Crystal structures, electronic properties and structural pathways of four [Cu(phen)2Cl][Y] complexes (phen = 1,10-phenanthroline; Y = BF4-·0.5H2O, PF6-, CF3SO3-·H2O or BPh4-)

Article abstract of DOI:10.1039/a702291c

The crystal structures of [Cu(phen)₂Cl][BF₄]·0.5H₂O 1 (phen = 1,10-phenanthroline), [Cu(phen)₂Cl][PF₆] 2, [Cu(phen)₂Cl][CF₃SO₃]·H₂O 3 and [Cu(phen)₂Cl][BPh₄] 4 have been determined by X-ray crystallography. Three of the complexes, 1-3, involve a CuN₄Cl chromophore with a square based pyramidal distorted trigonal bipyramidal stereochemistry, while 4 involves a trigonal bipyramidal distorted square based pyramidal stereochemistry. The geometries of the CuN₄Cl chromophores in 1-4 were compared by scatter-plot analysis with those of four other [Cu(phen)₂Cl][Y] complexes of known structure. The scatter plots of the eight cation distortion isomers of the [Cu(phen)₂Cl][Y] complex suggest that all the complexes involve a -A + B route distortion of the CuN₄Cl chromophore, -A (ca. 60%) and +B (ca. 40%), The observation of linear and parallel correlations are alternatively interpreted as a direct observation of vibronic coupling of a mixture of the symmetric, v_sym, C₂ mode and the asymmetric, v_asym, non-C₂ mode of vibration of the CuN₄Cl chromophore. This emphasises the need to determine the structure of more than one complex in a series of cation distortion isomers, in which the limits of the range of stereochemistries are indicated by the measurement of the electronic reflectance spectra.

Full text of DOI:10.1039/a702291c

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Crystal structures, electronic properties and structural pathways of
four [Cu(phen)2Cl][Y] complexes (phen = 1,10-phenanthroline;
Ϫ
Ϫ
Ϫ
Ϫ
Y = BF4 ؒ0.5H2O, PF6 , CF3SO3 ؒH2O or BPh4 )†
Gillian Murphy, Pat Nagle, Brian Murphy and Brian Hathaway*
The Chemistry Department, University College Cork, Ireland
The crystal structures of [Cu(phen)2Cl][BF4]ؒ0.5H2O 1 (phen = 1,10-phenanthroline), [Cu(phen)2Cl][PF6] 2,
[Cu(phen)2Cl][CF3SO3]ؒH2O 3 and [Cu(phen)2Cl][BPh4] 4 have been determined by X-ray crystallography. Three
of the complexes, 1–3, involve a CuN4Cl chromophore with a square based pyramidal distorted trigonal
bipyramidal stereochemistry, while 4 involves a trigonal bipyramidal distorted square based pyramidal
stereochemistry. The geometries of the CuN4Cl chromophores in 1–4 were compared by scatter-plot analysis with
those of four other [Cu(phen)2Cl][Y] complexes of known structure. The scatter plots of the eight cation
distortion isomers of the [Cu(phen)2Cl][Y] complex suggest that all the complexes involve a ϪA ϩ B route
distortion of the CuN4Cl chromophore, ϪA (ca. 60%) and ϩB (ca. 40%), The observation of linear and parallel
correlations are alternatively interpreted as a direct observation of vibronic coupling of a mixture of the
symmetric, νsym, C2 mode and the asymmetric, νasym, non-C2 mode of vibration of the CuN4Cl chromophore. This
emphasises the need to determine the structure of more than one complex in a series of cation distortion isomers,
in which the limits of the range of stereochemistries are indicated by the measurement of the electronic reflectance
spectra.
The concept of
a
structural pathway2,3 for [Cu(chelate
solution yielded turquoise needles after 1 d (Found: C, 48.2; H,
2.9; Cl, 5.55; Cu, 9.75; N, 9.45. C25H18ClCuF3N4O4S requires C,
47.95; H, 2.9; Cl, 5.65; Cu, 10.15; N, 8.95%).
ligand)2X][Y] type complexes has recently been developed for
nine complexes of the [Cu(bipy)2Cl]ϩ cation 1 (bipy = 2,2Ј-
bipyridyl) using scatter plots, Fig. 1. The present paper exam-
ines the consequences of changing the chelate ligand from bipy
to phen (1,10-phenanthroline), to form a corresponding series
of [Cu(phen)2Cl][Y] complexes, where phen is a more rigid
bidentate nitrogen chelate ligand than bipy. The structures of
four [Cu(phen)2Cl][Y] complexes,4–6 5–8, are already known
and this paper reports the preparation and crystal structure
determination of four additional [Cu(phen)2Cl]ϩ cation distor-
tion isomers, 1–4.
The complex [Cu(phen)2Cl][BPh4] 4 was prepared by adding
a hot solution of phen (0.36 g, 2 mmol) in acetonitrile (300 cm3)
to a hot aqueous solution (20 cm3) of CuCl2ؒ2H2O (0.17 g, 1
mmol). A hot aqueous solution (10 cm3) of NaBPh4 (0.34 g,
1 mmol) was then added. Large olive-green crystals were
obtained after 1 d (Found: C, 73.8; H, 4.7; Cl, 4.6; Cu, 8.15;
N, 6.95. C48H36BClCuN4 requires C, 74.05; H, 4.65; Cl, 4.55;
Cu, 8.15; N, 7.2%).
Crystallography
Experimental
The crystallographic data for complexes 1–4 are summarised in
Table 1. For 1 and 2 the unit-cell data (25 reflections, θ 3–25Њ)
and the intensity data were collected at 298 K on a Philips PW
1100 four-circle diffractometer with graphite-monochromatised
Mo-Kα radiation (λ = 0.710 69 Å). An ω–2θ scan mode was
used with reflections in the range 3 < θ < 25Њ and in one quarter
of the reciprocal lattice space. A constant scan speed of 0.05Њ
Preparations
The complex [Cu(phen)2Cl][BF4]ؒ0.5H2O 1 was prepared by
adding a boiling solution of phen (0.46 g, 2.55 mmol) in
methanol (200 cm3) to a boiling solution of Cu(BF4)2ؒ6H2O
(0.44 g, 1.27 mmol), H2NOHؒHCl (0.2 g, 2.88 mmol) and 0.88
mol dmϪ3 NH4OH (1 cm3) in water (20 cm3). The resulting red
copper() solution was filtered and left to oxidise slowly in air.
Green crystals of 1 were deposited after several days and were
filtered off and dried at the pump (Found: C, 52.15; H, 2.9; Cl,
6.25; Cu, 11.15; N, 10.15. Calc. for C24H17BClCuF4N4O0.5: C,
51.6; H, 3.05; Cl, 6.25; Cu, 10.05; N, 10.1%).
The complex [Cu(phen)2Cl][PF6] 2 was prepared by mixing
boiling solutions of CuCl2ؒ2H2O (0.2 g, 2.6 mmol) in water (80
cm3) and phen (0.47 g, 2.6 mmol) in ethanol (80 cm3) with KPF6
(0.24 g, 1.3 mmol). The resulting precipitate was recrystallised
from acetonitrile–1,3-dimethoxypropane (5:1, 60 cm3) and
yielded green crystals of 2 (Found: C, 48.05; H, 3.05; Cl, 6.05;
Cu, 10.05; N, 8.95. Calc. for C24H16ClCuF6N4P: C, 47.7; H, 2.65;
Cl, 5.85; Cu, 10.5; N, 9.25%).
s
Ϫ1 was used with a variable scan width of (0.7 ϩ 0.1 tan θ). The
acceptance criterion I > 2.5σ(I ) was used. Lorentz-polarisation
corrections were applied, but no correction was made for
absorption.
The unit-cell parameters of complexes 3 and 4 were deter-
mined and the intensity data collected on an Enraf-Nonius
CAD4 diffractometer. Reflections in the range 3.0 < θ < 24Њ in
one hemisphere were collected for both complexes. The data
were collected at room temperature. A constant scan speed of 7Њ
minϪ1 was used with a variable scan width (0.8 ϩ 0.2 tan θ).
Other details as above.
All four structures were solved by Patterson and Fourier
techniques, developed by Fourier difference techniques,
(|Fo| Ϫ |Fc|), and refined by full-matrix least-squares analysis,
with the Σw(|Fo| Ϫ |Fc|)2 function minimised, and initially w = 1/
[σ2(Fo)]. Anisotropic thermal parameters were used on all the
non-hydrogen atoms. The positions of the hydrogen atoms were
calculated geometrically, with C᎐H and O᎐H distances of 1.08
Å, and floated on the associated carbon or oxygen atom with a
fixed thermal parameter of 0.07 Å2. Finally, a refined weighting
The complex [Cu(phen)2Cl][CF3SO3]ؒH2O 3 was prepared by
mixing a hot solution of phen (0.36 g, 2 mmol) in propanone
(150 cm3) with a hot aqueous solution (30 cm3) of Cu(CF3SO3)2
(0.36 g, 1 mmol) and NaCl (0.06 g, 1 mmol). The resulting
† Comparative crystallography. Part 3.1
J. Chem. Soc., Dalton Trans., 1997, Pages 2645–2652
2645

View Article Online
N1
N1
N1
115o
2.1 Å
2.15 Å
95o
N2
2.2 Å
N2
105o
Cu
N2
2.25 Å
Cl
100o
120o
N4
140o
Cl
Cl
Cu
Cu
2.0 Å
N3
145o
2.1 Å
2.45 Å
125o
2.35 Å
135o
N4
VI'
N4
V'
νsym
2.05 Å
N3
N3
IV'
Route +A-B
Route -A-B
C2
Route -B
Route -A
N1
N1
N1
110o
130o
120o
2.35 Å
N2
140o
N4
N2
N4
N2
N4
2.45 Å
Cl
2.25 Å
Route +A
C2
100o
120o
Cl
Cu
2.15 Å
Cu
Cu
Cl
120o
110o
130o
2.1 Å
2.05 Å
N3
N3
N3
III
II
I
Route +A+B
Route -A+B
RTB
Route +B
N1
N1
N2 2.05 Å
N1
2.0 Å
135o
2.35 Å
125o
2.45 Å
2.1 Å
N2
N2
145o
Cu
140o
100o
120o
N4
Cu
Cu
Cl
Cl
105o
2.15 Å
Cl
95o
N4
VI
2.25 Å
115o
N4
V
2.1 Å
N3
2.2 Å
asym
N3
IV
N3
Fig. 1 The forms of distortion of the RTB CuN4Cl chromophore involving the ±A, ±B and ±A ± B routes (bond distances are rounded off to the
nearest 0.05 Å)
Table 1 Crystallographic and structure refinement data for [Cu(phen)2Cl][BF4]ؒ0.5H2O 1, [Cu(phen)2Cl][PF6] 2, [Cu(phen)Cl][CF3SO3]ؒH2O 3 and
[Cu(phen)Cl][BPh4] 4
1
2
3
4
Formula
M
C24H17BClCuN4F4N4O0.5
554.8
C24H16ClCuF6N4P
603.4
C25H18ClCuF3N4O4S
626.5
C48H36BClCuN4
778.6
Crystal system
Space group
a/Å
b/Å
c/Å
α/Њ
β/Њ
Monoclinic
P21 /c (C52h, no. 14)
12.507(4)
11.493(4)
17.246(5)
Monoclinic
P21 /c (C52h, no. 14)
12.973(4)
11.127(4)
17.499(5)
Triclinic
P1 (Ci , no. 2)
Triclinic
P1 (Ci , no. 2)
1
1
¯
¯
10.349(2)
12.111(2)
12.379(2)
61.65(2)
79.11(1)
65.99(2)
1247.20
2
11.177(3)
11.423(1)
15.514(2)
87.08(1)
76.63(1)
78.45(1)
1888.03
2
111.08(3)
110.73(3)
γ/Њ
U/Å3
2313.16
4
1.59
2362.52
4
1.70
Z
Dc/g cmϪ3
1.62
1.37
F(000)
1132
10.63
2603
1212
11.13
2842
614
10.71
3739
806
6.50
5575
µ/cmϪ1
No. unique reflections (N)
No. varied parameters (P)
317
398
353
497
N/P
8.21
7.14
10.59
11.22
R
RЈ
k
g
0.0731
0.0785
1.0000
0.005 172
0.010
ϩ0.89, Ϫ1.27
36
0.0610
0.0674
0.3853
0.013 114
0.005
ϩ0.75, Ϫ1.30
37
0.0532
0.0565
1.0000
0.044 245
0.010
0.0485
0.0474
37.6548
0.000 356
0.020
Maximum final shift/e.s.d.
Residual electron density/e ÅϪ3
No. atoms with anisotropic
thermal parameters
ϩ0.59, Ϫ0.88
39
ϩ0.34, Ϫ0.44
55
scheme was introduced with w = k/[σ2(Fo) ϩ g(Fo)2] (see Table 1
for the final values of k and g).
graphic Data Centre (CCDC). See Instructions for Authors,
J. Chem. Soc., Dalton Trans., 1997, Issue 1. Any request to the
CCDC for this material should quote the full literature citation
and the reference number 186/553.
The diffuse reflectance spectra in the range 5000–30 000
cmϪ1 were measured as polycrystalline samples on a Shimadzu
UV–VIS 3101 spectrometer.
The [BF4]Ϫ anion of complex 1 was disordered and refined as
a rigid body with fixed B᎐F and F ؒ ؒ ؒ F distances of 1.370 and
2.237 Å, respectively. Attempts to refine the [BF4]Ϫ anion as
two disordered interpenetrating BF4 groups were unsuccess-
ful. The highest residual electron density in 1 was associated
with the disordered [BF4]Ϫ anion and probably accounts for the
relatively high R value of 0.073. Complex neutral atom scatter-
ing factors were used for the non-hydrogen atoms and for the
Cu, Cl and P atoms.7
Results and Discussion
Crystal structures
All calculations were carried out with the SHELX 76,8
SHELX 86,9 XANADU,10 PUBTAB11 and XCAD 12 programs
on an VAX 6310 mainframe computer; PLUTON 9213 was run
on a Memorex 386 personal computer.
Selected bond lengths and angles for the eight [Cu(phen)2-
Cl][Y] complexes are given in Table 2. Fig. 2 shows a representa-
tive molecular structure for the [Cu(phen)2Cl]ϩ cation, the atom
numbering scheme and the angle notation used.
The crystal structures of complexes 1–4 consist of discrete
[Cu(phen)2Cl]ϩ cations and [BF4]Ϫ, [PF6]Ϫ, [CF3SO3]Ϫ and
[BPh4]Ϫ anions, respectively. In addition 1 and 3 involve mole-
cules of water in the unit cell, 0.5 and 1.0 mol, respectively.
None of the anions or water molecules is close enough (<3.0 Å)
to be considered even weakly semi-co-ordinated to the
copper() cation.14 The cations all involve a five-co-ordinate
Atomic coordinates, thermal parameters, and bond lengths
and angles have been deposited at the Cambridge Crystallo-
CuN4Cl chromophore, with
stereochemistry having a square based pyramidal distor-
a near trigonal bipyramidal
2646
J. Chem. Soc., Dalton Trans., 1997, Pages 2645–2652

View Article Online
Table 2 Selected bond lengths (Å) and angles (Њ) for the [Cu(phen)2Cl][Y] complexes
Y
Clؒ1.5H2Oؒ
Clؒ1.5H2Oؒ
(CH3)2CO
85
BF4ؒ0.5H2O
1
ClO4
PF6
2
(CH3)2CO
NO3ؒH2O
CF3SO3ؒH2O
3
BPh4
4
54
65
76
Cu᎐N(Cl)*
Cu᎐Cl
Cu᎐N(1)
Cu᎐N(2)
Cu᎐N(3)
Cu᎐N(4)
2.014(2)
2.304(2)
1.995(6)
2.078(5)
2.011(6)
2.121(6)
2.008(2)
2.298(2)
1.986(6)
2.077(6)
2.004(6)
2.136(6)
2.004(2)
2.294(2)
2.001(4)
2.076(4)
2.003(4)
2.157(4)
1.991(1)
2.281(1)
1.999(4)
2.126(3)
1.995(3)
2.138(3)
2.002(1)
2.292(1)
1.988(4)
2.091(2)
1.989(4)
2.132(2)
1.967(1)
2.257(1)
1.990(4)
2.108(2)
1.993(4)
2.151(4)
1.990(1)
2.280(1)
1.998(2)
2.127(2)
1.996(2)
2.151(2)
1.964(1)
2.254(1)
2.024(2)
2.057(2)
2.008(2)
2.242(2)
α1
α2
α3
α4
α5
α6
α7
α8
α9
α10
126.6(2)
118.9(2)
114.5(2)
92.8(2)
91.2(2)
81.3(2)
80.6(2)
175.3(2)
98.1(2)
95.4(2)
127.6(2)
119.0(2)
113.4(2)
92.3(2)
90.9(2)
81.7(2)
80.5(2)
176.2(2)
98.2(2)
96.0(2)
131.6(1)
114.4(1)
114.1(2)
93.4(1)
91.0(1)
81.0(2)
80.1(2)
175.2(2)
97.5(2)
96.3(2)
130.4(1)
129.6(1)
100.0(1)
94.1(1)
95.0(1)
80.1(2)
80.5(1)
170.8(1)
95.1(2)
92.5(1)
135.8(1)
119.2(1)
105.0(1)
92.7(1)
91.8(1)
81.4(1)
80.8(1)
175.6(1)
95.8(1)
96.5(1)
133.0(1)
120.6(1)
106.4(1)
96.8(1)
94.2(1)
81.1(1)
80.6(2)
168.6(2)
93.8(1)
91.0(2)
138.7(1)
127.9(1)
93.4(1)
93.2(1)
94.6(1)
80.7(1)
80.2(1)
172.1(1)
92.8(1)
95.7(1)
157.7(1)
105.9(1)
96.4(1)
92.7(1)
91.4(1)
81.0(1)
79.2(1)
169.2(1)
91.5(1)
109.1(1)
τ
0.81
0.81
0.73
0.67
0.66
0.59
0.56
0.19
* The Cu᎐Cl distances are corrected to Cu᎐N values using the relationship Cu᎐Cl Ϫ 0.29 Å = Cu᎐N(Cl).
Table 3 Maxima, minima, difference (∆) and average values of the bond lengths (Å) and angles (Њ) for the [Cu(phen)2Cl][Y] complexes
Cu᎐Cl
Cu᎐N(Cl)
Cu᎐N(1)
Cu᎐N(2)
Cu᎐N(3)
Cu᎐N(4)
τ
Maximum
Minimum
∆
2.304(2)
2.254(1)
0.050
2.014(2)
1.964(1)
0.050
2.024(2)
1.986(6)
0.038
2.127(2)
2.057(2)
0.070
2.011(6)
1.989(4)
0.022
2.242(2)
2.121(6)
0.121
0.81
0.19
0.62
Average
2.283(1)
1.993(1)
1.998(4)
2.093(3)
2.000(4)
2.154(4)
α1
α2
α3
α4
α5
α6
α7
α8
α9
α10
Maximum
Minimum
∆
157.7(1)
126.6(2)
31.1
129.6(1)
105.9(1)
23.7
114.5(2)
93.4(1)
21.1
96.8(1)
92.3(2)
4.5
95.0(1)
90.9(2)
4.1
81.7(2)
80.1(2)
1.6
80.8(1)
79.2(1)
1.6
176.2(2)
168.6(2)
7.6
98.2(2)
91.5(1)
6.7
109.1(1)
91.0(2)
18.1
Average
135.2(1)
119.4(1)
105.4(1)
93.5(1)
92.5(1)
81.0(2)
80.3(1)
172.9(2)
95.4(2)
96.6(2)
tion 1 (SBPDTB) in 1, 2 and 3, and a trigonal bipyramidal
distorted square based pyramidal stereochemistry (TBDSBP)
for 4. All four complexes are further examples of distortion
isomers of the [Cu(phen)2Cl]ϩ cation, whose stereochemistries
are related by the structural pathways1 of Fig. 1. No attempt
will be made to describe the individual structures of complexes
1–4, Table 2, but scatter-plot analysis will be used to compare
their structures with those of four [Cu(phen)2Cl][Y] complexes
of known crystal structure.4–6 Table 2 summarises the selected
bond lengths and angles of all eight complexes, sequenced in
order of their τ values, where τ = (α8 Ϫ α1)/60,15 and Table 3
summarises the maximum, minimum, difference (∆) and aver-
age bond length and angle values for the series of eight
[Cu(phen)2Cl][Y] complexes. Table 4 gives the sums of the in-
plane angles, α1–3, and distances, Cu᎐N(2), Cu᎐N(4) and Cu᎐Cl.
Relative to a RTB stereochemistry, the out-of-plane dis-
tances, Table 2, show only small differences, Table 3, with
∆Cu᎐N(1) = 0.038 Å and ∆Cu᎐N(3) = 0.022 Å. The largest
variations in bond lengths are present in the equatorial bond
distances Cu᎐Cl, Cu᎐N(2) and Cu᎐N(4), respectively. The
Cu᎐N(4) distances show the largest variation ranging from
2.121(6) to 2.242(2) Å, with ∆ = 0.121 Å and average = 2.154(4)
Å. The Cu᎐N(2) distances vary from 2.057(2) to 2.127(2) Å,
with ∆ = 0.070 Å and average = 2.093(3) Å. The Cu᎐Cl dis-
tances range from 2.254(1) to 2.304(2) Å, with ∆ = 0.050 Å and
average = 2.283(1) Å. The average of the in-plane Cu᎐N(2,4)
distances, 2.124(4) Å, is greater than the average of the axial
Cu᎐N(1,3) distances, 1.999(4) Å, by 0.125 Å, consistent with
a TB stereochemistry and slightly greater than the difference
of 0.1 Å normally observed,16 which is probably associated
with the exceptionally large value of the Cu᎐N(4) distance of
2.242(2) Å for complex 4.
The [Cu(phen)2Cl][Y] data
The out-of-plane bond angles, Table 2, show only small dif-
ferences, Table 3, with ∆α4–7 ranging from 1.6 to 4.5Њ but with
the α8–10 angles showing larger differences than expected, 7.6–
18.1Њ. The α1 in-plane angles show the largest variation ranging
from 126.6(2) to 157.7(1)Њ, with ∆ = 31.1Њ and average =
135.2(1)Њ. The α2 angles vary from 105.9(1) to 129.6(1)Њ, with
∆ = 23.7Њ and average = 119.4(1)Њ. The α3 angles show the
smallest variation ranging from 93.4(1) to 114.5(2)Њ, with
∆ = 21.1Њ and average = 105.4(1)Њ.
The structures of the eight five-co-ordinate CuN4Cl chromo-
phores vary from near TB to near SBP, reflected in a range of τ
values15 of 0.81 to 0.19, ∆τ = 0.62. This is a substantial vari-
ation in τ, the largest seen to date for cation distortion isomers
of the [Cu(chelate ligand)2X][Y] series of complexes.1 None of
the complexes has a near-RTB (regular trigonal bipyramidal)
stereochemistry or a two-fold axis of symmetry. Seven com-
plexes have τ values in the more limited range of 0.81 to 0.56
and their stereochemistries are best described as SBPDTB.
Complex 4 has a τ value of 0.19 and a stereochemistry best
described as TBDSBP.
From Table 2 it is noticeable that within the range of τ values
of 0.81–0.19 there is a significant gap of 0.37 in τ value between
the extreme TBDSBP value of 0.19 for 4 and the next highest
J. Chem. Soc., Dalton Trans., 1997, Pages 2645–2652
2647

View Article Online
Table 4 Sums of the in-plane bond angles and distances for the [Cu(phen)2Cl][Y] complexes
Complex
1
5
2
6
7
8
3
4
α1 /Њ
α2 /Њ
α3 /Њ
Sum/ Њ
126.6
118.9
114.5
360.0
127.6
119.0
113.4
360.0
131.6
114.4
114.1
360.1
130.4
129.6
100.0
360.0
135.8
119.2
105.0
360.0
133.0
120.6
106.4
360.0
138.7
127.9
93.4
157.7
105.9
96.4
360.0
360.0
Cu᎐Cl/Å
Cu᎐N(2)/Å
Cu᎐N(4)/Å
Sum/Å
2.304
2.078
2.121
6.503
2.298
2.077
2.136
6.511
2.294
2.076
2.157
6.527
2.281
2.126
2.138
6.545
2.292
2.091
2.132
6.515
2.257
2.108
2.151
6.516
2.280
2.127
2.151
6.558
2.254
2.057
2.242
6.553
C2
C2
Cl
Cl
2.354 Å
2.228 Å
135o 135o
120o
2.0 Å
120o
2.0 Å
-A Route
2.0 Å
2.0 Å
N3
N1
N3
N1
Cu
120o
Cu
90o
str
2.092 Å -νsym
2.092 Å
N2
2.155 Å
2.155 Å
bend
N4
N2
-νsym
N4
RTB
Extreme -A route
seesaw
Fig. 3 Distortion of the CuN4Cl chromophore from RTB to an
extreme ϪA route or ‘seesaw’ stereochemistry
discussed are as follows: (a) τ versus Cu᎐N(4), (b) α3 versus α1,
(c) α3 versus Cu᎐Cl and (d) Cu᎐N(2) versus Cu᎐N(4). An over-
view of the range of stereochemistries is provided by the plot of
τ versus Cu᎐N(4). However, as τ involves two simultaneous
angle changes, it will not be used further. A number of sug-
gested extreme data points, Table 5, are included in the plots,
with the geometry of the extreme ‘seesaw’ stereochemistry
illustrated in Fig. 3.
The eight data points in Fig. 4(a) vary from near regular
trigonal bipyramidal, RTB, to near regular square based pyr-
amidal, RSBP, with the τ values decreasing from 0.81 to 0.19 as
the Cu᎐N(4) distances increase from 2.121(6) to 2.242(2) Å.
The data points show a broad inverse trend, and clearly do not
cluster about RTB. This plot provides an overview of the
observed stereochemistries of the [Cu(phen)2Cl][Y] complexes
as a whole. There are no data points at RTB (τ = 1.0), but there
is one data point, 4, with an exceptionally low τ value of 0.19 at
near SBP. Seven of the eight data points have τ values in the
range 0.81 to 0.56. The main correlation involving the RTB and
RSBP data points contains one data point, 1, with the remain-
ing seven data points lying nearby. To confirm the exceptional
structure of 4 the crystallographic data have been independ-
ently recollected 17 at 150 K. There were no significant differ-
ences in the room temperature and the 150 K structures and
also the low-temperature structure confirms that the stereo-
chemistry of 4 is a static non-fluxional stereochemistry3 of the
copper() cation.
The data points in Fig. 4(b) show the α3 values decreasing
from 114.5(2) to 93.4(1)Њ as the α1 values increase from 126.6(2)
to 157.7(1)Њ. All eight data points have α1 values >120Њ and α3
values <120Њ, Table 2. All eight data points are found in the
ϪA ϩB section of the graph, with one data point 6 lying very
close to the pure ϪA pathway. There are no data points on the
RTB → ϩ A or on the RTB → RSBP (ϪA ϩ B) distortion
pathways. Four data points, 1, 5, 7 and 8, and the RTB data
point, show an inverse trend. Each of these data points has α2
120 ± 1Њ. The remaining data points, 3, 6, 2 and 4, lie on
possible parallel correlations (- - -) displaying α2 values of 130,
130, 115 and 105Њ, consistent with α1 ϩ α2 ϩ α3 = 360Њ, Table 4,
and possibly suggesting the occurrence of preferred or ‘magic
angles’. This series of four possible parallel correlations (- - -)
have the same slopes. The data points show a SBP distortion,
Fig. 2 (a) The molecular structure of the [Cu(phen)2Cl]ϩ cation of
complex 3; (b) the atom numbering scheme and αn notation for the
CuN4Cl chromophore
value of 0.56 for 3. This gap corresponds with a change in the
ratio of the α9 and α10 angles, for τ values > 0.56, α9 > α10, but
for τ values < 0.56, α9 < α10. Equally, while the phen ligand is
constrained to be essentially planar, with angles between the
pyridine rings of 0–5Њ, in complex 4 both of these angles are less
than 1.02Њ. This suggests that once formed the geometry of the
TBDSBP stereochemistry is inherently more stable, than the
range of SBDTB stereochemistries, τ 0.56–0.81, a stability that
could be locked in place by the essential planarity of the phen
ligand. This is also reflected in the near trigonal α1 angles of
126.6–138.7Њ of the SBPDTB stereochemistries, relative to an α1
angle of 157.7Њ in 4.
Scatter-plot analysis for the [Cu(phen)2Cl][Y] complexes
This section presents the data for the [Cu(phen)2Cl][Y] com-
plexes, Table 2, using scatter-plot analysis. The scatter plots
2648
J. Chem. Soc., Dalton Trans., 1997, Pages 2645–2652

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Table 5 Limiting values for the ±A, ϩB, ϪA ϩ B and ϩA ϩ B route distortions
ϩA
ϪA
ϪA ϩ B
ϩA ϩ B
RTB
(RSBP)
(seesaw)
ϩB
(RSBP)
(RSBP)
α1 /Њ
α2 /Њ
α3 /Њ
120
120
120
97.5
97.5
165
135
135
90
150
90
120
165
105
90
105
90
165
Cu᎐N(4)/Å
Cu᎐N(2)/Å
Cu᎐Cl/Å
2.092
2.092
2.354
1.998
1.998
2.543
2.155
2.155
2.228
2.199
1.985
2.354
2.262
2.048
2.228
2.025
1.971
2.543
Fig. 4 Standard scatter plots for the [Cu(phen)2Cl][Y] complexes
but only the correlation with an α2 value of 105Њ can correlate
with the RSBP data point. For these parallel correlations, the α2
values remain constant, therefore ∆α1 ↑ ≈ ∆α3 ↓. The % ϪA
and % ϩB distortion values calculated from the in-plane α1 and
α3 bond angle data of Fig. 4(b) are shown in Table 6.
pure ϪA route distortion of the RTB stereochemistry. In prac-
tice, the α1 and α2 angles are not even approximately equal,
varying from ∆(α1 Ϫ α2) = 7.7–51.8Њ, Table 2. An exceptional
data point 6, with ∆(α1 Ϫ α2) = 0.8Њ, does not lie on any of
the three lines, but with an α3 value of 100.0Њ represents the
most extreme, but distorted, near ‘seesaw’ structure of the
[Cu(phen)2Cl][Y] complexes. The extreme ϪA route distortion
is clearly five-co-ordinate, with three short bonds, Cu᎐N(1) =
Cu᎐N(3) ≈ 2.0 Å, Cu᎐N(Cl) ≈ 2.05 Å, and two longer bonds,
Cu᎐N(2) = Cu᎐N(4) ≈ 2.15 Å, with in-plane angles of α1 =
α2 = 135 and α3 = 90Њ. The best description of this unique
extreme ϪA route distortion is a five-co-ordinate ‘seesaw’
stereochemistry,18 SSDTB, Fig. 3. In general, in view of the
non-equivalence of the α1 and α2 angles and the Cu᎐N(2) and
Cu᎐N(4) distances, the two-fold axis of symmetry of the pure
ϪA route distortion is not appropriate and there must also be a
corresponding ϩB route distortion occurring, which cannot be
observed from this graph.
The eight data points in Fig. 4(c) show the α3 values decreas-
ing from 114.5(2) to 93.4(1)Њ as the Cu᎐Cl distances decrease
from 2.304(2) to 2.254(1) Å. All the data points have α3 values
<120Њ and Cu᎐Cl distances <2.354 Å. There is a normal correl-
ation involving two data points, 7 and 4, connecting the RTB
data point to the extreme ‘seesaw’18 data point (the ϪA route
distortion, SSDTB, Fig. 3). There is a parallel correlation
involving four data points, 1, 2, 5 and 8, which have α3 values 9Њ
higher than the corresponding points on the RTB → Ϫ A
correlation (data point 7 has α3 = 105.0Њ, while data point 2,
lying almost directly above it on the parallel correlation,
has α3 = 114.1Њ). An isolated data point, 3, may lie on another
parallel correlation, since it has an α3 value 9Њ lower than the
corresponding point on the RTB → Ϫ A correlation.
The data points in Fig. 4(d) show the Cu᎐N(2) distances
decreasing from 2.127(2) to 2.057(2) Å, as the Cu᎐N(4) dis-
tances increase from 2.121(6) to 2.242(2) Å. All eight data
If the data of Fig. 4(c) are related to those of Fig. 1, then
both the α3 angles and the Cu᎐Cl distances correspond to a
J. Chem. Soc., Dalton Trans., 1997, Pages 2645–2652
2649

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Symmetric Mode (C2)
Table 6 The % ϪA and % ϩB distortion values of the complexes
calculated using the in-plane angle data of Fig. 4(b)
bend
str
νsym
-L/2
νsym
N2
+L
N4
N2
N4
-L/2
α1
+L
Cu
α3
Cl
Complex
Cl
α2
Cu
-L/2
-L/2
1
5
2
6
7
8
3
4
Asymmetric Mode (non-C2)
% ϪA
% ϩB
18
13
22
14
20
29
67
1
50
28
45
21
89
18
79
86
str
bend
νasym
νasym
+L
N2
0
N2
N4
-L
0
α1
α3
Cl
Cl
Cu
Cu
α2
+L
Table 7 The % ϪA and % ϩB distortion values of the complexes
measured using the in-plane angle data of Fig. 4(d)
N4
-L
Fig. 5 The symmetric and asymmetric modes of vibration for the five-
co-ordinate CuN4Cl chromophore, including the relative magnitudes
(L)19,20
Complex
1
5
2
6
7
8
3
4
% ϪA
% ϩB
12
20
23
28
39
38
63
6
31
19
60
20
75
11
91
86
both have stretching and bending components.19,20 They predict
variations in the in-plane parameters, α1–3, Cu᎐Cl, Cu᎐N(2) and
Cu᎐N(4), which show the largest ranges in distances and angles,
Table 2. The symmetric mode of vibration has a two-fold axis
of symmetry, so Cu᎐N(2) = Cu᎐N(4) and α 1 = α2, and all six in-
plane distances and angles are involved. The asymmetric mode
of vibration does not have a two-fold axis of symmetry. Here
only the Cu᎐N(2) and Cu᎐N(4) distances and the α1 and α2
angles are involved, with the Cu᎐Cl distance and the α3 angle
invariant. In the next section the [Cu(phen)2Cl][Y] data are
compared by scatter-plot analysis of the in-plane bond lengths
and angles, to determine if the distribution of data points is
random or determined by the νsym and νasym modes of vibration
as the dominant modes of distortion of the CuN4Cl chromo-
phore, Fig. 5.
The first problem associated with this suggestion is that the
effect of a single mode of vibration of the nuclear framework
of the CuN4Cl chromophore, of ca. 200 cmϪ1, would only result
in bond distance and angle changes of 0.005 Å and 1Њ, respect-
ively.21 These values are at least an order of magnitude too
small to account for the observed changes, Table 3. Con-
sequently, either a progression of 10–30 modes of vibration
must be involved or the ‘amplification factor’22 of the pseudo-
Jahn–Teller effect 23 must be in operation, with the possibility
that the former accounts for the latter.
points are observed in the ϪA ϩ B quadrant of the graph.
There are no data points on the RTB → ± A or
RTB → ± B route pathways. There is one data point 2 on
the RTB → RSBP (ϪA ϩ B) pathway, with two more data
points, 4 and 5, lying close by. Table 7 shows the % ϪA and %
ϩB distortion values of the complexes calculated using the
in-plane Cu᎐N(2) and Cu᎐N(4) distance data. The values are
closely comparable to those in Table 6 using the corresponding
in-plane angle data. In general, Tables 6 and 7 show that ϪA
distortion dominates over ϩB route distortion. Data point 4 is
exceptional because it shows both a large % ϪA and a large %
ϩB distortion value, 91 and 86% respectively. It also explains
why the Cu᎐N(2) distances of 6 and 3 are well above 2.092 Å,
due to a significant ϪA route distortion and not to a ϪB route
distortion.
General conclusions. The information obtained from the
scatter-plot analysis of this series of eight [Cu(phen)2Cl][Y]
complexes can be summarised as follows.
(1) The distribution of the data points is not random, with
respect to the RTB and RSBP data points. They involve a
significant spread of 31Њ and 0.12 Å.
(2) The τ plot is consistent with a SBP distortion of the RTB
CuN4Cl chromophore, but with neither the RTB or RSBP
structures present. Seven complexes have τ values in the range
of 0.81–0.56. Data point, 4, has an exceptional τ value of 0.19,
which equates with an unusual TBDSBP stereochemistry for a
[Cu(phen)2Cl][Y] complex.
(3) The plot of α3 versus α1 shows data points lying on parallel
correlations, with fixed α2 values of 120 ± 5, 10 or 15Њ, suggest-
ing the existence of preferred angles or ‘magic angles’, consist-
ent with α1 ϩ α2 ϩ α3 = 360Њ, Table 4.
The most convincing evidence for the vibronic coupling
model has been in accounting for the dynamic pseudo-Jahn–
Teller distortion of the high-symmetry RTB [CuCl5]3Ϫ anion,
D3h symmetry, to the lower-symmetry RSBP stereochemistry,
C2v or C2 symmetry, with distortion via the εЈ mode of
vibration 19,20,24,25 (equivalent to νsym ϩ νasym), with C2 sym-
metry along the three in-plane directions at 120Њ to each
other. While the authors admit 19 that this model is only justi-
fied for small distortions, the above ‘amplification factors’22
or progressions could equally be operating to account for the
larger distortions observed. If the same model is applied to
the CuN4Cl chromophore it must have the effective symmetry
D3h and ignores the presence of non-equivalent donor atoms
and the effect of two chelate ligands. If this assumption can
be accepted, then the εЈ mode of vibration, in D3h symmetry,
(4) The ±A and ±B axes of Fig. 1 can be superimposed on
the plots. All data points lie in the ϪA ϩ B section of the
graphs. Tables 6 and 7 show the % ϪA and % ϩB distortion
values of the complexes calculated from the in-plane angle and
distance data and show that, in general, ϪA distortion is pre-
dominant over ϩB distortion. The tables also show that data
point 4 is exceptional because of the large % values of both ϪA
and ϩB distortion. The ϩA → RTB → Ϫ A pathway
generates a novel ϪA or ‘seesaw’ stereochemistry.18
str
bend
and the νsym and νsym
modes of vibration (C2 symmetry)
models are equivalent. However, we consider this too large an
assumption and prefer the ν modes of vibration notation as
it is chemically more informative than the ε mode notation.
The highest possible symmetry for the CuN4Cl chromophore is
C2, which is restricted to the Cu᎐Cl direction of the CuN4Cl
chromophore (±A route) and one that is quite distinct from
the two ±B route distortions, which are related by a two-fold
axis.
One of the most significant features of Fig. 4(c) is that two
of the data points lie strictly along the ϩA → RTB → Ϫ A
pathway, suggesting that the changes in the α3 angle and Cu᎐Cl
distance are closely linked. One such linking process suggests
that the changes in these parameters is determined only by the
Possible interpretation of the ±A and ±B route distortions in
terms of modes of vibration
The extensive range of the Cu᎐L distances and of the αn angles,
Table 3, 0.12 Å and 31Њ, respectively, have only been interpreted
in terms of the ±A and ±B route distortions. It has been sug-
gested earlier 1 that these routes may be understood, alter-
natively, in terms of the modes of vibration of the CuN4Cl
chromophore, Fig. 5. The symmetric, νsym, and asymmetric,
νasym, modes of vibration of the CuN4Cl chromophore, Fig. 5,
2650
J. Chem. Soc., Dalton Trans., 1997, Pages 2645–2652

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Comparison of the [Cu(phen)2Cl][Y] and [Cu(bipy)Cl][Y] series
of complexes
The most obvious difference is in the range of τ values, with the
phen complexes ranging from 0.81 to 0.19, while the bipy com-
plexes1 range from 1.00 to 0.53. In both series the bulk of the
data points lie in the range τ 0.8–0.5, with the bipy series having
four or five near RTB structures and the phen series involving
an exceptional data point with a TBDSBP stereochemistry.
Unfortunately, it is not possible to rationalise these differences
in terms of the differences in structure of the bipy and phen
ligands or in terms of the intramolecular non-bonding contacts
of the [Cu(chelate ligand)2Cl]ϩ cations.
Implications
The four scatter plots of the eight [Cu(phen)2Cl][Y] data points
clearly suggest that the distribution with respect to the RTB and
RSBP data points is not random, with some support for linear
and parallel structural pathways. As there are no obvious dif-
ferences in the local crystal environments between the extreme
structures of complexes 1 and 4, these extreme structures must
reflect the structural pathways of the ϪA ϩ B route of Fig. 1,
which are determined by the effect of vibronic coupling. The
precise stereochemistry displayed can be understood in terms
of the possible linear combination of the coupled nuclear
Fig. 6 Diagram illustrating how the linear and parallel pathways are
str
bend
formed by a progression of the coupled νsym and νsym
modes of
vibration
underlying nuclear modes of vibration,20,26 Fig. 5, suggesting a
vibronic coupling mechanism.23 A feature of the parameters of
bend
str
modes of vibration νsymstr, νsymbend, νasym and νasymbend. Each
Fig. 4(c) is that the α3 angle can only be changed by the νsym
mode of vibration and the Cu᎐Cl distance can only be changed
complex describes the local molecular stereochemistry of a
point on the potential-energy surface of the structural pathway
from RTB to RSBP, Fig. 1. The [Cu(phen)2Cl][Y] data then
represent the best evidence for the involvement of vibronic
coupling to account for the structural consequences of the
plasticity effect 27 in the series of cation distortion isomers28 of
the copper() ion. Of equal importance is the wide range of
stereochemistry displayed by the same [Cu(phen)2Cl]ϩ cation,
from near RTB, τ = 0.81, to TBDSBP, τ = 0.19. In the past, a
number of accounts have been given 29–31 to describe the static
geometries of the five-co-ordinate stereochemistries of different
ML5 chromophores and try to account for these changes in
terms of the different bonding roles of the ligands present.30
The present paper emphasises that, in the special case of the
low-symmetry CuN4X chromophore, vibronic coupling associ-
ated with the pseudo-Jahn–Teller effect,23 can also produce the
same range in stereochemistry of the five-co-ordinate ML5
chromophore with the same set of ligands. The present study
suggests a dynamic involvement of a number of the modes of
vibration of the central chromophore to produce the changes
associated with the movements about the potential-energy
surface of the structural pathway in which individual points
are characterised by single-crystal structure determinations of
the same cation distortion isomers.28
str
by the νsym mode of vibration. If such modes operated separ-
ately from the RTB (point I) in Fig. 6, the former would only
produce a vertical linear correlation of data points and the
latter a horizontal correlation. While such limited correlations
can be identified in Fig. 4(c), the most convincing correlation of
two data points occurs at an angle of 34Њ to the Cu᎐Cl axis. The
only way such a positive correlation can occur is if the two
modes of vibration are strongly coupled (they both transform
as the A1 representation in C2v symmetry or as A in C2 sym-
metry), as shown in Fig. 6, to produce a stepped displacement.
However, such a single displacement due to one quantum of
each mode of vibration would still be too small to be observed
on the scale of Fig. 4(c), namely, 0.005 Å and 1Њ. For the scale
of the ϩA → RTB → Ϫ A pathway in Fig. 4(c) to be
observed, that is a change of 0.05 Å in the Cu᎐Cl distance and
a change of 21Њ in the α3 angle, a progression of 10–30 coupled
vibrations must occur to account for the magnitude of the
observed changes. Such a progression can be considered as
plot of the structural pathway from the ϩA route to the ϪA
str
bend
route of Fig. 6, involving the coupled νsym ϩ νsym
modes
of vibration, with the two data points representing two separ-
ate individual steps along the structural pathway, and each
point characterised by a full single-crystal structure determin-
ation.
In order to explain the occurrence of the parallel correlations
in Fig. 4(c), n modes of a single vibration, ±ν, where n = 8–10,
must be involved in order that the parallel displacement can be
observed, Fig. 6, II and III. This is then followed by a progres-
sion of the coupled modes, separate but parallel to the central
linear correlation. This observation of linear and parallel
correlations in the same plot, Fig. 4(c), is one of the best pieces
of evidence for both structural pathways and parallel pathways
and stems from the ‘amplification factor’22 in the pseudo-Jahn–
Teller effect.23
Electronic properties of the [Cu(phen)2Cl][Y] complexes
The polycrystalline electronic reflectance spectra of complexes
1–5 and 7 are shown in Fig. 7. For 1, 2 and 5 a single d → d
transition occurs at 12 200, 12 100 and 12 200 cmϪ1, respect-
ively, with some evidence for a possible low-energy shoulder at
10 900, 10 500 and 10 800 cmϪ1, respectively, consistent with
near TB stereochemistries (τ = 0.81–0.73). The one-electron
2
2
2
ground-state configuration is dz > dxy ≈ dx Ϫy > dxz ≈ dyz. The
principal absorption may be assigned 1,32 as a dxz ≈ dyz → dz
transition, with the low-energy shoulder assigned as a
2
The various plots also suggest that the directions of distor-
tion from RTB to RSBP could be associated with the modes
of vibration of the CuN4Cl chromophore, Fig. 5. The ±A
2
2
2
dx Ϫy → dz transition.
The spectrum of complex 7, τ = 0.66, shows a broad peak
beginning to split into two. These two peaks involve energies of
10 200 and 13 300 cmϪ1 and appear to evolve from the single
peak at 12 000 cmϪ1 for a RTB stereochemistry. The spectrum
of 3, τ = 0.56, which has an intermediate stereochemistry
between RTB and RSBP, involves two clearly resolved peaks at
9800 and 13 700 cmϪ1, with the higher-energy peak showing a
str
bend
routes are associated with the νsym and νsym
modes of
str
vibration and the ±B route distortions with the νasym and
bend
νasym
modes of vibration. However, as the actual data points
rarely involve pure %A or %B contributions, all four modes are
generally involved in the distortion of each complex, Tables 6
and 7.
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Fig.
complexes
7
Electronic reflectance spectra of some [Cu(phen)2Cl][Y]
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2
2
2
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2
2
2
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2
peak.
Complex 4, τ = 0.19, which has a TBDSBP stereochemistry,
involves a high-energy, high-intensity peak at 14 500 cmϪ1
,
with a low-intensity, low-energy shoulder at 11 500 cmϪ1. The
2
2
2
one-electron ground-state configuration is dx Ϫy > dz > dxy
dxz ≈ dyz. The transitions may be assigned as the dz → dx Ϫy
transition for the low-energy peak and the dxz ≈ dyz → dx Ϫy
>
2
2
2
2
2
transition for the high-energy peak. This is consistent with the
change in stereochemistry from near RTB to TBDSBP, the elec-
tronic criterion of stereochemistry33 and emphasises the value
of the electronic reflectance spectra, Fig. 7, in identifying
the extreme stereochemistries in a series of cation distortion
isomers, [Cu(phen)2Cl]ϩ, along with the need to determine the
structure of more than one isomer to establish both the range
and a typical structure in such a series.
20 M. Bacci, J. Chem. Phys., 1986, 104, 191.
21 P. Brint, personal communication.
22 I. B. Bersuker, Coord. Chem. Rev., 1975, 14, 357.
23 I. B. Bersuker, The Jahn–Teller Effect and Vibronic Interations in
Modern Chemistry, Plenum, New York, 1983.
24 D. Reinen, Comments Inorg. Chem., 1983, 2, 227.
25 D. Reinen, in Vibronic Processes in Inorganic Chemistry, ed.
C. D. Flint, Kluwer, Dordrecht, 1989.
26 K. Nakamoto, Infrared Spectra of Inorganic and Coordination
Compounds, 3rd edn, Wiley, New York, 1978.
27 J. Gazo, I. B. Bersuker, J. Garaj, M. Kabesova, J. Kohout,
H. Langfeldorova, M. Melnik, M. Serator and F. Valach, Coord.
Chem. Rev., 1976, 21, 253.
28 N. J. Ray, L. Hulett, R. Sheahan and B. J. Hathaway, J. Chem. Soc.,
Dalton Trans., 1981, 1463.
29 E. L. Muetterties and L. T. Guggenberger, J. Am. Chem. Soc., 1974,
96, 1748.
30 R. R. Holmes and J. A. Deiters, J. Am. Chem. Soc., 1977, 99, 3318.
31 T. P. Auf der Heyde and H.-B. Burgi, J. Am. Chem. Soc, 1989, 28,
3960, 3970, 3982.
Acknowledgements
The authors acknowledge the award of an Irish Science and
Technology Agency (EOLAS) grant for the diffractometer,
EOLAS, Forbairt and University College Cork (U.C.C.) for
Studentships (to G. M., P. N. and B. M.), data collection for
complexes 1 and 2 by Professor M. McPartlin and Mr A.
Bashall (University of North London), the Computer Bureau,
U.C.C., for computing facilities, Professor G. M. Sheldrick,
Drs P. Roberts, K. Henrick, A. L. Spek and P. McCardle for the
use of their crystallography programs and the Microanalysis
Section, U.C.C., for analysis.
32 B. J. Hathaway and D. E. Billing, Coord. Chem. Rev., 1970, 5, 143.
33 B. J. Hathaway, J. Chem. Soc., Dalton Trans., 1972, 1192.
Received 26th March 1997; Paper 7/02291C
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J. Chem. Soc., Dalton Trans., 1997, Pages 2645–2652