Repetitively citing studies in a literature review
You should definitely go with Structure 2. It is far more helpful to you (that is, it forces you to engage more deeply with the literature) and your readers (that is, it gives them a more useful review of the literature).

The article that is probably the most seminal in my field (information systems) on literature-review methodology is mostly famous because they clearly addressed precisely this distinction. Webster and Watson (2002) argued that author-centric literature reviews (your Structure 1) are not very useful. They are simply an extended bibliography. (When you think of it, all that does is little more than summarize the abstracts of each article, which are already summaries of the articles.) They argued instead for what they called a concept-centric approach to reviewing the literature.

The concept-centric approach is not quite the same as what you describe in Structure 2: what you describe, I would call a topic-centric approach. Webster and Watson’s concept-centric approach identifies the theoretical concepts in each article and then presents them as the structure of the review. Your Structure 2 identifies common topics in each article. While not as useful for developing theory as the concept-centric approach (and maybe developing theory is not your goal at all), it is far more useful than the author-centric (or more accurately, article-centric) approach of your Structure 1.

Reference

Webster, Jane, and Richard T. Watson. Analyzing the past to prepare for the future: Writing a literature review. MIS quarterly (2002): xiii-xxiii.