Cobalt(ii), iron(ii), zinc(ii) and palladium(ii) complexes of di-topic 4′-{4-[bis(2-pyridyl)aminomethyl]phenyl}-2,2′:6′, 2″-terpyridine. Synthetic and X-ray structural studies

Article abstract of DOI:10.1039/c4ce00414k

The di-topic terpy/dpa hybrid ligand, 4′-{4-[bis(2-pyridyl) aminomethyl]phenyl}-2,2′:6′,2″-terpyridine (L), incorporating both 2,2′:6′,2″-terpyridine (terpy) and 2,2′- dipyridylamino domains has been synthesised. The metal complexes [CoLCl ₂], [ZnLCl₂], [ZnL(CH₃CO₂) ₂], [Fe(L)₂(PF₆)₂] and [Fe(L)(HL)](PF₆)_0.5(ClO₄)_2.5 have been isolated. X-ray structures of all five structures show that the respective metal ions preferentially bind to the terpy site of L, with the dpa site in the first four complexes remaining empty. In the fifth complex, which was isolated following the attempted reaction of silver perchlorate with [Fe(L) ₂(PF₆)₂], one dpa site is protonated. The crystal packing of all these species is dominated by extensive π-interactions. The 5-coordinate zinc(ii) and cobalt(ii) complexes are isostructural and exhibit a 3D network of interactions involving π-stacking as well as CH...Cl and CH...N hydrogen bonding. Similar interactions occur in the packing of [ZnL(CH₃CO₂)₂] and [Fe(L)(HL)](PF₆)_0.5(ClO₄)_2.5 giving rise to 3D arrays. Reaction of palladium(ii) with L yields a product of stoichiometry Pd₂LCl₄ for which the evidence suggests that palladium binds at both the terpy and dpa domains. Based on this result, addition of [Pd(CH₃CN)₂Cl₂] to [Fe(L) ₂](PF₆) in acetonitrile yielded a heterometallic complex in which the free dpa sites of [Fe(L)₂](PF₆) are now occupied by palladium ions to form a heterometallic product of type [FePd₂(L)₂Cl₄](PF₆) ₂·1.5CH₃CN.

Full text of DOI:10.1039/c4ce00414k

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PAPER
Cobalt(II), iron(II), zinc(II) and palladium(II) complexes
of di-topic 4′-{4-[bis(2-pyridyl)aminomethyl]phenyl}-
2,2′:6′,2′′-terpyridine. Synthetic and X-ray
structural studies†
Cite this: CrystEngComm, 2014, 16,
6476
a
a
David J. Bray,a Jack. K. Clegg,ab Katrina A. Jolliffe and Leonard F. Lindoy
*
*
The di-topic terpy/dpa hybrid ligand, 4′-{4-[bis(2-pyridyl)aminomethyl]phenyl}-2,2′:6′,2′′-terpyridine (L),
incorporating both 2,2′:6′,2′′-terpyridine (terpy) and 2,2′-dipyridylamino domains has been synthesised.
The metal complexes [CoLCl2], [ZnLCl2], [ZnL(CH3CO2)2], [Fe(L)2(PF6)2] and [Fe(L)(HL)](PF6)0.5(ClO4)2.5 have
been isolated. X-ray structures of all five structures show that the respective metal ions preferentially bind
to the terpy site of L, with the dpa site in the first four complexes remaining empty. In the fifth complex,
which was isolated following the attempted reaction of silver perchlorate with [Fe(L)2(PF6)2], one dpa site
is protonated. The crystal packing of all these species is dominated by extensive π-interactions. The
5-coordinate zinc(II) and cobalt(II) complexes are isostructural and exhibit a 3D network of interactions
involving π-stacking as well as CH⋯Cl and CH⋯N hydrogen bonding. Similar interactions occur in the
packing of [ZnL(CH3CO2)2] and [Fe(L)(HL)](PF6)0.5(ClO4)2.5 giving rise to 3D arrays. Reaction of palladium(II)
with L yields a product of stoichiometry Pd2LCl4 for which the evidence suggests that palladium binds at
both the terpy and dpa domains. Based on this result, addition of [Pd(CH3CN)2Cl2] to [Fe(L)2](PF6) in aceto-
nitrile yielded a heterometallic complex in which the “free” dpa sites of [Fe(L)2](PF6) are now occupied by
palladium ions to form a heterometallic product of type [FePd2(L)2Cl4](PF6)2·1.5CH3CN.
Received 27th February 2014,
Accepted 9th May 2014
DOI: 10.1039/c4ce00414k
www.rsc.org/crystengcomm
with our focus being on the supramolecular aspects of the
resulting solid state structures. As an extension of these studies
Introduction
Di-, tri- and poly-pyridyl based ligands systems have been
widely used as components in metallo-supramolecular chem-
istry, reflecting the coordination versatility of this hetero-
cyclic amine ligand class.1,2 For example, the metal ion
chemistry of 2,2′:6′,2′′-terpyridine (terpy) and its derivatives
has received a great deal of attention over many decades3–6
as has 2,2′-dipyridylamine (dpa) and its extended (secondary
amine-substituted) derivatives.7,8 Thus, in the latter case a
range of bridging groups have been employed to connect
from two to four dpa units via their respective secondary
amine sites for use in metal coordination/metallo-supramo-
lecular studies and a variety of such systems have now been
investigated in some detail.7,8 As an example, in previous
studies we have investigated the interaction of copper(II),9
palladium(II)9 and silver(I)10,11 with such linked dpa ligands,
we now report the synthesis of the new linked “hybrid” ligand
4′-{4-[di-(2-pyridyl)aminomethyl]phenyl}-2,2′:6′,2′′-terpyridine (L)
incorporating both dpa and 2,2′:6′,2′′-terpyridine domains
together with an investigation of its interaction with selected
metal ions.
a School of Chemistry F11, The University of Sydney, NSW, 2006, Australia.
E-mail: kate.jolliffe@sydney.edu.au, len.lindoy@sydney.edu.au
b School of Chemistry and Molecular Biosciences, The University of Queensland,
Brisbane, St Lucia, QLD 4072, Australia. E-mail: j.clegg@uq.edu.au
† CCDC 988029–988033. For crystallographic data in CIF or other electronic
format see DOI: 10.1039/c4ce00414k
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(Rmerge 0.0630), Nobs 4912 (I > 2σ(I)), Nvar 378, residuals§
R1(F) 0.0583, wR2(F2) 0.1841, GoF (all) 1.020, Δρmin,max −0.687,
1.154 e− Å−3.
Experimental
NMR spectra were recorded on a Bruker Avance DPX200 or
DPX300 spectrometer. Electrospray mass spectra (ESI-MS)
were obtained on a Finnigan LCQ-8 spectrometer. FTIR spec-
tra were determined on a Bio-Rad FTS-40 spectrometer. All
commercially available reagents were used as received.
[ZnL(CH3CO2)2]. Formula C36H30N6O4Zn,
M
676.03,
¯
triclinic, space group P1 (#2), a 13.7825(9), b 14.8655(10),
c 18.2258(11) Å, α 70.210(2), β 79.959(3), γ 64.388(3)°,
V 3166.7(4) Å3, Dc 1.418 g cm−3, Z 4, crystal size 0.300 by
0.250 by 0.075 mm, colour colourless, habit plate, temperature
150(2) Kelvin, λ(MoKα) 0.71073 Å, μ(MoKα) 0.826 mm−1,
T(SADABS)min,max 0.846, 0.940, 2θmax 60.14, hkl range −19 19,
−20 20, −19 25, N 84 652, Nind 18 409 (Rmerge 0.0495), Nobs 13 160
(I > 2σ(I)), Nvar 851, residuals¶ R1(F) 0.0437, wR2(F2) 0.1179,
GoF (all) 1.030, Δρmin,max −0.377, 0.731 e− Å−3.
Crystal structure determinations
Data were collected on either a Bruker-Nonius APEX2-X8-FR591
diffractometer employing graphite-monochromated Mo-Kα
generated from a rotating anode (0.71073 Å) with ω and ψ
scans to approximately 56° 2θ or a Bruker SMART 1000 diffrac-
tometer employing graphite-monochromated Mo-Kα generated
from a sealed tube (0.71073 Å) with ω scans to approximately
56° 2θ. Data integration and reduction were undertaken with
SAINT and XPREP12 and subsequent computations were car-
ried out using the WinGX-32 graphical user interface.13 Multi-
scan empirical absorption corrections were applied to the data
using the program SADABS.14 Gaussian absorption corrections
were applied using XPREP.12 Structures were solved by direct
methods using SIR9715 then refined and extended with
SHELXL-97.16 Unless otherwise stated, ordered non-hydrogen
atoms were refined anisotropically while partial occupancy
non-hydrogen atoms were refined isotropically. Hydrogen
atoms attached to carbon atoms were included in idealised
positions and a riding model was used for their refinement.
Hydrogen atoms bound to solvent water molecules that could
not be located in the difference Fourier map were not included
in the model. CCDC 988029–988033.
[Fe(L)2(PF6)2]·2.5H2O. The crystals employed in this study
displayed poor diffraction properties and despite careful
handling at low temperatures prior to quenching in the
cryostream and long exposure times from a high-intensity
laboratory source few reflections were observed at better than
1.0 Å resolution and a lower than ideal data/parameter ratio
resulted. Despite this and the presence of disordered water
solvent, the data is more than sufficient to unambiguously
establish the connectivity of the structure.
Formula C64H53F12FeN12O2.50P2, M 1375.97, monoclinic,
space group P21/n (#14), a 13.964(2), b 14.768(2), c 31.254(4) Å,
β 102.320(9)°, V 6296.8(15) Å3, Dc 1.451 g cm−3, Z 4, crystal size
0.300 by 0.150 by 0.100 mm, colour purple, habit blade, temper-
ature 150(2) Kelvin, λ(MoKα) 0.71073 Å, μ(MoKα) 0.382 mm−1,
T(SADABS)min,max 0.705, 0.963, 2θmax 41.60, hkl range −13 13,
−14 14, −31 31, N 27263, Nind 6373 (Rmerge 0.0874), Nobs 4043
(I > 2σ(I)), Nvar 856, residuals‖ R1(F) 0.0571, wR2(F2) 0.1599,
GoF (all) 1.035, Δρmin,max −0.254, 0.571 e− Å−3.
[CoLCl2]·0.25DCM·0.5H2O. The solvent molecules are
[Fe(L)(HL)](PF6)0.5(ClO4)2.5·H2O·1.5MeOH. The solvent molecules
disordered over
a
two-fold special position. Formula
are disordered. Formula
C65.50H57Cl2.50F3FeN12O12.50P0.50,
¯
C32.25H25.50Cl2.5CoN6O0.5, M 652.64, triclinic, space group P1
M 1429.19, monoclinic, space group P21 (#4), a 9.1075(10),
b 33.618(4), c 11.0207(12) Å, β 107.945(2)°, V 3210.2(6) Å3,
Dc 1.479 g cm−3, Z 2, crystal size 0.3 by 0.3 by 0.05 mm, colour
purple, habit plate, temperature 150(2) Kelvin, λ(MoKα)
0.71073 Å, μ(MoKα) 0.435 mm−1, T(SADABS)min,max 0.6752,
0.7457, 2θmax 56.56, hkl range −12 12, −43 43, −14 14, N 31618,
Nind 14651 (Rmerge 0.0547), Nobs 9266 (I > 2σ(I)), Nvar 859,
residuals** R1(F) 0.0823, wR2(F2) 0.2357, GoF (all) 1.004, Δρmin,max
−0.914, 1.005 e− Å−3.
(#2), a 8.2650(10), b 11.1740(10), c 16.397(2) Å, α 91.485(5),
β 91.295(5), γ 94.105(5)°, V 1509.5(3) Å3, Dc 1.436 g cm−3, Z 2,
crystal size 0.300 by 0.250 by 0.150 mm, colour green, habit
block, temperature 150(2) Kelvin, λ(MoKα) 0.71073 Å,
μ(MoKα) 0.825 mm−1, T(SADABS)min,max 0.753, 0.884, 2θmax
72.80, hkl range −13 13, −18 18, −27 27, N 70 587, Nind 14 630
(Rmerge 0.0342), Nobs 11 328 (I > 2σ(I)), Nvar 391, residuals‡ R1(F)
0.0377, wR2(F2) 0.1063, GoF (all) 1.055, Δρmin,max −0.484,
0.969 e− Å−3.
[ZnLCl2]·0.7MeOH·0.3H2O. The solvent molecules are
disordered over a number of positions and required the use of
bond length restraints to facilitate realistic modelling. One of
Ligand synthesis
the dpa pyridyl rings is disordered over two positions. Formula
¯
4′-(4-Bromomethylphenyl)-2,2′:6′,2′′-terpyridine. This precursor
was prepared as described by Johansson et al.17 1H NMR
(200 MHz, CDCl3, 300 K): δ 4.57 (s, CH2, 2PH), 7.36 (m, Paromatic,
C
65.40H56.80Cl4N12O3Zn2, M 1331.37, triclinic, space group P1
(#2), a 8.4229(5), b 11.1372(6), c 17.7581(11) Å, α 79.110(3),
β 79.382(4), γ 84.189(3)°, V 1604.02(16) Å3, Dc 1.378 g cm−3, Z 1,
crystal size 0.477 by 0.061 by 0.043 mm, colour colourless,
habit needle, temperature 150(2) Kelvin, λ(MoKα) 0.71073 Å,
μ(MoKα) 0.970 mm−1, T(SADABS)min,max 0.539, 0.950, 2θmax
57.08,Phkl rangeP−11 11, −14 14, −23 23P, N 39311, Nind 7979
P
P
2
§ R1
=
‖Fo| − |Fc‖/ |Fo| for Fo > 2σ(Fo); wR2 = ( w(Fo − Fc2)2/ (wFc2)2)1/2
all reflections. w = 1/[σ2(Fo2) + (0.1018P)2 + 0.9483P] where P = (Fo2 + 2Fc2)/3.
P
P
P
P
2
¶ R1
=
‖Fo| − |Fc‖/ |Fo| for Fo > 2σ(Fo); wR2 = ( w(Fo − Fc2)2/ (wFc2)2)1/2
all reflections. w = 1/[σ2(Fo2) + (0.0523P)2 + 1.5804P] where P = (Fo2+2Fc2)/3.
P
P
P
P
‖ R1
=
‖Fo| − |Fc‖/ |Fo| for Fo > 2σ(Fo); wR2 = ( w(Fo − Fc2)2/ (wFc2)2)1/2
2
all reflections. w = 1/[σ2(Fo2) + (0.08283P)2 + 4.8947P] where P = (Fo2 + 2Fc2)/3.
P
P
P
P
P
2
‡ R1
=
‖Fo| − |Fc‖/ |Fo| for Fo > 2σ(Fo); wR2 = ( w(Fo − Fc2)2/ (wFc2)2)1/2
** R1
=
‖Fo| − |Fc‖/ |Fo| for Fo > 2σ(Fo); wR2 = ( w(Fo − Fc2)2/ (wFc2)2)1/2
2
all reflections. w = 1/[σ2(Fo2) + (0.0501P)2 + 0.5408P] where P = (Fo2 + 2Fc2)/3.
all reflections. w = 1/[σ2(Fo2) + (0.1437P)2] where P = (Fo2 + 2Fc2)/3.
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2H), 7.54 (m, aromatic, 2H), 7.87 (m, aromatic, 2H), 8.66–8.74
(m, aromatic, 6H) (corresponding to that reported previously).
4′-{4-[Di-(2-pyridyl)aminomethyl]phenyl}-2,2′:6′,2′′-
Water (10 mL) was added to this solution followed by
saturated aqueous NH4PF6. This resulted in precipitation of a
purple product, which was filtered off, washed with ether and
dried. Yield, 0.6 g (90%). MS (ESI) m/z = 1185 [M − PF6]+.
1H NMR (acetonitrile-d3, 300 MHz, 300 K), δ: 5.70 (s, 4H, CH2),
6.99–7.09 (m, 8H), 7.17 (d, 4H), 7.31 (d, 4H), 7.70 (t, 4H), 7.81
(d, 4H), 7.90 (t, 4H) 8.22 (d, 4H), 8.37 (d, 4H), 8.60 (d, 4H), 9.15
(s, 4H). 13C NMR (acetonitrile-d3, 75 MHz, 300 K), δ: 50.4,
114.3, 121.2, 123.4, 126.9, 127.5, 128.2, 134.7, 137.3, 138.4,
142.9, 147.8, 150.0, 152.7, 156.7, 157.7, 159.9. IR (KBr disc, cm−1)
1581 m, 1468 m, 1432 m, 1376 w, 851 s, 839 s, 783, m, 557 m.
X-ray quality crystals of [Fe(L)2(PF6)2]·2.5H2O were obtained
by the slow diffusion of diethyl ether into an acetonitrile
solution of the title complex.
[Fe(L)(HL)](PF6)0.5(ClO4)2.5·H2O·1.5MeOH. AgClO4·H2O (2.23 mg,
0.01 mmol) in methanol (1 mL) was added to [Fe(L)2](PF6)2·2.5H2O
(12.5 mg, 0.01 mmol) in warm acetonitrile (5 ml). The solution
was warmed and stirred for 30 min. Ether vapour was diffused
into this solution resulting in the formation of small number
of crystals suitable for diffraction studies. No further analysis
was performed or accurate yield determined.
terpyridine (L). Di-(2-pyridyl)amine (0.213 g, 1.24 mmol) and
potassium hydroxide (0.348 g, 6.2 mmol) were stirred in DMF
(20 mL) at 40 °C for 20 min. 4′-(4-Bromophenyl)-2,2′:6′,2′′-
terpyridine (0.500 g, 1.24 mmol) was dissolved in DMF (10 mL)
and added slowly while stirring was continued at 40 °C for a
further 30 h. The solvent was removed under reduced pressure
and the residue partitioned between dichloromethane (100 mL)
and water (50 mL). The organic layer was washed twice with
water (2 × 25 mL) and then the combined aqueous phases
washed with dichloromethane (2 × 20 mL). The combined
dichloromethane layers were dried (Na2SO4) and then taken to
dryness on a rotary evaporator, resulting in a pale yellow solid.
This was recrystallised from ethanol yielding 420 mg (70%) of a
yellow crystalline solid; m.p. 181–183 °C. Found: C, 77.74; H,
4.99; N, 16.89. Calc. for C32H24N6: C, 78.01; H, 4.91; N, 17.06%.
1H NMR (300 MHz, CDCl3, 300 K) δ 5.58 (2H, s, CH2), 6.87
(2H, m, Ar), 7.21 (2H, m, Ar), 7.33 (2H, m, Ar), 7.51 (4H, m, Ar),
7.83 (4H, m, Ar), 8.34 (2H, m, Ar) 8.68 (6H, m, Ar). 13C NMR
(100 MHz, CDCl3, 300 K) δ 51.1, 114.6, 117.3, 118.8, 121.3,
123.7, 127.3, 127.7, 136.8, 136.8, 137.3, 140.6, 148.3, 149.1,
150.2, 155.8, 156.3, 157.1. MS (ESI): m/z 493 (M + H)+.
[Pd2LCl3]Cl. PdCl2 (15 mg, 0.08 mmol) in 2 M HCl (2 mL)
was slowly added to L (20 mg, 0.04 mmol) in dichloromethane/
methanol (1: 1; 10 mL). The resulting solution was heated and
stirred for 30 min resulting in formation of a pale yellow
precipitate. This product was filtered off and dried under
vacuum. Yield, 30 mg (86%). MS (ESI) m/z = 811 (M − Cl)+.
Found: C, 39.39; H, 3.53; N, 8.99. C32H24Cl4N6Pd2·7H2O requires:
C, 39.59; H, 3.94; N, 8.66%.
Metal complex synthesis
[CoLCl2]. CoCl2·6H2O (20 mg, 0.8 mmol) in warm acetonitrile
(5 mL) was added to L (20 mg, 0.4 mmol) in dichloromethane
(3 mL). This solution was heated and stirred, resulting in a dark
green precipitate which was filtered off, washed with ether and
dried in a vacuum. Yield, 24 mg (60%). MS (ESI) m/z = 1210
(L2Co2Cl3)+, 586 (LCoCl)+. Found: C, 49.76; H, 3.18; N, 10.75.
C32H24Cl4Co2N6·H2O requires: C, 49.90; H, 3.40; N, 10.91%.
Crystals for X-ray analysis were obtained upon slow evaporation
of the mother liquor over one week.
[FePd2(L)2Cl4](PF6)2·1.5CH3CN. Pd(CH3CN)2Cl2 (4.9 mg,
0.02 mmol) in acetonitrile (3 mL) was added to
[Fe(L)2](PF6)2·2.5H2O (25 mg, 0.02 mmol) in warm acetonitrile
(5 ml). The solution was warmed and stirred for 30 min. Ether
vapour was diffused into this solution resulting in the
formation of a purple microcrystalline product over 2 days.
1
Yield, 25 mg (80%). MS (ESI) m/z = 1541 (M − PF6)+. H NMR
[ZnLCl2]. ZnCl2 (27 mg, 2 mmol) in warm methanol (5 mL)
was added to L (100 mg, 2 mmol) in warm dichloromethane
(5 mL). The solution was left to evaporate resulting in a pale
yellow crystalline product, a crystal of which was employed for
an X-ray structure determination. Yield, 90 mg (71%). MS (ESI)
m/z = 1221 (L2Zn2Cl3)+, 591 (LZnCl)+. Found: C, 57.90; H, 3.76; N,
12.34. C32H24Cl2N6Zn·2H2O requires: C, 57.80; H, 4.24; N, 12.63%.
[ZnL(CH3CO2)2]. Zn(CH3CO2)2·2H2O (9 mg, 0.4 mmol) in
warm acetonitrile (5 mL) was added to L (20 mg, 0.4 mmol)
in warm dichloromethane (3 mL). The pale yellow solution
was reduced in volume and left to evaporate resulting in
small yellow crystals, which were filtered off and dried under
vacuum. Yield, 10 mg (35%). MS (ESI) m/z = 615 [LZn(OAc)]+.
Found: C, 58.48; H, 4.72; N, 11.16. C36H30N6O4Zn·3.5H2O
requires: C, 58.50; H, 5.04; N, 11.37%.
(acetonitrile-d3, 300 MHz, 300 K), δ: 5.63 (s, 4H, CH2), 6.92–7.05
(m, 8H), 7.12 (d, 4H), 7.33 (d, 4H), 7.65 (t, 4H), 7.79 (d, 4H), 7.88
(t, 4H) 8.19 (d, 4H), 8.35 (d, 4H), 8.55 (d, 4H), 9.12 (s, 4H). Found:
C, 46.95; H, 3.22; N, 10.50. C64H48Cl4 F12FeN12P2Pd2·1.5CH3CN
requires: C, 47.05; H, 3.02; N, 10.82%.
Results and discussion
The difunctional ligand L containing terpy and dpa moieties
was obtained in 70% yield by the direct reaction of dpa with pre-
viously reported 4′-(4-bromomethylphenyl)-2,2′:6′,2′′-terpyridine17
in dimethylformamide in the presence of KOH.
The reaction of L with cobalt(II) chloride in acetonitrile/
dichloromethane resulted in dark green crystals of
[CoLCl2]·0.25DCM·0.5H2O whose X-ray structure (Fig. 1)
showed that the cobalt cation coordinates at the terpy
site (in a second experiment a similar product showing
the absence of coordination at the dpa site was also
obtained even when a several-fold excess of CoCl2 was
employed for the reaction). The cobalt(II) centre is five-
[Fe(L)2](PF6)2. Fe(NH4)2(SO4)2·6H2O (0.2 g, 0.5 mmol) in
hot methanol/water (1 : 1) (15 mL) was added to L (0.5 g,
1 mmol) in dichloromethane/methanol (1 : 1; 20 mL). A dark
purple solution formed immediately and this was heated
and stirred until the volume was reduced to 20 mL.
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Fig. 2 Representation of the one-dimensional stack that propagates
parallel to the crystallographic āb vector in [CoLCl2]·0.25DCM·0.5H2O.
Double headed arrows indicate the presence of arene–arene interactions.
Fig. 1 X-ray structure of [CoLCl2]·0.25DCM·0.5H2O. Solvent molecules
have been removed for clarity. Thermal ellipsoids are shown at the 50
percent probability level.
coordinate, adopting a distorted trigonal bipyramidal geometry
(Addison τ parameter18 = 1.19) with the Ni(1) and N(3) pyridine
nitrogens occupying the axial positions and the remaining
pyridyl group and two chloride ions in the equatorial positions.
The coordination bond lengths and angles of the cobalt(II) cen-
tre are similar to other cobalt(II) chloride terpyridyl complexes
of type [Co(terpy)Cl2].19
Adjacent complexes are involved in a complex web of
intermolecular interactions forming an infinite three dimen-
sional network; the close to planar “tolylterpy” sections of the
molecule undergo a series of offset face-to-face arene–arene
interactions indicated by ring centroid–ring centroid separa-
tions of 3.5–3.7 Å forming a one-dimensional stack that
extends parallel to the crystallographic āb vector (Fig. 2). This
arrangement is further stabilised by a series of hydrogen
bonds between aromatic protons and coordinated chloride
ions (CH⋯Cl distances of between 3.0 and 3.2 Å). More of
these hydrogen bonds (CH⋯Cl distances of between 2.81
and 2.86 Å) and further arene–arene interactions bridge these
one-dimensional chains resulting in two-dimensional sheets.
Each of these sheets is further bridged by interactions involv-
ing the dpa part of the ligand. The N(5)-containing dpa pyri-
dine acts as a hydrogen bond acceptor from an adjacent
terpy pyridyl hydrogen donor (C(14)H⋯N(5) = 2.6 Å) and is
also involved in edge-to-face π stacking, forming a three-
dimensional network of interactions.
Fig.
3 X-ray structure of [ZnLCl2]·0.7MeOH·0.3H2O. Solvent
molecules and protons have been removed for clarity. Thermal
ellipsoids are shown at the 50 percent probability level. The pyridyl
group comprising N(4) exhibits minor positional disorder and was
modelled over two sites. For clarity only one of these is shown.
network of interactions consisting of arene-stacking and both
CH⋯Cl and CH⋯N hydrogen bonding. Indeed, interactions of
this type appear to dominate the crystal packing of each of
[M(L′)Cl2] (where L′ is any ligand incorporating the “tolylterpy”
motif); similar crystal packing arrangements to those found in
the present study for both the zinc(II) and cobalt(II) complexes
of L are present in each of the eight other [M(L′)Cl2] structures
in the literature.20
Reaction of zinc acetate in acetonitrile with
L in
dichloromethane resulted in yellow crystals whose X-ray struc-
ture is shown in Fig. 4. The zinc centre again has a distorted
trigonal bipyramidal geometry with the metal bound to the
terpy domain of L; the remaining two coordination sites are
occupied by oxygens from monodentate acetate ions. Once
again two pyridyl group occupy the axial positions, with the
third and the anions in the equatorial plane, an arrangement that
Interaction of zinc(II) chloride with L under similar condi-
tions to those employed for the cobalt(II) complex (with meth-
anol substituted for acetonitrile) resulted in formation of a
pale yellow species of type [ZnLCl2]. This 5-coordinate zinc(II)
complex is isostructural (Fig. 3) with the cobalt(II) complex
described above and forms the same three-dimensional
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has been observed in two other [Zn(terpyR)(OAc)2] structures
reported previously.21 Unlike the two chloride-bound complexes
above, [ZnL(CH3CO2)2] crystallises with two chemically identical
but crystallographically distinct molecules in the asymmetric unit.
The dpa site is again not coordinated to a metal ion. In a
similar fashion to the two chloride complexes, the relatively
planar “tolylterpy” sections of the ligands lie closely above
and below each other forming infinite one-dimensional
chains which are further stabilised by CH⋯O hydrogen
bonds. These chains interact with adjacent stacks through
further dpapyridylH⋯O hydrogen bonds.
Fig. 5 X-ray structure of [Fe(L)2(PF6)2]·2.5H2O. Solvent water molecules
and protons have been removed for clarity. Thermal ellipsoids are shown
at the 30 percent probability level.
Reaction of ferrous ammonium sulfate with L followed by
addition of ammonium hexafluorophosphate led to isolation
of a purple product of type [Fe(L)2(PF6)2]. The nature of this
compound was investigated by mass spectrometry, NMR and
IR spectroscopy as well as by an X-ray structure determina-
tion (Fig. 5). The ESI mass spectrum of this product showed
a parent peak corresponding to [Fe(L)2(PF6)]+ and the X-ray
structure determination showed that the iron(II) is six coordi-
nate with the two terpy units of two molecules of L coordi-
nated in the commonly observed bis-terpy octahedral motif.
The dpa units are, once again, not coordinated. The crystal
packing of the complex is dominated by arene–arene interac-
tions and aromatic CH⋯F hydrogen bonds resulting in a
three-dimensional array, with the uncoordinated dpa groups
participating in a series of edge-to-face and offset face-to-face
arene–arene stacking. The “tolylterpy” parts of the molecule
interact with each other in a ‘terpy embrace’ motif similar to
that observed previously in the iron(II) and ruthenium(II)
complexes of 4′-phenylterpy22 and 4′-pyridylterpy.23
solid gave a Pd : L ratio of 2 : 1. The mass spectrum also
revealed a parent peak corresponding to two palladium and
one L in solution, in accord with formation of a homo-
dinuclear species of type 1. Unfortunately crystals of 1 suit-
able for an X-ray diffraction study were not obtained.
The strong coordination of palladium(II) to both dpa9,24,25
and terpy26 has been well documented and this provided a
motivation for investigating the interaction of this metal ion
with L. Reaction of L in dichloromethane/methanol (1 : 1)
with palladium(II) chloride in 2 M hydrochloric acid resulted
in a pale yellow precipitate. Elemental analysis of the isolated
In view of the above result bis(acetonitrile)dichloropalladium(II)
in acetonitrile was added to [Fe(L)2](PF6)2 in acetonitrile and
the warm solution stirred for 30 minutes. The solution
remained dark purple. Ether vapour was then diffused into the
reaction mixture to yield a dark purple precipitate. The 1H NMR
spectrum of this product exhibited a noticeable shift of the (sin-
gle) methylene proton signal relative to the starting complex (in
keeping with the occurrence of palladium coordination at both
dpa sites). The mass spectrum revealed a parent peak corre-
sponding to [FePd2L2Cl4PF6]+; such a stoichiometry corresponds
to a structure of type 2. Further, the isotopic distribution of this
ion (Fig. 6) is in agreement with a trinuclear structure and the
elemental analysis of the isolated product also corresponded to
the proposed stoichiometry. Unfortunately, crystals suitable for
an X-ray structure determination were again not obtained; how-
ever, on the basis of the above evidence the product was
assigned the trinuclear structure 2.
Fig.
4 X-ray structure of [ZnL(CH3CO2)2]. Only one of the two
chemically identical but crystallographically unique complexes in the
asymmetric unit are shown for clarity. Thermal ellipsoids are at the
50 percent probability level.
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crystal packing dominated by extensive π-interactions. Con-
trasting with the above, reaction of palladium(II) with L gives
a complex for which the evidence indicates that this metal
ion binds at both the terpy and dpa domains. Based on this
result, addition of [Pd(CH3CN)2Cl2] to [Fe(L)2](PF6) in acetoni-
trile yielded a heterometallic Fe/Pd (1 : 2) complex in which
the evidence indicates that both non-metal bound dpa sites
of [Fe(L)2](PF6) are now occupied by palladium ions to form a
species of type [FePd2(L)2Cl4](PF6)2·1.5CH3CN. An initial
attempt to form a related Fe(II)/Ag(I) species led instead to a
silver-free [FeL2H]3+ species in which protonation of one of
the two unoccupied dpa sites of dpa has occurred. Further
studies involving L directed towards the synthesis of other
heteronuclear species are planned for the future.
Fig. 6 (a) Predicted mass spectral distribution for [FePd2L2Cl4PF6]+.
(b) Observed isotopic distribution for this ion in the ESI mass spectrum
of [(L)2FePd2(L)2Cl4](PF6)2.
Acknowledgements
We thank the Australian Research Council for support.
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7 X-ray structure of [Fe(L)(HL)](PF6)0.5(ClO4)2.5·H2O·1.5MeOH.
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Conclusions
A new di-functional hybrid terpy/dpa ligand L along with five
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