Systematic　substituent　variations　on　amidinate　ligands　bring　delicate　changes　of　CrN4　coordination　in　a　family　of　chromium(II)　complexes　with　the　common　formula　of　Cr(RNC(CH3)NR)2,　where　R　=　iPr　(1),　Cy　(2),　Dipp　(Dipp　=　2,　6-diisopropylphenyl)　(3),　and　tBu　(4).　With　the　largest　substituent　group,　4　shows　the　largest　distortion　of　the　N4　coordination　geometry　from　square-planar　to　seesaw　shape,　which　leads　to　its　field-induced　single-molecule　magnet　(SMM)　behavior.　This　is　an　indication　that　4　has　the　strongest　axial　magnetic　anisotropy　and/or　optimized　magnetic　relaxation　process.　Combined　with　high-frequency/field　electron　paramagnetic　resonance　(HF-EPR)　experiments　and　ab　initio　calculations,　we　deduce　that　the　smallest　energy　gap　between　ground　4ψ0　and　the　first　excited　4ψ1　orbitals　in　4　contributes　the　most　to　its　strongest　magnetic　anisotropy.　Moreover,　the　lower　E　value　of　4　ensures　its　being　a　field-induced　SMM.　Specifically,　the　D　and　E　values　were　found　to　be　correlated　to　the　dihedral　angle　between　the　ΔN1CrN2　and　ΔN3CrN4　triangles,　indicating　that　distortion　from　ideal　square-planar　geometry　to　the　seesaw　help　increase　axial　magnetic　anisotropy　and　suppress　the　transversal　part.　Thus,　the　study　on　this　system　not　only　expands　the　family　of　Cr(II)-based　SMMs　but　also　contributes　to　a　deeper　understanding　of　magneto-structural　correlation　in　four-coordinate　Cr(II)　SMMs.　©　2021　American　Chemical　Society.　All　rights　reserved.