Chiral Photomagnets Based on Copper(II) complexes of 1,2-Diaminocyclohexane and Octacyanidomolybdate(IV) Ions

Abstract

Chiral photomagnets compose a class of multifunctional molecule-based materials with light-induced alteration of magnetization and chiral properties. The rational design and synthesis of such assemblies is a challenge, and only few such systems are known. Herein, the remarkable octacyanide-bridged enantiomeric pair of 1-D chains [Cu­((R,R)-chxn)2]2[Mo­(CN)8]·H2O (1R) and [Cu­((S,S)-chxn)2]2[Mo­(CN)8]·H2O (1S) exhibiting enantiopure structural helicity, which results in optical activity in the 350–800 nm range as confirmed by natural circular dichroism (NCD) spectra, is reported. The photomagnetic effects of 1R, 1S, and 1rac result from the blue light excitation (436 nm) of the photomagnetically active octacyanidomolybdate­(IV) ions. In the excited state MoIV HS centers with S = 1 couple antiferromagnetically with the neighboring CuII centers with J CuMo values of −1.3, −1.0, and −1.1 cm–1 for 1R, 1S, and 1rac, respectively. The values of thermal relaxation energy barriers have been estimated as 142 and 356 K for 1R and 1S, being comparable with the energy range of the thermal bath. The value for 1rac reveals a significantly lower value of 75 K. On the basis of these results the value of g Mo HS has been estimated to be in the range 4.8–5.8.

Magnetic interactions controlled by light in the family of Fe(ii)–M(iv) (M = Mo, W, Nb) hybrid organic–inorganic frameworks

“…[18][19][20] The alternative approach to future magnetic memory devices is based on photo-switchable assemblies, where multiple magnetic states may be addressed with light. [21][22][23][24] Introduction of suitable building units into 1-D coordination polymers led to the discovery of photo-switchable chain compounds showing light-induced changes in the paramagnetic properties [25][26][27] and in some cases slow magnetic relaxation triggered by UV-vis irradiation. [28][29][30][31][32] Herein we demonstrate three analogous cyanido-bridged chains based on iron(II) and three different octacyanidometallates(IV), which are organized into a three-dimensional (3D) architecture by an organic linker molecule -4,4′-bipyridine dioxide (4,4′-bpdo): {[Fe II (µ-4,4′-bpdo)(H 2 O) 2 ] 2 [M IV (CN) 8 ]• 9H 2 O} n (M = Mo, W and Nb; Fe 2 Mo, Fe 2 W and Fe 2 Nb).…”

“…18–20 The alternative approach to future magnetic memory devices is based on photo-switchable assemblies, where multiple magnetic states may be addressed with light. 21–24 Introduction of suitable building units into 1-D coordination polymers led to the discovery of photo-switchable chain compounds showing light-induced changes in the paramagnetic properties 25–27 and in some cases slow magnetic relaxation triggered by UV-vis irradiation. 28–32…”

Experimental and theoretical insights into the photomagnetic effects in trinuclear and ionic Cu(ii)–Mo(iv) systems

“…Up to now, photomagnetic processes in Cu(II)-Mo(IV) systems have been considered in terms of two possible mechanisms: metal-to-metal charge transfer (MMCT): paramagnetic Cu II (S = 1/2)⋯Mo IV-LS (S = 0)⋯Cu II (S = 1/2) → ferromagnetic Cu I (S = 0)⋯[Mo V-LS -Cu II ](S total = 1), 27,[29][30][31]33,36,[38][39][40][41]43,44,[46][47][48][49][50][51][52][53][54][55] and a Light-Induced Excited Spin-State Trapping (LIESST) effect on the Mo(IV) centre: paramagnetic Cu II (S = 1/2) ⋯Mo IV-LS (S = 0)⋯Cu II (S = 1/2) → ferromagnetic [Cu II -Mo IV-HS -Cu II ](S total = 2). [27][28][29][31][32][33]35,37,42,45 The latter case may result from the photoinduced formation of an intermediate geometry between the ideal geometries of TDD-8 and SAPR-8 (Fig. 5) 32,35,60 or the photodissociation of the single cyanide leading to a reduction of the coordination number to 7.…”

“…[13][14][15][16][17][18][19][20][21][22][23][24] The greatest successes in developing photomagnetic materials were achieved for octacyanidometallate based systems, 25,26 in particular for copper(II)-molybdenum(IV) ones. 27 Furthermore, it was found that Cu II -Mo IV photomagnetic assemblies can be based on polynuclear molecules, [28][29][30][31][32][33][34][35][36][37][38][39][40][41] chains, 33,[42][43][44] layers 33,[45][46][47] and three-dimensional networks 33,[48][49][50][51][52][53][54][55] with at least one bridging cyanide per single copper(II) centre. Surprisingly, ionic systems with an isolated [Mo(CN) 8 ] 4− anion were not considered, assuming that the photomagnetic phenomenon in Cu II -Mo IV compounds originates from the light-induced MMCT mechanism.…”

Photoinduced magnetic hysteresis in a cyanide-bridged two-dimensional [Mn2W] coordination polymer

“…This is not only due to the variable dimensionalities of its architecture but also its characteristic photomagnetic behavior showing the singlet (S = 0) to triplet (S = 1) transition. [44][45][46][47][48][49][50][51][52][53][54][55][56] The photomagnetic action of octacyanotungstate(IV) is related entirely to itself in contrast to other photoinduced W-3d systems. Very recently, Pinkowicz and Mathonière et al found that light irradiation can induce the singlet to triplet transition in K 4 [Mo IV (CN) 8 ] accompanied by reversible dissociation/recombination of the Mo-CN bonds.…”