Crown-linked dipyridylamino-triazine ligands and their spin-crossover iron(II) derivatives: magnetism, photomagnetism and cooperativity.
The syntheses, crystallography and magnetic properties of a series of compounds of formula trans-[Fe(II)(L(1))2(NCX)2] (X = S, Se, BH3 (1-3)), cis-[Fe(II)(L(2))(NCX)2]·CH2Cl2 (X = S, Se, BH3 (4-6)) and trans-[Fe(II)(L(3))(NCX)2]n (X = S, Se (7-8)) are described (L(1) = 6-chloro-N(2),N(2)-diethyl-N(4),N(4)-di(pyridin-2-yl)-1,3,5-triazine-2,4-diamine, L(2) = 6,6'-(1,4,10,13-tetraoxa-7,16-diazacyclooctadecane-7,16-diyl)bis(N(2),N(2)-diethyl-N(4),N(4)-di(pyridin-2-yl)-1,3,5-triazine-2,4-diamine, L(3) = 6,6'-(1,4,10,13-tetraoxa-7,16-diazacyclooctadecane-7,16-diyl)bis(N(2),N(2),N(4),N(4)-tetra(pyridin-2-yl)-1,3,5-triazine-2,4-diamine)). The magnetostructural properties of 1-8 have been probed in detail by variable temperature magnetic measurements and crystallographic methods. 1-6 display mononuclear structures while 7 and 8 form 1-D chain structures. Complexes 4-6 have the potential to form 1D-chains via L(2) bridging, but instead form mononuclear complexes. Magnetic studies show that complexes 1, 2, and 4 remain in the high-spin (HS) state at all temperatures. An aged, dry, powdered sample of 3 gives an abrupt HS to LS transition (T1/2 = 200 K), while a freshly prepared, powdered sample of 3·1.5H2O displays thermal hysteresis (Δ = 7 K). Complexes 5, 6 and 7 undergo a gradual spin transition with T1/2 values of 100 K, 150 K and 130 K, respectively. Cooperativity parameters are compared, with 3 showing cooperativity (positive C) and 5 and 6 showing anticooperativity. Photomagnetic LIESST (light induced excited spin state trapping) studies were performed on complexes 5 and 6 and reveal T(LIESST) values lower than 60 K. An attempt has been made to understand the electronic structure of complex 3 and its cooperativity behaviour using density functional methods, the calculations reproducing the sign and, in part, the magnitude of the cooperativity.
School of Chemistry, Building 23, Monash University, Clayton, Victoria 3800, Australia. keith.murray@monash.edu.
Hayley S
HS
Scott
Tamsyn M
TM
Ross
Nicholas F
NF
Chilton
Ian A
IA
Gass
Boujemaa
B
Moubaraki
Guillaume
G
Chastanet
Nicolas
N
Paradis
Jean-François
JF
Lètard
Kuduva R
KR
Vignesh
Gopalan
G
Rajaraman
Stuart R
SR
Batten
Keith S
KS
Murray