Preparation and structural characterisation of terpy-cored dendrimers and dendriplexes

Article abstract of DOI:10.1039/b408605h

2,2′:6′,2″-Terpyridine (terpy) ligands and their iron(n) and cobalt(n) complexes bearing first and second generation Frechet-type dendritic wedges have been prepared and structurally characterised. The rotational freedom within the dendritic wedge results

Full text of DOI:10.1039/b408605h

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F U L L P A P E R
Preparation and structural characterisation of terpy-cored
dendrimers and dendriplexes
Edwin C. Constable,* Catherine E. Housecroft,* Markus Neuburger, Silvia Schaffner and
Lukas J. Scherer
Department of Chemistry, University of Basel, Spitalstrasse 51, CH 4056 Basel, Switzerland.
E-mail: edwin.constable@unibas.ch; Fax: +41 61 267 1005; Tel: +41 61 267 1001
Received 7th June 2004, Accepted 9th July 2004
First published as an Advance Article on the web 9th August 2004
2,2′:6′,2″-Terpyridine (terpy) ligands and their iron(II) and cobalt(II) complexes bearing first and second generation
Fréchet-type dendritic wedges have been prepared and structurally characterised. The rotational freedom within the
dendritic wedge results in a great diversity in conformational space. Structural studies are reported on first generation
species and their metal complexes, and the variety of inter- and intramolecular interactions which dominate the
conformation of the dendrimer and the packing of the molecules (ions) in the lattice are discussed.
Introduction
Experimental
Metallodendrimers are currently the subject of considerable
synthetic and theoretical interest as they provide a new structural
motif which can be utilised in numerous applications.1–3 The
metal centres may play a structural role in the assembly or in
determining the geometry of the overall architecture, or they
may be incorporated to imbue the resultant structure with defined
redox, photochemical, photophysical or catalytic properties.
Dendrimers containing multiple metal centres are of particular
interest as they may display cooperative effects in their reactivity
leading to an overall ‘dendritic effect’. Metallodendrimers have
potential applications in areas as diverse as the design of specific
redox active molecular recognition components for sensors
to photoactive dyes for the modification of nanocrystalline
semiconductors used in photovoltaics. A subset of compounds
which have recently been investigated involve those in which
a single metal centre or a single metal-containing cluster unit is
placed at the core of a system bearing multiple dendritic wedges.1
The synthetic strategy for the preparation of such compounds
involves the use of ligands bearing one or more dendritic wedges,
and the resultant complexes have novel properties as a result
of the metal ion being embedded within the macromolecular
structure. In the case of multiple dendron functionalised ligands
being coordinated to the metal centre, self-assembly processes
represent a facile and ergonomically beneficial methodology for
the construction of nano-dimensioned structures with divergent
dendritic domains. In particular, these systems are of interest
as models for metal sites in metalloproteins and porphyrin4 and
cluster5 domains have commonly been incorporated at the centre.
The choice of the dendritic wedge allows the metal centre to
be incorporated in an environment with tailored hydrophobic
or hydrophilic characteristics. Not surprisingly, pyridine
and oligopyridine ligands have been popular candidates for
decoration with dendritic wedges,6–8 although only one type has
been described with terpy metal-binding domains. A 2,2′:6′,2″-
terpyridine (terpy) ligand has been described with a long spacer
separating the terpy from a Fréchet-type dendritic wedge.8 The
aromatic-rich Fréchet motif is of great interest to us, as it provides
a readily modified hydrophobic region which can be utilised for
intermolecular or interfacial aromatic–aromatic interactions. We
are currently investigating the use of Fréchet dendritic wedge
functionalised oligopyridines for the formation of monolayers
on graphite substrates9 which exhibit a mechanical or electrical
response to metal ions or protons. In this paper we describe the
preparation and structural characterisation of terpy-based ligands
and their iron(II) and cobalt(II) complexes with directly attached
first, second and third generation Fréchet-type dendritic wedges.
General
Commercially available chemicals were reagent grade and were
used without further purification. H and 13C NMR spectra (for
full assignments: COSY, DEPT, HMBC and HMQC experiments)
were recorded on Bruker DRX500 or AC300 spectrometers;
chemical shifts are defined with TMS = 0 for H and 13C spectra
1
1
and are measured relative to residual CHCl3 or CHD2CN. Infrared
spectra were recorded on a Shimadzu FTIR-8300 or FTIR-8400S
spectrophotometers with neat samples on a Golden Gate diamond
ATR accessory. UV/VIS measurements were performed using a
Shimadzu UV 3101 PC spectrophotometer and were recorded in
MeCN. EI mass spectra were recorded on a VG ProSpec mass
spectrometer and electrospray (ES) mass spectra on Micromass
LCT or Bruker Esquire 3000plus mass spectrometers. The micro-
analyses were performed with a Leco CHN-900 apparatus. Melting
points were measured using an electrothermal digital melting
point apparatus. The G2 and G3 alcohols were prepared using the
literature methods involving reaction of G1 or G2 mesylate with
3,5-dihydoxybenzyl alcohol;10 4′-hydroxy-2,2′:6′,2″-terpyridine
was also prepared using the published method.11 The G1, G2 and
G3 mesylates V, VII and IX were prepared from the G1, G2 or G3
alcohols IV, VI and VIII, respectively, by the literature methods
and spectroscopic data were consistent with those reported.10,12
Other compounds were used as supplied commercially.
Preparations
G1 alcohol IV. Amixture of 3,5-dihydroxybenzyl alcohol (5.00 g,
36 mmol) and K2CO3 (15.00 g, 0.11 mol) in dry acetone (200 cm3)
was stirred under a nitrogen atmosphere at reflux for 30 min.
Benzyl bromide (8.60 ml, 72 mmol) was added to the solution,
which was then refluxed for 72 h. The reaction mixture was poured
into water and extracted three times with dichloromethane. The
combined extracts were dried (Na2SO4), evaporated and the residue
chromatographed on silica gel with ethyl acetate/hexane (1:3) as
the eluent to give G1 alcohol IV as a colourless solid (9.2 g, 79%),
mp 75–77 °C (lit.13 77 °C). Rf (ethyl acetate/hexane (1:3)): 0.15 H
(300 MHz, CDCl3,) 7.2–7.5 (10H, m, Ph), 6.57 (2H, d, J 2.0 Hz, H2
G1), 6.50 (1H, t, J 2.0 Hz, H4 G1), 4.99 (4H, s, PhCH2), 4.58 (2H,
d, J 2.9 Hz, CH2O), 1.72 (1H, t, J 2.9 Hz, OH); νmax/cm−1 3368w,
2904w, 1595m, 1450m, 1159s; m/z (EI+) 320 (M), 214, 181, 91.

G1 ligand I. A mixture of 4′-hydroxy-2,2′:6′,2″-terpyridine
(HOterpy) (225 mg, 0.9 mmol) and oven-dried K2CO3 (360 mg,
2.7 mmol) in dry acetone (50 cm3) was refluxed for 30 min. A
solution of the mesylate V (450 mg, 1.1 mmol) in acetone (20 cm3)
T h i s j o u r n a l i s
©
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4
D a l t o n T r a n s . , 2 0 0 4 , 2 6 3 5 – 2 6 4 2
2 6 3 5

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was added and the reaction mixture refluxed for 20 h and then poured
into water, extracted with CH2Cl2, dried (Na2SO4) and the solvent
evaporated. Recrystallization from ethanol gave I (410 mg, 74%).
Found: C, 76.10; H, 5.42; N, 6.95%; calc. for C36H29N3O3.H2O:
C, 75.90; H, 5.49; N, 7.38%. Mp 146.1–147.4 °C. H (500 MHz,
CDCl3) 8.71 (2H, ddd, J 4.8, 1.7, 0.9 Hz, H6A), 8.64 (2H, ddd, J
7.9, 1.0, 1.0 Hz, H3A), 8.14 (2H, s, H3B), 7.85 (2H, ddd, J 7.6, 7.6,
1.8 H4A), 7.45 (4H, d, J 7.3 Hz, H2D), 7.39 (4H, dd, J 7.4, 7.4 Hz H3D),
7.32–7.35 (4H, m, H4D,5A), 6.77 (2H, d, J 2.3 Hz, H2C), 6.61 (1H, t,
J 2.4 Hz, H4C), 5.26 (2H, s, CH2Oterpy), 5.01 (4H, s, PhCH2O); C
(125 MHz, CDCl3) 166.87 (C4B), 160.21 (C3C), 157.16 (C2B), 156.00
(C2A), 149.04 (C6A), 138.51 (C1C), 136.90 (C4A), 136.81 (C1D),
128.63 (C3D), 128.04 (C4D), 127.60 (C2D), 123.93 (C5A), 121.43
(C3A), 107.70 (C3B), 106.30 (C2C), 101.97 (C4C), 70.17 (PhCH2),
H2C), 6.74 (2H, t, J 2.3 Hz, H4C), 5.62 (4H, s, CH2Oterpy), 5.19 (8H,
s, PhCH2O); C (125 MHz, CD3CN) 168.6 (C4B), 161.9 (C2B), 161.4
(C3C), 159.0 (C2A), 154.4 (C3A), 139.5 (C5A), 138.9 (C1C), 138.1
(C1D), 129.6 (C3D), 129.1 (C4D), 128.8 (C2D), 128.2 (C4A), 124.5
(C6A), 112.5 (C3B), 108.1 (C2C), 102.9 (C4C), 72.7 (CH2Oterpy),
70.9 (PhCH2); max/nm (MeCN) 554 (/dm3 mol−1 cm−1 13600), 357
(5320), 313 (42400), 280 (29100); m/z (ES) 1303 (M − PF6), 579
2+
({M − 2PF6} ); νmax/cm−1 1612s, 1474w, 1423m, 1389m, 1362m,

1211s, 1150s, 999m, 829s, 787s, 752s.
[Fe(II)2][PF6]2. Method as for [Fe(I)2][PF6]2; FeCl2·4H2O (5 mg,
0.026 mmol), II (25 mg, 0.025 mmol) in 1:1 CHCl3–MeOH
(50 cm3) for 2 h to give [Fe(II)2][PF6]2 (26.5 mg, 90%). Found: C,
65.46; H, 4.71; N, 3.68%; calc. for C128H112N6O14FeP2F12·2H2O: C,
65.70; H, 5.00; N, 3.59%. H (500 MHz, CD3CN) 8.50 (4H, s, H3B),
8.37 (4H, dd, J 8.1 Hz, J 0.4 Hz, H6A), 7.80 (4H, ddd, J 7.8, 7.8,
1.3 Hz, H5A), 7.41 (16H, d, J 6.8, 1.5 Hz, H2E), 7.35 (16H, dd, J 7.2,
6.1, Hz, H3E), 7.31 (8H, td, J 7.2, 1.4 Hz, H3D), 7.11 (4H, dd, J 5.7,
0.8 Hz, H3A), 7.01 (4H, ddd, J 6.6, 6.6, 0.7 Hz, H4A), 6.93 (4H, d, J
2.2 Hz, H2C), 6.74 (8H, d, J 2.1 Hz, H2D), 6.69 (2H, t, J 2.3 Hz, H4C),
6.59 (4H, t, J 2.2 Hz, H4D), 5.61 (4H, s, CH2Oterpy), 5.11 (8H, s,
ArDCH2O), 5.07 (16H, s, PhCH2O); C (125 MHz, CD3CN) 168.6
(C4B), 161.8 (C2B), 161.2 (C3C), 161.1 (C3D), 158.9 (C2A), 154.3
(C3A), 140.8 (C1D),139.5 (C5A), 138.9 (C1C), 138.1 (C1E), 129.5 (C3E),
128.8 (C4E), 128.6 (C2E), 128.0 (C4A), 124.5 (C6A), 112.5 (C3B), 108.1
(C2C), 107.6 (C2D), 103.1 (C4C), 102.3 (C4D), 72.6 (CH2Oterpy), 70.8
(PhCH2), 70.6 (ArDCH2); max/nm 554 (/dm3 mol−1 cm−1 12900),
69.80 (CH2Oterpy); m/z (EI+) 551 (M); νmax/cm−1 1581s, 1562s,

1470m, 1439m, 1358s, 1292w, 1200m, 1157s, 1061m, 1030m,
791s, 730s; max/nm (CH2Cl2) 280 (/dm3 mol−1 cm−1 12500).
G2 ligand II. As for I with HOterpy (11 mg, 0.044 mmol), K2CO3
(16 mg, 0.12 mmol), acetone (20 cm3) and G2 mesylate VII (40 mg,
0.049 mmol) in acetone (10 cm3) for 40 h to give II (33 mg, 78%).
Found: C, 77.53; H, 5.80; N, 4.05%; calc. for C64H53N3O7.H2O:
C, 77.32; H, 5.58; N, 4.23%. Mp 161.7–163.0 °C. H (500 MHz,
CDCl3) 8.71 (2H, ddd, J 4.8, 1.6, 0.9 Hz, H6A), 8.65 (2H, d, J 7.7 Hz,
H3A), 8.17 (2H, s, H3B), 7.88 (2H, dd, J 7.3, 7.3 Hz, H4A), 7.42 (8H,
d, J 7.4 Hz, H2E), 7.37 (8H, dd, J 7.5 Hz, J 7.5 Hz, H3E), 7.30–7.35
(6H, m, H4E,5A), 6.75 (2H, d, J 2.0 Hz, H2C), 6.70 (4H, d, J 2.2 Hz,
H2D), 6.57–6.60 (3H, m, H4C,4D), 5.28 (2H, s, CH2Oterpy), 5.04 (8H,
s, PhCH2O), 5.00 (4H, s, ArDCH2O), C NMR (125 MHz, CDCl3)
 167.1 (C4B), 160.29 (C3D), 160.20 (C3C), 156.91 (C2B), 155.78
(C2A), 148.88 (C6A), 139.34 (C1D), 138.54 (C1C), 137.35 (C4A),
136.91 (C1E), 128.71 (C3E), 128.12 (C4E), 127.71 (C2E), 124.16
(C5A), 121.73 (C3A), 108.06 (C3B), 106.44 (C2C + C2D), 102.06 (C4C),
359 (5140), 313 (39500), 282 (43900); m/z (ES) 2154 (M − PF6),
2+
1004 ({M − 2PF6} ); νmax/cm−1 1593s, 1150m, 833m, 791w, 667s.

[Fe(III)2][PF6]2. As above with FeCl2·4H2O (5.6 mg,
0.028 mmol) and III (103 mg, 0.056 mmol) in 1:1 CHCl3–MeOH
(50 cm3) for 2 h followed by column chromatography on silica gel
(10:1 CH2Cl2–MeOH) to give [Fe(III)2][PF6]2 (80 mg, 77%). H
(250 MHz, CDCl3) 8.37 (4H, br s, H3B), 8.24 (4H, br s, H6A), 7.67
(4H, br s, H5A), 7.39 (32H, d, J 7.0, H2F), 7.34 (32H, dd, J 7.4,
H3F), 7.29 (16H, t, J 7.0, H4F), 7.08 (4H, br s, H3A), 6.98 (8H, br s,
H4A + H2C), 6.75 (8H, br s, H2D), 6.68 (18H, br s, H2E + H4C), 6.56
(4H, br s, H4D), 6.54 (8H, br s, H4E), 5.63 (4H, br s, CH2Oterpy),
5.09 (8H, br s, ArDCH2O), 5.00 (32H, s, PhCH2O), 4.99 (16H, s,
ArECH2O); C (125 MHz, CD3CN) 167.74 (C4B), 160.51 (C2A),
160.31 (C3C), 160.10 (C3E), 160.06 (C3D), 157.59 (C2B), 153.02
(C3A), 139.45 (C1D), 139.43 (C1E), 138.42 (C5A), 137.27 (C1C),
136.91 (C1F), 128.48 (C3F), 127.95 (C4F), 127.61 (C4A), 127.58 (C2F),
123.52 (C6A), 111.40 (C3B), 106.98 (C2C), 106.46 (C2D), 106.34 (C2E),
102.27 (C4C), 101.44 (C4D), 101.37 (C4E), 72.10 (CH2Oterpy), 70.15
(ArDCH2), 70.03 (PhCH2), 69.92 (ArECH2); max/nm (MeCN) 556
101.79 (CD4),70.23 (PhCH2), 70.15 (DCH2), 70.03 (CH2Oterpy);
+
m/z (ES) 998.5(M + Na); νmax/cm−1 1597s, 1562m, 1439w, 1358s,

1157s, 1030m, 791w, 729m; max/nm (CH2Cl2) 280 (/dm3 mol−1
cm−1 25400).
G3 ligand III. As for I with HOterpy (53.7 mg, 0.22 mmol),
K2CO3 (90 mg, 0.65 mmol), the G3 mesylate IX (400 mg,
0.24 mmol) in acetone (20 cm3) for 40 h followed by column
chromatography on silica gel (10:1 CH2Cl2–MeOH) to give III
(250 mg, 63%). Found: C, 76.42; H, 5.59; N, 2.57%; calc. for
C120H101N3O15.3H2O: C, 76.70; H, 5.74; N, 2.24%. H (500 MHz,
CDCl3) 8.67 (2H, ddd, J 5.3, 1.8, 0.9 Hz, H6A), 8.61 (2H, d, J
7.9 Hz, H3A), 8.11 (2H, s, H3B), 7.83 (2H, dd, J 7.9 Hz, J 7.4 Hz,
H4A), 7.22–7.48 (42H, m, H2F,3F,4F,5A), 6.75 (2H, d, J 2.2 Hz, H2C),
6.65–6.70 (12H, m, H2D,2E), 6.52–6.58 (7H, m, H4D,4E,4C), 5.23 (2H,
s, CH2Oterpy), 5.01 (16H, s, PhCH2O), 4.99 (4H, s,ArDCH2O), 4.96
(8H, s,ArECH2O); C (125 MHz, CDCl3) 167.00 (C4B), 160.28 (C3E),
160.24 (C3C), 160.20 (C3D), 157.35(C2B), 156.16 (C2B), 149.20 (C6A),
139.36 (C1E), 138.66 (C1C), 136.93 (C1D), 136.91 (C1F,4A), 128.72
(C3F), 128.13 (C4F), 127.71 (C2F), 124.01 (C5A), 121.49 (C3A),
107.76 (C3B), 106.52 (C2D,2E), 106.46 (C2C), 102.03 (C4C), 101.81
(C4D), 101.76 (C4E), 70.23 (PhCH2, DCH2), 70.13 (ECH2), 69.89
(/dm3 mol−1 cm−1 12100), 356 (5250), 313 (36100), 272 (111000);
2+
m/z (ES) 1852 ({M − 2PF6} ); νmax/cm−1 1589s, 1450w, 1142s,

1042m, 833s, 733m, 694m.
[Co(I)2][PF6]2. CoCl2·4H2O (10.7 mg, 0.045 mmol) was added
to a boiling solution of I (50 mg, 0.09 mmol) in EtOH (70 cm3) the
mixture refluxed for 30 min, ethanolic NH4PF6 was then added to
give orange–red [Co(I)2][PF6]2 (24 mg, 37%). Found: C 59.05, H
4.24, N 6.22%; calc. for C72H58N6O6CoP2F12: C 59.55, H 4.03, N
5.79%. H (500 MHz, CD3CN) 113.9 (4H, br s, H6A), 76.6 (4H, br s,
H3B), 71.7 (4H, br s, H3A), 35.1 (4H, br s, H5A), 16.1 (4H, br s, H3A,
CH2Oterpy), 12.3 (4H, br s, H2C), 8.55 (8H, d, J 7.6 Hz, H2D), 8.47
(2H, br s, H2C), 7.78 (4H, t, J 7.7 Hz, H4D), 7.53 (8H, t, J 7.5 Hz,
H3D), 6.93 (8H, s, PhCH2O), 6.37 (4H, br s, H4A); C (125 MHz,
CD3CN) 504 (C5A), 392 (C3B), 354 (C3A), 308 (C4B), 164.6 (C3C),
162.9 (C4A), 147.9 (C1C), 139.4 (C1D), 130.1 (C3D), 129.8 (C2D),
129.5 (C4D), 113.2 (C2C), 105.6 (C4C), 82.4 (CH2Oterpy), 72.7
(PhCH2), −59 (C2A or C2B), −76 (C6A), −134 (C2A or C2B); max/nm
(CH2Oterpy); m/z (ES) 1825 (M + H); νmax/cm−1 1589s, 1443m,

1296w, 1142s, 1026m, 825m; max/nm (CH2Cl2) 281 (/dm3 mol−1
cm−1 42600).
[Fe(I)2][PF6]2. FeCl2·4H2O (5.1 mg, 0.026 mmol) was added to a
boiling solution of I (29 mg, 0.052 mmol) in MeOH (10 cm3). The
deep purple solution was refluxed for 30 min, and then a methanol
solution of NH4PF6 (10 mg, 0.12 mmol) was added. The precipitate
was filtered and washed well with methanol to give [Fe(I)2][PF6]2
as a deep purple crystalline solid (20 mg, 53%). Found: C, 59.68;
H, 4.29; N, 5.61%; calc. for C72H58N6O6FeP2F12: C, 59.68; H, 4.03;
N, 5.80%. H (500 MHz, CD3CN) 8.53 (4H, s, H3B), 8.42 (4H, ddd,
J 8.0, 1.2, 0.8 Hz, H6A), 7.87 (4H, ddd, J 7.8, 7.8, 1.5 Hz, H5A), 7.50
(8H, dd, J 8.3, 1.9 Hz, H2D), 7.42 (8H, dd, J 8.1, 6.4 Hz, H3D), 7.36
(4H, td, J 7.3, 1.8 Hz, H4D), 7.14 (4H, ddd, J 5.6, 1.4, 0.6 Hz, H3A),
7.06 (4H, ddd, J 7.6, 5.6 Hz, J 1.3 Hz, H4A), 6.96 (4H, d, J 2.3 Hz,
(MeCN) 454 (/dm3 mol−1 cm−1 1530), 305 (47300), 277 (52100);
2+
m/z (ES) 1307 (M − PF6), 581 ({M − 2PF6} ); νmax/cm−1 1597(s),

1358m, 1219m, 1146s, 1030m, 991w, 829s, 791s, 725m, 694m.
[Co(II)2][PF6]2. As above with CoCl2·4H2O (3.5 mg,
0.015 mmol) and II (30 mg, 0.03 mmol) in 1:1 CHCl3–MeOH
2 6 3 6
D a l t o n T r a n s . , 2 0 0 4 , 2 6 3 5 – 2 6 4 2

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(15 cm3) for 2 h followed by column chromatography on silica
gel (H2O, MeCN, KNO3 (aq), 1:7:0.5) to give orange–red
[Co(II)2][PF6]2 (26 mg, 76%). H (400 MHz, CD3CN) 112.9 (4H,
br s, H6A), 76.4 (4H, br s, H3B), 71.2 (4H, br s, H3A), 35.1 (4H, br
s, H5A), 16.2 (4H, br s, H3A, CH2Oterpy), 12.5 (4H, br s, H2C), 8.70
(8H, s, H4C), 8.04 (8H, d, J 2.4 Hz, H2D), 7.66 (16H, d, J 8 Hz, H2E),
7.3–7.5 (24H, m, H3E,4E), 7.05 (8H, s, ArDCH2O), 7.01 (4H, t, J 2.4,
H4D), 6.41 (4H, br s, H4A), 5.54 (16H, s, PhCH2O); max/nm (MeCN)
CCDC reference numbers 228012–240888.
See http://www.rsc.org/suppdata/dt/b4/b408605h/ for crystallo-
graphic data in CIF or other electronic format.
Discussion
Ligand design, synthesis and characterisation
Our synthetic target was a series of terpy ligands bearing
Fréchet-type dendritic wedges of various generations. Synthetic
considerations led us to consider the attachment of the dendritic
wedge through an ether link to the terpy metal-binding domain
(Scheme 1). Two strategies are commonly adopted for the post-
functionalisation of terpy ligands at the 4′-position:17 either a
nucleophile is reacted with an electrophilic 4′-haloterpy or an
electrophile reacts with nucleophilic HOterpy.18 The strategy
adopted on this occasion was the reaction of HOterpy with
electrophilic dendritic wedges (Scheme 2). The key dendritic
components for the synthesis of terpy-based ligands I, II and III
were the G1, G2 or G3 dendritic wedge mesylates V, VII, and IX.
The mesylates were prepared in near quantitative yields by the
reaction of the corresponding G1, G2 or G3 alcohols IV, VI or
VIII with methanesulfonyl chloride in CH2Cl2 in the presence of
NEt3 at −10 °C.10,12 The G1 alcohol IV has been prepared by the
453 (/dm3 mol−1 cm−1 1900), 309 (47900), 277 (43600); m/z (ES)
2+
2156 (M − PF6), 1005 ({M − 2PF6} ); νmax/cm−1 1597(s), 1474w,

1443w, 1300m, 1142s, 1030m, 829s, 791s, 737m, 694m.
[Co(III)2][PF6]2. As above with CoCl2·4H2O (6.3 mg,
0.025 mmol) and III (90 mg, 0.049 mmol) in 1:1CHCl3–MeOH
(15 cm3) for 2 h, adding methanolic NH4PF6 (4.1 mg, 0.049 mmol)
to give brown [Co(III)2][PF6]2 (91 mg, 98%). H (500 MHz, CDCl3)
105.7 (4H, br s, H6A), 71.9 (4H, br s, H3B), 66.6 (4H, br s, H3A), 32.9
(4H, br s, H5A), 16.0 (4H, br s, H3A, CH2Oterpy), 12.4 (4H, br s, H2C),
8.0 (8H, s, H4C), 7.6 (8H, s, H2D), 7.0–7.5 (80H, m, H2,3,4F + H5A),
6.86 (8H, s, ArDCH2O), 6.5–6.7 (28H, m, H4D,2E,4E), 6.45 (4H, br
s, H4A), 5.47 (16H, s, ArECH2O), 4.95 (32H, s, PhCH2O); max/nm
(MeCN) 449 (/dm3 mol−1 cm−1 2170), 305 (47600), 274 (185500);
2+
m/z (ES) 1854 ({M − 2PF6} ); νmax/cm−1 1589s, 1443m, 1366w,

13,19
1296w, 1142s, 1034m, 825s, 731m, 694m.
reduction of (3,5-bis(benzoyloxy)benzoate esters with LiAlH4
or by the alkylation of 3,5-dihydroxybenzyl alcohol with benzyl
bromide in acetone20 or butan-2-one21 containing 18-crown-6 and
K2CO3. In our hands, the most convenient preparation of IV was
from the reaction of 3,5-dihydroxybenzyl alcohol with benzyl
bromide in acetone in the presence of K2CO3, and we found that
good (79%) yields were obtained in the absence of 18-crown-6. The
G2 and G3 alcohols were prepared in convergent syntheses using
G1 and G2 mesylates10 V and VII rather than the corresponding
halo compounds originally used by Fréchet22 as we consistently
obtain higher yields of more tractable materials.
The reaction of HOterpy11 with each mesylate derivative in
refluxing acetone in the presence of finely powdered oven-dried
K2CO3 proceeded smoothly to give the desired dendrimer-
functionalised compounds III, VI and VII in 74, 78 and 63%
yield, respectively. Much lower yields (40 and 13%, respectively)
of III and VI were obtained when the reactions were conducted in
DMF at 100 °C. Optimal yields are obtained when the potassium
carbonate is rigorously oven-dried and finely pulverised. The first,
second and third-generation functionalised ligands I, II and III
were fully characterised by conventional spectroscopic methods
and I was also structurally characterised. The new ligands behave
as typical terpy derivatives and the preparative reactions are
conveniently monitored using TLC and developing the plates with
iron(II) solutions to give purple spots for terpy containing species.
All of the new ligands are solids and exhibit well-resolved 1H NMR
spectra in CDCl3 solution. The 1H NMR spectrum of each ligand is
sharp and well-resolved. The 13C NMR spectra for the ligands are
also sharp and, like the 1H NMR spectra, are consistent with each
ligand having average C2 symmetry. Thus, in solution, there is free
rotation around the C–O bonds.
Crystal structure determinations
Data were collected on an Enraf Nonius Kappa CCD instrument;
data reduction, solution and refinement used the programmes
COLLECT,14 SIR9215 and CRYSTALS.16
Crystal structure determination of mesylate V
Crystal data. C22H22O5S, M = 398.48, monoclinic, space
group P21/c, a = 19.5057(6), b = 5.5699(2), c = 19.7910(7) Å,
 = 112.010(2)°, U = 1993.48(12) Å3, Z = 4, Dc = 1.328 Mg m−3,
(Mo K) = 0.193 mm−1, T = 173 K, 5279 reflections collected
on an Enraf Nonius Kappa CCD instrument. Refinement of 2210
reflections (253 parameters) with I > 2.0(I) converged at final
R1 = 0.0418, wR2 = 0.0445, GOF = 1.1252.
Crystal structure determination of ligand I
Crystal data. C36H29N3O3, M = 551.64, triclinic, space
group P1, a = 5.1617(4), b = 12.7116(9), c = 21.585(2) Å,
 = 83.845(3),  = 89.741(4),  = 83.643(3)°, U = 1399.4(2) Å3,
Z = 2, Dc = 1.309 Mg m−3, (Mo K) = 0.084 mm−1, T = 173 K,
11944 reflections collected. Refinement of 3378 reflections (379
parameters) with I > 3.0(I) converged at final R1 = 0.0528,
wR2 = 0.0602, GOF = 0.9457.
Crystal structure determination of [Co(I)2][PF6]2·0.5H2O·0.5-
CH3CN
Crystal data. C73H60CoF12N6.5O6.5P2, M = 1481.18, triclinic,
space group P1, a = 9.0494(1), b = 16.7293(2), c = 22.7775(4) Å,
 = 90.9851(7),  = 94.0895(7),  = 103.9639(8)°, U = 3335.8(8) Å3,
Z = 2, Dc = 1.475 Mg m−3, (Mo K) = 0.400 mm−1, T = 173 K,
15232 reflections collected on an Enraf Nonius Kappa CCD
instrument. Refinement of 8610 reflections (1064 parameters)
with I > 2.0 (I) converged at final R1 = 0.0683, wR2 = 0.0561,
GOF = 0.9839.
Each compound is characterised by an intense peak in its mass
spectrum at m/z 551 (I+), 998 (II + Na+) and 1825 (III + H+),
respectively. The electronic spectra of ligands I, II and III all
exhibit absorptions at 280 nm which are assigned to *← or *←n
transitions. The absorption coefficients of the 280 nm band increase
in a non-linear manner on passing from I to III.
Crystal structure determination of [Fe(I)2][PF6]2·1.75CH3CN
Solid state characterisation
Crystal data. C75.50H63.25F12FeN7.75O6P2, M = 1520.90, triclinic,
space group P1, a = 18.1303(2), b = 18.5998(1), c = 22.1775(2) Å,
 = 71.9742(4),  = 86.4516(4),  = 78.0943(3)°, U = 6958.6(1) Å3,
Z = 4, Dc = 1.452 Mg m−3, (Mo K) = 0.355 mm−1, T = 173 K,
31897 reflections collected on an Enraf Nonius Kappa CCD
instrument. Refinement of 14334 reflections (1333 parameters)
with I > 3 (I) converged at final R1 = 0.0536, wR2 = 0.0631,
GOF = 1.1109.
Although Fréchet-type dendrimers have been very widely
investigated, the number of structural determinations of these
systems is remarkably small7,23,24 and of these, one refers to an
aldehyde rather than the claimed alcohol.24 During the course of
this study, we obtained single-crystal structures of ligand I and
of its mesylate precursor IV. As we have previously shown that
dendron-functionalised ligands have a rich conformational hyper-
surface with a plethora of shallow minima corresponding to syn or
D a l t o n T r a n s . , 2 0 0 4 , 2 6 3 5 – 2 6 4 2
2 6 3 7

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Scheme 2 Synthetic route adopted for the preparation of the three
dendrimer-functionalised terpy ligands.
Scheme 1 Structures of the three dendron-functionalised ligands, and
ring labelling scheme used for the NMR spectra. The phenyl rings of the
outermost benzyl groups are assigned the next available letter.
anti conformations at each of the ether links,9,25 it is of interest to
obtain as wide a data base of solid-state structural information for
these systems as possible.
Scheme 3 The definition of syn and anti used to describe the conforma-
tion in the dendrimer-functionalised ligands. The descriptor refers to the
orientation with respect to the aryl H4 proton.
Analysis of all structures within the Cambridge Crystallographic
Data Base showed that in the vast majority of compounds contain-
ing an ArOCH2Ar′ moiety, the CAr–O–C–CAr′ and CAr–CAr–O–C
torsion angles were within 20° of planarity. Furthermore, in the
absence of other constraints, the conformation of the two aryl
substituents about the O–CH2 bond was anti. These are presumably
stereoelectronic effects, although we have not investigated the
origin in any detail. Thus, in the case of ligands I, II and III we
may assume that the ArOCH2Ar sub-units will be close to planar,
as will the three pyridine rings of the terpy metal-binding domain.
The conformational freedom then relates (i) to the cis or trans
conformation of the pyridine rings of the terpy, (ii) to the syn
or anti conformation relating to H4 (as defined in Scheme 3) at
each ArOCH2Ar moiety, and (iii) to the interplanar angle that the
pendant benzylic rings make with the CAr–O–C–CAr′ plane. Note
that in this case, the syn and anti conformations at the terpy ether
are degenerate.
benzyloxy substituents adopt anti-conformations giving an anti,
anti compound as defined in Scheme 3; this is in contrast to the
structures discussed later in this paper. Bonds C5–O6 and C7–O5
are shorter than O6–C16 and O5–C9 indicating some degree of
electron delocalisation extending from the central aryl ring to the
phenyl ether O atoms. This is a feature that we have previously
commented on in the context of the molecularly resolved STM
images of related bipy ligands in which the frontier orbitals are
directly observed to extend over the phenyl ether oxygen atoms.9
The angles C5–O6–C16 and C7–O5–C9 are 119.4(2) and 117.4(2)°,
respectively, suggesting that each O atom is close to sp2, rather than
sp3, hybridised. This latter observation is not unexpected, but has
the consequence of limiting the conformational diversity to minima
with near-planar CAr–O–CH2 groups as found through data-base
mining. Molecules are packed in a head-to-tail arrangement such
that the methanesulfonate groups form channels along the b axis
with intermolecular hydrogen–bonded C(2)–HO(3) interactions
along the chains. The planes of the two benyzl group phenyl rings
The solid-state structure of G1 mesylate V is shown in Fig. 1 and
important bond lengths and angles are given in the caption. Both
2 6 3 8
D a l t o n T r a n s . , 2 0 0 4 , 2 6 3 5 – 2 6 4 2

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are orthogonal to the central homoaryl ring (angles between least
squares planes = 83.9 and 87.2°). This appears to be a conse-
quence of edge-to-face phenyl(C–H)(phenyl) interactions26,27
between adjacent molecules; the H–centroid distance is 3.62 Å and
C–H–centroid angle is 143°. There are no face-to-face -stacking
interactions in the lattice.
Fig. 2 Solid-state structure of I showing the atom numbering scheme.
Selected bond lengths and angles: N1–C15 = 1.345(5), N1–C16 =
1.333(5), C14–C15 = , N2–C14 = 1.340(4), N2–C20 = 1.340(4), C20–
C21 = 1.487(4), N3–C21 = 1.341(4), N2–C25 = 1.329(5), O2–C12 =
1.363(4), O2–C11 = 1.428(4), C10–C11 = 1.503(5), C8–O1 = 1.370(4),
C7–O1 = 1.422(4), C6–C7 = 1.495(5), C28–O3 = 1.374(4), C29–O3 =
1.435(4), C29–C30 = 1.497(5) Å; C11–O2–C12 = 117.0(3), C7–O1–C8 =
116.5(3), C28–O3–C29 = 117.7(3)°.
Fig. 1 Solid-state structure of
V showing the atom numbering
scheme. Selected bond lengths and angles: S1–O2 = 1.418(2), S1–O3 =
1.415(2), S1–O1 = 1.567(2), S1–C1 = 1.741(3), O1–C2 = 1.480(3),
C2–C3 = 1.502(3), C5–O6 = 1.365(3), O6–C16 = 1.446(3), C16–C17 =
1.502(4), C7–O5 = 1.368(3), O5–C9 = 1.441(3), C9–C10 = 1.497(3) Å;
O2–S1–O3 = 118.6(2), O1–S1–O2 = 109.1(1), O1–S1–O3 = 105.1(1),
S1–O1–C2 = 116.9(2), O1–C2–C3 = 107.3(2), C5–O6–C16 = 119.4(2),
C7–O5–C9 = 117.4(2)°.
Fig. 3 Packing of molecules in the solid state structure of I showing face-
to-face -stacking of terminal pyridine rings in adjacent molecules, and the
edge-to-face aryl(C–H)-phenyl interaction.
The solid-state structure of G1 ligand I is presented in Fig. 2
and confirms the proposed structure; important bond lengths and
angles are given in the figure caption. The terpy metal-binding
domain adopts the trans–trans conformation expected for a free
ligand,28 and all bond lengths and angles within the heterocyclic
system are typical; the terpy unit is slightly riffled with least
squares planes angles between the plane of the ring containing N2
and those containing N1 and N3 being 7.5 and 1.9°, respectively.
The C12–O2 and C11–O2 distances of 1.363(4) and 1.428(4) Å are
typical for an alkoxy-functionalised terpy29 and the central pyridine
ring makes a least squares plane angle of 24.4° with the trisubsti-
tuted benzene ring. The benzyloxy substituents resemble those in
all previously reported first generation structures with one adopting
a syn (C36–C8–O1–C7) and the other an anti conformation (C36–
C28–O3–C29); the trends in C–O bond lengths are as described
for compound IV. The phenyl ring of the anti substituent is almost
orthogonal to the central pyridine ring (least squares planes 80.2°)
whereas the syn substituent makes a least squares planes angle of
26.2°. The conformation of the anti substituent appears to be a
crystal-packing effect similar to that in IV caused by edge-to-face
aryl(C–H)(phenyl) interactions26,27 between adjacent molecules
(Fig. 3). The H–centroid distance is 3.24 Å and C–H–centroid angle
is 147°. Individual molecules are lined up along the a-axis with
extensive terpy–terpy face-to-face -stacking interactions (Fig. 3)
but only weak van der Waals interactions between syn-benzyl rings
on adjacent molecules.
at reflux gave deep purple solutions, from which [Fe(I)2][PF6]2
was precipitated in 53% yield upon treatment with ammonium
hexafluorophosphate. The purple, diamagnetic complex was
1
characterised by H and 13C NMR spectroscopies and the spectra
were fully assigned by routine techniques. As expected, complex
formation results in characteristic and diagnostic30 shifting of the
1H resonances for the terpy domain of ligand I. Proton 3A which is
adjacent to the site of attachment of the dendritic wedge, shows the
most significant shift difference, conveniently quantified through
the parameter  = +1.5 ppm ( = (ligand, CDCl3) − (complex,
CD3CN)). This upfield shift is a result of the conformational
change from the trans,trans free ligand to the cis,cis ligand in
the complex and has been discussed in detail elsewhere.28,30 In the
ESMS of [Fe(I)2][PF6]2, peaks at m/z 1303 and 579 corresponded to
[M − PF6]+ and [M − 2PF6]2+, respectively. Ligands II and III react
with FeCl2·4H2O under the same conditions as ligand I to give purple
solutions from which solid purple [FeL2][PF6]2 complexes may be
isolated in reasonable yields. The dominant peaks in the ESMS of
[Fe(II)2][PF6]2 at m/z 2154 and 1004 were assigned to [M − PF6]+
and [M − 2PF6]2+; for [Fe(III)2][PF6]2, the highest mass peak came
at m/z 1852 and was assigned to [M − 2PF6]2+. For all peaks, the
observed isotope distributions matched those simulated.31 The
1
solution H NMR spectrum of [Fe(II)2][PF6]2 closely resembled
that of [Fe(I)2][PF6]2 in respect of the chemical shifts and coupling
constants of the signals assigned to the terpy protons. The remaining
signals in the spectrum were assigned using standard COSY tech-
niques. The room temperature CD3CN solution 1H NMR spectra of
both [Fe(I)2][PF6]2 and [Fe(II)2][PF6]2 were sharp and well-resolved.
In contrast, that of [Fe(III)2][PF6]2 at 295 K showed significant
broadening of the signals assigned to the terpy and inner genera-
tion aryl protons, while the remaining signals were relatively sharp.
Warming the sample to 315 K resulted in the disappearance of the
Coordination behaviour of ligands I, II and III
Complex formation between ligands I, II and III and iron(II) and
cobalt(II) was investigated; each ligand behaves as a typical terpy
and spontaneously forms thermodynamically stable, six-coordinate
{ML2} complexes. Reaction of ligand I with FeCl2·4H2O in MeOH
D a l t o n T r a n s . , 2 0 0 4 , 2 6 3 5 – 2 6 4 2
2 6 3 9

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peaks that were broad at room temperaure and the broadening of all
other signals. Cooling the sample to 223 K (in CD2Cl2) did not result
in any sharpening of the signals. To date we have not succeeded in
obtaining limiting high- or low-temperature spectra.At temperatures
below 223 K the solubility of the complex is very low indeed. We
tentatively assign these processes to restricted motion within the
dendritic wedge at higher generations and significant energy barri-
ers to interconversion of the conformers in this complex.
Each of the iron complexes is purple and exhibits an
MLCT absorption at ≈555 nm, typical of a {Fe(terpy)2}2+
chromophore.28 Within experimental error, all of these have
identical absorption maxima and molar extinction coefficients
indicating that no significant perturbation of the metal–ligand
interaction occurs with increasing generation of the dendritic
substituent. The absorption maximum corresponds closely to
that observed in [Fe(EtOterpy)2][PF6]2 (EtOterpy = 4′-ethoxy-
2,2′:6′,2″-terpyridine).32
to signals for the free ligand, while those for the  and  13C nuclei
were shifted to higher frequences, the shift difference for  C atoms
being greater than for  C atoms. As expected, the effects of the
paramagnetic cobalt(II) centre were much less on values of  13C for
atoms in rings C and D.
The cobalt complexes are all redox active and show a poorly
resolved but near-reversible cobalt(II)/cobalt(III) process close to
0 V {−0.171 V for [Co(I)2][PF6]2, −0.161 V for [Co(II)2][PF6]2
and −0.141 V for [Co(III)2][PF6]2 versus ferrocene/ferrocenium
(±30 mV)}. There appears to be no marked dendritic effect
although it might be that the drift to less negative potentials with
increasing generation is significant. In addition, three quasi-
reversible ligand reductions are observed for each complex
{−1.198, −1.339 and −1.556 V for [Co(I)2][PF6]2, −1.113, −1.319
and −1.732 V for [Co(II)2][PF6]2 and −1.148, −1.349 and −1.420 V
for [Co(III)2][PF6]2}.
The iron complexes [FeL2][PF6]2 (L = I, II or III) are all redox
active and each shows an iron(II)/iron(III) process at +0.600 V
(±20 mV, versus ferrocene/ferrocenium) in MeCN solution. Once
again, there is no dendritic effect observed at the iron centre as
the model complex [Fe(EtOterpy)2][PF6]2 shows a redox process
at exactly the same potential.32 The complexes also show quasi-
reversible ligand-based processes at −1.098 and −1.320 V for
[Fe(I)2][PF6]2, −1.118 and −1.611 V for [Fe(II)2][PF6]2, and −1.274
and −1.974 V for [Fe(III)2][PF6]2. The reduction processes are
localised on the terpy ligands and the first reduction potentials
are within experimental error identical for all of the complexes
and for [Fe(EtOterpy)2][PF6]2. The variation in second reduction
potential (which corresponds to the second terpy ligand on the metal
centre33). The shifting of the second reduction potential is likely to
be associated with absorption processes.
Structural characterisation of first generation complexes
Crystals of X-ray quality were obtained for solvates of [Fe(I)2][PF6]2
and [Co(I)2][PF6]2, and the molecular structures of the [Fe(I)2]2+
and [Co(I)2]2+ cations are shown in Fig. 4 and 5, respectively. Both
structures confirm that the ligands bind to the metal centre in the
expected manner through the terpy domains and that the dendritic
wedges are in essentially extended conformations. There are two
independent molecules in the asymmetric unit of [Fe(I)2][PF6]2·
1.75CH3CN. The gross structures of the two molecules are
essentially the same, although both ligands suffer from disorder. In
molecule 1, the phenyl ring of one benzyl group is disordered over
two closely related positions with equal occupancies. In molecule
2, the phenyl ring of a benzyl group on each ligand is disordered.
In the first ligand, the disorder that affects the phenyl ring is
essentially the same as that in molecule 1 with a rotational disorder
over two sites. In the second ligand of molecule 2, the phenyl ring
is disordered over two positions with equal occupanices associated
with the presence of a half-occupancy MeCN solvent molecule. If
the MeCN molecule is not present, the phenyl ring occupies roughly
the same region of space. The ring orientations of both independent
molecules can be described as follows. In one ligand, the aryl ring
(containing C119 and C135 in Fig. 4) is approximately coplanar
with the central pyridine ring of the terpy unit (angles between least
squares planes = 9.7°); both terminal phenyl rings are close to being
orthogonal with respect to the central aryl ring (angles between least
squares planes = 89.4 and 71.4°). In the second ligand, the aryl ring
(containing C157 and C159 in Fig. 4) lies orthogonal to the central
pyridine ring (angle between least squares planes = 88°); both
phenyl rings are tending towards being coplanar with the central
aryl ring (angles between least squares planes = 9.6 and 16.1°). The
conformation is best described as anti, anti:syn, anti.
The reactions of ligands I, II and III with CoCl2·4H2O in EtOH
at reflux, followed by anion exchange and chromatographic
workup for II and III, resulted in the formation of the orange–red
or brown salts [Co(I)2][PF6]2, [Co(II)2][PF6]2 and [Co(III)2][PF6]2
in 37, 76 and 98% yields, respectively. The electrospray mass
spectrum of each complex showed a dominant peak corresponding
to the molecular ion [M − 2PF6]2+, and for [Co(I)2][PF6]2 and
[Co(II)2][PF6]2, peaks corresponding to [M − PF6]+ were also
observed. For each peak, the observed isotope distribution matched
that calculated. We have previously observed that the paramagneti-
1
cally shifted H NMR spectra of Co(II) bis(terpy) complexes are,
although broadened, usually well resolved.29,34,35 The spectra of the
present complexes are no exception. The 1H NMR signals that are
affected the most by the presence of the paramagnetic d7 cobalt(II)
centre are those belonging to the terpy protons. These signals were
assigned by comparison with those for Co(II) complexes of other
4′-OR and 4′-NR2 substituted terpy ligands.29,35 The signal for the
H6A proton appears at  113.9, 112.9 and 105.7 in CD3CN solutions
of [Co(I)2][PF6]2, [Co(II)2][PF6]2 and [Co(III)2][PF6]2, respectively.
Since H6A is in closest proximity to the Co(II) centre, the corres-
ponding signal experiences the greatest shift to higher frequency
1
of any proton in these complexes. In the H NMR spectrum of
[Co(I)2]2+, signals at  76.6, 71.7, 35.1 and 6.37 are assigned to H3B,
H3A, H5A and H4A, respectively; similar shifts are observed for the
corresponding protons in [Co(II)2]2+ and [Co(III)2]2+. For [Co(I)2]2+,
broadened signals assigned to H2C and H4C appear at  12.3 and 8.47
compared to  6.77 and 6.61 in the free ligand, while the signals for
the protons in the peripheral rings D are relatively sharp and come
at  8.55 (H2D), 7.53 (H3D) and 7.78 (H4D) compared to  7.45, 7.39
and 7.32 in the free ligand. Similar behaviour is observed in the 1H
NMR spectra of [Co(II)2][PF6]2 and [Co(III)2][PF6]2. We were able
to record a well-resolved 13C NMR spectrum of a CD3CN solution
of [Co(I)2][PF6]2 and assign the signals using proton-coupled 13C
spectra and DEPT experiments. The shift range was from  +504
to −134; the  shift were the greatest for 13C nuclei within 5 Å of
the cobalt(II) centre, the distances being taken from the solid-state
structure (see below). Signals for 13C nuclei  to the coordinated N
atoms were shifted to significantly lower frequency with respect
Fig. 4 A PLUTO plot of the least disordered (see text) of the
two independent cations in the solid state structure of the cation in
[Fe(I)2][PF6]2·1.75CH3CN showing the atom numbering scheme; for clarity,
not all atoms are numbered and only position of the disordered phenyl ring
is shown; hydrogen atoms are omitted. Selected bond lengths and angles for
both molecules: Fe–N(central ring) range 1.879(2)–1.893(2), Fe–N(terminal
ring) range 1.971(2)–1.984(2), C(pyridine)–O range 1.343(3)–1.356(3),
C(aryl)–O range 1.363(3)–1.388(3) Å; N–Fe–N in chelate rings range
80.39(8)–81.34(8)°.
2 6 4 0
D a l t o n T r a n s . , 2 0 0 4 , 2 6 3 5 – 2 6 4 2

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Fig. 6 Stick representation of the dimer-of-cations motif in the structure
of [Co(III)2][PF6]2·0.5H2O·0.5CH3CN showing the phenyl (C–H)-aryl
interaction.
Fig. 5 A PLUTO plot of the solid state structure of the cation in
[Co(I)2][PF6]2·0.5H2O·0.5CH3CN showing the atom numbering scheme;
selected numbering is used for clarity. Hydrogen atoms are omitted.
Selected bond lengths and angles: Co1–N1 = 2.091(3), Co1–N2 = 1.970(3),
Co1–N3 = 2.109(3), Co1–N4 = 2.138(4), Co1–N5 = 1.983(3), Co1–N6 =
2.159(3), O1–C8 = 1.348(5), O1–C16 = 1.449(5), O2–C19 = 1.368(6),
O2–C23 = 1.429(6), O3–C21 = 1.369(7), O3–C30 = 1.543(10), O4–C44 =
1.348(7), O4–C52 = 1.427(8), O5–C55 = 1.384(11), O5–C59 = 1.398(15),
O6–C57 = 1.375(11), O6–C66 = 1.432(11) Å; N1–Co1–N2 = 78.0(1),
Morphology of the dendritic complexes
The structurally characterised complexes allow us to make some
more detailed comments about the overall morphology of the
species and to assess the value of molecular modelling techniques
for these metallodendrimers. The two structurally characterised
complexes of the G1 ligand I are dumbell shaped (Fig. 7) with a
diameter of ≈14.4 Å at the ends and a diameter of ≈11 Å at the
central {M(terpy)2} domain. The wingtip-to-wingtip overall length
is ≈31 Å.
N2–Co1–N3 = 77.70(12),
77.73(13), C8–O1–C16 = 119.2(3), C19–O2–C23 = 118.4(4), C21–O3–
C30 = 117.7(5), C44–O4–C52 = 118.8(5), C55–O5–C59 = 119.3(7),
C57–O6–C66 = 119.3(6)°.
N4–Co1–N5 = 77.01(14),
N5–Co1–N6 =
In the structure of the complex [Co(I)2][PF6]2·0.5H2O·0.5CH3CN,
there is considerable disorder associated with the phenyl ring of a
benzyl group of each ligand. Despite this problem, a number of
interesting features are evident in the structure. Firstly, as expected,
the terpy is terdentate and adopts a cis, cis conformation. The
Co–Nterminal bonds are longer (average 2.124 Å) than the Co–Ncentral
bonds (average 1.977 Å) and correlate well with those in other
structurally characterised cobalt(II) complexes with 4′-alkoxy-
substituted terpy ligands.36,37 It is well-known that [Co(terpy)2]2+
complexes are spin-crossover species28,38 in which the spin state
in the solid state is dependent upon the anion, lattice solvent and
temperature.39–41 The Co–N bond lengths correlate well with the
spin state in complexes of terpy itself, with longer Co–Ncentral
distances being a particularly sensitive indicator of spin character.
Shortage of material prevented a solid-state magnetic measurement,
but in CD3CN solution the complex [Co(I)2][PF6]2 is low-spin.
The Co–N distances in our complex indicate significant low-spin
character in the solid state,39–41 although one must bear in mind that
the electronic effect of the 4′-alkoxy substituent is likely to lead to
a slight shortening of this bond (as seen in the iron complex above
when compared to [Fe(terpy)2]2+ salts42).
When we consider the conformation, the central ring of the
substituent of one ligand is significantly twisted with respect
to the central ring of the attached terpy (65.6°) whereas in the
other ligand they are almost coplanar (8.4°). The near-coplanar
ring has a anti, anti conformation (C56–C55–O5–C59, 174.5°;
C56–C57–O6–C66, 175.0°), with the phenyl ring attached to
C66 having a 50% disorder over two sites. The phenyl ring
attached to C59 is almost orthogonal (84.3°) to the central ring.
The substituents on the orthogonal dendritic wedge show a more
complex disorder associated with the benzyl group on O3 and the
acetonitrile solvent molecule; however, a syn, anti conformation is
adopted (C20–C19–O2–C29, 167.7°; C20–C21–O3–C30, −39.7,
8.4°) with the disordered substituent adopting the syn conformation.
A most noteworthy feature of the structure is the formation of
dimers by virtue of phenyl(C–H)-aryl interactions26,27 between
adjacent molecules (Fig. 6). The H–centroid distance of 2.60 Å is
significantly shorter than corresponding distances discussed in the
structures of I and IV, and the C–H–centroid angle of 152° is larger
than in I and IV indicating a stronger, more centred interaction
than in either of I and IV. We are currently investigating the
possibilities of controlled crystal engineering within these systems
with a particular emphasis upon using interactions of this type to
tailor receptor cavities within host structures. Interactions between
phenyl rings in the so-called ‘phenyl embraces’ have been shown
by Dance43 to play a hitherto unrecognised role in the assembly of a
wide range of supramolecular structures.
Fig. 7 Solvent accessible surface for the cation [Co(I)2]2+ using X-ray
derived dimensions and with a solvent probe of radius 1.8 Å.
To our considerable surprise, the dimensions obtained
correspond remarkably well to those coming from a gas phase
MM+ (Hyperchem 7) calculation on the cation. At this stage we
note that similar level of calculation upon the third generation
complexes consistently produces minima with ‘globular’ confor-
mations in which the dendritic arms are folded back (Fig. 8). These
globular structures have a diameter of ≈30 Å. However, even in
these conformations, the {M(terpy)2} domains are exposed and no
unusual effects in the electrochemistry are expected. Although we
treat these preliminary results with caution, they may offer a clue to
the line-broadening effects observed in the NMR spectra of the G3
ligand complexes.
Fig. 8 Energy minimised (gas phase, MM+, HyperChem 7) solvent
accessible (probe 1.8 Å) structure of an [M(III)2] complex. The dendritic
wedges are shown in blue whilst the {M(terpy)2} domain is red.
Conclusions
We have prepared terpy ligands functionalised with Fréchet-type
dendrimers through the third generation and investigated their
structural and coordination behaviour. No dendritic effect apears
to be present in the complexes, although some conformational
restriction appears to be present in the case of the iron(II) complex
of the third generation ligand. Structural studies reveal a rich
D a l t o n T r a n s . , 2 0 0 4 , 2 6 3 5 – 2 6 4 2
2 6 4 1

View Article Online
12 K. Ichinose, Y. Ebizuka and U. Sankawa, Chem. Pharm. Bull., 2001, 49,
192.
13 J. L. M. van Nunen, B. F. B. Folmer and R. J. M. Nolte, J. Am. Chem.
Soc., 1997, 119, 283.
conformational diversity in which syn or anti conformations at
the ether moieties are amplified by intermolecular C–H)-aryl
interactions. In a future publication we will report self-assembly
processes of these ligands and complexes on graphite surfaces.
14 COLLECT, Nonius BV, 1997–2001.
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Acknowledgements
We should like to thank the Swiss National Science Foundation,
the University of Basel, the University of Birmingham and the
Portlandcement Fabrik for generous financial support. We wish to
thank Dr Klaus Kulicke for invaluable assistance with obtaining
NMR spectroscopic data and Professor Dieter Seebach for helpful
discussions. We should also like to thank Stefan Graber for useful
discussions and studies on related compounds.
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2 6 4 2
D a l t o n T r a n s . , 2 0 0 4 , 2 6 3 5 – 2 6 4 2