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DOI: 10.1039/C5RA15752H (Paper) RSC Adv., 2015, 5, 93470-93479

The new dicyanoruthenium(III) building block with 2′-hydroxyacetophenone imine for heterobimetallic complexes†

Jing Rua, Tian-Xiang Zonga, Jing-Yuan Gea, Min-Xia Yaob and Jing-Lin Zuo*a
aState Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, P. R. China. E-mail: zuojl@nju.edu.cn; Fax: +86-25-83314502
bSchool of Science, Nanjing University of Technology, Nanjing 210009, P. R. China

Received 6th August 2015 , Accepted 23rd October 2015

First published on 23rd October 2015

Abstract

A new ruthenium(III)-based building block, trans-(Ph4P)[RuIII(L)2(CN)2] (L = 2′-hydroxyacetophenone imine), has been synthesized and characterized. Reactions of this building block with different MnIII Schiff base (SB) complexes, [Mn(SB)(H2O)2]ClO4, result in 1-D zigzag chain complexes, [RuIII(L)2(CN)2MnIII(SB)]n (SB = salen, 1; salcy, 2; nappa, 4; napcy, 5), respectively. X-ray crystallographic studies reveal that each of the MnIII centers has a distorted octahedral environment, while complex 3 possesses a single cationic chain structure consisting of [Cu(chxn)2][Ru(L)2(CN)2]n units and their corresponding [Ru(L)2(CN)2]− anions. Compounds 1–3 exhibit antiferromagnetic coupling between the RuIII and MnIII/CuII centers, whereas 4 and 5 reveal ferromagnetic coupling between the RuIII and MnIII centers through the cyano bridges. Furthermore, magneto-structural correlation for some typical cyano-bridged heterobimetallic RuIII–MnIII/CuII compounds is discussed.

Introduction

Low-dimensional magnetic materials, such as single-molecule magnets (SMMs) and single-chain magnets (SCMs) with slow magnetic relaxation, have been extensively studied due to their unique potential applications for molecular devices, high-density information storage, and quantum computers.1

Recently, more and more molecule-based magnets based on 4d and 5d metal ions have been reported.2 An essential driving force for the interest in this area is because the heavier metal ions can contribute significantly to the physical properties of paramagnetic compounds. More specifically, the heavier metals possess more diffuse valent orbitals than 3d metals, which can result in stronger magnetic exchange interactions.3 The 4d/5d metal ions are characterized by large spin–orbit coupling that is instrumental in magnetic anisotropy.4,5 In the synthesis of paramagnetic materials, most efforts have been devoted to cyanide precursors, especially to those of Nb,6 Mo,7 W,8 and Re9 compounds, whereas low-dimensional magnetic materials incorporating Ru and Os units received less attention. With regard to the Ru(III)-containing building blocks, such like trans-[RuIII(L1)2(CN)2]− (L1 = 8-quinolinolato (Q) and acetylacetone anion (acac))10 and trans-[RuIII(salen)(CN)2]− (H2salen = N,N′-bis(salicylidene)ethylenediamine),11 they are used to construct a series of RuIII-3d and RuIII-4f polynuclear complexes that exhibit a variety of novel structural and magnetic properties. Recently, a new heteroleptic cyanido-Schiff base complex [K(H2O)2RuIII(valen)(CN)2]·H2O as a building block and its corresponding RuIII-4f heterometallic complexes with one-dimensional structures have been reported.12

Given the above mentioned trans-dicyano Ru complexes as useful building blocks, low-dimensional magnetic materials are easily constructed via the cyano bridges.13 For example, when building blocks of ((R,R) or (S,S))-[Bu4N][Ru(5-Cl-salcy)](CN)2] (salcy = N,N′-(1,2-cyclohexanediylethylene)bis(salicylideneiminato)dianion) and [Ru(salen)(CN)2]− are employed, a series of cyano-bridged chains and clusters that behave as ferrimagnets, SCMs, or metamagnets have been investigated in our previous work.14 And the design of novel cyanoruthenium(III) building blocks continues to be intriguing to us. Phenolic oxime ligands are extensively studied in extractive hydrometallurgy,15 however, the cooperative electronic properties in materials formed by transition metal complexes with cyanide ligands have been overlooked to date.

Herein, a new dicyanoruthenium(III) complex incorporating a relevant phenolic oxime, 2-hydroxyethanoneoxime, is reported. During the reaction, the oxime is reduced to imine by Ru(PPh3)3Cl2 (ref. 16) and thus leading to the formation of complex PPh4[Ru(L)2(CN)2] (L = 2′-hydroxyacetophenone imine). Based on the Ru-containing building block and its relevant hetorometallic units, five cyano-connected heterobimetallic one-dimensional (1D) chain complexes, [Ru(L)2(CN)2Mn(salen)]n (1), [Ru(L)2(CN)2Mn(salcy)]n (2), [Ru(L)2(CN)2Cu(chxn)]n (3), [Ru(L)2(CN)2Mn(nappa)]n (4), and [Ru(L)2(CN)2Mn(napcy)]n (5), have been synthesized and fully studied. In addition, magneto-structural correlation for some typical cyano-bridged heterobimetallic RuIII–MnIII/CuII compounds is accordingly discussed (Scheme 1).


image file: c5ra15752h-s1.tif
Scheme 1

Experimental section

General methods

All reagents and solvents were commercially available and used as received without further purification. [Mn(salen)(H2O)2]ClO4,17 [Mn(salcy)(H2O)2]ClO4,17 [Mn(nappa)(H2O)2]ClO4,17 [Mn(napcy)(H2O)2]ClO4,17 [Cu(chxn)2(H2O)2](NO3)2,18 Me-saoH2 and Ru(L)(PPh3)Cl were prepared according to previously reported methods.16 (Ph4P)[Ru(L)2(CN)2] was carried out by a procedure similar to that for (Bu4N)[Ru(salen)(CN)2] with minor modifications.19
(Ph4P)[Ru(L)2(CN)2]. Ru(L)PPh3Cl (1.33 g, 2.00 mmol) was refluxed with NaCN (25.0 mg, 5.00 mmol) in 50 mL of methanol for 1 h. The solution was evaporated to dryness and the residue then dissolved in 10 mL of water. Addition of Ph4PCl (556 mg, 2.00 mmol) to the aqueous solution produced a purple precipitate which was collected, washed with water, and dried in vacuo. Yield: 48%. Anal. calcd for C38H54N5O2Cl2Ru: C, 58.15; H, 6.93; N, 8.92. Found: C, 58.32; H, 6.71; N, 8.79. ESI-MS: (m/z) 544 (M−). Selected IR data (KBr, cm−1): 2096 (ν(C[triple bond, length as m-dash]N)).
Preparation of [Ru(L)2(CN)2Mn(salen)]n (1). A solution of [Mn(salen)(H2O)2]]ClO4 (18.2 mg, 40.0 μmol) in 10 mL of methanol was added to a solution of (Ph4P)[Ru(L)2(CN)2] (35.6 mg, 40.0 μmol) in 10 mL of acetonitrile. After stirring for 10 min, the resulted dark-brown solution was filtered off and then left undisturbed. The slow evaporation of the filtrate at room temperature gave dark-brown rod-like crystals of 1 after two weeks. Yield: 54%. Anal. calcd for C68H56Mn2N12O8Ru2: C, 55.14; H, 3.81; N, 11.35. Found: C, 55.36; H, 3.57; N, 11.01. Selected IR data (KBr, cm−1): 2106 (ν(C[triple bond, length as m-dash]N)).
Preparation of [Ru(L)2(CN)2Mn(salcy)]n (2). Preparation was similar to that of 1 by using [Mn(salcy)(H2O)2]ClO4 (20.4 mg, 40.0 μmol) instead of [Mn(salen)(H2O)2]]ClO4. The slow evaporation of the filtrate resulted in dark-green needles of 2 after two weeks. Yield: 60%. Anal. calcd for C38H32MnN6O4Ru: C, 57.58; H, 4.07; N, 10.60. Found: C, 57.35; H, 4.28; N, 10.85. Selected IR data (KBr, cm−1): 2113 (ν(C[triple bond, length as m-dash]N)).
Preparation of [Ru(L)2(CN)2Cu(chxn)]n (3). Preparation was similar to that of 1 by using Cu(chxn)2(NO3)2 (16.8 mg, 40.0 μmol) instead of [Mn(salen)(H2O)2]]ClO4. The slow evaporation of the filtrate gave dark-green needles of 3 after two weeks. Yield: 60%. Anal. calcd for C48H44CuN12O4Ru2: C, 51.54; H, 3.96; N, 15.03. Found: C, 51.27; H, 4.12; N, 15.22. Selected IR data (KBr, cm−1): 2094 (ν(C[triple bond, length as m-dash]N)).
Preparation of [Ru(L)2(CN)2Mn(nappa)]n (4). Complex 4 was obtained as black block crystals by slow diffusion of a methanol solution (5 mL) of (Ph4P)[Ru(L)2(CN)2] (35.6 mg, 40.0 μmol) and an acetonitrile solution (5 mL) of [Mn(nappa)(H2O)2]ClO4 (22.8 mg, 40.0 μmol) through an H-shaped tube at room temperature for about one month. The resulting crystals were collected, washed with methanol, and dried in air. Yield: 52%. Anal. calcd for C43H34MnN6O4Ru: C, 60.42; H, 4.01; N, 9.83. Found: C, 60.13; H, 4.25; N, 10.01. Selected IR data (KBr, cm−1): 2113 (ν(C[triple bond, length as m-dash]N)).
Preparation of [Ru(L)2(CN)2Mn(napcy)]n (5). Preparation was similar to that of 4, with the exception of [Mn(napcy)(H2O)2]ClO4 (24.4 mg, 40.0 μmol) used instead. The slow evaporation of the filtrate gave dark-green needles of 5 after one month. Yield: 55%. Anal. calcd for C46H32MnN6O4Ru: C, 62.16; H, 3.63; N, 9.46. Found: C, 62.39; H, 3.81; N, 9.21. Selected IR data (KBr, cm−1): 2114 (ν(C[triple bond, length as m-dash]N)).

X-ray structure determination

The crystal structures were determined with a Siemens (Bruker) SMART CCD diffractometer using monochromated Mo Kα radiation (λ = 0.71073 Å). The cell parameters were retrieved using SMART software and refined using SAINT20 for all observed reflections. Data were collected using a narrow-frame method with scan widths of 0.30° in ω and an exposure time of 10 s per frame. The absorption corrections were applied using SADABS21 supplied by Bruker. Structures were solved by direct methods using the SHELXL program.22 The positions of metal atoms and their first coordination spheres were located from direct methods E-maps. The other non-hydrogen atoms were found in alternating difference Fourier syntheses and least-squares refinement cycles and, during the final cycles, refined anisotropically. Hydrogen atoms were placed in calculated positions and refined as riding atoms with a uniform value of Uiso. Final crystallographic data and values of R1 and wR2 are listed in Table 1. Selected bond distances and angles for complexes 1–5 are listed in Tables 2–6. CCDC reference numbers are 1400054 (1), 1400055 (2), 1400056 (3), 1400057 (4), and 1400058 (5), respectively (Table 7).
Table 1 Summary of crystallographic data for complexes 1–5a
  1 2 3 4 5
a R1a = Σ||Fo| − |Fc||/Σ|Fo|. wR2b = [Σw(Fo2 − Fc2)2/Σw(Fo2)2]1/2.
Formula C68H60Mn2N12O8Ru2 C38H34MnN6O4Ru C48H48CuN12O4Ru2 C43H36MnN6O4Ru C46H34MnN6O4Ru
fw 1485.30 794.72 1122.66 856.79 890.80
Crystal system Triclinic Triclinic Triclinic Triclinic Triclinic
Space group P[1 with combining macron] P[1 with combining macron] P[1 with combining macron] P[1 with combining macron] P[1 with combining macron]
a, Å 12.573(2) 11.3228(8) 9.9611(13) 11.2322(11) 11.680(3)
b, Å 15.090(3) 13.2197(10) 12.0243(16) 12.9655(13) 13.560(3)
c, Å 21.612(4) 14.3410(11) 12.4374(17) 17.3258(18) 17.386(4)
α, deg 100.154(3) 79.9650(10) 103.509(2) 84.393(2) 82.361(4)
β, deg 103.996(3) 85.0240(10) 102.368(2) 81.625(2) 78.858(4)
γ, deg 94.967(3) 81.5080(10) 94.169(2) 71.103(2) 67.126(3)
V, Å3 3880.5 2086.5(3) 1403.0(3) 2358.3(4) 2484.2(10)
Z 2 2 1 2 2
ρcalcd, g cm−3 1.268 1.262 1.324 1.204 1.188
T/K 296(2) 293(2) 293(2) 296(2) 293(2)
μ, mm−1 0.754 0.706 0.955 0.630 0.600
F(000) 1504 810 569 874 906
Data/restraints/parameters 13[thin space (1/6-em)]506/0/836 7306/0/470 6244/24/365 8285/0/490 8712/0/499
GOF (F2) 0.932 1.179 1.061 1.143 1.103
R1a, wR2b (I > 2σ(I)) 0.0567, 0.1475 0.0591, 0.1392 0.0425, 0.1484 0.0345, 0.1060 0.0655, 0.1723
R1a, wR2b (all data) 0.0824, 0.1610 0.0671, 0.1429 0.0459, 0.1541 0.0461, 0.1119 0.0904, 0.1825

Table 2 Selected bond lengths (Å) and angles (°) for complex 1a
a Symmetry transformations used to generate equivalent atoms: #1: −x + 2, −y + 2, −z + 2; #2: −x + 1, −y + 1, −z.
C(9)–Ru(1) 2.057(5) C(26)–Ru(2) 2.067(5)
O(5)–Ru(2) 1.969(3) Ru(1)–C(9)#1 2.057(5)
N(1)–Ru(1) 2.040(4) N(6)–Ru(2) 2.037(4)
N(7)–Ru(2) 2.049(4) Ru(1)–N(1)#1 2.040(4)
Ru(1)–O(1)#1 1.986(3) Mn(1)–O(2) 1.902(4)
Mn(1)–O(3) 1.883(4) Mn(1)–N(4) 1.989(4)
Mn(1)–N(3) 1.975(4) Mn(1)–N(5) 2.298(4)
Mn(1)–N(2) 2.248(4) Mn(2)–O(6) 1.879(3)
Mn(2)–N(8) 2.288(4) N(8)–C(43)–Ru(2) 178.9(5)
N(2)–C(9)–Ru(1) 177.8(5) N(5)–C(26)–Ru(2) 173.9(5)
C(9)–N(2)–Mn(1) 163.6(4) C(26)–N(5)–Mn(1) 158.2(5)
C(43)–N(8)–Mn(2) 161.8(4) C(60)–N(11)–Mn(2) 159.9(5)

Table 3 Selected bond lengths (Å) and angles (°) for complex 2
C(37)–Ru(1) 2.062(6) C(38)–Ru(2) 2.066(6)
Mn(1)–N(1) 1.994(5) Mn(1)–N(2) 2.011(5)
Mn(1)–O(1) 1.864(4) Mn(1)–O(2) 1.873(4)
Mn(1)–N(5) 2.396(5) Mn(1)–N(6) 2.315(5)
N(3)–Ru(2) 2.045(4) N(4)–Ru(1) 2.021(5)
O(3)–Ru(2) 2.005(3) O(4)–Ru(1) 1.982(4)
N(5)–C(37)–Ru(1) 174.5(5) N(6)–C(38)–Ru(2) 175.4(5)
C(37)–N(5)–Mn(1) 150.1(5) C(38)–N(6)–Mn(1) 153.3(4)

Table 4 Selected bond lengths (Å) and angles (°) for complex 3a
a Symmetry transformations used to generate equivalent atoms: #1: −x, −y + 2, −z + 1; #2: −x + 1, −y + 2, −z + 1; #3: −x + 1, −y + 1, −z + 1.
N(5)–Cu(1) 2.051(3) N(6)–Cu(1) 2.002(4)
Cu(1)–N(6′)#2 2.002(4) Cu(1)–N(6)#2 2.002(4)
Cu(1)–N(5′)#2 2.051(3) Cu(1)–N(5)#2 2.051(3)
Cu(1)–N(4) 2.411(4) Cu(1)–N(4)#2 2.411(4)
N(1)–Ru(2) 2.048(4) N(3)–Ru(1) 2.046(3)
O(1)–Ru(2) 1.988(3) O(2)–Ru(1) 1.982(3)
N(4)–C(18)–Ru(1) 177.9(4) C(18)–N(4)–Cu(1) 123.5(3)

Table 5 Selected bond lengths (Å) and angles (°) for complex 4a
a Symmetry transformations used to generate equivalent atoms: #1: −x + 2, −y, −z; #2 −x + 1, −y + 1, −z + 1.
Ru(1)–O(1)#1 1.9904(17) Ru(1)–O(1) 1.9904(17)
Ru(1)–N(1) 2.036(2) Ru(1)–N(1) 2.036(2)
Ru(1)–C(9)#1 2.077(3) Ru(1)–C(9) 2.077(3)
Ru(2)–C(35) 2.072(3) Ru(2)–C(35)#2 2.072(3)
Ru(2)–N(6) 2.037(2) Ru(2)–N(6)#2 2.037(2)
Ru(2)–O(4) 1.988(2) Ru(2)–O(4)#2 1.988(2)
Mn(1)–O(3) 1.8847(19) Mn(1)–O(2) 1.8978(19)
Mn(1)–N(3) 1.971(2) Mn(1)–N(4) 1.974(2)
Mn(1)–N(5) 2.292(3) Mn(1)–N(2) 2.347(3)
N(2)–C(9)–Ru(1) 178.4(3) C(35)–N(5)–Mn(1) 171.9(3)
N(5)–C(35)–Ru(2) 175.3(3) C(9)–N(2)–Mn(1) 176.2(3)

Table 6 Selected bond lengths (Å) and angles (°) for complex 5a
a Symmetry transformations used to generate equivalent atoms: #1: −x, −y + 1, −z + 2; #2 −x + 1, −y, −z + 1.
Mn(1)–O(2) 1.889(4) Mn(1)–O(3) 1.909(4)
Mn(1)–N(5) 1.941(6) Mn(1)–N(4) 1.974(5)
Mn(1)–N(3) 2.296(5) Mn(1)–N(6) 2.322(5)
Ru(1)–O(1)#1 1.998(4) Ru(1)–O(1) 1.998(4)
Ru(1)–N(1) 2.050(4) Ru(1)–N(1)#1 2.050(4)
Ru(1)–C(44) 2.101(5) Ru(1)–C(44)#1 2.101(5)
Ru(2)–O(4)#2 1.977(4) Ru(2)–O(4) 1.978(4)
Ru(2)–C(45)#2 2.067(6) Ru(2)–N(7) 2.007(6)
N(3)–C(44)–Ru(1) 174.0(5) N(6)–C(45)–Ru(2) 177.6(7)
C(44)–N(3)–Mn(1) 172.1(5) C(45)–N(6)–Mn(1) 172.9(7)

Table 7 Structural and magnetic parameters for related cyano-bridged RuIII–MnIII complexesa
Complexes dMn–N/Å Ru–C–N (deg) Mn–N–C (deg) Jexp/cm−1 Ref.
a H2TPP = meso-tetra(4-phenyl)-porphyrin.
Ru(salen)CN2[Mn(L1)] 2.292–2.307 169.9–170.6 143.1–144.3 1.34 13
{[Ru(Q)2](μ-CN)2[Mn(salcy)]}n 2.286 175.7 154.2–149.6 −0.75 10a
[{Mn(5,5′-Me2salen)}2{Ru(acac)2(CN)2}][Ru(acac)2(CN)2]·2CH3OH 2.165 178.3 168.1 0.87, 0.24 26
{[Ru(acac)2(CN)2][Mn(TPP)]}{[Ph3(PhCH2)P]PF6}2CH3OH 2.251 177.5 152.3 3.25 25
{[Ru(acac)2(CN)2][Mn(TPP)]}{[Ph3(PhCH2)P]ClO4}2CH3OH 2.250 177.7 153.0 3.43 25
[Ru(salen)(CN)2Mn(R,R-salcy)]n 2.325–2.354 174.2–175.4 156.4–154.3 −0.40, −1.32 14a
[Ru(salen)(CN)2Mn(R,R-salphen)]n 2.331–2.349 168.9–178.0 158.7–174.8 −1.25, −1.87 14a
1 2.248–2.298 177.8 158.2–163.6 −0.37, −0.08 This paper
2 2.315–2.396 174.5 150.1–153.3 −3.57, −1.71 This paper
4 2.292–2.347 178.4 171.9–176.2 0.90 This paper
5 2.296–2.322 174.0 172.9–172.1 0.37 This paper

Physical measurements

Elemental analyses for C, H, and N were performed on a Perkin-Elmer 240C analyzer. Infrared spectra were recorded on a Vector22 Bruker Spectrophotometer with KBr pellets in the 400–4000 cm−1 region. Magnetic susceptibilities for polycrystalline samples were measured with the use of a Quantum Design MPMS-SQUID-VSM magnetometer in the temperature range of 1.9–300 K. Field dependences of magnetization were measured using Quantum Design MPMS-SQUID-VSM system in an applied field up to 70 kOe.

Results and discussion

Syntheses and spectroscopic studies

In this paper, Na[RuIII(L)2(CN)2] was synthesized from the reaction of Ru(L)2(PPh3)Cl and NaCN. After the reaction with Ph4PCl, the dicyanometalate precursor, (PPh4)[RuIII(L)2(CN)2], was prepared in good yield. (PPh4)[RuIII(L)2(CN)2] is soluble in most common organic solvents, such as methanol, acetonitrile, chloroform, and N,N-dimethylformamide. The C[triple bond, length as m-dash]N stretching frequency is located at 2096 cm−1, which is comparable to those reported in Ru(III) dicyanides, such as (PPh4)[Ru(Q)2(CN)2] (2095 cm−1),10 Na[RuIII(salen)(CN)2] (2080 cm−1),19 and ((R,R) or (S,S))-[Bu4N][Ru(5-Cl-salcy)](CN)2] (2096 cm−1).14

The reactions of (PPh4)[RuIII(L)2(CN)2] and its corresponding metallic counter parts [Mn(SB)(H2O)2]+ or [Cu(chxn)]2+ in methanol (or methanol/acetonitrile) lead to the formation of one-dimensional heterobimetallic complexes 1–5. In IR spectra, C[triple bond, length as m-dash]N stretching vibrations are observed (2106 cm−1 for 1, 2113 cm−1 for 2, 2096 cm−1 for 3, 2113 cm−1 for 4, and 2114 cm−1 for 5), which is consistent with other RuIII–M bimetallic compounds.10a

Structural description

The structural parameters such as key bond lengths and angles are listed in Table 2. The crystal structures of complexes 1–5 are shown in Fig. 1–5, respectively. With the use of different Schiff base ligands, complexes 1, 2, 4, and 5 show similar structures, demonstrated by the crystal cell parameters listed in Table 1 that all crystals sit in the triclinic space group. The asymmetric unit of 1, 2, 4, and 5 is composed of one [MnIII(SB)]+ cation and two [Ru(L)2(CN)2]− anions. For the [MnIII(SB)]+ cations, SB ligands adopt a quasi-planar chelating mode, resulting in the coordination to the MnIII ion along the equatorial plane. Such coordination mode leaves the axial sites available to be trans-coordinated by N atoms from cyanide bridges, thus forming a 1-D (–Ru–C[triple bond, length as m-dash]N–Mn–N[triple bond, length as m-dash]C–)n liner chain. The axial Mn–Ncyanide bond lengths (2.248(4)–2.396(5) Å) are significantly longer than the equatorial Mn–N(O) (1.883(4)–2.011(5) Å) lengths, forming the elongated octahedral configuration derived from Jahn–Teller distortion of MnIII. The bond angles of Mn–N–Ccyanide are: 158.2(5)–163.6(4)° for 1, 150.1(5)–153.3(4)° for 2, 171.9(3)–176.2(4)° for 4, and 172.1(5)–172.9(7)° for 5, respectively. With regard to the moiety of [Ru(L)2(CN)2]−, the coordination environment of RuIII can also be described as a distorted octahedron, consisting of two N atoms (salen ligand), two C atoms (cyanide groups), and two O atoms (phenolic oxygen). The average Ru–N(O) bond length is 2.015(4) Å, whereas the mean Ru–C length is 2.079(4) Å, which trend agrees well with other RuIII–M bimetallic compounds.10a The Ru–C[triple bond, length as m-dash]N angles (174.0(5)–178.4(3)°) show slight deviation from linearity. With respect to the molecular chains, complex 1, for instance, is running along the b axis with the intrachain Ru⋯Mn separation of 5.457(3) Å through the bridging cyanide. The shortest interchain Ru⋯Ru, Mn⋯Mn, and Ru⋯Mn distances are 7.232, 6.732, and 8.099 Å, respectively, obviously longer than the intrachain metal⋯metal distances.
image file: c5ra15752h-f1.tif
Fig. 1 Asymmetric unit (top) and one-dimensional chain structure (bottom) of complex 1. Hydrogen atoms are omitted for clarity.

image file: c5ra15752h-f2.tif
Fig. 2 Asymmetric unit (top) and one-dimensional chain structure (bottom) of complex 2. Hydrogen atoms are omitted for clarity.

image file: c5ra15752h-f3.tif
Fig. 3 Asymmetric cationic unit (top) and one-dimensional cationic chain structure (bottom) of complex 3. Hydrogen atoms are omitted for clarity.

image file: c5ra15752h-f4.tif
Fig. 4 Asymmetric unit (top) and one-dimensional chain structure (bottom) of complex 4. Hydrogen atoms are omitted for clarity.

image file: c5ra15752h-f5.tif
Fig. 5 Asymmetric unit (top) and one-dimensional chain structure (bottom) of complex 5. Hydrogen atoms are omitted for clarity.

There is no significant interaction between two neighboring chains except for 4. Each chain interacts with the two adjacent chains via π–π stacking between aromatic rings of the salcy ligands with a centroid distance of 3.353 Å, thus forming the 3D structure (Fig. S1†).

Treatment of Cu(chxn)2(NO3)2 with trans-(Ph4P)[Ru(L)2(CN)2] in methanol at room temperature gives complex 3 (Fig. 3). Complex 3 displays a single cationic chain structure consisting of a [Cu(chxn)2][Ru(L)2(CN)2]n unit and a free [Ru(L)2(CN)2]− anion. The CuII center has a distorted octahedral environment coordinated by four equatorial nitrogen atoms from two chxn ligands and two axial nitrogen atoms from [Ru(L)2(CN)2]− units with a trans configuration. The Cu–Ncyanide length of 2.411(4) Å is slightly longer than the Cu–Nchxn lengths [2.002(4) and 2.051(3) Å]. The bridging Ru–C[triple bond, length as m-dash]N angle is 177.9(4)°. The bond lengths in each [Ru(L)2(CN)2]− unit [Ru–O of 1.982(3)–1.988(3) Å and Ru–N of 2.046(4)–2.048(3) Å] are similar to those found in trans-(Ph4P)[Ru(acac)2(CN)2].10a Furthermore, the intramolecular Cu⋯Ru distance is 4.981 Å, along with the Cu–N–C–Ru torsion angle of −160.2° and the closest intermolecular Ru⋯Ru separation of 6.012 Å.

Magnetic properties

Magnetic susceptibility measurements were performed on polycrystalline samples of complexes 1–5 using the SQUID magnetometer at temperatures ranging from 1.9 K to 300 K.
Magnetic properties of 1 and 2. As shown in Fig. 6 and 7, the temperature dependence on susceptibilities provides the following χMT values (χM is the magnetic susceptibility per RuIIIMnIII unit) at room temperature, 3.41 cm3 K mol−1 for 1 and 3.19 cm3 K mol−1 for 2, respectively, both of which are close to the value of 3.38 cm3 K mol−1 expected for one low-spin Ru(III)-centered (S = 1/2) and one high-spin Mn(III)-centered (S = 2) complexes when g = 2.00 and no exchange coupling are assumed. By lowering the temperature, the observed χMT values decrease smoothly and attain a minimum amount of 2.59 cm3 K mol−1 at 5 K for 1 and 2.87 cm3 K mol−1 at 19 K for 2, indicating the presence of antiferromagnetic coupling between the cyanide-bridged RuIII–MnIII complexes. Upon further cooling, χMT value increases sharply to reach a maximum of 2.68 cm3 K mol−1 at 2.70 K for 1 and 3.71 cm3 K mol−1 at 3.40 K for 2. When temperature of 1.90 K is applied, both χMT values of 1 and 2 decrease to 2.40 cm3 K mol−1 for 1 and 1.20 cm3 K mol−1 for 2, respectively. Curie–Weiss fitting for 1 and 2 in the temperature range 50–300 K affords C = 3.44(1) cm3 K mol−1, θ = −1.89(3) K for 1 (Fig. S2†) and C = 3.25(1) cm3 K mol−1, θ = −4.41(4) K for 2 (inset of Fig. 7), respectively. The negative θ indicates a dominant antiferromagnetic (AF) coupling between spin centers. The magnetization of these compounds per [MnIIIRuIII] unit reaches values of 3.45 Nβ mol−1 for 1 and 2.94 Nβ mol−1 for 2 at 1.90 K and 50 kOe (Fig. S3 and S4,† respectively), which is close to the value of 3.00 Nβ for the subtraction of one RuIII and one MnII magnetic moment (ST = SMn − SRu = 3/2; Ms = gSTNβ).
image file: c5ra15752h-f6.tif
Fig. 6 Temperature dependence of χMT (□) at 1 kOe and (inset) χMT for complex 1 at 1.9–6 K.

image file: c5ra15752h-f7.tif
Fig. 7 Temperature dependence of χMT (□) and (inset) 1/χM (□) for complex 2 at 1 kOe.

According to the structures, the RuIII–C[triple bond, length as m-dash]N–MnIII linkages are obviously different. An alternating ferrimagnetic chain model image file: c5ra15752h-t1.tif was used,23 where the local spins are SRu and SMn, the local Zeeman factors gRu and gMn, and the couplings between nearest neighbors J(1 + α) and J(1 − α). The best fit between 30 and 300 K gives gMn = 2.01(1), gRu = 1.96(1), J = −0.23(1) cm−1, α = 0.63(1), and zJ′ = 0.12(3) (R = 3.64 × 10−4) for 1 and gMn = 1.95(1), gRu = 1.99(1), J = −2.67(1) cm−1, α = −0.34(1), and zJ′ = −0.56(2) (R = 1.16 × 10−4) for 2, where R = ∑[(χMT)obs − (χMT)calc]2/∑(χMT)obs2. The above mentioned result confirms that antiferromagnetic couplings between RuIII and MnIII ions within the chain are observed.

Magnetic properties of 3. The temperature-dependent χMT for 3 is shown in Fig. 8. The χMT value at 300 K is 1.30 cm3 K mol−1 in each Ru2IIICuII unit, which is close to the theoretical value of 1.13 cm3 K mol−1 calculated from two non-coupled Ru(III) centers (S = 1/2) and a Cu(II) (S = 1/2) spin, assuming gRu = gCu = 2.00. The abrupt decrease of χMT below 10 K and the negative θ values indicate a dominant antiferromagnetic (AF) coupling between RuIII and CuII via C[triple bond, length as m-dash]N bridges in 3.10a In order to gain further insights into the underlying magnetic nature of 3, the field dependence of magnetization was measured at 1.90 K (Fig. 9). The magnetization increases slowly to a maximum value of 2.82 Nβ at 70 kOe, which is smaller than the expected value of 3.00 Nβ with the antiferromagnetic coupling between RuIII and MnIII ions. Alternating current magnetic measurements (Fig. S5†) show undetectable frequency-dependent χM′ and χM′′ signals for 3, indicating a completely paramagnetic behavior without any magnetic ordering.
image file: c5ra15752h-f8.tif
Fig. 8 Temperature dependence of the χMT product for 3 at 1 kOe. (Inset) field dependence of the magnetization for 3, the lines represent the Brillouin function that correspond to S = 1/2 + 2 with g = 2.0.

image file: c5ra15752h-f9.tif
Fig. 9 Left: temperature dependence of χMT (□) at 1 kOe and (inset) χMT for complex 4 at 1.9–10 K. Right: field dependence of the magnetization for 4, the red line represent the Brillouin function that correspond to S = 1/2 + 2 with g = 2.0. (Inset) dM/dH vs. H plot at 1.9 K.
Magnetic properties of 4 and 5. The temperature-dependent magnetic susceptibilities of 4 and 5 were collected at 1 kOe in the temperature range of 1.90–300 K (Fig. 9 and 10). The χMT values at 300 K for 4 and 5 are 3.45 and 3.60 cm3 K mol−1, respectively, both of which are close to the spin-only value of 3.38 cm3 K mol−1 assumed for a magnetically diluted spin system (one SRu = 1/2, SMn = 2) with g = 2.00. By lowering the temperature, the χMT values increase slowly by 20 K and abruptly reach a maximum of 7.40 cm3 K mol−1 at 2.20 K for 4 and 4.91 cm3 K mol−1 at 1.90 K for 5. The continuous rise in χMT at lower temperatures clearly indicates the operation of intrachain ferromagnetic couplings between RuIII and MnIII entities communicated by cyanide bridges. Below 2.20 K, the χMT value of 4 decreases sharply again and a value of 6.70 cm3 K mol−1 at 1.90 K was observed. No minimum was observed in the χM vs. T plots for 5.13 The downturn of χMT below 2.20 K pertains to zero-field splitting (ZFS) effect and/or interchain antiferromagnetic interactions.12a From the data, the Curie–Weiss fitting for 4 and 5 based on χM = C(T − θ) can be carried out between 4.50 and 300 K, affording C = 3.70(1) cm3 K mol−1, θ = 1.92(8) K for 4 (Fig. S6†), and C = 3.49(1) cm3 K mol−1, θ = 0.14(3) K for 5 (Fig. S8†), respectively. The positive θ indicates a dominant ferromagnetic coupling for 4 and 5, the behavior of which is consistent with that of other cyanide-bridged Ru–Mn compounds.13 According to the structural data, an alternating chain model (also called the Seiden model) of quantum spins (si = 1/2 for RuIII ion) and the classical spins (si = for MnIII ion) based on the following spin Hamiltonian are employed.24
image file: c5ra15752h-t2.tif
image file: c5ra15752h-f10.tif
Fig. 10 Temperature dependence of χMT (□) 1 kOe and (inset) χMT for complex 5 at 1.9–10 K.

Between 4.5 K and 300 K, the best least-squares fit yields g = 2.01(1), J = 0.90(1) cm−1, with R = 2.5 × 10−4 for complex 4. The susceptibility data were fitted over 4.5 K using the same expression that gives g = 2.05(1), J = 0.37(1) cm−1, with R = 8.7 × 10−4 for complex 5. The fitting results imply that the effect of ferromagnetic couplings between RuIII and MnIII ions in 4 is stronger than those in 5.

Field-dependent magnetizations for 4 and 5 were measured from 0–70 kOe at 1.9 K (Fig. 9 and S9†). As the intensity of applied field increases, the magnetizations continuously increase until reaching 4.10 Nβ and 3.95 Nβ at 70 kOe for 4 and 5, respectively, which are slightly lower than the ferromagnetic result (5.00 Nβ) calculated from Ms = g(SRu + SMn) with g = 2.00.

To gain further insight into the underlying magnetic nature of 4, from the dM/dH vs. H plot at 1.90 K (inset of Fig. 9), the critical field is estimated to be about 920 kOe. To investigate the phase transition at low temperature, ZFC and FC curves show an abrupt increase below 2.20 K with a divergence (Fig. 11), suggesting the occurrence of a long-range magnetic ordering below this temperature. Furthermore, alternating current (ac) magnetic susceptibilities measurements were carried out at zero direct current (dc) field (Fig. 11). The results show that only in-phase (χM) signals display a peak around 2.20 K, demonstrating the field-induced three-dimensional antiferromagnetic ordering below this temperature.


image file: c5ra15752h-f11.tif
Fig. 11 Left: temperature dependence of the in-phase χ′ (top) and out-of-phase χ′′ (bottom) at different frequencies in 2 Oe ac field oscillating at 1–999 Hz with zero applied dc field for 4. Right: temperature dependence of the magnetization for 4 at 10 Oe.

It is noted that the related magneto-structurally characterized analogues based on RuIII–M systems were found to be either ferro- or antiferromagnetic coupling systems.10,13,14,25,26 According to Kahn's orbital symmetry model,20 the nature of Cu(II) and Ru(III) interaction should be ferromagnetic (JF). The observed antiferromagnetic interaction (JAF) of CuII and RuIII via cyano bridges in 3 may be ascribed to the very acute Cu–N[triple bond, length as m-dash]C angle (123.5(3)°) and long Cu⋯Ru distance (4.981 Å). A similar antiferromagnetic interaction (JAF) has also been observed in the compound {[RuIII(Q)2(CN)]2(μ-CN)2[CuII(cyclam)]}.10a In previous studies, the ferromagnetic coupling could be universally observed in cyanide-bridged Ru(III)–Mn(III) systems.25 For the nature of RuIII and MnIII interaction, it is expected that when the dπ orbitals on RuIII and MnIII are overlapped, antiferromagnetic interactions (JAF) will emerge and vice versa. As shown in Table 6, the most complexes are in accordance with the above theoretical analysis. The magnetic behaviors of complexes 1, 2, 4, and 5 appear to be slightly unusual. Especially, the bond lengths of Mn–N(cyanide) in 4 (2.292(3)–2.347(3) Å) and 5 (2.296(5)–2.322(5) Å) are in accord with those in [RuIII(salen)(CN)2][MnIII(L2)]13 (L2 = N,N′-(1-methylethylene)bis(2-hydroxynaphthalene-1-carbaldehydeneiminate)dianion); and the bond angles of Mn–N[triple bond, length as m-dash]C(cyanide) (171.9(3)–176.2(4)°) for 4 and 172.1(5)–172.9(7)° for 5 are remarkably larger than those in [RuIII(salen)(CN)2][MnIII(L2)].13 Magnetic investigation reveals ferromagnetic coupling in 4 and 5. The t2g orbitals of RuIII and MnIII overlap efficiently, resulting in the un-production of antiferromagnetic coupling and its mechanism for a magnetic exchange in the pathway of RuIII–C[triple bond, length as m-dash]N–MnIII was well analyzed by Lau et al. through DFT calculations.26 In conclusion, both the relative symmetries and relative energies of the magnetic orbitals are valuable in determining the overall magnetic coupling in bimetallic assemblies. Therefore, the full understanding of this magnetic behavior induced by energies of the magnetic orbitals deserves further investigation.

Conclusions

Five 1-D zigzag RuIII–MnIII/CuII chains obtained on a basis of a new paramagnetic ruthenium(III)-derived building block, trans-[Ru(L)2(CN)2]−, have been synthesized and structurally characterized. Complexes 1–3 exhibit intrachain antiferromagnetic coupling between RuIII and MnIII/CuII entities through cyanide ligands, while intrachain ferromagnetic coupling between RuIII and MnIII through cyanide ligands can be observed for complexes 4 and 5. It is noteworthy that complex 4 shows interesting metamagnetic behaviors with a critical field of about 920 Oe at 1.9 K. Furthermore, magneto-structural correlation for some typical cyano-bridged heterobimetallic RuIII–MnIII/CuII compounds has been discussed in this work. It can be assumed that the relative symmetries and their corresponding magnetic orbital energies are valuable in determining the overall magnetic coupling in bimetallic assemblies. On the basis of the above mentioned results, the present work shows that the type of [Ru(L)2(CN)2]− building block is useful for the construction of low-dimensional 3d–4d magnetic materials.

Abbreviations

salenN,N′-Ethylenebis(salicylideneimine)dianion
salcyN,N′-(1,2-Cyclohexanediylethylene)bis(salicylideneiminato)dianion
chxn1,2-Diaminocyclohexane
nappaN,N′-(1-Methylethylene)bis(2-hydroxynaphthalene-1-carbaldehydene-iminate)dianion
napcyN,N′-(1,2-Cyclohexanediylethylene)bis(2-hydroxynaphthalene-1-carbaldehydene-iminate)dianion

Acknowledgements

This work was supported by the Major State Basic Research Development Program (2013CB922101), the National Natural Science Foundation of China (51173075), and the Natural Science Foundation of Jiangsu Province (BK20130054). We also thank Dr Tian-Wei Wang for the experimental assistance on magnetic measurements.

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Footnote

† Electronic supplementary information (ESI) available: Additional structures, spectroscopic data, magnetic characterization data, and X-ray crystallographic files in CIF formats for 1–5. CCDC 1400054–1400058. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c5ra15752h
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