I took the models from: https://pdb101.rcsb.org/learn/3d-printing/3d-print-hemoglobin

and sliced it in two parts. Then I added four holes (I modelled the holes for 10x2mm magnets but I used 3dprinted pins).

The original Parts are also here if you like to use them instead. I didnt print the heme molecule and so I dont know if it will fit. Use some wool to build your own heme molecules like me, if you dont want to printe the heme.

The pins might be to big (little tolerance). Its just a cylinder and you can scale it to a smaller size.

From Wikipedia:

Hemoglobin, (haemoglobin BrE) (from the Greek word αἷμα, haîma 'blood' + Latin globus 'ball, sphere' + -in) (/ˌhiːməˈɡloʊbɪn, ˈhɛmoʊˌ-/), abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein in red blood cells (erythrocytes) of almost all vertebrates (the exception being the fish family Channichthyidae) as well as the tissues of some invertebrates. Hemoglobin in blood carries oxygen from the respiratory organs (e.g. lungs or gills) to the rest of the body (i.e. tissues). There it releases the oxygen to permit aerobic respiration to provide energy to power functions of an organism in the process called metabolism. A healthy individual human has 12 to 20 grams of hemoglobin in every 100 mL of blood.