Compressed Jahn-Teller Octahedra and Spin Quintet-Triplet Switching in Coordinatively Elastic Manganese(III) Complexes

Complex assembly preferences and resultant spin state choice and Jahn-Teller distortion mode in twelve Mn(III) complexes of varying nuclearity with Schiff base chelate ligands of different sizes are compared. Mononuclear complexes Mn(5-F-sal2323)]OTf (1), [Mn(5-F-sal2323)]ClO4 (2) and [Mn(5-F-sal2323)]NO3, (3) with the 8-carbon R-Sal2323 chelate type show rare axial compression at room temperature and complexes (2) and (3) also show reversible thermal spin state switching from spin quintet to triplet states on cooling. The prevalence of atypical axial compression is further probed by single crystal diffraction studies on high spin mononuclear complexes (4)-(7) with the longer 9-carbon R-Sal2333 chelate series using [Mn(3-OEt-sal2333)]BF4, (4) [Mn(3,5-diOMe-sal2333)]BF4·0.5PrOH, (5), [Mn(5-F-sal2333)]BPh4, (6) and Mn(5-NO2-sal2333)]BPh4, (7) as examples. Ring closure of both the 8-carbon R-Sal2323 and longer 9-carbon R-Sal2333 ligands was also observed yielding a ligand with a 6-membered ring in the mononuclear complex [Mn(3-OMe,5-NO2-sal23336R)·0.07MeOH·0.93MeCN (8) in contrast to a protonated 5-membered ring in the dimeric complex [Mn2(5-Cl-sal2323H5R)2](ClO4)2·1.85EtOH·0.33MeCN, (9) with the R-Sal2323 chelate type. Finally comparison of the assembly modes of Mn(III) complexes of the 8-carbon R-Sal2323 and 9-carbon R-Sal2333 series with those of the shorter 7-carbon R-Sal2322 ligand series reveal that the mononuclear assembly mode is not favoured with the smaller chelate. Instead three dimeric or cluster complexes with rearranged ligands were recovered in low yield. The structures of these complexes [Mn2(5-NO2-sal23225R)2]·2BuOH, (10), [Mn2(3,5-diBr-sal23225R)(3,5-diBr-sal)3]·0.7EtOH·2.61MeCN, (11) and [Mn2Na(3-NO2,5-OMe-sal23225R)]ClO4·0.5MeCN (12) are reported and compared with examples with the longer chain chelate ligands.