Role of ligand conformation in the structural diversity of divalent complexes containing phosphinic amide ligand

Article abstract of DOI:10.1016/j.inoche.2011.04.023

Reactions of the phosphinic amide ligand N-(4-methyl-2-pyrimidinyl)-P,P- diphenyl-phosphinic amide, L, with the corresponding metal salts afforded the complexes [Zn(L)Cl₂]_∞, 1, and Co₃(L) ₄Br₆, 2, which have been structurally characterized by X-ray crystallography. The molecules of the free L ligands are interlinked through N-H - N and C-H - O hydrogen bonds to form a linear chain, whereas complex 1 shows the 1D helical chain structure, which is the first coordination polymer containing phosphinic amide ligands, and 2 is a linear Co(II) trimer with a rare mixed T_d-O_h-T_d geometry. While the free L ligand adopts the aligned conformation, those in 1 and 2 adopts the cis and both the cis and trans conformations, respectively.

Full text of DOI:10.1016/j.inoche.2011.04.023

Inorganic Chemistry Communications 14 (2011) 1212–1216
Contents lists available at ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Role of ligand conformation in the structural diversity of divalent complexes
containing phosphinic amide ligand
⁎
Chun-Wei Yeh, Jhy-Der Chen
Department of Chemistry, Chung-Yuan Christian University, Chung-Li, Taiwan, R.O.C.
a r t i c l e i n f o
a b s t r a c t
Article history:
Reactions of the phosphinic amide ligand N-(4-methyl-2-pyrimidinyl)-P,P-diphenyl-phosphinic amide, L,
with the corresponding metal salts afforded the complexes [Zn(L)Cl2]∞, 1, and Co3(L)4Br6, 2, which have been
structurally characterized by X-ray crystallography. The molecules of the free L ligands are interlinked
through N–H―N and C–H―O hydrogen bonds to form a linear chain, whereas complex 1 shows the 1D helical
chain structure, which is the first coordination polymer containing phosphinic amide ligands, and 2 is a linear
Co(II) trimer with a rare mixed Td–Oh–Td geometry. While the free L ligand adopts the aligned conformation,
those in 1 and 2 adopts the cis and both the cis and trans conformations, respectively.
Received 7 March 2011
Accepted 15 April 2011
Available online 23 April 2011
Keywords:
Zinc
Cobalt
Phosphinic amide
1-D coordination polymer
© 2011 Elsevier B.V. All rights reserved.
The bis(2-pyridyl)amine (Hdpa) ligand and its anion (dpa−) has
been subjected to many investigations of their coordination abilities
to metal centers. Three types of conformations were found for these
ligands (Fig. 1, top). In the bidentate mode of coordination, the two
pyridyl nitrogen atoms are arranged in a cis conformation, which was
found in the crystal structure of a copper(II) complex [1], while the
trans conformation was found in the crystal structure of the free Hdpa
ligand [2]. The dpa− ligands in the linear trinuclear complexes were
found to possess the aligned conformations [3], in which the three
nitrogen atoms are arranged in a near linear array for coordination to
the metals. Dimolybdenum complexes of Hdpa and dpa−ligands
which show the three conformations have also been reported [4].
To investigate the coordination chemistry of the phosphinic amide
ligand, we have synthesized N-(4-methyl-2-pyrimidinyl)-P,P-diphenyl-
phosphinic amide (L) and reacted with metal salts. We found that the L
ligand can adopt various ligand conformations similar to the Hdpa and
dpa−ligands. Based on the relative orientations of the pyrimidyl
nitrogen atom adjacent to the methyl group, the amide nitrogen atom
and the amide oxygen atom, the ligand L can also possibly show three
conformations in the solid state (Fig. 1, bottom). We report herein the
crystal structures of the free L ligand, the 1D helical chain [Zn(L)Cl2]∞, 1,
and the linear trinuclear complex Co3(L)4Br6, 2, in which the three
ligand conformations can be observed.
to the P O stretching vibrations. These energies are smaller than that
of the free ligand (1235 cm−1), indicating the coordination of the
oxygen atoms to the metal centers (see Fig. S1 in the supplementary
materials). The solid state emission spectra of 1 and 2 show emissions
at 397 and 399 nm, respectively, upon excitations at 245 nm, which
are similar to those of the free L (397 nm) ligand (see Table S1 and
Fig. S2 in the supplementary materials). Since the identity of the
metal center and the structural type hardly changes the emission
wavelength, these emission bands may be tentatively assigned as
intraligand (IL) π→π* transitions.
The crystals of L conform to the space group P21/c with four
molecules in each unit cell. Fig. 2(a) depicts the molecular structure for L
[7]. The molecules are held together by a series of the donor–acceptor–
donor–acceptor (DADA) quadruple hydrogen bonds and the donor–
acceptor (DA) double hydrogen bonds (Fig. 2b) to form 1D linear chains.
The centrosymmetric DADA:ADAD self-complementary interaction
involves two N–H―N [H―N=2.084 (3) Å; ∠N–H―N=173.2 (2)°]
and two C–H―O [H―O=2.657 (3) Å; ∠C–H―O=138.1 (2)°]
hydrogen bonds, while thecentrosymmetric DA:AD interactioninvolves
two C–H―O [H―O=2.551 (2) Å; ∠C–H―O=138.1 (2)°] hydrogen
bonds. The free ligand adopts the aligned conformation, presumably due
to the constraints from the N–H―N and C–H―O hydrogen bonds.
The structure of [Zn(L)Cl2]∞, 1, was solved in the space group P32
with three molecules in the unit cell. Fig. 3(a) depicts a drawing
showing the environment about the Zn(II) center which is coordi-
nated by one nitrogen atom of pyrimidyl group, one oxygen atom of
the phosphinic amide group and two Cl atoms to form a distorted
tetrahedral geometry. The Zn(II) metal centers are bridged by the L
ligands to form the 1D helical chain(Fig. 3b and c). The Zn―Zn
distance separated by the bridging L ligand is 6.595 (1) Å and the
length of the repeating unit of the helical chain involving four zinc
The reactions of L with ZnCl2 and CoBr2 in MeOH/THF afforded the
1D helical chain complex [Zn(L1)Cl2]∞, 1, and the discrete linear
trinuclear complex Co3(L1)4Br6, 2, respectively [5]. The IR spectra for
1 and 2 show bands at 1129 and 1125 cm−1, respectively, assignable
⁎
Corresponding author. Tel.: +886 3 2653351; fax: +886 3 2653399.
E-mail address: jdchen@cycu.edu.tw (J.-D. Chen).
1387-7003/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2011.04.023

C.-W. Yeh, J.-D. Chen / Inorganic Chemistry Communications 14 (2011) 1212–1216
1213
trans
aligned
cis
N
N
N
N
N
H
N
N
N
H
N
N
H
CH3
O
P
N
N
P
3HC
N
N
H
P
3HC
N
N
H
N
N
H
O
O
Fig. 1. The three possible conformations for 2,2'-dipyridylamine (top) and L (bottom).
atoms and three L ligands is 12.480 (2) Å along the 31 screw axis. The L
ligands adopt the cis conformation which is required to form the 1D
helical chain. The 1D chains are also interlinked through C–H―Cl
hydrogen bonds [H―Cl=2.926 (2) Å, ∠C–H―Cl=133.0 (5)°] (see
Fig. S3 in the supplementary materials). To our best knowledge
complex 1 is the first coordination polymeric complex containing
phosphinic amide ligand.
The structure of Co3(L)4Br6, 2 was solved in the space groups P21/n
with two molecules in the unit cell, and Fig. 4(a) depicts the molecular
structure showing the arrangements about the Co(II) metal centers.
The central Co(1) atom which is located at a crystallographic
inversion center is chelated by two L ligands and coordinated by
two trans oxygen atoms from two bridging L ligands to form a
distorted octahedral geometry, while the two terminal Co(II) atoms
adopts the tetrahedral coordination environment, resulting in a
linear trimeric cobalt(II) complex with a mixed Td–Oh–Td geometry.
The Co(1)―Co(2) distance separated by the bridging L ligand is
7.319 (1) Å and the angle of Co(2)–Co(1)–Co(2A) is 180.0°. Two types
of the ligand conformation are found for the L ligands. While the two L
ligands that chelate the central Co(II) atoms adopt the cis conformation,
those that bridge the Co(II) atoms adopt the trans conformation. Fig. 4(b)
and (c) shows the intermolecular C–H―π interactions [H―π=2.866 (1)
Å, ∠C–H―π = 164.74 (24)°] and C–H―Br hydrogen bonds
[H―Br=2.984 (1) and 3.023 (1) Å, ∠C–H―Br=163.19 (21) and
135.34 (23)°], respectively, among the trimeric molecules in the solid
state. The Td–Oh–Td geometry in 2 is in marked contrast to those
(a)
(b)
Fig. 2. (a) A drawing showing the molecular structure of L. Selected bond distances (Å) and angles (°): P–O=1.474(3), P–N(3)=1.664(3), P–C(6)=1.793(4), P–C(12)=1.801(3),
O–P–N(3)=106.8(2), O–P–C(6)=112.0(2), N(3)–P–C(6)=108.6(2), O–P–C(12)=112.6(2), N(3)–P–C(12)=109.0(2), C(6)–P–C(12)=107.6(2). (b) A drawing showing the
hydrogen-bonded linear chain of L.

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C.-W. Yeh, J.-D. Chen / Inorganic Chemistry Communications 14 (2011) 1212–1216
(a)
(b)
(c)
Fig. 3. (a) Coordination environment about the Zn(II) center of 1. The hydrogen atoms are omitted for clarity. Selected bond distances (Å) and angles (°): Zn–O(A)=1.958(4),
Zn–N(1)=2.077(5), Zn–Cl(1)=2.202(2), Zn–Cl(2)=2.226(2), O(A)–Zn–N(1)=103.5(2), O(A)–Zn–Cl(1)=113.2(1), N(1)–Zn–Cl(1)=108.8(2), O(A)–Zn–Cl(2)=104.4(1),
N(1)–Zn–Cl(2)=107.6(2), Cl(2)–Zn–Cl(1)=118.3(1). Symmetry transformations used to generate equivalent atoms: (A) −x+y+1, −x+2, z+1/3. (b) A view of the
helical structure looking down the aaxis. (c) A view of the helical structure looking down the caxis.
reported for cobalt complexes with the trimeric unit which adopt
the Oh–Td–Oh or Oh–Oh–Oh geometry [3,11]. Noticeably, the complex
Co3(OH)2(pa)2(ina)2 [pa = 3-(1 H-benzimidazol-2-yl)propanoic
carboxylate, ina=isonicotinate] consists of the linear Co(II) trimeric
units with the mixed Td–Oh–Td geometry, which are linked by the
single-carboxylate-aromatic amine ligands to form 2D layers [11].
Complex 2 is thus the first discrete linear trinuclear Co(II) complex
containing phosphinic amide ligand, where the metal centers adopt
the mixed Td–Oh–Td geometry.
In summary, we have successfully structurally characterized the
phosphinic amide ligand L and two divalent metal complexes contain-
ing the L ligands. Complex 1 is the first coordination polymer containing
the phosphinic amide ligand, and 2 is a discrete linear Co(II) trimer with
a rare mixed Td–Oh–Td geometry. The L ligand exhibits three ligand
formations similar to those reported for Hdpa and dpa−ligands. In the
solid state, the molecules of the free L ligands are constrained by the N–
H―N and C–H―O interactions, resulting in the aligned conformation,
while those in 1 and 2 adopts the cis and both the cis and trans
conformations, respectively. The L ligand adopts the proper conforma-
tion that maximizes the intra- and intermolecular forces. This study
shows that the phosphinic amide ligand L ligand may display a rich
coordination chemistry which is under investigation.
Acknowledgments
We are grateful to the National Science Council of the Republic of
China for support. This research was also supported by the project of
the specific research fields in Chung-Yuan Christian University,
Taiwan, R.O.C. under grant CYCU-98-CR-CH. We also thank Miss
C.-W. Lu of the Instrumentation Center, National Taiwan University, for
CHNS (EA) analysis experiments.
Appendix A. Supplementary material
Crystallographic data (CIF files) for the structures of L and 1–2 have
been deposited with the Cambridge Crystallographic Data Centre,

C.-W. Yeh, J.-D. Chen / Inorganic Chemistry Communications 14 (2011) 1212–1216
1215
(a)
(b)
(c)
Fig. 4. (a) A drawing showing the trimeric structure of 2. The hydrogen atoms are omitted for clarity. Selected bond distances (Å) and angles (°): Co(1)–O(1)=2.068(3),
Co(1)–O(2)=2.094(3), Co(1)–N(1)=2.192(3), Co(2)–N(4)=2.074(4), Co(2)–Br(3)=2.373(1), Co(2)–Br(2)=2.372(1), Co(2)–Br(1)=2.410(1), O(1A)–Co(1)–O(1)=180.0, O(1A)–Co
(1)–O(2)=91.8(1), O(1A)–Co(1)–O(2A)=88.2(1), O(2)–Co(1)–O(2A)=180.0, O(1A)–Co(1)–N(1)=90.3(1), O(1)–Co(1)–N(1)=89.7(1), O(2)–Co(1)–N(1)=92.4(1), O(2A)–Co(1)–N
(1)=87.6(1), O(1A)–Co(1)–N(1A)=89.7(1), O(2)–Co(1)–N(1A)=87.6(1), O(2A)–Co(1)–N(1A)=92.4(1), N(1)–Co(1)–N(1A)=180.0, N(4)–Co(2)–Br(3)=101.7(1), N(4)–Co(2)–Br
(2)=105.2(1), Br(3)–Co(2)–Br(2)=118.4(0), N(4)–Co(2)–Br(1)=109.3(1), Br(3)–Co(2)–Br(1)=109.4(0), Br(2)–Co(2)–Br(1)=111.9(0). Symmetry transformations used to generate
equivalent atoms: (A) −x, −y+1, −z+1. (b) Thetrimeric molecules arelinkedthrough theintermolecular C–H―π interactions along thea axis. (c) A view showing theC–H―Brhydrogen
bonds among the trimeric molecules, looking down the a axis.
CCDC 815928–815930. Copies of this information may be obtained free
of charge from the Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ,
UK (Fax: +44-1223-336-033; e-mail: deposit@ccdc.cam.ac.uk or
www: http://www.ccdc.cam.ac.uk). Supplementary data associated
with this article can be found, in the online version, at doi:10.1016/j.
inoche.2011.04.023.

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C.-W. Yeh, J.-D. Chen / Inorganic Chemistry Communications 14 (2011) 1212–1216
[7] Crystal data for L: C17H16N3OP, Monoclinic, space group P21/c, Fw=309.30,
References
a=10.5252(17), b=9.1960(11), c=16.659(3), β=99.483(13)o, V=1590.4(4)
Å3, Z=4, dcalc=1.292 g cm−3, = 0.178 mm−1, F(000)=648. R1=0.0584 and
wR2=0.1322, respectively, for IN2σ(I). Crystal data for 1: C17H16ZnN3Cl2PO,
Trigonal, space group P32, Fw=445.57, a=b = 11.5828(9), c = 12.4803(12),
α=β = 90, γ =120o, V = 1450.0(2) Å3, Z = 3, dcalc = 1.531 g cm−3, =
1.639 mm−1, F(000) = 678. R1 = 0.0346 and wR2 = 0.0824, respectively, for I N
2σ(I). Crystal data for 2: C69H68Co3Br6N12O5P4, Monoclinic, space group P21/n,
Fw = 1925.48, a = 11.7876(8), b=14.9731(10), c = 23.2481(16), β=92.271(1)o,
V = 4100.0(5) Å3, Z = 2, dcalc=1.560 g cm−3, = 3.654 mm−1, F(000) = 1914.
R1=0.0450, and wR2=0.1345, respectively, for IN2σ(I). The diffraction data for L
ligand and complex 1 were collected on a Bruker AXS P4 diffractometer [8] at 22 °C
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MeOH/THF (30 mL; 1:1) and ZnCl2 (0.14 g, 1.0 mmol) was added. The mixture
was then stirred at room temperature for 24 h to afford a yellow solution with
some white solid. The solution was filtered and then diethyl ether added to
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2 on a Bruker AXS SMART-1000 diffractometer [9] at 22 °C,
respectively, which was equipped with a graphite-monochromated Mo Kα (λα =
0.71073 Å) radiation. Data reduction was carried by standard methods with use of
well-established computational procedures. The structure factors were obtained
after Lorentz and polarization correction. An empirical absorption correction based
on a series of ψ-scans was applied to the data for L ligand and complex 1, while the
empirical absorption correction based on “multi-scan” was applied to the data for
complex 2. The positions of some of the heavier atoms, including the zinc atom, were
located by the direct method. The remaining atoms were found in a series of
alternating difference Fourier maps and least-square refinements [10]. All the
hydrogen atoms were added by using the HADD program in SHELXTL 5.10.
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a
methanol solution of the compound for several weeks. Yield: 0.25 g (56 %
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3.62; N, 9.43. Found: C, 45.75; H, 3.24; N, 9.56 %. IR (cm−1): 3902(w), 3597
(m), 3191(br), 2365(m), 1962(m), 1612(s), 1433(m), 1326(m), 1258(s), 1129
(s), 1019(w), 905(w), 798(s), 757(m), 696(m), 544(w), 452(m), 440(s), 422
[9] SMART/SAINT/ASTRO, Release 4.03, Siemens Energy and Automation, Inc.,
Madison, Wisconsin, USA, 1995.
(w). Preparation for 2: Prepared as described for
1 except CoBr2 (0.22 g,
1.0 mmol) was used. Yield: 0.58 g (71% based on Co). Anal. Calcd for
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containing linear trimeric cobalt(II) of mixed Td-Oh-Td geometries linked by two
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properties, Dalton Trans. (2008) 2428–2432 and references therein.
C
68H64Co3Br6N12O4P4 (MW=1925.48): C, 43.14; H, 3.41; N, 8.88. Found: C,
43.22; H, 3.41; N, 8.91 %. IR (cm− 1): 3382(b), 2995(b), 2742(w), 2366(w),
1970(m), 1828(m), 1665(s), 1530(m), 1477(w), 1430(m), 1328(m), 1257(m),
1125(s), 1017(s) 897(s), 760(w), 697(m), 623(w), 551(m), 502(m), 458(m).
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