the aqueous layer
was washed with CHCl3 (2 ꢂ 30 mL) and the combined CHCl3 solu-
tion was dried with anhydrous Na2SO4. After removal of the solvent,
1-LH was obtained as a yellow solid. Yield: 0.60 g, 91%. IR (KBr,
cmꢀ1): 1745(s), 1636(s), 1583(m), 1556(m), 1446(s), 1419(m),
1379(m), 1340(w), 1307(m), 1260(w), 1230(w), 1145(w), 1106(w),
1082(w), 1040(w), 1021(w), 913(w), 877(m), 831(m), 799(m),
746(m), 710(w), 640(w), 621(m), 511(w), 466(w). ESI-MS: m/z Calc.
for C20H13N3O2 327.1041, found (M+ꢀH) 328.1042. 400 MHz 1H
NMR (d (J, Hz), CDCl3): 7.754–7.779 (2H, m), 7.887–7.937 (2H, m),
8.671 (1H, d, 5.6), 9.638–9.663 (1H, m), 13.537 (NH, s). Anal. Calc.
for C20H13N3O2 (327.34): C 73.38, H 4.00, N 12.84. Found: C 73.31,
H 3.98, N 12.80%.
2.3.2. Isoquinoline-1-carbonitrile
IR (KBr, cmꢀ1): 2228(s), 1637(s), 1622(s), 1580(m), 1552(m),
1492(m), 1455(m), 1389(s), 1344(m), 1322(w), 1297(w),
1226(w), 1198(w), 1032(m), 877(s), 838(s), 788(m), 746(s),
695(w), 660(m), 539(m), 464(m). 400 MHz 1H NMR (d (J, Hz),
CDCl3): 7.718 (2H, t, 7.6), 7.855 (1H, d, 5.2), 7.911 (1H, d, 8.0),
8.168 (1H, d, 8.4), 8.333 (1H, d, 8.4).
2.3.3. 1-Aminomethylisoquinoline (1-ami)
1-ami was isolated as a red solid. Yield: 1.9 g, 92%. IR (KBr,
cmꢀ1): 3425(b), 1681(s), 1622(s), 1584(s), 1558(s), 1502(s),
1446(s), 1378(s), 1314(s), 1258(m), 1188(m), 1142(s), 1107(s),
1008(m), 956(m), 870(m), 827(s), 800(m), 746(s), 665(w),
634(w), 617(w), 593(w), 528(w), 503(w), 464(m), 439(w).
400 MHz 1H NMR (d (J, Hz), CDCl3): 2.351 (NH2, s), 4.543 (CH2, s),
7.577 (1H, d, 5.2), 7.626 (1H, t, 7.8), 7.705 (1H, t, 7.4), 7.852 (1H,
d, 8.4), 8.108 (1H, d, 8.8), 8.468 (1H, d, 5.6).
3. Results and discussion
3.1. Synthesis
2.3.4. 3-Aminomethylisoquinoline (3-ami)
3-ami was isolated as a red solid. Yield: 0.925 g, 90%. IR (KBr,
cmꢀ1): 3282(b), 1630(s), 1593(s), 1584(s), 1558(s), 1502(s),
1493(s), 1439(s), 1387(s), 1345(s), 1327(s), 1262(s), 1196(w),
1124(m), 1091(s), 1064(s), 1028(s), 957(s), 870(m), 881(s),
801(s), 751(s), 628(w), 488(w), 470(m). 400 MHz 1H NMR (d (J,
Hz), CDCl3): 2.772 (NH2, s), 4.013 (CH2, s), 7.440–7.601 (3H, m),
7.673 (1H, d, 8.0), 7.830 (1H, d, 8.4), 9.092 (1H, d, 11.2).
The following synthetic methodology [10] was adopted for the
synthesis of 1-aminomethylisoquinoline (Scheme 1) and whilst
the synthetic procedures are not detailed here, the spectroscopic
data are included in the experimental section. In the first step, iso-
quinoline was converted to isoquinoline-N-oxide using meta-chlo-
roperbenzoic acid in chloroform. A cyano group was introduced at
the 1-position of the isoquinoline nucleus, using trimethylsilylcya-
nide in the presence of dimethylcarbamylchloride. This method
offered 1-cyanoisoquinoline from isoquinoline-N-oxide in good
yields. 1-Cyanoisoquinoline was then converted to 1-ami by
reduction with molecular hydrogen in the presence of a Pd/C cata-
lyst in acetic acid. Commercially available 3-cyanoisoquinoline was
converted to 3-ami in a similar manner.
An ethanolic solution of 1-ami, on stirring with half equivalent
of [Cu(OAc)2(H2O)] in air, generated a green solution which on
standing deposited a green precipitate of the composition [Cu(1-
L)(OAc)] (1) in a good yield, as shown in Scheme 2. In a similar
manner, 3-ami also reacted with copper(II) acetate affording
[Cu(3-L)(OAc)] (2) in similar yields {1-L = bis(1-isoquinolylcarbon-
yl)amide ion and 3-L = bis(3-isoquinolylcarbonyl)amide ion}. The
reported compounds 1 and 2 were not obtained if the reaction
was carried out under anaerobic conditions. It is pertinent to note
that other mononuclear copper(II) salts did not show the observed
conversion [11–13] and a related 2-(aminomethyl)pyridine on
reaction with copper(II) acetate in acetonitrile yielded a simple
coordination product [13]. It has also been previously observed
that bis(2-picolyl)amine yields a simple coordinated complex and
does not show oxidation of the methylene group under the same
[6] and other conditions [14]. Free 1-LH was isolated as a yellow
crystalline solid from 1 by extrusion of the Cu2+ ion using Na2EDTA.
2.3.5. [Cu(1-L)(OAc)] (1)
To Cu(OAc)2ꢁH2O (0.250 g, 1.25 mmol) dissolved in ethanol
(80 mL) was added 1-ami (0.396 g, 2.50 mmol) and the resulting
mixture was stirred for 24 h with occasional purging of air. The
solution was left undisturbed and a green precipitate deposited
after two week of standing, which was collected and washed with
ice-cold ethanol. Yield 0.380 g, 65%. IR (KBr, cmꢀ1): 1706(s),
1618(s), 1586(s), 1555(s), 1500(m), 1450(m), 1408(s), 1359(m),
1312(s), 1228(w), 1163(m), 1101(w), 1048(w), 1020(m), 929(w),
881(m), 834(m), 817(m), 763(m), 746(m), 710(w), 672(w),
636(m), 591(w), 518(w), 473(m), 288(w). UV–Vis [kmax, nm (e,
Mꢀ1 cmꢀ1), DMF solution]: 710 (147), 373 (16975), 326 (29020).
EPR (CH3OH solution, 77 K): g|| = 2.169, A|| = 85 G; g\ = 2.029. leff
(polycrystalline, 25 °C) = 2.30 B.M. Anal. Calc. for C22H15N3O4Cu:
C, 58.86; H, 3.37; N, 9.36. Found: C, 58.80; H, 3.32; N, 9.27%. ESI-
MS: m/z Calc. for [63Cu(1-L)]+ 389.0226. Found 389.0224. Violet
crystals of the composition 1ꢁ2.5H2O were obtained by slow evap-
oration of a methanol solution of 1.
2.3.6. [Cu(3-L)(OAc)] (2)
To Cu(OAc)2ꢁH2O (0.250 g, 1.25 mmol) dissolved in ethanol
(50 mL) was added 3-ami (0.396 g, 2.50 mmol) and the resulting
mixture was stirred for 24 h with occasional purging of air. The
solution was left undisturbed and a green precipitate of 2 depos-
ited after a week, which was collected, washed with ice-cold etha-
nol and dried in vacuo over P2O5. Yield: 0.360 g, 65%. IR (KBr,
cmꢀ1): 1701(s), 1613(s), 1578(s), 1494(w), 1460(s), 1390(m),
1332(s), 1313(s), 1254(m), 1149(w), 1111(w), 1052(w), 1018(w),
980(m), 912(m), 802(m), 786(w), 775(w), 747(m), 688(m),
651(w), 621(w), 588(w), 541(m), 498(w), 469(m), 371(w). UV–
3.2. Molecular structure
The molecular structure of 1ꢁ2.5H2O has been established using
the single crystal X-ray diffraction method. The complex crystallized
ꢀ
in the P1 space group (Table 1) and the asymmetric unit contained 1
and lattice water molecules. The copper(II) center has a pseudo
square-planar N3O environment (Fig. 1) and has a distorted geome-
try. The two chelate bite angles have a value of 81.5(1)° and 81.9(1)°,
while the two non-chelated cis angles are 97.9(1)° and 98.7(1)°. The
two trans angles are N1–Cu1–N3, 163.4(1) and N2–Cu1–O3,
Vis [kmax, nm (e
, Mꢀ1 cmꢀ1), MeOH solution]: 700 (126), 400
(7455), 365 (16280), 336 (22400). EPR (DMF solution, 77 K):
g|| = 2.164, A|| = 80 G; g\ = 2.016. leff (polycrystalline, 25 °C) = 2.31
B.M. Anal. Calc. for C22H15N3O4Cu: C, 58.86; H, 3.37; N, 9.36. Found:

R. Sahu et al. / Polyhedron 33 (2012) 9–12
11
H2 , Pd/C
MCPBA
Me3SiCN
N+
N
N
CH3COOH
N
-
Me2NCOCl
O
CN
NH2
Scheme 1. Synthesis of 1-ami.
O
O
[Cu(OAc)2(H2O)]
O2, EtOH
N
NH2
NH2
N
N
2
N
N
Cu
OAc
O
O
[Cu(OAc)2(H2O)]
O2, EtOH
N
2
N
N
Cu
OAc
Scheme 2. Synthesis of 1 and 2.
179.2(1)°. The Cu–NQ (NQ = isoquinolyl-N and NA = amide-N) dis-
tances are longer by 0.085(3) and 0.066(3) Å than the Cu–NA and
Cu–O distances, respectively. The bond parameters around the coor-
dination environment are listed in Table 2.
Fig. 1. ORTEP (30% probability) diagram of 1, H-atoms are omitted for clarity.
Table 2
Selected bond distances (Å) and angles (°) in 1ꢁ2.5H2O.
In the packing diagram the complex exists as a centrosymmetric
dimer in which two copper centers are intermolecularly linked by
the O2 atom of the amide function (Fig. 2). As a result a Cu2O2 unit
is present with the Cu1–O2 contact having a length of 2.753(3) Å. In
this unit, the non-bonded Cuꢁ ꢁ ꢁCu, O2ꢁ ꢁ ꢁO2 and O2ꢁ ꢁ ꢁCu distances,
respectively, are 5.1218(5), 4.528(3) and 3.973(2) Å. The angles
subtended at Cu1 and O2, respectively, are 82.5(1)° and 97.5(1)°.
As a result of O2 linking, the C11 and O2 atoms of the amide func-
tion deviate respectively by 0.18 and 0.64 Å from the plane contain-
ing the O1C10N2C12 atoms.
Cu1–N1
Cu1–N2
Cu1–N3
Cu1–O3
Cu1–O4
Cu1–O2A
1.992(3)
1.909(2)
1.995(3)
1.928(2)
2.736(3)
2.753(3)
N1–Cu1–N2
N1–Cu1–N3
N1–Cu1–O3
N1–Cu1–O4
N1–Cu1–O2A
N2–Cu1–N3
N2–Cu1–O3
N2–Cu1–O4
N2–Cu1–O2A
N3–Cu1–O3
N3–Cu1–O4
N3–Cu1–O2A
O3–Cu1–O4
O3–Cu1–O2A
O2A–Cu1–O4
81.5(1)
163.4(1)
97.9(1)
96.7(1)
92.9(1)
81.9(1)
179.1(1)
128.2(1)
91.32(9)
98.7(1)
93.3(1)
87.7(1)
52.5(1)
88.1(1)
140.3(1)
Also a
p p interaction between the isoquinolyl rings is pres-
ꢁ ꢁ ꢁ
ent, with a distance of 3.57 Å between the centroids formed by
the N1C1C2C3C8C9 and C13C14C15C16C1718 atoms. The aromatic
rings of the complex form hydrophobic layers and water molecules
Table 1
Crystallographic data for 1ꢁ2.5H2O.
Formula
Formula weight
T (K)
C44H40N6O13Cu2
987.91
293(2)
Crystal system
Space group
Unit cell dimensions
a (Å)
b (Å)
c (Å)
triclinic
ꢀ
P1
10.5812(7)
11.0568(7)
11.3189(8)
80.081(4)
66.806(4)
78.244(4)
1185.44(14)
a
(°)
b (°)
c
(°)
0
V (ÅA3)
Z
1
Dcalc (g cmꢀ3
)
1.482
0.977
1.054
l
(mmꢀ1
)
Goodness-of-fit (GOF)a on F2
R[I > 2 (I)]
r
bR1 = 0.0532; cwR2 = 0.1560
bR1 = 0.0690; cwR2 = 0.1689
Rindices (all data)
P
GOF = [ [w(F20 ꢀ F2c )2]/M ꢀ N]1/2
(M = number
of
reflections,
a
N = number of parameters refined).
P
P
b
c
R1
=
||F0| ꢀ |Fc||/ |F0|.
P
P
wR2 = [ [w(F20 ꢀ F2c )2]/ [w(F20)2]]1/2
.
Fig. 2. ORTEP (30% probability) diagram depicting the dimer containing Cu2O2 unit
found in 1ꢁ2.5H2O, H-atoms are omitted for clarity.

12
R. Sahu et al. / Polyhedron 33 (2012) 9–12
g|| > g\ > 2, consistent with a b11 ground electronic configuration for
the Cu2+ ion.
4. Conclusion
In conclusion, ortho aminomethyl substituted isoquinolines
readily form the respective bis(carbonyl)amide complexes on
treatment with [Cu(OAc)2(H2O)] in air and in hydrated ethanol.
This reaction involves oxidation of the methylene group and for-
mation of a bond between nitrogen and carbon in N–C(@O)
through coupling. The determination of the molecular structure
of 1ꢁ2.5H2O confirmed the presence of a bis(1-isoquinolylcarbon-
yl)amide complex of the copper(II) ion. Other spectroscopic evi-
dence corroborates the observed conversion. With this result we
believe that an ortho aminomethyl substituted pyridine nucleus
having alkyl/aryl substituents or having fused aromatic/carbocyclic
rings can be converted to the respective bis(carbonyl)amides, using
copper(II) acetate in ethanol and in the presence of molecular oxy-
gen. Our investigations in this direction are under scrutiny.
Fig. 3. Packing diagram of 1ꢁ2.5H2O, viewed down the b-axis.
Acknowledgments
Table 3
Selected non-bonded distances (Å) and angles (°) in 1ꢁ2.5H2O.
We are grateful to DST New Delhi for a financial grant and the
single crystal X-ray diffractometer facility. The authors are thank-
ful to Mr. Babulal Das for the X-ray data.
Dꢁ ꢁ ꢁA
Distance
Symmetry operator
O1ꢁ ꢁ ꢁO2
O1ꢁ ꢁ ꢁO6
O3ꢁ ꢁ ꢁO5
O5ꢁ ꢁ ꢁO6
O5ꢁ ꢁ ꢁO7
O6ꢁ ꢁ ꢁO7
2.815(5)
2.876(5)
2.825(5)
2.908(8)
2.79(1)
–
–
–
Appendix A. Supplementary data
ꢀx + 1, ꢀy + 1, ꢀz + 1
ꢀx + 1, ꢀy + 1, ꢀz + 1
ꢀx + 1, ꢀy + 1, ꢀz + 1
CCDC 809572 contains the supplementary crystallographic data
for compound 1ꢁ2.5H2O. 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: de-
posit@ccdc.cam.ac.uk. Supplementary data associated with this
article can be found, in the online version, at doi:10.1016/j.poly.
2011.10.038.
2.79(1)
Angle
O6ꢁ ꢁ ꢁO5ꢁ ꢁ ꢁO7
O5ꢁ ꢁ ꢁO6ꢁ ꢁ ꢁO7
O6ꢁ ꢁ ꢁO7ꢁ ꢁ ꢁO5
139.6(3)
106.2(3)
110.2(3)
are amalgamated between these layers. The water molecules are
further confined into a channel in which the methyl group of the
acetate ion serves as a separator of the layers containing water
molecules (Fig. 3). The water molecules form a cyclic centrosym-
metric hexamer (O5, O6 and O7), having a chair shape [15], and
are linked to O9 and O10. Relevant non-bonded distances and an-
gles are included in Table 3. These are also linked to the complex
molecule through hydrogen bonds with the carbonyl oxygen atom
O1 through O6ꢁ ꢁ ꢁO1, 2.88(1) Å as well as to the acetate oxygen
atom O4, through O4ꢁ ꢁ ꢁO5, 2.83(1) Å and O4ꢁ ꢁ ꢁO9, 2.77(1) Å non-
bonded interactions.
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The IR spectrum of 1 shows a characteristic 1706 cmꢀ1 peak for
m
CO, which shifts to 1745 cmꢀ1 in the free 1-LH, and 2 shows the
same peak at 1701 cmꢀ1. The ESI-MS of 1 exhibits m/z = 389.0224
(Calc. 389.0226) that can be assigned to the [63Cu(1-L)]+ fragment.
In the case of 2, a peak at m/z = 389.0223 corresponding to the
[
63Cu(3-L)]+ fragment was observed. Free 1-LH shows
a m/
z = 328.1042 peak in the ESI-MS for the 1-LH2+ fragment. The room
temperature magnetic moments of 1 and 2 are ꢃ2.30 B.M., being
assigned as one electron paramagnets. The EPR spectra of both com-
plexes in frozen solution (77 K) exhibit a typical axial spectrum with