Structural properties of platinum(II) biphenyl complexes containing 1,10-phenanthroline derivatives

Article abstract of DOI:10.1016/j.molstruc.2013.03.006

Seven platinum(II) complexes formulated as Pt(bph)L, where bph is the 2,2′-biphenyl dianion and L = 4-methyl-1,10-phenanthroline (4-Mephen), 5-methyl-1,10-phenanthroline (5-Mephen), 5-chloro-1,10-phenanthroline (5-Clphen), 5,6-dimethyl-1,10-phenanthroline (5,6-Me₂phen), 4,7-dimethyl-1,10-phenanthroline (4,7-Me₂phen), 4,7-diphenyl-1,10- phenanthroline (4,7-Ph₂phen) and 3,4,7,8-tetramethyl-1,10- phenanthroline (3,4,7,8-Me₄phen) are reported. Protons attached to the phen ligand resonate downfield from those attached to the bph ligand and two proton signals are split by interaction with ¹⁹⁵Pt. Pt(bph)(3,4,7,8-Me₄phen), Pt(bph)(4,7-Me₂phen), Pt(bph)(5,6-Me₂phen), Pt(bph)(4,7-Ph₂phen) and Pt(bph)(5-Mephen) crystallize in the space groups Pna2₁, P2 ₁/n, P2₁/c, P - 1 and Pca2₁, respectively. The structures of the complexes deviate from true planarity and divide themselves into two groups where the bph and phen ligands cross in an X configuration or bow out in a butterfly (B) configuration. Circular dichroism revealed two different spectra with respect to the X and B configurations.

Full text of DOI:10.1016/j.molstruc.2013.03.006

Journal of Molecular Structure 1041 (2013) 82–91
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Structural properties of platinum(II) biphenyl complexes containing
1,10-phenanthroline derivatives
b
a
a
c
a
D. Paul Rillema a, , Arvin J. Cruz , Brandon J. Tasset , Curtis Moore , Khamis Siam , Wei Huang
⇑
a Department of Chemistry, Wichita State University, Wichita, KS 67260, United States
b Department of Chemistry, Fort Hays State University, Hays, KS 67601, United States
c Department of Chemistry, Pittsburg State University, Pittsburg, KS 66762, United States
h i g h l i g h t s
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
X-ray structures deviate from square planar into two types of structures, X and bowed (B) forms.
X and B forms exhibit circular dichroism in the solid state.
Circular dichroism spectra can be correlated with optimized structures determined by DFT calculations.
Heteronuclear interactions are observed by NMR between 195Pt and ring protons of phenanthroline and biphenyl ligand.
A Hammett sigma correlation exists with the most downfield proton resonance.
a r t i c l e i n f o
a b s t r a c t
Seven platinum(II) complexes formulated as Pt(bph)L, where bph is the 2,20-biphenyl dianion and
L = 4-methyl-1,10-phenanthroline (4-Mephen), 5-methyl-1,10-phenanthroline (5-Mephen), 5-chloro-
1,10-phenanthroline (5-Clphen), 5,6-dimethyl-1,10-phenanthroline (5,6-Me2phen), 4,7-dimethyl-1,
10-phenanthroline (4,7-Me2phen), 4,7-diphenyl-1,10-phenanthroline (4,7-Ph2phen) and 3,4,7,8-tetra-
methyl-1,10-phenanthroline (3,4,7,8-Me4phen) are reported. Protons attached to the phen ligand reso-
nate downfield from those attached to the bph ligand and two proton signals are split by interaction
with 195Pt. Pt(bph)(3,4,7,8-Me4phen), Pt(bph)(4,7-Me2phen), Pt(bph)(5,6-Me2phen), Pt(bph)(4,7-Ph2-
phen) and Pt(bph)(5-Mephen) crystallize in the space groups Pna21, P21/n, P21/c, P ꢁ 1 and Pca21, respec-
tively. The structures of the complexes deviate from true planarity and divide themselves into two groups
where the bph and phen ligands cross in an X configuration or bow out in a butterfly (B) configuration.
Circular dichroism revealed two different spectra with respect to the X and B configurations.
Ó 2013 Elsevier B.V. All rights reserved.
Article history:
Received 14 December 2012
Received in revised form 5 March 2013
Accepted 5 March 2013
Available online 13 March 2013
Keywords:
Platinum (II)
Biphenyl dianion
Phenanthroline
X-ray
1H NMR
CD
1. Introduction
about their structural properties. Single X-ray crystal structures
were obtained for five of the complexes leading to two types of
The solid-state properties of platinum(II) biphenyl complexes
with monodentate and bidentate ligands have been reported
[1–9]. The complexes are known to absorb light in the near-UV
structures which gave different CD spectra. The synthesis, 1H
NMR and structural properties of these complexes are described
in this paper.
region assigned to d
p
(Pt) ? p⁄ (bph) transitions and undergo
emission assigned to triplet ligand-centered (3LC) and triplet
metal-to-ligand charge transfer (3MLCT) states. Previous reports
show that dicarbonyl complexes like Pt(bph)(CO)2 also display
2. Experimental section
2.1. Materials
p
? p stacking in the solid state which underwent optical transi-
tions in the solid state located at 580 nm attributed to a d2 ! pz
z
All syntheses were performed under a dry and oxygen-free
nitrogen atmosphere using standard Schlenk-ware techniques.
[Pt(bph)(C2H5)2S]2 was prepared as described [10–13] and charac-
terized by 1H NMR. 1H NMR (CDCl3): d 7.32 (dd, 2H, J = 7.5 Hz,
1.3 Hz), 7.03 (ddd, 2H, J = 7.3 Hz, J = 1.09 Hz), 6.98 (dd, 2H, J = 7.4,
J = 1.1 Hz), 6.88 (ddd, 2H, J = 7.4 Hz, J = 1.4 Hz), 3.82 (q, 4H,
J = 7.4 Hz), 1.75 (t, 6H, J = 7.4 Hz). Methylene chloride and hexane
transition [6].
In this paper we focus our attention on platinum(II) biphenyl
complexes with derivatized 1,10-phenanthroline ligands to learn
⇑
Corresponding author.
E-mail address: paul.rillema@wichita.edu (D.P. Rillema).
0022-2860/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2013.03.006

D.P. Rillema et al. / Journal of Molecular Structure 1041 (2013) 82–91
83
were purchased from Fisher Scientific and were used as received.
Spectrometric grade acetonitrile was received from ACROS. All
the diimine ligands were commercially purchased and used as
obtained.
5.04. Found: C, 56.40; H, 3.82; N, 5.25. IR (KBr pellet): 3038, 1423,
1034, 847, 746, 715 cmꢁ1. 1H NMR (CD2Cl2): listed in Table 1.
2.8. Pt(bph)(5,6-Me2phen)
2.2. Instrumentation and physical measurements
Compound Pt(bph)(5,6-Me2phen) was prepared similar to 4-
Mephen except 4-Mephen was replaced by 5,6-Me2phen. Color,
IR spectra were acquired using a Nicolet Avatar 360 FT-IR spec-
trophotometer. All samples were prepared in KBr. Proton (1H-)
NMR spectra were obtained using a Varian Inova 400 FT-NMR
spectrometer. All samples are referenced against TMS. Deuterated
methylene chloride (CD2Cl2) was used as solvent in all NMR
samples. Elemental (C, H, and N) analysis was performed by
MHW Laboratories in Phoenix, AZ. CD spectra were obtained with
a Jasco J-810 CD spectrometer interfaced with a Jasco spectral
analysis software program compatible with Windows Operating
system. All samples are prepared in dried acetonitrile (CH3CN)
and CD spectra were obtained in a 5-cm quartz cell.
C
26H20N2Pt: Red Crystal. Anal. Calcd for C26H20N2Pt: C, 56.21; H,
3.63; N, 5.04. Found: C, 55.99; H, 3.90; N, 4.96. IR (KBr pellet):
3046, 2924, 1610, 1416, 1383, 796, 736, 718 cmꢁ1
.
1H NMR (CD2-
Cl2): listed in Table 1.
2.9. Pt(bph)(3,4,7,8-Me4phen)
Compound Pt(bph)(3,4,7,8-Me4phen) was prepared similar to
4-Mephen except 4-Mephen was replaced by 3,4,7,8-Me4phen.
Color, C28H24N2Pt: Orange Solid. Anal. Calcd for C28H24N2Pt: C,
57.63; H, 4.15; N, 4.80. Found: C, 57.31; H, 4.20; N, 4.66. IR (KBr
pellet): 3041, 2959, 1521, 1423, 1380, 1015, 911, 808, 738,
715 cmꢁ1 1H NMR (CD2Cl2): listed in Table 1.
.
2.3. Calculations
Calculations were effected using Gaussian ’03 (Rev. B. 03) for
UNIX [14]. The molecules were optimized using Becke’s three-
parameter hybrid functional B3LYP [15] with the local term [16]
of Lee, Young, Parr and the nonlocal term [17] of Vosko, Wilk,
and Nassiar. Geometry optimization was conducted using different
basis sets: MP2/SDD [18–20], MP2/LanL2DZ [15b,18,20–22] and
DFT/SDD [23–25] in order to determine the lowest-energy molec-
ular configuration. All atoms and geometry optimization were run
in the gas phase.
2.10. Pt(bph)(4,7-Ph2phen)
Compound Pt(bph)(4,7-Ph2phen) was prepared similar to 4-Me-
phen except 4-Mephen was replaced by 4,7-Ph2phen. Color, C36H24-
N2Pt: Red Solid. Anal. Calcd for C36H24N2Pt: C, 63.62; H, 3.53; N, 4.12.
Found: C, 64.03; H, 3.90; N, 4.36. IR (KBr pellet): 3038, 2976, 1431,
1018, 835, 761, 734, 707 cmꢁ1. 1H NMR (CD2Cl2): listed in Table 1.
2.11. Pt(bph)(5-Clphen)
2.4. Preparation of complexes
A solution of 5-chloro-1,10-phenanthroline (5-Clphen, 54 mg,
0.25 mmol) in methylene chloride (10 mL) was added dropwise
to a solution of [Pt(bph)(C2H5)2S]2 (100 mg, 0.114 mmol) in meth-
ylene chloride (20 mL) under continuous stirring. The solution was
heated at reflux for 30 min, rotary-evaporated to reduce its volume
to about 5 mL, and was dripped into 500 mL of hexane. The precip-
itate was removed by vacuum filtration and dried under vacuum.
Color, C24H15N2PtCl: Brown Solid. Anal. Calcd for C24H15N2PtCl: C,
51.30; H, 2.69; N, 4.99. Found: C, 50.93; H, 2.73; N, 4.71. IR (KBr
All reactions were carried out using the same procedure but
varying the 1,10-phenanthroline derivative. Yields were on the or-
der of 80%. The following are examples of sample preparations.
2.5. Pt(bph)(4-Mephen)
A
solution of 4-methyl-1,10-phenanthroline, (4-Mephen,
49 mg, 0.25 mmol) in methylene chloride (10 mL) was added
drop-wise to solution of [Pt(bph)(C2H5)2S]2 (100 mg,
pellet): 3040, 1617, 1576, 1416, 1424, 961, 743, 715, 732 cmꢁ1
1H NMR (CD2Cl2): listed in Table 1.
.
a
0.114 mmol) in methylene chloride (20 mL) with continuous stir-
ring. The reaction mixture was stirred at room temperature for
30 min and rotary-evaporated to reduce its volume to approxi-
mately 10 mL. The crystals were isolated and washed with ether.
Color, C25H18N2Pt: Purple Crystal. Anal. Calcd for C25H18N2Pt: C,
55.45; H, 3.35; N, 5.18. Found: C, 55.34; H, 3.41; N, 5.26. IR (KBr
pellet): 3030, 2924, 1629, 1411, 832, 738, 715 cmꢁ1. 1H NMR (CD2-
Cl2): listed in Table 1.
3. Results
3.1. 1H NMR spectra
The 1H NMR spectra of platinum biphenyl phenanthroline com-
plexes reported here along with Pt(bph)(phen) and [Pt(bph)
(C2H5)2S]2 are listed in Table 1. All proton signals can be divided
into resonances associated with the biphenyl ring, those associated
with the phenanthroline ring and those associated with substitu-
ents attached to the phenanthroline rings. Chemical shifts of
hydrogen atoms attached to bph ligand rings were located be-
tween 6.9 and 7.5 ppm with coupling constants ranging between
2 and 7 Hz. Those attached to phenanthroline rings were located
further downfield from 7.6 to 9.9 ppm with coupling constants
ranging between 2 and 8 Hz. The remaining resonances are associ-
ated with methyl and phenyl groups attached to phenanthroline
and the ethyl groups attached to bridging sulfide groups.
2.6. Pt(bph)(5-Mephen)
Compound Pt(bph)(5-Mephen) was prepared similar to
4-Mephen except 4-Mephen was replaced by 5-Mephen. Color,
C25H18N2Pt: Deep Red Crystal. Anal. Calcd for C25H18N2Pt: C,
55.45; H, 3.35; N, 5.18. Found: C, 54.47; H, 3.61; N, 4.98. IR (KBr
pellet): 3033, 2924, 1630, 1422, 876, 794, 745, 720 cmꢁ1
.
1H
NMR (CD2Cl2): listed in Table 1.
2.7. Pt(bph)(4,7-Me2phen)
3.2. X-ray crystallographic data
Compound Pt(bph)(4,7-Me2phen) was prepared similar to 4-Me-
phen except 4-Mephen was replaced by 4,7-Me2phen. Color, C26H20-
N2Pt: Orange Crystal. Anal. Calcd for C26H20N2Pt: C, 56.21; H, 3.63; N,
Crystals of Pt(bph)(3,4,7,8-Me4phen), Pt(bph)(4,7-Me2phen),
Pt(bph)(5,6-Me2phen), Pt(bph)(4,7-ph2phen) and Pt(bph)(5-Mephen)

84
D.P. Rillema et al. / Journal of Molecular Structure 1041 (2013) 82–91
Table 1
Chemical shifts and coupling constants in 1H NMR spectra of complexes.
Complexes
phen (protons)
NA
bph (protons)
other (protons)
[Pt(bph)SEt]2
7.29 (dd, 4H, J = 6.8, 2.0), 7.01 (dd, 4H, J = 6.8, 3.83(q, 8H, J = 7.2),
2.0), 6.90 (m, 8H, J = 6.8, 2.0)
1.76(t, 12H, J = 7.2)
(diethyl)
Pt(bph)(phen)
9.93 (dd, 2H, J = 5.2, 1.2), 8.69 (dd, 2H, J = 8.0, 1.2), 8.02 (s, 2H) 8.00 (dd, 2H, 7.55 (dd, 2H, J = 6.8, 2.0), 7.34 (dd, 2H, J = 6.8, NA
J = 8.0, 5.2)
2.0), 6.97 (m, 4H, J = 6.8, 2.0)
Pt(bph)(4-
Mephen)
Pt(bph)(5-
Mephen)
9.821 (d, 1H, J = 5.3), 9.74 (d, 1H, J = 5.3), 8.69 (d, 1H, J = 8.3), 8.19 (d, 1H,
J = 9.2), 8.02 (d, 1H, J = 9.2), 7.98 (dd, 1H, J = 8.3, 5.4), 7.82 (d, 1H, J = 5.4)
9.91 (dd, 1H, J = 5.3, 1.2), 9.85 (dd, 1H, J = 5.3, 1.2), 8.80 (dd, 1H, J = 8.3, 1.2), 7.54 (m, 2H), 7.34 (m, 2H, J = 6.8), 6.96 (td, 4H, 2.88 (s, 3H) (methyl)
7.54 (m, 2H), 7.33 (dd, 2H, J = 6.8, 2.0), 6.98 (td, 2.86 (s, 3H) (methyl)
2H, J = 6.8, 2.0), 6.94 (td, 2H, J = 6.8, 2.0)
8.59 (dd, 1H, J = 8.3, 1.2), 8.02 (dd, 1H, J = 8.3, 5.4), 7.96 (dd, 1H, J = 8.3, 5.4), J = 6.8, 2.0)
7.85 (s, 1H)
Pt(bph)(4,7-
Me2phen)
9.75 (d, 2H, J = 5.3), 8.22 (s, 2H), 7.71 (d, 2H, J = 5.3)
7.54 (dd, 2H, J = 6.8, 2.0), 7.33 (dd, 2H, J = 6.8, 2.86 (s, 6H) (methyl)
2.0), 6.99 (td, 2H, J = 6.8, 2.0), 6.92 (td, 2H,
J = 6.8, 2.0)
Pt(bph)(5,6-
Me2phen)
9.87 (d, 2H, J = 5.3), 8.73 (d, 2H, J = 8.0), 7.91 (dd, 2H, J = 8.0, 5.3)
7.48 (d, 2H, J = 6.8), 7.37 (dd, 2H, J = 6.8, 2.0), 2.78 (s, 6H) (methyl)
6.99 (td, 2H, J = 6.8, 2.0), 6.92 (td, 2H, J = 6.8,
2.0)
Pt(bph)(3,4,7,8- 9.61 (s, 2H), 8.20 (s, 2H)
Me4phen)
7.52 (dd, 2H, J = 6.9, 2.0), 7.33 (dd, 2H, J = 6.9, 2.73 (s, 6H), 2.69(s,
2.0), 6.95 (m, 4H, J = 6.9, 2.0)
7.64 (m, 2H), 7.35 (dd, 2H, J = 6.8, 2.0), 6.92 (m, 7.64 (m, 10H)
4H, J = 6.8, 2.0) (phenyl)
6H) (methyl)
Pt(bph)(4,7-
ph2phen)
Pt(bph)(5-
Clphen)
9.98 (d, 2H, J = 5.3), 8.08 (s, 2H), 7.95 (d, 2H, J = 5.3)
9.96 (d, 1H, J = 5.2), 9.89 (d, 1H, J = 5.2), 9.03 (dd, 1H, J = 8.0, 1.2), 8.60 (dd, 1H, 7.48 (td, 2H, J = 6.9, 2.0), 7.39 (dd, 2H, J = 6.9, NA
J = 8.0, 1.2), 8.17 (s, 1H), 8.08 (dd, 1H, J = 8.0, 5.2), 7.97 (dd, 2H, J = 8.0, 5.2) 2.0), 6.92 (m, 4H, J = 6.9, 2.0)
were obtained by slow evaporation of the reaction mixture from satu-
rated methylene chloride solutions, affixed to a nylon cryoloop using
oil (Paratone-n, Exxon) and mounted in the cold stream of a Bruker
Kappa-Apex-II [26] area-detector diffractometer. The temperature
was maintained at 150 K using a Cryostream 700EX Cooler (Oxford
Cryosystems). The unit cell was determined from the setting angles
of 383 reflections collected in 36 frames of data for Pt(bph)(4,7-Me2-
phen), 250 reflections for Pt(bph)(5-Mephen), 151 reflections for
Pt(bph)(4,7-Ph2phen), 108 reflections for Pt(bph)(3,4,7,8-Mephen)
and 1037 reflections collected in 100 frames for Pt(bph)(5,6-Me2phen).
Data were measured with a redundancy of 7.9 for Pt(bph)(4,7-Me2-
phen), 7.1 for Pt(bph)(5-Mephen), 6.45 for Pt(bph)(4,7-ph2phen), 9.2
for Pt(bph)(3,4,7,8-Me4phen) and 5.5 for Pt(bph)(5,6-Me2phen) using
a CCD detector at a distance of 50 mm from the crystal with a combi-
nation of phi and omega scans. A scan width of 0.5° and time of 10 s
was employed along with graphite monochromatic molybdenum,
distances and angles are provided in Tables 3 (see Tables S1–S25 for
additional crystallographic data).
Bond lengths between each platinum and carbon were be-
tween 1.980 and 2.016 Å; bond lengths between each platinum
and nitrogen were between 2.084 and 2.165 Å. These are normal
compared to those of similar complexes [3a,6,9,27–33]. Bond
angles of C–Pt–C varied from 80.06° to 80.7°. N–Pt–N angles were
76.82° to 77.52°. Fig. 1 shows examples of ORTEP diagrams at 50%
thermal probability for Pt(bph)(5,6-Me2phen) and Pt(bph)(4,7-
ph2phen).
Fig. 2 shows the capped-stick X-ray structures of the complexes
reported here including Pt(bph)(phen) [13]. In all cases, deviation
from planarity (X- and B-configuration) exhibited by the com-
plexes are reflected by the angles shown in the figure.
3.3. Intermolecular Interactions
MoKaradiation (k = 0.71073 Å) that was collimated to a 0.6 mm diam-
eter. Data collection, reduction, structure solution, and refinement
were performed using the Bruker Apex2 suite (v2.0-2) [26]. All avail-
able reflections were harvested {39,773 reflections, 6312 unique for
Pt(bph)(4,7-Me2phen), 39,161 reflections, 5825 unique for
Pt(bph)(4,7-ph2phen), 54,385 reflections, 7982 unique for Pt(bph)(5-
Mephen), 40,071 reflections, 4352 unique for Pt(bph)(5,6-Me2phen)
and 36,639 reflections, 4012 unique for Pt(bph)(3,4,7,8-Me4phen)}
and corrected for Lorentz and polarization factors with Bruker SAINT
(v6.45) [26]. Reflections were then corrected for absorption (numerical
correction interframe scaling, and other systematic errors with SAD-
ABS 2004/1 [26] (combined transmission and other correction factors
min./max. = 0.1681/0.4282 for Pt(bph)(4,7-Me2phen), 0.3537/0.8610
for Pt(bph)(5-Mephen), 0.4346/0.6347 for Pt(bph)(4,7-Ph2phen),
0.2145/0.5243 for Pt(bph)(5,6-Me2phen) and 0.3447/0.6136 for
Pt(bph)(3,4,7,8-Me4phen)). The structure was solved (direct methods)
and refined (full-matrix least-squares against F2) with the Bruker
SHELXTL package (v6.14-1) [26]. All non-hydrogen atoms were refined
using anisotropic thermal parameters. All hydrogen atoms were in-
cluded at idealized positions; hydrogen atoms were not refined. The
compound Pt(bph)(4,7-Me4phen) sits on a general position in the
monoclinic space group P21/n, Pt(bph)(4,7-Ph2phen) in the triclinic
space group P ꢁ 1, Pt(bph)(5-Mephen) in the orthorhombic space
group Pca21, Pt(bph)(5,6-Me2phen) in the monoclinic space group
P21/c and Pt(bph)(3,4,7,8-Me4phen) in the orthorhombic space group
Pna21. Crystal data for the compounds is listed in Table 2. Selected bond
Intermolecular Pt–Pt and
p–p stacking of ligand interactions
between adjacent molecules in the solid state were examined
from solid state packing for the five compounds, two of which
are shown in Fig. 3. Upon analyzing the crystal structures of the
five compounds, there is really no evidence for Pt–Pt interactions
in any of the structures, but each of the five shows minimal
stacking of the ring systems. The crystal structures of Pt(bph)(5,6-
Me2phen), Pt(bph)(4,7-Me2phen), and Pt(bph)(5-Mephen) all
show evidence for a small amount of
phenanthroline ligands of adjacent molecules in the lattice with
minimal distances of 3.274 ÅA, 3.381 ÅA, and 3.339 ÅA, respectively.
Unlike the others, the crystal structure of Pt(bph)(3,4,7,8-Me4-
p–p
p–p stacking between
0
0
0
phen) shows evidence for
between the biphenyl ligand and phenanthroline ligand of adja-
a small amount of p–p stacking
cent molecules in the solid state with a minimal distance of
0
3.386 ÅA. Packing in the crystals structure of Pt(bph)(4,7-Ph2phen)
seems to exhibit the best
p–p stacking for adjacent molecules as
far as visual overlap of the phenanthroline rings is concerned, but
the minimal distance between the rings is long, 3.749 ÅA, com-
pared to the other structures.
0
3.4. Optimized structures from DFT calculation
Calculated structures were optimized by DFT [23–25]. The con-
figurations of the molecules were initially set to X or B based on

D.P. Rillema et al. / Journal of Molecular Structure 1041 (2013) 82–91
85
Table 2
X-ray crystallographic data of complexes.
Pt(bph)(4,7-Ph2phen)
36H24N2Pt1
Pt(bph)(4,7-Me2phen)
Pt(bph)(5,6-Me2phen)
Pt(bph)(3,4,7,8-Me4phen) Pt(bph)(5-Mephen)
Empirical formula
Formula weight
Temperature
C
C26H20N2Pt1
555.53
C26H20N2Pt1
555.53
C28H24N2Pt1
583.58
C25H18N2Pt1
541.50
679.66
150 K
150 K
150 K
150 K
150 K
0
0
0
0
0
Wavelength
0.71073 ÅA
0.71073 ÅA
0.71073 ÅA
0.71073 ÅA
0.71073 ÅA
Crystal system
Space group
Unit cell dimensions
Triclinic
P ꢁ 1
Monoclinic
P21/n
a = 7.5789(3) Å
b = 17.5687(6) Å
c = 14.6214(5) Å
Monoclinic
P21/c
a = 13.7203(8) Å
b = 7.2507(4) Å
c = 19.9177(11) Å
Orthorhombic
Pna21
a = 22.5861(13) Å
b = 12.9073(7) Å
c = 7.1333(4) Å
Orthorhombic
Pca21
a = 17.1538(8) Å
b = 10.2883(5) Å
c = 20.6414(9) Å
a = 10.6706(4) Å
b = 11.2351(4) Å
c = 11.8621(5) Å
a
= 90.406(2)°
a
= 90°
a
= 90°
a
= 90°
a
= 90°
b = 108.796(2)°
b = 98.1480(10)°
b = 106.855(3)°
b = 90°
b = 90°
c
= 108.229(2)°
c
= 90°
c
= 90°
c
= 90°
c = 90°
Volume
Z
Calculated density
Absorption coefficient
F(000)
1269.45(8) Å3
1927.21(12) Å3
4
1896.33(18) Å3
4
2079.5(2) Å3
4
3642.9(3)Å3
8
2
1.778 g/cm3
5.556 mmꢁ1
664
1.915 g/cm3
7.296 mmꢁ1
1072
1.946 g/cm3
7.414 mmꢁ1
1072
1.864 g/cm3
6.766 mmꢁ1
1136
1.974 g/cm3
7.717 mmꢁ1
2080
Crystal size
Crystal habit
Crystal color
h Range for data
collection
0.18 ꢂ 0.16 ꢂ 0.09 mm
0.38 ꢂ 0.24 ꢂ 0.14 mm
0.30 ꢂ 0.30 ꢂ 0.10 mm
Hexagonal Plate
Red
0.20 ꢂ 0.16 ꢂ 0.08 mm
Hexagonal Plate
Red
0.17 ꢂ 0.14 ꢂ 0.02 mm
Plate
Block
Plate
Red
3.29–27.51°
Orange
3.23–32.91°
Red
3.25–27.49°
1.55–27.50°
3.13–27.53°.
ꢁ13 6 h 6 13
ꢁ14 6 k 6 14
ꢁ15 6 l 6 15
39,161/5825
[R(int) = 0.0747]
99.8%
ꢁ11 6 h 6 9
ꢁ21 6 k 6 26
ꢁ22 6 l 6 16
39,773/6312
[R(int) = 0.0240]
99%
ꢁ17 6 h 6 17
ꢁ9 6 k 6 8
ꢁ25 6 l 6 23
40,071/4352
[R(int) = 0.0527]
100%
ꢁ28 6 h 6 29
ꢁ16 6 k 6 16
ꢁ7 6 l 6 9
ꢁ22 6 h 6 22
ꢁ13 6 k 6 13
ꢁ25 6 l 6 26
54,385/7982
[R(int) = 0.0606]
99.7%
Limiting indices
Reflections collected /
unique
Completeness to
h = 25.00
36,639/4012
[R(int) = 0.1021]
99.6%
Refinement method
Full-matrix least-squares Full-matrix least-squares
Full-matrix least-squares
on F2
Full-matrix least-squares
on F2
Full-matrix least-squares
on F2
on F2
on F2
Data/restraints/
parameters
5825/0/352
6312/0/264
4352/0/264
4012/1/284
7982/1/516
Refinement threshold
Data > threshold
GOF
I > 2
5005
1.033
r
(I)
I > 2
4946
1.037
r
(I)
I > 2
3528
1.035
r
(I)
I > 2
3250
1.017
r
(I)
I > 2r(I)
6914
1.025
Final R indices [I > 2
r
(I)] R1 = 0.0298,
wR2 = 0.0537
R1 = 0.0406,
R1 = 0.0237,
wR2 = 0.0473
R1 = 0.0384,
R1 = 0.0319,
wR2 = 0.0790
R1 = 0.0493,
R1 = 0.0328,
wR2 = 0.0674
R1 = 0.0461,
R1 = 0.0309,
wR2 = 0.0518
R1 = 0.0434,
R indices (all data)
wR2 = 0.0569
wR2 = 0.0503
wR2 = 0.0953
wR2 = 0.0728
wR2 = 0.0551
Largest diff. peak and
hole
0.921 and ꢁ1.103 e Åꢁ3
1.095 and ꢁ0.512 e Åꢁ3
3.746 and ꢁ1.779 e Åꢁ3
0.960 and ꢁ1.273 e Åꢁ3
0.940 and ꢁ0.885 e Åꢁ3
Table 3
0
Selected bond lengths (ÅA) and bond angles (deg).
Pt(bph)(3,4,7,8-Me4phen)
Pt(bph)(4,7-Me2phen)
Pt(bph)(5,6-Me2phen)
Pt(bph)(4,7-ph2phen)
Pt(bph)(5-Mephen)
Bond lengths(Å)
Pt–C
Pt–C
Pt–N
Pt–N
2.014(6)
2.009(6)
2.125(5)
2.138(4)
1.999(3)
2.013(3)
2.084(2)
2.131(2)
2.002(6)
2.009(6)
2.123(5)
2.117(5)
2.016(4)
2.015(4)
2.133(3)
2.114(3)
1.980(7)
2.007(6)
2.165(5)
2.097(4)
Bond angles(deg)
C–Pt–C
N–Pt–N
C–Pt–N
C–Pt–N
80.2(2)
80.06(10)
77.52(7)
99.79(9)
102.35(9)
80.5(2)
80.54(15)
77.12(12)
104.04(14)
101.10(14)
80.7(3)
77.2(2)
106.3(2)
98.8(2)
76.82(18)
101.4(2)
101.6(2)
77.20(19)
103.0(2)
102.3(2)
Dihedral (deg)
C–C–N–N
1.86(3)
6.48(6)
20.35(4)
21.01(11)
19.07(3)
Configuration
B
B
X
X
X
B = bow-shaped stereoisomer.
X = x-shaped stereoisomer.
crystallographic structures. Selected bond lengths, bond angles and
dihedral angles are listed in Table 4 with the values from crystallog-
raphy in parentheses. The calculated bond lengths from platinum to
carbon atoms were between 2.016 and 2.033 Å. The bond lengths
between platinum to nitrogen atom were between 2.126 and
2.169 Å. C–Pt–C and N–Pt–N bond angles were around 77° and 81°.

86
D.P. Rillema et al. / Journal of Molecular Structure 1041 (2013) 82–91
Fig. 1. ORTEP diagrams of Pt(bph)(5,6-Me2phen) (left) and Pt(bph)(4,7-Ph2phen) (right).
Fig. 2. Capped-stick X-ray structures of the X (X-shaped) and B (Bow-Shaped) Pt(II)-complexes.
3.5. Circular dichroism
Pt(bph)(4,7-Ph2phen) showed upward behavior. Not shown are
the CD spectra of Pt(bph)(5-Mephen) and Pt(bph)(phen) which be-
haved upwards and downwards, respectively.
Solid-state circular dichroism (CD) spectra [34–36] were col-
lected for all complexes in the series. All samples were prepared
as pellets with an IR-grade KBr background [36]. Approximately
20,000 lbs load-pressure was applied to each pulverized sample
to ensure transparency of the pellets. Fig. 4 shows an overlay of se-
lected CD spectra in the UV region. All complexes showed elliptic-
ity around 215 nm. As illustrated in the figure, Pt(bph)(5-Clphen),
Pt(bph)(4,7-Me2phen) and Pt(bph)(3,4,7,8-Me4phen) exhibited
downward behavior while those of Pt(bph)(5,6-Me2phen) and
4. Discussion
4.1. Preparation of complexes
Preparation of the complexes is summarized in Fig. 5. The start-
ing material, [Pt(bph)(C2H5)2S]2, was prepared using procedures

D.P. Rillema et al. / Journal of Molecular Structure 1041 (2013) 82–91
87
Fig. 3. Left: packing in Pt(bph)(5,6-Me2phen); right: Pt(bph)(4,7-Ph2phen).
Table 4a
Selected bond lengths (Å) from DFT optimized structures.a
Pt-C
Pt-C
Pt-N
Pt-N
Pt(bph)(4-Mephen)
Pt(bph)(5-Mephen)
Pt(bph)(4,7-Me2phen)
Pt(bph)(5,6-Me2phen)
Pt(bph)(3,4,7,8-Me4phen)
Pt(bph)(4,7-Ph2phen)
Pt(bph)(5-Clphen)
2.032
2.033
2.164
2.160
2.032 (1.980)
2.016 (2.015)
2.022 (2.002)
2.033 (2.014)
2.033 (2.016)
2.033
2.033 (2.007)
2.016 (2.016)
2.022 (2.009)
2.034 (2.009)
2.033 (2.015)
2.032
2.160 (2.165)
2.126 (2.114)
2.129 (2.123)
2.168 (2.125)
2.156 (2.133)
2.164
2.163 (2.097)
2.126 (2.133)
2.129 (2.117)
2.169 (2.138)
2.155 (2.114)
2.160
a
Experimental values in parenthesis.
Table 4b
Selected bond angles and dihedral angles in degrees from DFT optimized structures.a
N–Pt–N
C–Pt–C
C–Pt–N
C–Pt–N
102.95
C–C–N–N
Pt(bph)(4-Mephen)
Pt(bph)(5-Mephen)
Pt(bph)(4,7-Me2phen)
Pt(bph)(5,6-Me2phen)
Pt(bph)(3,4,7,8-Me4phen)
Pt(bph)(4,7-Ph2phen)
Pt(bph)(5-Clphen)
76.98
80.76
102.89
22.17
77.08 (77.2)
77.79 (77.52)
77.99 (76.9)
76.30 (77.2)
76.69 (77.12)
77.08
80.77 (80.7)
80.04 (80.06)
80.90 (80.5)
80.09 (80.2)
80.72 (80.54)
80.78
102.83 (106.3)
101.02 (99.79)
102.54 (103.4)
101.66 (101.4)
103.21 (104.04)
102.94
102.89 (98.8)
22.10 (19.07)
0.0 (6.48)
23.23 (20.35)
0.38 (1.86)
22.58 (21.01)
22.28
101.02 (102.35)
102.54 (102.5)
101.87 (101.6)
103.09 (101.10)
102.81
a
Experimental values in parenthesis.
4.2. Analysis of 1H NMR spectra
Pt(bph)(5-Clphen)
Pt(bph)(5,6-Me2 phen)
Pt(bph)(4,7-Me2 phen)
Pt(bph)(4,7-ph2 phen)
Pt(bph)(3,4,7,8-Me4 phen)
60
50
40
30
20
10
0
Fig. 6 displays the assignments for different types of hydrogen
atoms for the bph and phen ligands. The same letter assignments
apply to the protons on the other half of the molecule. The bar
graph shown on the bottom of the figure summarizes the location
of the 1H resonances as assigned (Table 1) relative to TMS for both
ligands. Of particular note are the positions of a and x which have
1H resonances furthest downfield for each ligand. The position of
the 1H resonance for the a proton is 7.5 0.1 ppm, but x proton res-
onance is dependent on the substituent bound to the phenanthro-
line ring as shown in Fig. 6.
Fig. 7 shows the 1H NMR spectrum of Pt(bph)(phen) and
Pt(bph)(5-Clphen). There are satellite peaks observed around
7.4 ppm and unresolved satellite peaks seen at 9.9 ppm. The inten-
sity of the satellite peaks are about 1/4–1/5 the size of its center
peaks. The signals at 7.4 and 9.9 ppm are assigned to hydrogen
atoms located at the a and x positions, respectively. The origin of
the satellite peaks is due to splitting of the proton signal upon cou-
pling with the 195Pt isotope, which has a nuclear spin state of 1/2
and a natural abundance of 33.8% [37]. This coupling constant J
(Pt, H) is about 48 Hz. The coupling and splittings due to 195Pt is
shown in the scheme as an inset in Fig. 7.
-10
-20
200
250
300
Wavelength (nm)
Fig. 4. CD spectra of Pt(bph)(5-Clphen), Pt(bph)(5,6-Me2phen), Pt(bph)(4,7-Me2-
phen), Pt(bph)(4,7-ph2phen) and Pt(bph)(3,4,7,8-Me4phen) in KBr pellets.
previously published [13]. Addition of the desired ligand in a 1:1
Pt:ligand ratio to a methylene chloride solution of [Pt(bph)(C2H5)2-
S]2 led to the desired product in high yield. Slow evaporation of the
solutions resulted in formation of single crystals for a number of
complexes.
Electron donating substituents shifts these 1H resonances up-
field and correlate quite well with the sum of the Hammett rs
function, where rs
= rp + rm [38]. As shown in Fig. 8, two correla-
tions for different types of complexes based on their crystal

88
D.P. Rillema et al. / Journal of Molecular Structure 1041 (2013) 82–91
Fig. 5. Schematic diagram for preparation of complexes.
Fig. 6. 1H NMR assignments.
structures are found. The different types of structures will be dis-
cussed later.
platinum complexes have. In Pt(bph)(5,6-Me2phen), Pt(bph)
(5-Mephen) and Pt(bph)(4,7-ph2phen) coordination of bph and
phen ligands about the platinum metal center are pivoted with re-
spect to each other at the Pt-center by an angle of ꢃ30° giving rise
to the X configurations. The C–C–N–N torsion angles were 20.19°,
22.40° and 21.01°, respectively. But for Pt(bph)(3,4,7,8-Me4phen)
and Pt(bph)(4,7-Me2phen), the rings of the bph and phen ligands
4.3. X-ray structures and DFT optimization
As shown in Fig. 2, the solid-state structures of the complexes
deviate from the standard ‘square-planar’ configuration that most

D.P. Rillema et al. / Journal of Molecular Structure 1041 (2013) 82–91
89
Fig. 7. 1H NMR of Pt(bph)(phen) and Pt(bph)(5-Clphen). Inset: Scheme for 195Pt–1H coupling.
4,7-ph2
10.00
9.95
9.90
9.85
9.80
9.75
9.70
9.65
9.60
configuration, the first step was the same as for the X configuration
determination. The second step involved folding of the bph ligand
by an angle b1 and then folding of the phen ligand by an angle b2.
5-me
5-cl
phen
For Pt(bph)(3,4,7,8-Me4phen),
Pt(bph)(4,7-Me2phen), = 27°, b1 = 12° and b2 = 5°, for
Pt(bph)(phen), = 5°, b1 = 14° and b2 = 8°. The angles for the B con-
a = 7°, b1 = 11° and b2 = 6°, for
5,6-me2
a
a
figurations shown in Fig. 9 are the sum of b1 and b2.
4-me
Density-functional theory (DFT) [15–17,23–25] has been used
to optimize structures of the complexes in gas-phase [23–25].
As shown in Table 4a and 4b, theoretical bond lengths, bond an-
gles and dihedral angles are consistent with those determined by
X-ray crystallography. In the coordination sphere, the C–C–N–N
dihedral angle was ꢃ23° for the X configuration and ꢃ0° for the
B configuration. Optimized structures agree with the crystal
structures very well. The difference in bond lengths between opti-
mized structures and crystal structures is ꢃ0.02 Å. These slight
positive deviations are normal for gas phase calculations vs.
experimental results [23]. The calculated dihedral C–C–N–N an-
gles verify the results found experimentally for the X and B
configurations.
4,7-me2
-0.4
3,4,7,8-me4
-1.0
-0.8
-0.6
-0.2
0.0
0.2
0.4
σT = σp + σm
Fig. 8. Correlation of the 1H chemical shifts with the Hammett
rp functions. (phen
data from Ref. [13]) Black line (X-shaped); Red line (B-shaped) [vide infra]. (For
interpretation of the references to color in this figure legend, the reader is referred
to the web version of this article.)
were slightly bent over in opposite directions resulting in angles
that vary from 17° to 22° giving rise to the bowed B configuration.
The C–C–N–N torsion (dihedral) angles for these complexes were
less than 7°. Unlike Pt(bph)(phen), no Pt–Pt interactions in the so-
lid state are observed in all five crystal lattices as noted by the unit
cell configurations. The shortest Pt–Pt distance is over 6 Å which is
too long for any Pt–Pt interactions in the solid state.
4.4. Circular dichroism and optical activity
Owing to the non-planar configuration of metal complexes in
the series, the possibility of optical activity was explored using
CD spectroscopy. As mentioned, among the eight platinum
biphenyl phenanthroline complexes, including Pt(bph)(phen)
[13], six crystal structures were obtained. Pt(bph)(5-Mephen),
Pt(bph)(4,7-Ph2phen) and Pt(bph)(5,6-Me2phen) were in the X-
configuration and Pt(bph)(phen), Pt(bph)(4,7-Me2phen) and
Pt(bph)(3,4,7,8-Me4phen) were in the B-configuration. Based on
these observations, CD spectroscopy can be used to tentatively as-
sign stereochemical structures of Pt(bph)(4-Mephen) and
Pt(bph)(5-Clphen) where X-ray data are lacking. Results show that
both of these complexes gave downward behavior in their CD
The angles formed between the ligands when the complexes are
viewed on edge are represented using the scheme in Fig. 9. For the
X configuration, first the bph ligand was bent by an angle
a from
the plane derived from the complex in the square planar configu-
ration leaving the phen ligand in the plane. This was followed by
a rotation of the bph ligand by an angle d. For Pt(bph)(5,6-Me2-
phen),
a
ꢃ 0 and d = 30°; for Pt(bph)(5-Mephen),
a
ꢃ 0 and
d = 29°; for Pt(bph)(4,7-ph2phen),
a
= 15° and d = 27°. For the B

90
D.P. Rillema et al. / Journal of Molecular Structure 1041 (2013) 82–91
Fig. 9. Illustration of bending and folding of chelate rings.
spectra; hence, their structures are assigned as having the B-
configuration.
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