Unraveling Concomitant Packing Polymorphism in Metallosupramolecular Polymers

Abstract

The phenomenon of polymorphism is ubiquitous in biological systems and has also been observed in various types of self-assembled materials in solution and in the solid state. In the field of supramolecular polymers, different kinetic vs thermodynamic self-assembled species may exist in competition, a phenomenon termed as pathway complexity. In these examples, the transient kinetic species often has a very short lifetime and rapidly converts into the thermodynamic product. In this work, we report a π-conjugated Pt­(II) complex 1 that self-assembles in nonpolar medium into two competing supramolecular polymers with distinct molecular packing (slipped (A) vs pseudoparallel (B)) that do not interconvert over time in a period of at least six months at room temperature. Precise control of temperature, concentration, and cooling rate enabled us to ascertain the stability conditions of both species through a phase diagram. Extensive experimental studies and theoretical calculations allowed us to elucidate the packing modes of both supramolecular polymorphs A and B, which are stabilized by unconventional N–H···Cl–Pt and N–H···O-alkyl interactions, respectively. Under a controlled set of conditions of cooling rate and concentration, both polymorphs can be isolated concomitantly in the same solution without interconversion. Only if A is annealed at high temperature for prolonged time, does a slow transformation into B then take place via monomer formation. Our system, which in many respects bears close resemblance to concomitant packing polymorphism in crystals, should help bridge the gap between crystal engineering and supramolecular polymerization.

Revising Complex Supramolecular Polymerization under Kinetic and Thermodynamic Control

“…Recently,o ur groups reported an example of as upramolecular polymer that exists as two concomitant, stable, polymorphic structures.V T-UV/Vis and AFM experiments showed that OPE-based Pt II complex 10 forms two competing aggregates in MCH depending on the cooling rate and concentration (species A and B in Figure 10 b). [45] Polymorph A with as lipped molecular arrangement stabilized by N À H···Cl À Pt interactions is obtained at high rates (2 Kmin À1 ) through an isodesmic mechanism. Thecooperative formation of B,c haracterized by ap seudoparallel stacking driven by NÀH···O alkoxy hydrogen bonding,ispreferred at lower cooling rates (0.1 Kmin À1 ).…”

Revision komplexer supramolekularer Polymerisation unter kinetischer und thermodynamischer Kontrolle

“…Vor kurzem berichteten unsere Gruppen über ein Beispiel eines supramolekularen Polymers, das als zwei zeitgleich stabile, polymorphe Strukturen existiert. VT‐UV/Vis‐ und AFM‐Experimente zeigten, dass der OPE‐basierte Pt II ‐Komplex 10 in Abhängigkeit von Kühlungsrate und Konzentration zwei kompetitive Aggregate in MCH bildet (Spezies A, B in Abbildung b) . Polymorph A , das durch N‐H⋅⋅⋅Cl‐Pt Wechselwirkungen stabilisiert wird und eine verschobene molekulare Anordnung einnimmt, wird bei schnellen Kühlraten (2 K min −1 ) in einen isodesmischen Mechanismus erhalten.…”

“…VT-UV/Vis-und AFM-Experimente zeigten, dass der OPE-basierte Pt II -Komplex 10 in Abhängigkeit von Kühlungsrate und Konzentration zwei kompetitive Aggregate in MCH bildet (Spezies A, Bi nA bbildung 10 b). [45] Polymorph A,d as durch N-H···Cl-Pt Wechselwirkungen stabilisiert wird und eine verschobene molekulare Anordnung einnimmt, wird bei schnellen Kühlraten (2 Kmin À1 )i ne inen isodesmischen Mechanismus erhalten. Die kooperative Bildung von B,g ekennzeichnet durch eine pseudoparallele molekulare Anordnung, die durch N-H···O alkoxy Bindungen stabilisiert wird, wird bei langsameren Raten (0.…”

Controlled Supramolecular Polymerization of d8 Metal Complexes through Pathway Complexity and Seeded Growth

“…Depending on the cooling rate and concentration, 13 self-assembles in methylcyclohexane (MCH) into two highly stable competing supramolecular polymorphs (A and B) with distinct molecular packing (slipped vs. pseudo-parallel, respectively). [44] The formation of two distinct supramolecular polymers was monitored by VT UV/Vis spectroscopy (Figure 9b-d). The polymorph A is preferentially obtained upon cooling hot monomer solutions of 13 at relatively fast cooling rates of 2 K min À 1 .…”

“…The red spectra correspond to the monomer species, which converts into aggregate type A (cyan), type B (royal blue), or a mixture of A and B (green) on cooling. Reproduced from ref[44] with permission. Copyright 2019, American Chemical Society.…”