Synthesis and coordination chemistry of 4',4''-disubstituted 2,2':6',2'':6'',2'''-quaterpyridines and crystal and molecular structures of nickel(II) and cobalt(II) complexes

Article abstract of DOI:10.1016/S0277-5387(99)00318-6

A range of symmetrical 4',4''-disubstituted 2,2':6',2'':6'',2'''-quaterpyridines has been prepared and their coordination behaviour with metal ions having a preference for tetrahedral and octahedral geometries has been studied. The new ligands reacted with copper(I) and silver(I) salts to form dinuclear double-helical complexes; reaction with nickel(II) or cobalt(II) salts gave mononuclear species. The crystal structures of three mononuclear complexes are reported and demonstrate that the ligand binds in a tetradentate mode to the equatorial plane of the octahedral metal centre. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0277-5387(99)00318-6

www.elsevier.nl/locate/poly
Polyhedron 19 (2000) 23–34
Synthesis and coordination chemistry of 49,40-disubstituted
2,29:69,20:60,2--quaterpyridines and crystal and molecular structures of
nickel(II) and cobalt(II) complexes
*
Edwin C. Constable , Michael J. Hannon, Peter Harverson, Markus Neuburger, Diane
R. Smith, Verena F. Wanner, Louise A. Whall, Margareta Zehnder
¨
¨
Institut fur Anorganische Chemie der Universitat Basel, Spitalstrasse 51, CH 4056 Basel, Switzerland
Received 16 July 1999; accepted 30 September 1999
Abstract
A range of symmetrical 49,40-disubstituted 2,29:69,20:60,2--quaterpyridines has been prepared and their coordination behaviour with metal
ions having a preference for tetrahedral and octahedral geometries has been studied. The new ligands reacted with copper(I) and silver(I)
salts to form dinuclear double-helical complexes; reaction with nickel(II) or cobalt(II) salts gave mononuclear species. The crystal structures
of three mononuclear complexes are reported and demonstrate that the ligand binds in a tetradentate mode to the equatorial plane of the
octahedral metal centre.
q2000 Elsevier Science Ltd All rights reserved.
Keywords: Helical structures; Supramolecular chemistry; Transition metals; X-ray crystal structures
1. Introduction
2. Experimental
2.1. General procedures
Oligopyridines are versatile ligands that form coordination
complexes with almost all metal ions [1–6]. We and others
have investigated the coordination behaviour of
2,29:69,20:60,2--quaterpyridine (1) [2,7–35] and have
shown that coordination to octahedral six-coordinate metal
centres results in the formation of mononuclear complexes,
whereas bonding to four-coordinate tetrahedral metal ions
gives dinuclear double-helical complexes [4,5]. As part of
our ongoing interest in the use of supramolecular interactions
in the synthesis of extended dendritic or starburst systems
[36,37], we intended to incorporate a dinuclear double hel-
Infrared spectra were recorded on a Mattson Genesis Fou-
rier-transform spectrophotometer with samples in com-
pressed KBr discs. Proton nuclear magnetic resonance (1H
NMR) spectra were recorded on Varian Gemini 300, Bruker
AM 400 or WM 250 spectrometers. Electron impact (EI)
and fast atom bombardment (FAB) mass spectra were
recorded using Kratos MS-50, Kratos MS-890, VG 70-250
or Kratos MS-902 instruments; for FAB spectra the sample
was loaded using acetonitrile as a solvent and 3-nitrobenzyl
alcohol assupportingmatrix. Matrix-assistedlaserdesorption
ionization time-of-flight (MALDI-TOF) mass spectra were
measured using a PerSeptive Biosystems Voyager-RP Bios-
pectrometry Workstation. Electrochemical measurements
were performed with an Eco Chemie Autolab PGSTAT 20
system using platinum bead working and auxiliary electrodes
with an Ag/AgCl electrode as reference, purified acetonitrile
icate at the centre of
a
metallodendrimer using
2,29:69,20:602--quaterpyridines bearing substituents on the
two central rings. However, we have recently shown that the
introduction of substituents onto the terminal rings of
2,29:69,20:60,2--quaterpyridinesresultsinsignificantchanges
in the coordination behaviour and has a major effect on the
pitch of helicates. Accordingly, we decided to make prelim-
inary investigations of the coordination behaviour of sym-
metrical 49,40-disubstituted 2,20:69,20:60,2--quaterpyridines.
as solvent and 0.1 M [Bun N][BF4] as supporting electro-
lyte. Ferrocene was added at the end of each experiment as
4
an
internal
reference.
N-[2-(2-Pyridyl)-2-
oxethyl]pyridinium iodide was prepared according to the
procedure in the literature [38]. All other compounds were
used as supplied.
* Corresponding author. Tel.: q41-61-267-1001; fax: q41-61-267-1015;
e-mail: constable@ubaclu.unibas.ch
0277-5387/100/$ - see front matter q2000 Elsevier Science Ltd All rights reserved.
PII S0277-5387(99)00318-6
Thursday Jan 20 11:55 AM
StyleTag -- Journal: POLY (Polyhedron) Article: 3276

24
E.C. Constable et al. / Polyhedron 19 (2000) 23–34
2.2. 1,6-Diarylhexa-1,5-diene-3,4-diones (9–14)
(2H, ddd, Js7.5, 4.8, 1 Hz, H5), 7.92 (6H, m, Ho,4), 8.72
(2H, m, H6), 8.76 (2H, m, H3), 8.74 (H, d, Js1.7 Hz, H39/
59), 8.92 (2H, d, Js1.7 Hz, H39/59).
Piperidine (0.2 ml, 0.17 g, 20 mmol) and glacial acetic
acid (0.12 ml, 20 mmol) were added to a stirred solution of
diacetyl (0.88 ml, 0.86 g, 10 mmol) and the substituted
benzaldehyde (40 mmol) in methanol (5 ml). The mixture
was heated under reflux for 2 h and then the methanol and
unreacted diacetyl were removed in vacuo. The solution was
placed in a freezer overnight and the orange crystals that had
formed were isolated by filtration.
6 (0.157 g, 32%): m.p.)2508C. Found: C, 80.29; H, 5.46;
N, 10.89. Calc. for C34H26N4PH2O: C, 80.29; H, 5.55; N,
11.02%. IR: 1595 m, 1582 s, 1568 m, 1546 m, 1514 m, 1469
m, 1379 m, 822 m, 795 m, 733 w, 718 w, 661 w cmy1. Mass
spectrum (MALDI-TOF): m/z 490 {M}. 1H NMR (CDCl3):
d 1.57 (6H, s, CH3), 7.38 (6H, m, Hm,5), 7.86 (4H, d, Js8.1
Hz, Ho), 7.91 (2H, td, Js7.8, 1.5 Hz, H4), 8.72 (2H, d,
Js7.8 Hz, H6), 8.74 (2H, m, H3), 8.77 (2H, d, Js1.7 Hz,
H39/59), 8.94 (2H, d, Js1.7 Hz, H39/59).
9, 10: properties as previously reported [39,40].
11 (0.210 g, 7%): m.p. 172–1738C. Found: C, 74.32; H,
5.61. Calc. for C20H18O4: C, 74.52; H, 5.63%. IR: 2959 w,
2836 w, 1679 m, 1597 s, 1251 s, 1176 m, 1029 m, 995 m,
830 w, 816 w, 789 w, 686 w, 552 w cmy1. Mass spectrum
(EI): m/z 322 {M}. 1H NMR (CDCl3): d 3.87 (6H, s, OMe),
6.95 (4H, d, Js8.7 Hz, Hm), 7.34 (2H, d, Js16 Hz, H1),
7.62 (4H, d, Js8.7 Hz, Ho), 7.83 (2H, d, Js16 Hz, H2).
12 (0.330 g, 11%): m.p. 185–1868C. Found: C, 82.49; H,
6.32. Calc. for C20H18O2: C, 82.73; H, 6.25%. IR: 1669 s,
1596 vs, 1509 w, 1328 w, 1305 w, 1294 w, 1181 m, 994 s,
805 s, 682 s, 518 w cmy1. Mass spectrum (EI): m/z 290
{M}. 1H NMR (CDCl3): d 2.40 (6H, s, Me), 7.23 (4H, d,
Js7.8 Hz, Hm), 7.41 (2H, d, Js16 Hz, H1), 7.55 (4H, d,
Js7.8 Hz, Ho), 7.85 (2H, d, Js16 Hz, H2).
7 (122 mg, 41%): m.p.)2508C. Found: C, 67.6; H, 3.4;
N, 9.2. Calc. for C34H20F6N4P0.5H2O: C, 67.2; H, 3.5; N,
9.2%. IR: 1619 vw, 1597 w, 1584 m, 1567 w, 1549 m, 1475
w, 1380 m, 1331 vs, 1164 m, 1119 s, 1109 s, 1074 s, 1037
vw, 1016 w, 840 m, 795 m, 723 w cmy1. Mass spectrum
1
(MALDI-TOF): m/z 598 {M}. H NMR (CDCl3): d 7.38
(2H, ddd, Js6.0, 4.8, 1.1 Hz, H5), 7.82 (4H, d, Js8.0 Hz,
Hm), 7.91 (2H, td, Js7.7, 1.7 Hz, H4), 8.01 (4H, d, Js8.2
Hz, Ho), 8.68 (2H, d, Js8.0 Hz, H3), 8.74 (2H, dd, Js4.3,
0.9 Hz, H6), 8.77 (2H, d, Js1.7 Hz, H59/39, 8.92 (2H, d,
Js1.7 Hz, H39/59).
8 (0.055 g, 52%): m.p.)2508C. Found: C, 68.88; H, 3.87;
N, 10.07. Calc. for C32H20Cl2N4P1.5H2O: C, 68.82; H, 4.16;
N, 10.03%. IR: 1602 m, 1585 s, 1566 m, 1547 m, 1494 m,
1472 w, 1379 m, 1090 m, 1012 w, 821 m, 790 m, 752 w, 739
13 (0.16 g 4%): m.p. 1908C. Found: C, 59.67; H, 3.13.
Calc. for C20H12F6O2: C, 60.31; H, 3.04%. IR: 1673 s, 1605
vs, 1574 s, 1415 m, 1319 vs, 1278 m, 1206 w, 1171 s, 1137
s, 1113 m, 1067 s, 1015 m, 992 w, 825 m, 714 m cmy1. Mass
1
w cmy1. Mass spectrum (EI): m/z 530 {M}. H NMR
(CDCl3): d 7.39 (2H, ddd, Js7.7, 4.8, 1.4 Hz, H5), 7.55
(4H, d, Js8.7 Hz, Hm), 7.88 (4H, d, Js8.7 Hz, Ho), 7.93
(2H, td, Js7.7, 1.4 Hz, H4), 8.70 (2H, d, Js7.8 Hz, H6),
8.75 (2H, d, Js1.5 Hz, H39/59), 8.76 (2H, m, H3), 8.90 (2H,
d, Js1.5 Hz, H39/59).
1
spectrum (EI): m/z 398 {M}. H NMR (CDCl3): d 7.66
(2H, d, Js16.2 Hz, H1), 7.68 (4H, d, Js8.2 Hz, Hm), 7.76
(4H, d, Js8.2 Hz, Ho), 7.89 (2H, d, Js16.2 Hz, H2).
14 (0.88 g, 3%): m.p. 219–2208C. Found: C, 64.90; H,
3.73. Calc. for C18H12Cl2O2: C, 65.28; H, 3.65%. IR: 1670 s,
1607 vs, 1588 s, 1562 m, 1489 m, 1326 m, 1295 m, 1096 m,
998 s, 809 s, 748 s cmy1. Mass spectrum (EI): m/z 332/330
2.4. Copper complexes [Cu2L2][PF6]2 (Ls3–8)
1
{M}. H NMR (CDCl3): d 7.42 (4H, d, Js8.0 Hz, Hm),
The appropriate ligand (20 mg) and an equimolar amount
of [Cu(MeCN)4][PF6] were heated under dinitrogen in
degassed methanol (10 ml) for 3 h. After cooling, the red–
brown precipitate was collected by filtration and washed with
diethyl ether.
7.48 (2H, d, Js16 Hz, H1), 7.60 (4H, d, Js8.0 Hz, Ho),
7.83 (2H, d, Js16 Hz, H2).
2.3. 49,40-Diaryl-2,29:69,20:60,2--quaterpyridines (3–8)
[Cu2(3)2][PF6]2 (0.020 g, 77%): m.p.)2508C. IR:1608
s, 1542 w, 1459 w, 1403 m, 841 vs, 766 m, 558 s cmy1. Mass
spectrum (MALDI-TOF): m/z 1197 {Cu2(3)2(PF6)}q,
1052 {Cu2(3)2}, 525 {Cu(3)}. 1H NMR (CD3COCD3): d
7.21 (2H, dd, Js6,8, 5.9 Hz, H5), 7.60 (6H, m, Hm,p), 7.80
(6H, m, Ho,4), 8.14 (2H, d, Js4.4 Hz, H6], 8.19 (6H, m,
H3,39,59). UV–Vis (MeCN): lmax (log ´) 553 (3.78), 443
(4.03), 274 (4.99), 240 (sh), 198 nm (5.14).
The appropriate 1,6-diarylhexa-1,5-diene-3,4-dione (0.5
mmol) was added to a solution of N-[2-(2-pyridyl)-2-
oxethyl]pyridinium iodide (0.4 g, 1 mmol) and anhydrous
ammonium acetate (4 g, excess) in ethanol (40 ml) and the
mixture heated under reflux for 4 h. After cooling, the off-
white precipitate was filtered off and recrystallized from eth-
anol to give the desired ligand.
3, 4: properties as previously reported [39,40].
[Cu2(4)2][PF6]2 (0.014 g, 51%): m.p.)2508C. IR:2923
m, 1601 m, 1368 m, 1115 w, 1016 w, 842 s, 739 w, 557 m
5 (0.100 g, 38%): m.p.)2508C. Found: C, 75.79; H, 5.25;
N, 10.34. Calc. for C34H26N4O2PH2O: C, 75.54; H, 5.21; N,
10.36%. IR: 1583 s, 1567 m, 1547 m, 1515 s, 1472 m, 1383
m, 1255 m, 1185 m, 831 m, 794 m, 575 m cmy1. Mass
spectrum (MALDI-TOF): m/z 522 {M}. 1H NMR (CDCl3):
d 3.87 (6H, s, OCH3), 7.10 (4H, d, Js8.7 Hz, Hm), 7.38
cmy1
.
Mass spectrum (MALDI-TOF): m/z 1419
{Cu2(4)2(PF6)}, 1281 {Cu2(4)2}. 1H NMR (CD3COCD3):
d 1.39 (18H, s, C(CH3)3), 6.72 (2H, m, H5), 6.93 (4H, d,
Js7.6 Hz, Hm), 7.14 (4H, d, Js7.6 Hz, Ho), 7.30 (2H, m,
H4), 7.76 (2H, dm, Js7.6 Hz, H6), 7.84 (6H, m, H3,3959).
Thursday Jan 20 11:55 AM
StyleTag -- Journal: POLY (Polyhedron) Article: 3276

E.C. Constable et al. / Polyhedron 19 (2000) 23–34
25
UV–Vis (MeCN): lmax (log ´) 550 (3.58), 444 (3.80), 298
(4.66), 207 (4.69).
[Ag2(3)2][PF6]2 (0.018 g, 58%): m.p.)2508C. IR:
1597 s, 1552 m, 1480 w, 1449 w, 1396 w, 844 vs, 763 s, 558
s cmy1. Mass spectrum (MALDI-TOF): m/z 1285
{Ag2(3)2(PF6)}, 1139 {Ag2(3)2}, 1032 {Ag(3)2}, 677
{Ag2(3)}. 1H NMR (CD3CN): d 7.15 (2H, dd, Js6.8, 5.1
Hz, H5), 7.65 (6H, m, Hm,p), 7.95 (8H, m, Ho,4,6), 8.13 (2H,
d, Js8.1 Hz, H3), 8.22 (2H, s, H39/59), 8.43 (2H, s, H3959).
[Ag2(4)2][PF6]2 (0.019 g, 67%): m.p.)2508C. IR:
[Cu2(5)2][PF6]2 (0.029 g, 94%): m.p.)2508C. Found:
C, 55.94; H, 3.67; N, 7.41. Calc. for C68H52Cu2F12N8O4P2:
C, 55.86; H, 3.58; N, 7.66%. Massspectrum(MALDI-TOF):
m/z 1316 {Cu2(5)2(PF6)}, 1171 {Cu2(5)2}. 1H NMR
(CD3COCD3): d 2.17 (6H, s, OCH3), 6.48 (4H, d, Js8.5
Hz, Hm), 6.72 (2H, td, Js6.6, 1 Hz, H5), 7.24 (4H, d, Js8.5
Hz, Ho), 7.30 (2H, td, Js3.2, 1.6 Hz, H4), 7.72 (2H, d,
Js1 Hz, H39/59), 7.76 (2H, dm, Js4.9 Hz, H6), 7.78 (2H,
d, Js1 Hz, H39/59), 7.86 (2H, d, Js8.2 Hz, H3). UV–Vis
(MeCN): lmax (log ´) 554 (3.64), 438 (3.90), 315 (4.76),
199 nm (4.87).
[Cu2(6)2][PF6]2 (0.027 g, 93%): m.p.)2508C. Found:
C, 57.42; H, 3.71; N, 7.99. Calc. forC68H52Cu2F12N8P2PH2O:
C, 57.67; H, 3.84; N, 7.91%. IR: 1601 m, 843 s, 787 w, 557
m cmy1. Mass spectrum (MALDI-TOF): m/z 1252
{Cu2(6)2(PF6)}, 1107 {Cu2(6)2}, 699 {Cu(6)}. 1H NMR
(CD3COCD3): d 1.57 (6H, s, CH3), 6.72 (2H, ddd, Js7.1,
6.3, 1 Hz, H5), 6.78 (4H, d, Js8.1 Hz, Hm), 7.18 (4H, d,
Js8.1 Hz, Ho), 7.32 (2H, td, Js7.2, 1.2 Hz, H4), 7.74, (2H,
dm, Js4.5 Hz, H6), 7.80 (2H, s, H39/59), 7.82 (2H, s, H39/
59), 7.88 (2H, d, Js8.1 Hz, H3). UV–Vis (MeCN): lmax
(log ´) 551 (3.50), 440 (3.73), 281 nm (4.71).
[Cu2(7)2][PF6]2 (0.019 g, 80%): m.p.)2508C. Found:
C, 50.22; H, 2.57; N, 6.87. Calc. forC68H40Cu2F24N8P2PH2O:
C, 50.60; H, 2.50; N, 6.94%. IR: 1609 m, 1543 w, 1395 w,
1322 s, 1170 m, 1114 m, 1061 m, 1016 w, 852 s, 834 vs, 789
m, 557 m cmy1. Mass spectrum (MALDI-TOF): m/z 1469
{Cu2(7)2(PF6)}, 1343 {Cu2(7)2}, 662 {Cu(7)}. 1H NMR
(CD3COCD3): d 7.44 (2H, ddd, Js7.0, 6.7, 1 Hz, H5), 7.94
(4H, d, Js8.0 Hz, Hm), 8.03 (2H, td, Js7.3, 1.3 Hz, H4),
8.18 (4H, d, Js8.0 Hz, Ho), 8.46, (2H, d, Js4.3 Hz, H6),
8.58 (2H, d, Js8.1 Hz, H3), 8.62 (2H, s, H39/59), 8.66 (2H,
s, H39/59). UV–Vis (MeCN): lmax (log ´) 563 (3.52), 4.42
(3.71), 283 nm (4.85).
[Cu2(8)2][PF6]2 (0.025 g, 88%): m.p.)2508C. IR:1608
m, 844 s, 789 m, 558 m cmy1. Mass spectrum (MALDI-
TOF): m/z 1334 {Cu2(8)2(PF6)}, 1189 {Cu2(8)2}, 740
{Cu(8)}. 1H NMR (CD3COCD3): d 6.78 (2H, ddd, Js7.2,
5, 1 Hz, H5), 6.98 (4H, d, Js8.7 Hz, Hm), 7.32 (4H, d,
Js8.7 Hz, Ho), 7.36 (2H, m, H4), 7.76 (2H, d, Js4.9, H6),
7.88 (2H, d, Js1.2 Hz, H39/59), 7.89 (2H, d, Js8.1 Hz,
H3), 7.90 (2H, d, Js1.2 Hz, H39/59). UV–Vis (MeCN):
lmax (log ´) 555 (3.48), 445 (3.70), 286 (4.90), 226 nm
(4.94).
2962 w, 1597 m, 1479 w, 1390 w, 844 s, 791 w, 558 m cmy1
.
Mass spectrum (MALDI-TOF): m/z 1364 {Ag2(4)2}, 1256
1
{Ag(4)2}, 790 {Ag2(4)}. H NMR (CD3COCD3): d 1.43
(18H, s, C(CH3)3), 6.66 (2H, ddd, Js7.7, 5.0, 1 Hz, H5),
7.02 (4H, d, Js8.5 Hz, Hm), 7.32 (4H, d, Js5 Hz, Ho),
7.44 (2H, td, Js7.7, 1.5 Hz, H4), 7.70 (2H, dm, Js5 Hz,
H6), 7.82 (2H, d, Js7.7 Hz, H3), 7.86 (2H, d, Js1Hz, H39/
59), 8.06 (2H, d, Js1 Hz, H39/59). UV–Vis (MeCN): lmax
(log ´) 281 (4.98), 255 (sh), 221 (sh), 198 nm (5.19).
[Ag2(5)2][PF6]2: (0.027 g, 92%): m.p.)2508C. IR:
2924 w, 1599 s, 1518 m, 1257 w, 1184 w, 843 m, 789 w
cmy1. Mass spectrum (MALDI-TOF):m/z1260{Ag2(5)2},
1152 {Ag(5)2}, 738 {Ag2(5)}. 1H NMR (CD3COCD3): d
3.93 (6H, s, OCH3), 7.16 (6H, m, H5,m), 7.90 (6H, m, Ho,4),
8.04 (2H, dm, Js4.5 Hz, H6), 8.10 (2H, d, Js8.2 Hz, H3),
8.15 (2H, d, Js1 Hz, H39/59), 8.33 (2H, d, Js1 Hz, H39/
59). UV–Vis (MeCN): lmax (log ´) 307 (sh), 294 (4.95),
247 (4.81), 221 (sh), 197 nm (5.20).
[Ag2(6)2][PF6]2 (0.027 g, 88%): m.p.)2508C. Found:
C, 53.9; H, 3.6; N, 8.0. Calc. for C68H52N8Ag2P2F12PH2O:
C, 54.3; H, 3.6; N, 7.5%. IR: 1598 m, 1546 w, 1392 m, 842
s, 788 m, 557 m cmy1. Mass spectrum (MALDI-TOF): m/z
1
1196 {Ag2(6)2}, 1088 {Ag(6)2}, 598 {Ag(6)}. H NMR
(CD3COCD3) d 1.57 (6H, s, CH3), 6.66 (2H, ddd, Js7.0,
6.7, 1 Hz, H5), 6.82 (4H, d, Js8.0 Hz, Hm), 7.32 (4H, d,
Js8.0 Hz, Ho), 7.42 (2H, td, Js7.3, 1.3 Hz, H4), 7.64, (2H,
dm, Js4.3 Hz, H6), 7.84 (2H, d, Js8.1 Hz, H3), 7.86 (2H,
s, H39/59), 8.04 (2H, s, H39/59). UV–Vis (MeCN): lmax
(log ´) 279 (4.93), 257 (4.86), 220 (sh), 196 nm (5.2).
[Ag2(7)2][PF6]2 (0.038 g, 76%): m.p.)2508C. Found:
C, 47.1; H, 2.5; N, 6.4. Calc. for C68H40N8P2F24Ag2P2H2O:
C, 47.0; H, 2.6; N, 6.4%. IR: 1597 m, 1548 m, 1481 w, 1450
w, 1388 m, 1327 vs, 1173 m, 1120 s, 1075 m, 1065 m, 1016
m, 840 vs, 792 m, 730 w, 558 m cmy1. Mass spectrum
(MALDI-TOF): m/z 1412 {Ag2(7)2}, 1304 {Ag(7)2}, 814
1
{Ag2(7)}, 706 {Ag(7)}. H NMR (CD3COCD3): d 7.21
(2H, ddd, Js7.0, 6.7, 1 Hz, H5), 7.89 (6H, m, H4,m), 8.01
(4H, d, Js8.0 Hz, Ho), 8.17, (4H, m, H3,6), 8.26 (2H, s,
H39/59), 8.49 (2H, s, H39/59).
2.5. Silver complexes [Ag2L2][PF6]2 (Ls3–7)
2.6. Nickel(II) complexes (Ls3–7)
The appropriate ligand (20 mg) and an equimolar amount
of silver acetate were heated under dinitrogen in degassed
methanol (10 ml) for 3 h. After cooling to room temperature,
a methanolic solution of [NH4][PF6] was added. The off-
white precipitate that formed was isolated by filtration and
washed with diethyl ether.
The ligand(20mg)andanequimolaramountofnickel(II)
acetate were heated under dinitrogen in methanol or ethanol
(10 ml) for 3 h. After cooling to room temperature, a meth-
anolic solution of [NH4][PF6] was added and the yellow
precipitate that formed was collected by filtration andwashed
with diethyl ether.
Thursday Jan 20 11:55 AM
StyleTag -- Journal: POLY (Polyhedron) Article: 3276

26
E.C. Constable et al. / Polyhedron 19 (2000) 23–34
[Ni(3)(OAc)(H2O)][PF6]
(0.016
g,
63%):
{Co(3)(H2O)}, 521 {Co(3)}. 1H NMR (CD3CN): d 6, 9,
12, 22, 32, 40, 50, 71, 72, 159. UV–Vis (MeCN): lmax
(log ´) 296 (4.70), 225 (4.66), 202 nm (4.91).
[Co(4)(MeCN)(H2O)][PF6]2 (0.013 g, 67%):
m.p.)2508C. Recrystallized from MeCN–diethyl ether.
Found: C, 51.4; H, 4.6; N, 6.8. Calc. for C42H43N5OCoP2F12:
C, 51.3; H, 4.4; N, 7.1%. IR: 2966 w, 1608 m, 1547 w, 1448
w, 1400 s, 1050 m, 848 s, 793 w, 557 m cmy1. Massspectrum
m.p.)2508C. Found: C, 55.0; H, 3.5; N, 7.6. Calc. for
C34H29N4O3NiPF6: C, 54.9; H, 3.7; N, 7.5%. IR: 1606 s, 1533
vs, 1460 m, 1406 s, 1243 w, 1017 w, 843 vs, 792 w, 766 s,
734 w, 691 w, 642 w, 632 w, 557 s cmy1. Mass spectrum
(MALDI-TOF): m/z 744 {Ni(3)(OAc)(PF6)(F)}, 725
{Ni(3)(OAc)(PF6)}, 580 {Ni(3)(OAc)}, 521 {Ni(3)}.
1H NMR (CD3CN): d 10, 11, 34, 39, 46, 50, 60.
[Ni(4)(MeCN)(H2O)][PF6]2 (0.014 g, 51%):
m.p.)2508C. Recrystallized from MeCN–diethyl ether.
Found: C, 51.3; H, 4.4; N, 6.8. Calc. for C42H43N5NiOP2F12:
C, 51.3; H, 4.4; N, 7.1%. IR: 2964 w, 1605 m, 1550 w, 1460
w, 1400 w, 1016 w, 842s, 798w, 559mcmy1. Massspectrum
(MALDI-TOF): m/z 651 {Ni(4)(H2O)}, 633 {Ni(4)}. 1H
NMR (CD3COCD3): d 3, 8 (=2), 12, 13, 34, 63, 67, 91.
UV–Vis (MeCN): lmax (log ´) 349 (4.2), 292 (4.66), 238
(4.56), 202 nm (4.88).
[Ni(5)(MeCN)2][PF6]2 (22 mg, 80%): m.p.)2508C.
Recrystallized from MeCN–diethyl ether. Found: C, 47.7; H,
3.5; N, 8.9. Calc. for C38H32N6O2NiP2F12: C, 47.9; H, 3.4;
N, 8.8%. IR: 1559 s, 1552 w, 1520 m, 1460 m, 1404 m, 1246
m, 1191 m, 1024 m, 845 s, 794 m, 558 m cmy1. Mass
spectrum (MALDI-TOF): m/z 726 {Ni(5)(PF6)}, 581
{Ni(5)}. 1H NMR (CD3COCD3): d 4, 7, 11, 12, 33, 62, 65,
89. UV–Vis (MeCN): lmax (log ´) 334 (4.68), 298 (4.64),
245 (4.70), 200 nm (4.73).
(MALDI-TOF):
{Co(4)(H2O)(MeCN}, 669 {Co(4)(H2O)2}, 651
{Co(4)(H2O)}, 633 {Co(4)}. H NMR (CD3COCD3): d
4, 6, 9, 21, 30, 48, 69, 73, 164. UV–Vis (MeCN): lmax
(log ´) 297 (4.74), 223 (4.72), 202 nm (4.93).
[Co(5)(H2O)2][PF6]2 (0.026 g, 94%): m.p.)2508C.
Found: C, 47.2; H, 3.3; N, 6.6. Calc. forC34H30N4O2CoP2F12:
C, 46.6; H, 3.45; N, 6.4%. IR: 1603 s, 1554 m, 1523 m, 1460
m, 1404 m, 1302 w, 1244 m, 1194 m, 1018 w, 849 s, 793 w,
559 m cmy1. Mass spectrum (MALDI-TOF): m/z 871
{Co(5)(PF6)2}, 640 {Co(5)(H2O)(MeCN)}, 617
m/z
923
{Co(4)(PF6)2},
692
1
1
{Co(5)(H2O)2}, 599 {Co(5)(H2O)}, 581 {Co(5)}. H
NMR (CD3COCD3): d 6, 9, 48, 63, 73, 169. UV–Vis
(MeCN): lmax (log ´) 356 (sh), 332 (4.57), 292 (4.65),
226 (sh), 202 nm (4.90).
[Co(6)(OAc)(MeCN)][PF6] (0.024 g, 83%):
m.p.)2508C. Recrystallized from MeCN–diethyl ether.
Found: C, 56.8; H, 4.0; N, 9.1. Calc. for C38H32N5O2CoPF6:
C, 57.5; H, 4.1; N, 8.8%. IR: 1610 m, 1553 m, 1460 w, 1400
w, 1246 w, 1014 w, 846 s, 791 m, 558 m cmy1. Mass spec-
trum (MALDI-TOF): m/z 839 {Co(6)(PF6)2}, 694
{Co(6)(PF6)}, 608 {Co(6)(H2O)(MeCN)}, 585
[Ni(6)(OAc)(H2O)][PF6]
(25
mg,
85%):
m.p.)2508C. Found: C, 54.8; H, 3.8; N, 7.2. Calc. for
C36H31N4O3NiPF6PH2O: C, 54.8; H, 4.2; N, 7.1%. IR: 1604
m, 1552 w, 1459 w, 1400 w, 1020 w, 840 s, 794 m, 558 m
cmy1 Mass spectrum (MALDI-TOF): m/z 585
1
{Co(6)(H2O)2}, 567 {Co(6)(H2O)}, 549 {Co(6)}. H
1
{Ni(6)(H2O)2}, 549 {Ni(6)}. H NMR (CD3COCD3): d
NMR (CD3COCD3): d 4 (=2), 9 (=2), 21, 28, 47, 68, 72,
162. UV–Vis (MeCN): lmax 297 (4.71), 224 (4.72), 204
nm (4.92).
10 (=2), 11 (=2), 12, 33, 62, 66, 90. UV–Vis (MeCN):
lmax (log ´) 348 (4.20), 293 (4.68), 238 (4.56), 202 nm
(4.91).
[Co(7)(OAc)(MeCN)][PF6] (0.020 g, 75%):
m.p.)2508 C. Found: C, 50.4; H, 3.1; N, 7.7. Calc. for
C38H26N5OPF12Co: C, 50.6; H, 2.9; N, 7.8%. IR: 1613 m,
1577 m, 1555 m, 1460 m, 1397 m, 1327 vs, 1169 w, 1132
m, 1120 m, 1016 m, 844 vs, 795 w, 557 m cmy1. Mass
spectrum (MALDI-TOF): m/z 807 {Co(7)(PF6)}, 657
[Ni(7)(OAc)(MeCN)][PF6]2 (0.017 g, 72%):
m.p.)2508C. Recrystallized from MeCN–diethyl ether.
Found: C, 49.7; H, 3.0; N, 7.6. Calc. for
C38H26N5NiO2PF12PH2O: C, 49.6; H, 3.1; N, 7.6%. IR: 1612
s, 1566 m, 1460 m, 1397 m, 1328 vs, 1172 m, 1121 s, 1070
m, 1015 m, 843 vs, 794 m, 735 w, 558 m cmy1. Mass spec-
trum (MALDI-TOF): m/z 744 {[Ni(7)(OAc)(PF6)(F)},
725 {Ni(7)(OAc)(PF6)}, 580 {Ni(7)(OAc)}, 521
{Ni(7)}. 1H NMR (CD3COCD3): d 10, 11, 32, 39, 46, 50,
60. UV–Vis (MeCN): lmax (log ´) 349 (4.22), 292 (4.65),
240 (4.62), 204 nm (4.93).
1
{Co(7)}. H NMR (CD3COCD3): d 6, 10, 22, 35, 49, 71,
159.
2.8. Crystal structure determinations of
[Ni(4)(MeCN)2][PF6]2 (15),
[Ni(3)(OAc)(MeOH)][PF6]P2MeOHPH2O (16) and
[Co(3)(OAc)(MeCN)][PF6]P1.64MeCNP0.36PH2O (17)
2.7. Cobalt(II) complexes (Ls3–7)
In each case, crystals were grown by the diffusion of die-
thyl ether vapour into a solution of the crude complex in
acetonitrile. Measurements were made, as previously
described, using an Enraf-Nonius CAD4 diffractometer
[41]. The conditionsusedforcrystallographicdatacollection
and structure refinement are summarized in Table 1; selected
geometric data are given in Table 2. Structures were eluci-
dated by direct methods using SIR92 [42]. Anisotropicleast-
Preparation was the same as for the nickel complexes but
using cobalt(II) acetate; orange–yellow solids were formed.
[Co(3)(OAc)(H2O)][PF6]
(0.025
g,
78%):
m.p.)2508C. Found: C, 54.9; H, 3.6; N, 7.6. Calc. for
C34H27N4O3CoPF6: C, 54.9; H, 3.7; N, 7.5%. IR: 1614 s,
1576 m, 1557 s, 1488 w, 1463 m, 1407 m, 848 vs, 768 m,
559m cmy1
.
Mass spectrum (FAB): m/z 537
Thursday Jan 20 11:55 AM
StyleTag -- Journal: POLY (Polyhedron) Article: 3276

E.C. Constable et al. / Polyhedron 19 (2000) 23–34
27
Table 1
Crystal data and structure refinement for 15–17
15
16
17
Formula
C44H44N6NiP2F6P
C35H18NiN4O3PF6PP2CH4OPH2O
C36H28CoN5O2PF6PP1.64C2H3NP0.36H2O
Crystal system
Space group
orthorhombic
Pbn21
triclinic
P1
triclinic
P1
¯
¯
Crystal colour, habit
Crystal dimensions (mm)
pale green plate
0.05=0.16=0.18
9.8573(7)
20.1490(17)
23.2486(38)
90
90
90
4
1.45
yellow–green needle
0.12=0.14=0.28
10.709(1)
13.089(1)
14.809(1)
65.369(5)
88.515(6)
87.626(8)
2
yellow–orange cube
0.20=0.26=0.42
11.959(1)
12.738(2)
13.124(2)
89.75(1)
71.53(1)
87.07(1)
2
˚
a (A)
˚
b (A)
˚
c (A)
a (8)
b (8)
g (8)
Z
Dc (g cmy3
)
1.46
1.47
Temperature (K)
Radiation, Cu Ka (l, A)
Scan type
293
1.54180
v-2u
223
1.54180
v-2u
223
1.54180
v-2u
˚
Maximum 2u
No. data collected
No. unique data
No. observed data
No. variables
Absorption correction
Weighting scheme
R
133.48
3239
3124
3124
155.0
6997
6638
4635, I)3.00s(I)
497
DIFABS [45]
Chebychev [44]
0.0827
0.0795
0.954, y0.906
155.0
6699
6457
4354, I)3.00s(I)
549
DIFABS [45]
Chebychev [44]
0.0757
0.0865
0.71, y0.92
586
psi-scans
Chebychev [44]
0.1160 (all data)
0.2370 (all data)
0.72, y0.92
RW
y3
˚
Drmax, Drmax (e, A
)
squares full-matrix refinement was carried out on all
non-hydrogen atoms using the program CRYSTALS [43]
and a Chebychev weighting scheme [44]. The positions of
the hydrogen atoms were determined geometrically.
For compound 15, a poor dataset was obtained and the
structure was refined against F2 using all the data. For 17,
problems were encountered refining disordered solvent mol-
ecules. The space around the special position 0.5, 0, 0.5 is
occupied by MeCN and H2O molecules. The frequency was
not constrained during refinement, but the total site occu-
pancy was fixed to 1. The ratio of 0.64–0.36 suggests that the
two solvent molecules can have two alternative orientations
created by the centre of symmetry, or that two MeCN mole-
cules are present in the cavity without H2O. Another disor-
dered MeCN molecule has been localized in the difference
map. The two alternating positions have been refined using
appropriate restraints. Because of difficulties in centering the
sample on the diffractometer using the oil-drop method at
low temperature, psi-scans did not give a good estimate of
the absorption;refinementwasthereforemadeusingDIFABS
[45].
bipyridines in the presence of copper powder [28]; this
method has also been utilized in the preparation of 2 [23].
More recently, nickel reagents have been utilized for the
synthesis of 1 [7]. The preparation of 49,40-disubstituted
ligands by the coupling reactions of halo-2,29-bipyridines is
not easy, but they can be obtained using the methodology
described by Sorenson [40]. We have shown that diacetyl is
an excellent precursor for the formation of oligopyridinesand
that the 49,40-diaryl-substituted compounds 3 and 4 can be
prepared from this starting material [39].
3. Results and discussion
We havenowextendedthismethodologytothepreparation
of a range of 49,40-disubstituted-2,29:69,20:60,20-quaterpyri-
dines (3–8), which were synthesized according to Scheme
1. The reaction of diacetyl with the appropriate substituted
3.1. Ligand synthesis
2,29:69,20:60,2--Quaterpyridine (1) was first synthesized
in 1938 by the high-temperature coupling of 6-halo-2,29-
Thursday Jan 20 11:56 AM
StyleTag -- Journal: POLY (Polyhedron) Article: 3276

28
E.C. Constable et al. / Polyhedron 19 (2000) 23–34
Table 2
˚
Selected bond lengths (A) and angles (8) for 15–17
15
16
17
Ni(1)–N(1)
Ni(1)–N(2)
Ni(1)–N(3)
Ni(1)–N(4)
Ni(1)–N(5)
Ni(1)–N(6)
2.11(1)
1.982(9)
2.06(1)
2.091(9)
2.09(1)
2.09(1)
Ni(1)–N(1
Ni(1)–N(2)
Ni(1)–N(3)
Ni(1)–N(4)
Ni(1)–O(1
Ni(1)–O(2)
2.140(4)
2.020(4)
2.009(4)
2.174(4)
2.133(3)
2.052(3)
Co(1)–N(1)
Co(1)–N(2)
Co(1)–N(3)
Co(1)–N(4)
Co(1)–O(1)
Co(1)–O(2)
Co(1)–N(51)
2.211(5)
2.156(4)
2.158(4)
2.196(4)
2.171(4)
2.293(3)
2.156(5)
N(1)–Ni(1)–N(2)
N(1)–Ni(1)–N(3)
N(2)–Ni(1)–N(3)
N(1)–Ni(1)–N(4)
N(2)–Ni(1)–N(4)
N(3)–Ni(1)–N(4)
N(1)–Ni(1)–N(5)
N(2)–Ni(1)–N(5)
N(3)–Ni(1)–N(5)
N(4)–Ni(1)–N(5)
N(1)–Ni(1)–N(6)
N(2)–Ni(1)–N(6)
N(3)–Ni(1)–N(6)
N(4)–Ni(1)–N(6)
N(5)–Ni(1)–N(6)
76.4(4)
156.1(4)
79.7(4)
127.7(4)
155.9(4)
76.3(4)
88.6(4)
93.3(4)
93.9(4)
86.3(4)
90.2(4)
91.6(4)
89.4(4)
90.2(4)
174.5(4)
N(1)–Ni(1)–N(2)
N(1)–Ni(1)–N(3)
N(2)–Ni(1)–N(3)
N(1)–Ni(1)–N(4)
N(2)–Ni(1)–N(4)
N(3)–Ni(1)–N(4)
N(1)–Ni(1)–O(1)
N(2)–Ni(1)–O(1)
N(3)–Ni(1)–O(1)
N(4)–Ni(1)–O(1)
N(1)–Ni(1)–O(2)
N(2)–Ni(1)–O(2)
N(3)–Ni(1)–O(2)
N(4)–Ni(1)–O(2)
O(1)–Ni(1)–O(2)
76.7(2)
154.1(2)
77.6(2)
128.9(2)
153.6(2)
76.4(2)
88.1(2)
91.1(2)
89.6(2)
84.5(2)
90.3(1)
91.7(2)
93.2(2)
94.0(2)
176.4(2)
N(1)–Co(1)–N(3)
N(2)–Co(1)–N(3)
N(1)–Co(1)–N(4)
N(2)–Co(1)–N(4)
N(3)–Co(1)–N(4)
N(1)–Co(1)–O(1)
N(2)–Co(1)–O(1)
N(3)–Co(1)–O(1)
N(4)–Co(1)–O(1)
N(1)–Co(1)–O(2)
N(2)–Co(1)–O(2)
N(3)–Co(1)–O(2)
N(4)–Co(1)–O(2)
O(1)–Co(1)–O(2)
N(1)–Co(1)–N(51)
N(1)–Co(1)–N(2)
N(2)–Co(1)–N(51)
N(3)–Co(1)–N(51)
N(4)–Co(1)–N(51)
O(1)–Co(1)–N(51)
O(2)–Co(1)–N(51)
145.0(1)
72.4(1)
140.6(2)
144.0(1)
72.5(1)
97.4(1)
91.0(1)
87.7(1)
95.4(1)
78.1(1)
134.4(1)
131.8(1)
77.2(1)
58.7(1)
80.8(2)
72.9(1)
93.0(2)
96.4(2)
83.2(2)
175.0(1)
116.3(1)
benzaldehyde in MeOH with piperidinium acetate as catalyst
resulted in the formation of 1,6-diarylhexa-1,5-diene-3,4-
diones 9–14 as bright orange crystals. Although the yields
were poor, unreacted material can be recovered; moreover,
the convenience of this synthesis and the low cost of the
starting materials make these attractive intermediates for oli-
gopyridine synthesis. The compounds were all isolated with
the E,E configuration, as confirmed by the observation of a
single AB system with a coupling constant JAB of f16 Hz
3.2. Complexes with metals favouring tetrahedral
coordination
The four nitrogen donor atoms of quaterpyridine ligands
can bepartitionedintotwodidentatebipyridinedomainsupon
interaction with metal ions favouring tetrahedral coordina-
tion, because it is not possible for all four donors to occupy
the vertices of a tetrahedron [1–5].
1
in each of the H NMR spectra. The carbonyl group of the
3.2.1. Copper(I) complexes
enone gives rise to a characteristic absorption in the IR spec-
Copper(I) forms dinuclear double-helical complexes with
2,29:69,20:60,2--quaterpyridines [1–5] in which the precise
geometrical properties are dependent upon the nature and
position of any ligand substituents. The reaction of 3–8 with
an equimolar amount of [Cu(MeCN)4][PF6] in methanol
under nitrogen gave deep red–brown solutions from which
the salts [Cu2L2][PF6]2 (Ls3–8) were isolated as solids
varying in colour from red–brown through purple to black in
50–90% yield. Microanalysis confirmed the 1:1 metal:ligand
stoichiometry, and evidence for the dinuclear structurescame
from mass spectrometry, which revealed ions corresponding
to {[Cu2L2][PF6]}q and {[Cu2L2]}q in each case (where
L represents quaterpyridine (qtpy) or substituted quaterpyr-
idine). Molecular modelling combined with structural data
for a number of [Cu2L2]2q complexes confirms that a din-
uclear formulation requires a double-helical structure; no
trum, with ns1669–1679 cmy1. Characterization data for
¯
these compounds are collated in Section 2.
The quaterpyridines 3–8 were isolated as off-white solids
in yields of 30–60% from the reaction of 9–14 with the
¨
Krohnke reagent, N-[2-(2-pyridyl)-2-oxethyl]pyridinium
iodide [38], in the presence of ammonium acetate. The 1H
NMR spectra of these compounds are characteristic, with
ligands 3–6 giving nine resonances and 7 and 8 giving only
eight resonances. All of the chemical shifts and coupling
constants were within the normal ranges and the spectra were
fully assigned (see Section 2) by inspection, comparison
with known compounds and by correlation spectroscopy
(COSY).
Thursday Jan 20 11:56 AM
StyleTag -- Journal: POLY (Polyhedron) Article: 3276

E.C. Constable et al. / Polyhedron 19 (2000) 23–34
29
achiral structure is possible. The 1H NMR spectra of
CD3COCD3 or CD3CN solutions of the complexes were sim-
ple and assigned with the aid of 1H NMR COSY experiments.
Only nine (3–6) or eight (7, 8) different proton environ-
ments were observed, indicating a single symmetrical solu-
tion species. Comparison with the 1H NMR spectra of
solutions of [Cu2(qtpy)2][PF6]2, for which X-ray data have
established a double-helical solid-state species, indicatesthat
the solution species are similar. Although the 1H NMR data
cannot distinguish between dinuclear and mononuclear solu-
tion species, we have used chiral ligands to unambiguously
establish that the solution species are dinuclear [17]. Taken
in conjunction with the electrochemical data, we can now
confidently state that the 49,40-disubstituted quaterpyridine
ligands give dicopper(I) double-helical complexes in both
the solid state and solution. The complexes are indefinitely
stable in air in the solid state or in MeCN, although they are
slowly oxidized in MeOH solution.
The electronic spectra of the dicopper(I) complexes in
MeCN solution show absorption maxima at very similar
wavelengths (550–555 and 438–445 nm), with the exception
of the complex with 7, which is significantly red-shifted(563
and 448 nm). Compared with [Cu2(qtpy)2][PF6]2 (lmax
543, 432 nm) [11], the metal-to-ligand charge transfer
(MLCT) bands of the complexes with 3–8 have been red-
shifted, consistent with the lowering of the energy of the
ligand p* acceptor orbital upon the introduction of the con-
jugated aromatic substituents.
The dicopper(I) complexes are all electrochemically
active and show irreversible metal-centred oxidation and
reduction processes (Table 3) together with ligand-based
reductions at fy1.50 and fy1.75 V. The separation
between the metal-centred processes is variable and the data
are in accord with earlier studies of simple quaterpyridine
derivatives and are compatible with the electrochemicalproc-
esses outlined in Scheme 2 [22–25].
Scheme 1.
Table 3
Cyclic voltammetric data for copper complexes in MeCN (vs. internal Fc/
Fcq
)
Complex
[Cu(I)2L2]2q
/
[Cu(II)L]2q
[Cu(I)L]q (V) (V)
/
EayEc
[Cu(I)Cu(II)L2]3q (V)
[Cu2(qtpy)2]2q
[Cu2(3)2]2q
[Cu2(4)2]2q
[Cu2(5)2]2q
[Cu2(6)2]2q
[Cu2(7)2]2q
[Cu2(8)2]2q
0.005
y0.030
0.044
0.028
0.133
y0.420
y0.360
y0.294
y0.331
y0.370
y0.371
y0.289
0.470
0.330
0.338
0.359
0.503
0.641
0.360
3.2.2. Silver(I) complexes
The reaction of 3–7 with an equimolar amount of AgOAc
in methanol gave pale yellow solutions from which the salts
[Ag2L2][PF6]2 (Ls3–7) were isolated as white solids in
58–92% yield. Microanalysis confirmed the 1:1 metal:ligand
formulations and mass spectrometry confirmed a dinuclear
0.270
0.071
Scheme 2.
Thursday Jan 20 11:56 AM
StyleTag -- Journal: POLY (Polyhedron) Article: 3276

30
E.C. Constable et al. / Polyhedron 19 (2000) 23–34
formulation. Arguments similar to thosepresentedabovelead
to unambiguous assignment of dinuclear double-helical
1
structures to both solid-state and solution species. The H
NMR spectra of CD3COCD3 or CD3CN solutions of the com-
plexes were simple and only nine (3–6) or eight (7) proton
environments were observed, indicating a single symmetrical
solution species. The complexes are air-stable both in the
solid state and in solution.
All of the complexes exhibit an irreversible process in the
range y0.30 and y0.4 V (versus Fc/Fcq), leading to com-
plex decomposition and plating of silver on the electrode.
All of these data are in accord with the formation of din-
uclear double-helical complexes (Scheme 3) with copper(I)
and silver(I) in which the 49,40-substituents will, at most,
control the pitch of the double helix. Despite numerous
attempts, we have been unable to obtain X-ray-quality crys-
tals of copper or silver complexes with any of these ligands.
As the original aim was to ascertain that the introduction of
the 49,40-substituents did not affect the formationofdinuclear
double helicates, the non-structural evidence was strong
enough for us to develop more highly functionalized quater-
pyridine ligands for use as dendritic cores [46]. Fig. 1 shows
an MM2 minimized structure representing the dicopper(I)
complex with 3. The crystallographic coordinates for the
[Cu2(qtpy)2]2q cation were taken [9,11] and the 49- and
40-H atoms replaced by phenyl groups. The core structure
was constrained and the phenyl groups were minimized.
There are no short contacts between the substituents and the
dinuclear core, and the phenyl substituents are arrayed in a
quasi-tetrahedral fashion.
Fig. 1. Modelled structure of the dicopper(I) double helicate obtained with
3, showing the distribution of the aryl substituents. For clarity, hydrogen
atoms have been omitted and one of the ligand strands has been shaded.
of cobalt(II) [29,30] and nickel(II) [7,11] complexes are
all of type (a), the desired {M0(bpy0)2X2} coordination
subunit is present in the dinuclear double-helical complexes
[M2(qpy)2(OAc)]3q
qpys2,29:69,20:60,2-:6-,200-quinquepyridine; X2sOAc).
We hoped that the introduction of substituents onto the qua-
terpyridine might force the adoption of structure (b).
(MsNi,
Co;
3.3.1. Nickel(II) complexes
The reaction of 3–7 with an equimolar amount of
nickel(II) acetate in MeOH or EtOH gave yellow solutions
from which yellow-green salts were obtained upon the addi-
tion of [NH4][PF6]. In all cases, microanalysis indicated
complexes with a 1:1 M:L stoichiometry. It was alsoapparent
that a number of additional ligands or anions were present in
each case. In particular, microanalysis indicated that acetate
was present in many of the isolated complexes. Because we
had previously characterized the acetate-free mononuclear
cations [Ni(qtpy)(S)2]2q (SsMeCN or H2O), we hoped
that the inclusion of acetate was evidence for the formation
of the dinuclear double helices.
3.3. Complexes with metals favouring octahedral
coordination
Octahedral metal centres could form two types of com-
plexes with quaterpyridine ligands: (a) the four nitrogen
donors of the ligand could occupy the equatorial sites of a
mononuclear octahedral complex, or the ligand could be par-
titioned into two bipyridine domains to give (b) a dinuclear
double helix with two additional ligands per metal centre or
(c) a dinuclear triple helix. Modelling suggests that the triple
helix (c) is too strained with quaterpyridine ligands, but both
(a) and (b) should be possible. Although known structures
The precise species formed depended upon the ligand, but
isolated complexes included {[NiL(OAc)(S)][PF6]}n
Scheme 3.
Thursday Jan 20 11:56 AM
StyleTag -- Journal: POLY (Polyhedron) Article: 3276

E.C. Constable et al. / Polyhedron 19 (2000) 23–34
31
(Ls3, 6, 7, SsMeCN, H2O) and {[NiL(S)2][PF6]2}n
(Ls4, 5, SsMeCN, H2O). Mass spectrometry only pro-
vided evidence for the formation of mononuclear complexes
in each case (see Section 2), although the complexes con-
taining acetate gave ions {NiL(OAc)(PF6)}q and
{[NiL(OAc)}q, thereby providing evidence for coordina-
1
tion of the carboxylate. The H NMR spectra of acetone
solutions of the complex were very broad, with paramagh-
etically shifted resonances observed between d 10 and 100.
It has not been possible to assign these spectra fully, but they
are consistent with the formation of a single, symmetrical,
solution species. Cyclic voltammetry of MeCN solutions of
the complexes revealed no nickel(II/III) redox processes,
but in each case two-ligand-centred reduction was observed
at fy1.60 and y1.85 V. IR spectroscopy did not provide
unambiguous data regarding the coordination mode of the
carboxylate in the complexes containing acetate. The mass-
spectrometric data suggest that the substitutedquaterpyridine
ligands form mononuclear complexes similar to thoseformed
with quaterpyridine itself. In order to confirm this and to
establish the nature of the acetate in these complexes, we
Fig. 3. Molecular structure of the cation present in
[Ni(3)(OAc)(MeOH)][PF6]P2MeOHPH2O; hydrogen atoms have been
omitted for clarity.
planar with interplanar angles of 1.98, 4.78 and 2.68 between
the pyridine rings. The aryl substituents are twisted out of the
plane of the ligand, one by 21.78 and the other by 35.18.
Nickel(II) is slightly too small to fit in the ligand cavity and
the pyridine rings flex inwards towards the metal ion, result-
ing in small distortions quantified by the bite angles:/N(1)–
Ni(1)–N(2), 76.4(4)8; N(2)–Ni(1)–N(3), 79.7(4)8;
/N(3)–Ni(1)–N(4), 76.3(4)8. As expected, the metal–
ligand bond lengths to the central pyridyl rings are longer
than those to the terminal rings: Ni–Nterminal, 2.11(1),
determined
the
solid-state
structures
of
[Ni(4)(MeCN)2][PF6]2
and
[Ni(3)(OAc)(MeOH)][PF6]P2MeOHPH2O.
3.3.2. Crystal structures of [Ni(4)(MeCN)2][PF6]2 and
[Ni(3)(OAc)(MeOH)][PF6]P2MeOHPH2O
The crystal structures of [Ni(4)(MeCN)2][PF6]2 and
[Ni(3)(OAc)(MeOH)][PF6]P2MeOHPH2O were deter-
mined; the relevant data are presented in Tables 1 and 2. The
crystal structure of [Ni(4)(MeCN)2][PF6]2 (15) revealed
a mononuclear complex with a pseudo-octahedralcationcon-
taining an equatorial 4 ligand and two axial acetonitrile
ligands (Fig. 2), closely resembling that in
[Ni(qtpy)(MeCN)2]2q [7,11]. The quaterpyridine is near
˚
˚
2.091(9) A; Ni–Ncentral, 1.982(9), 2.06(1) A. The axial
ligands are close to ideally located: /N(5)–Ni(1)–N(6),
174.5(4)8. There are no short contacts between the cations
and anions in the lattice.
Fig. 2. Molecular structure of the cation present in [Ni(4)(MeCN)2][PF6]2; hydrogen atoms have been omitted for clarity.
Thursday Jan 20 11:56 AM
StyleTag -- Journal: POLY (Polyhedron) Article: 3276

32
E.C. Constable et al. / Polyhedron 19 (2000) 23–34
Analysis of the crystal structure also revealed
[Ni(3)(OAc)(MeOH)][PF6] (16) contains a mononu-
clear cation, with an equatorial 3 ligand and axial MeOH and
monodentate acetate ligands (Fig. 3). The quaterpyridine is
near planar (interplanar angles between pyridine rings of
5.38, 1.28 and 3.68), but the phenyl substituents are twisted
out of this plane, one by 23.78 and the other by 27.28. Bond
lengths and anglesinvolvingthenickelandthequaterpyridine
ligand resemble those for 15 (Table 2). The axial ligands are
again near-ideallylocated:/O(1)–Ni(1)–O(2),176.4(2)8.
˚
The acetate is monodentate (Ni(1)∆O(3), 3.004 A), with
the non-coordinated oxygen lying in the void between the
two terminals rings of the quaterpyridine ligand. Conse-
˚
quently, there are two short (2.642, 2.606 A) contacts
between the carboxylate O(3) and the H6 protons of the
terminal rings (Fig. 4). There are no other short contacts
between the cations and anions in the lattice. To conclude, in
the two structures discussed, the quaterpyridines behave as
tetradentate ligands occupying the equatorial sites in near-
octahedral cations.
Fig.
4.
A
view
of
the
cation
present
in
[Ni(3)(OAc)(MeOH)][PF6]P2MeOHPH2O, showing the contacts
between the acetate and pyridine H6; all hydrogen atoms except H(11) and
H(201) have been omitted for clarity, as have the methanol ligand and the
acetate methyl group.
3.3.3. Cobalt(II) complexes
The reaction of 3–7 with an equimolar amount of
cobalt(II) acetate in MeOH or EtOH gave orange solutions
from which orange salts were obtained upon the addition of
[NH4][PF6]. In general, the isolated complexes closely
resembled those with nickel(II), and microanalysisindicated
complexes with a 1:1 M:L stoichiometry with additional
ligands or anions present. Once again, acetate was present in
many of the isolated complexes. On standing in air, some of
the complexes decomposed to give green powders.
Mass spectrometry indicated only the formation of mon-
onuclear complexes (see Section 2). We have shown that 1H
NMR spectroscopy is a powerful technique for the study of
paramagnetic cobalt(II) complexes [47] and, in each case,
shifted resonances were observed in the range y20 to 170
ppm. A typical example is seen for the complex
[Co(3)(OAc)(H2O)][PF6], which in CD3CN solution
exhibits ten resonances at d 6, 9, 12, 22, 32, 40, 50, 71, 72,
159. The resonance at d 6 is tentatively assigned to the acetate
group on the basis of signal intensity. Cyclic voltammetry of
MeCN solutions of the complexes showed no cobalt(II/III)
redox processes, but ligand-centred reduction was observed
at fy1.60 and y1.85 V. The data suggest that the substi-
tuted ligandsformmononuclearcobalt(II)complexessimilar
to those formed with nickel(II). In order to confirm this we
molecules; data are presented in Tables 1 and 2. Discussion
centres upon the mononuclear [Co(3)(OAc)(MeCN)]q
cation, the structure of which is presented in Fig. 5. Thecation
is best described as seven-coordinate and contains an equa-
torial 3 ligand, an axial MeCN and an axial chelating but
asymmetric didentate acetate ligand. The quaterpyridine is
essentially planar (interplanar angles 2.58, 0.28, 0.48) with
the phenyl substituents twisted out of the plane by 10.18 and
26.98. The metal–ligand bond lengths to the central pyridyl
rings are longer than those to the terminal rings. The major
difference from the cation in 16 arises in the bonding mode
of the acetate. In the the nickel(II) complex, the acetate is
essentially monodentate, with the non-bonded contact
˚
Ni(1)«O(3) greater than 3 A; in complex 17, the two
˚
Co«_ distances are similar (2.171(4) and 2.293(3) A),
with the shorter contact being to the ‘axial’ position and the
longer to the oxygen bent into the void between the terminal
˚
pyridine rings. Once again, f2.5 A contacts between O(2)
and the pyridine H6 protons are observed.
4. Conclusions
A series of 2,29:69,20:60,2--quaterpyridine ligands bearing
substituents in the 49- and 40-positions have been prepared
and theircoordinationchemistryhasbeeninvestigated.Incor-
poration of the substituents does not change the basic patterns
of reactivity: with silver(I) and copper(I), dinuclear double
helicatesareformed, whereas, withcobalt(II)andnickel(II),
a variety of mononuclear structures are formed.
have
determined
the
solid-state
structure
of
[Co(3)(OAc)(MeCN)][PF6]P1.64MeCNP0.36H2O.
3.3.4. Crystal structure of
[Co(3)(OAc)(MeCN)][PF6]P1.64MeCNP0.36H2O (17)
Recrystallization of [Co(3)(OAc)(H2O)][PF6] from
MeCN gave orange crystals of
[Co(3)(OAc)(MeCN)][PF6]P1.64MeCNP0.36H2O.
Severe problems were encountered in the refinement of this
structure as a result of extensive disorder of the lattice solvent
Supplementary data
Supplementary data are available, upon request, from the
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK, quoting
the deposition numbers 124959, 124960 and 124961.
Thursday Jan 20 11:56 AM
StyleTag -- Journal: POLY (Polyhedron) Article: 3276

E.C. Constable et al. / Polyhedron 19 (2000) 23–34
33
Fig. 5. Molecular structure of the cation present in [Co(3)(OAc)(MeCN)][PF6]P1.64MeCNP0.36H2O; hydrogen atoms have been omitted for clarity.
[16] G. Baum, E.C. Constable, D. Fenske, C.E. Housecroft, T. Kulke,
Chem. Commun. (1999) 195.
Acknowledgements
[17] G. Baum, E.C. Constable, D. Fenske, C.E. Housecroft, T. Kulke,
Chem. Eur. J. 5 (1999) 1862.
[18] C.-M. Che, C.-W. Chan, S.-M. Yang, C.-X. Guo, C.-Y. Lee, S.-M.
Peng, J. Chem. Soc., Dalton Trans. (1995) 2961.
[19] C.W. Chan, T.F. Lai, C.M. Che, J. Chem. Soc., Dalton Trans. (1994)
895.
We gratefully acknowledge the Schweizerischer Nation-
¨
alfonds zur Forderung der wissenenschaftlichen Forschung,
the European Community (associated contract CEC
ERBCHRXCT 940492/A2) and the University of Basel for
financial support.
[20] S.M. Yang, K.K. Cheung, C.M. Che, J. Chem. Soc., Dalton Trans.
(1993) 3515.
[21] C.-W. Chan, C.-M. Che, M.-C. Cheng, Y. Wang, Inorg. Chem. 31
(1992) 4874.
[22] K.T. Potts, M. Keshavarz-K, F.S. Tham, H.D. Abruna, C.R. Arana,
Inorg. Chem. 32 (1993) 4422.
References
[1] E.C. Constable, Tetrahedron 48 (1992) 10013.
[23] J.-M. Lehn, J.-P. Sauvage, J. Simon, R. Ziessel, C. Piccinni-Leopardi,
G. Germain, J.-P. Declercq, M. Van Meerssche, Nouv. J. Chim. 7
(1983) 413.
[2] E.C. Constable, Adv. Inorg. Chem. Radiochem. 30 (1987) 69.
[3] E.C. Constable, Progr. Inorg. Chem. 34 (1989) 1.
[4] E.C. Constable, in: J.L. Atwood, J.E.D. Davies, D.D. MacNicol, F.
[24] J.-P. Gisselbrecht, M. Gross, J.-M. Lehn, J.-P. Sauvage, R. Ziessel, C.
Piccinni-Leopardi, J.M. Arrieta, G. Germain, M. Van Meerssche,
Nouv. J. Chim. 8 (1984) 661.
[25] F. Arnaud-Neu, M. Sanchez, M.-J. Schwing-Weill, New J. Chem. 10
(1986) 165.
[26] K.N. Lam, K.Y. Wong, S.M. Yang, C.M. Che, J. Chem. Soc., Dalton
Trans. (1995) 1103.
[27] A. Juris, R. Ziessel, Inorg. Chim. Acta 225 (1994) 251.
[28] F.H. Burstall, J. Chem. Soc. (1928) 1662.
[29] E.N. Maslen, C.L. Raston, A.H. White, J. Chem. Soc., Dalton Trans.
(1975) 323.
[30] W. Von Henke, S. Kremer, D. Reinen, Z. Anorg. Allg. Chem. 491
(1982) 124.
[31] C.-W. Chan, C.-M. Che, S.-M. Peng, Polyhedron 12 (1993) 2169.
[32] C.-M. Che, Y.-P. Wang, K.-S. Yeung, K.-Y. Wong, S.-M. Peng, J.
Chem. Soc., Dalton Trans. (1992) 2675.
¨
Vogtle (Eds.), Comprehensive Supramolecular Chemistry, vol. 9,
Pergamon Press, Oxford, 1996, p. 213 and references therein.
[5] C. Piguet, G. Bernardinelli, G. Hopfgartner, Chem. Rev. 97 (1997)
2005.
[6] E.C. Constable, D.R. Smith, The Polymeric Materials Encyclopedia,
CRC Press, Boca Raton, 1996, p. 4237.
[7] E.C. Constable, S.M. Elder, J.A. Healy, D.A. Tocher, J. Chem. Soc.,
Dalton Trans. (1990) 1669.
[8] E.C. Constable, S.M. Elder, D.A. Tocher, Polyhedron 11 (1992)
1337.
[9] E.C. Constable, M.J. Hannon, A. Martin, P.R. Raithby, D.A. Tocher,
Polyhedron 11 (1992) 2967.
[10] E.C. Constable, S.M. Elder, D.A. Tocher, Polyhedron 11 (1992)
2599.
[11] E.C. Constable, S.M. Elder, M.J. Hannon, A. Martin, P.R. Raithby,
D.A. Tocher, J. Chem. Soc., Dalton Trans. (1996) 2423.
[12] E.C. Constable, F.R. Heirtzler, M. Neuburger, M. Zehnder, J. Am.
Chem. Soc. 119 (1997) 5606.
[33] F. Calderazzo, L. Labella, F. Marchetti, J. Chem. Soc., Dalton Trans.
(1998) 1485.
[34] E.C. Constable, T. Kulke, G. Baum, D. Fenske, Inorg. Chem. Com-
mun. 1 (1998) 80.
[13] G. Baum, E.C. Constable, D. Fenske, T. Kulke, Chem. Commun.
(1997) 2043.
[35] S.-M. Yang, K.-K. Cheung, C.-M. Che, J. Chem. Soc., Dalton Trans.
(1993) 3515.
[14] E.C. Constable, S.M. Elder, J.A. Healy, M.D. Ward, D.A. Tocher, J.
Am. Chem. Soc. 112 (1990) 4590.
[36] E.C. Constable, Chem. Commun. (1997) 1073 and referencestherein.
[37] E.C. Constable, P. Harverson, Polyhedron (in press).
[15] E.C. Constable, F.R. Heirtzler, M. Neuburger, M. Zehnder, Supramol.
Chem. 5 (1995) 197.
Thursday Jan 20 11:56 AM
StyleTag -- Journal: POLY (Polyhedron) Article: 3276

34
E.C. Constable et al. / Polyhedron 19 (2000) 23–34
¨
F. Krohnke, Synthesis (1976) 1.
[38]
[39]
[43]
[44]
D.J. Watkin, J.R. Carruthers, P. Betteridge, CRYSTALS, Chemical
Crystallography Laboratory, Oxford, 1985.
E.C. Constable, M.J. Hannon, D.R. Smith, Tetrahedron Lett. 35
(1994) 6657.
N.A. Sorenson, E. Samuelsen, F.R. Oxaal, Acta Chem. Scand. 1
(1947) 458.
E.C. Constable, T. Kulke, M. Neuburger, M. Zehnder, New J. Chem.
21 (1997) 633.
J.R. Carruthers, D.J. Watkin, Acta Crystallogr., Sect. A 35 (1979)
698.
[40]
[41]
[45]
[46]
[47]
N. Walker, D. Stuart, Acta Crystallogr., Sect. A 39 (1983) 158.
E.C. Constable, P. Harverson, unpublished results.
E.C. Constable, T. Kulke, M. Neuburger, M. Zehnder, New J. Chem.
21 (1997) 1091.
[42] A. Altomare, G. Cascarano, G. Giacovazzo, A. Guagliardi, M.C.
Burla, G. Polidori, M. Camalli, J. Appl. Crystallogr. 27 (1994) 435.
Thursday Jan 20 11:56 AM
StyleTag -- Journal: POLY (Polyhedron) Article: 3276