Useful and essential structures can be made by self–assembly. In fact, life–forms were first made po — Organic Chemistry Chemistry Question
Self–assembly
Useful and essential structures can be made by self–assembly. In fact, life–forms were first made possible by the self–assembly of cell membranes about 4 billion years ago. Self–assembly is a fundamental principle that generates structural organization on all scales from molecules to galaxies. Self–assembly is defined as reversible processes in which pre–existing parts or disordered components of a pre–existing system form stable structures of well–defined patterns.
Some transition metal complexes can participate in the self–assembly. For example, a Ni complex with a long alkyl chain can be formed from many separate parts in the following reaction.
[VISUAL]
Predict the structure around the Ni(II) cation.
Model Answer
square planar
Determine whether A2+ is paramagnetic or not, using the d–orbital splitting pattern of Ni(II) in this structure.
Model Answer
Ni2+, d8, square planar, diamagnetic
Indicate the hydrophobic portion in A2+.
Model Answer
a long alkyl side chain: –C16H33.
Figure 18.1. The molecular structure for A2+ and the packing structure of A(ClO4)2 ⋅ H2O.
[VISUAL]
What is the driving force for such assembly? (Hint: Its ionic compound, A(ClO4)2⋅H2O, is found to float on the surface of water although its density is greater than 1.0 g cm-3.)
Model Answer
hydrophobicity due to the long alkyl chains
Metal complexes of TCNQ (7,7,8,8–tetracyano–p–quinodimethane) have been studied due to magnetic and electric conducting properties.
(TCNQ) = [VISUAL]
The infrared spectrum is diagnostic for the formal oxidation state and the coordinative status of the TCNQ molecules.
For TCNQ as pictured, which bond (among a – e) has the highest vibrational frequency?
Model Answer
bond a
Point out the bond(s) (among a – e) which might be shortened when TCNQ is reduced to form the radical anion.
Model Answer
bonds b and d are shortened upon reduction.
The TCNQ derivative of A2+ ([A2+(TCNQ)2](TCNQ)⋅(CH3COCH3)) also shows an interesting structural feature as shown in Figure 18–2.
Figure 18.2. The molecular structure for A2+ and the packing structure of [A2+(TCNQ)2](TCNQ⋅CH3COCH3)
[VISUAL]
What is the coordination number for atom Ni in the TCNQ derivative of A2+?
Model Answer
coordination number 6
In this structure, TCNQ molecules overlap one another. What is the driving force for such organization?
Model Answer
π – π stacking interactions