Supramolecular Assembly of Organophosphonate Diesters
Using Paddle-Wheel Complexes: First Examples in Porphyrin Series
- Publication date
- Publisher
Abstract
The reactions of dicopper tetrapivalate
complex Cu<sub>2</sub>(μ-OOC-<i>t-</i>Bu)<sub>4</sub>(NCMe)<sub>2</sub> (<b>1</b>) with triphenylphosphine
oxide and diethyl phosphite allow paddle-wheel
(PW) copper(II) complexes with phosphorus-containing axial ligands
(<b>2</b>, <b>3</b>) to be obtained. When <i>meso</i>-bis(diethoxyphosphoryl)porphyrins <b>4M</b> were employed
in this ligand exchange reaction, a series of one-dimensional (1D)
homo- and heterometallic coordination polymers <b>5M</b> composed
of PW subunits and organophosphonate diesters were prepared and characterized
by means of single crystal X-ray analysis. Planar porphyrinate <b>4Pd</b> and nonplanar metalloporphyrinates <b>4Cu</b> and <b>4Ni</b> proved to be appropriate molecular structural blocks for
assembly of coordination polymers. The structural parameters of the
tetrapyrrolic macrocycles incorporated into the polymer chain are
determined by the nature of the metal center of the porphyrin moiety.
While the geometry of palladium(II) and nickel(II) porphyrinates <b>4Pd</b> and <b>4Ni</b> does not change significantly in
the polymer chain, saddle-shaped Cu(II) porphyrinate <b>4Cu</b> exhibits a nearly planar core configuration, being coordinated to
the copper centers of PW fragments by two peripheral phosphoryl groups
in the polymer chain. The geometry of the tetrapyrrolic core is a
key parameter influencing the structural properties of the polymeric
materials. For <b>5Pd</b> and for isostructural <b>5Cu</b>, all metal centers of the polymeric chain are aligned. The planar
macrocycles of adjacent chains are parallel and are shifted one to
another in such a way that the angle between the Pd···P
and Pd···Pd directions is 40.4°, and the distance
between the nearest palladium(II) atoms of neighboring chains is 11.668
Å. There is no free volume in these crystals. In the crystals
of <b>5Ni</b>, formed by nonplanar porphyrinates, only copper
atoms of the PW pivalate moiety are located in one plane, and zigzag
chains are formed so that two adjacent tetrapyrrolic macrocycles are
located in alternating positions with respect to this plane, the nickel
atoms being displaced from this plane by 1.548 Å. This arrangement
naturally leads to the formation of regular pores. The resulting channels
have an effective cross-section of about 10 × 12 Å and represent
ca. 18% of the volume of the crystal. The exchange reaction between
the free-base porphyrin <b>4H</b><sub><b>2</b></sub> and
an excess of copper(II) pivalate complex <b>1</b> is accompanied
by the metalation of the porphyrin core affording the polymer <b>5Cu</b>. Moreover, self-assembly of metalloporphyrinate <b>4Zn</b> is observed under studied experimental conditions, which
interferes with the formation of the target mixed coordination polymers
