Structure and Magnetism of 3D Anionic Metal Dicyanamide (MePh3P

Delivered at the International Conference on Materials for. Advanced Technologies ... Department of Chemistry, Trinity College, Dublin 2, Ireland, and...
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Delivered at the International Conference on Materials for Advanced Technologies 2003, Singapore, December 7-12, 2003

CRYSTAL GROWTH & DESIGN 2004 VOL. 4, NO. 3 503-508

Structure and Magnetism of 3D Anionic Metal Dicyanamide (MePh3P)[M(dca)3] (M ) Fe, Co, Ni) and (EtPh3P)[M(dca)3] (M ) Mn, Co, Ni) Networks Patricia M. van der Werff,† Stuart R. Batten,*,† Paul Jensen,†,‡ Boujemaa Moubaraki,† Keith S. Murray,*,† and John D. Cashion§ School of Chemistry, P.O. Box 23, Monash University 3800, Australia, Department of Chemistry, Trinity College, Dublin 2, Ireland, and School of Physics and Materials Engineering, Monash University 3800, Australia Received December 23, 2003;

Revised Manuscript Received March 1, 2004

ABSTRACT: The structures of (MePh3P)[M(dca)3] (M ) Fe, Co, Ni and dca ) dicyanamide, N(CN)2-) are isomorphous and contain anionic [M(dca)3]- networks in which octahedral metal ions are bridged by bidentate µ1,5 dca anions, to generate three-dimensional (3D) five-connected networks. The structures of (EtPh3P)[M(dca)3] (M ) Mn, Co, Ni) are also isomorphous and contain similar anionic networks to the MePh3P+ structures. In both sets of structures, the cations appear to perform a templating function and lie in pairs within cavities in the anionic network. These cation pairs show pseudo-6-fold phenyl embraces. No long-range magnetic ordering intrinsic to these materials was observed, although traces of the ferromagnets R-[Co(dca)2] and R-[Ni(dca)2] were observable in very small applied fields, at 9 and 21 K, respectively. Introduction The engineering of metal-organic polymeric networks to produce compounds with novel chemical, physical, and magnetic properties is an area of current research interest.1-5 The pseudohalide ligands dicyanamide [dca, N(CN)2-] and tricyanomethanide [tcm, C(CN)3-] have been used widely due to their polydentate character and their bridging ability, yielding a variety of structures and interesting magnetic properties.6 The binary rutilelike R-[M(dca)2] structures display long-range ferromagnetic (Co, Tc ) 9 K; Ni, Tc ) 21 K; Cu, Tc ) 1.7 K) and canted spin antiferromagnetic ordering (Cr, TN ) 47 K; Mn, TN ) 16 K; Fe, TN ) 19 K).7-11 The [M(tcm)2] series consists of two interpenetrating rutile networks and displays weak intraframework coupling without longrange order or interframework effects.12 The mixed ligand [M(dca)(tcm)] series has an unusual self-penetrating three-dimensional (3D) structure and shows long-range order but with lower Tc values than the corresponding [M(dca)2] compounds.13 Many Lewis-base adducts of [M(dca)2L], where L ) pyrazine, 4,4′-bipyridine, dabco, or 2-aminopyrimidine, have been synthesized.14-18 Anionic species of type M(dca)3- were first reported by Ko¨hler in 1966 but were not fully characterized. We have recently reported the structure and magnetism of * To whom correspondence should be addressed. (S.R.B.) E-mail: [email protected]. (K.S.M.) E-mail: keith.s.murray@ sci.monash.edu.au. † School of Chemistry, Monash University. ‡ Department of Chemistry, Trinity College. § School of Physics and Materials Engineering, Monash University.

the anionic species (Ph4As)[M(dca)3], where M ) Co(II), Ni(II),19 and Mn(II),20 and (Ph4P)[Mn(dca)3].20 The anions form extended sheets with (4,4) connectivity and octahedral geometry about the individual d-block ions. The anions display the long, bidentate µ1,5 bridging mode (i.e., they coordinate via the nitrile nitrogens only). The cations lie between the sheets and display cationcation interactions of the π-π and “multiple phenyl embrace” type.21 The Ni(II) complex, (Ph4As)[Ni(dca)3], showed long-range order, with an ordering temperature of 20.1 K. (Ph4As)[Co(dca)3] showed unusual field dependence of the magnetic moment below 20 K but without long-range order. The Mn(II) complexes showed weak antiferromagnetic coupling with no long-range order. The synthesis of the [M(dca)3]- species gave a second product (Ph4As)2[M2(dca)6(H2O)]‚H2O‚xMeOH, M ) Co(II) or Ni(II),19 where incorporation of the solvent into the coordination sphere of the metal resulted in a change in structure. These ladderlike one-dimensional polymers were cross-linked by hydrogen bonding into sheets, with the sheets separated by layers of cations. These structures did not display long-range order. Modification of the network topology by cation variation was achieved in the synthesis of (MePh3P)[Mn(dca)3], showing that the structures are cation templated.20 Substitution of the smaller MePh3P+ cation for the Ph4E+ cation (E ) As, P) had two effects. First, it disrupted the many subtle cation-cation and cationanion interactions, and second, the structural flexibility of the [M(dca)3]- network was not sufficient to incorporate the smaller cations without reducing the packing efficiency of the cation layer. These two effects changed

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the structure of the (MePh3P)[Mn(dca)3] network from a two-dimensional (2D) to a 3D [M(dca)3]- network. The [M(dca)3]- network consists of sheets of singly and doubly bridged metal atoms, which are then connected to the sheets above and below by single dca bridges, giving an overall five-connected 3D network with hexagonal channels. As for the Ph4E+ derivatives, the dca anions show the long µ1,5 bridging mode. The MePh3P+ cations occur in pairs within the network cavities, rather than in the discrete layers seen in the (Ph4E)[M(dca)3] 2D networks. A number of other cation templated [M(dca)3]- and [M(dca)4]2- networks have also been reported.22-25 We report here further examples of 3D [M(dca)3]networks containing the cations MePh3P+ and EtPh3P+. We were particularly interested to see if long-range magnetic order was obserable in these 3D systems. Experimental Procedures General Synthetic Details. Na(dca) was supplied by Fluka Chemicals, and MePh3PBr and EtPh3PBr were supplied by Aldrich. K(dca) was prepared by adding an aqueous solution (125 cm3) of Na(dca) (20.1 g, 0.226 mol) to a hot aqueous solution (80 cm3) of Zn(NO3)2‚6H2O (33.7 g, 0.113 mol). Zn(dca)2 deposited immediately and was filtered off. After the Zn(dca)2 was dissolved in 300 cm3 of hot water and cooled, an aqueous solution (200 cm3) of potassium hydroxide (13 g, 0.23 mol) was added, slowly, until the pH was 9. The precipitated Zn(OH)2 was removed. Concentration of the solution then yielded K(dca), which was recrystallized from acetone (10.3 g, 43%). EtPh3P(dca) was prepared by adding an aqueous solution (5 cm3) of Na(dca) (0.357 g, 4.010 mmol) to a hot aqueous solution (20 cm3) of EtPh3PBr (1.485 g, 4.000 mmol). EtPh3P(dca) precipitated immediately as a white powder but after 30 min had transformed into a yellow oil. This was separated out using a buret. Synthesis of (MePh3P)[Fe(dca)3]. MePh3PBr (0.358 g, 0.998 mmol) in methanol (4 cm3) was added to Na(dca) (0.268 mg, 3.010 mmol) in water (4 cm3). Fe(BF4)2‚6H2O (0.338 g, 1.001 mmol) was added with stirring. After 1 h, crystals of (MePh3P)[Fe(dca)3] were isolated, washed with water and then methanol, and dried. Yield: 0.099 g, 19%. Anal. obs. (calcd): C 56.65 (56.51), H 3.30 (3.41), N 23.83 (23.73)%. Infrared spectrum (Nujol): 3564w, 2315m, 2285s, 2249m, 2230m, 2187vs, 2158vs,br, 1588w, 1438s, 1352s, 1336s, 1117s, 998w, 902s, 788w, 744s, 720m, 690s cm-1. Powder XRD: the diffractogram of the bulk material matches that calculated from the crystal structure. Magnetism: µFe (295 K) ) 5.4 µB. Mo¨ssbauer spectra (fitted using a Voigt profile) two quadrupole doublets were observed in 54:46 ratio. δ1 ) 0.85 mm s-1, ∆EQ(1) ) 1.42 mm s-1; δ2 ) 0.84 mm s-1, ∆EQ(2) ) 0.83 mm s-1. Synthesis of (MePh3P)[Co(dca)3]. Na(dca) (0.267 g, 3.000 mmol) and Co(NO3)2‚6H2O (0.293 g, 1.007 mmol) were dissolved in water (6 cm3). MePh3PBr (0.360 g, 1.008 mmol) in methanol (5 cm3) was added, and the solution was covered. After 48 h, dark pink crystals of (MePh3P)[Co(dca)3] were isolated and washed with water and then with methanol. Yield: 0.302 g, 57%. Anal. obs. (calcd): C 56.42 (56.19), H 3.23 (3.40), N 24.02 (23.60)%. Infrared spectrum (Nujol): 3571w, 2392w, 2313s, 2288vs, 2253s, 2232s,br, 2191vs, 2162vs,sh, 1588w, 1438s, 1392m, 1381s, 1355s, 1337s, 1327m, 1163w, 1118s, 998m, 903s, 788w, 744s,721s, 690s cm-1. Powder XRD: the diffractogram of the bulk material matches that calculated from the crystal structure. Electronic absorption spectrum (diffuse reflectance; λmax): 32 362 s, 18 939 s, vbr, 8481 m, vbr cm-1. Magnetism: µCo (295 K) ) 5.0 µB. Synthesis of (MePh3P)[Ni(dca)3]. MePh3PBr (0.357 g, 0.999 mmol) in methanol (6 cm3) was added to Na(dca) (0.267 g, 3.000 mmol) in water (6 cm3). Ni(NO3)2‚6H2O (0.291 g, 0.999 mmol) was added, stirred to dissolve, and covered. After several hours, green crystals of (MePh3P)[Ni(dca)3] (0.174 g,

van der Werff et al. 33%) had formed, and after 7 days, they were collected and washed with water and then methanol. Yield: 0.174 g, 33%. Anal. obs. (calcd): C 56.41 (56.21), H 3.26 (3.40), N 23.85 (23.61)%. Infrared spectrum (Nujol): 3630w, 3578w, 2313m, 2290s, 2258m, 2239m, 2197vs, 2166vs,br, 1654w, 1589w, 1560w, 1508w, 1439m, 1394m, 1382m, 1357m, 1339m, 1324m, 1118m, 998w, 904m, 788w, 744m, 721m, 690m, 669m cm-1. Powder XRD: the diffractogram of the bulk material matches that calculated from the crystal structure. Electronic absorption spectrum (diffuse reflectance; λmax): 36 364s, 25 316m, 15 385m, br, 13 605sh, 9116m, vbr cm-1. Magnetism: µNi (295 K) ) 3.2 µB. Synthesis of (EtPh3P)[Mn(dca)3]. Mn(NO3)2‚4H2O (0.125 g, 0.498 mmol) in n-propanol (2 cm3) was added to a solution of EtPh3P(dca) (0.554 g, 1.498 mmol) in n-propanol (8 cm3) and covered. After 24 h, large colorless crystals (0.034 g) had formed and were filtered off and washed with cold n-propanol. After a further 5 days, smaller colorless needle-shaped crystals (0.031 g) were collected. All characterization, including crystal structure determination, was carried out on this sample. Yield: 0.065 g, 24%. Anal. obs. (calcd): C 57.51 (57.36), H 3.65 (3.70), N 23.51 (23.16)%. Infrared spectrum (Nujol): 3568w, 2287s, 2239m, 2230m, 2190s,sh, 2170vs, ∼2155s, sh, 1654w, 1587w, 1441s, 1376m, 1346m, 1329w, 1163vw, 1114s, 996w, 922w, 768w, 737m, 724m, 690m cm-1. Powder XRD: the diffractogram of the bulk material matches that calculated from the crystal structure. Magnetism: µMn (295 K) ) 5.7 µB. Synthesis of (EtPh3P)[Co(dca)3]. Na(dca) (0.269 g, 3.021 mmol) in water (3.5 cm3) was added to a solution of EtPh3PBr (0.371 g, 0.999 mmol) in MeOH (3.5 cm3). Co(NO3)2‚6H2O (0.291 g, 1.000 mmol) was added, and the solution was swirled to dissolve the Co and covered. After several days, clusters of pink needle-shaped crystals had formed. These were filtered off and washed with a cold water-methanol solution. A single crystal was removed for X-ray crystallography. Yield: 0.021 g, 4%. Anal. obs. (calcd): C 56.76 (56.94) H 3.67 (3.68), N 22.57 (22.99)%. Infrared Spectrum (Nujol): 3597w, 2361w, 2342w, 2288m, 2259w, 2246w, 2236w, 2196m, 2177s, 2166s, sh,1588w, 1442m, 1365m, 1343m, 1324m, 1115m, 992w, 921w, 735m, 725w, 690m, 668w cm-1. Powder XRD: the diffractogram of the bulk material matches that calculated from the crystal structure. Electronic absorption spectrum (diffuse reflectance; λmax) 32 786s br, 19 157s br, 8482s vbr cm-1. Magnetism: µCo (295 K) ) 4.9 µB. Synthesis of (EtPh3P)[Ni(dca)3]. Na(dca) (0.268 g, 3.010 mmol) dissolved in water (6 cm3) was added to a solution of EtPh3PBr (0.373 g, 1.005 mmol) in methanol (6 cm3). Ni(NO3)2‚ 6H2O (0.290 g, 0.997 mmol) was added, and the solution was swirled to dissolve the Ni and covered. After several days, clusters of small green needles had formed. The crystals were collected and washed with cold methanol and water. Yield: 0.147 g, 27%. Anal. obs. (calcd): C 57.08 (56.96), H 3.65 (3.68) N 22.74 (23.00)%. Infrared spectrum (Nujol): 3450w, 2362w, 2291m, 2242w, 2182s, ∼2170s, sh, 1588w, 1444m, 1369m, 1343m, 1324w, 1116m, 997w, 920w, 738w, 725w, 690w cm-1. Powder XRD: the diffractogram of the bulk material matches that calculated from the crystal structure. Electronic absorption spectrum (diffuse reflectance; λmax): 36 101s, 25 316s, 15 408m, br, 13 550sh, 9050s, vbr cm-1. Magnetism: µNi (295 K) ) 3.0 µB. Crystal Structure Determinations. Single-crystal data and details of the structure determinations are presented in Table 1. Data were collected at 123 K on a Nonius KappaCCD diffractometer with graphite monochromated Mo KR radiation (λ ) 0.71073 Å), using φ and ω rotations with 1° frames. The images were processed with the HKL suite of programs.26 Solutions were obtained using either SHELXS-9727 or TEXSAN28 followed by successive difference Fourier methods, and structures were refined against F2 using SHELXL-97.27 Faceindexed absorption corrections were applied to all structures except (EtPh3P)[M(dca)3], where M ) Mn, Co. All hydrogen atoms were placed at calculated positions and not refined; all nonhydrogen atoms were refined anisotropically. Powder X-ray Diffraction. Patterns were measured on a Scintag Automated Powder Diffractometer using a Cu KR

Structure and Magnetism of 3D (RPh3P)[M(dca)3] Nets

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Table 1. Crystallographic Data

formula fw crystal system space group a (Å) b (Å) c (Å) V (Å3) Z Dc (g cm-3) µ (mm-1) data collected unique data (Rint) obs. data [I > 2σ(I)] R1, wR2 (obs. data) R1, wR2 (all data) Flack parameter

(MePh3P)[Fe(dca)3]

(MePh3P)[Co(dca)3]

(MePh3P)[Ni(dca)3]

(EtPh3P)[Mn(dca)3]

(EtPh3P)[Co(dca)3]

(EtPh3P)[Ni(dca)3]

C25H18N9FeP 531.30 orthorhombic P212121 13.9104(4) 17.0365(2) 20.8150(5) 4932.83(19) 8 1.431 0.710 35917 16270 (0.0578) 10519 0.0537, 0.0737 0.1120, 0.0852 0.015(9)

C25H18N9CoP 534.38 orthorhombic P212121 13.8718(2) 16.9489(2) 20.7720(3) 4883.74(12) 8 1.454 0.802 76560 16521 (0.0521) 13171 0.0387, 0.0609 0.0658, 0.0670 -0.003(6)

C25H18N9NiP 534.16 orthorhombic P212121 13.8039(3) 16.8679(2) 20.7639(6) 4834.73(18) 8 1.468 0.903 39177 14573 (0.0905) 8767 0.0639, 0.0672 0.1388, 0.0790 -0.015(8)

C26H20MnN9P 544.42 orthorhombic P212121 14.3759(1) 16.9055(1) 21.6345(2) 5257.87(7) 8 1.376 0.596 63658 12619 (0.0397) 11055 0.0310, 0.0639 0.0409, 0.0673 -0.008(8)

C26H20CoN9P 548.41 orthorhombic P212121 14.2228(2) 16.7050(1) 21.6020(3) 5132.46(11) 8 1.419 0.765 90513 13043 (0.0993) 10717 0.0600, 0.0698 0.0856, 0.0738 -0.001(9)

C26H20NiN9P 548.19 orthorhombic P212121 14.1192(1) 16.6545(1) 21.5833(2) 5075.27(7) 8 1.435 0.862 36451 11953 (0.0567) 9695 0.0446, 0.0636 0.0672, 0.0685 0.003(8)

Table 2. Selected IR Frequencies

MePh3P[Fe(dca)3] MePh3P[Co(dca)3] MePh3P[Ni(dca)3] EtPh3P[Mn(dca)3] EtPh3P[Co(dca)3] EtPh3P[Ni(dca)3]

νs (C-N) + νas(C-N)

νas (CtN)

νs (CtN)

νas (C-N)

2285s 2288s 2290s 2287s 2288m 2291m

2248w/2230w 2253w/2232w 2258w/2239w 2239w/2230w 2246w/2236w 2250w/2242w

2187vs/2158vs 2191vs/2162vs 2197vs/2166vs 2189s,sh/2169vs/2155 2196m/2177s/2166s,sh 2202m,sh/2182s/2170s,sh

1352w/1336w 1355w/1336w 1357w/1337w 1365w/1346w 1365m/1343m 1369m/1343m

monochromatic radiation source (λ ) 1.54059 Å), a solid state Ge detector, a 2 mm divergence slit, and a 3 mm receiving slit. Magnetic Measurements. Magnetic measurements were carried out as described previously19 using a Quantum Design MPMS 5 Squid magnetometer for DC magnetization measurements and PPMS 7 system fitted with option P-500 (ACMS) for AC susceptibility measurements. The AC field was 3.5 Oe oscillating at 20 Hz. To check for crystallite orientation effects, the variable field DC magnetization data were determined for neat powdered and Vaseline dispersed samples, and both showed the same results. Mo1 ssbauer Measurements. Spectra were measured using a Co(Rh) γ-ray source with an R-Fe foil calibrant. Electronic Absorption Measurements. Electronic absorption spectra were recorded in the range of 200-2500 nm on a Varian-Cary 5 spectrophotometer as diffuse reflectance on solid samples. Intensities are described by the abbreviations used for infrared spectra.

Results and Discussion Synthesis and Characterization. Reaction of RPh3PBr (R ) Me or Et), Na(dca), and the metal nitrate M(NO3)2‚xH2O (M ) Mn, Co, Ni) or the metal tetrafluoroborate (M ) Fe) resulted in the precipitation of crystals of (MePh3P)[M(dca)3] (M ) Fe, Co, Ni) or (EtPh3P)[M(dca)3] (M ) Mn, Co, Ni). The IR spectra, like those of the (Ph4E)[M(dca)3] analogues,19,20 have ν(CtN) bands in the ranges quoted by Ko¨hler29 consistent with the bidentate µ1,5 coordination of the dca ligand. However, the IR spectra also show some significant differences. The MePh3P+ and EtPh3P+ complexes have two distinct bands for νas(C-N), νs(CtN), and νas(CtN) (Table 2), indicating that the dca ligands are in two distinct environments. Crystal Structures. The structures were determined by X-ray crystallography and found to be isomorphous with the previously solved structure of (MePh3P)[Mn(dca)3].20 Both the MePh3P+ and the EtPh3P+ structures

are essentially the same and crystallize in the same chiral space group P212121, although the positioning of the unit cell differs between the two cations. The structures consist of anionic 3D [M(dca)3]- networks, in which the cations occur in pairs within the network cavities. Each structure contains two cations, two octahedral metals (each coordinated to six separate dca ligands), and six bidentate µ1,5 dca anions (coordinating via the nitrile nitrogen atoms) in the asymmetric unit. The M-N distances are shown in Table 3. The anionic network consists of sheets lying in the xz plane, which are then cross-linked in the y direction into a 3D net. The sheets are formed by metal atoms connected by single dca bridges and double dca bridges (in a 2:1 ratio) into a (6,3) hexagonal network. The double dca bridges occur on opposite sides of the hexagonal windows. All sheets are crystallographically equivalent but display two different orientations. Each sheet is then connected to sheets above and below by single dca bridges, giving the overall five-connected 3D network with hexagonal channels (Figure 1). The Scha¨fli symbol of this net is 46.64. The structure of Cu2(dca)4(2,5Me2pyz), 2,5-Me2pyz ) 2,5-dimethylpyrazine, also displays a five-connected net (two interpenetrating); however, the topology of this net is different (Scha¨fli symbol 44.66).30 The anionic [M(dca)3]- network contains cavities defined by one hexagonal window each from two adjoining hexagonal sheets and the six dca bridges connecting the two windows. Within these cavities are the two crystallographically distinct RPh3P+ cations (Figure 2). The cations make a number of close C-H‚‚‚C/N contacts with the anionic framework around them. The two cations within each cavity also engage in moderate pseudo-6-fold phenyl embraces (pseudo-6PEs),21 which in fact involve three phenyl groups from one cation and two phenyl groups and the alkyl group from the other

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van der Werff et al.

Table 3. Selected Bond Lengths (Å) and Angles (°)a

M1-N11 M1-N21 M1-N31 M1-N41 M1-N32i M1-N62ii M2-N12 M2-N22 M2-N51 M2-N61 M2-N42ii M2-N52iii

(MePh3P)[Fe(dca)3]

(MePh3P)[Co(dca)3]

(MePh3P)[Ni(dca)3]

(EtPh3P)[Mn(dca)3]

(EtPh3P)[Co(dca)3]

(EtPh3P)[Ni(dca)3]

2.147(2) 2.186(2) 2.188(2) 2.1439(19) 2.170(2) 2.1148(18) 2.169(2) 2.160(2) 2.165(2) 2.1312(19) 2.1189(19) 2.214(2)

2.1090(15) 2.1501(15) 2.1506(15) 2.1107(15) 2.1362(15) 2.0902(14) 2.1280(17) 2.1297(16) 2.1266(17) 2.0959(15) 2.0879(15) 2.1852(15)

2.063(2) 2.110(3) 2.105(3) 2.074(2) 2.093(3) 2.055(2) 2.081(3) 2.093(3) 2.082(3) 2.063(2) 2.049(2) 2.141(3)

2.2076(17) 2.2580(16) 2.2384(17) 2.1864(16) 2.2461(15) 2.1959(16) 2.2177(17) 2.2288(17) 2.2214(17) 2.2296(16) 2.2095(17) 2.2184(16)

2.103(2) 2.168(2) 2.135(3) 2.086(2) 2.145(2) 2.099(2) 2.101(2) 2.137(2) 2.132(2) 2.125(2) 2.116(2) 2.111(2)

2.059(2) 2.119(2) 2.094(2) 2.056(2) 2.101(2) 2.070(2) 2.062(2) 2.094(2) 2.090(2) 2.087(2) 2.085(2) 2.073(2)

a Symmetry operations: For MePh P+, (i) x - 1/2, (1/2) - y, -z; (ii) -x, y - (1/2), (1/2) - z; (iii) x - (1/2), (1/2) - y, 1 - z. For EtPh P+, 3 3 (i) x - (1/2), (1/2) - y, 2 - z; (ii) -x, y - (1/2), (3/2) - z; (iii) x - (1/2), (1/2) - y, 1 - z.

Figure 1. (a) Three-dimensional [M(dca)3]- net in the structure of (MePh3P)[Co(dca)3]. Co is represented in purple, carbon is represented in green, and nitrogen is represented in blue; cations are omitted for clarity. The networks contained in the other compounds reported here are similar. (b) Schematic representation of the 3D five-connected [M(dca)3]- network.

cation [P1‚‚‚P2 ) 6.807 (Fe), 6.790 (Co), 6.773 (Ni) Å for MePh3P+; 6.724 (Mn), 6.672 (Co), 6.640 (Ni) Å for EtPh3P+]. By use of the Dance notation, these are 5P1Y interactions.21 The phenyl rings of the cations also display intercavity edge-to-face and vertex-to-face interactions.

Magnetic Measurements. The magnetic behavior of the complex (EtPh3P)[Mn(dca)3] is similar to that of the previously reported complexes (Ph4As)[Mn(dca)3], (Ph4P)[Mn(dca)3], and (MePh3P)[Mn(dca)3]20 and indicates that very weak antiferromagnetic coupling occurs between the high-spin MnΙΙ (6A1g) centers, combined with single-ion zero-field splitting effects. In a field of 1 T, the µMn values remain constant at 5.7 µB between 300 and 50 K and then decrease rapidly toward 2.95 µB at 2 K in a manner similar to that also noted for polymeric adducts of the type [Mn(dca)2L2] [where L ) pyridine, (pyrazine)0.5, CH3OH] containing Mn-NCNCN-Mn bridges.16,31 The µMn data are independent of the applied field value used, and there is no evidence of long-range magnetic ordering. The magnetic data for the 3D network system (MePh3P)[Fe(dca)3] again display weak antiferromagnetic coupling, very similar to that shown by the 2D (Ph4As)[Fe(dca)3].32 These samples have to be dispersed in Vaseline to prevent torquing of crystallites, which produces anomalous data. In a field of 1 T, the µFe values increase slightly from 5.4 µB to 5.5 µB between 300 and 100 K, then decrease, at first slowly then more rapidly, from 5 µB at 20 K to reach 2.5 µB at 2 K. This is normal for essentially noncoupled high-spin octahedral FeΙΙ (5T2g) centers.33 Interestingly, in a small field of 20 Oe, a small but sharp inflection in µeff occurs at about 19 K, which is most likely indicative of the presence of a trace of R-[Fe(dca)2], a spin-canted antiferromagnet.6,8 The 77 K Mo¨ssbauer spectrum of (MePh3P)[Fe(dca)3] was fitted using a Voigt profile. Two quadrupole doublets were observed in area ratio 54:46, with isomer shift δ1 ) 0.85 mm s-1, quadrupole splitting ∆EQ(1) )1.42 mm s-1; δ2 ) 0.84 mm s-1, ∆EQ(2) ) 0.83 mm s-1. This indicates that on the Mo¨ssbauer time scale, there are two rather similar iron(II) environments, albeit with different ∆EQ values. This is consistent with the crystallographic results, which showed two crystallographically unique, but chemically similar, metal environments, with Fe2 being closer to regular octahedral than Fe1 [N-Fe-N angles for Fe2 (Fe1): 87.37(8)-93.45(9)° (83.78(8)-98.11(8)°) and 174.22(8)-176.82(9)° (169.12(8)-175.78(8)°)]. The Mo¨ssbauer parameters are indicative of high-spin octahedral d6 Fe(II) but both the δ and the ∆EQ values are significantly lower than we have observed in other Fe(II)-dca species, such as the 2D (Ph4As)[Fe(dca)3], δ ) 1.25 mm s-1, ∆EQ ) 2.79 mm

Structure and Magnetism of 3D (RPh3P)[M(dca)3] Nets

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Figure 3. Plots of magnetic moment, µCo, vs temperature for (EtPh3P)[Co(dca)3] in fields of 1 and 0.002 T. The rapid increase to reach a sharp maximum in µCo, at 9 K, is due to traces of R-[Co(dca)2]. The solid lines are not calculated values.

Figure 4. Plots of magnetic moment, µNi, vs temperature for (EtPh3P)[Ni(dca)3] in fields of 1 and 0.002 T. The rapid increase to a sharp maximum at 21 K (H ) 20 Oe) is due to traces of R-[Ni(dca)2] (see text). The solid lines are not calculated values.

Figure 2. Two cations contained in an anionic cavity of (a) (MePh3P)[Co(dca)3] and (b) (EtPh3P)[Co(dca)3]. Hydrogens are omitted for clarity.

s-1, and the rutile-like 3D network of R-[Fe(dca)2], with δ ) 1.21 mm s-1, ∆EQ )3.17 mm s-1.6 The µCo vs T plots for the 3D complexes (MePh3P)[Co(dca)3] and (EtPh3P)[Co(dca)3] show a room temperature magnetic moment of 4.9 µB and follow a similar

µCo/T curve to the 2D Ph4As+ and 3D R-Po-like (PhCH2)(Bu)3N+ salts,19,25 decreasing to 3.5 µB at 4 K. Such behavior, shown in Figure 3 for the EtPh3P+ salt, arises from orbitally degenerate 4T1g Co(II) centers undergoing spin-orbit coupling and weak, nearest neighbor antiferromagnetic exchange coupling perturbations. Despite their different dimensionalities, these complexes utilize only the Co-N(nitrile) bridging pathways. The 3D rutile-like parent species R-[Co(dca)2], which utilizes both the Co-N(amide) and the Co-N(nitrile) pathways, shows ferromagnetic order with Tc ) 9 K.6-10 The EtPh3P+ salt shows a very sharp increase in µCo at ∼9 K in low fields, which is not present in the 1 T data and is due to traces of R-[Co(dca)2] being present.6 Sun et al.34 have made similar observations in the 2D species [Co(dca)2(pyrazine dioxide)]. The 3D complexes of (MePh3P)[Ni(dca)3] and (EtPh3P)[Ni(dca)3] do not show any intrinsic long-range order, with the µNi vs temperature plots being independent of field and characteristic of very weak antiferromagnetic coupling combined with zero-field splitting of the 3A2g states. In a field of 1 T, the µNi values of (MePh3P)[Ni(dca)3] decrease from 3.2 µB at 300 K to 3.1 µB at 50 K and then more rapidly to 2.7 µB at 4 K. The µNi vs T plot of (EtPh3P)[Ni(dca)3] is similar but shows a sharp increase in µNi at 21 K, when a field of 20 Oe was used, due to traces of the ferromagnet R-[Ni(dca)2] being present in the crystalline sample. This is saturated out

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when fields of 1000 Oe or greater are used and plots of the type described above are observed (Figure 4). We have noted that this rapid increase in µNi at ∼21 K, in low fields, has occurred in a number of analytically pure, highly crystalline Ni(II)-dca species of both the anionic and the neutral (Lewis-base adduct) types. It is difficult to unambiguously assign this ordered species to a trace impurity of R-[Ni(dca)2], or a trace of a different impurity, or to the neat material. In the Ph4As+ salt, detailed studies, including doping with R-[Ni(dca)2], pointed to the last two possibilities.19 In the present EtPh3P+ salt, the first possibility is most likely. Conclusions The topologies of anionic metal dca networks are very sensitive to the nature of the cation.19,20,22-25 Use of RPh3P+ (R ) Me, Et) cations results in 3D fiveconnected anionic [M(dca)3]- networks of metal atoms bridged by µ1,5 dca anions. The cations lie in pairs within the cavities of the network and show numerous, structure-directing weak interactions between the cations and between the cations and the anionic net. Unfortunately, as a result of the long µ1,5 dca bridging, no longrange magnetic ordering is observed, although this is also present in the Ph4E+ structures, which have lower dimensionality (2D vs 3D) and have been found to have long-range order [although impurities cannot be ruled out (vide supra)]. These results do, however, illustrate the importance of cation choice in the design of anionic nets. Acknowledgment. We thank the Australian Research Council for funding and Degussa AG for their generous donation of Na(dca). Supporting Information Available: Crystallographic information files (CIF) for the structures reported herein. This material is available free of charge via the Internet at http:// pubs.acs.org.

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