Synthesis, characterization and crystal structure of a phenol-functionalized diazamesocyclic derivative with unexpected configuration

Article abstract of DOI:10.1016/S0022-2860(02)00711-1

A bis-substituent diazamesocyclic compound containing bulky phenolic donor pendants, 1,4-bis(3-tert-butyl-5-methyl-2-hydroxybenzyl)-1,4-diazacycloheptane, has been prepared from 1,4-diazacycloheptane (DACH) and 2-tert-butyl-4-methylphenol by the Mannich reaction, and structurally characterized by NMR, IR and X-ray diffraction techniques. The crystal structure of the title compound reveals that 1,4-diazacycloheptane (DACH) ring is folded up into unusual chair configuration, and the two phenol pendants of the compound are in unexpected trans positions, which is different from those in the transition metal complexes of DACH and its derivatives. There exist intra-molecular O-H···N hydrogen bonds between the phenolic O atoms and the DACH N donors which stabilize the crystal structure.

Full text of DOI:10.1016/S0022-2860(02)00711-1

Journal of Molecular Structure 646 (2003) 191–196
www.elsevier.com/locate/molstruc
Synthesis, characterization and crystal structure
of a Phenol-functionalized diazamesocyclic derivative with
unexpected configuration
a
Ya-Mei Guo , Miao Du , Xian-He Bu
b
b,*
a
Department of Chemistry, Tianjin University, Tianjin 300072, People’s Republic of China
b
Department of Chemistry, Nankai University, Tianjin 300071, People’s Republic of China
Received 1 September 2002; accepted 25 November 2002
Abstract
A bis-substituent diazamesocyclic compound containing bulky phenolic donor pendants, 1,4-bis(3-tert-butyl-5-methyl-2-
hydroxybenzyl)-1,4-diazacycloheptane, has been prepared from 1,4-diazacycloheptane (DACH) and 2-tert-butyl-4-
methylphenol by the Mannich reaction, and structurally characterized by NMR, IR and X-ray diffraction techniques. The
crystal structure of the title compound reveals that 1,4-diazacycloheptane (DACH) ring is folded up into unusual chair
configuration, and the two phenol pendants of the compound are in unexpected trans positions, which is different from those in
the transition metal complexes of DACH and its derivatives. There exist intra-molecular O–H· · ·N hydrogen bonds between the
phenolic O atoms and the DACH N donors which stabilize the crystal structure.
q 2003 Elsevier Science B.V. All rights reserved.
Keywords: Synthesis; Crystal structure; 1,4-Diazacycloheptane; Configuration
1
. Introduction
the interesting ‘boat/chair’ configuration in their
transition metal complexes, in which the hydrogen
atoms of the trimethylene of DACO could effectively
block the sixth-coordination to the metal centre to
form penta-coordination complexes [7,8]. Recently,
we have demonstrated that the configuration of
DACO ring in its diprotonated salt [H2-
Diazamesocyclic ligands occupy an important role
in the coordination chemistry between acyclic and
macrocyclic polyamine ligands due to their unique
conformational feature [1–3] and the potential for
further fuctionalization [4–6]. 1,5-Diazacyclooctane
(
DACO) and 1,4-Diazacycloheptane (DACH) are the
DACO]Br·ClO [9] and its imidazole-functionalized
4
most typical examples of such diazamesocyclic
compounds. DACO and its derivatives usually exhibit
derivative (the two imidazole pendants are in cis
positions) [10] is also ‘boat/chair’, which is consistent
with those in their metal complexes.
*
Corresponding author. Tel.: þ86-22-235-02809; fax: þ86-22-
However, relative to the special attention on
DACO, studies on DACH are still rare and it always
2
35-30850.
E-mail address: buxh@nankai.edu.cn (X.-H. Bu).
0022-2860/03/$ - see front matter q 2003 Elsevier Science B.V. All rights reserved.
PII: S0022-2860(02)00711-1

192
Y.-M. Guo et al. / Journal of Molecular Structure 646 (2003) 191–196
takes the boat configuration in its metal complexes
3,11,12]. In our efforts to systematically investigate
1.40(s, 18H), 1.85(m, 2H), 2.23(s, 6H), 2.75(m, 4H),
2.80(s, 4H), 3.73(s, 4H), 6.64(s, 2H), 6.99(s, 2H).
[
2
1
the structures and properties as well as the
coordination chemistry of diazamesocyclic ligands
by modification of their backbone [6–16], we found
that the study of structure and configuration on
DACH derivatives in uncoordinated solid state is
FT-IR (KBr pellet, cm ): 3431b, 2954vs, 2915s,
2870s, 1608w, 1462s, 1435vs, 1389m, 1302w,
1239s, 1147m, 864m, 774m.
still unexplored. As
work, we report herein the synthesis and crystal
structure of tetradentate DACH ligand
a
continuation of our
2.3. Crystallographic data collection and structure
determination
a
containing bulky phenolic donor pendants,
namely 1,4-bis(3-tert-butyl-5-methyl-2-hydroxyben-
zyl)-1,4-diazacycloheptane.
A block crystal with approximate dimensions of
0
.35 £ 0.25 £ 0.15 mm was mounted on a BRU-
KER SMART 1000 CCD diffractometer equipped
with a graphite monochromator for data collection.
The determination of unit cell parameters (17514
reflections with least-squares refinement) and
data collections were performed with Mo Ka
2
. Experimental
2
.1. Materials and general methods
All reagents for syntheses and analyses are of
analytical grade and used as received. FT-IR spectra
˚
radiation (l ¼ 0.71073 A). A total of 14668
independent reflections were collected in the
range of 1.87 , u , 25.038 with Rint ¼ 0.0395 by
v scan mode at 298(2) K. All data were corrected
by semi-empirical method using SADABS program.
The program SAINT [17] was used for integration
of the diffraction profiles.
(
(
KBr pellets) were taken on a FT-IR 170SX
Nicolet) spectrometer, and melting point was
obtained without correction. Carbon, hydrogen and
nitrogen analyses were performed on a Perkin–
1
Elmer 240C analyser. H NMR spectra were
measured on a Bruker AC-P 400 spectrometer
The structure was solved by direct methods using
SHELXS program of the SHELXL-97 package and
refined with SHELXL [18]. All the non-hydrogen
atoms were located in successive difference Fourier
syntheses. The final refinement was performed by
full matrix least-squares methods with anisotropic
(400 MHz) at room temperature with TMS as the
internal reference.
2
.2. Synthesis of the title compound
2
thermal parameters for non-hydrogen atoms on F .
The hydrogen atoms were added theoretically,
riding on the concerned atoms and refined
with fixed thermal factors. The weighting
Paraformaldehyde (0.70 g, 23 mmol) was added
to a solution of 1,4-diazacycloheptane (1.00 g,
0 mmol) in methanol (40 ml). After heating the
1
2
1
2
2
2
scheme was W ¼ s (Fo ) þ (0.0398P) , where
solution to reflux for ca. 1 h, 2-tert-butyl-4-methyl-
phenol (3.45 g, 21 mmol) was added and heating at
reflux for ca. 24 h. Then the solvent was removed by
rotary evaporation, and the residue was dissolved in
anhydrous ethanol. White crystalline solids were
precipitated from this solution after standing at room
temperature. Well-shaped colourless single crystals
of the title compound suitable for X-ray diffraction
were obtained by slow diffusion of CH OH/CH Cl
2
2
2
P ¼ (Fo þ 2Fc )/3. The refinement converged to
final R ¼ 0.0569, wR ¼ 0.0884, S ¼ 1.010, (D/
s)
and minimum residual peaks are 0.245
¼ 0.002 and (D/s) ¼ 0.000. The maximum
max
min
3
and 2 0.240 e/A , respectively. Molecular graphics
˚
were drawn with the program package XP. Further
crystallographic data and experimental details for
structural analyses are summarized in Table 1.
Positional parameters and atomic coordinates are
listed in Table 2, and selected bond lengths and
angles with their estimated standard deviations in
Table 3.
3
2
solution of the above solids at room temperature.
Yield: 2.38 g (50%). mp: 126–128 8C. Found: C,
7
7
6.77; H, 9.78; N, 6.15. Calc. for C H N O : C,
29 44 2 2
1
6.94; H, 9.80; N, 6.19%. H NMR (CDCl , d):
3

Y.-M. Guo et al. / Journal of Molecular Structure 646 (2003) 191–196
193
Table 1
Table 2
4
Crystallographic data and structure refinement summary for the title
compound
Atomic coordinates ( £ 10 ) and equivalent isotropic displacement
2
3
˚
parameters (A £ 10 )
Formula
C
87
H
132
N
6
O
6
Atom
x
y
z
U
eq
Mr
1357.99
Crystal size (mm)
Crystal system
Space group
˚
a (A)
˚
b (A)
0.15 £ 0.25 £ 0.35
Triclinic
P 2 1
N(1)
N(2)
4359(3)
4408(3)
6054(2)
2247(2)
3240(4)
3808(5)
4484(5)
5339(4)
4676(4)
3954(4)
3924(4)
5008(3)
5049(3)
3950(3)
2849(4)
2852(3)
6217(3)
7724(3)
6076(4)
6070(3)
1672(4)
4752(4)
4364(4)
3089(4)
2674(3)
3579(4)
4836(4)
5225(4)
1285(4)
214(4)
1331(4)
1084(4)
5733(4)
1105(3)
2590(3)
2113(2)
9068(2)
7727(2)
9335(1)
7735(1)
8257(2)
7504(3)
7272(3)
8607(3)
9215(2)
9780(2)
9762(2)
9572(2)
9601(2)
9835(2)
6021(1)
5185(1)
6910(1)
4520(1)
6012(1)
6027(2)
5624(2)
5292(1)
5521(1)
6247(1)
6801(1)
7116(1)
7632(1)
7812(1)
7513(2)
7006(2)
7978(1)
7930(1)
7846(1)
8526(1)
7737(1)
4758(1)
4266(1)
4156(1)
3694(1)
3351(1)
3441(1)
3905(1)
3576(1)
3601(1)
3944(1)
3054(1)
3036(1)
8019(1)
7168(1)
8629(1)
6348(1)
7569(1)
7179(1)
7184(1)
7669(1)
7945(1)
8460(1)
8948(1)
9015(1)
9460(1)
9834(1)
9784(2)
9330(2)
9541(2)
9453(2)
9162(2)
65(1)
73(1)
74(1)
76(1)
86(1)
108(2)
127(2)
86(1)
77(1)
76(1)
58(1)
55(1)
54(1)
60(1)
63(1)
65(1)
59(1)
92(1)
90(1)
82(1)
94(1)
90(1)
63(1)
57(1)
55(1)
68(1)
67(1)
69(1)
70(1)
102(1)
100(1)
108(1)
101(1)
57(1)
55(1)
77(1)
72(1)
89(1)
85(1)
71(1)
62(1)
65(1)
70(1)
60(1)
59(1)
65(1)
78(1)
77(1)
71(1)
85(1)
126(2)
107(1)
O(1)
O(2)
9.8502(16)
16.526(3)
27.243(5)
94.371(4)
98.420(4)
106.412(4)
4175.7(12)
2
C(1)
C(2)
˚
c (A)
a (8)
b (8)
g (8)
C(3)
C(4)
C(5)
C(6)
3
˚
V (A )
C(7)
C(8)
Z
2
3
D
calc (g cm
)
1.080
2
1
C(9)
m (cm
F(000)
)
0.67
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)
N(3)
1488
10028(2)
9980(2)
9373(2)
9931(2)
8432(2)
9505(2)
10261(2)
7264(2)
7581(2)
7785(2)
8042(2)
8031(2)
7820(2)
7603(2)
8275(2)
7515(2)
9037(2)
8554(2)
7786(2)
6837(2)
7405(2)
8212(1)
6313(1)
6492(2)
7088(3)
7751(2)
7370(2)
6712(2)
6443(2)
6887(3)
7767(3)
8188(3)
7678(3)
6810(3)
6422(2)
9144(3)
9629(2)
9367(2)
Range of h,k,l
211/11, 212/19, 232/32
17568
Total reflections
Independent reflections
Parameters
14668
893
R indices (I . 2sðIÞ)
0.0569, 0.0884
3
. Results and discussion
3
.1. Synthesis and general characterization
The doubly substituted compound was produced
by the reaction of paraformaldehyde, DACH and
-tert-butyl-4-methylphenol in methanol through the
2
Mannich reaction in satisfactory yield as shown in
Scheme 1. The analytical and spectral data are in good
agreement with the theoretical requirements. In the IR
spectrum of the title compound, the bands in the
N(4)
O(3)
2
1
1400–1600 cm
vibrations of the aromatic rings. The broad band
region arise from the skeletal
O(4)
21797(2)
1517(4)
1729(4)
967(3)
2
1
C(30)
C(31)
C(32)
C(33)
C(34)
C(35)
C(36)
C(37)
C(38)
C(39)
C(40)
C(41)
C(42)
C(43)
C(44)
centred at ca. 3400 cm indicates the O–H stretch-
ing of the phenol group. The characteristic absorption
band with strong intensity of C–O stretching of
2928(3)
2457(3)
1571(3)
1420(3)
1716(3)
1570(3)
1198(3)
951(4)
2
1
phenol appears at 1239 cm , while the correspond-
ing values in its metal complexes shift to higher
2
1
frequencies (1260 ^ 10 cm ), suggesting the depro-
tonation of the phenolic group when chelated with the
metal ions [19].
1057(3)
1816(4)
3330(4)
677(4)
3
.2. Description of the crystal structure
The ORTEP structure of the title compound with
atom labelling is shown in Fig. 1. It should be noted
(
continued on next page)

194
Y.-M. Guo et al. / Journal of Molecular Structure 646 (2003) 191–196
Table 2 (continued)
Table 3
˚
Selected bond lengths (A) and angles (8) for the title compound
Atom
x
y
z
U
eq
Bond lengths
C(45)
C(46)
C(47)
C(48)
C(49)
C(50)
C(51)
C(52)
C(53)
C(54)
C(55)
C(56)
C(57)
C(58)
N(5)
1646(5)
589(4)
9464(3)
6299(3)
7911(2)
7807(2)
7006(2)
6875(2)
7606(3)
8416(3)
8503(2)
5996(2)
5580(2)
6028(3)
5438(2)
9173(2)
7141(2)
5590(2)
7313(1)
5322(1)
7405(2)
7098(2)
6271(2)
5570(2)
6303(2)
7774(2)
7637(2)
7432(2)
7341(2)
7488(2)
7707(2)
7766(2)
7106(2)
6248(2)
7800(2)
7024(2)
7878(2)
4766(2)
4709(2)
4967(2)
4863(2)
4522(2)
4290(2)
4389(2)
5113(2)
6072(2)
4658(2)
4883(2)
3945(2)
10060(2)
10214(1)
6882(1)
6338(1)
6086(1)
5582(1)
5346(1)
5582(2)
6079(1)
5309(1)
5556(1)
4756(1)
5315(2)
5295(1)
9641(1)
8988(1)
10486(1)
8079(1)
9144(1)
8906(1)
9032(1)
9468(1)
9603(1)
9948(1)
10494(1)
10739(1)
11254(1)
11490(1)
11262(1)
10757(1)
11530(1)
11294(1)
11513(1)
12078(1)
11548(1)
8811(1)
8275(1)
7913(1)
7407(1)
7284(1)
7635(2)
8125(1)
7007(1)
7087(1)
7029(1)
6474(1)
7471(1)
135(2)
115(2)
64(1)
53(1)
55(1)
58(1)
68(1)
70(1)
66(1)
75(1)
111(1)
110(1)
114(2)
110(2)
63(1)
55(1)
72(1)
66(1)
92(1)
86(1)
70(1)
69(1)
72(1)
79(1)
59(1)
55(1)
51(1)
54(1)
59(1)
67(1)
55(1)
74(1)
84(1)
80(1)
85(1)
67(1)
56(1)
52(1)
52(1)
64(1)
64(1)
65(1)
60(1)
80(1)
81(1)
93(1)
100(1)
N(1)–C(5)
N(1)–C(1)
N(2)–C(4)
O(1)–C(8)
C(1)–C(2)
1.465(4) N(1)–C(6)
1.472(4) N(2)–C(3)
1.464(4) N(2)–C(18)
1.375(3) O(2)–C(20)
1.502(4) C(2)–C(3)
1.491(4) N(3)–C(30)
1.475(3) N(3)–C(35)
1.453(3) N(4)–C(32)
1.471(3) O(3)–C(37)
1.379(3) C(30)–C(31)
1.493(4) C(33)–C(34)
1.451(4) N(5)–C(59)
1.485(4) N(6)–C(61)
1.468(4) N(6)–C(62)
1.374(3) O(6)–C(78)
1.501(4) C(60)–C(61)
1.509(4)
1.466(4)
1.464(4)
1.476(4)
1.375(3)
1.446(5)
1.472(4)
1.484(3)
1.470(3)
1.368(3)
1.499(4)
1.507(4)
1.472(3)
1.465(3)
1.474(3)
1.380(3)
1.483(4)
21359(3)
21239(3)
21484(3)
21372(3)
21029(3)
2774(4)
2891(3)
21626(4)
2537(4)
21468(4)
23155(4)
2379(4)
5922(3)
5977(3)
7801(2)
4461(2)
6083(4)
7158(4)
7332(3)
5455(3)
4895(3)
5484(4)
5579(4)
6751(3)
6899(3)
5826(3)
4658(3)
4550(3)
8165(3)
8227(3)
9561(3)
8042(3)
3557(3)
6138(3)
6341(3)
5448(3)
5517(3)
6579(3)
7528(4)
7380(3)
4511(3)
4779(3)
2934(3)
4744(4)
8691(4)
C(4)–C(5)
N(3)–C(34)
N(4)–C(33)
N(4)–C(47)
O(4)–C(49)
C(31)–C(32)
N(5)–C(63)
N(5)–C(64)
N(6)–C(76)
O(5)–C(66)
C(59)–C(60)
C(62)–C(63)
N(6)
O(5)
O(6)
C(59)
C(60)
C(61)
C(62)
C(63)
C(64)
C(65)
C(66)
C(67)
C(68)
C(69)
C(70)
C(71)
C(72)
C(73)
C(74)
C(75)
C(76)
C(77)
C(78)
C(79)
C(80)
C(81)
C(82)
C(83)
C(84)
C(85)
C(86)
C(87)
Bond angles
C(5)–N(1)–C(1)
N(1)–C(6)–C(7)
111.8(3)
113.1(3)
C(3)–N(2)–C(4)
111.7(3)
N(2)–C(18)–C(19) 112.9(3)
C(33)–N(4)–C(32) 111.1(2)
N(4)–C(47)–C(48) 110.9(3)
C(61)–N(6)–C(62) 110.2(3)
N(6)–C(76)–C(77) 112.3(3)
C(30)–N(3)–C(34) 110.9(3)
N(3)–C(35)–C(36) 112.5(3)
C(63)–N(5)–C(59) 111.2(3)
N(5)–C(64)–C(65) 113.3(3)
The title compound consists of a DACH ring
substituted with two 3-tert-butyl-5-methyl-2-hydro-
xybenzyl groups on the N donors. The mesocyclic
ring DACH is folded up into unusual chair configur-
ation, and the folding angles in three independent
molecules are 111.8(3) vs. 111.7(3)8 for C(5)–N(1)–
C(1) and C(3)–N(2)–C(4), 110.9(3) vs. 111.1(2)8 for
C(30)–N(3)–C(34) and C(33)–N(4)–C(32), and
111.2(3) vs. 110.2(3)8 for C(63)–N(5)–C(59) and
C(61)–N(6)–C(62), respectively. This is remarkably
different from the reported results of the configuration
of DACH ring in most of the metal complexes with
DACH and its derivatives, even for the metal
complexes with the title compound [19], in which
the DACH ring always displays the normal boat
configuration [3,11,12,15]. It is rather interesting that
the two phenol pendant arms depart from the parent
DACH ring in unexpected trans-position with the
joint angles of 113.1(3) vs. 112.9(3)8 for N(1)–C(6)–
C(7) and N(2)–C(18)–C(19), 112.5(3) vs. 110.9(3)8
for N(3)–C(35)–C(36) and N(4)–C(47)–C(48),
113.3(3) vs. 112.3(3)8 for N(5)–C(64)–C(65) and
that three similar but different crystallographically
independent neutral molecules were found to exist in
the crystal structure of this compound. They have
similar DACH configurations and phenol-pendants
arrangements but only slight differences in bond
distances and angles.

Y.-M. Guo et al. / Journal of Molecular Structure 646 (2003) 191–196
195
Scheme 1.
N(6)–C(76)–C(77) in three subunits, respectively. To
the best of our knowledge, for all the bis-substituted
functionalised DACH or DACO dervatives and their
metal complexes the two pendent arms have the cis-
arrangements. That is, the most stabilized configur-
ation of the title compound in solid state is the DACH
backbone in the unusual chair form and the two
phenol pendants in unexpected trans-arrangement,
and the configuration of the DACH ring spon-
taneously converted into the normal boat form and
the two side-arms to the cis-positions when chelated
to the metal centres. The dihedral angle between the
two planes of the phenyl rings is 13.68, 5.58 and 11.28
for three independent molecules. Two nitrogen atoms
of the parent DACH ring and two oxygen donors of
the pendant arms form a pseudo-torsion angle of
intra-molecular O–H· · ·N hydrogen bonds between
the phenolic O atoms and the DACH N donors, which
may further stabilize the crystal structure. The O· · ·N
˚
separations are in 2.657–2.676 A range with the
˚
H· · ·N separations ranging of 1.968–2.013 A, respect-
ively, and the bond angles are from 135.08 to 142.18,
all being normal weak hydrogen bond interactions
[20]. Further studies on the structure and configur-
ation of other DACH derivatives are under way in our
laboratory.
4. Supplementary materials
Crystallographic data for the structure reported in
1
58.78 for N(1)· · ·O(1) vs. N(2)· · ·O(2), 162.48 for
this paper have been deposited with the Cambridge
Crystallographic Data Centre as supplementary
materials (CCDC No. 190989). Copies of available
material can be obtained free of charge on application
to the Director, CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK (fax: þ44-1223-336033, e-mail:
deposit@ccdc.cam.ac.uk).
N(3)· · ·O(3) vs. N(4)· · ·O(4) and 169.78 for
N(5)· · ·O(5) vs. N(6)· · ·O(6), respectively. All the
bond distances and angles of DACH ring are in
normal range with the mean C–C and C–N distances
˚
of 1.492 and 1.466 A, and the bond angles
ranging from 110.2(3) to 119.8(3)8. There exist
Fig. 1. ORTEP structure of the title compound with 30% probability thermal ellipsoids.

1
96
Y.-M. Guo et al. / Journal of Molecular Structure 646 (2003) 191–196
[9] M. Du, X.H. Bu, G.C. Wang, Y.M. Guo, R.H. Zhang, Inorg.
Acknowledgements
Chim Acta 320 (2001) 192.
[
[
10] M. Du, X.H. Bu, Q. Xu, Z.L. Shang, R.H. Zhang, J. Chem.
Crystallogr. 30 (2000) 531.
This work was financially supported by the
National Natural Science Foundation of China (No.
11] M. Du, Y.M. Guo, X.H. Bu, J. Ribas, M. Monfort, New
J. Chem. 26 (2002) 939.
2
9971019) and 985 project of Tianjin University.
[
[
12] Y.M. Guo, M. Du, X.H. Bu, J. Mol. Struct. 610 (2002) 27.
13] X.H. Bu, M. Du, L. Zhang, D.Z. Liao, J.K. Tang, R.H. Zhang,
M. Shionoya, J. Chem. Soc. Dalton Trans. (2001) 593.
14] M. Du, Z.L. Shang, X.B. Leng, X.H. Bu, Polyhedron 20
References
[
[
[
[
[
(
2001) 3065.
[
[
1] D.O. Nielson, M.L. Larsen, R.D. Wallett, J.I. Legg, J. Am.
Chem. Soc. 93 (1971) 5079.
15] M. Du, Y.M. Guo, X.H. Bu, J. Ribas, M. Monfort, New
J. Chem. 26 (2002) 645.
2] D.K. Mills, J.H. Reibenspies, M.Y. Darensbourg, Inorg.
Chem. 29 (1990) 4364.
16] M. Du, X.H. Bu, Y.M. Guo, L. Zhang, D.Z. Liao, J. Ribas,
Chem. Commun. (2002) 1478.
[
[
3] W.K. Musker, Coord. Chem. Rev. 117 (1992) 133.
4] C.A. Grapperhaus, M.Y. Darensbourg, Acc. Chem. Res. 31
17] Bruker AXS, SAINT Software Reference Manual, Madison,
WI, 1998.
(1998) 451.
18] G.M. Sheldrick, SHELXTL NT Version 5.1. Program for
Solution and Refinement of Crystal Structures, University of
G o¨ ttingen, Germany, 1997.
[
[
[
[
5] J.A. Halfen, J.M. Uhan, D.C. Fox, M.P. Mehn, L. Que Jr,
Inorg. Chem. 39 (2000) 4913.
6] X.H. Bu, M. Du, Z.L. Shang, R.H. Zhang, D.Z. Liao, M.
Shionoya, T. Clifford, Inorg. Chem. 39 (2000) 4190.
7] X.H. Bu, M. Du, L. Zhang, Z.L. Shang, R.H. Zhang, M.
Shionoya, J. Chem. Soc. Dalton Trans. (2001) 729.
8] X.H. Bu, M. Du, Z.L. Shang, L. Zhang, Q.H. Zhao, R.H.
Zhang, M. Shionoya, Eur. J. Inorg. Chem. (2001) 1551.
[
19] Y.M. Guo, M. Du, G.C. Wang, X.H. Bu, J. Mol. Struct. (2002)
643–677.
[20] Y. Sasada, Molecular and Crystal Structures, Chemistry
Handbook, third ed., The Chemical Society of Japan,
Maruzen, Tokyo, 1984.