The molecular and supramolecular aspects in mononuclear manganese(iii) Schiff-base spin crossover complexes

Abstract

Manganese(iii) hexadentate Schiff base complexes ([Mn(sal-N-1,5,8,12)]Y·S, Y = AsF (1); Y = SbF (2); Y = NO, S = CHOH (3) and Y = Cl (4)) have been investigated to determine the impact of anion effects, intramolecular ligand distortions, and intermolecular supramolecular structures on the spin crossover (SCO) behavior. The crystal structure of [Mn(sal-N-1,5,8,12)]PF, a complex known to exhibit an abrupt SCO behavior with an 8 K hysteresis window, reveals that this complex has a temperature-dependent anion order-disorder transition that disrupts the hydrogen-bonding chain upon SCO, indicating that hydrogen bonds between cations and anions greatly influence the magnetic properties. The SCO in 1 is mediated by intermolecular hydrogen-bonding interactions. The subtle balance of these hydrogen bonds induces a cooperative SCO process with a hysteresis width of 18 K, which is the largest one reported in the d SCO chemistry. For 2, crystal structural analysis indicates that changing the anion from AsF to SbF led to close stackings between phenyl groups from ligands. These stackings preclude the spin transition of the [Mn(sal-N-1,5,8,12)] cations. With NO and Cl as counterions, the [Mn(sal-N-1,5,8,12)] cations are arranged more loosely and exhibit gradual SCO in the temperature range of 300-100 K. Careful evaluation of the supramolecular structures of these complexes and similar complexes reported previously revealed strong correlation between the supramolecular packing forces and their magnetic properties.

The First Conducting Spin‐Crossover Compound Combining a MnIII Cation Complex with Electroactive TCNQ Demonstrating an Abrupt Spin Transition with a Hysteresis of 50 K

“…This means that the spin‐state transition should be associated with the occupation/deoccupation of the d orbital belonging to the e g orbital. In turn, this should lead to a decrease in the basal Mn−N bond lengths on going from the HS state to the LS state, as is observed in the case of compound I (Figure and Table ) and other similar Mn III complexes described in the literature . Without thermal expansion effects, the average displacement over all six donor atoms upon spin crossover in I is 0.045, which is in line with the expected trend upon transition to S =1 in d 4 complexes …”

“…Unlike I , complex II , which is isomorphic with I , evidences no spin‐crossover phenomena. It is known that supramolecular aspects in mononuclear Mn III SCO complexes associated with intermolecular hydrogen bonding and π–π stacking interactions between phenyl groups in the ligands greatly influence the magnetic properties of these compounds . The wide hysteretic profile of the spin crossover in I indicates the cooperative behavior of the magnetic centers that may occur as a result of a subtle balance of the hydrogen bonds between cations and cations and anions in the crystals of I .…”

“…This gives rise to a marked Jahn–Teller distortion (axial compression of Mn−O bonds), which has a dramatic effect on the spin state of the Mn III complex and as a result promotes thermal SCO . Current research on this class of Mn III SCO compounds is aimed at tuning the Mn III spin state by varying the substituents on the phenolate ring, the anion, and the co‐crystallized solvent molecules . However, it should be noted that the vast majority of Mn III SCO complexes with the ligand L and its derivatives show a gradual and often incomplete SCO.…”

“…In the last decade,h exacoordinated (N 4 (O À ) 2 )M n III cation complexes with the sal-N-1,5,8,12 Schiff-base ligand L (Scheme 1) andi ts derivativesh ave been actively studied as SCO systems. [11][12][13][14][15][16][17][18][19][20][21] This ligand is ap roduct of the condensation reactionb etween salicylaldehyde and af lexible N,N'-bis(3-aminopropyl)ethylenediamine.…”

“…[11,12,16] Current research on this class of Mn III SCO compounds is aimed at tuning the Mn III spin state by varying the substituents on the phenolate ring, the anion,a nd the co-crystallized solvent molecules. [11][12][13][14][15][16][17][18][19][20][21] However,i ts hould be noted that the vast majority of Mn III SCO complexes with the ligand La nd its derivatives show ag radual and often incomplete SCO. To the best of our knowledge,o nly three manganese complexes are known, and thesee xhibit abrupt SCO behavior with hysteresis windows of 8, 14, and 18 K. [15,19,21] SCO systems with wide hysteresisl oops attract considerable attention,b ecause they have great potentialf or practical applications in memory devices.…”