Dear J.W J.W many thanks for sharing this interesting technical question with other RG members. In fact, the compound [NH2-CH+-NH2][Mn(HCOO)3] (FMDMn) has been reported in the literature to form "light pink crystals":

Perovskite Metal Formate Framework of [NH2‐CH+‐NH2]Mn(HCOO)3]: Phase Transition, Magnetic, Dielectric, and Phonon Properties

Article Perovskite Metal Formate Framework of [NH2-CH+-NH2]Mn(HCOO)(...

Pink is the typical color of divalent manganese compounds. Of course it is difficult to judge from the outside what perhaps went wrong in your experiment. The greenish-brown color of your product indicates that some oxidation has taken place. For example, the product could be contamined with small amounts of brown MnO2. Thus it might be worth a try to charge the Teflon-lined microwave autoclave with the starting materials under nitrogen as protective gas to avoid oxidation. Also make sure that you use very pure starting materials in the exact amounts as described in the literature.

Good luck with your experiments and best wishes, Frank Edelmann

Dear J.W J.W please let me add a few minor remarks:

1. I assume that the "yellow-white powder and crystal" which you observed in your experiment are unreacted starting materials. If you used cyclobutane-1,1′-dicarboxylic acid as starting material as described in the original synthetic procedure, chances are that this will form some white / colorless crystals after the reaction. Cyclobutane-1,1′-dicarboxylic acid is known to crystallize rather easily and form nice colorless crystals.

2. Just one personal advice: You will certainly get more expert answers to your interesting question when you avoid or explain rather special and uncommon abbreviations such as FMDMn. I assume that even many inorganic chemists are not familiar with this term.

Good luck with your work!