Polyamine Macrocycles Incorporating a Phenanthroline Unit: Their Synthesis, Basicity, and Cu(II) Coordination

Synthesis and characterization of the two new polyamine
macrocycles
2,5,8,11,14-pentaaza[15]-16,29-phenanthrolinophane (L1) and
8-methyl-8-aza-1(1,4),11(1,4)-dipiperazina[15]-16,29-phenanthrolinophane
(L2) are reported. Both ligands incorporate a 2,9-phenanthroline unit as
integral part of their cyclic structure. L1
contains
a pentaamine chain linking the 2,9-phenanthroline positions.
L2 contains two piperazine rings within the
macrocyclic framework. The basicity constants and the formation
constants of their complexes with Cu(II) have been
determined by potentiometric measurements in aqueous solution (298.1 K,
I = 0.1 mol dm-3). Both
L1 and L2
form mono- and binuclear complexes in aqueous solution. In the
[CuL1]2+ and
[CuL2]2+ complexes, the metal
ion is coordinated by the aromatic nitrogens and one or two nitrogens
adjacent to the phenanthroline moiety.
The remaining polyamine chain is not coordinated. These
results are confirmed by the crystal structure of
[H2L2Cu(NCS)2](ClO4)2·3H2O
(space group P1̄, a =
9.770(10) Å, b = 12.027(5) Å, c =
18.006(7) Å, α = 106.87(3)°,
β = 90.22(8)°, γ = 104.48(8)°, V =
1954(2) Å3, Z = 2, R =
0.0971, wR2 = 0.2553). The metal ion is
five-coordinated by the phenanthroline nitrogens, by one adjacent amine nitrogen,
and by two isothiocyanate ions. The
noncoordinated polyamine chain can bind a second Cu(II) ion in
aqueous solution, giving binuclear
[Cu2L]4+
complexes (L = L1 or L2). In
the case of L2, the formation of the binuclear complex leads
to piperazine inversion
from the chair to the boat conformation, as shown by the crystal
structure of
[Cu2L2(μ-OH)(H2O)(ClO4)](ClO4)2·2H2O (space group
P21/a, a =
19.573(2) Å, b = 9.320(10) Å, c =
21.552(2) Å, β = 108.556(9)°, V =
3727(4) Å3, Z = 4, R =
0.0835, wR2 = 0.2759). This structure displays a
piperazine ring unusually bridging
two metal cations.