Peer review of: Complex k-uniform tilings by a simple bitopic precursor self-assembled on Ag(001) surface (2020)

Reviewers' comments: 

Reviewer #1 (Remarks to the Author): 

Čechal et al used STM to study molecular assembly of 4,4’-biphenyl dicarboxylic acid (BDA) on a Ag(100) 
surface. Depending on the chemical states, i.e., step-wise deprotonation of the carboxylic groups, BDA 
molecules form different structures. The authors ascribed these structures as k-uniform tilings. 

In reviewer's opinion, however,this claim is over-stated. In standard language of the 2D molecular 
assembly community, what they report is simply close-packed molecular organizations stabilized by 
inter-molecular hydrogen bonds, which is a phenomenon well-studied for 20 years. The step-wise 
deprotonation induced structure transformation has also been reported previously. The reviewer does 
not see a genuine relationship between the data and the interpretation which is in the framework of 
tiling. Thus the significance of this work is in doubt. In this regard, the reviewer cannot support its 
publication in NC. 

Reviewer #2 (Remarks to the Author): 

The authors report the on-surface design of complex k-uniform tilings by exploiting carboxylic ditopic 
species on Ag(001) and decarboxylation through thermal annealing. 

They observe the formation of three different k-tilings going from rgular to 2-uniform to finally 3-
uniform tiling. 

I like the manuscript, it is well written and the results are sound. 

However, the authors claim the presence of three distinct carboxylic species (2H-BDA, 1H-BDA or 0H-
BDA), depending on conditions of annealing, without providing evidence by XPS or STS. Thus I will not 
recommend publication till such an evidence is provided. 



Reviewer #3 (Remarks to the Author): 

The paper proposes that the supramolecular assemblies formed by 4,4’-biphenyl dicarboxylic acid (BDA) 
and the carboxylated BDA on Ag(001) enable expression of complex k-uniform tilings. Namely, 2-
uniform tiling was realized by 1:1 mixture of partially carboxylated BDA (1H-BDA) and fully carboxylated 
BDA (0H-BDA), and 3-uniform tiling was realized by 1:2:1 mixture of pristine, 1H-, and 0H-BDA 
molecules. The observed long-range ordered molecular phase were attributed to the controlled 
carboxylation reaction and the distinct intermolecular binding between BDA. Overall the manuscript is 
well written with a persuasive model. I would like to recommend its publication if the authors could 
further clarify the following issues. 

1.I believe the observed complex tilings are resulted from the combination of BDA and underlying 
Ag(001) substrate. BDA has been widely studied molecule and so is carboxylic acid group, what is their 
unique role in the presented tiling? What is the general applicability of the self-assembly criteria 
illustrated by BDA? 
2.The XPS spectra should be more careful explained. Are there adatoms incorporated with carboxylated 
BDA in the self-assembly? 
3.I would like to ask for more details about LEED pattern and its simulation. How is the adsorption site 
determined in the calculation? 
4.Apparently, different rows of BDA undergo different carboxylate reaction in 2U-and 3U- phases, i.e. 
partial versus full carboxylation. This is intriguing and not explained. 
5.The 2U-and 3U- phases are both commensurate with the substrate, therefore a random sequence of 
these two phases in the assembly is expected. It is not possible to obtain a pure phase using BDA or its 
carboxylated derivatives. The implication of molecular self-assembly in complex k-uniform tilings is 
arguable. 



Reviewer #4 (Remarks to the Author): 

The authors report an investigation of fabricating complex k-uniform tilings by utilizing a simple bitopic 
molecular precursor (4,4’-biphenyl dicarboxylic acid, BDA) on Ag(001) surface. Through the controlled 
chemical transformation of the precursor, long-range ordered structures exhibiting 2-uniform and 3-
uniform tilings have been achieved. The structures of those tilings are well studied with STM, LEEM and 
XPS. The formation routines of those tilings are proposed based on above experiments. The manuscript 
is nicely written and the conclusions supported by the experiments and analyses. 

However, the deprotonation of the carboxylic acid groups, which results in different self-assembly 
structures, has been used and studied in the on-surface construction of supramolecular structures. 
Moreover, there is a similar supramolecular self-assembly using the same precursor has been reported 
previously (ref 44). In comparison with previous and recent reported molecular tilings on surfaces 
(ref25, 26), the analysis of the k-uniform tilings appears in a preliminary status, and the novelty of this 
work do not merit consideration in the high standards of Nature Communications. 

So, I cannot recommend the publication of the present submission in Nature Communications.