Structural Diversity of Mn(II) Complexes with Acetylene Dicarboxylate and Hexadentate Ancillary Ligands under Ambient Conditions: Effect of Methylene Chain Length on Coordination Architectures

For
Mn­(II)-adc (adc = acetylene dicarboxylate) chemistry, diversity
of product formation is demonstrated with five similar hexadentate
polypyridyl ancillary ligands differing in methylene chain lengths
between the alkyl nitrogens, such as tpen (N,N,N′,N′-tetrakis-(2-pyridylmethyl)-1,2-diaminoethane),
1,2-tppn (N,N,N′,N′-tetrakis-(2-pyridylmethyl)-1,2-diaminopropane),
tppn (N,N,N′,N′-tetrakis-(2-pyridylmethyl)-1,3-diaminopropane),
tpbn (N,N′,N″,N‴-tetrakis-(2-pyridylmethyl)-1,4-diaminobutane),
and tppen (N,N′,N″,N‴-tetrakis-(2-pyridylmethyl)-1,5-diaminopentane).
Five new compounds, [Mn2(adc)2(tpbn)­(H2O)2]·2­(solvent)}n (solvent
= H2O, 1a; solvent = CH3OH, 1b), [Mn2(tppn)­(H2O)6]­(adc)2·3H2O (2), [Mn2(adc)­(1,2-tppn)2]­(ClO4)2·2­(solvent) (solvent =
H2O, 3a; solvent = CH3CN, 3b), [Mn2(adc)­(tpen)2]­(ClO4)2·2­(solvent) (solvent = H2O, 4a; solvent = CH3CN, 4b), and {[Mn2(adc)­(tppen)­(H2O)4]­(adc)·4H2O}n (5), have been isolated
in good yields from the self-assembly reactions of raw materials at
ambient conditions and structurally characterized by elemental analysis,
IR and Raman spectroscopy, ESI mass spectrometry, single crystal and
powder X-ray diffraction, and thermogravimetric analysis. Compound 1b with hexacoordinated Mn­(II) centers is a three-dimensional
(3D) metal–organic coordination network (MOCN) held together
by strong hydrogen bonding and π–π interactions.
Compound 2 with hexacoordinated Mn­(II) centers is a 3D
supramolecular assembly comprised of Mn2(tppn)­(H2O)6 dinuclear subunits, lattice water molecules, and adc
anions through strong hydrogen bonding interactions. On the other
hand, compounds 3b and 4b are the first
examples of heptacoordinated Mn­(II) complexes where the two Mn­(II)
centers are bridged by a dicarboxylate. Compound 5 is
a one-dimensional coordination polymer comprised of the Mn2(tppen)­(H2O)4 dinuclear subunits and the adc
group that is further connected via both hydrogen bonding and π–π
interactions. This is a rare example of having adc as a linker and
a counteranion in the same compound.