New Square S=1/2 Heisenberg Antiferromagnetic Lattices: Pyridinium Tetrahalocuprates and Bispyrazinecopper(II) Tetrafluoroborate

Abstract

As part of a program to create new low dimensional S=1/2 antiferromagnetic Heisenberg compounds with moderate exchange, we have prepared four new copper complexes with square magnetic lattices. The complexes L2[Cu&] have been prepared (L = 2-amino-5-methylpyridiniuq X = C1, Br; L = 2-amino-5chloropyriduq X = Br). The compounds are isomorphous, giving monoclinic crystals; space group C2/c. The tetrahalometallate ions lie in C-centered layers, forming a square magnetic lattice. The layers are separated by the organic cations. P r e l i i analysis of the magnetic data shows that the exchange constant, J, increases in the order Br > C1 and 2-amino-5-chloropyridinium > 2-amino-5-methylpyridinium. A new member of the pyrazine bridged family M(pyrazinehXz has also been prepared and studied. Cu(p+ (BF& also crystallizes in the space group C2/c. Analysis of the temperature dependence of the susceptibility yields and exchange value of -7.98 K., similar to that found for the known Cu(pzh(C10,h complex. 333 Downloaded by [Heriot-Watt University] at 00:57 27 December 2014 334 A.S. ALBRECHT el al.

Magnetic order in theS=1∕2two-dimensional molecular antiferromagnet copper pyrazine perchlorateCu(Pz)2Lancaster1, Blundell2, Brooks3 et al. 2007Phys. Rev. B610210View full textAdd to dashboardCite

“…We have examined the 2D Heisenberg antiferromagnet Cu(Pz) 2 (ClO 4 ) 2 using specific heat and µ + SR techniques. The value of the exchange strength obtained (J = 17.7(3) K) from the magnetic specific heat is in excellent agreement with values obtained from susceptibility 7,8,9,10 and neutron scattering 16 experiments. The muon spin relaxation studies demonstrated the existence of 3D long range magnetic order throughout the bulk of the sample in Cu(Pz) 2 (ClO 4 ) 2 at temperatures below T N = 4.21(1) K. The value of T N /J (0.24) corresponds to a very low ratio of interlayer to intralayer exchange strengths (|J ′ /J|=6.8×10 −4 ).…”

“…This results in a herring-bone configuration, rather than a square lattice. Despite this distortion, magnetic susceptibility measurements fit very well to the 2DSLQHA model 7,8,10 with J = 17.5 K and g = 2.11.…”

“…In this paper we present an investigation of the magnetic properties of the twodimensional analogue of CuPz(NO 3 ) 2 , namely copper pyrazine perchlorate (Cu(Pz) 2 (ClO 4 ) 2 ). This material has been the subject of several studies aimed at elucidating its properties 5,6,7,8,9,10 , although hitherto, no evidence of a magnetic transition has been found. We have carried out detailed specific heat and muon-spin relaxation measurements.…”

Design and synthesis of magnetic ladders: structure and magnetic properties of Cu(2,3-dimethylpyrazine)Br2

“…We have long been interested in the use of pyrazine and pyrazine derivatives for the preparation of low-dimensional magnetic systems and have prepared and studied a number of linear chain [13] and square systems [14]. More recently we have begun studies on the synthesis and properties of magnetic ladders, which employ pyrazine derivatives as bridging ligands.…”

Impedance Spectroscopy Study of Bis(2-Amino-6-Methylpyridinium) Tetrachloridozincate

“…Considerable interest has been devoted to compounds of the general formula A 2 MX 4 where A is an organic cation, M a divalent metal and X a halogen (Cl, Br). 1,2 OrganicÀinorganic hybrid metal halides have received extensive attention in recent years owing to their great fundamental and practical interest. 3,4 This is because of their special magnetic, 5 electronic 6 and optoelectronic properties.…”