Synthesis, characterization, and structures of zinc(II) and cadmium(II) complexes with phosphoramides bearing cyclic amino groups

Article abstract of DOI:10.1080/00958972.2020.1731485

Twelve new zinc(II) and cadmium(II) complexes with symmetric ligands, [MCl₂((R₂N)₃PO)₂] (M = Zn, R₂N = pyrrolidinyl (1), piperidinyl (2); M = Cd, R₂N = pyrrolidinyl (3), piperidinyl (4)), and differently substituted ligands of the general formula [MCl₂(R₂N)PO(R’₂N)₂] (M = Zn or Cd; R₂N = Pyrr, Pip or Mor; R’₂N = Pyrr, Pip or Mor (5–12) have been synthesized from reaction of zinc(II) or cadmium(II) chlorides with the ligands, giving yields of 43–76%. The complexes were characterized with multinuclear (¹H, ¹³C and ³¹P) NMR, conductivity, IR spectroscopy, and X-ray analyses. Complexes 1, 3, 11, and 12 are comprised of two ligands coordinated to the metal center in a distorted monomeric tetrahedral arrangement. The P = O bond lengths of 1.490(3) (1), 1.497(4) (3), 1.480(4) (11), and 1.479(5) ? (12) are in the order observed for analogous phosphoramide complexes. The results are compared with those reported for related chalcogen counterparts.

Full text of DOI:10.1080/00958972.2020.1731485

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: https://www.tandfonline.com/loi/gcoo20
Synthesis, characterization, and structures
of zinc(II) and cadmium(II) complexes with
phosphoramides bearing cyclic amino groups
Mohamed M’haiham, Khaled Ebeid, Fatimetou Ebnou, Cameron L.
Carpenter-Warren, Alexandra M. Z. Slawin, John Derek Woollins, Med Taieb
Ben Dhia & Med Abderrahmane K. Sanhoury
To cite this article: Mohamed M’haiham, Khaled Ebeid, Fatimetou Ebnou, Cameron L. Carpenter-
Warren, Alexandra M. Z. Slawin, John Derek Woollins, Med Taieb Ben Dhia & Med Abderrahmane
K. Sanhoury (2020): Synthesis, characterization, and structures of zinc(II) and cadmium(II)
complexes with phosphoramides bearing cyclic amino groups, Journal of Coordination Chemistry,
DOI: 10.1080/00958972.2020.1731485
To link to this article: https://doi.org/10.1080/00958972.2020.1731485
Published online: 28 Feb 2020.
Submit your article to this journal
View related articles
View Crossmark data
Full Terms & Conditions of access and use can be found at
https://www.tandfonline.com/action/journalInformation?journalCode=gcoo20

JOURNAL OF COORDINATION CHEMISTRY
https://doi.org/10.1080/00958972.2020.1731485
Synthesis, characterization, and structures of zinc(II) and
cadmium(II) complexes with phosphoramides bearing
cyclic amino groups
a,b
a
a
Mohamed M’haiham , Khaled Ebeid , Fatimetou Ebnou ,
c
c
d
Cameron L. Carpenter-Warren , Alexandra M. Z. Slawin , John Derek Woollins ,
b
a,b
Med Taieb Ben Dhia and Med Abderrahmane K. Sanhoury
a
Department of Chemistry, Research Unit in Materials Chemistry, Faculty of Sciences and Techniques,
b
UNA, Nouakchott, Mauritania; Laboratory of Structural Organic Chemistry: Synthesis and
Physicochemical Studies, Department of Chemistry, Faculty of Sciences of Tunis, University of Tunis
c
El Manar, Tunis, Tunisia; EaStCHEM School of Chemistry, University of St Andrews, St Andrews, Fife,
d
UK; Khalifa University, Abu Dhabi, UAE
ABSTRACT
ARTICLE HISTORY
Twelve new zinc(II) and cadmium(II) complexes with symmetric
Received 7 October 2019
Accepted 3 February 2020
ligands, [MCl
2
((R
2
N)
3
PO)
2
2
] (M ¼ Zn, R N ¼ pyrrolidinyl (1), piperi-
2
dinyl (2); M ¼ Cd, R N ¼ pyrrolidinyl (3), piperidinyl (4)), and
KEYWORDS
differently substituted ligands of the general formula
Phosphoramides; zinc(II);
cadmium(II); metal complex;
NMR; X-ray analysis
[
MCl
2
2
(R
2
N)PO(R’
2
N)
2
] (M ¼ Zn or Cd; R N ¼ Pyrr, Pip or Mor;
2
R’ N ¼ Pyrr, Pip or Mor (5–12) have been synthesized from reac-
tion of zinc(II) or cadmium(II) chlorides with the ligands, giving
yields of 43–76%. The complexes were characterized with multi-
1
13
31
nuclear ( H, C and P) NMR, conductivity, IR spectroscopy, and
X-ray analyses. Complexes 1, 3, 11, and 12 are comprised of two
ligands coordinated to the metal center in a distorted monomeric
tetrahedral arrangement. The P ¼ O bond lengths of 1.490(3)
(1), 1.497(4) (3), 1.480(4) (11), and 1.479(5) Å (12) are in the order
observed for analogous phosphoramide complexes. The results
are compared with those reported for related chalcogen counter-
parts.
CONTACT Med Abderrahmane K. Sanhoury
senhourry@yahoo.com
ß 2020 Informa UK Limited, trading as Taylor & Francis Group

2
M. M’HAIHAM ET AL.
1. Introduction
Phosphoramides increasingly attract attention due to their potential applications
in industry as flame retardants, in medicine as prodrugs, in catalysis and syn-
thesis as chiral ligands [1, 2], as well as their ease of preparation, high solubil-
ity, and good reactivity toward different metal ions in many organic solvents
[
3–11]. The properties depend largely on the nature of substituents on the
phosphorus [12]. In addition, studies into the coordination chemistry of phos-
phine chalcogenides R PE (E ¼ O, S, Se, and Te) toward the same metal would
3
be very informative as to the nature of metal–ligand interactions upon complex
formation [13] as well as to the stereochemistry and nuclearity of the resulting
complexes [14].
In this context, we have recently described the synthesis and characterization of
tetrahedral metal complexes derived from bidentate piperidine containing ligands
MeN(Pip PE) (Pip ¼ piperidinyl, E ¼ S or Se) [15] and from monodentate phosphine
2
2
chalcogenides n-Bu PE (E ¼ O, S, or Se) [16]. In all these compounds, the isolated com-
3
plexes exist as monomeric species. In contrast, we have shown more recently that
when the ligands Pip PE (E ¼ S or Se) were used, the nuclearity changed and dimers
3
with Hg(II), Cd(II), and even Zn(II) were produced [17]. This was tentatively interpreted
in terms of the presence of both the bulkier chalcogen atoms and the three piperi-
dinyl groups in the monodentate ligand. Inspired by these results, we decided to syn-
thesize the corresponding oxide analogues with phosphoramide ligands bearing
different cyclic amino moieties including pyrrolidinyl (Pyrr), piperidinyl (Pip), and mor-
pholinyl (Mor) groups. We were particularly interested to see how the chalcogen
nature would affect the nuclearity of such complexes. The present work reports on
the synthesis and characterization of new zinc(II) and cadmium(II) chloride complexes
with phosphoramides (R N)3PO (R N ¼ Pyrr or Pip and (R N)PO(R’ N) (R N ¼ Pyrr or
2
2
2
31
2
2
2
1
13
Pip; R’ N ¼ Pyrr or Mor) using multinuclear ( H, C, and P) NMR, IR spectroscopy,
2
conductivity measurements, and X-ray analyses.

JOURNAL OF COORDINATION CHEMISTRY
3
2. Experimental
2.1. General experimental procedures
Anhydrous zinc and cadmium chlorides (ꢀ99.9%) and ethanol puriss (ꢀ99.8%) were
used as received from the commercial supplier (SIGMA-ALDRICH). All preparations
were carried out under nitrogen in solvents dried by standard techniques [18] and
stored over molecular sieves.
2.2. Instrumentation
3
1
All NMR spectra were recorded on a Bruker AC-300 instrument in CDCl as solvent,
P
3
1
13
at 121 (85% H PO ), H at 300, and C at 75.4 MHz. IR spectra were obtained using a
3
4
ꢁ
3
YL 2000 FT-IR spectrometer. The conductivity measurements were carried out for 10
M solutions of the complexes dissolved in dichloromethane (dried on molecular
sieves). Phosphoramides were prepared and purified by vacuum distillation before use
according to methods described [19–21].
2.3. General procedure for the preparation of variously substituted
phosphoramide ligands R NP(O)(Rꢀ N) (R N or Rꢀ N ¼ Pip, Mor, or Pyrr)
2
2
2
2
2
The phosphoramides R NP(O)(RꢀN) were prepared in two steps. The first step is the
2
2
2
addition of two equivalents of the first amine (R NH) in anhydrous diethyl ether to a
2
ꢂ
cooled solution (0 C) of one equivalent of phosphoryl oxychloride (POCl ) in the same
3
solvent. The reaction mixture was stirred overnight at room temperature. The ammo-
nium salt was filtered off, solvent evaporated in vacuo and the residue was purified by
distillation to give the intermediate dichlorides, R NP(O)Cl . Four equivs of the second
2
2
amine (RꢀNH), in diethyl ether, were then added to a cooled solution of R NP(O)Cl in
2
2
2
the same solvent. The workup was the same as in the first step. The crude materials
were viscous liquids for PyrrP(O)Pip , PipP(O)Pyrr and MorP(O)Pyrr , which were
2
2
2
ꢂ
stirred at 100 C over CaH for 12 h and then purified by vacuum distillation, while the
2
resulting solid residue PyrrP(O)Mor was purified by recrystallization in toluene or vac-
2
31
1
uum distillation. The purity of these compounds was checked by their P and H
NMR spectra.
2
.3.1. PipP(O)Pyrr2
ꢂ
1
Yield ¼ 69%; b.p. ¼ 135 C/0.5 mmHg; H NMR (300 MHz, CDCl ), d (ppm): 2.8 (m,
3
ꢁ
1
12H), 1.4 (m, 8H), 1.2 (m, 6H); ꢀ
¼ 1223 cm
.
(
P¼O)
2
.3.2. PyrrP(O)Pip2
ꢂ
1
Yield ¼ 45%; b.p. ¼ 138 C/0.5 mmHg; H NMR (300 MHz, CDCl ), d (ppm): 3.1 (m,
3
ꢁ
1
12H), 1.8 (m, 4H), 1.5 (m, 12H); ꢀ
¼ 1232 cm
.
(
P¼O)
2
.3.3. MorP(O)Pyrr2
ꢂ
1
Yield ¼ 80%; b.p. ¼ 150 C/0.5 mmHg; H NMR (300 MHz, CDCl ), d (ppm): 3.9 (m, 4H),
3
¼ 1228 cmꢁ
1
.
3.5 (m, 12H), 2.2 (m, 8H); ꢀ
(
P¼O)

4
M. M’HAIHAM ET AL.
2
.3.4. PyrrP(O)Mor2
ꢂ
1
Yield ¼ 37%; 163 C/0.5 mmHg H NMR (300 MHz, CDCl ), d (ppm): 3.5 (m, 8H), 3.1 (m,
3
¼ 1269 cmꢁ
1
.
12H), 1.7 (m, 4H); ꢀ
(
P¼O)
2
.4. General procedure for the preparation of 1–12
To a solution of metal chloride (1 mmol) in ethanol (20 mL) was added the ligand
2 mmol) in anhydrous dichloromethane (5 mL). The reaction mixture was stirred at
(
room temperature for 2 h and concentrated in vacuo. Addition of dry diethyl ether led
to precipitation of the complex, which was washed with the same solvent and vacuum
dried for several hours.
2
.4.1. [ZnCl2(Pyrr3PO)2] (1)
ꢂ
Yield ¼ 0.30 g (45%); m. p. ¼ 151 C; Anal. Calcd for C H Cl N O P Zn: H, 7.43; C,
2
1
4
48
2 6 2 2
44.29; N, 12.91% found: H, 7.52; C, 44.01; N, 12.48%; H NMR (300 MHz, CDCl ), d
3
(
1
ppm): 3.20 (m, 12H), 1.80 (m, 12H); IR: 2979, 2881, 1462, 1348, 1251, 1211 (ꢀP ¼ O),
ꢁ
1
ꢁ1
2
ꢁ1
161, 1133, 1093, 1017, 917, 873, 770, 588, 538 cm ; K (X cm mol ) ¼ 9.73.
M
2
.4.2. [ZnCl2(Pip3PO)2] (2)
ꢂ
Yield ¼ 0.40 g (55%); m. p. ¼ 206 C; Anal. Calcd for C H Cl N O P Zn: H, 8.23; C,
3
1
0
60
2 6 2 2
49.02; N, 11.44% found: H, 8.86; C, 48.77; N, 11.09%; H NMR (300 MHz, CDCl ), d
3
(
1
ppm): 3.00 (m, 12H), 1.40 (m, 18H); IR: 2941, 2860, 1454, 1376, 1342, 1214 (ꢀP ¼ O),
ꢁ
1
ꢁ1
2
ꢁ1
169, 1123, 1074, 1030, 959, 857, 698, 584 cm ; K (X cm mol ) ¼ 6.22.
M
2
.4.3. [CdCl2(Pyrr3PO)2] (3)
ꢂ
Yield ¼ 0.49 g (70%). m. p. ¼ 131 C. Anal. Calcd for C H CdCl N O P : H, 6.93; C,
2
1
4
48
2 6 2 2
41.30; N, 12.04% found: H, 7.08; C, 41.11; N, 11.84%; H NMR (300 MHz, CDCl ), d
3
(
1
ppm): 3.10 (m, 12H), 1.70 (m, 12H); IR: 2967, 2864, 1452, 1346, 1245, 1206 (ꢀP ¼ O),
ꢁ
1
ꢁ1
2
ꢁ1
141, 1086, 1014, 915, 872, 767, 588 cm . K (X cm mol ) ¼ 4.25.
M
2.4.4. [CdCl2(Pip3PO)2] (4)
Yield ¼ 0.46 g (60%); Anal. Calcd for C H CdCl N O P : H, 7.73; C, 46.07; N, 10.75%
3
0
60
2 6 2 2
ꢁ
1
2
ꢁ1
found: H, 7.85; C, 45.93; N, 10.56%; K (X cm mol ) ¼ 1.98.
M
2
.4.5. [ZnCl2(MorP(O)Pyrr2)2] (5)
ꢂ
Yield ¼ 0.52 g (76%); m. p. ¼ 150 C. Anal. Calcd for C H Cl N O P Zn: H, 7.08; C,
2
1
4
48
2 6 4 2
42.21; N, 12.32% found: H, 7.21; C, 42.08; N, 12.42%; H NMR (300 MHz, CDCl ), d
3
(
(
ppm): 3.70 (m, 4H), 3.20 (m, 12H), 1.80 (m, 8H); IR: 2975, 2858, 2187, 1452, 1265, 1211
ꢀP ¼ O), 1165, 1085, 1023, 969, 909, 709, 584 cm ; KM (X cm mol ) ¼ 5.53.
ꢁ
1
ꢁ1
2
ꢁ1
2
.4.6. [ZnCl2(PipP(O)Pyrr2)2] (6)
ꢂ
Yield ¼ 0.38 g (56%); m. p. ¼ 150 C; Anal. Calcd for C H Cl N O P Zn: H, 7.72; C,
2
1
6
52
2 6 2 2
45.99; N, 12.38% found: H, 7.87; C, 46.13; N, 12.52%; H NMR (300 MHz, CDCl ), d
3
(
(
ppm): 3.52 (m, 12H), 1.87 (m, 8H), 1.32 (m, 6H); IR: 2949, 2867, 2195, 1452, 1336, 1219
ꢀP ¼ O), 1148, 1195, 1013, 960, 763, 709, 573 cm ; KM (X cm mol ) ¼ 9.12.
ꢁ
1
ꢁ1
2
ꢁ1

JOURNAL OF COORDINATION CHEMISTRY
5
2
.4.7. [ZnCl2(PyrrP(O)Mor2)2] (7)
ꢂ
Yield ¼ 0.52 g (73%); m. p. ¼ 100 C; Anal. Calcd for C H Cl N O P Zn: H, 6.77; C,
2
1
4
48
2 6 6 2
40.32; N, 11.76% found: H, 6.83; C, 40.57; N, 11.89%; H NMR (300 MHz, CDCl ), d
3
(
1
ppm): 3.70 (m, 8H), 3.22 (m, 12H), 1.91 (m, 4H); IR: 2957, 2853, 1450, 1352, 1298, 1257,
ꢁ
1
ꢁ1
2
205 (ꢀP ¼ O), 1133, 1109, 1018, 962, 915, 726, 684, 607, 543, 476 cm ; KM (X cm
ꢁ
1
mol ) ¼ 1.36.
2.4.8. [ZnCl2(PyrrP(O)Pip2)2] (8)
Yield ¼ 0.50 g (71%); Anal. Calcd for C H Cl N O P Zn: H, 7.98; C, 47.57; N, 11.89%
2
8
56
2 6 2 2
1
found: H, 8.13; C, 47.63; N, 11.95%; H NMR (300 MHz, CDCl ), d (ppm): 3.20 (m, 12H),
3
ꢁ
1
2
ꢁ1
1
.90 (m, 4H), 1.60 (m, 12H); KM (X cm mol ) ¼ 11.85.
2
.4.9. [CdCl2(MorP(O)Pyrr2)2] (9)
ꢂ
Yield ¼ 0.49 g (67%); m. p. ¼ 135 C; Anal. Calcd for C H CdCl N O P : H, 6.63; C,
24
48
2 6 4 2
1
3
3
9.49; N, 11.51% found: H, 6.72; C, 39.83; N, %; H NMR (300 MHz, CDCl ), d (ppm):
.66 (m, 4H), 3.18 (m, 12H), 1.85 (m, 8H); IR: 2956, 2860, 1450, 1343, 1295, 1253, 1208
3
ꢁ
1
(
ꢀP ¼ O), 1169, 1135, 1111, 1089, 1016, 969, 915, 870, 757, 702, 584, 487 cm ; KM
ꢁ
1 2
ꢁ1
(X
cm mol ) ¼ 1.51.
2
.4.10. [CdCl2(PipP(O)Pyrr2)2] (10)
ꢂ
Yield ¼ 0.50 g (69%); m. p. ¼ 102 C; Anal. Calcd for C H CdCl N O P : H, 7.22; C,
2
1
6
52
2 6 2 2
43.01; N, 11.58% found: H, 7.31; C, 43.46; N, 11.67%; H NMR (300 MHz, CDCl ), d
3
(
(
ppm): 3.18 (m, 12H), 1.85 (m, 8H), 1.55 (m, 6H); IR: 2938, 2856, 1447, 1339, 1206
ꢀP ¼ O), 1142, 1081, 1014, 957, 698, 584 cm ; KM (X cm mol ) ¼ 4.98.
ꢁ
1
ꢁ1
2
ꢁ1
2
.4.11. [CdCl2(PyrrP(O)Mor2)2] (11)
ꢂ
Yield ¼ 0.34 g (43%); m. p. ¼ 150 C; Anal. Calcd for C H CdCl N O P : H, 6.35; C,
2
1
4
48
2 6 6 2
37.83; N, 11.03% found: H, 6.64; C, 38.12; N, 11.35%; H NMR (300 MHz, CDCl ), d
3
ꢁ
1
2
ꢁ1
(ppm): 3.68 (m, 8H), 3.18 (m, 12H), 1.88 (m, 4H); KM (X cm mol ) ¼ 5.80.
2.4.12. [CdCl2(PyrrP(O)Pip2)2] (12)
Yield ¼ 0.43 g (54%); Anal. Calcd for C H CdCl N O P : H, 7.49; C, 44.60; N, 11.15%
2
8
56
2 6 2 2
1
found: H, 7.53; C, 44.77; N, 11.27%; H NMR (300 MHz, CDCl ), d (ppm): 3.22 (m, 12H),
3
ꢁ
1
2
ꢁ1
1
.86 (m, 4H), 1.58 (m, 12H); KM (X cm mol ) ¼ 11.12.
2.5. X-ray structural details
X-ray analyses for 1 and 12 were carried out at 173 K Rigaku SCXmini CCD diffractom-
eter with a SHINE monochromator [Mo Ka radiation (k ¼ 0.71075 Å)]. Data for 2 were
collected at 125 K using the St Andrews Automated Robotic Diffractometer
(STANDARD) [22], consisting of a Rigaku sealed-tube generator, equipped with a
SHINE monochromator [Mo Ka radiation (k ¼ 0.71075 Å)], and a Saturn 724 CCD area
detector, coupled with a Microglide goniometer head and an ACTOR SM robotic sam-
ple changer. Data for 3 were collected at 125 K using a Rigaku MM-007HF High
Brilliance RA generator/confocal optics with XtaLAB P200 diffractometer [Cu Ka

6
M. M’HAIHAM ET AL.
Table 1. Crystal data, data collection, and refinement parameters for 1, 3, 11, and 12.
1
3
11
12
Empirical formula
Formula weight
Crystal color, Habit
Crystal dimensions (mm)
Crystal system
Space group
a (Å)
C
24
H
48Cl
650.92
2
N
6
O
2
P
2
Zn
C
24
H
48CdCl
697.95
2
N
6
O
2
P
2
C
24
H
48CdCl
761.92
2
N
6
O
4
P
2
C
28
H
2 6 2 2
56CdCl N O P
754.02
Colorless, Prism
Colorless, Prism
Colorless, Prism
Colorless, Prism
0.30 ꢃ 0.17 ꢃ 0.15
0.15 ꢃ 0.06 ꢃ 0.06
0.15 ꢃ 0.15 ꢃ 0.15
Monoclinic
C 2/c
0.23 ꢃ 0.18 ꢃ 0.15
Monoclinic
C 2/c
Monoclinic
Monoclinic
P 2
1
/c
1
P 2 /c
13.8006(9)
12.7723(8)
17.7204(12)
102.907(6)
3044.6(4)
4
13.9491(4)
12.8405(4)
17.8032(6)
103.658(3)
3098.62(17)
4
13.7860(3)
14.2662(2)
17.3730(4)
108.195(2)
3245.97(12)
4
13.7783(10)
14.2980(10)
17.4136(13)
108.112(5)
3260.5(4)
4
b (Å)
c (Å)
ꢂ
B ( )
3
V (Å )
Z
3
Dcalc (g/cm )
1.420
1.496
1.559
1.536
F (0 0 0)
1376.0
1448.00
1576
1576
Data
2
Goodness-of-fit on F
1.081
0.0545
0.0717
0.1596
1.088
0.0850
0.0918
0.2348
1.092
0.0517
0.0554
0.1576
1.053
0.0545
0.0677
0.1540
Final R indices (I > 2r(I))
R indices (all data)
wR2
radiation (k ¼ 1.54187 Å)]. Data for 11 were collected at 173 K using a Rigaku FR-X
Ultrahigh Brilliance Microfocus RA generator/confocal optics with XtaLAB P200 diffract-
ometer [Mo Ka radiation (k ¼ 0.71075 Å)].
For all compounds, intensity data were collected using x steps accumulating area
detector images spanning at least a hemisphere of reciprocal space. CrystalClear [23]
was used to collect all data and to process 1 and 12, whereas CrysAlisPro [24] was
used to process 3 and 11. All data were corrected for Lorentz and polarization effects.
The CrystalStructure [25] interface was used during the refinement of 1 and 3, and
Olex2 [26] for 11 and 12.
The crystal structures were all solved using dual space methods (SHELXT) [27] and
refined using full matrix least square techniques (SHELEXT) [28]. All non-hydrogen
atoms were refined anisotropically and hydrogens were placed geometrically using
the riding model. Selected crystallographic data are presented in Table 1.
3
. Results and discussion
.1. Synthesis
The variously substituted phosphoramide ligands, R NP(O)(RꢀN) , are new compounds
3
2
2
2
and were prepared in two steps (Scheme 1). The first step is the addition of two
equivalents of amine (R NH) to phosphoryl chloride (POCl ) in diethyl ether. The
2
3
second is the addition of four equivalents of the second amine (RꢀNH) to the product
2
obtained in the first step. The resulting compounds are all colorless viscous liquids
except PyrrP(O)Mor , which is a light yellow sold.
2
The complexes [MCl L ] were produced by reaction of zinc(II) or cadmium(II) chlor-
2
2
ides in ethanol solution with the phosphoramide ligands (Scheme 2). These were puri-
fied by washing with anhydrous diethyl ether to give the pure complexes as white
solids that are soluble in dichloromethane, chloroform, and nitromethane. To further
confirm the adduct nature of these chloride complexes, their molar conductance in

JOURNAL OF COORDINATION CHEMISTRY
7
Scheme 1. Synthesis of differently substituted phosphoramides R NP(O)(N Rꢀ ) .
2
2 2
Scheme 2. Synthesis of zinc(II) and cadmium(II) complexes 1–12.
ꢁ
3
dichloromethane (10 M) was measured and shows values in the range 1.36–11.85
ꢁ
1
2
ꢁ1
X
cm mol . This indicates that these complexes are nonelectrolytes containing
chloride ions with the general formula [L MCl ], in good agreement with our previous
2
2
results obtained with other related complexes [16, 17].
3.2. Spectroscopic characterization
1
13
31
The complexes were characterized by IR and multinuclear ( H, C, and P) NMR spec-
troscopy. The IR spectra (Figure 1 and Table 2) show that the stretching vibration of
the P ¼ O band is shifted to lower frequencies compared to those of free ligands, con-
sistent with ligand P ¼ O bond weakening upon coordination to the metal center
through the oxygen of this group. This shift is more pronounced for the cadmium
adducts compared to the zinc complexes. For example, the shift (Dꢀ
) for Pyrr PO is
3
P¼O
ꢁ
1
55 and 77 cm in Zn complex 1 and its Cd analog 2, respectively. Such a difference
could be explained in terms of steric hindrance which would favor stronger interaction
with the larger Cd ion, leading to a more lengthened PO bond. Further confirmation
ꢁ
1
comes from the much higher Dꢀ
shift value (136 cm ) observed for the still larger
P¼O
metal atom in the corresponding uranium(IV) complex [UCl (Pyrr PO) ] [29]. These
4
3
2
results seem to be in agreement with those reported for similar complexes [30, 31]
31
and with our structural study discussed below. The P NMR spectra of the complexes
were obtained at room temperature (Figure 2) and the data are listed in Table 2. The
spectra show signals that are slightly shifted downfield compared to those of the free
ligands, confirming the coordination of these ligands with zinc and cadmium through
the P ¼ O group. Despite the stronger donor ability of the phosphoramide ligands, the
3
1
31
P NMR coordination chemical shift (D P) in 1-12 is less than 2 ppm while that of
the zinc complex with a similar donor ability phosphine oxide ligand, [ZnCl (n-
2
Bu PO) ], is much larger (14 ppm) [16]. This could be explained by the presence of a
3
2
nitrogen in the former ligands, which would compensate the loss of electron density

8
M. M’HAIHAM ET AL.
Figure 1. IR spectrum of 1 in CHCl3.
3
1
ꢁ1
Table 2. P NMR (d/ppm) and IR (v(P ¼ O)/cm ) data for [MCl L ] (1–12).
2
2
b
ꢀ
P¼O (DꢀP¼O)
31
31
a
P (Dd P)
[ZnCl ] [CdCl
Ligand (L)
Pyrr PO
Pip PO
MorP(O)Pyrr
L
2
L
2
2
L
2
]
L
[ZnCl
2
L
2
]
2 2
[CdCl L ]
3
14.20
20.12
15.49
16.23
16.47
18.44
15.72(1.52) 15.33(1.13)
21.08(0.96) 21.01(0.89)
16.77(1.28) 16.36(0.87)
17.45(1.22) 16.58(0.35)
17.55(1.08) 16.93(0.46)
18.53(0.09)
1219
1228
1229
1223
1212
1232
1161(58)
1170(58)
1157(72)
1148(75)
1159(53)
1142(77)
3
2
1169(60)
1143(80)
1113(99)
PipP(O)Pyrr
PyrrP(O)Mor
2
2
PyrrP(O)Pip
2
a
31
31
31
D(d P) ¼ j d P (ligand) - d P complex).
b
Dꢀ(P ¼ O) ¼ jꢀ(P ¼ O)(ligand) - ꢀ(P ¼ O)(complex)j.
31
around the phosphorus upon coordination, thus resulting in a more reduced D P. These
1
complexes were also characterized by their H NMR spectra, which display relatively
broader signals that are slightly downfield shifted compared to those of free ligands.
3.3. Structural study
In order to investigate the constitution of the complexes, as well as to gain insights
on the effect of the nature of the ligand donor atom on the stereochemistry and
nuclearity of these complexes, we examined the solid-state structure of [MCl L ].
2
2
Complexes 1, 3, 11, and 12 gave crystals suitable for X-ray analysis. However, the
other complexes were not sufficiently crystalline, even after multiple recrystallization
attempts. The geometries of 1, 3, 11, and 12 (Figures 3–6) are similar monomeric spe-
cies, two oxygens of the two ligands and two chlorides coordinate to the metal cen-
ter, giving it a distorted tetrahedral geometry. In contrast, the corresponding Zn and
Cd complexes containing the sulfur or selenium donor ligands, Pip PS and Pip PSe,
3
3

JOURNAL OF COORDINATION CHEMISTRY
9
3
1
ꢂ
Figure 2. P NMR spectrum of 1 in CDCl at 25 C.
3
Figure 3. The X-ray crystal structure (asymmetric unit) of [ZnCl (Pyrr PO) ] (1). All hydrogens have
2
3
2
been omitted for clarity.
exist as chloride bridged dimeric forms [17], showing the effect of bulkier chalcogen
atoms (S and Se) on the nuclearity of such complexes. Table 3 lists important bond
lengths and angles. When comparing the P ¼ O bond distances in the zinc complex 1
(1.490(3) Å) and Cd complex 3 (1.497(4) Å), we observed that they are similar to those
of corresponding Co (1.489(1) Å) [32] and Mn (1.493(2) Å) [33] complexes
MCl (Pyrr PO) ], but shorter than PO bond (1.515(7) Å) in the related uranium com-
[
2
3
2
plex [UCl (Pyrr PO) ] [29]. The P ¼ O bond lengths are 1.491(3), 1.484(17), 1.492(4),
4
3
2
1
.480(4) and 1.479(5) Å for 1, 3, 11, and 12, respectively. The average P ¼ O bond dis-
tances are all shorter than the sum of the representative covalent radii of P and O,

1
0
M. M’HAIHAM ET AL.
Figure 4. The X-ray crystal structure (asymmetric unit) of [CdCl (Pyrr PO) ] (3). All hydrogens have
2
3
2
been omitted for clarity.
Figure 5. The X-ray crystal structure (one molecule) of [CdCl (PyrrP(O)Mor ) ] (11). All hydrogens
2
2 2
have been omitted for clarity.
Figure 6. The X-ray crystal structure (one molecule) of [CdCl (PyrrP(O)Pip ) ] (12). All hydrogens
2
2 2
have been omitted for clarity.

JOURNAL OF COORDINATION CHEMISTRY
11
Table 3. Selected bond lengths and angles for 1, 3, 11, and 12.
[
2
ZnCl (Pyrr
3
PO)
2
] (1)
[CdCl
2
(Pyrr
3
PO)
2
] (3)
[CdCl
2
(PyrrP(O)Mor
2
)
2
] (11)
[CdCl
2
(PyrrP(O)Pip
2
)
2
] (12)
P1-O1
P2-O2
P1-N1
P2-N2
M-Cl1
M-Cl2
M-O1
M-O2
M-O1-P1
M-O2-P2
O1-M-Cl1
O2-M-Cl2
Cl1-M-Cl2
O1-M-O2
O1-P1-N1
1.490(3)
1.489(3)
1.631(3)
1.625(4)
2.244(10)
2.232(10)
1.962(3)
1.953(3)
157.17(18)
162.4(2)
107.20(8)
112.20(9)
117.51(4)
102.45(11)
108.23(17)
1.492(4)
1.502(4)
1.628(5)
1.630(5)
2.417(14)
2.403(15)
2.173(4)
2.153(4)
155.6(3)
158.2(3)
103.57(12)
111.83(12)
121.69(5)
98.23(16)
108.4(3)
1.480(4)
1.480(4)
1.636(4)
1.618(4)
2.382(13)
2.382(13)
2.158(4)
2.158(4)
156.4(3)
156.4(3)
106.99(14)
112.13(15)
121.54(9)
93.6(3)
1.479(5)
1.479(5)
1.624(6)
1.634(6)
2.386(17)
2.386(17)
2.156(4)
2.156(4)
157.0(4)
157.0(4)
107.05(17)
111.66(18)
121.89(11)
94.0(4)
108.6(3)
108.6(3)
implying some retention of p bonding in the complex. However, these P ¼ O distances
are longer than those observed in the free ligands [34, 35]. This indicates that the
P ¼ O bond is weakened upon complex formation with the singly bonded structure
becoming more pronounced with stronger donor ligands, in agreement with the order
obtained from our IR and NMR data for the magnitude of metal–ligand interaction
and with other related results [36]. These are also longer than the sum of covalent
radii for representative single P-O bond but much shorter than the sum of van der
Waals radii [37]. The structures of these complexes reveal that the average P-O-Zn
ꢂ
angle is 157.17(18)ꢁ162.4(2) for 1, while that of P-O-Cd is 155.6(3)ꢁ158.2(3) for 3,
ꢂ
ꢂ
1
56.4(3) for 11 and 157.0(4) for 12. All these angles (151.2–158.2 ) are similar to those
ꢂ
ꢂ
of Co (156.20(7) ) and Mn (158.9(1) ) analogs [32, 33], but much more axial than those
in the corresponding S and Se analogs, which display more bent angles (less than
ꢂ
1
09 ) [17]. This indicates that 1-12 could be classified as r-donors, employing P-O
r-non-bonding electrons (lone pairs) for donation, rather than p-bonding electrons
used for coordination in analogous S and Se derivatives [17], consistent with the
bonding model proposed by Burford et al. [38]. The M–O bonds show distances of
1.930(14) to 1.962(3) Å for zinc complexes and 2.153(4) to 2.173(4) Å for the cadmium
derivatives (Table 3). The average P-N distances in the complexes vary from 1.618(4)
to 1.636(4) for 11, which are shorter than in corresponding ligands [34, 36]. Finally,
the M-Cl bond distances (2.169(7)ꢁ2.417(14) Å) are also shorter than the sum of corre-
sponding covalent radii.
The degrees of tetrahedral distortion [39] in these complexes, calculated using
PLATON, are 0.92, 0.89, 0.90, and 0.90 for 1, 3, 11, and 12, respectively. This suggests
that the coordination around the metal center is almost a perfect tetrahedron. The
pyrrolidine ligands in 1 adopt a twisted conformation, except for the N13-C17 ring
which exhibits an envelope conformation on C15.
Molecular packing arrangements for 1, 3, 11, and 12 are shown in Figure 7. The
molecules in all four of the structures arrange themselves into sheets in the [110]
plane and stack in discrete columns down the [110] and [ꢁ110] crystallographic axes.
All four of the structures possess intermolecular C-HꢄꢄꢄCl interactions: In 1, Cl3 interacts
with the adjacent molecules in two neighboring columns, along the c and [110]

1
2
M. M’HAIHAM ET AL.
Figure 7. Molecular packing arrangements of 1 (a), 3 (b), 11 (c), and 12 (d).
directions (Figure 7(a)). In 3, Cl2 and Cl3 both interact with the same neighboring mol-
ecule, forming zig-zagging, double C-HꢄꢄꢄCl bonded columns down the b-axis. Cl3 also
interacts with another neighboring molecule, an interaction which propagates down
the c-axis (Figure 7(b)). 11 has a set of these C-HꢄꢄꢄCl interactions propagating down
the [110] and a-axes, along with a head to tail motif about the inversion center
(
Figure 7(c)). 12 shows head to tail C-HꢄꢄꢄCl interaction which propagates down the c-
axis. There is also a C-HꢄꢄꢄCl interaction which propagates down the crystallographic
110] axis in 12 (Figure 7(d)).
[
4. Conclusion
New zinc(II) and cadmium(II) complexes with phosphoramides containing cyclic amino
1
13
31
groups were prepared and characterized using multinuclear ( H, C, and P) NMR, IR
spectroscopy, and in some cases X-ray analysis. The X-ray data reveal that these com-
plexes exist as monomers, in contrast to their corresponding chalcogen counterparts
that form dimeric structures. In addition, the P-O-M bond angles were shown to
be much more axial than those of P-E-M (E ¼ S or Se) observed in corresponding
chalcogenide analogs. This was rationalized in terms of the nature of the chalcogen
donor atom involved in such complexes. The coordination chemistry of these ligands
toward other metal ions is under investigation.
Disclosure statement
No potential conflict of interest was reported by the authors.

JOURNAL OF COORDINATION CHEMISTRY
13
Funding
We are grateful to the Tunisian Ministry of High Education and Scientific Research for financial
support (LR99ES14), to the French Service for Cooperation and Cultural Action and Agence
Universitaire de la Francophonie (AUF) in Nouakchott, Mauritania for a scholarship to MM.
References
[
[
[
1] H. Garrido-Hermandez, K.D. Moon, R.I. Geahlen, R.F. Borch. J. Med. Chem., 49, 3368 (2006).
2] J.H. Tay, A.J. Arguelles, P. Nagorny. Org. Lett., 17, 3774 (2015).
3] C.M. Mikulski, J.S. Skryantzt, N.M. Karayannis, L.L. Pytlewski, L.S. Gelfand. Inorg. Chim. Acta,
2
7, 69 (1978).
[
[
[
4] K. Issleib, B. Mitscherling. Z Anorg. Allg. Chem., 304, 73 (1960).
5] D.M.L. Goodgame, F.A. Cotton. J. Chem. Soc., 2298 (1961).
6] (a) M. Afzall, D. Crouch, M.A. Malik, M. Motevalli, P. O’Brien, J.-H. Park, J.D. Woollins. Eur. J.
Inorg. Chem., 171–177 (2004); (b) J. Waters, D.J. Crouch, J. Raftery, P. O’Brien. Chem.
Mater., 16, 3289 (2004).
[
[
7] J. Jasieniak, C. Bullen, E.J. Van, P. Mulvaney. J. Phys. Chem. B, 109, 20665 (2005).
8] T. Chivers, J.S. Ritch, S.D. Robertson, J. Konu, H.M. Tuononen. Acc. Chem. Res., 43, 1053
(2010).
[9] N.M. Karayannis, C.M. Mikulski, L.L. Pytleweski. Inorg. Chim. Acta Rev., 5, 69 (1971).
[
[
[
[
10] K. Bania, N. Barooah, J.B. Baruah. Polyhedron, 26, 2612 (2007).
11] L. Qu, Z. Peng, X. Peng. Nano Lett., 1, 333 (2001).
12] C. McGuigan, R.N. Pathirana, J. Balzarini, E. De Clercq. J. Med. Chem., 36, 1048 (1993).
13] R.G. Rodr ꢁı guez, M.P. Hendricks, B.M. Cossairt, H. Liu, J.S. Owen. Chem. Mater., 25, 1233
(2013).
[
[
[
[
[
[
14] (a) H. Shen, H. Wang, X. Li, J.Z. Niu, H.X. Chen, L.S. Li, Dalton Trans., 10534 (2009);(b) L.S.
Dent Glasser, L. Ingram, M.G. King, G.P. McQuillan. J. Chem. Soc. A, 2501 (1969).
15] M.A. Sanhoury, T. Mbarek, A.M.Z. Slawin, M.T.B. Dhia, M.R. Khaddar, J.D. Woollins.
Polyhedron, 119, 106 (2016).
16] Z. Gouid, M.A.K. Sanhoury, R.B. Said, C.L. Carpenter-Warren, A.M.Z. Slawin, M.T.B. Dhia, J.D.
Woollins, S. Boughdiri. J. Coord. Chem., 70, 3859 (2017).
17] F. Ebnou, M. M’Haiham, K. Ebeid, C.L. Carpenter-Warren, A.M.Z. Slawin, J.D. Woollins, M.T.
Ben Dhia, M.A. Sanhoury. Polyhedron, 159, 206 (2019).
18] D.D. Perrin, W.L.F. Armarego. Purification of Laboratory Chemicals, 6th edn, Butterworth-
Heinemann, Oxford (2009).
19] M.S. Henriques, D.I. Gorbunov, A.N. Ponomaryov, A. Saneei, M. Pourayoubi, M. Du ꢂs ek, S.
Zvyagin, M. Uhlarz, J. Wosnitza. Polyhedron, 118, 154 (2016).
[
[
20] J.-C. Bollinger, G. Yvernault, T. Yvernault. Spechtrochim. Acta, 41, 399 (1985).
21] E.V. Goud, B.B. Pavan Kumar, Y. Shruthi, A. Paul, A. Sivaramakrishna, K. Vijayakrishna,
C.V.S. Brahmananda Rao, K.N. Sabharwal, H.S. Clayton. J. Coord. Chem., 66, 2647 (2013).
22] A.L. Fuller, L.A.S. Scott-Hayward, Y. Li, M. B u€ Hl, A.M.Z. Slawin, J.D. Woollins. J. Am. Chem.
[
[
Soc., 132, 5799 (2010).
23] CrystalClear-SM Expert v2.1. Rigaku Americas, The Woodlands, Texas, USA, and Rigaku
Corporation, Tokyo, Japan (2015).
[
[
24] CrysAlisPro v1.171.38.41. Rigaku Oxford Diffraction, Rigaku Corporation, Oxford, UK (2015).
25] CrystalStructure v4.2. Rigaku Americas, The Woodlands, Texas, USA, and Rigaku
Corporation, Tokyo, Japan (2015).
[26] O.V. Dolomanov, L.J. Bourhis, R.J. Gildea, J.A.K. Howard, H. Puschmann. J. Appl.
Crystallogr., 42, 339 (2009).
[27] A. Altomare, M. Burla, M. Camalli, G. Cascarano, C. Giacovazzo, A. Guagliardi, A. Moliterni,
G. Polidori, R. Spagna. J. Appl. Crystallogr., 32, 115 (1999).

1
4
M. M’HAIHAM ET AL.
[28] P.T. Beurskens, G. Admiraal, H. Behm, G. Beurskens, J.M.M. Smits, C. Smykalla. Z.
Kristallogr. Cryst. Mater., 99 (1991).
[
[
29] J.F. de Wet, M.R. Caira. J. Chem. Soc., Dalton Trans., 2043 (1986).
30] J G.H. Du Preez, H. E. Rohwer, B. J.A.M. van Brecht, B. Zeelie, U. Casellato, R. Graziani.
Inorg. Chim. Acta, 189, 67 (1991).
[
[
[
[
[
[
[
31] M. Mathew, G.J. Palenik. Can. J. Chem., 47, 1093 (1969).
32] CSD Refcode: IZOTUO - 10.5517/ccdc.csd.cczdqhk.
33] CSD Refcode: IZOVAW - 10.5517/ccdc.csd.cczdqln.
34] C. Romminig, J. Songstad. Acta Chem. Scand., A36, 665 (1982).
35] C.R. Hilliard, N. Bhuvanesh, J.A. Gladysz, J. Bl u€ mel. Dalton Trans., 41, 1742 (2012).
36] R. Davies. R. Soc. Chem., 286 (2007).
37] J.E. Huheey, E.A. Keiter, R.L. Keiter (Eds.). Inorganic Chemistry-Principles of Structure and
Reactivity, 4th edn, Harper Collins College Publishers, London (1993).
38] N. Burford, B.W. Royan, R.E.V.H. Spence, R.D. Rogers. J. Chem. Soc., Dalton Trans., 2111
[
[
(1990).
39] L. Yang, D.R. Powell, R.P. Houser. Dalton Trans., 955 (2007).
Appendix
CCDC numbers 1951187, 1951189, 1951190 and 1951191 contains the supplementarycrystallo-
graphic data for 1, 3, 11 and 12, respectively. 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.