A new six-coordinate organotin(IV) complex of OP[NC5H10]3: A comparison with an analogous five-coordinate complex by means of X-ray crystallography, Hirshfeld surface analysis and DFT calculations

Article abstract of DOI:10.1080/00958972.2018.1461847

A new six-coordinate organotin(IV)-phosphoric triamide complex of OP[NC₅H₁₀]₃?=?OP was synthesized ([Cl₂Sn(CH₃)₂(OP)₂], 1) and characterized by X-ray crystallography and spectroscopic methods (FT-IR, UV–Vis, and ¹H/¹³C/³¹P-NMR). The crystal structures of 1 and the analogous previously reported five-coordinate complex [Cl₂Sn(CH₃)₂(OP)] (IZOVIE) were compared on a structural level and by computational means using Hirshfeld surface analysis, density functional theory calculations and the atom in molecule method. The investigation of intermolecular interactions in the crystal structures of the two complexes by the Hirshfeld surface method indicates that in the absence of normal hydrogen bonds, the chlorine-based interactions H?Cl/Cl?H (for 1 and IZOVIE) and Cl?Sn/Sn?Cl (for IZOVIE) play a determinant role in the molecular assemblies. However, the prominent contacts are of H?H type. From calculated electronic parameters such as bond order, Mulliken charge and electron delocalization energy, it was found that the Sn-OP contact has a lower strength in IZOVIE than in 1, suggesting more ionic character of the metal-oxygen contact in five-coordinate complex IZOVIE. Furthermore, we discuss the similarities and differences of the two complexes 1 and IZOVIE derived from the same ligand OP by density functional theory calculations to present an insight into the organotin(IV)-phosphoric triamide coordination chemistry affected by different geometries and coordination numbers.

Full text of DOI:10.1080/00958972.2018.1461847

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
A new six-coordinate organotin(IV) complex of
OP[NC5H10]3: A comparison with an analogous
five-coordinate complex by means of X-ray
crystallography, Hirshfeld surface analysis and DFT
calculations
Atekeh Tarahhomi & Arie Van Der Lee
To cite this article: Atekeh Tarahhomi & Arie Van Der Lee (2018): A new six-coordinate
organotin(IV) complex of OP[NC5H10]3: A comparison with an analogous five-coordinate complex
by means of X-ray crystallography, Hirshfeld surface analysis and DFT calculations, Journal of
Coordination Chemistry, DOI: 10.1080/00958972.2018.1461847
To link to this article: https://doi.org/10.1080/00958972.2018.1461847
View supplementary material
Accepted author version posted online: 09
Apr 2018.
Submit your article to this journal
View related articles
View Crossmark data
Full Terms & Conditions of access and use can be found at
http://www.tandfonline.com/action/journalInformation?journalCode=gcoo20

Publisher: Taylor & Francis
Journal: Journal of Coordination Chemistry
DOI: http://doi.org/10.1080/00958972.2018.1461847
A new six-coordinate organotin(IV) complex of OP[NC5H10]3: A comparison
with an analogous five-coordinate complex by means of X-ray
crystallography, Hirshfeld surface analysis and DFT calculations
ATEKEH TARAHHOMI† and ARIE VAN DER LEE
†Department of Chemistry, Semnan University, Semnan 35351-19111, Iran
§Institut Européen des Membranes, Université de Montpellier, 34095 Montpellier, France
A new six-coordinate organotin(IV)-phosphoric triamide complex of OP(NC5H10)3 = OP was
synthesized ([Cl2Sn(CH3)2(OP)2], 1) and characterized by X-ray crystallography and
spectroscopic methods (FT-IR, UV-Visible and 1H/13C/31P-NMR). The crystal structures of 1
and the analogous previously reported five-coordinate complex [Cl2Sn(CH3)2(OP)] (IZOVIE)
were compared on a structural level and by computational means using Hirshfeld surface
analysis, density functional theory (DFT) calculations and the Atom In Molecule (AIM) method.
The investigation of intermolecular interactions in the crystal structures of the two complexes by
the Hirshfeld surface method indicates that in the absence of normal hydrogen bonds, the
chlorine-based interactions H…Cl/Cl…H (for 1 and IZOVIE) and Cl…Sn/Sn…Cl (for
IZOVIE) play a determinant role in the molecular assemblies. However, the prominent contacts
are of H…H type. From calculated electronic parameters such as bond order, Mulliken charge
and electron delocalization energy, it was found that the Sn-OP contact has a lower strength in
IZOVIE than in 1, suggesting a more ionic character of the metal-oxygen contact in five-
coordinate complex IZOVIE. Furthermore, we discuss the similarities and differences of the two
complexes 1 and IZOVIE derived from the same ligand OP by density functional theory
calculations to present an insight into the organotin(IV)-phosphoric triamide coordination
chemistry affected by different geometries and coordination numbers.
Keywords: Organotin(IV)-phosphoric triamide complex; X-ray Crystallography; Hirshfeld
surface analysis; DFT Calculation; Spectroscopic study
Corresponding author. Email: tarahhomi.at@semnan.ac.ir

1. Introduction
Phosphoramide compounds with O=P-N segments have a great potential for usage as O-donor
ligands in the preparation of metal coordination compounds. In recent years, the attention for
especially phosphoramide-based organotin(IV) complexes has increased because of the various
applications of these complexes in the pharmaceutical industry [1-4] and agriculture [5, 6].
Among these compounds, the use of the O=P[-N]3-based phosphoric triamide (PO) ligand as a
subclass of phosphoramides have attracted significant attention for novel syntheses of
coordination compounds [7, 8]. Crystal structures of many such complexes have been reported
(CSD, Version 5.38, Feb. 2017 update, [9]) which indicate five- and mainly six-coordinate
geometries. However, there have been no previous reports of both five- and six-coordinate
complexes prepared from the same PO ligand. Moreover, the focus of experimental and
computational researches are extended in different areas of chemistry such as the ones mentioned
above which can provide the appropriate information of different structural, electronic and
spectroscopic aspects. These studies can be useful for investigation and comparison of analogous
compounds.
In this paper, we present the synthesis and crystal structure of a new six-coordinate SnIV
phosphoric triamide complex ([Cl2Sn(CH3)2(OP)2] (1) prepared using water-soluble
tris(piperidin-1-yl)phosphine oxide (OP(NC5H10)3 = OP) ligand and compare it to the crystal
structure of a five-coordinate complex [Cl2Sn(CH3)2(OP)] (IZOVIE) with the same ligand
previously (scheme 1) [10]. Hirshfeld surface analysis [11] and other computational methods are
employed to analyze the interactions in 1 and IZOVIE.
2. Experimental
2.1. Materials and measurements
All chemicals were of analytical grade, obtained from commercial sources and used without
purification. The infrared (IR) spectrum was recorded on a Bruker ALPHA FT-IR spectrometer
using KBr disks. UV-Vis spectrum was recorded on a Shimadzu UV-1650 PC
spectrophotometer. 1H, 13C, 31P{1H} NMR spectra were recorded on a Bruker Avance DR X500
spectrometer. 1H/13C and 31P chemical shifts were determined relative to TMS and 85% H3PO4,
respectively, as external standards.

2.2. Syntheses
For the preparation of ligand OP(NC5H10)3, a solution of amine(piperidine) in dry acetonitrile
was added dropwise to a solution of P(O)Cl3 in the same solvent (6:1 molar ratio) at 273 K. After
stirring for 4 h, the solvent was removed and the crude product was used in complex reactions.
2.2.1. Syntheses of trans-dichloro-trans-dimethyl-trans-bis[tris(piperidine-1-yl)phosphine
oxide-O]tin(IV), [Cl2Sn(CH3)2{OP(NC5H10)3}2] (1). A solution of [Cl2Sn(CH3)2] (1 mmol) in
acetonitrile (5 ml) was added dropwise to an excess of ligand solution (2.5 mmo) in methanol
(15 ml). The clear solution was stirred under reflux for 24 h. Colorless crystals were obtained
after a few days at room temperature. Yield: 60%. IR (KBr, cm−1): 2962, 2918, 2847, 2768,
1452, 1354, 1304, 1259, 1233, 1157, 1136, 1115, 1097, 1068, 964, 916, 870, 845, 783, 731, 613,
575, 498, 478. 1H NMR (500.13 MHz, DMSO-d6, 298.0 K, TMS), δ(ppm): 1.05 (s, 6H, 2CH3,
2J(119Sn,H) = 115.0 Hz and 2J(117Sn,H)=135.0 Hz [satellites]), 3.00 (m, 12H, NC5H10 ring), 3.51
(m, 24H, NC5H10 ring), 3.77 (m, 24H, NC5H10 ring). 13C NMR (125.76 MHz, DMSO-d6,
298.0 K, TMS), δ(ppm): 25.33 (s, 2C, Sn-CH3), 34.60 (s, 6C, NC5H10 ring), 43.25 (s, 6C,
NC5H10 ring), 45.15 (s, 6C, NC5H10 ring), 63.95 (s, 6C, NC5H10 ring), 67.03 (s, 6C, NC5H10
ring). 31P{1H} NMR (202.45 MHz, DMSO-d6, 298.0 K, 85% H3PO4), δ(ppm): 28.82 (s).
2.3. X-ray measurements
A suitable single-crystal for compound 1 was selected for the X-ray diffraction experiment and
mounted in a Teflon cryo loop. Details of crystal data and structure refinement are provided in
table 1.
Measurements were made on a Gemini diffractometer with a Sapphire3 detector and
graphite monochromated MoKα radiation (λ = 0.7107 Å). The data were corrected for absorption
with CrysAlisPro [12]. The structure was solved using the charge-flipping method implemented
in the Superflip program [13] and refined using the CRYSTALS program [14]. Non-H atoms were
refined anisotropically. The H atoms were all located in a difference map, but those attached to
carbon atoms were repositioned geometrically. The H atoms were initially refined with soft
restraints on the bond lengths and angles to regularize their geometry (C-H in the range 0.93-

0.98 Å and Uiso(H) in the range 1.2-1.5 times Ueq of the parent atom). After which the positions
were refined with riding constraints [15].
The piperidine rings in one of the PO ligands appeared to be disordered. The disorder was
modelled with split positions. Two orientations of the piperidine rings were found, and they were
restrained to have a similar geometry. In addition, restraints were used in order to keep
reasonable C-C sp3-sp3 bond lengths. The anisotropic atomic displacement parameters of
adjacent atoms in the disordered fragment were restrained to be the same [16].
PLATON [17] and Mercury [18] programs were used for making the ORTEP and packing
diagrams, respectively.
2.4. Hirshfeld surface analysis
3D Hirshfeld surfaces (HSs) of 1 and IZOVIE were generated using CrystalExplorer 17.5 [19].
The bond lengths to hydrogen atoms were automatically set to standard neutron values (C-H =
1.083 Å) for calculations. The normalized contact distances dnorm ( = + , de and di being the
distances from the point to the nearest nucleus external and internal to the surface, respectively),
based on van der Waals radii [20], were mapped into the HSs. These surfaces display a simple
red-white-blue color scheme for an easy comparison of intermolecular contacts relative to van
der Waals radii. Where red spots exhibit short contacts (with distances shorter than the sum of
van der Waals radii), white areas represent contacts with distances equal to the sum of the van
der Waals radii, and blue regions are free of any close contacts [21].
The HS fingerprint plots (FPs) [22] were constructed from the pair distance de, di for each
individual surface spot displayed on the graph axes. In these plots, the frequency of occurrence
of interactions (the number of points with a given (de,di) pair) are represented by the different
colors blue (low frequency), green (medium) and red (high). Moreover, the (de > di) and (de < di)
regions are displayed on the FPs as complementary regions where one molecule acts as donor
(de > di) and the other as an acceptor (de < di) [23]. These quoted regions are introduced by the
reciprocal X…H/H…X contacts in which X atom is located inside (for X…H/de < di) or outside
(for H…X/de > di) the generated HS as an H-atom acceptor.
For 1, two separate HS analyses were performed for the structure with each orientation of
the piperidine ring. Both orientations appeared to have very similar interaction contributions
within 0.8% and therefore only one orientation was further analyzed as being fully occupied.

2.5. Computational details
All calculations were performed by density functional theory (DFT) in the Gaussian09 program
package [24]. The combined 6-311++G(d,pd) (for C, H, N, O, P and Cl atoms [25]) and
LANL2DZ (for Sn atom [26]) basis sets (designed as SDD) were used for all calculations.
Starting geometries for calculations were taken from the X-ray crystal structures with neutron
based carbon to hydrogen distances. The structures were fully optimized and characterized as
true minima by the absence of imaginary frequencies. Vibrational frequencies were determined
to provide an estimation of the zero point vibrational energies (ZPVE). The natural bond orbital
(NBO) analysis which suggested by Reed et al. [27, 28] was applied to determine the origin of
the structural behavior. UV-vis spectra and electronic transitions were computed with the time-
dependent DFT (TD-DFT) method at the B3LYP/SDD level. The solvent (CH3OH) was
considered as a uniform dielectric constant with a dielectric constant of 32.7.
Furthermore, the density functional theory was used to calculate the dipole moment (μ),
mean polarizability (α) and the total first static hyperpolarizability (β) in terms of x, y, z
components as given by following equations [29]:
α = ( +
+ )
where
;
and
=
. The GIAO method was used for calculating
the 1H NMR and 13C NMR chemical shifts at the HF/SDD/DGDZVP level with
dimethylsulfoxide (DMSO) as solvent. The Atom In Molecule (AIM) model [30] was employed
for the evaluation of Sn-OP contacts in two studied complexes by the calculated topological
properties of charge density (ρ(r)) and its Laplacian (L(r) = –2(ρ(r))) summarized by their critical
points (CPs), where 2(ρ(r)) < 0 and 2(ρ(r)) > 0 reveal the concentration and depletion of the
electron density, respectively.

3. Results and discussion
3.1. Structural description
The molecular structure of 1 is shown in figure 1. Selected bond lengths and angles are presented
in table 2. The asymmetric unit is composed of one-half of the complete molecule located on a
center of inversion. In one of the PO ligands, the piperidine rings are disordered over two sets of
sites with refined occupancies of 0.495(4) and 0.505(4).
The Sn coordination geometry in 1 is octahedral with the two phosphoramide ligands in a
trans position with respect to each other. Two chlorine atoms and two methyl groups separately
adopt a trans position (figure 1).
The piperidine rings adopt a chair conformation and the P atoms in the ligands adopt a
distorted tetrahedral environment. The Sn-O, Sn-Cl and Sn-C bond lengths and the Sn-O-P bond
angles of 1 are within the expected values [7, 8].
There is an analogous five-coordinate complex of OP(NC5H10)3,
[Cl2Sn(CH3)2{OP(C5H10N)3}] (IZOVIE [10]), in which the tin atom exhibits a distorted trigonal
bipyramidal coordination with the axial positions being occupied by one Cl and one phosphoric
triamide ligand. Two methyl groups and the other Cl atom of the [Cl2Sn(CH3)2] segment define
the equatorial plane. Moreover, for this complex, the parameter τ which represents the
percentage distortion from trigonal bipyramidal geometry calculated by the Addison method is
about 45%. In the Addison method, the parameter τ is defined as τ = × 100, where φ and θ are
the two observed basal angles [31].
A comparison of the bond lengths of 1 and IZOVIE show that the Sn-C, Sn-Cl and P=O
bond lengths are slightly longer in 1 than IZOVIE, while the Sn-O bond is longer in IZOVIE
than in 1. However, the structures of 1 and IZOVIE are determined in different temperatures,
175 K and 100 K, respectively. The most important structural difference between five
(IZOVIE)- and six (1)-coordinate tin complexes of OP[NC5H10]3 is the positions of cis-methyl
groups and cis-chlorine atoms in IZOVIE versus trans positions in 1. The assessment of various
properties affected by these structural features will be discussed in the next sections.
The bond valence sum (BVS) value for the tin ion in 1 was calculated as 4.096, which is
close to the formal oxidation states of SnIV.
No classical hydrogen bond is possible in the crystal structure of 1 because there are not
appropriate donors and acceptors for such interactions. Stabilization of 1 is produced via some

weak interactions. For example, the intermolecular interactions C61-H612…Cl2 hydrogen bonds
(C61…Cl2 = 3.422 (5) Å, C61-H612-Cl2 = 115.1° and symmetry code: -x + , y + , -z + ) in
the structure form a 2D network parallel to the (-101) plane as shown in figure 2.
3.2. Analysis of intermolecular interactions by HSs and FPs
The Hirshfeld surfaces of 1 and IZOVIE are given in figures 3 and 4, showing surfaces that have
been mapped over dnorm along with decomposed fingerprint plots. Table 3 presents the
percentage contributions of interactions for 1 and IZOVIE.
From the figures, it is realized that the interactions H…H in 1 and Sn…Cl/Cl…Sn in
IZOVIE represent the closest contacts highlighted as red spots on dnorm surfaces. The related FPs
comprise 90.8% (H…H) and 1.0% (Sn…Cl/Cl…Sn) of the total HS, for 1 and IZOVIE,
respectively. Other considerable interactions are C-H…Cl hydrogen bonds which are evidenced
by the H…Cl/Cl…H FPs comprising 9.1% of the total HS for 1 and 23.0% for IZOVIE.
Moreover, it results from the FPs that the highest proportions of interactions for both structures
are observed for H…H contacts which cover a wide range of HS (table 3) marked by the points
spread out in the center of FP. For details of the HS analysis, see the Supplementary Material.
In summary, the most important difference observed in the molecular assemblies of the
studied structures, caused by the reduction of coordination number from six in 1 to five in
IZOVIE, is the increased contribution of the chlorine-based interactions in IZOVIE (24.0%)
comparing to 1 (9.1%). Another difference is the presence of the dipolar Sn…Cl type
interactions in five-coordinate complex IZOVIE which can be rationalized by a smaller steric
hindrance, supported by the presence of only one PO ligand in the structure, and also by the cis-
orientation of coordinated chlorine atoms with respect to each other.
3.3. DFT Calculations
3.3.1. Geometry optimization. The geometry of complexes 1 and IZOVIE were optimized
using the B3LYP method with SDD basis set. Calculated geometrical parameters alongside
experimental values are presented in table 2. As can be seen, a good agreement is found between
the optimized parameters from the DFT calculations with experimental ones from X-ray
crystallography results in both complexes. For 1, the highest difference is about 0.1 Å in bond
lengths and about 2° in bond angles, while in IZOVIE for bond lengths the same difference

about 0.1 Å is found, but for the bond angles a discrepancy about 10° is observed for the
C1-Sn1-Cl1 angle. Such differences are expected, since the X-ray crystallography results
correspond to data that were obtained in the solid state whereas the calculated data are valid for
the gaseous state.
3.3.2. Vibrational analysis. Vibrational frequencies have been computed for the optimized
structures of 1 and IZOVIE on the DFT(B3LYP)/SDD level. The calculated (for 1 and
IZOVIE) and observed (for 1) FT-IR spectra are shown in figure 5. Experimental and calculated
vibrational frequencies are listed in table S1, where the observed bands of 1 are assigned by
comparison of calculated and experimental IR spectra with the reported IR spectra of similar
compounds [7, 32].
For complex 1, the experimental bands in the range 2700 cm-1 to 2970 cm-1 are assigned
to C-H stretching vibrational modes of CH2 (in the piperidine rings) and CH3 (in the Cl2Sn(CH3)2
segment) groups. The peaks in the range 1450 cm-1 to 1160 cm-1 are attributed to the different
types of vibrational modes scissoring, wagging, twisting and rocking of CH2 and CH3 groups.
The P=O stretching vibrational mode is found at 1115 cm-1. At wavenumbers lower than about
1100 cm-1, the stretching, bending and rocking vibrational modes of CH2 groups in the piperidine
rings or the combinations of them can be observed. The stretching vibrational modes of the Sn-C
bonds are assigned to the bands at 575 cm-1 and 498 cm-1. Similar calculated results are obtained
for IZOVIE (table S1). More details of the vibrational analysis are provided in the
Supplementary Material.
3.3.3. UV-vis spectra. The UV-vis spectrum of 1 in CH3OH shows a band at 201 nm
(absorbance: 0.310 a.u. = 8.43 eV) that may be assigned to the π→π* transition of the P=O unit.
The calculated results in the same solvent indicate that the calculated absorption band appears at
202 nm with bond energy of 6.15 eV (orbital excitation: HOMO-7→LUMO, 92% contribution).
The calculated wavelength is in good agreement with the experimental value.
For IZOVIE, the calculated UV-vis spectrum in CH3OH shows an absorption band at
205 nm with bond energy of 6.04 eV (orbital excitation: HOMO-6→LUMO, 71%) and a
shoulder at 239 nm with a bond energy of 5.19 eV (orbital excitation: HOMO-2→LUMO, 98%).
This band and shoulder may be attributed to a combination of the π→σ*/π* (empty tin d orbitals)

transition from Cl or PO ligand to Sn and the π→π* transition of the P=O unit. These
assignments in both complexes were discussed more extensively in the last section.
3.3.4. NMR spectral studies. The experimental (for 1) and theoretical (for 1 and IZOVIE)
chemical shifts of 1H and 13C NMR spectra are presented in table S2.
The experimental 1H NMR spectrum of 1 is composed of four signals appearing as one
singlet and three multiplet bands. The singlet signal located at 1.05 ppm is assigned to methyl
protons of the Cl2Sn(CH3)2 segment. Around this signal, two pairs of satellites are observed
which can be used to evaluate the 2J(119Sn,1H) and 2J(117Sn,1H) coupling constants, 115.0 and
135.0 Hz. Three multiplet signals at chemical shifts higher than 3.00 ppm are attributed to
protons of CH2 groups of piperidine rings in para-, meta- and ortho-positions, respectively. In the
13C NMR spectrum of 1, the six singlet signals for carbon atoms appear in order of increasing
chemicals shift as 2C of segment [Cl2Sn(CH3)2] (one signal), and then, para- (one signals), meta-
(two signals) and ortho- (two signals) C atoms of rings, respectively.
DFT calculations for NMR study were performed at the B3LYP/SDD level and also
using some other levels and basis sets, but the obtained results were not in agreement with the
experimental data. The CH3 carbon signal is calculated at higher chemical shift than some other
carbon atoms in the calculated 13C NMR spectra. Finally, the results obtained at the
HF/SDD/DGDZVP level are in fairly good agreement with the experimental chemical shifts
which are listed in table S2 and discussed.
The calculated chemical shifts of CH3 protons are at 0.46, 0.63 and 0.72 ppm for 1 and in
the range 0.54-0.72 ppm for IZOVIE. The CH2 protons of the piperidine rings are calculated at
higher chemical shifts than the CH3 protons, in the range 1.45-3.60 ppm for 1 and 1.33-3.50 ppm
for IZOVIE, for para-, meta- and ortho-positions. The calculated 13C NMR spectra show signals
at 24.45 ppm for 1 and at 13.31 and 13.69 ppm for IZOVIE corresponding to CH3 carbon atoms
and at the range 26.59-50.54 ppm for 1 and 32.00-52.74 ppm for IZOVIE corresponding to
para-, meta- and ortho-carbons. Generally, as seen in table S2, there is a relatively good
agreement between the results provided by the experimental and calculated 1H and 13C NMR
spectra of 1.

3.3.5. Nonlinear optical properties. Among NLO materials, there are some reports of
organotin(IV) complexes exhibiting nonlinear optical (NLO) properties [33]. For considering the
NLO properties of molecular systems, urea is used as a prototypical molecule with a threshold
value for the purpose of comparison.
Table 4 presents the non-linear optical property parameters of 1 and IZOVIE. As it is
seen, the total static dipole moment ( ) and mean polarizability ( ) are slightly greater for
complex 1 than for IZOVIE, whereas the first-order hyperpolarizability ( ) is calculated for
IZOVIE higher than 1. However, parameters and comparing with the corresponding values
for urea (3.8312 Å3 and 0.3728×10-30 cm5/esu, respectively) are lesser for both complexes. Based
on the obtained results, it can be concluded that the studied compounds cannot be a good
candidate of NLO materials.
3.3.6. NBO and NPA analyses. Natural bond orbital (NBO) analysis provides useful
information about intermolecular orbital interactions, in particular charge transfer. Indeed, this
method describes the Lewis-like molecular bonding pattern of electron pairs and facilitates the
analysis of intra- and intermolecular interactions. Natural population analysis (NPA) gives the
electron distribution and Mulliken charges in the molecules that play an important role in
electronic properties such as dipole moment and polarizability [34].
We focus here on the evaluation and comparison of Sn-O contacts in 1 and IZOVIE
which are affected by the Mulliken charge, bond order, the percentage of bond electron density,
hybridization and electron delocalization energy (E2). These parameters are listed in table 5.
The Sn-O bond is slightly stronger in the six-coordinate complex 1 than in the five-
coordinate complex IZOVIE. It is supported by the lowest bond order values of other bonds
Sn-C and Sn-Cl around tin in the segment [Cl2Sn(CH3)2(O)2] (as a result of the higher bond order
value for the bond Sn-O) for 1 compared to IZOVIE. The values of the Mullikan charges show a
similar trend. In 1, tin is attached to the more electronegative carbon and chlorine atoms and
hence has a higher positive value than that in IZOVIE, where the negative charge of the oxygen
atom is almost the same in both complexes. This supports the slightly stronger Sn-O bond in 1
compared to that in IZOVIE.
The calculation of the percentage of bond electron density is also in line with these
results. Higher differences between these percentages for the Sn-C and Sn-Cl bonds in the

environment around the tin center [(Cl)2Sn(C)2(O)n] (n = 1 for IZOVIE and 2 for 1) are found
for 1 than for IZOVIE, reflecting a higher ionic character of these bonds in 1. Based on these
data, it is predicted that the Sn-O bond in 1 has a lower ionic character than this bond in
IZOVIE, providing a stronger metal-oxygen bond with a more covalent character. This result is
also confirmed by the higher values of ρ(r) at the bond critical point (BCP) of Sn-O for 1
(1.403 a.u.) comparing to IZOVIE (1.298 a.u.) calculated using the Atom In Molecule (AIM)
theory (L(r) = -4.26×10-4 a.u. for 1 and -4.37×10-4 a.u for IZOVIE).
Finally, according to the electron delocalization energies (E2, kcal/mol) presented in
table 5, the delocalization of electrons from the lone pairs of oxygen to the antibonding orbitals
of SnIV results in a strong interaction of LP O with LP* Sn in 1 stabilizing the six-coordinate
complex by 27.84 (for LP(1) O) and 40.17 (for LP(3) O) kcal/mol, whereas the interaction of LP
O with BD* Sn in IZOVIE stabilizes the five-coordinate complex by a maximum energy
16.91 kcal/mol (for LP(1) O). These higher electron delocalization energies for the six-
coordinate complex 1 support the hypothesis of a stronger Sn-O bond in 1 than that in IZOVIE.
3.3.7. Analysis of frontier molecular orbitals
The Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital
(LUMO) are the most important orbitals in a molecule and play an effective role in estimating
chemical reactivity and physical properties. Energies of HOMO and LUMO in a molecule are
used for the determination of global reactivity parameters such as electronegativity (χ), chemical
potential (μ), chemical hardness (η), global softness (S) and global electrophilicity index (ω)
(table 6 for 1 and IZOVIE) that can be calculated using the following equations [35]:
χ =
μ = χ =
η =
S =
ω =

A molecule with a small frontier orbital gap (energy difference between HOMO and LUMO
orbitals) acts as a soft molecule, is more polarizable and has a high chemical reactivity. The
calculated values of these parameters are collected in table 6 for 1 and IZOVIE. The six-
coordinate complex 1 with a higher HOMO–LUMO energy gap is a slightly more stable
structure than five-coordinate complex IZOVIE, and complex 1 can be identified as a harder
molecule with a lower electrophilicity comparing to IZOVIE.
Frontier molecular orbitals for 1 and IZOVIE are shown in figure 6. In 1, the HOMO and
LUMO orbitals are mainly localized on non-metal atoms (HOMO: 95% on Cl and CH3 ligands,
4% on PO ligands and LUMO: 32% on Cl and CH3, 34% on PO ligands). For IZOVIE, the
HOMO orbital is mainly localized on non-metal atoms (97% on Cl and CH3 ligands), while the
LUMO orbital is located on metal and non-metal atoms equally (50% on Sn, 40% on Cl and CH3
ligands and 10% on PO ligands). No considerable transfer of electron density is observed
between these frontier orbitals for both complexes.
Moreover, in 1 the value of the contribution of the PO ligand in HOMO-7 is equal to 91%
and this value is reduced to 34% for LUMO as mentioned above. These data affirm that the
transfer HOMO-7→LUMO (observed in the calculated UV-vis spectrum) corresponds to
intraligand charge-transfer (ILCT) in the PO ligand; however, based on these data the probability
of occurrence of ligand-to-metal charge-transfer (LMCT) cannot be neglected (from the PO
ligand to Sn). For IZOVIE, in the HOMO-6 orbital, the PO ligand has less than 6% electron
population whereas the Cl and CH3 ligands have about 94% contribution. So, the orbital
excitation HOMO-6→LUMO (observed in the calculated UV-vis spectrum) in this complex can
be predicted mainly as a LMCT (from Cl ligand to Sn), where the chance of occurrence of ILCT
is very low. Moreover, in the HOMO-2 orbital, the electron populations are found to be 97% for
the PO ligand and 3% for the Sn metal and the Cl and CH3 ligands. So, the orbital excitation
HOMO-2→LUMO (observed in the calculated UV-vis spectrum) can be predicted as a LMCT
(from PO ligand to Sn) with a much lower probability of ILCT.
4. Conclusion
The synthesis of a new six-coordinate organotin(IV)-phosphoric triamide complex,
[Cl2Sn(CH3)2(OP)2] (1), bearing water-soluble phosphoric triamide ligand OP(NC5H10)3 = OP
and the characterization by spectroscopic and X-ray crystallography methods is reported. This

complex and its analogous five-coordinate complex [Cl2Sn(CH3)2(OP)] (IZOVIE) have been
compared using density functional theory (DFT) and Hirshfeld surface (HS) calculations. The
results show similar FT-IR and NMR spectra, but different UV-vis spectra for 1 and IZOVIE,
and also a slightly stronger Sn-OP interaction in 1 compared to IZOVIE, which is supported by
the X-ray crystallography. More stability, less electrophilicity and more hardness are found for 1
with a higher HOMO-LUMO energy gap compared to IZOVIE. Furthermore, HS analysis
reveals that H…H contacts are majority in both structures, whereas H…Cl/Cl…H are more
important in IZOVIE than in 1 because of less steric hindrance caused by the presence of only
one PO ligand.
Supplementary data
CCDC number 1556342 for 1 contains the supplementary crystallographic data for this paper.
These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
References
[1]
[2]
[3]
[4]
A.K. Saxena. Appl. Organomet. Chem., 1, 39 (1987).
T.S. Basu Baul. Appl. Organomet. Chem., 22, 195 (2008).
S.K. Hadjikakou, N. Hadjiliadis. Coord. Chem. Rev., 253, 235 (2009).
C.E. Carraher Jr., D. Siegmann-Louda, “Macromolecules Containing Metal and Metal-
Like Elements, Volume 3: Biomedical Applications”, Chapter 4, Pages 57-73, John Wiley
& Sons (2004).
[5]
[6]
[7]
H. Kuso. Agric. Biol. Chem., 29, 43 (1965).
A.J. Crowe. Appl. Organomet. Chem., 1, 331 (1987).
M. Pourayoubi, A. Tarahhomi, J.A. Golen, A.L. Rheingold. J. Coord. Chem., 70, 1285
(2017).
[8]
[9]
M. Pourayoubi, S. Shoghpour Bayraq, A. Tarahhomi, M. Necas, K. Fejfarova, M. Dusek.
J. Organomet. Chem., 751, 508 (2014).
(a) F.H. Allen. Acta Crystallogr., Sect. B, 58, 380 (2002). (b) C.R. Groom, F.H. Allen.
Angew. Chem. Int. Ed., 53, 662 (2014).

[10] A. Tarahhomi, M. Pourayoubi, J.A. Golen, A.L. Rheingold (2016) CSD Communication
(Private Communication).
[11] M.A. Spackman, D. Jayatilaka. CrystEngComm, 11, 19 (2009).
[12] Agilent, CrysAlis PRO. Agilent Technologies, Yarnton, Oxfordshire, England (2011).
[13] L. Palatinus, G. Chapuis. J. Appl. Crystallogr., 40, 786 (2007).
[14] P.W. Betteridge, J.R. Carruthers, R.I. Cooper, K. Prout, D.J. Watkin. J. Appl.
Crystallogr., 36, 1487 (2003).
[15] R.I. Cooper, A.L. Thompson, D.J. Watkin. J. Appl. Crystallogr., 43, 1100 (2010).
[16] P.W. Betteridge, J.R. Carruthers, R.I. Cooper, K. Prout, D.J. Watkin. J. Appl. Cryst., 36,
1487 (2003).
[17] A.L. Spek. Acta Crystallogr., Sect. D, 65, 148 (2009).
[18] C.F. Macrae, I.J. Bruno, J.A. Chisholm, P.R. Edgington, P. McCabe, E. Pidcock, L.
Rodriguez-Monge, R. Taylor, J. van de Streek, P.A. Wood. J. Appl. Crystallogr., 41, 466
(2008).
[19] S.K. Wolff, D.J. Grimwood, J.J. McKinnon, M.J. Turner, D. Jayatilaka, M.A. Spackman,
Crystal Explorer 17.5, University of Western Australia, Crawley, Australia (2013).
[20] J.J. McKinnon, D. Jayatilaka, M.A. Spackman. Chem. Commun., 3814 (2007).
[21] M.A. Spackman, J.J. McKinnon. CrystEngComm, 4, 378 (2002).
[22] J.J. McKinnon, M.A. Spackman, A.S. Mitchell. Acta Cryst. B, 60, 627 (2004).
[23] J.J. McKinnon, F.P.A. Fabbiani, M.A. Spackman. Cryst. Growth Des., 7, 755 (2007).
[24] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman,
J.A. Montgomery Jr., T. Vreven, K.N. Kudin, J.C. Burant, J.M. Millam, S.S. Iyengar, J.
Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G.A. Petersson, H.
Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T.
Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J.E. Knox, H.P. Hratchian,
J.B. Cross, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J.
Austin, R. Cammi, C. Pomelli, J.W. Ochterski, P.Y. Ayala, K. Morokuma, G.A. Voth, P.
Salvador, J.J. Dannenberg, V.G. Zakrzewski, S. Dapprich, A.D. Daniels, M.C. Strain, O.
Farkas, D.K. Malick, A.D. Rabuck, K. Raghavachari, J.B. Foresman, J.V. Ortiz, Q. Cui,
A.G. Baboul, S. Clifford, J. Cioslowski, B.B. Stefanov, G. Liu, A. Liashenko, P. Piskorz,
I. Komaromi, R.L. Martin, D.J. Fox, T. Keith, M.A. Al-Laham, C.Y. Peng, A.

Nanayakkara, M. Challacombe, P.M.W. Gill, B. Johnson, W. Chen, M.W. Wong, C.
Gonzalez, J.A. Pople, Gaussian 09 (Linux version) (2009).
[25] J. Frank. WIREs Comput. Mol. Sci., 3, 273 (2013).
[26] (a) T.H. Dunning Jr., P.J. Hay, “Methods of Electronic Structure Theory”, Chapter 1,
Pages 1 – 27, Springer, Boston, MA (1977). (b) E.G. Lewars, “Computational Chemistry:
Introduction to the Theory and Applications of Molecular and Quantum Mechanics”, 1st
Edn., Springer (2011).
[27] A.E. Reed, F. Weinhold. Chem. Rev., 88, 899 (1998).
[28] H.B. Schelegel, “Ab Initio Methods in Quantum Chemistry”, Pages 249 – 286, John
Wiley, New York (1998).
[29] S. Muthu, E. Isac Paulraj. Spectrochim. Acta, Part A, 112, 169 (2013).
[30] (a) R.F.W. Bader, “Atoms in Molecules, a Quantum Theory”, Oxford University Press,
New York (1990). (b) R.F.W. Bader. Monatsh. Chem., 136, 819 (2005).
[31] S. Sujatha, C. Arunkumar. Asian J. Chem., 27, 1843 (2015).
[32] A. Tarahhomi, M. Pourayoubi, A.L. Rheingold, J.A. Golen. Struct. Chem., 22, 201
(2011).
[33] B.M. Munoz-Flores, R. Santillan, N. Farfan, V. Alvarez-Venicio, V.M. Jimenez-Perez,
M. Rodriguez, O.G. Morales-Saavedra, P.G. Lacroix, C. Lepetit, K. Nakatani. J.
Organomet. Chem., 769, 64 (2014).
[34] (a) F. Weinhold, C.R. Landis. Chem. Educ. Res. Prac., 2, 91 (2001). (b) F. Weinhold,
C.R. Landis, “Discovering Chemistry With Natural Bond Orbitals”, Pages 132 – 133,
New Jersey: John Wiley & Sons (2012).
[35] R.G. Parr, L.V. Szentpály, S. Liu. J. Am. Chem. Soc., 121 (9), 1922 (1999).

Figure captions
Figure 1. The structure of [Cl2Sn(CH3)2{OP(NC5H10)3}2] (1) showing the atom-labeling scheme
for non-H atoms. Displacement ellipsoids are given at 50% probability and hydrogen atoms are
drawn as small spheres of arbitrary radii.
Figure 2. View of the crystal packing of 1 showing a 2D network generated by C61-H612…Cl2
hydrogen bonds (black dash lines) parallel to the (-101) plane. The SnIV centers and H and Cl
contact atoms are highlighted as "balls". Hydrogen atoms not involved in intermolecular
interactions are removed for clarity.
Figure 3. Upper: Views of dnorm HS for 1, in two orientations, surrounded by neighboring
molecules associated with close contacts H…H (identified as red spots); Lower: Decomposed
H…H and H…Cl/Cl…H FPs and related percentage contributions to the total HS area for 1. The
full FP (with the range values of 0.8 Å < de, di < 2.7 Å) appears as a grey shadow below each
decomposed plot.
Figure 4. View of dnorm HS for IZOVIE surrounded by neighboring molecule associated with
close contact Cl…Sn/Sn…Cl (identified as red spots). Decomposed H…H, H…Cl/Cl…H and
Cl…Sn/Sn…Cl FPs and related percentage contribution to the total HS area are also shown. The
full FP (with the range values of 1.1 Å < de, di < 2.4 Å) appears as a grey shadow below each
decomposed plot.
Figure 5. Calculated (upper) and experimental (lower) FT-IR spectra of 1 and IZOVIE in the
range 400-4000 cm-1.
Figure 6. Frontier molecular orbital plots for 1 (upper) and IZOVIE (lower).

Table 1. Crystal data and structure refinement for compound 1.
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
C32H65Cl2N6O2P2Sn
817.44
175
0.71073
Monoclinic
Space group
P21/n
Unit cell dimensions
a = 8.5838(1) Å
b = 15.3314(1) Å
c = 14.0269(1) Å
β = 91.711(1)°
1845.14(3)
Volume (Å3)
Z
2
Density (calculated) (g/cm3)
Absorption coefficient (mm-1)
F(000)
1.471
0.962
858
Crystal size (mm3)
Crystal color / habit
Theta range for data collection (°)
Index ranges
0.30 × 0.35 × 0.50
Colorless / block
1.968 to 37.614
-14 ≤ h ≤ 14
-25 ≤ k ≤ 25
-24 ≤ l ≤ 24
Reflections collected
108060
Independent reflections
Absorption correction
9569 [Rint = 0.043]
multi-scan / CrysAlisPro
1.00000 and 0.93970
Full-matrix least-squares on F2
9569 / 270 / 377
0.9044
Max. and min. transmission
Refinement method
Data / restraints / parameters
Goodness-of-fit on F2
Final R indices [I>2σ(I)]
R1 = 0.0511, wR2 = 0.1501
R1 = 0.0610, wR2 = 0.1583
1.72 and -1.49
R indices (all data)
Largest diff. peak and hole (e.Å-3)

Table 2. Selected calculated and experimental bond distances (Å) and angles (°) for 1 and
IZOVIE.
1
Experimental Calculated IZOVIE
Experimental Calculated
Sn1-O3
2.2043 (16)
2.5607 (6)
2.5607 (6)
2.2043 (16)
2.120 (3)
2.120 (3)
1.514 (4)
1.500 (4)
1.642 (5)
1.650 (5)
1.680 (2)
1.628 (5)
1.647 (5)
1.600 (2)
88.67 (6)
88.67 (9)
91.90 (10)
179.996
2.248
2.673
2.673
2.248
2.145
2.145
1.609
-
1.720
1.724
1.727
-
Sn1-O1
Sn1-Cl1
Sn1-Cl2
Sn1-C1
Sn1-C2
P1-O1
P1-N1
P1-N2
2.2231 (13)
2.3890 (5)
2.5511 (5)
2.1067 (19)
2.1013 (19)
1.4900 (14)
1.6370 (16)
1.6433 (16)
1.6341 (16)
86.81 (4)
178.73 (4)
86.60 (7)
85.62 (7)
103.74 (6)
103.26 (6)
151.40 (9)
94.187 (18)
159.53 (9)
2.338
2.487
2.529
2.144
2.144
1.609
1.716
1.736
1.715
84.69
179.38
85.10
85.80
113.99
112.24
131.66
95.49
161.04
Sn1-Cl2
Sn1-Cl2i
Sn1-O3i
Sn1-C4
Sn1-C4i
P40-O3
P41-O3
P40-N51
P1-N3
P40-N171
P40-N111
P41-N50
Cl1-Sn1-O1
Cl2-Sn1-O1
C1-Sn1-O1
C2-Sn1-O1
C1-Sn1-Cl1
C2-Sn1-Cl1
C1-Sn1-C2
Cl1-Sn1-Cl2
P1-O1-Sn1
P41-N170
P41-N110
Cl2i-Sn1-O3
Cl2i-Sn1-C4
O3i-Sn1-C4i
Cl2i-Sn1-Cl2
O3i-Sn1-Cl2
C4i-Sn1-Cl2
O3i-Sn1-O3
C4i-Sn1-O3
P40-O3-Sn1
P41-O3-Sn1
-
-
90.94
88.76
93.61
180.00
90.94
88.76
180.00
86.39
147.45
-
91.33 (6)
90.33 (9)
179.995
88.10 (10)
148.55 (17)
153.02 (18)
Symmetry transformations used to generate equivalent atoms for 1: (i): –x+1, –y+1, –z+1.

Table 3. Summary of the percentage contributions of interactions for 1
and IZOVIE.
H…H
H… Cl / Cl…H
Cl…Sn/Sn…Cl
1
90.8 (red spots)
75.9
9.1
-
IZOVIE
23.0
1.0 (red spots)
Table 4. The calculated electric dipole moments (μ) (a.u.) and total static dipole moment
( ) (Debye), static polarizability components ( ) (a.u.) and mean polarizability ( )
(Å3), and first hyperpolarizability components (β) (a.u.) and first-order
hyperpolarizability ( ) (cm5/esu) for 1 and IZOVIE at B3LYP/SDD level.
Parameters
1
IZOVIE
Parameters
1
IZOVIE
μx
μy
μz
-2.788
-4.545
-7.165
8.931
5.308
-1.369
-4.934
7.375
βxxx
βxxy
βxyy
βyyy
βxxz
βyyz
βxzz
βyzz
βzzz
3.963
3.013
1.547
-3.292
-1.093
1.400
-8.171
3.212
5.057
9.603
1.432
-1.276
1.217
-8.015
7.125
1.248
-1.249
0.160×10-30
αxx
αyy
αzz
4.870
4.500
4.385
0.679
2.752
2.638
2.533
0.391
-3.827
0.046×10-30

Table 5. Results of NBO and NPA analyses for 1 and IZOVIE determined by DFT method at the
B3LYP/SDD level.
Bond
order
1
0.200
0.644
%Bond electron
density
Atom
Mulliken charge
IZOVIE
1.501 1.254
Bond
1
IZOVIE
0.170
0.697
1
IZOVIE
Sn
O
Sn-O
Sn-C
-
-
-
-0.834
24.88-
75.12
11.53-
88.47
-
26.08-
73.92
17.28-
82.72
14.95-
85.05
26.64-
73.36
0.855
1.715 1.662
P
Sn-Cl
Sn-Cl
P=O
0.420
-
0.611
0.557
0.974
Cl
-
-0.441, -
0.603 0.495
C of CH3
-
-0.917, -
0.954
26.62-
73.38
0.947 0.921
Donor–Acceptor interactions
Compoun Dono Hybridizatio Occupatio Accepto Hybridizatio Occupatio E2
d
r
n
n number
1.909
r
n
n number (kcal/mol
)
1
LP
(1) O
LP
Sp1.1
Sp3.5
LP* (1) Sp1
0.232
27.84
Sn
1.857
LP* (1) Sp1
0.232
40.17
(3) O
Sn
IZOVIE
LP
(1) O
LP
(3) O
Sp0.7
Sp6.0
1.909
1.868
BD* (1) Sp8.0-Sp4.8
Sn-Cl
BD* (1) Sp8.0-Sp4.8
Sn-Cl
0.144
0.144
16.91
11.78

Table 6. Calculated global reactivity descriptors of 1 and IZOVIE at the
B3LYP/SDD level.
Parameter
1
IZOVIE
ELUMO - EHOMO (eV)
ELUMO + EHOMO (eV)
Electronegativity (χ)
Chemical potential (μ)
Chemical hardness (η)
Softness (S)
6.299
-4.890
2.445
-2.445
3.149
0.159
0.949
6.072
-6.831
3.415
-3.415
3.036
0.165
1.921
Electrophilicity index (ω)