Roger E. Gerkin

Electron paramagnetic resonance of triplet phenanthrene-d10 and naphthalene-d8 in single-crystal biphenyl from 5–80 K and characteriz

Abstract Previously reported single discontinuities in the zero-field splittings of triplet phenanthrene- d 10 and naphthalene- d 8 in biphenyl near 40 K are further characterized. The transition leading to these discontinuities in the mixed crystals is shown to set in at 42.0 ± 0.4 K upon lowering the temperature, and to occur over a temperature range of a few degree. Cooling and warming curves of pure and mixed-crystal biphenyl near the paramagnetic resonance transition temperature were measured, and a first order phase transition in pure fiphenyl at 42.4 ± 0.3 K is reported, for which Δ H ≈ 70 cal mole −1 . A second prominent feature in the temperature dependences of the zero-field splittings in these mixed crystals, which was not previously reported, has been shown to occur near 15 K. Although this second feature is only partially characterized by the present data, it is tentatively assigned as due to a transition intrinsic to pure biphenyl.

Electron Paramagnetic Resonance Absorption in Oriented Triphenylene in Its Phosphorescent State at Low Magnetic Fields

Electron paramagnetic resonance absorption in oriented triphenylene in its lowest triplet state has been investigated in static magnetic fields below 50 G at 77°K. The orienting medium was melt‐grown single crystals of symmetric dodecahydrotriphenylene, the structure of which has been briefly investigated and compared with that of vapor‐grown crystals. The lowest triplet state of triphenylene in this host has been shown to possess lower than threefold symmetry. Taking the normal to the mean molecular plane of triphenylene to be the C axis and the mean molecular plane to be the AB plane, the results have been described by the spin Hamiltonian H = g | β | H·S + S·T·S, where S = 1, g = 2.003 (isotropic), and, at 77°K, | TCC | / hc ≡ | D | / hc = 0.133526 cm−1, σ{| D | / hc} = 0.000048 cm−1, | TAA | / hc = | TBB | / hc ≡ | E | / hc = 0.000564 cm−1, σ{| E | / hc} = 0.000048 cm−1. The triplet‐state lifetime and the angular dependence of the resonance absorption linewidths have also been studied at 77°K, and the...

Electron Paramagnetic Resonance of Gd3+ in Single Crystals of Various Rare‐Earth Ethyl Sulfates at Room Temperature and at 77°K

Electron paramagnetic resonance studies of Gd3+ in single crystals of Ln(C2H5SO4)3· 9 H2O (where Ln3+ denotes La3+, Pr3+, Nd3+, Sm3+, Tb3+, Dy3+, Ho3+, Er3+, Yb3+, and Lu3+) have been carried out at X band at room temperature and at 77°K. The spin Hamiltonian parameters b20, b40, and b60 and g‖ have been evaluated at both temperatures for each host except terbium ethyl sulfate at 77°K. The absorption linewidths for each transition have been measured at both temperatures. The present results are compared with previous results. A principal conclusion is that the magnitude of b20 for Gd3+ in the various rare‐earth ethyl sulfates is more nearly a linear function of the ionic radius of the trivalent host ion than of its atomic number.

EPR of triplet phenanthrene-d10 and naphthalene-dg in single-crystal biphenyl-h10 from 5–80K and its structural implications

Abstract A previously unreported phase transition in mixed biphenyl single-crystals, confined to at most a 5 degree temperature interval near 39 K, is described. Single EPR absorptions by triplet phenanthrene-d10 and naphthalene-dg above 39 K are converted by it into multiplets of four prominent components.

Electron Paramagnetic Resonance Absorption in Oriented Phosphorescent Chrysene at Magnetic Fields below 125 G. I. Multiplet Structure in Low‐Field EPR Spectra

Multiple electron paramagnetic resonance absorptions by phosphorescent chrysene‐h12 and ‐d12 in single crystals of p‐terphenyl‐h14 and ‐d14 and symmetric octahydroanthracene (OHA) have been investigated, principally in static magnetic fields below 125 G, and in the temperature range from 64 to 250°K. The zero‐field splittings of the lowest triplet state of chrysene‐d12 have been determined very precisely in experiments at static fields from ·25 to ·3 G. The high‐precision splittings determined for the twenty resonance absorptions observed for chrysene‐d12 in p‐terphenyl (at ·0.116, 0.063, and 0.053 cm−1) could be correlated into seven triples corresponding to seven distinct triplet‐state species. Only six absorptions were observed for chrysene‐d12 in OHA, and these could be correlated into two triples of splittings. Decisive evidence is presented that all 26 resonance absorptions observed arise solely from chrysene‐d12 and not (in part) from impurities. For p‐terphenyl host, direct experimental evidence h...

Electron Paramagnetic Resonance of Gd3+ in Single Crystals of La(C2H5SO4)3· 9H2O, Bi2Mg3(NO3)12· 24H2O, and Sm(C2H5SO4)3· 9H2O Below 40 G

Electron paramagnetic resonance studies of Gd3+ ion in three types of magnetically dilute single crystals possessing C3 site symmetry have been carried out at magnetic fields below 40 G and at 77°K. The zero‐field splittings and g factors of Gd3+ obtained from these studies are compared with those obtained from: (a) a previous low‐field EPR study of Gd3+ in La(C2H5SO4)3· 9H2O, (b) conventional (high‐field) EPR studies in this laboratory of Gd3+ in the same three host‐crystal systems; (c) previous conventional (high‐field) EPR studies of Gd3+ in La(C2H5SO4)3· 9H2O and in Bi2Mg3(NO3)12· 24H2O. While all possible such comparisons involving ±7/2, ±5/2 and ±5/2, ±3/2 transitions showed agreement within the stated uncertainties of the various data sets, those involving ±3/2, ±1/2 transitions did not. Moreover, anomalous absorptions of lower intensity consistently were observed to the low‐field side of the +3/2, +1/2 and the −3/2, −1/2 transitions only. These anomalous signals are shown to be interpretable as ar...

Coumarin‐3‐carboxylic Acid

In the structure of the title compound, C10H6O4, there is a single intramolecular hydrogen bond. In addition, there are a number of significant intermolecular C-H...O attractive interactions. These interactions account in part for the rather high density for an ordinary monocarboxylic acid, 1.522 Mg m(-3).

Redetermination of the structures of 1-naphthoic acid and 2-naphthoic acid

The structures of 1-naphthoic acid and 2-naphthoic acid have been investigated in order to determine the degree of disorder of the carboxylic acid groups. 1-Naphthoic acid was found to be completely ordered with C--O bond lengths of 1.214 (3) and 1.312 (3) A, and C--C--O bond angles of 124.8 (2) and 114.2 (2) degrees. 2-Naphthoic acid was found to possess a significant degree of disorder with C--O bond lengths of 1.256 (3) and 1.274 (3) A, and C--C--O bond angles of 117.7 (2) and 119.1 (2) degrees. In 2-naphthoic acid, the acid H atom was refined at two sites with 0.5 occupancy at each. Analysis of the anisotropic displacement ellipsoids of the acid O atoms for each structure demonstrated that these parameters are consistent with thermal motion of the O atoms. These results indicated that the proton, but not the O atoms, is disordered in the carboxylic acid group of 2-naphthoic acid. In each structure, the acid molecules form cyclic dimers about inversion centers, with an O...O(acceptor) distance of 2.653 (3) in 1-naphthoic acid and 2.618 (3) A in 2-naphthoic acid. The cyclic dimers form layers in each of these structures wherein lateral closest intermolecular approaches to the acid O atoms are from ring H atoms. The intermolecular O...H close approaches, together with the intramolecular close approaches, are very uniform in distance and angle of approach for the two O atoms in the 2-naphthoic acid structure.(ABSTRACT TRUNCATED AT 250 WORDS)

Electron Paramagnetic Resonance Absorption in Oriented Phosphorescent Triphenylene‐h12 and Triphenylene‐d12 from 4 to 250°K

Electron paramagnetic resonance absorption by phosphorescent triphenylene‐h12 and ‐d12 oriented in single crystals of symmetric dodecahydrotriphenylene has been investigated in the temperature range from 4 to 250°K. It has been shown that both guest molecules are multiply oriented in this host. In addition, two distinct kinds of mixed crystals have been identified on the basis of the zero‐field splittings manifested by the guest molecules. In one kind of mixed crystal, guest splittings were found to change with time until stable, fixed values were established. Since splitting differences are related to orientational differences, guest rearrangement in the solid host is implied, which has not heretofore been reported. The temperature dependence of at least one zero‐field splitting parameter D is complex in that its magnitude does not increase monotonically with decreasing temperature. The temperature dependences of the zero‐field splitting parameters E are even more complex. X‐ray diffraction data indicate...

Structure of hexaaquacobalt(II) bromate

[Co(H2O)6](BrO3)2, Mr = 422.83, cubic, Pa-3, a = 10.3505 (7) A, V = 1108.88 (8) A3, Z = 4, Dx = 2.53 g cm-3, lambda(Mo K-alpha) = 0.71069 A, mu = 87.31 cm-1, F(000) = 820, T = 296 K, R = 0.027 for 365 unique reflections having I greater than sigma I. The single type of Co ion is coordinated by six water-molecule O atoms, each at an observed distance 2.095 (2) A, in an array which is regular octahedral within the estimated standard deviations of the relevant angles. The single type of bromate ion has a Br-O bond length 1.653 (2) A and O-Br-O bond angle 104.07 (9) degrees. The cobalt-oxygen complex manifested rigid-body behavior, but the bromate ion did not. The cobalt-oxygen distance corrected for rigid-body motion is 2.099 A. Location and refinement of the two inequivalent H atoms permitted detailed analysis of the hydrogen bonding, which occurs principally between the oxygen octahedra and the bromate groups. This structure is isomorphic to that of hexa-aquanickel(II) chlorate recently reported from this laboratory.