New crystalline polymers of Ag(TCNQ) and Ag(TCNQF4):: Structures and magnetic properties

Reaction of Ag(BF4) with [n-Bu4N][TCNQ] in CH3CN yields a nem phase of Ag(TCNQ) referred to as phase I (1). A second polymorph of Ag(TCNQ), denoted phase II (2), which had earlier been prepared by electrocrystallization methods, can be accessed directly from silver powder and neutral TCNQ. The products were characterized by a combination of spectroscopic and physical methods. A powder X-ray diffraction pattern of (1) was indexed as a tetragonal cell with a = b = 12.1422 Angstrom, c = 17.0498 Angstrom, and V = 2513.70 Angstrom(3). Compound (2) crystallizes in the orthorhombic system with a = 7.2892 Angstrom, b = 16.5790 Angstrom, c = 17.4448 Angstrom, and V = 2108 Angstrom(3), which correlates well with the lattice parameters a = 6.975 Angstrom, b = 16.686 Angstrom, c = 17.455 Angstrom, and V = 2031.5 Angstrom(3) reported for Ag(TCNQ) phase II. Ag(TCNQF(4)) (5), prepared by electrochemical reduction of TCNQF(4) at an Ag electrode, crystallizes in the monoclinic space group C2/c, a = 13.429(3) Angstrom, b = 6.9331(14) Angstrom, c = 25.735(5) Angstrom, beta = 116.66(3)degrees. Ag(TCNQF(4)) consists of coordinated TCNQF(4) radicals arranged in a parallel stacking arrangement along the b axis. The nearly eclipsed'' type stacking of the TCNQF(4) radicals leads to a short intradimer distance of 3.119(2) Angstrom and an interdimer separation of 3.330(2) Angstrom. Single crystal X-ray data for the salts [Bu4N][TCNQ] (3) and [n-Bu4N][TCNQF(4)] (4a) and (4b) are also included for comparison to the Ag(I) materials. [n-Bu4N][TCNQ] (3) crystallizes in the monoclinic space group P2(1)/n with a = 9.3028(7) Angstrom, b = 19.3520(14) Angstrom, c = 15.3880(11) Angstrom, beta = 100.979(2)degrees, V = 2719.6(3) Angstrom(3). [n-Bu4N] [TCNQF(4)] crystallizes in two forms; in a monoclinic space group P21/n (4a), a = 7.4244(15) Angstrom, b = 20.212(4) Angstrom, c = 19.758(4) Angstrom, beta = 97.32(3)degrees, V = 2940.8(10) Angstrom(3), and in the triclinic space group (4b), a = 9.6335(3) Angstrom, b = 14.9574(3) Angstrom, c = 21.3615(5) Angstrom, alpha = 107.440(1)degrees beta = 93.437(2)degrees, gamma = 104.785(2)degrees and V = 2808.07(12) Angstrom(3). Ring-edge slipped stacking arrangements are present in both (4a) and (4b), in which a strongly paired set of TCNQF(4) anions interacts with another set. The shortest distance within a dimer pair TCNQF(4) in (4a) is 3.09 Angstrom. In contrast, there are two independent types of TCNQF(4) interactions in (4b), one that invoices strongly interacting anions and one that comprises only weakly dimerized anions. The presence of the latter type in (4b) leads to magnetic properties indicative of thermal population of the triplet excited state at higher temperatures. (C) 2000 Academic Press.