Room-temperature thermally induced relaxation effect in a two-dimensional cyano-bridged Cu-Mo bimetal assembly and thermodynamic analysis of the relaxation process

Abstract

We observed a photo-switching effect in [CuII(1,4,8,11-tetraazacyclodecane)]2[MoIV(CN)8]·10H2O by irradiation with 410-nm light around room temperature using infrared spectroscopy. This photo-switching is caused by the photo-induced charge transfer from MoIV to CuII. The photo-induced phase thermally relaxed to the initial phase with a half-life time of 2.7 × 101, 6.9 ×101, and 1.7 × 102 s at 293, 283, and 273 K, respectively. The relaxation process was analyzedusing Hauser's equation, k =k0exp[−(Ea +Ea*γ) /kBT], where k is the rate constant of relaxation, k0 is the frequency factor, Eais the activation energy,Ea* is the additional activation energy due to the cooperativity,and γ is the fraction of the photo-induced phase. k0, Ea, and Ea* were evaluated as 1.28 × 107 ± 2.6 s−1, 4002 ± 188 cm−1, and 546 ± 318 cm−1, respectively. The value of Ea is much larger than that of the relaxation process for the typical light-induced spin crossover effect (Ea ≈1000 cm−1). Room-temperature photo-switching is an important issue in the field of optical functional materials. The present system is useful for the demonstration of high-temperature photo-switching material.

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.…”

“…[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.…”

Neutral Low-Dimensional Assemblies of a Mn(III) Schiff Base Complex and Octacyanotungstate(V): Synthesis, Characterization, and Magnetic Properties

“…Some of them are 1D polymers [53][54][55][56]; others possess layered [57][58][59][60][61][62][63] or 3D network structures [64][65][66][67][68]. The paramagnetic cyanotungstate(V) tectones have been used to build discrete molecules [69][70][71], chains [53][54][55][56], 2D [57] and 3D networks [64][65][66][67][68], and some of them have displayed variable magnetic properties such as high ordering temperatures [72], photo-induced magnetism [73,74], SMMs [75], and SCMs [17,54,55].…”

Neutral Low-Dimensional Assemblies of a Mn(III) Schiff Base Complex and Octacyanotungstate(V): Synthesis, Characterization and Magnetic Properties

“…Some of them are 1D polymers [53][54][55][56]; others possess layered [57][58][59][60][61][62][63] or 3D network structure [64][65][66][67][68]. The paramagnetic cyanotungstate(V) tectones have been used to build discrete molecules [69][70][71], chains [53][54][55][56], 2D [57] and 3D networks [64][65][66][67][68] and some of them have displayed variable magnetic properties such as high ordering temperatures [72], photo-induced magnetism [73,74], SMMs [75], and SCMs [17,54,55].…”