A structural study of (dibenzyldiaza-18-crown-6) lanthanum(III) thiocyanate

Article abstract of DOI:10.1016/S0022-2860(97)00084-7

The structure of the complex La(NCS)₃C₂₆H₃₈N₂O₄ (1) was determined by single-crystal X-ray diffraction and the structure of the coordinating ligand, C₂₆H₃₈N₂O₄ (2), was studied by the semi-empirical PM3 method. The bonding around La consists of a primary coordination of three thiocyanate N atoms and a secondary coordination of two N atoms and four O atoms of the macrocycle. The primary coordination about La gives an almost planar trigonal configuration that bisects the plane of the macrocycle with La lying in the centre of the macrocycle cavity. The benzyl groups that are attached to the macrocycle are in syn conformation with respect to the macrocycle plane with one of the La-NCS bonds pointing above the plane and the other two La-NCS bonds pointing below the plane in the direction of the benzyl groups. The PM3 calculation shows that the optimised diazacrown has an open structure of a pseudo D(2d) symmetry with the two benzyl side-arms positioned away from the cavity.

Full text of DOI:10.1016/S0022-2860(97)00084-7

MOLSTR 9835
Journal of Molecular Structure 415 (1997) 71–79
A structural study of (dibenzyldiaza-18-crown-6)
lanthanum(III) thiocyanate
Muhammad Idiris Saleha, Abdussalam Salhina, Bahruddin Saada,
,
Sharifuddin Mohd Zainb, Zainudin Arifinb *
aSchool of Chemical Sciences, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia
bDepartment of Chemistry, Universiti Malaya, 50603 Kuala Lumpur, Malaysia
Received 8 November 1996; revised 18 February 1997; accepted 18 February 1997
Abstract
The structure of the complex La(NCS)3C26H38N2O4 (1) was determined by single-crystal X-ray diffraction and the structure
of the coordinating ligand, C26H38N2O4 (2), was studied by the semi-empirical PM3 method. The bonding around La consists of
a primary coordination of three thiocyanate N atoms and a secondary coordination of two N atoms and four O atoms of the
macrocycle. The primary coordination about La gives an almost planar trigonal configuration that bisects the plane of the
macrocycle with La lying in the centre of the macrocycle cavity. The benzyl groups that are attached to the macrocycle are in
syn conformation with respect to the macrocycle plane with one of the La–NCS bonds pointing above the plane and the other
two La–NCS bonds pointing below the plane in the direction of the benzyl groups. The PM3 calculation shows that the
optimised diazacrown has an open structure of a pseudo D2d symmetry with the two benzyl side-arms positioned away from the
cavity. ᭧ 1997 Elsevier Science B.V.
Keywords: Dibenzyldiaza-18-crown-6; Lanthanum thiocyanate; PM3 calculation; X-ray crystallography
1. Introduction
crystal structure determination of metal ion crown-
ether complexes covering virtually all classes of
metal ions[4–6] including a number of lanthanum
crown-ether structures. The structure adopted by the
metal ion crown-ether complex is dependent on the
cavity size—metal ion fit ranges from the model
cation fitting directly into the cavity and interacting
with all the donor atoms equally to that of out-of-
cavity coordination when the metal ion is too large
to fit into the cavity[7]. Crown ethers bearing side-
arms, or lariat ethers, have also been much studied
especially with respect to their properties as flexible
and dynamic cation binders which utilize their
side-arms and macro-rings cooperatively[8].
The coordination chemistry of metals with crown
ethers and azacrown ethers has received considerable
attention because of the ability of the macrocycles to
act as excellent complexing agents. Studies on these
interactions have led to greater understanding of the
various factors such as cavity size, substituent effects,
shape, flexibility, and donor atoms, that influence the
selectivities of macrocycles for the cations[1–3].
There have been numerous reports on the X-ray
* Corresponding author. Tel: +60 3 759 4021; fax: +60 3 759
4193; e-mail: zai@kimia.um.edu.my
0022-2860/97/$17.00 Copyright ᭧ 1997 Elsevier Science B.V. All rights reserved
PII S0022-2860(97)00084-7

72
M.I. Saleh et al./Journal of Molecular Structure 415 (1997) 71–79
Since relatively few studies have been reported on
2.2. X-ray crystallographic studies
the structure of complexes of diazacrown with the
lanthanides[9,10], we have prepared a complex of
lanthanum thiocyanate with dibenzyldiaza-18-
crown-6 and studied its structure by X-ray crystallo-
graphy. In addition, we have performed a semi-
empirical quantum chemical PM3 calculation on the
parent diazacrown since it does not exist as suitable
crystals for X-ray crystal structure determination;
such an effort would enable us to compare the
structural features of the diazacrown before and
after coordination with the lanthanum salt.
The X-ray data collection was carried out by an
automated Enraf–Nonius CAD-4 diffractometer
with graphite-monochromated MoKa (l = 0.7170 A)
˚
radiation, and the determination of the crystal class,
orientation matrix and cell parameters were per-
formed according to standard procedures [11]. The
intensities were recorded at approximately 27ЊC up
to a 2⌰max of 50Њ. The unit cell constants for the
structure lattice were obtained from the angular
settings of 25 strong reflections. Crystal decay was
monitored by using three standard random reflections.
Absorption correction was neglected. The crystal data
and experimental details are summarized in Table 1.
The crystal structure was solved by the heavy atom
method from a Patterson synthesis and all the
remaining non-hydrogen atoms were located from
subsequent difference–Fourier maps. The H atoms
were fixed geometrically and allowed to ride on their
respective parent atoms and were included in struc-
ture–factor calculations. The structure solution and
refinement were performed using the shelxs86 and
shelxl93 programs [12] on a 486 personal computer.
2. Experimental
2.1. Preparation of the complex of La(NCS)3 with
dibenzyldiaza-18-crown-6
Equimolar amounts of lanthanum thiocyanate and
dibenzyldiaza-18-crown-6 were dissolved in a 1:1
mixture of warm methanol and acetonitrile. The
resulting solution was filtered immediately and on
cooling yielded colourless crystals of the complex.
Table 1
Crystal data for La(NCS)3C26H38N2O4
Formula weight
Temperature
Wavelength
Crystal system
Space group
755.73
293 K
0.71073 A
Monoclinic
P21/c
˚
˚
Unit cell dimensions
a = 15.5855(8) A a = 90Њ
˚
b = 9.6801(5) A b = 94.188(4)Њ
c = 21.8962(10) A g = 90Њ
˚
3
˚
Volume
3294.6(3) A
Z
4
Density (calculated)
Absorption coefficient
F(000)
Crystal size
⌰ range for data collection
Index ranges
Reflections collected
Independent reflections
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I Ͼ 2j(I)]
R indices (all data)
Largest diff. peak and hole
1.524 mg m−3
1.527 mm−1
1536
0.14 × 0.43 × 0.50 mm3
1.31 to 24.98Њ
−18 Յ h Յ 0, −11 Յ k Յ 0, −25 Յ l Յ 26
6027
5798 [R(int) = 0.0260]
Full-matrix least-squares on F2
5798/0/379
0.816
R1 = 0.0403, wR2 = 0.1057
R1 = 0.0487, wR2 = 0.1125
1.424 and − 1.710 e A
−3
˚

73
M.I. Saleh et al./Journal of Molecular Structure 415 (1997) 71–79
Fig. 1. The molecular structure of La(NCS)3.C26H28N2O4 showing La coordination.
2.3. Semi-empirical quantum chemical optimization
resident in a Silicon Graphics Indigo workstation
and partially minimized using the molecular
mechanics CVFF force-field method[15]. The par-
tially optimized structure was then converted into a
mopac Z-matrix input file and was fully optimized
without any constraints. Safety checks during the
optimization were also disabled. The key words
The azacrown structure was optimized in its lowest
energy state using the semiempirical quantum
chemical PM3 method [13] available in the mopac
6.0 package [14]. The initial structure of the azacrown
was built using the Insight II Builder module [15]
Fig. 2. The molecular structure of La(NCS)3.C26H28N2O4.

74
M.I. Saleh et al./Journal of Molecular Structure 415 (1997) 71–79
PRECISE and GEO-OK were used in the mopac
calculation. PRECISE increases the criteria for
terminating optimizations. GEO-OK overrides the
termination of jobs which results when two atoms
are found to be within 0.8 A of each other. The full
optimization was performed on a Cray J90 at the
CADCAM Centre, University of Malaya.
3. Results and discussion
The molecular structure of 1 is shown in Figs. 1 and
2. The atomic coordinates and selected bond distances,
angles and torsion angles are given in Tables 1 to 5. The
packing of the molecule is shown in Fig. 3. The
molecular structure of 2 is shown in Fig. 4(a) and (b).
˚
Table 2
4
2
Atomic coordinates ( × 10 ) and equivalent isotropic displacement parameters (A × 103). U(eq) is defined as one third of the trace of the
˚
orthogonalized Uij tensor
x
y
z
U(eq)
La
S(1)
S(2)
S(3)
2290(1)
5469(1)
−275(1)
1860(1)
3219(2)
2703(2)
716(2)
2117(1)
2088(2)
−1352(2)
−2838(2)
−88(3)
1609(1)
1483(1)
1015(1)
2220(1)
1685(1)
587(1)
1463(1)
2494(1)
1370(2)
1286(2)
2140(2)
2761(2)
533(2)
3972(2)
4569(3)
4728(3)
4305(3)
3704(2)
3535(2)
2890(2)
2767(2)
2227(2)
1149(2)
624(2)
32(1)
70(1)
66(1)
92(1)
40(1)
42(1)
44(1)
51(1)
50(1)
61(1)
60(1)
38(1)
36(1)
54(1)
68(2)
75(2)
69(2)
54(1)
43(1)
43(1)
43(1)
45(1)
50(1)
49(1)
46(1)
44(1)
42(1)
39(1)
53(1)
63(1)
61(1)
54(1)
46(1)
42(1)
44(1)
53(1)
51(1)
52(1)
48(1)
43(1)
43(1)
45(1)
O(1)
O(2)
O(3)
O(4)
N(1)
N(2)
N(3)
N(4)
N(5)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
C(9)
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
C(17)
C(18)
C(19)
C(20)
C(21)
C(22)
C(23)
C(24)
C(25)
C(26)
C(27)
C(28)
C(29)
978(3)
3143(3)
1896(4)
2967(4)
221(4)
1296(2)
3775(3)
1188(3)
2358(3)
3084(2)
1886(2)
4109(3)
4481(4)
5016(4)
5217(3)
4861(3)
4290(3)
3874(3)
3297(3)
3757(3)
3541(3)
2879(3)
2163(3)
2219(3)
2282(3)
2080(3)
2593(3)
2399(4)
1712(4)
1216(3)
1403(3)
937(3)
−5572(5)
1522(4)
3645(4)
3295(6)
3171(7)
2110(8)
1151(7)
1265(6)
2312(5)
2394(5)
33(5)
−429(5)
689(5)
−467(5)
1363(5)
2916(4)
5063(5)
6051(4)
−1120(5)
−2054(6)
−2933(5)
7891(5)
6959(4)
3741(5)
4172(5)
3289(6)
2030(6)
1248(6)
1792(5)
2609(5)
−444(5)
−4438(5)
58(2)
4(2)
598(2)
72(2)
4576(2)
4102(3)
4122(3
−385(3)
83(2)
448(2)
525(3)
233(3)
384(3)
1588(3)
2466(3)
4481(3)
584(3)
1012(2)
1993(2)
2379(2)
3060(2)
3229(2)
1410(2)
1181(2)
2199(2)
2166(3)

75
M.I. Saleh et al./Journal of Molecular Structure 415 (1997) 71–79
Table 3
Bond lengths (A), angles (Њ) and torsion angles (Њ) with e.s.d. in parentheses
˚
Atoms
X-ray
PM3
Atoms
X-ray
PM3
Atoms
X-ray
PM3
La–O(1)
La–O(2)
La–O(3)
La–O(4)
La–N(1)
La–N(2)
La–N(3)
La–N(4)
2.578(3)
–
–
–
–
–
–
–
–
–
–
–
–
N(1)–La–N(5)
N(1)–C(27)–S(1)
N(2)–LA–O(1)
N(2)–La–O(2)
N(2)–La–O(3)
N(2)–La–N(4)
N(2)–La–N(5)
N(2)–C(28)–S(2)
N(3)–C(29)–S(3)
N(3)–La–N(1)
N(3)–La–N(2)
N(3)–La–O(1)
N(3)–La–O(2)
N(3)–La–O(3)
N(3)–La–O(4)
N(3)–La–N(4)
N(3)–La–N(5)
N(4)–La–N(S)
N(4)–C(7)–C(6)
N(4)–C(8)–C(9)
N(4)–C(26)–C(25)
N(5)–C(13)–C(12)
N(5)–C(14)–C(15)
N(5)–C(21)–C(22)
O(1)–La–O(2)
O(1)–La–O(3)
O(1)–La–N(4)
O(1)–La–N(5)
O(1)–C(9)–C(8)
O(1)–C(10)–C(11)
O(2)–C(11)–C(10)
O(2)–C(12)–C(13)
O(2)–La–N(5)
O(3)–La–N(5)
O(3)–C(22)–C(21)
O(3)–C(23)–C(24)
O(2)–La–O(3)
O(2)–La–N(4)
O(3)–La–N(4)
O(4)–La–N(2)
O(4)–La–O(1)
O(4)–La–O(2)
O(4)–La–O(3)
O(4)–La–N(4)
O(4)–La–N(5)
O(4)–C(24)–C(23)
O(4)–C(25)–C(26)
C(1)–C(6)–C(7)
C(2)–C(3)–C(4)
C(2)–C(3)–C(1)
C(3)–C(4)–C(5)
C(5)–C(6)–C(1)
C(5)–C(6)–C(7)
C(6)–C(1)–C(2)
C(6)–C(5)–C(4)
79.0(1)
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
C(7)–N(4)–La
C(7)–N(4)–La
C(8)–N(4)–C(7)
C(8)–N(4)–C(26)
C(9)–O(1)–La
111.0(2)
107.1(2)
111.4(3)
108.9(3)
122.3(2)
111.3(3)
120.8(2)
113.6(3)
115.0(2)
114.5(2)
110.0(3)
109.5(2)
109.5(2)
121.8(5)
121.6(4)
120.4(5)
119.4(5)
120.5(5)
120.2(5)
120.6(4)
117.7(4)
107.4(2)
109.6(3)
110.7(3)
113.6(3)
119.5(2)
118.4(3)
116.1(3)
120.3(3)
121.1(2)
109.6(3)
108.8(2)
139.8(4)
166.7(4)
154.0(4)
−57.6(4)
−170.6(0)
−171.6(3)
54.9(3)
–
–
2.616(3)
2.645(3)
2.577(3)
2.548(4)
2.577(4)
2.519(4)
2.787(3)
2.814(3)
1.617(5)
1.620(5)
1.621(5)
1.440(5) 1.48
1.433(5) 1.45
1.427(5) 1.46
1.431(5) 1.48
1.420(5) 1.49
1.436(5) 1.47
1.433(5) 1.46
1.432(5) 1.48
178.6(4)
77.8(1)
70.5(1)
68.9(1)
110.1(1)
92.3(1)
178.3(5)
174.9(4)
78.4(1)
139.8(1)
134.4(1)
139.8(1)
74.3(1)
74.5(1)
76.4(1)
85.4(1)
157.5(1)
115.01
113.83
–
116.21
–
115.03
–
–
C(10)–O(1)–C(9)
C(10)–O(1)–La
C(11)–O(2)–C(12)
C(11)–O(2)–La
C(12)–O(2)–La
C(13)–N(5)–C(14)
C(13)–N(5)–La
C(14)–N(5)–La
C(15)–C(20)–C(19)
C(16)–C(15)–C(14)
C(17)–C(16)–C(15)
C(17)–C(18)–C(19)
C(18)–C(17)–C(16)
La–N(5)
S(1)–C(27)
S(2)–C(28)
S(3)–C(29)
O(1)–C(9)
O(1)–C(10)
O(2)–C(11)
O(2)–C(12)
O(3)–C(22)
O(3)–C(23)
O(4)–C(24)
O(4)–C(25)
N(1)–C(27)
N(2)–C(28)
N(3)–C(29)
N(4)–C(7)
N(4)–C(8)
N(4)–C(26)
N(5)–C(13)
N(5)–C(14)
N(5)–C(21)
C(1)–C(2)
111.6
–
–
122.77
123.14
122.65
120.01
119.58
119.44
122.83
115.63
–
111.6
113.64
112.76
–
115.8(3) 129.86 C(18)–C(19)–C(20)
113.8(3) 118.75 C(20)–C(15)–C(14)
113.5(4) 117.55 C(20)–C(15)–C(16)
112.9(3) 117.55 C(21)–N(5)–La
116.4(3) 131.08 C(21)–N(5)–C(13)
113.5(3) 119.18 C(21)–N(5)–C(14)
62.3(8)
146.2(9)
63.9(9)
1.151(6)
1.150(6)
1.148(6)
–
–
–
1.503(5) 1.56
1.480(5) 1.51
1.479(5) 1.53
1.480(5) 1.53
1.507(5) 1.57
1.480(5) 1.51
1.396(7) 1.41
1.391(6) 1.43
1.351(9) 1.41
1.364(9) 1.40
1.393(7) 1.41
1.379(7) 1.42
1.515(6) 1.62
1.495(6) 1.56
1.503(6) 1.56
1.511(6) 1.55
1.512(6) 1.63
1.397(6) 1.42
1.374(6) 1.43
1.392(7) 1.41
1.373(8) 1.40
1.374(8) 1.41
1.381(7) 1.41
1.492(6) 1.56
1.490(7) 1.56
1.487(6) 1.57
–
–
–
–
C(22)–O(3)–C(23)
C(22)–O(3)–La
C(23)–O(3)–La
C(24)–O(4)–C(25)
–
125.5(9)
120.09
–
–
116.86
–
–
107.3(3) 114.09 C(24)–O(4)–La
107.9(3) 115.71 C(25)–O(4)–La
107.6(3) 116.31 C(26)–N(4)–C(7)
106.7(3) 113.76 C(26)–N(4)–La
63.9(9)
63.4(9)
C(1)–C(6)
C(2)–C(3)
C(3)–C(4)
C(4)–C(5)
C(5)–C(6)
C(6)–C(7)
C(8)–C(9)
–
–
C(27)–N(1)–La
C(28)–N(2)–La
–
–
107.4(3) 118.64 C(29)–N(3)–La
108.0(4) 119.13 N(4)–C(8)–C(9)–O(1)
99.55
128.31
−178.84
−76.04
167.95
174.24
156.45
−91.64
70.29
−97.71
−175.47
172.17
62.19
122.73
136.98
142.70
−44.53
−59.18
109.8(9)
124.5(9)
122.2(9)
73.9(1)
104.4(1)
143.13(1)
61.2(9)
–
–
–
–
–
–
–
–
–
–
–
C(8)–C(9)–O(1)–C(11)
C(9)–O(1)–C(10)–C(11)
O(1)–C(10)–C(11)–O(2)
C(10)–C(11)–O(2)–C(12)
C(10)–C(11)
C(12)–C(13)
C(14)–C(15)
C(15)–C(16)
C(15)–C(20)
C(16)–C(17)
C(17)–C(18)
C(18)–C(19)
C(19)–C(20)
C(21)–C(22)
C(23)–C(24)
C(25)–C(26)
N(1)–La–O(1)
N(1)–La–O(2)
N(1)–La–O(3)
N(1)–La–O(4)
N(1)–La–N(2)
N(1)–La–N(4)
172.5(5)
C(11)–O(2)–C(12)–C(13) −163.3(5)
O(2)–C(12)–C(13)–N(5)
C(12)–C(13)–N(5)–C(21)
C(13)–N(5)–C(21)–C(22)
N(5)–C(21)–C(22)–O(3)
C(21)–C(22)–O(3)–C(23) −169.2(6)
C(22)–O(3)–C(23)–C(24) −170.8(5)
−63.0(3)
−82.0(0)
167.1(5)
−62.2(2)
63.5(9)
124.3(9)
106.6(4)
106.8(4)
120.7(4) 121.42 O(3)–C(23)–C(24)–O(4)
120.7(5) 120.00 C(23)–C(24)–O(4)–C(25)
120.7(5) 119.48 C(24)–O(4)–C(25)–C(26) −153.3(5)
119.4(6) 119.60 O(4)–C(25)–C(26)–N(4)
118.5(4) 115.63 C(25)–C(26)–N(4)–C(8)
120.8(4) 122.83 C(26)–N(4)–C(8)–C(9)
119.6(5) 122.71
54.6(0)
150.4(1)
76.5(1)
71.1(1)
134.7(1)
141.9(1)
140.5(1)
84.4(1)
–
–
–
–
–
–
−58.8(3)
−71.9(1)
167.0(9)
121.0(5) 122.57

76
M.I. Saleh et al./Journal of Molecular Structure 415 (1997) 71–79
Table 4
2
3
2
2
2
˚
Anisotropic displacement parameters (A × 10 ). The anisotropic displacement factor exponent takes the form: −2p [h a* U11 + … + 2hka*
b*U12]
U11
U22
U33
U23
0(1)
U13
0(1)
U12
2(1)
La
S(1)
S(2)
S(3)
33(1)
48(1)
50(1)
86(1)
47(2)
51(2)
42(2)
38(2)
46(2)
52(2)
72(3)
40(2)
38(2)
54(3)
65(3)
71(4)
55(3)
51(3)
44(2)
48(2)
50(2)
46(2)
56(3)
61(3)
54(3)
51(3)
45(2)
44(2)
57(3)
83(4)
77(4)
53(3)
47(3)
40(2)
36(2)
40(2)
34(2)
48(3)
53(3)
48(3)
41(2)
53(3)
32(1)
72(1)
70(1)
43(1)
35(2)
37(2)
49(2)
78(2)
57(3)
46(2)
50(3)
41(2)
36(2)
58(3)
92(4)
111(6)
86(4)
59(3)
46(2)
44(2)
40(2)
40(2)
44(2)
37(2)
50(3)
45(3)
39(2)
35(2)
49(3)
58(3)
52(3)
39(3)
39(2)
42(2)
45(2)
69(3)
75(4)
68(3)
56(3)
47(2)
44(2)
44(3)
30(1)
89(1)
74(1)
147(2)
38(2)
36(2)
41(2)
37(2)
47(2)
84(3)
56(3)
31(2)
33(2)
51(3)
49(3)
41(3)
62(3)
50(3)
37(2)
36(2)
38(2)
48(3)
48(3)
47(3)
31(2)
34(2)
42(2)
39(2)
53(3)
50(3)
53(3)
69(3)
52(3)
42(2)
51(3)
52(3)
44(3)
41(2)
33(2)
34(2)
45(2)
39(2)
−11(1)
5(1)
−21(1)
0(1)
−7(1)
3(1)
11(2)
2(2)
−2(1)
−9(1)
8(1)
−2(1)
4(1)
6(1)
4(1)
4(2)
1(2)
1(1)
−14(1)
3(1)
10(1)
6(1)
13(1)
−2(2)
−7(2)
−3(2)
5(2)
O(1)
O(2)
O(3)
O(4)
N(1)
N(2)
N(3)
N(4)
N(5)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
C(9)
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
C(17)
C(18)
C(19)
C(20)
C(21)
C(22)
C(23)
C(24)
C(25)
C(26)
C(27)
C(28)
C(29)
−8(2)
−7(2)
2(2)
−1(2)
0(1)
0(2)
1(2)
−2(1)
1(2)
9(3)
4(2)
−9(2)
−24(3)
9(3)
20(3)
4(2)
2(2)
3(2)
6(2)
3(2)
−6(2)
−9(2)
−7(2)
2(2)
−9(2)
−21(3)
−22(4)
−3(3)
−6(2)
−11(2)
−7(2)
−2(2)
8(2)
−9(3)
−18(3)
−11(2)
−2(2)
−2(2)
−3(2)
−10(2)
−2(2)
−5(2)
−5(2)
4(2)
14(2)
9(2)
6(2)
6(2)
−1(2)
−1(2)
4(2)
−3(2)
−8(2)
5(2)
−3(2)
−3(2)
9(2)
15(3)
−9(3)
−10(2)
0(2)
−3(2)
−5(2)
−1(2)
2(3)
16(3)
−5(2)
0(2)
0(2)
2(2)
6(2)
−11(3)
2(2)
−5(2)
−3(2)
10(2)
8(2)
3(2)
7(2)
9(2)
2(2)
8(2)
3(2)
9(2)
3(2)
−1(2)
5(2)
−3(2)
−1(2)
−7(2)
5(2)
4(2)
1(2)
−13(2)
3(2)
−6(2)
The lanthanum thiocyanate salt exists as an isolated
(individual) entity in the centre of the hole of the
macrocycle. The three thiocyanate N atoms surround
the La cation in a near planar trigonal arrangement
with the La ion being slightly out-of-plane (sum of
358.74Њ for the N–La–N angle around La) and with
unequally distributed N–La–N bond angles. The
trigonal plane is perpendicular to and bisects the
plane of macrocycle indicating the presence of a C2
symmetry. The bonding around La is made up of
primary coordination of the three thiocyanate N
atoms and secondary coordination of the two N
atoms and four O atoms of the macrocycle to
give La a distorted nanohedral environment. The

77
M.I. Saleh et al./Journal of Molecular Structure 415 (1997) 71–79
Table 5
4
2
Hydrogen coordinates ( × 10 ) and isotropic displacement parameters (A × 103)
˚
x
y
z
U(eq)
H(1)
H(2)
H(3)
H(4)
3743(3)
4358(4)
5249(4)
5588(3)
5011(3)
3722(3)
4297(3)
2769(3)
3653(3)
4308(3)
3859(3)
3643(3)
4080(3)
3096(3)
2358(3)
1574(3)
2358(3)
2814(3)
1893(3)
2901(3)
2093(3)
3066(3)
2739(4)
1582(4)
753(3)
4029(6)
3866(2)
4861(3)
5130(3)
4416(3)
3413(2)
2803(2)
2608(2)
2780(2)
3138(2)
2222(2)
2247(2)
1212(2)
1062(2)
245(2)
692(2)
105(2)
−305(2)
−29(2)
−368(2)
654(2)
65
82
90
83
65
51
51
51
51
55
55
60
60
58
58
55
55
52
52
51
51
63
76
73
65
56
50
50
53
53
64
64
61
90
63
63
57
57
3825(7)
2034(8)
427(7)
H(5)
626(6)
H(7A)
H(7B)
H(8A)
H(8B)
H(9A)
H(9B)
H(10A)
H(10B)
H(11A)
H(11B)
H(12A)
H(12B)
H(13A)
H(13B)
H(14A)
H(14B)
H(16)
3350(5)
2125(5)
−494(5)
−173(5)
38(5)
−1417(5)
−1669(5)
−255(5)
−791(5)
−974(5)
1081(5)
924(5)
3177(4)
3208(4)
4957(5)
5481(5)
−539(5)
−2082(6)
−3552(5)
8493(5)
6944(4)
2849(5)
4400(5)
5059(5)
4255(5)
3382(6)
4106(6)
228(6)
968(2)
4562(2)
3770(3)
3804(3)
−366(3)
414(2)
317(2)
125(2)
1154(2)
927(2)
1871(2)
2223(2)
2761(2)
2166(2)
3011(2)
3376(2)
3293(2)
3612(2)
H(17)
H(18)
H(19)
H(20)
1061(3)
708(3)
783(3)
750(3)
−92(3)
−375(3)
419(3)
112(3)
H(21A)
H(21B)
H(22A)
H(22B)
H(23A)
H(23B)
H(24A)
H(24B)
H(25A)
H(25B)
H(26A)
H(26B)
148(3)
1222(6)
253(6)
1468(6)
2781(5)
1376(5)
1605(3)
1205(3)
2430(3)
2683(3)
macro-ring donor atoms adopt a twist-boat conforma-
tion encapsulating the La ion. The primary bond dis-
tances for La–N range from 2.519 to 2.577 A while
Similar observations have been made for primary and
secondary bond distances for similar complexes such
as lanthanum nitrate with the tetraoxadiaza macro-
cycle[9]. The size of the hole of the macrocycle as
measured across the opposite-facing O1 and O3 atoms
˚
the secondary La–N bond distances are considerably
˚
longer, ranging from 2.787 to 2.814 A. The secondary
˚
˚
˚
La–O bond distances range from 2.577 to 2.645 A and
is 4.997 A, for O2 and O4 atoms it is 4.937 A while
˚
are much longer compared with primary bonds found
that across the opposite facing N atoms is 5.494 A.
˚
in lanthanum oxyhalides (average 2.40 A). These
The benzyl side-arms of the diazacrown are in syn
conformation with respect to the macrocyclic plane,
with the benzylic C atom in each side-arm occupying
a flag-pole position and with the phenyl groups
longer secondary bond distances reflect the weaker
electronic interactions between the La(NCS) moiety
and the macrocycle arising from steric requirements.

78
M.I. Saleh et al./Journal of Molecular Structure 415 (1997) 71–79
Fig. 3. Unit-cell packing diagram of La(NCS)3.C26H28N2O4 viewed along the Y-axis.
pointing away from the cavity and not participating in
bonding to the La as expected. The thiocyanate ions
are bent with the La–N–C bond angles ranging from
139.8 to 166.7Њ. One of the La–NCS bonds is posi-
tioned above the macrocyclic plane while the other
two are below and lie in the same direction as the
two benzyl substituents.
atoms point inwards of the cavity while O2 and O3
point outwards with the N atoms lying above and
below this plane to give a chair conformation for the
hetero atoms of the macrocycle. Each of the benzyl
side-arms attached to the macrocycle is in an
equatorial position relative to the mean plane of the
macrocycle, and is situated away from the hole, as is
expected in the absence of complexation to a cation.
The hole size changes upon coordination to La with
The torsion angles observed in the complexed
macrocyclic ring are nearly equally distributed
between gauche and anti conformations with the
˚
the O2 to O4 distance shortening from 5.1 to 4.9 A
following
sequence
g− aag+ aag− g− ag− aag+
and the O1 to O3 distance lengthening from 4.7 to
aag−g−a observed (gauche is equivalent to synclinal
at approximately 60Њ(g+) or −60Њ(g−); anti (a) is
equivalent to antiperiplanar, at approximately 180Њ
[16]).
5.0 A. However the N4 to N5 distance shortens
˚
˚
significantly from 9.7 to 5.5 A upon coordination.
These changes reflect the very flexible nature of the
macrocycle that enables the macrocycle to curl around
La, thereby changing the cavity size considerably
upon coordination. Such a structure is similar to the
coordination mode and conformations of other
The selected geometrical properties of the
dibenzyldiazacrown (molecule 2) in the free state
obtained from the semi-empirical PM3 calculation
are tabulated in Table 3 and the skeletal structures
are shown in Figs. 4a and 4b. The optimisation
shows that the free ligand is splayed open and the
cavity is elongated with a long-hole distance across
the opposite-facing N atoms but shorter distances
across the opposite facing O atoms. The free state
diazacrown adopts a pseudo D2d symmetry because
of the elongation and differs from other diaza-18-
crown-6 ligands that adopt the more symmetrical
D3d symmetry[17]. It appears that this elongation is
the most favoured conformation energetically for the
heteroatomic macrocycle with dibenzyl side-arms.
Lying approximately in a plane, the O1 and O4
Fig. 4. Views of the skeletal structure of dibenzyldiaza-18-crown-6.
(a) top view; (b) side view.

79
M.I. Saleh et al./Journal of Molecular Structure 415 (1997) 71–79
lanthanide 18-crown-6 ligands where the perfect
cavity-size–metal-ion-size fit is not realised thereby
causing the 18-crown-6 to fold around the metal
ion[7]. The PM3 calculation also shows changes in
the torsion angles for the free macrocycle which
now adopts the g+ aag+ aaa g− g+ g− aag+aaag−g−
sequence that is different from the coordinated
macrocycle above.
indebted to Chemistry Department, University of
Libya, Sheba, Libya, for financial support.
References
[1] I. Goldberg, Complexes of crown ethers with molecular
guests, in: J.L. Atwood, J.E.D. Davies, D.D. MacNicol
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London, 1984, p. 261.
[2] S. Tsurubou, M. Mitzutani, Y. Kadota, T. Yamamoto, S.
Umetani, T. Sasaki, Q.T.H. Le, M. Matsui, Anal. Chem. 67
(1995) 1465.
4. Conclusion
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[6] D. Bright, M.R. Truter, Nature 225 (1970) 176.
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Nonius CAD-4 User’s Manual, Version 5.0, Enraf–Nonius,
The Netherlands.
The X-ray determination shows the three-
dimensional configuration of complex 1. The bond
distances and bond angles observed are typical for
similar complexes. The PM3-calculated bond dis-
tances of the free diazacrown are in agreement with
the X-ray-generated bond distances for the complexed
diazacrown but the bond angles and the torsion angles
differ, reflecting the open structure of the free diaza-
crown compared with the highly constrained structure
of the ligating atoms encircling the lanthanum ion.
The cavity size of the azacrown changes minimally
across the opposite-facing oxygen atoms but
decreases markedly across nitrogen upon coordi-
nation, demonstrating the highly flexible nature of
the diazacrown.
[12] G.M. Sheldrik, Acta Crystallogr. A46 (1990) 467-473.
[13] J.J.P. Stewart, J. Comput. Chem. 10 (1989) 221.
[14] J.J.P. Stewart, mopac 6.0 Manual.
[15] Insight II User Guide, Oct. 1995, San Diego: Biosym MSI, 1995.
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[17] A.N. Chekov, A.I. Yurtanov, I.V. Martynov, Dokl. Akad.
Nauk SSSR 320 (1991) 733.
Acknowledgements
This work is financed by the Malaysian Govern-
ment under IRPA grant no. 190/9609/3403. A.S. is