Crystal Engineering Applied to Modulate the Structure
and Magnetic Properties of Oxamate Complexes Containing the [Cu(bpca)]<sup>+</sup> Cation
Willian
X. C. Oliveira
Carlos B. Pinheiro
Marinez M. da Costa
Ana P. S. Fontes
Wallace C. Nunes
Francesc Lloret
Miguel Julve
Cynthia L. M. Pereira
10.1021/acs.cgd.6b00613.s001
https://acs.figshare.com/articles/journal_contribution/Crystal_Engineering_Applied_to_Modulate_the_Structure_and_Magnetic_Properties_of_Oxamate_Complexes_Containing_the_Cu_bpca_sup_sup_Cation/3463223
This
work deals with the crystal engineering features of four related
copper(II)-based compounds with formulas {[{Cu(bpca)}<sub>2</sub>(H<sub>2</sub>ppba)]·1.33DMF·0.66DMSO}<sub><i>n</i></sub> (<b>2</b>), [{Cu(bpca)(H<sub>2</sub>O)}<sub>2</sub>(H<sub>2</sub>ppba)] (<b>3</b>), [{Cu(bpca)}<sub>2</sub>(H<sub>2</sub>ppba)]·DMSO (<b>4</b>), and
[{Cu(bpca)}<sub>2</sub>(H<sub>2</sub>ppba)]·6H<sub>2</sub>O (<b>5</b>) [H<sub>4</sub>ppba = <i>N</i>,<i>N</i>′-1,4-phenylenebis(oxamic acid) and Hbpca
= bis(2-pyridylcarbonyl)amide] and how their distinct molecular and
crystal structures translate into their different magnetic properties. <b>2</b> and <b>3</b> were obtained through the hydrolytic
reaction of the double-stranded oxamato-based dipalladium(II) paracyclophane
precursor of formula [{K<sub>4</sub>(H<sub>2</sub>O)<sub>2</sub>}{Pd<sub>2</sub>(ppba)<sub>2</sub>}] (<b>1</b>) with the mononuclear
copper(II) complex [Cu(bpca)(H<sub>2</sub>O)<sub>2</sub>]<sup>+</sup>, either in a water–DMSO–DMF solvent mixture
or in water, respectively. The straightforward reaction of the neutral
H<sub>4</sub>ppba molecule with [Cu(bpca)(H<sub>2</sub>O)<sub>2</sub>]<sup>+</sup> in a water–DMSO mixture afforded compound <b>4</b>, whereas compound <b>5</b> resulted from the reaction
between the copper(II) complex and the K<sub>2</sub>ppba salt in water.
The [Pd<sub>2</sub>(ppba)<sub>2</sub>]<sup>4–</sup> tetraanionic
unit which is present in <b>1</b> has a [3,3] metallacyclophane-type
motif connected by two N–Pd–N bonds. This entity acts
as a ligand toward partially hydrated potassium(I) cations through
its outer oxamate oxygens leading to a neutral three-dimensional network.
The structure of <b>2</b> consists of neutral chains made up
of double oxo(carboxylate-oxamate)-bridged di[{bis(2-pyridylcarbonyl)amidate}copper(II)]
units are which connected by the extended H<sub>2</sub>ppba<sup>2–</sup> ligand, each of its oxamate fragments adopting a bidentate/outer
monodentate coordination mode. Compounds <b>2</b>–<b>5</b> are neutral and centrosymmetric dicopper(II) complexes which
have in common the presence of peripheral bpca ligands and H<sub>2</sub>ppba<sup>2–</sup> as a bridge with each of its monoprotonated
oxamate groups exhibiting rare monodentate (<b>3</b>) and bis-bidentate
(<b>4</b> and <b>5</b>) coordination modes. Compounds <b>2</b>, <b>4</b>, and <b>5</b> share the same basic
[{Cu(bpca)}<sub>2</sub>(H<sub>2</sub>ppba)] unit, but besides
the difference in the cocrystallization solvent molecules and synthetic
strategies, they feature very different crystal structures. To better
understand the role of palladium(II) ions in the formation of <b>2</b> and <b>3</b>, some studies were carried out using
different mixtures of solvents such as water, DMSO, and DMF which
revealed a major importance of DMF in the formation of <b>2</b> and the dependence on the palladium(II) ions in the formation of <b>3</b>. A reaction pathway leading to the formation of <b>2</b> and <b>3</b> is then proposed. The variable-temperature (2.0–300
K) magnetic susceptibility measurements of <b>2</b>, <b>4</b>, and <b>5</b> revealed the occurrence of weak ferro- [<i>J</i> = +0.70 cm<sup>–1</sup> (<b>2</b>)] and antiferromagnetic
interactions [<i>J</i> = −0.90 (<b>4</b>) and
−0.79 cm<sup>–1</sup> (<b>5</b>)], the spin Hamiltonian
being defined as <b>H</b> = −<i>J</i><b>S</b><sub>1</sub>·<b>S</b><sub>2</sub>. The different
nature and strength of the magnetic coupling along this unique series
of compounds are discussed in the light of the structural data, and
they are compared with those of related dicopper(II) systems.
2016-06-13 00:00:00
K 2 ppba salt
H 4 ppba molecule
Oxamate Complexes Containing
H 4 ppba
DMF
crystal Engineering Applied
H 2 O
Cu
crystal structures
crystal engineering features
monoprotonated oxamate groups
DMSO