MATCH Commun. Math. Comput. Chem. 56 (2006) 97-111 MATCH Communications in Mathematical and in Computer Chemistry ISSN 0340 - 6253 Topological Research on Lattice Energies for Inorganic Compounds Lailong Mu*, Changjun Feng Department of Chemistry, Xuzhou Normal University, Xuzhou 221116, P. R. China Hongmei He XuZhou College of Industrial Technology, Xuzhou, 221006, P. R. China MULL@XZNU.EDU.CN (Received November 3, 2005) A novel connectivity index mG and its converse index mG’ based on adjacency matrix of molecular graphs are proposed as follows: mG = Σ (gi.gj.gk.…)0.5, mG’ = Σ (gi.gj.gk.…)-0.5. The gi element of adjacency matrix is defined as gi=(1+mi1.7).Xi0.3/(1+ri), where mi,Xi,ri, are the charge number, the electronegativity and Goldschmidt ionic radius of atom i respectively. By using the connectivity index mG and its converse index mG’, the multiple linear regression and multiple nonlinear regression can provide high-quality QSPR models for the lattice energies of 318 inorganic compounds. The results imply that the lattice energies may be expressed as a linear or nonlinear combination of the connectivity indices 0G,1G,0G’ and 1G’. For the nonlinear model, the correlation coefficient r and the standard error s are 0.9998 and 217.6 kJ.mol-1, respectively. The cross-validation by using the leave-one-out method demonstrates that the models are highly reliable from the point of view of statistics. 1. INTRODUCTION The quantitative structure-property/activity relationship (QSPR/QSAR) studies of organic compounds have been a focus of great attention by the scientists for a long time1-3. Large numbers of QSPR/QSAR models have been developed by using various model parameters to describe and predict the physical properties and biological activities of organic compounds from their molecular structures. However, there are only a few papers4-11 about the QSPR/ * Tel:+86-516-3403163;Fax: +86-516-3403164 E-mail address: mull@xznu.edu.cn - 98 - QSAR studies of inorganic compounds, due to the complexity of inorganic-compound composition. The lattice energy of an inorganic ionic crystal is a dominant term in the thermodynamic analysis of the existence and stability of an ionic crystal. It is one of the most important quantities in indicating the structure, character, and behavior (reactivity) of solids. Although lattice energy can be determined experimentally from the Born-Haber-Fajans thermochemical cycle, direct experimental determination is generally not possible since, in practice, the crystalline solid dissociates into atoms but not gaseous ions, as it is required in the lattice energy evaluation. Therefore, its indirect experimental determination, computation, or estimation is of considerable interest in modern materials science. Theoretical studies on lattice energy have been carried out almost since the beginning of 1900s, and a variety of estimation methods for lattice energies were available.12~29 In recent years, Feng et al.7,9-11 and Xu et al.8 etc., by using various model parameters, have developed some QSPR/QSAR models to estimate the lattice energies of inorganic compounds. In this study, the ionic polarization force parameter gi is defined based on ionic radii, electronegativity, ionic charge. A now topological index mG and its converse index mG’ are proposed based on the randic’s index and gi. The connectivity index mG together with mG’ has good correlations for lattice energies of inorganic ionic crystals. 2. METHODS Ionic crystals are made up of positive and negative ions, and the strongest interactions result from the nearest oppositely charged ions. The lattice energy contribution originates mainly from these nearest interactions, and the sum of the lattice energies of these interacting ion pairs is affected by the ionic radius, electronegativity, ionic charge. As mentioned above the polarization force parameter gi is defined as: gi=(1+mi1.7).Xi0.3/(1+ri) (1) where mi, Xi , ri are the charge number, the electronegativity30 and Goldschmidt31 ionic radius of atom i respectively. For ions of different atoms and ions of the same atom with different charges, the gi are different. The gi of 78 ions are calculated and listed in Table 1. Table 1. Ionic polarization force parameters No 1 2 3 4 Ionic Ag+ Al3+ As3+ Au3+ ri 1.13 0.55 0.69 1.37 Xi 1.93 1.61 2.18 2.54 mi 1 3 3 3 gi 1.1437 5.5618 5.5866 1.1162 No 40 41 42 43 Ionic Nd3+ Ni2+ P5+ Pb2+ ri 1.15 0.78 0.17 1.32 Xi 1.14 1.91 2.19 2.33 mi 3 2 5 2 gi 3.6152 2.8985 17.7613 2.3605 - 99 - 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 B3+ Ba2+ Be2+ Bi3+ Ca2+ Cd2+ Ce3+ Co2+ Co3+ Cr2+ Cr3+ Cs+ Cu+ Cu2+ Dy3+ Er3+ Fe2+ Fe3+ Ga3+ Gd3+ Ge2+ Hg2+ Ho3+ In3+ K+ La3+ Li+ Mg2+ Mn2+ Mn3+ Mn4+ Mo3+ Mo4+ Mo6+ Na+ 0.20 1.38 0.34 1.20 1.05 0.99 1.19 0.82 0.65 0.89 0.65 1.70 0.96 0.72 1.07 1.04 0.83 0.67 0.62 1.11 0.65 1.12 1.05 0.92 1.33 1.15 0.70 0.75 0.91 0.62 0.52 0.69 0.65 0.41 0.98 2.04 0.89 1.57 2.02 1.00 1.69 1.12 1.88 1.88 1.66 1.66 0.79 1.90 1.90 1.22 1.24 1.83 1.83 1.81 1.20 2.01 2.00 1.23 1.78 0.82 1.10 0.98 1.31 1.55 1.55 1.55 2.16 2.16 2.16 0.93 3 2 2 3 2 2 3 2 3 2 3 1 1 2 3 3 2 3 3 3 2 2 3 3 1 3 1 2 2 3 4 3 4 6 1 7.7126 1.7240 3.6304 4.1945 2.0727 2.4992 3.5303 2.8214 5.4734 2.6173 5.2728 0.6902 1.2371 2.9949 3.8321 3.9074 2.7834 5.3643 5.5117 3.7408 3.1751 2.4675 3.8789 4.6272 0.8088 3.5766 1.1694 2.6329 2.5372 5.2611 8.6709 5.5712 8.8239 19.6856 0.9883 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 Pb4+ Pd2+ Pr3+ Rb+ Rh3+ Sb3+ Sb5+ Sc3+ Si4+ Sm3+ Sn2+ Sn4+ Sr2+ Ti2+ Ti3+ Ti4+ Tl+ Tl3+ Tm3+ V2+ V3+ V5+ Y3+ Zn2+ Zr4+ BrClFHIN3O2S2Se2Te2- 0.84 0.80 1.12 1.49 0.75 0.90 0.62 0.83 0.40 1.13 1.02 0.74 1.18 0.76 0.70 0.64 1.49 1.05 1.04 0.88 0.75 0.36 0.95 0.83 0.80 1.96 1.81 1.33 2.08 2.20 1.71 1.35 1.82 1.93 2.12 2.33 2.20 1.13 0.82 2.28 2.05 2.05 1.36 1.90 1.17 1.96 1.96 0.95 1.54 1.54 1.54 2.04 2.04 1.25 1.63 1.63 1.63 1.22 1.65 1.33 2.96 3.16 3.98 2.20 2.66 3.04 3.44 2.58 2.55 2.10 4 2 3 1 3 3 5 3 4 3 2 4 2 2 3 4 1 3 3 2 3 5 3 2 4 1 1 1 1 1 3 2 2 2 2 8.0947 2.9905 3.6566 0.7568 5.4681 4.8783 12.5759 4.4782 10.0071 3.6777 2.5740 8.1271 1.9193 2.7481 5.0038 8.0209 0.9948 4.5147 3.9169 2.6169 4.9444 13.9844 4.0679 2.6982 6.9935 0.9357 1.0051 1.2991 0.8226 0.8382 3.8494 2.6193 2.0023 1.9204 1.7014 Based on adjacency matrix of molecular graphs, the novel connectivity index mG and its converse index mG’ can be defined as follows: G=Σ(gi.gj.gk.…)0.5 m (2) G’=Σ(gi.gj.gk.…)-0.5 m (3) 0 where, m is the order of the molecular connectivity index. The G, 1G, 0G’, and 1G’ are defined as follows: 0 G=Σ(gi)0.5 (4) G=Σ(gi.gj)0.5 (5) G’=Σ(gi)-0.5 (6) 1 0 1 G’=Σ(gi.gj) -0.5 (7) - 100 - In expressions (4) and (6), the “Σ” is the sum of atomic of inorganic compound chemical formula. In expressions (5) and (7), the “Σ” is the sum of chemical single bonds of chemical formula. For example, the 0G, 1G, 0G’, and 1G’ of Ba4NaSb3O12 are calculated as follows: For Ba4NaSb3O12, it can be treated as consisting of four Ba2+, one Na+, three Sb5+ and twelve O2-, it contains eight Ba-O single bonds, one Na-O single bonds and fifteen Sb-O single bonds, so: 0 G=4×1.72400.5+0.98830.5+3×12.57590.5+12×2.61930.5= 36.3060 1 G=8×(1.7240×2.6193)0.5+(0.9883×2.6193)0.5+15×(12.5759×2.6193)0.5=104.6993 0 G’=4×1.7240-0.5+0.9883-0.5+3×12.5759-0.5+12×2.6193-0.5=12.3129 1 G’=8×(1.7240×2.6193)-0.5+(0.9883×2.6193)-0.5+15×(12.5759×2.6193)-0.5=6.9998 The 0G, 1G, 0G’, and 1G’ of 318 inorganic compounds are calculated and listed in Table 2. Table2. The calculated and Experimental Lattice Energies of 318inorganic compounds (kJ.mol-1) No 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 Substance LiF NaF KF RbF CsF LiCl NaCl KCl RbCl CsCl LiBr NaBr KBr RbBr CsBr LiI NaI KI RbI CsI BeF2 MgF2 CaF2 SrF2 BaF2 BeCl2 MgCl2 CaCl2 SrCl2 BaCl2 BeBr2 MgBr2 CaBr2 SrBr2 BaBr2 0 G 2.2211 2.1339 2.0391 2.0097 1.9705 2.0839 1.9967 1.9019 1.8725 1.8333 2.0487 1.9615 1.8666 1.8372 1.7981 1.9969 1.9097 1.8148 1.7855 1.7463 4.1849 3.9022 3.7192 3.6649 3.5925 3.9105 3.6278 3.4448 3.3905 3.3181 3.8400 3.5572 3.3743 3.3200 3.2476 1 G 1.2325 1.1331 1.0250 0.9915 0.9469 1.0841 0.9967 0.9016 0.8722 0.8329 1.0460 0.9617 0.8699 0.8415 0.8036 0.9900 0.9102 0.8233 0.7965 0.7606 4.3434 3.6988 3.2818 3.1581 2.9930 3.8205 3.2536 2.8868 2.7779 2.6327 3.6861 3.1391 2.7852 2.6802 2.5401 0 G’ 1.8021 1.8832 1.9893 2.0269 2.0811 1.9222 2.0033 2.1094 2.1469 2.2011 1.9586 2.0397 2.1458 2.1833 2.2375 2.0170 2.0981 2.2042 2.2418 2.2960 2.2796 2.3710 2.4493 2.4765 2.5163 2.5197 2.6112 2.6895 2.7167 2.7565 2.5924 2.6839 2.7622 2.7894 2.8292 1 G’ 0.8113 0.8825 0.9756 1.0085 1.0561 0.9224 1.0033 1.1091 1.1466 1.2006 0.9560 1.0399 1.1496 1.1884 1.2444 1.0101 1.0987 1.2146 1.2556 1.3148 0.9209 1.0814 1.2188 1.2666 1.3364 1.0470 1.2294 1.3856 1.4399 1.5193 1.0852 1.2742 1.4362 1.4924 1.5747 U(ref) 1049 930 829 795 759 864 790 720 695 670 820 754 691 668 647 764 705 650 632 613 3526 2978 2651 2513 2373 3033 2540 2271 2170 2069 2914 2451 2134 2040 1995 U(pred) 1025 941 848 818 778 897 817 725 695 654 863 783 691 661 620 813 733 640 610 567 3505 3012 2678 2575 2435 3141 2681 2363 2264 2128 3047 2595 2280 2182 2046 Er. 24 -11 -19 -23 -19 -33 -27 -5 0 16 -43 -29 0 7 27 -49 -28 10 22 46 21 -34 -27 -62 -62 -108 -141 -92 -94 -59 -133 -144 -146 -142 -51 ref 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 9 9 32 - 101 - 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 BeI2 MgI2 CaI2 SrI2 BaI2 BeO MgO CaO SrO BaO BeS MgS CaS SrS BaS CuCl AgCl Al2O3 AgF AgBr AgI TiF2 VF2 CrF2 MnF2 FeF2 CoF2 NiF2 CuF2 ZnF2 TiCl2 VCl2 CrCl2 MnCl2 FeCl2 CoCl2 NiCl2 CuCl2 TiI2 VI2 CrI2 MnI2 FeI2 CoI2 NiI2 CuI2 TlF TlCl TlBr TlI Tl2O Tl2S Tl2Se Tl2Te TlF3 TlCl3 TlBr3 3.7364 3.4537 3.2707 3.2165 3.1441 3.5238 3.2410 3.0581 3.0038 2.9314 3.3204 3.0376 2.8547 2.8004 2.7280 2.1148 2.0720 9.5720 2.2092 2.0367 1.9850 3.9373 3.8972 3.8974 3.8724 3.9479 3.9593 3.9821 4.0101 3.9222 3.6629 3.6228 3.6230 3.5980 3.6735 3.6848 3.7076 3.7357 3.4888 3.4487 3.4489 3.4239 3.4994 3.5108 3.5336 3.5616 2.1372 1.9999 1.9647 1.9129 3.6132 3.4098 3.3805 3.2991 5.5441 5.1325 5.0267 3.4888 2.9711 2.6361 2.5367 2.4042 6.1674 5.2522 4.6601 4.4843 4.2500 5.3922 4.5921 4.0744 3.9207 3.7158 1.1151 1.0722 22.9008 1.2189 1.0345 0.9791 3.7789 3.6876 3.6879 3.6310 3.8031 3.8290 3.8810 3.9450 3.7445 3.3240 3.2437 3.2439 3.1939 3.3453 3.3680 3.4138 3.4701 3.0354 2.9621 2.9623 2.9166 3.0548 3.0756 3.1174 3.1688 1.1368 0.9999 0.9648 0.9131 3.2284 2.8226 2.7643 2.6019 7.2653 6.3907 6.1659 2.7094 2.8008 2.8791 2.9063 2.9461 1.1427 1.2342 1.3125 1.3397 1.3795 1.2315 1.3230 1.4013 1.4285 1.4683 1.8965 1.9325 2.7017 1.8124 1.9689 2.0273 2.3580 2.3729 2.3728 2.3825 2.3541 2.3501 2.3421 2.3326 2.3635 2.5981 2.6130 2.6130 2.6227 2.5943 2.5902 2.5822 2.5727 2.7878 2.8027 2.8026 2.8123 2.7839 2.7799 2.7719 2.7624 1.8800 2.0001 2.0364 2.0949 2.6231 2.7120 2.7269 2.7719 3.1027 3.4629 3.5720 1.1465 1.3463 1.5174 1.5768 1.6638 0.6486 0.7616 0.8584 0.8920 0.9412 0.7418 0.8711 0.9817 1.0202 1.0765 0.8968 0.9327 1.5720 0.8204 0.9667 1.0213 1.0585 1.0847 1.0846 1.1016 1.0518 1.0447 1.0307 1.0140 1.0682 1.2034 1.2332 1.2331 1.2524 1.1957 1.1876 1.1717 1.1527 1.3178 1.3504 1.3503 1.3715 1.3094 1.3005 1.2831 1.2623 0.8797 1.0001 1.0365 1.0951 1.2390 1.4171 1.4470 1.5373 1.2388 1.4083 1.4596 2813 2340 2087 1976 1890 4443 3791 3401 3223 3054 3770 3238 2966 2779 2643 996 918 15111 974 905 892 2757 2770 2939 2803 2967 3042 3089 3102 3053 2514 2593 2601 2551 2641 2706 2786 2824 2342 2470 2440 2388 2491 2561 2637 2694 850 751 734 710 2575 2258 2326 2172 5431 5278 5146 2909 2467 2156 2058 1922 4359 3738 3328 3204 3038 3842 3280 2906 2793 2640 925 886 15361 1013 852 802 3075 3003 3004 2959 3093 3113 3154 3203 3048 2740 2672 2673 2630 2757 2776 2814 2860 2524 2459 2459 2418 2541 2559 2596 2640 944 820 786 736 2661 2306 2253 2099 5704 5113 4962 -96 -127 -69 -82 -32 84 53 73 19 16 -72 -42 60 -14 3 71 32 -250 -39 53 90 -318 -233 -65 -156 -126 -71 -65 -101 5 -226 -79 -72 -79 -116 -70 -28 -36 -182 11 -19 -30 -50 2 41 54 -94 -69 -52 -26 -86 -48 73 73 -273 165 184 32 32 32 32 32 32 32 32 32 32 9 9 9 9 9 32 32 9 32 32 32 9 9 32 9 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 9 32 32 32 9 32 32 32 32 32 32 9 32 9 32 9 - 102 - 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 TiO2 PbF2 PbCl2 PbBr2 PbI2 PbO PbS PbSe PbTe PbF4 PbO2 AlF3 AlCl3 AlBr3 AlI3 TiBr2 TiO TiS TiF3 TiCl3 TiBr3 TiI3 Ti2O3 TiF4 TiCl4 TiBr4 TiI4 CuF CuBr CuI Cu2O Cu2S Cu2Se CdF2 HgF2 VO MnO FeO CoO NiO CuO ZnO CdO HgO GeO SnO PdO MnBr2 MnS MnSe MnTe MnF3 MnCl3 MnO2 MgSe MgTe ScBr3 6.0690 3.8159 3.5415 3.4710 3.3675 3.1548 2.9514 2.9222 2.8408 7.4042 6.0820 5.7777 5.3660 5.2602 5.1049 3.5923 3.2762 3.0728 5.6563 5.2446 5.1388 4.9835 9.3291 7.3912 6.8424 6.7013 6.4942 2.2520 2.0795 2.0278 3.8429 3.6395 3.6103 3.8604 3.8504 3.2361 3.2113 3.2868 3.2981 3.3209 3.3490 3.2611 3.1993 3.1893 3.4003 3.2228 3.3477 3.5275 3.0079 2.9786 2.8972 5.7130 5.3014 6.1815 3.0084 2.9270 5.0181 18.3343 3.5023 3.0807 2.9723 2.8132 4.9731 4.3481 4.2582 4.0080 12.9712 18.4185 8.0639 7.0932 6.8437 6.4774 3.2071 5.3659 4.6915 7.6488 6.7280 6.4914 6.1439 21.7218 12.9119 11.3576 10.9581 10.3715 1.2677 1.0759 1.0183 3.6002 3.1477 3.0826 3.6037 3.5808 5.2362 5.1559 5.4002 5.4370 5.5108 5.6017 5.3170 5.1171 5.0846 5.7677 5.1931 5.5975 3.0816 4.5078 4.4147 4.1553 7.8430 6.8988 19.0628 4.4971 4.2330 6.1410 1.5889 2.4056 2.6457 2.7185 2.8354 1.2688 1.3576 1.3725 1.4175 3.8609 1.5872 3.0561 3.4163 3.5254 3.7008 2.6708 1.2211 1.3099 3.0791 3.4394 3.5484 3.7238 2.7477 3.8626 4.3428 4.4883 4.7222 1.7764 1.9329 1.9913 2.4160 2.5049 2.5198 2.3873 2.3913 1.2361 1.2457 1.2173 1.2132 1.2053 1.1957 1.2267 1.2504 1.2545 1.1791 1.2412 1.1962 2.6954 1.3345 1.3494 1.3945 3.0681 3.4283 1.5754 1.3379 1.3829 3.5740 0.8727 1.1421 1.2984 1.3457 1.4219 0.8043 0.9200 0.9394 0.9980 1.2335 0.8687 1.1161 1.2688 1.3151 1.3895 1.2472 0.7455 0.8526 1.1767 1.3377 1.3865 1.4649 1.6573 1.2392 1.4088 1.4601 1.5427 0.7888 0.9295 0.9820 1.1111 1.2708 1.2976 1.1100 1.1171 0.7639 0.7758 0.7407 0.7357 0.7259 0.7141 0.7523 0.7817 0.7867 0.6935 0.7702 0.7146 1.2980 0.8873 0.9061 0.9626 1.1475 1.3046 0.8393 0.8895 0.9450 1.4656 12054 2543 2282 2230 2177 3520 3161 3144 3039 9468 11682 6252 5513 5360 5227 2430 3811 3357 5665 5153 5023 4971 14487 9908 9129 9059 8918 1088 978 966 3189 2865 2936 2830 2780 3863 3745 3865 3910 4010 4050 3971 3806 3907 3919 3652 3736 2482 3415 3330 3207 6012 5556 13150 3365 3202 4761 11923 2857 2534 2449 2324 3546 3105 3041 2860 9727 11973 6269 5638 5476 5240 2653 3816 3351 5977 5367 5211 4982 14617 9688 8734 8491 8137 1054 891 840 2939 2570 2515 2937 2919 3727 3672 3839 3864 3915 3977 3782 3645 3623 4089 3697 3974 2545 3220 3154 2969 6114 5494 12355 3213 3026 4942 131 -314 -252 -219 -147 -26 56 103 179 -259 -291 -17 -125 -116 -13 -223 -5 6 -312 -214 -188 -11 -130 220 395 568 781 34 87 126 250 295 421 -107 -139 136 73 26 46 95 73 189 161 284 -170 -45 -238 -63 195 176 238 -102 62 795 152 176 -181 9 32 32 32 32 9 9 9 9 9 9 32 32 32 32 32 32 9 9 32 32 9 25 32 9 32 32 9 32 32 32 32 9 32 9 32 32 32 32 32 32 32 9 9 9 9 9 32 9 9 9 9 9 9 9 9 32 - 103 - 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 YBr3 LaBr3 CeBr3 CdCl2 CdBr2 CdI2 CdS CdSe CoCl2 CoBr2 CoI2 CoS CoSe ZnCl2 HgCl2 SnCl2 FeBr2 NiBr2 CuBr2 ZnBr2 HgBr2 SnBr2 ZnI2 HgI2 SnI2 FeS CoS NiS CuS ZnS SnS Ag2O Ag2S Ag2Te AlH3 AsBr3 AsI3 AuBr AuCl AuH AuI BaH2 BeH2 BiCl3 CaH2 CeCl3 CeI3 Cr2O3 CrBr2 CrCl3 CrF3 CrI3 CrN Cs2O Cs2S CsH Cu2Te 4.9188 4.7931 4.7808 3.5860 3.5155 3.4119 2.9959 2.9667 3.6848 3.6143 3.5108 3.0947 3.0655 3.6478 3.5760 3.6095 3.6030 3.6371 3.6652 3.5772 3.5054 3.5390 3.4737 3.4019 3.4354 3.0834 3.0947 3.1175 3.1456 3.0577 3.0194 3.7573 3.5539 3.4433 5.0793 5.2655 5.1102 2.0238 2.0591 1.9635 1.9720 3.1270 3.7193 5.0558 3.2537 4.8866 4.6255 9.4478 3.5524 5.3040 5.7156 5.0429 4.2582 3.2800 3.0765 1.7378 3.5289 5.8529 5.4881 5.4525 3.1699 3.0584 2.8947 4.4740 4.3815 3.3680 3.2496 3.0756 4.7536 4.6554 3.2937 3.1497 3.2170 3.2276 3.2937 3.3480 3.1779 3.0389 3.1038 3.0078 2.8763 2.9377 4.7215 4.7536 4.8182 4.8976 4.6487 4.5404 3.4616 3.0266 2.7899 6.4170 6.8589 6.4918 1.0219 1.0592 0.9582 0.9672 2.3818 3.4563 6.1599 2.6116 5.6512 5.1606 22.2981 3.1298 6.9065 7.8517 6.3069 13.5157 2.6891 2.3511 0.7535 2.9015 3.5972 3.6302 3.6336 2.6274 2.7002 2.8171 1.3393 1.3542 2.5902 2.6629 2.7799 1.3020 1.3170 2.6037 2.6315 2.6182 2.6670 2.6550 2.6454 2.6764 2.7042 2.6909 2.7933 2.8211 2.8078 1.3061 1.3020 1.2941 1.2845 1.3155 1.3300 2.4880 2.5768 2.6368 3.7317 3.5245 3.6999 1.9803 1.9440 2.0491 2.0388 2.9667 2.7299 3.4806 2.8997 3.5245 3.8090 2.7246 2.6857 3.4278 3.0676 3.7123 0.9452 3.0253 3.1141 2.3063 2.5648 1.5377 1.6399 1.6506 1.2619 1.3079 1.3818 0.8941 0.9129 1.1876 1.2309 1.3005 0.8415 0.8592 1.2144 1.2699 1.2434 1.2393 1.2144 1.1947 1.2587 1.3162 1.2887 1.3299 1.3907 1.3616 0.8472 0.8415 0.8302 0.8167 0.8605 0.8810 1.1555 1.3216 1.4337 1.4025 1.3122 1.3864 0.9785 0.9441 1.0436 1.0339 1.6794 1.1573 1.4611 1.5317 1.5926 1.7440 1.6145 1.2780 1.3031 1.1463 1.4270 0.6659 1.4875 1.7013 1.3271 1.3786 4435 4280 4418 2565 2517 2455 3460 3310 2695 2643 2531 3653 3611 2748 2664 2310 2515 2721 2774 2689 2639 2256 2619 2624 2206 3506 3653 3694 3795 3674 3201 2910 2677 2600 5969 5365 5295 1059 1066 1108 1070 2133 3306 4707 2406 4348 4061 14957 2536 5529 6065 5294 8358 2063 1850 653 2683 4716 4421 4391 2610 2525 2398 3196 3130 2776 2689 2559 3395 3326 2714 2593 2650 2670 2726 2771 2628 2508 2564 2500 2382 2437 3372 3395 3441 3496 3320 3243 2836 2473 2263 5201 5487 5251 841 874 782 790 1901 2887 4936 2136 4535 4179 14981 2587 5500 6120 5109 8779 2247 1901 558 2358 -281 -141 27 -45 -8 57 264 180 -81 -46 -28 258 285 34 71 -340 -155 -5 3 61 131 -308 119 242 -231 134 258 253 299 354 -42 74 204 337 768 -122 44 218 192 326 280 232 419 -229 270 -187 -118 -24 -51 29 -55 185 -421 -184 -51 95 325 9 9 9 32 32 32 9 9 9 32 9 9 9 32 32 32 9 32 32 32 32 32 32 32 32 9 9 9 9 9 9 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 - 104 - 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 CuH DyCl3 ErCl3 Fe2O3 FeCl3 Ga2O3 GaBr3 GaCl3 GaF3 GaI3 GdCl3 HoCl3 InBr3 InCl3 InI3 K2O K2S KH LaCl3 LaH3 LaI3 LaN Li2O Li2S LiH MgH2 Mn2O3 MoBr4 MoCl3 MoCl4 ZrBr4 ZrCl4 ZrF4 ZrI4 Na2O Na2S Na2Te NaH NdCl3 PdBr2 PdCl2 PdI2 PrCl3 PrI3 Rb2O Rb2S RbH RhCl3 SbBr3 SbCl3 SbF3 SbI3 Sc2O3 ScCl3 ScF3 ScN SmCl3 2.0192 4.9653 4.9844 9.4875 5.3238 9.5507 5.2496 5.3554 5.7670 5.0943 4.9418 4.9772 5.0530 5.1588 4.8977 3.4170 3.2136 1.8063 4.8989 4.6122 4.6378 3.8532 3.7812 3.5778 1.9884 3.4366 9.4427 6.8397 5.3680 6.9808 6.5137 6.6548 7.2036 6.3066 3.6067 3.4033 3.2927 1.9011 4.9091 3.6639 3.7344 3.5604 4.9199 4.6588 3.3583 3.1549 1.7769 5.3461 5.1106 5.2164 5.6280 4.9553 9.0877 5.1239 5.5355 4.0782 4.9254 1.0088 5.8878 5.9454 22.4907 6.9662 22.7975 6.8128 7.0612 8.0275 6.4482 5.8173 5.9237 6.2423 6.4699 5.9082 2.9109 2.5451 0.8157 5.6882 5.1459 5.1943 11.1315 3.5002 3.0603 0.9808 2.9434 22.2733 11.4935 7.0992 11.9126 10.2322 10.6053 12.0566 9.6845 3.2179 2.8135 2.5935 0.9017 5.7187 3.3455 3.4675 3.1665 5.7515 5.2521 2.8159 2.4620 0.7890 7.0332 6.4094 6.6431 7.5522 6.0664 20.5493 6.3649 7.2359 12.4557 5.7680 2.0016 3.5031 3.4982 2.7172 3.4241 2.7055 3.5274 3.4183 3.0580 3.7027 3.5093 3.5001 3.5663 3.4572 3.7417 2.8418 2.9306 2.2145 3.5211 3.8364 3.8056 1.0385 2.4674 2.5562 2.0273 2.8214 2.7256 4.4718 3.4160 4.3264 4.5133 4.3679 3.8876 4.7472 2.6296 2.7185 2.7784 2.1084 3.5182 2.6459 2.5731 2.7628 3.5153 3.7997 2.9169 3.0057 2.2521 3.4200 3.5542 3.4451 3.0849 3.7296 2.7987 3.4649 3.1046 0.9822 3.5138 0.9913 1.5286 1.5138 1.6007 1.2920 1.5791 1.3210 1.2746 1.1211 1.3957 1.5471 1.5193 1.4418 1.3911 1.5233 1.3741 1.5717 1.2260 1.5822 1.7490 1.7327 0.8085 1.1428 1.3071 1.0196 1.3590 1.6163 1.3921 1.2678 1.3431 1.5637 1.5087 1.3271 1.6521 1.2430 1.4217 1.5423 1.1090 1.5738 1.1956 1.1536 1.2632 1.5648 1.7136 1.4205 1.6247 1.2674 1.2796 1.4042 1.3548 1.1917 1.4836 1.7519 1.4140 1.2438 0.7226 1.5603 1254 4529 4591 14774 5436 15220 5569 5665 6238 5496 4495 4572 5117 5183 5001 2232 1979 713 4242 4493 3986 6793 2814 2472 918 2718 15035 9500 5253 9603 7984 8144 8971 7801 2478 2203 2095 807 4415 2751 2818 2760 4387 4101 2161 1949 684 5665 4776 4857 5324 4692 13708 4901 5540 7506 4450 831 4724 4769 15103 5544 15296 5453 5614 6244 5217 4668 4752 5021 5173 4796 2420 2073 632 4564 4172 4208 7322 2864 2500 804 2446 14966 8862 5642 9113 7980 8212 9121 7641 2653 2299 2092 725 4589 2769 2858 2638 4615 4257 2347 2000 601 5594 5149 5304 5909 4921 13867 5094 5682 8135 4628 423 -195 -178 -329 -108 -76 116 51 -6 279 -173 -180 96 10 205 -188 -94 81 -322 321 -222 -529 -50 -28 114 272 69 638 -389 490 4 -68 -150 160 -175 -96 3 82 -174 -18 -40 122 -228 -156 -186 -51 83 71 -373 -447 -585 -229 -159 -193 -142 -629 -178 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 25 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 - 105 - 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 SnBr4 SnCl4 SrH2 TiH2 TiN TmCl3 TmI3 V2O3 VBr2 VBr3 VCl3 VI3 VN YCl3 YH3 YI3 BN AlN CaSe MgAl2O4 FeAl2O4 CaMoO4 SrMoO4 ZrSiO4 YVO4 Ce2O2S YPO4 LaFeO3 LaMnO3 LaCrO3 LaCoO3 LaAlO3 NdFeO3 CaSiO3 MgSiO3 Ba2SiO4 Ca2SiO4 Mg2SiO4 YAlO3 ZnFe2O4 PrMnO3 Y3Al5O12 Y3Fe5O12 Ba2In2O5 CaMgSiO4 Ca2Fe2O5 Al2SiO5 CaMgSi2O6 LiAlSi2O6 NaAlSi2O6 CaAl2Si2O8 KAlSi3O8 Ba4NaSb3O12 Ba4LiSb3O12 Sr4NaSb3O12 6.7200 6.8611 3.1994 3.4717 4.1989 4.9868 4.7257 9.3025 3.5523 5.1255 5.2313 4.9702 4.1856 5.0246 4.7379 4.7635 4.7391 4.3203 2.8255 12.8130 12.8587 12.3502 12.2960 12.2816 12.2302 8.4097 12.7050 9.0626 9.0402 9.0428 9.0860 9.1048 9.0727 9.4584 9.6413 12.2631 12.5165 12.8823 9.2305 12.7485 9.0612 37.2635 37.0523 15.0203 12.6994 15.6037 15.9722 19.0997 19.4771 19.3899 25.4306 25.6953 36.3060 36.3933 36.5956 11.0304 11.4326 2.5131 3.0071 13.1664 5.9526 5.4358 21.5924 3.1296 6.4527 6.6879 6.1073 13.0880 6.0663 5.4879 5.5396 16.3462 13.8810 3.9901 28.1530 28.3010 47.7444 47.5687 37.5988 40.0538 17.4810 43.8963 20.4276 20.3190 20.3313 20.5414 20.6327 20.4770 25.1390 25.7311 28.9789 29.7990 30.9833 21.2430 27.8076 20.4211 86.6299 85.6045 29.3884 30.3912 31.8108 43.3798 50.8701 54.1584 54.0173 68.5187 74.3427 104.6993 104.8404 105.6366 4.4860 4.3405 2.9269 2.8083 0.9567 3.4976 3.7821 2.7531 2.6858 3.5511 3.4420 3.7265 0.9594 3.4881 3.8035 3.7726 0.8698 0.9337 1.4162 3.9359 3.9190 3.3915 3.4187 3.1658 3.2348 3.0069 3.2046 2.8142 2.8184 2.8179 2.8098 2.8064 2.8113 2.8644 2.7861 4.3109 4.1768 4.0202 2.7735 3.9438 2.8126 11.0222 11.0608 5.5424 4.0985 5.3421 4.2536 5.6504 5.6883 5.7694 7.1179 7.4274 12.3129 12.2318 12.1537 1.4505 1.3995 1.5917 1.3302 0.6836 1.5119 1.6557 1.6672 1.2781 1.3948 1.3457 1.4736 0.6877 1.4836 1.6400 1.6247 0.5506 0.6484 1.0025 2.3336 2.3127 1.6939 1.7276 1.7159 1.7452 2.0676 1.6521 1.7805 1.7883 1.7874 1.7725 1.7661 1.7752 1.6396 1.5429 2.6636 2.4980 2.3045 1.7051 2.3530 1.7775 6.6872 6.7588 3.6058 2.4012 3.3174 2.3533 3.1825 2.9200 2.9701 3.9929 3.8169 6.9998 6.9496 6.8030 8852 8930 2265 2864 8033 4608 4340 14520 2534 5224 5329 5136 8233 4524 4910 4258 10911 8405 2862 19128 19216 29521 29403 24058 25846 12131 27207 13364 13487 13678 13805 13856 13854 16439 16725 19300 19831 20697 14570 18972 14084 58006 56504 20065 20364 21811 28687 33324 34815 35020 45005 47626 64996 65181 65481 8542 8785 2038 2503 8567 4775 4412 14534 2586 5182 5337 4953 8520 4864 4462 4498 10471 8999 2844 19133 19240 29240 29121 24022 25256 11839 27416 13781 13712 13720 13854 13912 13813 16531 16932 19195 19825 20691 14308 18914 13778 57449 56636 19861 20260 21664 28331 33192 35301 35166 44714 48036 64918 65146 66027 310 145 227 361 -534 -167 -72 -14 -52 42 -8 183 -287 -340 448 -240 440 -594 18 -5 -24 281 282 36 590 292 -209 -417 -225 -42 -49 -56 41 -92 -207 105 6 6 262 58 306 557 -132 204 104 147 356 132 -486 -146 291 -410 78 35 -546 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 9 9 32 9 9 9 9 9 9 9 9 25 25 25 25 25 25 25 25 25 25 25 28 28 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 - 106 - 3. REGRESSION ANALYSIS The experimental values of 318 inorganic-compounds lattice energies (U) are taken from Ref.9, Ref.25, Ref.28 and Ref.32, and listed in Table 2. Only multiple regression analysis (MRA) is used to construct the prediction models in this study, because the results obtained by using approach MRA are good enough. Linear regression analysis is carried by SPSS. The results of the best subsets regression of U versus 0G, 1G, 0G’, and 1G’ show: if only the index 1G is used, a good correlation for the U of the 318 can be obtained, and the correlation coefficient r is 0.9987. When the index 0G is included, the model can be significantly improved (r = 0.9993); whereas the results obtained by using three-parameters, 1G, 0G, and 1G’, as well as four-parameters, 1G, 0G, 1G’, and 0G’ are better than the results of single-parameter and two-parameters (r = 0.9995 and 0.9996, respectively). Four models are shown as follows: U=641.688+633.3101G (8) r = 0.9987, r2 = 0.9974, s = 503.60, F = 118971.0, N = 318 U=-88.043+525.4261G+ 325.2660G (9) r = 0.9993, r2 =0.9986, s = 365.16, F = 113280.1, N = 318 U=185.578+487.0761G+ 558.9610G-829.6991G’ (10) r = 0.9995, r2 =0.9991, s = 293.46, F = 116993.6, N = 318 U=153.238+502.9371G+ 51.1400G-1076.5051G’+177.442 0G’ (11) r = 0.9996, r2 =0.9992, s =280.98, F = 95718.9, N = 318 If the nonlinear regression analysis is carried by SPSS, the best nonlinear model by using four parameters is shown as follows: U=-315.953+831.2161G0.896+ 44.5760G1.644-140.7121G’2.150+110.0960G’1.474 (12) 2 r = 0.9998, r =0.9995, s =217.6, F = 159603.7, N = 318 The results of t-test show that these variables in these models are significant. Obviously, five models are excellent QSPR models without exception. The model (12) explains more than 99.95% of the variance in the experimental values of U for these inorganic compounds. The calculated results from Eq. (12) for 318 inorganic compounds show in Table 2. that the average absolute deviation is 156.78 kJ. mol-1. The calculated U versus experimental data is shown in Figure 1. Fig.1 shows that the model (12) is quite excellent. - 107 - Figure 1. A plot of calculated versus experimental U for 318 inorganic compounds. Finally, the models above generated for 318 inorganic compounds are verified by the cross-validation using leave-one-out method, and the correlation coefficients rcv and standard deviations scv together with the normal r and s are shown in Table 3. This table reveals that the results of the cross-validations for each model are very close to the normal results of the models, which means that the models constructed in this work are stable. Table3. Statistics of MLR and Leave-One-Out Cross-Validation for the Five Models properties Model (8) Model (9) Model (10) Model (11) Model (12) r 0.9987 0.9993 0.9995 0.9996 0.9998 r2 0.9974 0.9986 0.9991 0.9992 0.9995 s 503.60 365.16 293.46 280.98 217.63 rcv 0.9986 0.9992 0.9995 0.9995 0.9997 rcv2 0.9972 0.9985 0.9990 0.9991 0.9995 scv 521.99 381.29 303.36 295.53 226.15 4. RESULTS AND DISCUSSION The gi defined in this paper are different for ions of different elements due to their different electronegativities. Even for the ions of the different valence states of the same element, the gi are also different. Therefore, the gi can reflect the characteristics of different ions. - 108 - In inorganic compounds, the lattice energy is positively correlated with the number of ions of chemical formula. The topological indices 0G and 0G’ are proportional to the number of ions of chemical formula, so the lattice energy is positively correlated with 0G and 0G’. The more chemical single bonds there are in inorganic compound, the greater lattice energy the compound has, so the lattice energy is positively correlated with 1G and 1G’ too. This fact is in agreement with the results of the regression analysis. Among the 1G, 1G’, 0G , and 0G’, the index 1G has the best correlation with the lattice energy, r=0.9987, When the index 0G is included, the double-parameter model can be significantly improved (r = 0.9993). In the two models, the coefficients of 0G and 1G are all positive. However in the three-parameter model, 1 G , 0G, and 1G’,(r=0.9995), as well as four-parameters model, 1G,0G,, 1G’, and 0G’(r=0.9996), the coefficients of both 1G are negative. The results show that the infection factors contained in index 1G’ are different from indices 1G, 0G and 0G’. Index 1G together with 0G, 1G’and 0G’ reflects the essential influencing factor of lattice energy. The estimated lattice energies of 318 inorganic compounds containing 282 binary ionic crystals and 36 complex ionic crystals are listed in Table 2. As shown in Table 2, our calculated values agree well with the available experimental values. The average error of 318 crystals is 4.28 %( 5.18% for U<5000 kJ mol-1, 2.32% for U>5000 kJ mol-1). The average error of 36 complex ionic crystals is only 0.82%. If the regression is carried only for the experimental values of 36 complex ionic crystals, the best linear and nonlinear threeparameter models are shown as: U=486.290+505.2211G+622.6750G-886.780G’ (13) 2 r=0.9999, r =0.9997, s=292.12, F=36722.6, N=36 U=-96.116+650.8061G0.955+138.9160G1.322-31.3950G’ 2.114 (14) 2 r=0.9999, r =0.9998, s=218.23, F=65807.1, N=36 The average errors of the estimated lattice energies of 36 complex ionic crystals are 1.08% and 0.67% for linear model (13) and nonlinear model (14), respectively. The results show that the current method is more effective than literature methods7-11,23,25-26,28 for complex ionic crystals. In addition, the current method is very simple comparing with literature methods23,25-26,28, for the following reasons: (a) In current method, the gi of an ion can be easily calculated from the charge number, the electronegativity and Goldschmidt ionic radius of atom i. The electronegativity and Goldschmidt ionic radii for any atomic can obtained from the handbooks. - 109 - (b) The calculations of 0G, 1G, 0G’, and 1G’ of inorganic compounds are simple too. The 0 G, and 0G’ are the summation of all the atoms of the chemical formula. The 1G, 1G’ are the summation of all chemical single bonds. For every ion, the numbers of chemical single bonds bonding to other ions equal to the charge numbers. (c) The models can be used for calculating the lattice energies of binary ionic crystals and complex crystals. 5. CONCLUSION A novel connectivity index mG and its converse index mG’ are proposed for predicting the lattice energies of inorganic ionic compounds. The excellent QSPR models for the lattice energies can be constructed by using 0 G, 1G, 0G’,and 1G’. For the nonlinear model, the correlation coefficient r, the standard error, and the average error of the nonlinear model are 0.9998, 217.6 kJ.mol-1 and 4.28%, respectively, for the 318 inorganic ionic crystals. However, the average error of 36 complex ionic crystals is only 0.82%. The cross-validation by using the leave-one-out method demonstrates that the models are highly reliable from the point of view of statistics. The results show that the current method is not only more effective, but also simpler than literature methods for estimating the lattice energies of inorganic ionic crystals, especially for estimating the lattice energies of complex ionic crystals. 6. 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