New insights into the chemistry of oxomolybdenum(VI) complexes with N-salicylidene-2-aminoethanol

Article abstract of DOI:10.1016/S0020-1693(03)00301-3

Oxomolybdenum(VI) complexes with tridentate Schiff base, N-salicylidene-2-aminoethanol (H₂sae), has been synthesised by the reaction of Mo(O)₂(sal)₂ (where Hsal=salicylic aldehyde) with 2-aminoethanol. This reaction leads to dimeric [MoO(μ-O)(sae)] ₂ and new monomeric [Mo(O)₂(sae){1,2-O^(-)C ₆H₄C(H)N⁽⁺⁾(H)C₂H₄OH}] (1) compounds. Also substitution of acetylacetonate ligand in Mo(O) ₂(acac)₂ by H₂sae in EtOH leads to the same complexes (vide infra), but in MeOH monomeric compound Mo(O)₂(sae) (MeOH) (2) was formed. The molecular structure of complexes 1 and 2 have been determined by X-ray studies, which confirm that one of the H₂sae co-ordinates as η³-tridentate O,N,O′ ligand, while in complex 1 this ligand exists also in zwitterionic form with intramolecular hydrogen bonding, O?H-N, 2.584(3) A?, of phenolic oxygen bonded to the molybdenum atom. The crystals of 1 are triclinic, space group P1?, a=8.483(2) A?, b=10.187(3) A?, c=11.034(3) A?, α=105.26(2)°, β=95.29(2)°, γ=95.10(2)°, and D _calcd=1.666(1) g cm^-3 for Z=2. The crystals of 2 are monoclinic, space group P2₁/c, a=6.697(2) A?, b=7.375(2) A?, c=24.100(3) A?, β=92.76(5)°, and D_calcd=1. 805(1) g cm^-3 for Z=4.

Full text of DOI:10.1016/S0020-1693(03)00301-3

Inorganica Chimica Acta 356 (2003) 387ꢃ392
/
www.elsevier.com/locate/ica
Note
New insights into the chemistry of oxomolybdenum(VI) complexes
with N-salicylidene-2-aminoethanol
Tadeusz G lowiak, Lucjan Jerzykiewicz, Jaros law M. Sobczak *, Jo´zef J. Zio´ lkowski
Faculty of Chemistry, University of Wroc law, 14 F. Joliot-Curie, 50383 Wroc law, Poland
Received 28 February 2003; accepted 3 May 2003
Dedicated to Professor Frausto da Silva
Abstract
Oxomolybdenum(VI) complexes with tridentate Schiff base, N-salicylidene-2-aminoethanol (H2sae), has been synthesised by the
reaction of Mo(O)2(sal)2 (where Hsalꢀsalicylic aldehyde) with 2-aminoethanol. This reaction leads to dimeric [MoO(m-O)(sae)]2
/
and new monomeric [Mo(O)2(sae){1,2-O(ꢁ)C6H4C(H)N(ꢂ)(H)C2H4OH}] (1) compounds. Also substitution of acetylacetonate
ligand in Mo(O)2(acac)2 by H2sae in EtOH leads to the same complexes (vide infra), but in MeOH monomeric compound
Mo(O)2(sae)(MeOH) (2) was formed. The molecular structure of complexes 1 and 2 have been determined by X-ray studies, which
confirm that one of the H2sae co-ordinates as h3-tridentate O,N,O? ligand, while in complex 1 this ligand exists also in zwitterionic
˚
N, 2.584(3) A, of phenolic oxygen bonded to the molybdenum atom. The
form with intramolecular hydrogen bonding, Oꢀ ꢀ ꢀHÃ
/
˚
˚
˚
¯
crystals of 1 are triclinic, space group P1; aꢀ
95.10(2)8, and Dcalcd 2. The crystals of 2 are monoclinic, space group P21/c, aꢀ
1.666(1) g cmꢁ3 for Zꢀ
24.100(3) A, bꢀ92.76(5)8, and Dcalcd 4.
1.805(1) g cmꢁ3 for Zꢀ
# 2003 Elsevier B.V. All rights reserved.
/
8.483(2) A, bꢀ
/
10.187(3) A, cꢀ
/
11.034(3) A, aꢀ
/
105.26(2)8, bꢀ
/
95.29(2)8, gꢀ
/
˚
ꢀ
/
/
/
6.697(2) A, bꢀ7.375(2)
/
˚
˚
A, cꢀ
/
/
ꢀ
/
/
Keywords: cis-Dioxomolybdenum(VI) complexes; Schiff base; Zwitterionic ligand
1. Introduction
Generally, such molybdenum complexes were pre-
pared by condensation method of Mo(O)2(sal)2 (where
Hsalꢀsalicylic aldehyde) and amine derivatives (adap-
tation of Yamanouchi method [8]) or by reaction of H2L
with Mo(O)2An which proceed through the elimination
of the corresponding acid HA.
The molybdenum Schiff base complexes have con-
tinued to play the role of one of the most important
models of molybdoenzymes [1] due to their preparative
accessibility [2].
/
Complexes containing cis-dioxomolybdenum(VI)
fragment dominate co-ordination chemistry of molyb-
denum(VI) [3]. Depending on the preparation method,
molybdenum precursor and reaction conditions, the
complexes synthesised with dibasic tridentate Schiff
bases are of the type: monomeric - Mo(O)2(L)(S), which
In this paper, we have show that different oxomo-
lybdenum(VI) complexes can be formed depending on
the kind of tridentate Schiff bases, procedure and
experimental conditions. In the case of H2sae, adapta-
tion of Yamanouchi procedure can leads to known
dimeric complex [MoO(m-O)(sae)]2 [5] and to a new
compound of type [Mo(O)2(sae){1,2-O(ꢁ)C6H4C-
(H)N(ꢂ)-(H)C2H4OH}] with a charge-separated (zwit-
terionic) form of bonded tridentate Schiff base. Sub-
stitution of acetylacetonate ligand in Mo(O)2(acac)2 by
H2sae in EtOH leads to the same complexes (vide
supra), but in MeOH monomeric compound Mo(O)2-
(sae)(MeOH) was formed. While in the case of N-
salicylidene-2-aminophenol (H2sap), independent of the
is dominant, where Lꢀ
/
Schiff base, Sꢀmonodentate
/
neutral ligand [4], or dimeric-[MoO(m-O)(L)]2 with
asymmetric double oxygen bridge [5,6], or polymeric
with single oxygen bridge [7].
* Corresponding author. Tel.: ꢂ
/
48-71-375 7386; fax: ꢂ48-71-328
/
2348.
E-mail address: js@wchuwr.chem.uni.wroc.pl (J.M. Sobczak).
0020-1693/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0020-1693(03)00301-3

388
T. G lowiak et al. / Inorganica Chimica Acta 356 (2003) 387ꢃ392
/
procedure and solvents, monomeric complexes of type
Mo(O)2(sap)(ROH) are formed [2,4,9,10]. In principle,
the properties of Schiff bases as ligands are determined
by possibilities for tautomeric transformations, forma-
tion of different types of hydrogen bond as well as by
conformational effects [11].
was added. The mixture quickly turned clear yellow. It
was refluxed for 30 min, then cooled to room tempera-
ture and left for crystallisation. The yellow crystals were
collected, washed with alcohol and dried in vacuum to
afford 1.97 g (68%) of [MoO(m-O)(sae)]2.
Anal. Calcd for C18H18Mo2N2O8: C, 37.13; H, 3.12;
Mo, 32.96; N, 4.81. Found: C, 36.8; H, 3.1; Mo, 33.3; N,
4.7%.
2. Experimental
IR (hexachlorobuta-1,3-diene mulls and KBr disk)
and Raman (in parentheses), cmꢁ1: n(CÃ
/
H) 3069 w
(3076 w), 2966 w (2966 w), 2941 w (2942 w), 2919 w
(2919 w), 2856 w (2854 w); n(CÄN) 1633 vs (1630 m),
n(CÃC) 1604 m, 1559 m (1604 m, 1557 m); d(CÃC) 1479
m, 1464 m, 1448 m, 1397 m (1481 w, 1446 m); d(CÃOPh)
1292 s (1333 s, 1291 w); d(CÃOEt) 1045 m (1045 w, 1034
m); n(MoÄO) 928 s (935 s), 898 m; g(CÃHAr) 871 m;
n(Mo2O2) 843 vs (838 vs); d(CÃCPh) 767 m, 635 m (638
m); d(MoꢃO) 580 m (572 w), 466 w, 451 w (411 w).
1H NMR (d6-DMSO, at 20 8C): d 4.00 (td, 2H, Ä
NÃ
CH2Ã), 4.40 (t, 2H, ÃOÃCH2Ã), 6.88 (d, 1H, Ph), 6.95
(td, 1H, Ph), 7.47 (m, 1H, Ph), 7.56 (dd, 1H, Ph), 8.75 (s,
1H, ÃCHÄNÃ).
13C NMR (d6-DMSO, at 20 8C): d 60.9 (Ã
71.4 (ÄNÃCH2Ã), 119.3 (2C, Ph), 120.8, 133.8, 134.7,
161.4 (Ph), 164.0 (ÃCHÄNÃ).
All the reagents and the solvents employed were
commercial and used without further purification.
Ammonium paramolybdate (POCh), salicylic aldehyde
and 2-aminoethanol (REACHIM) were used.
Mo(O)2(sal)2 was prepared by method reported by
Yamanouchi and Yamada [8]. Mo(O)2(acac)2 was
obtained by published method [12].
/
/
/
/
/
/
/
/
/
2.1. Preparation of N-salicylidene-2-aminoethanol
(H2sae)
/
/
/
/
/
/
The Schiff base, H2sae, was obtained via condensa-
tion of 2-hydroxy-benzaldehyde (12.21 g, 0.1 mol) and
2-aminoethanol (6.11 g, 0.1 mol) in toluene (100 ml)
with Dean-Stark trap. Progress of the condensation
reaction was monitored by an amount of water formed
and by GC/MS. After completion of the reaction (ca. 12
h), the solvent was evaporated on rotary evaporator and
the brown oil was distilled under reduced pressure to
afford 12.26 g (74.2%) of the yellow product.
/
/
/
/
OÃ
/
CH2Ã
/
),
/
/
/
/
/
/
From the filtrate (after isolation of dimeric complex),
after several days complex 1 is crystallising. The yellow
crystals of 1 were collected by filtration, washed with
cold ethanol and dried in vacuum (yield, 0.96 g (21%)).
Independently, complex 1 was obtained by the reac-
tion of dimeric compound with the free Schiff base,
H2sae. A mixture of 0.5 g (0.86 mmol) of [MoO(m-
O)(sae)]2 and 0.284 g (1.72 mmol) of H2sae in 20 ml of
absolute alcohol was refluxed for 20 h. The solution was
filtered from unreacted dimeric complex (0.25 g of
[MoO(m-O)(sae)]2 was recovered) and yellow prisms
crystallised from the filtrate, 0.24 g (61% based on
Anal. Calcd for C9H11NO2: C, 65.44; H, 6.71; N, 8.48.
Found: C, 64.9; H, 5.8; N, 8.7%.
IR (film), cmꢁ1: n(OÃ
/
H) 3368 m, br; n(CÃ
vw, 3013 vw, 2938 w, 2879 w, 2845 sh, 2740 vw, br, 2660
vw; n(CÄN) 1633 vs, 1612 m; n(CÃC) 1580 m; 1528 w;
d(CÃC) 1496 m, 1461 w, 1439 w, 1419 w, 1339 w; d(CÃ
OPh) 1278 s, 1215 m, 1150 m, 1119 w; d(CÃOEt) 1065 m,
1043 m, 915 w, 879 w; d(CÃCPh) 757 s; g(CÃHAr) 737
m, 677 vw, 669 w, 639 w, 570 w, 526 w.
UVꢃ
Vis (MeOH) [lmax (nm)/o (Mꢁ1 cmꢁ1)]: 454
/
H) 3057
/
/
/
/
/
/
/
reacted dimer) of 2 (m.p. 159ꢃ160 8C).
/
Anal. Calcd for C18H20MoN2O6: C, 47.38; H, 4.42;
Mo, 21.02; N, 6.14. Found: C, 47.3; H, 4.3; Mo, 21.2; N,
6.2%.
/
(444), 356 (11 330), 346 (11 100), 276 (11 520), 230
(17 500) 216 (22 610).
1H NMR (CDCl3, at 20 8C): d approximately 2 (s br,
1H, OH), 3.74 (t, 2H, Ã
6.87 (td, 1H, Ph), 6.94 (d, 1H, Ph), 7.24 (dd, 1H, Ph),
7.30 (td, 1H, Ph), 8.37 (s, 1H, ÃHCÄNÃ), approxi-
mately 13.2 (s br, 1H, OH).
IR (hexachlorobuta-1,3-diene mulls and KBr disk)
and Raman (in parentheses), cmꢁ1: n(NÃ
/
H) 3350 m,
H) 3069 w, 3055 w (3063 w), 3030 w, 3017
w (3030 w, 3015 w), 2947 w, 2918 w, 2870 w, 2845 w
(2960 w, 2922 w, 2902 w, 2870 w); n(CÄN) 1651 vs, 1606
m, 1599 s (1609 s, 1586 m, 1579 m); n(CÃC) 1553 w,
1536 m (1556 vs, 1540 m); d(CÃC) 1488 m, 1474 m, 1447
m (1481 m, 1450 w, 1435 m); d(CÃOPh) 1271 s (1275 m,
1258 m), 1209 m, 1152 m (1175 m); d(CÃOEt) 1047 m
(1026 w); n(MoÄO) 920 s, 883 s (928 m, 919 w); g(CÃ
HAr) 862 m (897 w), 797 w; d(CÃCPh) 782 m, 774 m (811
w, 756 w), 621 m (632 w); d(MoÃO) 553 m (574 w).
1H NMR (CD2Cl2, at 20 8C): d 3.7 (m, 4H, Ä
NÃ
CH2Ã and Å CH2Ã), 3.9 (m, 4H, ÃCH2ÃOÃ), 4.5
ꢂ Ã
(t, 1H, ÅCÃOH), 6.8 (m, 4H, Ph), 6.95 (t, 1H, Ph), 7.2
/
CH2Ã
/
), 3.90 (t, 2H, Ã
/
CH2Ã/),
3339 m; n(CÃ
/
/
/
/
/
/
/
2.2. Preparation of [MoO(m-O)(sae)]2 and
[Mo(O)2(sae){1,2-O(ꢁ)C6H4C(H)N(ꢂ)(H)C2H4-
/
/
OH}] (1)
/
/
/
The synthesis of these complexes was based upon
adaptation of Yamanouchi method [8]. To a stirred
suspension of 3.7 g (10 mmol) of Mo(O)2(sal)2 in 30 ml
of absolute ethanol, 1.2 ml (20 mmol) of 2-aminoethanol
/
/
/
/
/N
/
/
/
/
/
/
/

T. G lowiak et al. / Inorganica Chimica Acta 356 (2003) 387ꢃ
/392
389
(d, 4H, Ph), 8.3 (m, 2H, Ã
13.1 (s, br, 1H, Å ).
Nꢂ(H)Ã
13C NMR (CD3OD, at 20 8C): d 61.4, 62.4 (Ã
CH2Ã), 62.2 (Å CH2Ã), 72.9 (ÄNÃCH2Ã), 118.3,
ꢂ Ã
119.0, 119.7, 120.4, 121.3, 133.1, 134.0, 134.9, 136.2
(Ph), 166.3 (ÃCHÄ ), 168.2 (ÃCHÄNÃ).
ꢂ Ä
/
CHÄ
/
NÃ
/
and Ã
/
CHÄ
/
N
ꢂ Ä
/
),
DTA 16 instrument was used for thermal analysis. A
Hewlett Packard 5890 II series gas chromatograph
coupled with Hewlett Packard Model mass selective
detector was used for the GC/MS analyses. Elemental
analyses were performed in the Microanalytical Labora-
tory of the Faculty of Chemistry, University of Wroc-
/
/
/
OÃ
/
/
/
N
/
/
/
/
/
/
/
N
/
/
/
/
law. Melting points were obtained on a Boetius
¨
apparatus and are uncorrected.
2.3. Preparation of [MoO2(sae)(MeOH)] (2)
To a stirred solution of 1.141 g (3.5 mmol) of
Mo(O)2(acac)2 in 15 ml of methanol, a methanolic
solution (5 ml) of H2sae (0.578 g, 3.5 mmol) was added.
The solution quickly turned yellow and after few
minutes a light-yellow precipitate of Mo(O)2(sae)-
(MeOH) was formed. The reaction mixture was stirred
at room temperature for 23 h. The solid was collected by
filtration, washed with diethyl ether, and finally dried in
vacuum to afford 0.835 g (73.9%) of product. The
compound was crystallised from methanol.
2.5. Determination and refinement of the structure
Crystal data for compounds 1 and 2, along with other
experimental details, are summarised in Table 1. In-
tensities data collections were carried out on a Syntex
P21 four-circle diffractometer and on a KUMA KM-4
k-axis diffractometer with graphite-monochromated Mo
Ka for 1 and 2, respectively. All data were corrected for
Lorentz and polarisation effects. The structures were
solved by heavy atom method and refined by full-matrix
least-squares using Syntex (1976) XTL system [13] for 1
and SHELXTL 5.1 package [14] for 2. After refinement
with isotropic displacement parameters for all atoms,
absorption correction was also applied to the data for
structure 2. Carbon-bonded hydrogen atoms were
included in calculated positions and refined in the riding
mode. Other hydrogen atoms were located in a differ-
Anal. Calcd for C10H13MoNO5: C, 37.17; H, 4.05;
Mo, 29.69; N, 4.33. Found: C, 37.0; H, 3.9; N, 4.3%.
IR (hexachlorobuta-1,3-diene mulls and KBr disk)
and Raman (in parentheses), cmꢁ1: n(OÃ
/
H) approxi-
mately 3050 w, br (3054 w), 2779 w, br and 2538 vw;
n(CÃH) 3038 sh, 2992 vw, 2941 w (2949 w, 2939 w),
2918 w (2918 w), 2865 w (2864 w), 2832 vw, 2715 vw;
n(CÄN) 1641 vs (1641 s), 1601 s (1598 m); n(CÃC) 1555
m (1554 s); d(CÃC) 1473 m (1471 w), 1450 s (1450 w),
1429 w (1427 w), 1412 vw, 1394 w, 1365 vw (1327 s),
1321 w (1320 s); d(CÃOPh) 1278 vs (1279 w), 1257 m
(1260 w, 1248 w), 1214 m (1215 m), 1152 w (1151 w),
1127 w, 1096 w (1095 w); d(CÃO) 1042 s (1031 m), 989
vw; n(MoÄO) 928 vs (920 vs), 906 vs (901 m); g(CÃHAr
864 sh, 805 m (803 w); d(CÃCPh) 760 s, 635 s (638 m),
600 w; d(MoÄO) 553 s, 541 s, 515 w (515 w), 465 w, 438
m, 419 m (420 m, 283 m, 258 w, 242 w, 199 m).
1H NMR (CD3OD, at 20 8C): d 4.04 (td, 2H, Ä
CH2Ã), 4.51 (t, 2H, ÃCH2ÃOÃ), 6.98 (m, 2H, Ph), 7.51
(m, 2H, Ph), 8.72 (s, 1H, ÃHCÄNÃ).
1H NMR (d6-DMSO, at 20 8C): d 3.36 (s, 3H, CH3Ã
OÃ), 4.0 (td, 2H, ÄNÃCH2Ã), 4.40 (t, 2H, ÃCH2ÃOÃ),
6.9 (dd, 1H, Ph), 6.95 (td, 1H, Ph), 7.47 (m, 1H, Ph),
7.56 (dd, 1H, Ph), 8.76 (s, 1H, ÃHCÄNÃ).
13C NMR (d6-DMSO, at 20 8C): d 60.9 (Ã
71.4 (ÄNÃCH2Ã), 119.37, 119.40, 120.9, 133.9, 134.7,
161.4 (Ph), 164.0 (ÃCHÄNÃ).
/
/
/
/
Table 1
Crystal data and structure refinement for 1 and 2
/
Compound
1
2
Empirical formula
Colour
C
18H20MoN2O6 C10H13MoNO5
/
yellow
456.3
yellow
323.15
299(2)
monoclinic
P21/c
/
/
)
Formula weight
T (K)
/
291(2)
triclinic
¯
P1
/
Crystal system
Space group
/
˚
a (A)
8.483(2)
10.187(3)
11.034(3)
105.26(2)
95.29(2)
95.10(2)
909.6(4)
2
6.697(2)
7.375(2)
24.100(3)
90
/
NÃ
/
˚
b (A)
/
/
/
/
˚
c (A)
/
/
/
a (8)
b (8)
g (8)
/
92.76(5)
90
/
/
/
/
/
/
/
3
˚
V (A )
Z
1188.9(5)
4
648
/
/
/
F(0 0 0)
Dcalcd (Mg mꢁ3
464
1.666
/
OÃ
/
CH2Ã/),
)
1.805
none
Dmeasd (Mg mꢁ3
Radiation
)
1.67(1)
Mo Ka
0.752
/
/
/
/
/
/
Mo Ka
1.112
m (mmꢁ1
)
Crystal size (mm3)
0.25ꢄ
0.25
18B
/
0.25ꢄ
/
0.5ꢄ
/
0.5ꢄ
/
0.3
2.4. Physical measurements
Range for data collection (8)
/
2u B
/
32
7.2B
/
2u B50
/
IR and Raman spectra were measured using Impact
400 (Nicolet) and Nicolet 860 with Raman Accessory
Number of reflections collected 4195
Number of reflections observed 3888
4029
1796
(I ]/2.0s(I))
spectrophotometers, respectively. UVꢃVis electronic
/
Number of variable parameters 244
R1, wR2, S
171
0.023, 0.057,
1.10
spectra were obtained by using a Cary 500 and Hewlett
Packard Model 8452A Diode Array spectrophot-
0.027, 0.040,
4.005
1
ometers. H and 13C NMR spectra were recorded on
Brucker 300 spectrometer. A SETARAM Setsys TG-
1=2
/
R1ꢀ
/
SjjFojꢁ
/
jFcjj/SjFoj; wR2 ꢀfa[w(F2 ꢁF2)2]=a[w(F2)2]g
:
o
c
o

390
T. G lowiak et al. / Inorganica Chimica Acta 356 (2003) 387ꢃ392
/
ence map and refined freely. All non-hydrogen atoms
were refined with anisotropic displacement parameters.
Neutral atomic scattering factors were taken from
International Tables for X-ray Crystallography [15].
via more basic terminal oxygen atoms and leads to the
formation of the dimer with asymmetric double oxygen
bridge [5]. In case of H2sap, formation of dimeric
complex is not observed although starting with
Mo(O)2(sap)(ROH), after heating or azeotropic distilla-
tion of alcohol such dimers can be obtained [5,6,10].
Similarly, Mo(O)2(sae)(MeOH) in ethanol when heated
under reflux is converted into the dimer (Scheme 1). This
is obvious that those dimers can be easily converted into
monomeric cis-dioxomolybdenum(VI) complexes of
3. Results and discussion
3.1. Synthesis
Mo(O)2(L)(S) formula (where Lꢀ
monodentate neutral ligand).
/
Schiff base, Sꢀ
/
It was found that independent of reaction conditions
(temperature, kind of solvent (alcohol) used), starting
with Mo(O)2(sal)2 or Mo(O)2(ae)2 complexes (where
Haeꢀ/2-aminoethanol) in reaction in situ with suitable
3.2. Spectra
component (Hae and/or Hsal) to form Schiff base
ligand, the formation of mainly dimeric immediately
crystallising complex (70%) yield is observed. From the
filtrate, after several days complex 1 is crystallising.
Similar substitution reaction of acetylacetonate ion in
Mo(O)2(acac)2 by H2sae depending on kind of alcohol
used leads to complex 2 (when reaction proceeds in
methanol) or to dimeric and 1 complexes, which may be
separate because of significant differences in solubility
of those compounds. Complex 1 may be obtained also
from complex 2 or from the dimer in reaction with
H2sae. All the pathways of above-mentioned reactions
are shown in Scheme 1.
In our opinion, the formation of dimeric molybdenum
complexes with dibasic tridentate Schiff base ligand is
determined by electron density on nitrogen atom, which
may be correlated to pKa value of appropriate amines.
In case of H2sae and H2sap, suitable values of pKa for
amines are 9.6 and 4.8 for 2-aminoethanol and 2-
aminophenol [16], respectively. The basicity increase of
nitrogen atom in H2sae should induce increase of
electron density on Mo and next on the terminal oxygen
in trans-position to nitrogen. Therefore, such a freshly
formed 5-co-ordinate Mo(O)2(sae) species may interact
The 1H NMR spectra of the Schiff base ligand
showed a chemical shift of about 13.2 and 2 ppm
characteristic for OH group bonded to aromatic ring
1
and alkyl chain, respectively. The H NMR spectra of
the complexes are indicative of binding of the ligand
through phenoxo, alkoxo and imine group. The chemi-
cal shift of imine carbon proton was at 8.37 ppm for free
ligand and co-ordination of nitrogen shifted of the
resonance signals about 0.35ꢃ
1H NMR spectra of complex 1 also showed a singlet
(13.1 ppm, ) and triplet of unbounded
/
0.38 ppm downfield. The
Å
/
Nꢂ(H)Ã
/
CH2OH group (4.5 ppm) for zwitterionic form of ligand.
The IR spectra of the complexes show two strong
absorption bands at 880ꢃ
are due to asymmetric and symmetric MoÄ
respectively. Co-ordination of the imine centre through
nitrogen is seen in the n(CÄ
N) (at 1651 and 1641 cmꢁ1
/
910 and 920ꢃ
/
930 cmꢁ1, which
O stretches,
/
/
for complex 1 and 2, respectively) which is slightly
higher than in uncoordinated Schiff base (1633 cmꢁ1).
Raman spectra of these complexes exhibited peaks in
the range 1641ꢃ
and asymmetric stretching of Ã
In the MoÄO region, a medium and weak peaks at 928
/
1579 cmꢁ1 corresponding to symmetric
HCÄNÃCPh framework.
/
/
/
/
Scheme 1.

T. G lowiak et al. / Inorganica Chimica Acta 356 (2003) 387ꢃ
/392
391
and 919 cmꢁ1 and very strong and medium peaks at 920
and 901 cmꢁ1 are observed for complexes 1 and 2,
respectively.
1
Generally, H and 13C NMR, IR and Raman spectra
are in good agreement with those reported for compar-
able cis-dioxomolybdenum(VI) complexes [5,6,10,17].
3.3. Structures of complexes
The molecular structures of complexes 1 and 2 are
shown in Figs. 1 and 2, respectively, with the relevant
bond distances and angles collected in Table 2. The co-
ordination geometry around the MoVI cation is quite
similar in both complexes studied. The Schiff base
ligand is bonded to the cis-MoO22ꢂ ion in a xy-plane
through an alkoxide and a phenolic oxygen atoms and
an imine nitrogen atom, which is trans to an oxo group.
A zwitterionic form of Schiff base bonded by a
phenoxide oxygen atom and a methanol molecule
completes the distorted octahedral co-ordination sphere
in compounds 1 and 2, respectively. In both complexes,
Fig. 2. The molecular structure of 2 with atom numbering scheme.
The displacement ellipsoids are drawn at the 50% probability level.
complexes with Schiff base H2sae. Formation of differ-
ent oxomolybdenum(VI) complexes can be depended on
the properties of tridentate Schiff base (basicity of N
atom), synthetic methodology and reaction conditions.
the OÄ
/
MoÄ
/
O angles (105.9(1)8 and 106.1(1)8) and MoÄ
/
˚
O distances (1.704(2) and 1.697(2) A) for 1 and 2,
respectively, are typical for cis-dioxomolybdenum(VI)
complexes [6,9,10,17].
4. Supplementary material
Intramolecular and intermolecular hydrogen bonds
are observed for complexes 1 and 2, respectively (Table
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
3). Two different hydrogen bonding Oꢀ ꢀ ꢀHÃ
/
O are
observed for complex 2. The consequence of this is an
interesting crystal packing of molecules (Fig. 3).
The structures of compounds 1 and 2 are very similar
to those of cis-dioxomolybdenum(VI) complexes with
other Schiff base ligands [6,9,10,17].
Table 2
˚
Selected bond lengths (A) and angles (8) for 1 and 2
In conclusion, we have reported herein the synthesis
and the characterisation of the new molybdenum
Compound 1
Compound 2
Bond lengths
MoÃ
MoÃ
MoÃ
MoÃ
MoÃ
MoÃ
/
O(1)
1.704(2)
1.706(2)
1.987(2)
1.916(2)
2.228(2)
2.272(2)
MoÃ
MoÃ
MoÃ
MoÃ
MoÃ
MoÃ
/
O(1)
O(2)
1.697(2)
1.704(2)
1.933(2)
1.963(2)
2.339(2)
2.252(2)
/O(2)
/
/
O(11)
O(12)
O(21)
N(11)
/
O(11)
O(12)
O(3)
/
/
/
/
/
/
N(11)
Bond angles
O(1)Ã
O(1)Ã
O(1)Ã
O(1)Ã
O(1)Ã
O(2)Ã
O(2)Ã
O(2)Ã
O(2)Ã
O(11)Ã
O(11)Ã
O(11)Ã
O(12)Ã
O(12)Ã
O(21)Ã
/
MoÃ
MoÃ
MoÃ
MoÃ
MoÃ
MoÃ
MoÃ
MoÃ
MoÃ
MoÃ
MoÃ
MoÃ
MoÃ
MoÃ
MoÃ
/
O(2)
105.9(1)
103.8(1)
97.5(1)
88.6(1)
163.4(1)
92.6(1)
98.8(1)
90.0(1)
163.0(1)
152.1(1)
75.2(1)
79.6(1)
75.0(1)
87.6(1)
76.4(1)
O(1)Ã
O(1)Ã
O(2)Ã
O(1)Ã
O(2)Ã
O(11)Ã
O(1)ÃMoÃ
O(2)ÃMoÃ
O(11)Ã
O(12)Ã
O(1)ÃMoÃ
O(2)ÃMoÃ
O(11)Ã
O(12)Ã
N(11)Ã
/
MoÃ
MoÃ
MoÃ
MoÃ
MoÃ
MoÃ
/
O(2)
106.1(1)
96.8(1)
102.7(1)
98.6(1)
96.2(1)
151.2(1)
94.2(1)
158.9(1)
79.9(1)
74.8(1)
170.3(1)
83.6(1)
80.2(1)
80.6(1)
76.2(1)
/
/
O(11)
O(12)
O(21)
N(11)
O(11)
O(12)
N(11)
O(21)
/
/
O(11)
O(11)
O(12)
O(12)
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/O(12)
/
/
/
/
N(11)
/
/
/
/
N(11)
/
/
/
MoÃ
/
N(11)
/
/
O(12)
O(21)
N(11)
N(11)
O(21)
N(11)
/
MoÃ
/
N(11)
/
/
/
/
O(3)
O(3)
/
/
/
/
/
/
/
MoÃ
MoÃ
MoÃ
/
O(3)
O(3)
O(3)
/
/
/
/
/
/
/
/
Fig. 1. The molecular structure of 1 with atom numbering scheme.
Hydrogen bond is indicated by dashed lines.

392
T. G lowiak et al. / Inorganica Chimica Acta 356 (2003) 387ꢃ392
/
Table 3
Acknowledgements
˚
Hydrogen bonds for 1 and 2 (A and 8)
DÃHꢀ ꢀ ꢀA d(DÃH) d(Hꢀ ꢀ ꢀA) d(Dꢀ ꢀ ꢀA)
Compound 1
This work was supported by the Polish State Com-
mittee for Scientific Research (KBN) under grant PBZ
15/T09/99/01D.
/
/
B(DHA)
/
N(21)ÃH(15)ꢀ ꢀ ꢀO(21)
/
0.844(2) 1.868(2)
2.584(3)
141.7(2)
Compound 2
O(3)Ã
/
H(3O)ꢀ ꢀ ꢀO(12)a 0.74(3)
1.89(3)
2.489
2.630(3)
3.397(3)
175(4)
165(4)
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C(17)Ã
/
H(5)ꢀ ꢀ ꢀO(1)b
0.930
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